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1. The NANOGrav 12.5-year Data Set: Search for Non-Einsteinian Polarization Modes in the Gravitational-wave Background

Author: Zaven Arzoumanian, Paul T. Baker, Harsha Blumer, Bence Bécsy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Maria Charisi, Shami Chatterjee, Siyuan Chen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Dallas M. DeGan, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Justin A. Ellis, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Nathan Garver-Daniels, Peter A. Gentile, Deborah C. Good, Jeffrey S. Hazboun, A. Miguel Holgado, Kristina Islo, Ross J. Jennings, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Joey Shapiro Key, Nima Laal, Michael T. Lam, T. Joseph W. Lazio, Duncan R. Lorimer, Tingting Liu, Jing Luo, Ryan S. Lynch, Dustin R. Madison, Alexander McEwen, Maura A. McLaughlin, Chiara M. F. Mingarelli, Cherry Ng, David J. Nice, Ken D. Olum, Timothy T. Pennucci, Nihan S. Pol, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Renée Spiewak, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), and NANOGrav
Subjects: noise, family, gravitation: model, FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), power spectrum, 01 natural sciences, Bayesian, General Relativity and Quantum Cosmology, 0103 physical sciences, 010303 astronomy & astrophysics, pulsar, High Energy Astrophysical Phenomena (astro-ph.HE), polarization, 010308 nuclear & particles physics, gravitational radiation: background, Astronomy and Astrophysics, NANOGrav, solar system, Astrophysics - Astrophysics of Galaxies, transverse, space-time, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), correlation, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We search NANOGrav's 12.5-year data set for evidence of a gravitational wave background (GWB) with all the spatial correlations allowed by general metric theories of gravity. We find no substantial evidence in favor of the existence of such correlations in our data. We find that scalar-transverse (ST) correlations yield signal-to-noise ratios and Bayes factors that are higher than quadrupolar (tensor transverse, TT) correlations. Specifically, we find ST correlations with a signal-to-noise ratio of 2.8 that are preferred over TT correlations (Hellings and Downs correlations) with Bayesian odds of about 20:1. However, the significance of ST correlations is reduced dramatically when we include modeling of the Solar System ephemeris systematics and/or remove pulsar J0030$+$0451 entirely from consideration. Even taking the nominal signal-to-noise ratios at face value, analyses of simulated data sets show that such values are not extremely unlikely to be observed in cases where only the usual TT modes are present in the GWB. In the absence of a detection of any polarization mode of gravity, we place upper limits on their amplitudes for a spectral index of $\gamma = 5$ and a reference frequency of $f_\text{yr} = 1 \text{yr}^{-1}$. Among the upper limits for eight general families of metric theories of gravity, we find the values of $A^{95\%}_{TT} = (9.7 \pm 0.4)\times 10^{-16}$ and $A^{95\%}_{ST} = (1.4 \pm 0.03)\times 10^{-15}$ for the family of metric spacetime theories that contain both TT and ST modes., Comment: 24 pages, 18 figures, 3 appendices. Please send any comments/questions to Nima Laal (laaln@oregonstate.edu)
Published: 2021

2. Refined Mass and Geometric Measurements of the High-mass PSR J0740+6620

Author: Shriharsh P. Tendulkar, Deborah C. Good, V. M. Kaspi, J. W. McKee, Wenbai Zhu, Cherry Ng, Ross J. Jennings, Harsha Blumer, Fengqiu Adam Dong, D. R. Lorimer, Paul S. Ray, A. Naidu, E. C. Ferrara, H. A. Radovan, I. H. Stairs, Paul Demorest, William Fiore, Paul R. Brook, Zaven Arzoumanian, Paul T. Baker, Joseph K. Swiggum, C. M. Tan, Michael T. Lam, Timothy T. Pennucci, N. Garver-Daniels, Timothy Dolch, Natasha McMann, Alexander McEwen, B. W. Meyers, David J. Nice, M. A. McLaughlin, Brent J. Shapiro-Albert, Ismaël Cognard, J. Luo, Haley M. Wahl, L. Guillemot, A. Yu. Kirichenko, Aditya Parthasarathy, Matthew Kerr, Nihan Pol, M. L. Jones, Scott M. Ransom, Emmanuel Fonseca, H. T. Cromartie, M. E. DeCesar, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, General relativity, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Neutron star, Pulsar, Space and Planetary Science, [SDU]Sciences of the Universe [physics], 0103 physical sciences, High mass, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], 010303 astronomy & astrophysics
Abstract: We report results from continued timing observations of PSR J0740+6620, a high-mass, 2.8-ms radio pulsar in orbit with a likely ultra-cool white dwarf companion. Our data set consists of combined pulse arrival-time measurements made with the 100-m Green Bank Telescope and the Canadian Hydrogen Intensity Mapping Experiment telescope. We explore the significance of timing-based phenomena arising from general-relativistic dynamics and variations in pulse dispersion. When using various statistical methods, we find that combining $\sim 1.5$ years of additional, high-cadence timing data with previous measurements confirms and improves upon previous estimates of relativistic effects within the PSR J0740+6620 system, with the pulsar mass $m_{\rm p} = 2.08^{+0.07}_{-0.07}$ M$_\odot$ (68.3\% credibility) determined by the relativistic Shapiro time delay. For the first time, we measure secular variation in the orbital period and argue that this effect arises from apparent acceleration due to significant transverse motion. After incorporating contributions from Galactic differential rotation and off-plane acceleration in the Galactic potential, we obtain a model-dependent distance of $d = 1.14^{+0.17}_{-0.15}$ kpc (68.3\% credibility). This improved distance confirms the ultra-cool nature of the white dwarf companion determined from recent optical observations. We discuss the prospects for future observations with next-generation facilities, which will likely improve the precision on $m_{\rm p}$ for J0740+6620 by an order of magnitude within the next few years., Final version after minor corrections during referee process. Published in the Astrophysical Journal Letters on 1 July 2021
Published: 2021

3. Astrophysics Milestones for Pulsar Timing Array Gravitational-wave Detection

Author: Paul R. Brook, Megan E. Decesar, David J. Nice, Chiara M. F. Mingarelli, Sarah Burke-Spolaor, Timothy T. Pennucci, H. Thankful Cromartie, Brent J. Shapiro-Albert, Nathan Garver-Daniels, Timothy Dolch, Daniel R. Stinebring, Paul Demorest, Alexander McEwen, Ryan S. Lynch, Siyuan Chen, James M. Cordes, Scott M. Ransom, Paul T. Baker, Luke Zoltan Kelley, Ingrid H. Stairs, Megan L. Jones, Neil J. Cornish, Ross J. Jennings, Paul S. Ray, Haley M. Wahl, Adam Brazier, Joseph Simon, William Fiore, Jeffrey S. Hazboun, Joseph K. Swiggum, T. Joseph W. Lazio, Cherry Ng, Joey Shapiro Key, Elizabeth C. Ferrara, Michael T. Lam, Xavier Siemens, Jing Luo, D. R. Madison, Deborah C. Good, Maura McLaughlin, Sarah J. Vigeland, B. Bécsy, Michele Vallisneri, Zaven Arzoumanian, David L. Kaplan, Caitlin A. Witt, Fronefield Crawford, Shami Chatterjee, Emmanuel Fonseca, Stephen Taylor, Andrew R. Kaiser, Nihan Pol, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), and NANOGrav
Subjects: 010504 meteorology & atmospheric sciences, gravitational radiation: stochastic, FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), Astrophysics, 01 natural sciences, Gravitational-wave astronomy, Bayesian, General Relativity and Quantum Cosmology, Gravitational wave background, Pulsar timing array, Pulsar, Millisecond pulsar, 0103 physical sciences, black hole, gravitational radiation: spectrum, cosmic string, 010303 astronomy & astrophysics, spectrum: slope, 0105 earth and related environmental sciences, pulsar, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Gravitational wave, gravitational radiation: background, Astronomy and Astrophysics, NANOGrav, Astrophysics - Astrophysics of Galaxies, Cosmic string, Amplitude, black hole: binary, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), correlation, fractional, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], spectral, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: The NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its 12.5-yr pulsar timing array dataset, with median characteristic strain amplitude at periods of a year of $A_{\rm yr} = 1.92^{+0.75}_{-0.55} \times 10^{-15}$. However, evidence for the quadrupolar Hellings \& Downs interpulsar correlations, which are characteristic of gravitational wave signals, was not yet significant. We emulate and extend the NANOGrav dataset, injecting a wide range of stochastic gravitational wave background (GWB) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones: (I) Given the amplitude measured in the 12.5 yr analysis and assuming this signal is a GWB, we expect to accumulate robust evidence of an interpulsar-correlated GWB signal with 15--17 yrs of data, i.e., an additional 2--5 yrs from the 12.5 yr dataset; (II) At the initial detection, we expect a fractional uncertainty of $40\%$ on the power-law strain spectrum slope, which is sufficient to distinguish a GWB of supermassive black-hole binary origin from some models predicting more exotic origins;(III) Similarly, the measured GWB amplitude will have an uncertainty of $44\%$ upon initial detection, allowing us to arbitrate between some population models of supermassive black-hole binaries. In addition, power-law models are distinguishable from those having low-frequency spectral turnovers once 20~yrs of data are reached. Even though our study is based on the NANOGrav data, we also derive relations that allow for a generalization to other pulsar-timing array datasets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier., 15 pages, 7 figures
Published: 2021

4. Multimessenger gravitational-wave searches with pulsar timing arrays: Application to 3C 66B using the NANOGrav 11-year data set

Author: Maria Charisi, Ryan S. Lynch, Daniel R. Stinebring, David J. Nice, Timothy Dolch, Justin A. Ellis, Paul Demorest, Weiwei Zhu, Dustin R. Madison, Jing Luo, Peter A. Gentile, Jeffrey S. Hazboun, Maura McLaughlin, K. Islo, Nathan Garver-Daniels, Scott M. Ransom, Rodney D. Elliott, Nihan Pol, Stephen Taylor, Ingrid H. Stairs, H. Thankful Cromartie, Fronefield Crawford, Michael T. Lam, Timothy T. Pennucci, Joseph Simon, Michele Vallisneri, James M. Cordes, Luke Zoltan Kelley, Andrew R. Kaiser, Shami Chatterjee, Kevin Stovall, Joseph K. Swiggum, David L. Kaplan, Cherry Ng, Ross J. Jennings, Elizabeth C. Ferrara, Paul R. Brook, Xavier Siemens, Chiara M. F. Mingarelli, Joey Shapiro Key, Sarah Burke-Spolaor, Adam Brazier, Megan E. DeCesar, Caitlin A. Witt, Emmanuel Fonseca, Brent J. Shapiro-Albert, Paul T. Baker, Neil J. Cornish, Bence Bécsy, Kathryn Crowter, Megan L. Jones, Paul S. Ray, Renée Spiewak, Deborah C. Good, Zaven Arzoumanian, Lina Levin, T. Joseph W. Lazio, Robert D. Ferdman, and Sarah J. Vigeland
Subjects: Physics, Supermassive black hole, Active galactic nucleus, 010504 meteorology & atmospheric sciences, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Binary number, Astronomy and Astrophysics, Astrophysics, Orbital period, 01 natural sciences, Galaxy, Pulsar timing array, Pulsar, Space and Planetary Science, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M ⊙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.
Published: 2020

5. Precision Timing of PSR J0437-4715 with the IAR Observatory and Implications for Low-Frequency Gravitational Wave Source Sensitivity

Author: J. S. Hazboun and Michael T. Lam
Subjects: Brightness, 010504 meteorology & atmospheric sciences, media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, 01 natural sciences, 7. Clean energy, Pulsar timing array, Pulsar, Millisecond pulsar, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 0105 earth and related environmental sciences, media_common, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, 13. Climate action, Space and Planetary Science, Sky, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Radio astronomy
Abstract: While observations of many high-precision radio pulsars of order $\lesssim1~\mu$s across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronom\'ia) has begun observations of the brightest-known millisecond pulsar, J0437$-$4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR's capability to monitor this pulsar daily coupled with the pulsar's brightness allows for high-precision pulse arrival-time measurements. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437$-$4715 will provide a significant sensitivity increase in NANOGrav's "blind spot" in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array's sensitivity will improve by a factor of $\approx$2-4 over 10 years for 20% of the sky with the inclusion of this pulsar as compared to a static version of the PTA used in NANOGrav's most recent limits. More modest instrumentation result in factors of $\approx$1.4-3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data given the potential achievable sensitivity., Comment: 14 pages, 2 figures, 4 tables, published in ApJ
Published: 2020

6. NANOGrav 11 yr Data Set: Evolution of Gravitational-wave Background Statistics

Author: Lina Levin, Scott M. Ransom, J. E. Turner, Jing Luo, D. R. Stinebring, I. H. Stairs, D. R. Lorimer, Peter A. Gentile, E. C. Ferrara, Joseph K. Swiggum, Paul Demorest, Deborah C. Good, A. M. Holgado, Adam Brazier, D. R. Madison, Robert D. Ferdman, R. van Haasteren, Paul R. Brook, Sarah Burke-Spolaor, J. M. Cordes, H. T. Cromartie, K. Islo, M. E. DeCesar, Fronefield Crawford, Nihan Pol, M. L. Jones, Luke Zoltan Kelley, Kevin Stovall, Timothy Dolch, N. Garver-Daniels, Andrea N. Lommen, Kathryn Crowter, Caitlin A. Witt, Andrew R. Kaiser, Paul S. Ray, E. A. Huerta, Sourav Chatterjee, Paul T. Baker, Cherry Ng, G. Jones, Xavier Siemens, David L. Kaplan, Neil J. Cornish, Ross J. Jennings, Joseph Simon, Michael T. Lam, Stephen Taylor, Joey Shapiro Key, Emmanuel Fonseca, Zaven Arzoumanian, Maura McLaughlin, Michele Vallisneri, Chiara M. F. Mingarelli, T. J. W. Lazio, R. S. Lynch, Sarah J. Vigeland, Sean T. McWilliams, David J. Nice, Timothy T. Pennucci, R. Spiewak, Wenbai Zhu, Jeffrey S. Hazboun, and J. A. Ellis
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, Supermassive black hole, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, General Relativity and Quantum Cosmology (gr-qc), 01 natural sciences, General Relativity and Quantum Cosmology, Gravitational wave background, Pulsar, 13. Climate action, Space and Planetary Science, Colors of noise, Millisecond pulsar, 0103 physical sciences, Statistics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Noise (radio)
Abstract: An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a spectral index of -2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11-year data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red noise process with low-spectral index noise, and use a tailored noise model to remove these effects., 14 pages, 13 figures, fixed typo in abstract of earlier version
Published: 2020

7. The NANOGrav 11 yr Data Set: Limits on Gravitational Wave Memory

Author: A. M. Holgado, K. Islo, Timothy Dolch, Glenn Jones, Nihan Pol, Paul R. Brook, Renée Spiewak, R. van Haasteren, Stephen Taylor, Ryan S. Lynch, Scott M. Ransom, Megan E. DeCesar, Caitlin A. Witt, J. Luo, Adam Brazier, Emmanuel Fonseca, Sean T. McWilliams, Cherry Ng, Peter A. Gentile, Elizabeth C. Ferrara, Chiara M. F. Mingarelli, David J. Nice, Timothy T. Pennucci, Xavier Siemens, Ross J. Jennings, Robert D. Ferdman, David L. Kaplan, Paul Demorest, Duncan R. Lorimer, Fronefield Crawford, Shami Chatterjee, Kevin Stovall, Kathryn Crowter, Zaven Arzoumanian, Neil J. Cornish, Megan L. Jones, Paul S. Ray, E. A. Huerta, N. Garver-Daniels, Joseph Simon, Jeffrey S. Hazboun, Daniel R. Stinebring, Lina Levin, P. T. Baker, Joey Shapiro Key, Sarah Burke-Spolaor, Maura McLaughlin, Michele Vallisneri, James M. Cordes, Michael T. Lam, Wenbai Zhu, Deborah C. Good, Joseph K. Swiggum, H. T. Cromartie, Sarah J. Vigeland, D. R. Madison, Kshitij Aggarwal, J. A. Ellis, Ingrid H. Stairs, Luke Zoltan Kelley, and T. J. W. Lazio
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, 010504 meteorology & atmospheric sciences, Gravitational wave, media_common.quotation_subject, FOS: Physical sciences, Astronomy and Astrophysics, General Relativity and Quantum Cosmology (gr-qc), Astrophysics, 01 natural sciences, General Relativity and Quantum Cosmology, Gravitation, Amplitude, Pulsar, 13. Climate action, Space and Planetary Science, Millisecond pulsar, Observatory, Sky, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, media_common
Abstract: The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays (PTAs), the non-oscillatory GW memory effect is detectable. Further, any burst of gravitational waves will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GW memory. This dataset is sensitive to very low frequency GWs of $\sim3$ to $400$ nHz (periods of $\sim11$ yr $-$ $1$ mon). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of $2.5\times10^{-14}$, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at $, Comment: 10 pages, 6 figures, submitted to ApJ
Published: 2020

8. The NANOGrav 12.5-Year Data Set: Monitoring Interstellar Scattering Delays

Author: Jacob E. Turner, Maura A. McLaughlin, James M. Cordes, Michael T. Lam, Brent J. Shapiro-Albert, Daniel R. Stinebring, Zaven Arzoumanian, Harsha Blumer, Paul R. Brook, Shami Chatterjee, H. Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Justin A. Ellis, Robert D. Ferdman, Elizabeth C. Ferrara, Emmanuel Fonseca, Nathan Garver-Daniels, Peter A. Gentile, Deborah C. Good, Megan L. Jones, T. Joseph W. Lazio, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Cherry Ng, David J. Nice, Timothy T. Pennucci, Nihan S. Pol, Scott M. Ransom, Renée Spiewak, Ingrid H. Stairs, Kevin Stovall, Joseph K. Swiggum, and Sarah J. Vigeland
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Space and Planetary Science, Astrophysics::High Energy Astrophysical Phenomena, 0103 physical sciences, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 01 natural sciences
Abstract: We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timing program. Dynamic spectra for the observing epochs of each pulsar were used to obtain estimates of scintillation timescales, scintillation bandwidths, and the corresponding scattering delays using a stretching algorithm to account for frequency-dependent scaling. We were able to measure scintillation bandwidths for 28 pulsars at 1500 MHz and 15 pulsars at 820 MHz. We examine scaling behavior for 17 pulsars and find power-law indices ranging from $-0.7$ to $-3.6$, though these may be biased shallow due to insufficient frequency resolution at lower frequencies. We were also able to measure scintillation timescales for six pulsars at 1500 MHz and seven pulsars at 820 MHz. There is fair agreement between our scattering delay measurements and electron-density model predictions for most pulsars. We derive interstellar scattering-based transverse velocities assuming isotropic scattering and a scattering screen halfway between the pulsar and earth. We also estimate the location of the scattering screens assuming proper motion and interstellar scattering-derived transverse velocities are equal. We find no correlations between variations in scattering delay and either variations in dispersion measure or flux density. For most pulsars for which scattering delays were measurable, we find that time of arrival uncertainties for a given epoch are larger than our scattering delay measurements, indicating that variable scattering delays are currently subdominant in our overall noise budget but are important for achieving precisions of tens of ns or less., Comment: Accepted to ApJ
Published: 2020
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9. A pulsar-based time-scale from the International Pulsar Timing Array

Author: Sourav Chatterjee, Daniel J. Reardon, Ismaël Cognard, Gemma H. Janssen, Sarah Burke-Spolaor, Zaven Arzoumanian, Michael T. Lam, Kejia Lee, Michael Kramer, Benetge Perera, J. B. Wang, L. Guo, Renée Spiewak, Ryan Shannon, David J. Nice, Richard N. Manchester, N. D. R. Bhat, D. Matsakis, E. Graikou, Joseph Simon, Ingrid H. Stairs, R. N. Caballero, Shi Dai, Matthew Bailes, Christopher J. Russell, Alberto Sesana, Robert D. Ferdman, Lucas Guillemot, Delphine Perrodin, Xing-Jiang Zhu, Andrew Lyne, Chiara M. F. Mingarelli, C. G. Bassa, Benjamin Stappers, A. Brazier, R. van Haasteren, Timothy T. Pennucci, J. W. McKee, Yue-Fei Wang, Maura McLaughlin, Michael Keith, L. Toomey, Matthew Kerr, William A. Coles, Timothy Dolch, Stefan Oslowski, M. L. Tong, Stephen Taylor, D. J. Champion, Kang Liu, S. A. Sanidas, George Hobbs, J. K. Swiggum, Gregory Desvignes, Gilles Theureau, A. Possenti, T. J. W. Lazio, R. S. Lynch, G. Shaifullah, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Théories (LUTH (UMR_8102)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Hobbs, G, Guo, L, Caballero, R, Coles, W, Lee, K, Manchester, R, Reardon, D, Matsakis, D, Tong, M, Arzoumanian, Z, Bailes, M, Bassa, C, Bhat, N, Brazier, A, Burke-Spolaor, S, Champion, D, Chatterjee, S, Cognard, I, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Graikou, E, Guillemot, L, Janssen, G, Keith, M, Kerr, M, Kramer, M, Lam, M, Liu, K, Lyne, A, Lazio, T, Lynch, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Nice, D, Osłowski, S, Pennucci, T, Perera, B, Perrodin, D, Possenti, A, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Toomey, L, van Haasteren, R, Wang, J, Wang, Y, Zhu, X, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), ITA, USA, GBR, FRA, DEU, AUS, CAN, NLD, CHN, and HUN
Subjects: Astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Stability (probability), general [pulsars], Pulsar, Millisecond pulsar, Observatory, pulsars: general, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, time, Physics, 010308 nuclear & particles physics, Gravitational wave, Spectral density, Astronomy and Astrophysics, Atomic clock, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics - Instrumentation and Methods for Astrophysics, Noise (radio), Astronomical and Space Sciences
Abstract: We have constructed a new timescale, TT(IPTA16), based on observations of radio pulsars presented in the first data release from the International Pulsar Timing Array (IPTA). We used two analysis techniques with independent estimates of the noise models for the pulsar observations and different algorithms for obtaining the pulsar timescale. The two analyses agree within the estimated uncertainties and both agree with TT(BIPM17), a post-corrected timescale produced by the Bureau International des Poids et Mesures (BIPM). We show that both methods could detect significant errors in TT(BIPM17) if they were present. We estimate the stability of the atomic clocks from which TT(BIPM17) is derived using observations of four rubidium fountain clocks at the US Naval Observatory. Comparing the power spectrum of TT(IPTA16) with that of these fountain clocks suggests that pulsar-based timescales are unlikely to contribute to the stability of the best timescales over the next decade, but they will remain a valuable independent check on atomic timescales. We also find that the stability of the pulsar-based timescale is likely to be limited by our knowledge of solar-system dynamics, and that errors in TT(BIPM17) will not be a limiting factor for the primary goal of the IPTA, which is to search for the signatures of nano-Hertz gravitational waves., Comment: accepted by MNRAS
Published: 2020

10. The NANOGrav 12.5-year Data Set: Wideband Timing of 47 Millisecond Pulsars

Author: Cherry Ng, Yhamil Garcia, Xavier Siemens, Jing Luo, Robert D. Ferdman, Timothy Dolch, Jordan A. Gusdorff, Paul Demorest, Joseph Simon, Duncan R. Lorimer, Joshua Ramette, Luke Zoltan Kelley, Keeisi Caballero, Emmanuel Fonseca, Justin A. Ellis, Megan E. Decesar, Fronefield Crawford, Scott M. Ransom, David J. Nice, Maura McLaughlin, Shami Chatterjee, Ryan S. Lynch, Megan L. Jones, Kevin Stovall, Cody Jessup, Paul S. Ray, Jeffrey S. Hazboun, D. R. Madison, Joey Shapiro Key, Daniel Halmrast, Chiara M. F. Mingarelli, Daniel R. Stinebring, Caitlin A. Witt, Andrew R. Kaiser, Timothy T. Pennucci, Peter A. Gentile, Renée Spiewak, Faisal Alam, Michael T. Lam, Rachel L. Chamberlain, Michael Tripepi, Paul T. Baker, Harsha Blumer, David L. Kaplan, Ross J. Jennings, Benjamin M. X. Nguyen, Deborah C. Good, Stephen Taylor, Zaven Arzoumanian, James M. Cordes, Richard Camuccio, Neil J. Cornish, Keith E. Bohler, Sarah Burke-Spolaor, K. Islo, Paul R. Brook, Elizabeth C. Ferrara, H. Thankful Cromartie, Brent J. Shapiro-Albert, Michele Vallisneri, Nihan Pol, William Fiore, Weiwei Zhu, Joseph K. Swiggum, T. Joseph W. Lazio, Kaleb Maraccini, Adam Brazier, Nathan Garver-Daniels, Sarah J. Vigeland, and Ingrid H. Stairs
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Data set, Pulsar timing array, Narrowband, Pulsar, Space and Planetary Science, Observatory, Millisecond pulsar, 0103 physical sciences, Wideband, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM)
Abstract: We present a new analysis of the profile data from the 47 millisecond pulsars comprising the 12.5-year data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), which is presented in a parallel paper (Alam et al. 2021a; NG12.5). Our reprocessing is performed using "wideband" timing methods, which use frequency-dependent template profiles, simultaneous time-of-arrival (TOA) and dispersion measure (DM) measurements from broadband observations, and novel analysis techniques. In particular, the wideband DM measurements are used to constrain the DM portion of the timing model. We compare the ensemble timing results to NG12.5 by examining the timing residuals, timing models, and noise model components. There is a remarkable level of agreement across all metrics considered. Our best-timed pulsars produce encouragingly similar results to those from NG12.5. In certain cases, such as high-DM pulsars with profile broadening, or sources that are weak and scintillating, wideband timing techniques prove to be beneficial, leading to more precise timing model parameters by 10-15%. The high-precision, multi-band measurements of several pulsars indicate frequency-dependent DMs. Compared to the narrowband analysis in NG12.5, the TOA volume is reduced by a factor of 33, which may ultimately facilitate computational speed-ups for complex pulsar timing array analyses. This first wideband pulsar timing data set is a stepping stone, and its consistent results with NG12.5 assure us that such data sets are appropriate for gravitational wave analyses., Comment: 62 pages, 55 figures, 5 tables, 3 appendices. Data available at http://nanograv.org/data/ and via DOI 10.5281/zenodo.4312887
Published: 2020
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11. Deconvolving Pulsar Signals with Cyclic Spectroscopy: A Systematic Evaluation

Author: Glenn Jones, Michael T. Lam, Tyler Cohen, Paul Demorest, Timothy Dolch, Maura McLaughlin, Ryan S. Lynch, Nipuni Palliyaguru, Hengrui Zhu, Dan Stinebring, and Lina Levin
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010504 meteorology & atmospheric sciences, Scattering, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Green Bank Telescope, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, 01 natural sciences, 3. Good health, Computational physics, Interstellar medium, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Spectroscopy, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Radio astronomy
Abstract: Radio pulsar signals are significantly perturbed by their propagation through the ionized interstellar medium. In addition to the frequency-dependent pulse times of arrival due to dispersion, pulse shapes are also distorted and shifted, having been scattered by the inhomogeneous interstellar plasma, affecting pulse arrival times. Understanding the degree to which scattering affects pulsar timing is important for gravitational wave detection with pulsar timing arrays (PTAs), which depend on the reliability of pulsars as stable clocks with an uncertainty of ~100ns or less over ~10yr or more. Scattering can be described as a convolution of the intrinsic pulse shape with an impulse response function representing the effects of multipath propagation. In previous studies, the technique of cyclic spectroscopy has been applied to pulsar signals to deconvolve the effects of scattering from the original emitted signals. We present an analysis of simulated data to test the quality of deconvolution using cyclic spectroscopy over a range of parameters characterizing interstellar scattering and pulsar signal-to-noise ratio. We show that cyclic spectroscopy is most effective for high-S/N and/or highly scattered pulsars. We conclude that cyclic spectroscopy could play an important role in scattering correction to distant populations of highly scattered pulsars not currently included in PTAs. For future telescopes and for current instruments such as the Green Bank Telescope upgraded with the ultrawide bandwidth (UWB) receiver, cyclic spectroscopy could potentially double the number of PTA-quality pulsars., Comment: 21 pages, 10 figures. Typo fixed, conclusions unchanged. Accepted for publication in ApJ
Published: 2020
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12. PINT: A Modern Software Package for Pulsar Timing

Author: Matthew Kerr, Kevin Stovall, Jing Luo, Fredrick A. Jenet, Jonathan Colen, Chloe A. Champagne, Paul S. Ray, Ross J. Jennings, Camryn Phillips, Paul Demorest, Scott M. Ransom, Rutger van Haasteren, Anne M. Archibald, Josef Zimmerman, Michael T. Lam, Matteo Bachetti, ITA, and USA
Subjects: 010308 nuclear & particles physics, business.industry, Computer science, NumPy, Software development, FOS: Physical sciences, Astronomy and Astrophysics, Modular design, Python (programming language), computer.software_genre, 01 natural sciences, Extensibility, Software, Pulsar, Space and Planetary Science, 0103 physical sciences, Test suite, Operating system, business, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, computer, Instrumentation and Methods for Astrophysics (astro-ph.IM), computer.programming_language
Abstract: Over the past few decades, the measurement precision of some pulsar-timing experiments has advanced from ~10 us to ~10 ns, revealing many subtle phenomena. Such high precision demands both careful data handling and sophisticated timing models to avoid systematic error. To achieve these goals, we present PINT (PINT Is Not Tempo3), a high-precision Python pulsar timing data analysis package, which is hosted on GitHub and available on Python Package Index (PyPI) as pint-pulsar. PINT is well-tested, validated, object-oriented, and modular, enabling interactive data analysis and providing an extensible and flexible development platform for timing applications. It utilizes well-debugged public Python packages (e.g., the NumPy and Astropy libraries) and modern software development schemes (e.g., version control and efficient development with git and GitHub) and a continually expanding test suite for improved reliability, accuracy, and reproducibility. PINT is developed and implemented without referring to, copying, or transcribing the code from other traditional pulsar timing software packages (e.g., TEMPO and TEMPO2) and therefore provides a robust tool for cross-checking timing analyses and simulating pulse arrival times. In this paper, we describe the design, usage, and validation of PINT, and we compare timing results between it and TEMPO and TEMPO2., Comment: Re-submitted to the Astrophysical Journal at December 31st, 2020
Published: 2020
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13. The NANOGrav 12.5 yr Data Set: Observations and Narrowband Timing of 47 Millisecond Pulsars

Author: Benjamin M. X. Nguyen, Yhamil Garcia, Jordan A. Gusdorff, Paul R. Brook, Chiara M. F. Mingarelli, Rachel L. Chamberlain, Paul Demorest, Scott M. Ransom, Fronefield Crawford, Timothy Dolch, Stephen Taylor, Luke Zoltan Kelley, Sarah Burke-Spolaor, Joshua Ramette, Shami Chatterjee, Kevin Stovall, Elizabeth C. Ferrara, Robert D. Ferdman, Nathan Garver-Daniels, William Fiore, Peter A. Gentile, T. Joseph W. Lazio, Harsha Blumer, Cody Jessup, Kaleb Maraccini, Caitlin A. Witt, Joseph K. Swiggum, David L. Kaplan, Daniel Halmrast, Paul S. Ray, H. Thankful Cromartie, Brent J. Shapiro-Albert, James M. Cordes, D. R. Madison, Cherry Ng, Daniel R. Stinebring, Sarah J. Vigeland, Joseph Simon, Renée Spiewak, Deborah C. Good, Xavier Siemens, Faisal Alam, Keith E. Bohler, Michael T. Lam, Ryan S. Lynch, Ingrid H. Stairs, Megan E. Decesar, Justin A. Ellis, Emmanuel Fonseca, Maura McLaughlin, Keeisi Caballero, Weiwei Zhu, Joey Shapiro Key, David J. Nice, Timothy T. Pennucci, Duncan R. Lorimer, Paul T. Baker, Richard Camuccio, Neil J. Cornish, Ross J. Jennings, Jing Luo, Andrew R. Kaiser, Megan L. Jones, K. Islo, Jeffrey S. Hazboun, Nihan Pol, Michael Tripepi, Adam Brazier, Zaven Arzoumanian, and Michele Vallisneri
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrometry, Astrophysics, 01 natural sciences, Shapiro delay, Binary pulsar, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Arecibo Observatory, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Radio astronomy
Abstract: We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes. We detail our observational methods and present a set of TOA measurements, based on "narrowband" analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. A separate set of "wideband" TOAs will be presented in a companion paper. We detail a number of methodological changes compared to our previous work which yield a cleaner and more uniformly processed data set. Our timing models include several new astrometric and binary pulsar measurements, including previously unpublished values for the parallaxes of PSRs J1832-0836 and J2322+2057, the secular derivatives of the projected semi-major orbital axes of PSRs J0613-0200 and J2229+2643, and the first detection of the Shapiro delay in PSR J2145-0750. We report detectable levels of red noise in the time series for 14 pulsars. As a check on timing model reliability, we investigate the stability of astrometric parameters across data sets of different lengths. We report flux density measurements for all pulsars observed. Searches for stochastic and continuous gravitational waves using these data will be subjects of forthcoming publications., Comment: 54 pages, 52 figures, 7 tables, 1 appendix. Data are available at http://nanograv.org/data/ and via the DOI 10.5281/zenodo.4312297
Published: 2020
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14. The NANOGrav 11-year Data Set: Constraints on Planetary Masses Around 45 Millisecond Pulsars

Author: Wenbai Zhu, Glenn Jones, Timothy Dolch, Kathryn Crowter, Scott M. Ransom, Paul S. Ray, Kevin Stovall, Joseph K. Swiggum, Paul Demorest, Zaven Arzoumanian, Megan L. Jones, Megan E. DeCesar, Renée Spiewak, Emmanuel Fonseca, Robert D. Ferdman, Peter A. Gentile, E. A. Behrens, Duncan R. Lorimer, J. A. Ellis, Elizabeth C. Ferrara, Ingrid H. Stairs, Ryan S. Lynch, David J. Nice, Timothy T. Pennucci, Cherry Ng, D. R. Madison, Benetge Perera, Maura McLaughlin, Michael T. Lam, and Lina Levin
Subjects: Earth and Planetary Astrophysics (astro-ph.EP), High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Pulsar planet, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy, Binary number, Astronomy and Astrophysics, Star (graph theory), 01 natural sciences, Data set, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics - Earth and Planetary Astrophysics
Abstract: We search for extrasolar planets around millisecond pulsars using pulsar timing data and seek to determine the minimum detectable planetary masses as a function of orbital period. Using the 11-year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), we look for variations from our models of pulse arrival times due to the presence of exoplanets. No planets are detected around the millisecond pulsars in the NANOGrav 11-year data set, but taking into consideration the noise levels of each pulsar and the sampling rate of our observations, we develop limits that show we are sensitive to planetary masses as low as that of the moon. We analyzed potential planet periods, P, in the range 7 days < P < 2000 days, with somewhat smaller ranges for some binary pulsars. The planetary mass limit for our median-sensitivity pulsar within this period range is 1 M_moon (P / 100 days)^(-2/3)., Revised and accepted by ApJ Letters
Published: 2019

15. Evaluating Low-frequency Pulsar Observations to Monitor Dispersion with the Giant Metrewave Radio Telescope

Author: Jayanta Roy, James M. Cordes, Megan L. Jones, Bhaswati Bhattacharyya, Maura McLaughlin, Michael T. Lam, Lina Levin, and David L. Kaplan
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Giant Metrewave Radio Telescope, 010504 meteorology & atmospheric sciences, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Green Bank Telescope, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Pulsar timing array, Pulsar, 13. Climate action, Space and Planetary Science, Observatory, Millisecond pulsar, 0103 physical sciences, Arecibo Observatory, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project has the primary goal of detecting and characterizing low-frequency gravitational waves through high-precision pulsar timing. The mitigation of interstellar effects is crucial to achieve the necessary precision for gravitational wave detection. Effects like dispersion and scattering are more influential at lower observing frequencies, with the variation of these quantities over week-month timescales requiring high-cadence multi-frequency observations for pulsar timing projects. In this work, we utilize the dual-frequency observing capability of the Giant Metrewave Radio Telescope (GMRT) and evaluate the potential decrease in dispersion measure (DM) uncertainties when combined with existing pulsar timing array data. We present the timing analysis for four millisecond pulsars observed with the GMRT simultaneously at 322 and 607 MHz, and compare the DM measurements with those obtained through NANOGrav observations with the Green Bank Telescope (GBT) and Arecibo Observatory at 1400 to 2300 MHz frequencies. Measured DM values with the GMRT and NANOGrav program show significant offsets for some pulsars, which could be caused by pulse profile evolution in the two frequency bands. In comparison to the predicted DM uncertainties when incorporating these low-frequency data into the NANOGrav dataset, we find that higher-precision GMRT data is necessary to provide improved DM measurements. Through the detection and analysis of pulse profile baseline ripple in data on test pulsar B1929+10, we find that, while not important for this data, it may be relevant for other timing datasets. We discuss the possible advantages and challenges of incorporating GMRT data into NANOGrav and International Pulsar Timing Array datasets., 14 pages, 8 figures. Accepted to The Astrophysical Journal
Published: 2021

16. Relativistic Shapiro delay measurements of an extremely massive millisecond pulsar

Author: Paul R. Brook, Scott M. Ransom, Renée Spiewak, Ingrid H. Stairs, Megan L. Jones, H. Thankful Cromartie, Paul Demorest, Timothy Dolch, Justin A. Ellis, Duncan R. Lorimer, Kevin Stovall, Weiwei Zhu, Maura McLaughlin, Elizabeth C. Ferrara, Harsha Blumer, Zaven Arzoumanian, Megan E. DeCesar, Emmanuel Fonseca, Michael T. Lam, Cherry Ng, Joseph K. Swiggum, Timothy T. Pennucci, Ryan S. Lynch, David J. Nice, Robert D. Ferdman, N. Garver-Daniels, and P. A. Gentile
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Solar mass, 010504 meteorology & atmospheric sciences, Gravitational wave, Equation of state (cosmology), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Shapiro delay, Binary pulsar, Neutron star, Pulsar, Millisecond pulsar, 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract: Despite its importance to our understanding of physics at supranuclear densities, the equation of state (EoS) of matter deep within neutron stars remains poorly understood. Millisecond pulsars (MSPs) are among the most useful astrophysical objects in the Universe for testing fundamental physics, and place some of the most stringent constraints on this high-density EoS. Pulsar timing - the process of accounting for every rotation of a pulsar over long time periods - can precisely measure a wide variety of physical phenomena, including those that allow the measurement of the masses of the components of a pulsar binary system (Lorimer & Kramer 2005). One of these, called relativistic Shapiro delay (Shapiro 1964), can yield precise masses for both an MSP and its companion; however, it is only easily observed in a small subset of high-precision, highly inclined (nearly edge-on) binary pulsar systems. By combining data from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set with recent orbital-phase-specific observations using the Green Bank Telescope, we have measured the mass of the MSP J0740+6620 to be $\mathbf{2.14^{+0.10}_{-0.09}}$ solar masses (68.3% credibility interval; 95.4% credibility interval is $\mathbf{2.14^{+0.20}_{-0.18}}$ solar masses). It is highly likely to be the most massive neutron star yet observed, and serves as a strong constraint on the neutron star interior EoS., 12 pages, 3 figures, 1 table, published in Nature Astronomy (2019)
Published: 2019

17. Estimates of Fast Radio Burst Dispersion Measures from Cosmological Simulations

Author: Nihan Pol, James M. Cordes, T. J. W. Lazio, Maura McLaughlin, and Michael T. Lam
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, media_common.quotation_subject, Dark matter, Population, FOS: Physical sciences, Astrophysics, 01 natural sciences, symbols.namesake, 0103 physical sciences, education, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, education.field_of_study, Fast radio burst, Balmer series, Astronomy and Astrophysics, Galaxy, Redshift, Universe, Space and Planetary Science, symbols, Intergalactic travel, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We calculate the dispersion measure (DM) contributed by the intergalactic medium (IGM) to the total measured DM for fast radio bursts (FRBs). We use the MareNostrum Instituto de Ciencias del Espacio (MICE) Onion Universe simulation (Fosalba et al. 2008) to track the evolution of the dark matter particle density over a large range of redshifts. We convert this dark matter particle number density to the corresponding free electron density and then integrate it to find the DM as a function of redshift. This approach yields an intergalactic DM of $\rm DM_{\rm IGM}(z = 1) = 800^{+7000}_{-170}$ pc cm$^{-3}$, with the large errors representative of the structure in the IGM. We place limits on the redshifts of the current population of observed FRBs. We also use our results to estimate the host galaxy contribution to the DM for the first repeater, FRB 121102, and show that the most probable host galaxy DM contribution, $\rm DM_{\rm host} \approx 310$ pc cm$^{-3}$, is consistent with the estimate made using the Balmer emission lines in the spectrum of the host galaxy, $\rm DM_{\rm Balmer} = 324$ pc cm$^{-3}$ (Tendulkar et al. 2017). We also compare our predictions for the host galaxy contribution to the DM for the observations of FRB 180924 (Bannister et al. 2019) and FRB 190523 (Ravi et al. 2019), both of which have been localized to a host galaxy., Resubmitted to ApJ following second round of referee comments. Expanded sub-section comparing our results to those from other works (Sec. 3.3)
Published: 2019

18. Large High-precision X-Ray Timing of Three Millisecond Pulsars with $NICER$: Stability Estimates and Comparison with Radio

Author: Samuel R. Price, R. Spiewak, Paul Demorest, Sarah J. Vigeland, Slavko Bogdanov, W. W. Zhu, Timothy Dolch, Michael T. Lam, Julia S. Deneva, Peter A. Gentile, Cherry Ng, Zaven Arzoumanian, Harsha Blumer, D. R. Lorimer, N. Garver-Daniels, Maura McLaughlin, K. S. Wood, Matthew Kerr, J. Doty, Paul S. Ray, Scott M. Ransom, C. B. Markwardt, C. Malacaria, Joseph K. Swiggum, J. A. Ellis, Ingrid H. Stairs, M. L. Jones, Sebastien Guillot, Emmanuel Fonseca, Andrea N. Lommen, Paul R. Brook, Alice K. Harding, Kevin Stovall, Kevin Black, L. Guillemot, Robert D. Ferdman, David J. Nice, Timothy T. Pennucci, Luke M. Winternitz, Ismaël Cognard, M. T. Wolff, E. C. Ferrara, Ryan S. Lynch, H. T. Cromartie, M. E. DeCesar, Paul T. Baker, Natalia Lewandowska, Keith Gendreau, Institut de recherche en astrophysique et planétologie (IRAP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, 7. Clean energy, Stability (probability), stars: neutron, Pulsar, Millisecond pulsar, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Neutron Star Interior Composition Explorer, Sigma, Order (ring theory), Astronomy and Astrophysics, Interstellar medium, pulsars: individual, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Noise (radio)
Abstract: The Neutron Star Interior Composition Explorer (NICER) is an X-ray astrophysics payload on the International Space Station. It enables unprecedented high-precision timing of millisecond pulsars without the pulse broadening and delays due to dispersion and scattering within the interstellar medium that plague radio timing. We present initial timing results from a year of data on the millisecond pulsars PSR B1937+21 and PSR J0218+4232, and nine months of data on PSR B1821-24. NICER time-of-arrival uncertainties for the three pulsars are consistent with theoretical lower bounds and simulations based on their pulse shape templates and average source and background photon count rates. To estimate timing stability, we use the $\sigma_z$ measure, which is based on the average of the cubic coefficients of polynomial fits to subsets of timing residuals. So far we are achieving timing stabilities $\sigma_z \approx 3 \times 10^{-14}$ for PSR B1937+21 and on the order of $10^{-12}$ for PSRs B1821$-$24 and J0218+4232. Within the span of our \textit{NICER} data we do not yet see the characteristic break point in the slope of $\sigma_z$; detection of such a break would indicate that further improvement in the cumulative root-mean-square (RMS) timing residual is limited by timing noise. We see this break point in our comparison radio data sets for PSR B1821-24 and PSR B1937+21 on time scales of $> 2$ years., Comment: 30 pages, 15 figures; accepted to ApJ
Published: 2019

19. The International Pulsar Timing Array: Second data release

Author: Sarah Burke-Spolaor, Robert D. Ferdman, Stephen Taylor, Lei Zhang, Janna Goldstein, Caterina Tiburzi, Alberto Sesana, Ingrid H. Stairs, Elizabeth C. Ferrara, N. D. R. Bhat, Benetge Perera, Aditya Parthasarathy, Michael Kramer, H. Hu, Richard N. Manchester, Joseph Simon, L. Lentati, Matthew Kerr, Shi Dai, R. N. Caballero, Megan E. DeCesar, Paul Demorest, A. Possenti, Xing-Jiang Zhu, Kathryn Crowter, Weiwei Zhu, C. G. Bassa, Emmanuel Fonseca, Kejia Lee, Scott M. Ransom, Michael Keith, Stefan Oslowski, Chiara M. F. Mingarelli, D. J. Champion, Ramesh Karuppusamy, David J. Nice, Andrew Lyne, Timothy T. Pennucci, Timothy Dolch, J. K. Swiggum, Benjamin Stappers, K. Islo, Lucas Guillemot, Michele Vallisneri, J. B. Wang, X. Siemens, Gregory Desvignes, Gilles Theureau, James M. Cordes, Ismaël Cognard, Renée Spiewak, Siyuan Chen, Jing Luo, S. A. Sanidas, P. T. Baker, A. Brazier, Songbo Zhang, Alberto Vecchio, George Hobbs, Delphine Perrodin, Michael T. Lam, Jeffrey S. Hazboun, M. Burgay, Daniel J. Reardon, Zaven Arzoumanian, G. Shaifullah, J. W. McKee, Maura McLaughlin, Christopher J. Russell, Sourav Chatterjee, Kang Liu, Matthew Bailes, Gemma H. Janssen, Ryan Shannon, E. Graikou, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Théories (LUTH (UMR_8102)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Perera, B, Decesar, M, Demorest, P, Kerr, M, Lentati, L, Nice, D, Osłowski, S, Ransom, S, Keith, M, Arzoumanian, Z, Bailes, M, Baker, P, Bassa, C, Bhat, N, Brazier, A, Burgay, M, Burke-Spolaor, S, Caballero, R, Champion, D, Chatterjee, S, Chen, S, Cognard, I, Cordes, J, Crowter, K, Dai, S, Desvignes, G, Dolch, T, Ferdman, R, Ferrara, E, Fonseca, E, Goldstein, J, Graikou, E, Guillemot, L, Hazboun, J, Hobbs, G, Hu, H, Islo, K, Janssen, G, Karuppusamy, R, Kramer, M, Lam, M, Lee, K, Liu, K, Luo, J, Lyne, A, Manchester, R, Mckee, J, Mclaughlin, M, Mingarelli, C, Parthasarathy, A, Pennucci, T, Perrodin, D, Possenti, A, Reardon, D, Russell, C, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Siemens, X, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Vallisneri, M, Vecchio, A, Wang, J, Zhang, S, Zhang, L, Zhu, W, Zhu, X, Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Université de Franche-Comté (UFC)-Centre National de la Recherche Scientifique (CNRS)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Technologie de Belfort-Montbeliard (UTBM), PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Ephemeris, 01 natural sciences, Pulsar timing array, stars: neutron, neutron [stars], Pulsar, Millisecond pulsar, Observatory, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, methods: data analysis, European Pulsar Timing Array, gravitational waves, Space and Planetary Science, [SDU]Sciences of the Universe [physics], pulsars, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Noise (radio), Methods: data analysi
Abstract: In this paper, we describe the International Pulsar Timing Array second data release, which includes recent pulsar timing data obtained by three regional consortia: the European Pulsar Timing Array, the North American Nanohertz Observatory for Gravitational Waves, and the Parkes Pulsar Timing Array. We analyse and where possible combine high-precision timing data for 65 millisecond pulsars which are regularly observed by these groups. A basic noise analysis, including the processes which are both correlated and uncorrelated in time, provides noise models and timing ephemerides for the pulsars. We find that the timing precisions of pulsars are generally improved compared to the previous data release, mainly due to the addition of new data in the combination. The main purpose of this work is to create the most up-to-date IPTA data release. These data are publicly available for searches for low-frequency gravitational waves and other pulsar science., Comment: Submitted to MNRAS and in review, 23 pages, 5 figures
Published: 2019
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20. Tests of gravitational symmetries with pulsar binary J1713+0747

Author: Michael Kramer, Kang Liu, Robert D. Ferdman, Lina Levin, P. Lazarus, Marjorie Gonzalez, Michael T. Lam, Gemma H. Janssen, Kejia Lee, Timothy Dolch, Norbert Wex, Scott M. Ransom, Kathryn Crowter, A. Jessner, Ramesh Karuppusamy, J. K. Swiggum, Andrew Lyne, K. Lazaridis, M. L. Jones, Gregory Desvignes, J. W. McKee, Gilles Theureau, Ismaël Cognard, R. Smits, Maura McLaughlin, A. Krieger, Weiwei Zhu, M. Burgay, D. J. Champion, Timothy T. Pennucci, Delphine Perrodin, Caterina Tiburzi, L. Lentati, Kevin Stovall, Joris P. W. Verbiest, A. Possenti, Christine Jordan, Glenn Jones, G. Shaifullah, E. Graikou, J. A. Ellis, David J. Nice, R. N. Caballero, Ingrid H. Stairs, Stefan Oslowski, Jason W. T. Hessels, C. G. Bassa, Emmanuel Fonseca, Benjamin Stappers, S. A. Sanidas, Zaven Arzoumanian, Lucas Guillemot, Paul Demorest, High Energy Astrophys. & Astropart. Phys (API, FNWI), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Théories (LUTH (UMR_8102)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace ( LPC2E ), Centre National de la Recherche Scientifique ( CNRS ) -Université d'Orléans ( UO ) -Institut national des sciences de l'Univers ( INSU - CNRS ), Unité Scientifique de la Station de Nançay ( USN ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire Univers et Théories ( LUTH ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Zhu, W, Desvignes, G, Wex, N, Caballero, R, Champion, D, Demorest, P, Ellis, J, Janssen, G, Kramer, M, Krieger, A, Lentati, L, Nice, D, Ransom, S, Stairs, I, Stappers, B, Verbiest, J, Arzoumanian, Z, Bassa, C, Burgay, M, Cognard, I, Crowter, K, Dolch, T, Ferdman, R, Fonseca, E, Gonzalez, M, Graikou, E, Guillemot, L, Hessels, J, Jessner, A, Jones, G, Jones, M, Jordan, C, Karuppusamy, R, Lam, M, Lazaridis, K, Lazarus, P, Lee, K, Levin, L, Liu, K, Lyne, A, Mckee, J, Mclaughlin, M, Osłowski, S, Pennucci, T, Perrodin, D, Possenti, A, Sanidas, S, Shaifullah, G, Smits, R, Stovall, K, Swiggum, J, Theureau, G, Tiburzi, C, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)
Subjects: General relativity, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astronomy, FOS: Physical sciences, Astrophysics, Lorentz covariance, 01 natural sciences, Binary pulsar, Gravitation, stars: neutron, General Relativity and Quantum Cosmology, Pulsar, Gravitational field, 0103 physical sciences, pulsars: individual (PSR J1713+0747), 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astronomy and Astrophysics, Gravitational constant, European Pulsar Timing Array, binaries: general, Space and Planetary Science, [SDU]Sciences of the Universe [physics], gravitation, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: Symmetries play an important role in modern theories of gravity. The strong equivalence principle (SEP) constitutes a collection of gravitational symmetries which are all implemented by general relativity. Alternative theories, however, are generally expected to violate some aspects of SEP. We test three aspects of SEP using observed change rates in the orbital period and eccentricity of binary pulsar J1713+0747: 1. the gravitational constant's constancy as part of locational invariance of gravitation; 2. the post-Newtonian parameter $\hat{\alpha}_3$ in gravitational Lorentz invariance; 3. the universality of free fall (UFF) for strongly self-gravitating bodies. Based on the pulsar timing result of the combined dataset from the North American Nanohertz Gravitational Observatory (NANOGrav) and the European Pulsar Timing Array (EPTA), we find $\dot{G}/G = (-0.1 \pm 0.9) \times 10^{-12}\,{\rm yr}^{-1}$, which is weaker than Solar system limits, but applies for strongly self-gravitating objects. Furthermore, we obtain the constraints $|\Delta|< 0.002$ for the UFF test and $-3\times10^{-20} < \hat{\alpha}_3 < 4\times10^{-20}$ at 95% confidence. These are the first direct UFF and $\hat{\alpha}_3$ tests based on pulsar binaries, and they overcome various limitations of previous tests., Comment: 11 pages, 6 figures, and 1 table; submitted to MNRAS
Published: 2019

21. A Study in Frequency-dependent Effects on Precision Pulsar Timing Parameters with the Pulsar Signal Simulator

Author: Maura McLaughlin, Brent J. Shapiro-Albert, Michael T. Lam, and Jeffrey S. Hazboun
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010504 meteorology & atmospheric sciences, Scattering, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Covariance, 01 natural sciences, Signal, Pulse (physics), Root mean square, Radio telescope, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Simulation, 0105 earth and related environmental sciences
Abstract: In this paper we introduce a new Python package, the Pulsar Signal Simulator, or PsrSigSim, which is designed to simulate a pulsar signal from emission at the pulsar, through the interstellar medium, to observation by a radio telescope, and digitization in a standard data format. We use the PsrSigSim to simulate observations of three millisecond pulsars, PSRs J1744--1134, B1855+09, and B1953+29, to explore the covariances between frequency-dependent parameters, such as variations in the dispersion measure (DM), pulse profile evolution with frequency, and pulse scatter broadening. We show that the PsrSigSim can produce realistic simulated data and can accurately recover the parameters injected into the data. We also find that while there are covariances when fitting DM variations and frequency-dependent parameters, they have little effect on timing precision. Our simulations also show that time-variable scattering delays decrease the accuracy and increase the variability of the recovered DM and frequency-dependent parameters. Despite this, our simulations also show that the time-variable scattering delays have little impact on the root mean square of the timing residuals. This suggests that the variability seen in recovered DM, when time-variable scattering delays are present, is due to a covariance between the two parameters, with the DM modeling out the additional scattering delays., Comment: 21 pages, 9 figures, 7 tables, accepted for publication in ApJ
Published: 2021

22. A Measurement of the Galactic Plane Mass Density from Binary Pulsar Accelerations

Author: Sarah J. Vigeland, Michael T. Lam, Philip Chang, Sukanya Chakrabarti, and Alice C. Quillen
Subjects: Physics, 010504 meteorology & atmospheric sciences, Milky Way, Dark matter, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Galactic plane, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Binary pulsar, Radial velocity, Pulsar, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Astrophysics::Earth and Planetary Astrophysics, Halo, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy rotation curve, 0105 earth and related environmental sciences
Abstract: We use compiled high-precision pulsar timing measurements to directly measure the Galactic acceleration of binary pulsars relative to the Solar System barycenter. Given the vertical accelerations, we use the Poisson equation to derive the Oort limit, i.e., the total volume mass density in the Galactic mid-plane. Our best-fitting model gives an Oort limit of $0.08^{0.05}_{-0.02} M_{\odot}/\rm pc^{3}$, which is close to estimates from recent Jeans analyses. Given the accounting of the baryon budget from McKee et al. (2015), we obtain a local dark matter density of $-0.004^{0.05}_{-0.02}~M_{\odot}/\rm pc^{3}$, which is slightly below other modern estimates but consistent within the current uncertainties of our method. While this first measurement of the Oort limit (and other Galactic parameters) has error bars that are currently several times larger than kinematical estimates, they should improve in the future. We also constrain the oblateness of the potential, finding it consistent with that expected from the disk and inconsistent with a potential dominated by a spherical halo, as is appropriate for our sample which is within a $\sim$ kpc of the Sun. We find that the slope of the rotation curve is not constrained by current measurements of binary pulsar accelerations. We give a fitting function for the vertical acceleration $a_{z}$: $a_{z} = -\alpha_{1}z$; $\log_{10} (\alpha_{1}/{\rm Gyr}^{-2})=3.69^{0.19}_{-0.12}$. By analyzing interacting simulations of the Milky Way, we find that large asymmetric variations in $da_{z}/dz$ as a function of vertical height may be a signature of sub-structure. We end by discussing the power of combining constraints from pulsar timing and high-precision radial velocity (RV) measurements towards lines-of-sight near pulsars, to test theories of gravity and constrain dark matter sub-structure., Comment: accepted to ApJ Letters, changes following referee comments
Published: 2021

23. The NANOGrav 12.5 yr Data Set: Search for an Isotropic Stochastic Gravitational-wave Background

Author: Harsha Blumer, D. R. Madison, Ryan S. Lynch, Paul Demorest, Deborah C. Good, Paul R. Brook, Megan L. Jones, Renée Spiewak, Paul T. Baker, Nathan Garver-Daniels, Jeffrey S. Hazboun, Luke Zoltan Kelley, A. Miguel Holgado, Scott M. Ransom, Caitlin A. Witt, Neil J. Cornish, Nima Laal, Joseph Simon, Timothy T. Pennucci, Michele Vallisneri, Jing Luo, Siyuan Chen, Fronefield Crawford, Zaven Arzoumanian, Ross J. Jennings, Chiara M. F. Mingarelli, Joey Shapiro Key, Elizabeth C. Ferrara, Shami Chatterjee, Cherry Ng, Adam Brazier, Jerry P. Sun, Kevin Stovall, Sarah Burke-Spolaor, Sarah J. Vigeland, Xavier Siemens, James M. Cordes, William Fiore, Timothy Dolch, Joseph K. Swiggum, Peter A. Gentile, H. Thankful Cromartie, Brent J. Shapiro-Albert, Jacob E. Turner, Paul S. Ray, B. Bécsy, David J. Nice, David L. Kaplan, T. Joseph W. Lazio, Ingrid H. Stairs, K. Islo, Nihan Pol, Duncan R. Lorimer, Justin A. Ellis, Maura McLaughlin, Andrew R. Kaiser, Michael T. Lam, Megan E. DeCesar, Emmanuel Fonseca, Stephen Taylor, Daniel R. Stinebring, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Franche-Comté Électronique Mécanique, Thermique et Optique - Sciences et Technologies (UMR 6174) (FEMTO-ST), Université de Technologie de Belfort-Montbeliard (UTBM)-Ecole Nationale Supérieure de Mécanique et des Microtechniques (ENSMM)-Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), NANOGrav, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES)
Subjects: noise, gravitational radiation: stochastic, 010504 meteorology & atmospheric sciences, General relativity, Population, Astrophysics, Bayesian, 01 natural sciences, General Relativity and Quantum Cosmology, Gravitational wave background, Pulsar, Millisecond pulsar, 0103 physical sciences, general relativity, black hole, education, 010303 astronomy & astrophysics, pulsar, 0105 earth and related environmental sciences, [PHYS]Physics [physics], Physics, education.field_of_study, Gravitational wave, gravitational radiation: background, Astronomy and Astrophysics, solar system, Astrophysics - Astrophysics of Galaxies, observatory, Black hole, Amplitude, black hole: binary, [SDU]Sciences of the Universe [physics], Space and Planetary Science, correlation, slope, [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc], spectral, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We search for an isotropic stochastic gravitational-wave background (GWB) in the $12.5$-year pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. Our analysis finds strong evidence of a stochastic process, modeled as a power-law, with common amplitude and spectral slope across pulsars. The Bayesian posterior of the amplitude for an $f^{-2/3}$ power-law spectrum, expressed as the characteristic GW strain, has median $1.92 \times 10^{-15}$ and $5\%$--$95\%$ quantiles of $1.37$--$2.67 \times 10^{-15}$ at a reference frequency of $f_\mathrm{yr} = 1 ~\mathrm{yr}^{-1}$. The Bayes factor in favor of the common-spectrum process versus independent red-noise processes in each pulsar exceeds $10,000$. However, we find no statistically significant evidence that this process has quadrupolar spatial correlations, which we would consider necessary to claim a GWB detection consistent with general relativity. We find that the process has neither monopolar nor dipolar correlations, which may arise from, for example, reference clock or solar system ephemeris systematics, respectively. The amplitude posterior has significant support above previously reported upper limits; we explain this in terms of the Bayesian priors assumed for intrinsic pulsar red noise. We examine potential implications for the supermassive black hole binary population under the hypothesis that the signal is indeed astrophysical in nature., Comment: 25 pages, 14 figures, 5 tables, 3 appendices. Published in The Astrophysical Journal Letters. Please send any comments/questions to Joseph Simon (joe.simon@nanograv.org). Jupyter notebook tutorials and some MCMC chain files are available at https://github.com/nanograv/12p5yr_stochastic_analysis
Published: 2020

24. From spin noise to systematics: stochastic processes in the first International Pulsar Timing Array data release

Author: R. van Haasteren, Scott M. Ransom, S. Babak, Antoine Petiteau, Paul Demorest, L. Toomey, Gemma H. Janssen, Alberto Sesana, Marjorie Gonzalez, Sourav Chatterjee, A. Lassus, Ryan Shannon, Justin A. Ellis, Glenn Jones, E. Graikou, J. W. McKee, Kang Liu, Kejia Lee, Matthew Kerr, Sarah Burke-Spolaor, William A. Coles, Maura McLaughlin, G. Shaifullah, Stephen Taylor, Weiwei Zhu, P. Lazarus, S. A. Sanidas, D. J. Champion, Delphine Perrodin, R. N. Caballero, Kevin Stovall, Joris P. W. Verbiest, Benetge Perera, Richard N. Manchester, C. G. Bassa, Emmanuel Fonseca, Jonathan R. Gair, George Hobbs, D. R. Madison, R. Smits, Alberto Vecchio, Daniel R. Stinebring, Michael T. Lam, Daniel J. Reardon, X. P. You, Zaven Arzoumanian, Paul D. Lasky, Yue-Fei Wang, Lucas Guillemot, R. S. Lynch, Pablo Rosado, Lina Levin, Xing-Jiang Zhu, Chiara M. F. Mingarelli, L. Lentati, Benjamin Stappers, A. Possenti, T. J. W. Lazio, Robert D. Ferdman, Stefan Oslowski, J. K. Swiggum, X. Siemens, Gregory Desvignes, Gilles Theureau, Ramesh Karuppusamy, Ismaël Cognard, M. Burgay, Timothy T. Pennucci, Michele Vallisneri, J. B. Wang, James M. Cordes, Sean T. McWilliams, David J. Nice, P. Brem, W. van Straten, Caterina Tiburzi, N. D. R. Bhat, Shi Dai, Jason W. T. Hessels, Ingrid H. Stairs, Timothy Dolch, Michael Kramer, Michael Keith, Lentati, L, Shannon, R, Coles, W, Verbiest, J, van Haasteren, R, Ellis, J, Caballero, R, Manchester, R, Arzoumanian, Z, Babak, S, Bassa, C, Bhat, N, Brem, P, Burgay, M, Burke-Spolaor, S, Champion, D, Chatterjee, S, Cognard, I, Cordes, J, Dai, S, Demorest, P, Desvignes, G, Dolch, T, Ferdman, R, Fonseca, E, Gair, J, Gonzalez, M, Graikou, E, Guillemot, L, Hessels, J, Hobbs, G, Janssen, G, Jones, G, Karuppusamy, R, Keith, M, Kerr, M, Kramer, M, Lam, M, Lasky, P, Lassus, A, Lazarus, P, Lazio, T, Lee, K, Levin, L, Liu, K, Lynch, R, Madison, D, Mckee, J, Mclaughlin, M, Mcwilliams, S, Mingarelli, C, Nice, D, Osłowski, S, Pennucci, T, Perera, B, Perrodin, D, Petiteau, A, Possenti, A, Ransom, S, Reardon, D, Rosado, P, Sanidas, S, Sesana, A, Shaifullah, G, Siemens, X, Smits, R, Stairs, I, Stappers, B, Stinebring, D, Stovall, K, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Toomey, L, Vallisneri, M, van Straten, W, Vecchio, A, Wang, J, Wang, Y, You, X, Zhu, W, Zhu, X, High Energy Astrophys. & Astropart. Phys (API, FNWI), Cavendish Laboratory, University of Cambridge [UK] (CAM), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), University of California, University of California (UC), Max-Planck-Institut für Radioastronomie (MPIFR), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), NASA Goddard Space Flight Center (GSFC), Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Max-Planck-Gesellschaft, Netherlands Institute for Radio Astronomy (ASTRON), Curtin University [Perth], Planning and Transport Research Centre (PATREC), INAF - Osservatorio Astronomico di Cagliari (OAC), Istituto Nazionale di Astrofisica (INAF), National Radio Astronomy Observatory (NRAO), Center for Radiophysics and Space Research [Ithaca] (CRSR), Cornell University [New York], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Department of Astronomy [Ithaca], Department of Physics, Hillsdale College, Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), University of British Columbia (UBC), Vancouver Coastal Health, Department of Nuclear Medicine, Netherlands Institute for Radio Astronomy ( ASTRON ), ARC Centre of Excellence for Coral Reef Studies (CoralCoE), James Cook University (JCU), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Vrije Universiteit Medical Centre (VUMC), Vrije Universiteit Amsterdam [Amsterdam] (VU), Kavli Institute for Astronomy and Astrophysics [Beijing] (KIAA-PKU), Peking University [Beijing], National Radio Astronomy Observatory [Green Bank] (NRAO), Jodrell Bank Centre for Astrophysics (JBCA), Department of Physics, West Virginia University, West Virginia University, Theoretical Astrophysics [Pasadena] (TAPIR), California Institute of Technology (CALTECH), Physics Department, Lafayette College, Lafayette College [Easton], Department of Astronomy [Charlottesville], University of Virginia, APC - Gravitation (APC-Gravitation), AstroParticule et Cosmologie (APC (UMR_7164)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Max-Planck-Gesellschaft-Max-Planck-Gesellschaft, Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Anton Pannekoek Institute for Astronomy, University of Amsterdam [Amsterdam] (UvA), University of Wisconsin - Milwaukee, Department of Physics and Astronomy, University of British Columbia, Department of Physics and Astronomy [Oberlin], Oberlin College, Institute of Meteoritics [Albuquerque] (IOM), The University of New Mexico [Albuquerque], Department of Physics and Astronomy, West Virginia University, West Virginia University [Morgantown], Birmingham City University (BCU), Xinjiang Astronomical Observatory, Chinese Academy of Sciences [Beijing] (CAS), Huazhong University of Science and Technology [Wuhan] (HUST), School of Physical Science and Technology, Southwest University [Chongqing], Australian Research Council Discovery Project DP140102578NASA through Einstein Fellowship grant PF3-140116West Light Foundation of CAS XBBS201322 and NSFC project no.11403086National Science Fundation of China (NSFC) award number 11503007NNSF of China (U1231120) and FRFCU (XDJK2015B012), European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), European Project: 227947,EC:FP7:ERC,ERC-2008-AdG,LEAP(2009), European Project: 610058,EC:FP7:ERC,ERC-2013-SyG,BLACKHOLECAM(2014), Cornell University, Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Division of Physics, Mathematics and Astronomy [Pasadena], California Institute of Technology (CALTECH)-California Institute of Technology (CALTECH), Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), California Institute of Technology (CALTECH)-NASA, Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), University of Virginia [Charlottesville], Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI)
Subjects: Astrophysics::High Energy Astrophysical Phenomena, data analysis, pulsars: general [methods], FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), Methods: Data analysi, Astrophysics, Astronomy & Astrophysics, general [pulsars], 01 natural sciences, General Relativity and Quantum Cosmology, pulsars:individual, Binary pulsar, Pulsar, 0103 physical sciences, data analysis [methods], Coherence (signal processing), Sensitivity (control systems), Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Stochastic process, Noise (signal processing), Model selection, Pulsars: General, Astronomy and Astrophysics, methods: data analysis, LIGO, Computational physics, Astrophysics - Solar and Stellar Astrophysics, [SDU]Sciences of the Universe [physics], 13. Climate action, Space and Planetary Science, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astronomical and Space Sciences
Abstract: We analyse the stochastic properties of the 49 pulsars that comprise the first International Pulsar Timing Array (IPTA) data release. We use Bayesian methodology, performing model selection to determine the optimal description of the stochastic signals present in each pulsar. In addition to spin-noise and dispersion-measure (DM) variations, these models can include timing noise unique to a single observing system, or frequency band. We show the improved radio-frequency coverage and presence of overlapping data from different observing systems in the IPTA data set enables us to separate both system and band-dependent effects with much greater efficacy than in the individual PTA data sets. For example, we show that PSR J1643$-$1224 has, in addition to DM variations, significant band-dependent noise that is coherent between PTAs which we interpret as coming from time-variable scattering or refraction in the ionised interstellar medium. Failing to model these different contributions appropriately can dramatically alter the astrophysical interpretation of the stochastic signals observed in the residuals. In some cases, the spectral exponent of the spin noise signal can vary from 1.6 to 4 depending upon the model, which has direct implications for the long-term sensitivity of the pulsar to a stochastic gravitational-wave (GW) background. By using a more appropriate model, however, we can greatly improve a pulsar's sensitivity to GWs. For example, including system and band-dependent signals in the PSR J0437$-$4715 data set improves the upper limit on a fiducial GW background by $\sim 60\%$ compared to a model that includes DM variations and spin-noise only., Comment: 29 pages. 16 figures. Accepted for publication in MNRAS
Published: 2016

25. The International Pulsar Timing Array: First data release

Author: Lucas Guillemot, Sourav Chatterjee, N. Garver-Daniels, D. R. Madison, Scott M. Ransom, J. K. Swiggum, Daniel R. Stinebring, Delphine Perrodin, Ingrid H. Stairs, Alberto Vecchio, Timothy Dolch, X. Siemens, Gregory Desvignes, Antoine Petiteau, Gilles Theureau, W. van Straten, J. B. Wang, X. P. You, Jason W. T. Hessels, Renée Spiewak, R. N. Caballero, Alberto Sesana, Stefan Oslowski, R. S. Lynch, Xing-Jiang Zhu, C. G. Bassa, Emmanuel Fonseca, Daniel J. Reardon, Yue-Fei Wang, Chiara M. F. Mingarelli, Benjamin Stappers, Kejia Lee, Stanislav Babak, Benetge Perera, Pablo Rosado, Zaven Arzoumanian, Richard N. Manchester, Paul Demorest, A. Brazier, Jonathan R. Gair, R. van Haasteren, Nipuni Palliyaguru, Lina Levin, R. Smits, Joseph Simon, P. Brem, Michele Vallisneri, Michael Kramer, James M. Cordes, Andrew Lyne, L. Lentati, Weiwei Zhu, Matthew Kerr, Peter A. Gentile, Michael Keith, A. Possenti, D. J. Champion, Caterina Tiburzi, T. J. W. Lazio, N. D. R. Bhat, A. Lassus, Stephen Taylor, Linqing Wen, Ryan Shannon, Glenn Jones, Shi Dai, E. Graikou, Gemma H. Janssen, S. J. Chamberlin, Kevin Stovall, Kang Liu, P. Lazarus, Ramesh Karuppusamy, S. A. Sanidas, Ismaël Cognard, George Hobbs, Robert D. Ferdman, Timothy T. Pennucci, M. Burgay, Sean T. McWilliams, David J. Nice, B. Christy, G. Shaifullah, L. Toomey, Justin A. Ellis, J. W. McKee, Maura McLaughlin, Paul D. Lasky, Michael T. Lam, Sarah Burke-Spolaor, Joris P. W. Verbiest, Marjorie Gonzalez, High Energy Astrophys. & Astropart. Phys (API, FNWI), Verbiest, J, Lentati, L, Hobbs, G, van Haasteren, R, Demorest, P, Janssen, G, Wang, J, Desvignes, G, Caballero, R, Keith, M, Champion, D, Arzoumanian, Z, Babak, S, Bassa, C, Bhat, N, Brazier, A, Brem, P, Burgay, M, Burke-Spolaor, S, Chamberlin, S, Chatterjee, S, Christy, B, Cognard, I, Cordes, J, Dai, S, Dolch, T, Ellis, J, Ferdman, R, Fonseca, E, Gair, J, Garver-Daniels, N, Gentile, P, Gonzalez, M, Graikou, E, Guillemot, L, Hessels, J, Jones, G, Karuppusamy, R, Kerr, M, Kramer, M, Lam, M, Lasky, P, Lassus, A, Lazarus, P, Lazio, T, Lee, K, Levin, L, Liu, K, Lynch, R, Lyne, A, Mckee, J, Mclaughlin, M, Mcwilliams, S, Madison, D, Manchester, R, Mingarelli, C, Nice, D, Osłowski, S, Palliyaguru, N, Pennucci, T, Perera, B, Perrodin, D, Possenti, A, Petiteau, A, Ransom, S, Reardon, D, Rosado, P, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Siemens, X, Simon, J, Smits, R, Spiewak, R, Stairs, I, Stappers, B, Stinebring, D, Stovall, K, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Toomey, L, Vallisneri, M, van Straten, W, Vecchio, A, Wang, Y, Wen, L, You, X, Zhu, W, Zhu, X, Max-Planck-Institut für Radioastronomie (MPIFR), Cavendish Laboratory, University of Cambridge [UK] (CAM), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), National Radio Astronomy Observatory [Socorro] (NRAO), National Radio Astronomy Observatory (NRAO), Netherlands Institute for Radio Astronomy (ASTRON), Xinjiang Astronomical Observatory, Chinese Academy of Sciences [Beijing] (CAS), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], NASA Goddard Space Flight Center (GSFC), Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Max-Planck-Gesellschaft, Curtin University [Perth], Planning and Transport Research Centre (PATREC), Cornell Center for Astrophysics and Planetary Science (CCAPS), Cornell University [New York], INAF - Osservatorio Astronomico di Cagliari (OAC), Istituto Nazionale di Astrofisica (INAF), Pennsylvania State University (Penn State), Penn State System, Center for Radiophysics and Space Research [Ithaca] (CRSR), University of Maryland [College Park], University of Maryland System, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Department of Astronomy [Ithaca], Department of Physics, Hillsdale College, University of British Columbia (UBC), University of Edinburgh, Department of Physics and Astronomy, West Virginia University, West Virginia University [Morgantown], Vancouver Coastal Health, Department of Nuclear Medicine, Department of Physics, Columbia University, Columbia University [New York], Monash Centre for Astrophysics (MoCA), Monash University [Clayton], Kavli Institute for Astronomy and Astrophysics [Beijing] (KIAA-PKU), Peking University [Beijing], National Radio Astronomy Observatory [Green Bank] (NRAO), Theoretical Astrophysics [Pasadena] (TAPIR), Division of Physics, Mathematics and Astronomy [Pasadena], California Institute of Technology (CALTECH)-California Institute of Technology (CALTECH), Physics Department, Lafayette College, Lafayette College [Easton], Physics Department, Texas Tech University, Texas Tech University [Lubbock] (TTU), Department of Astronomy [Charlottesville], University of Virginia [Charlottesville], APC - Gravitation (APC-Gravitation), AstroParticule et Cosmologie (APC (UMR_7164)), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Max-Planck-Gesellschaft-Max-Planck-Gesellschaft, Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Anton Pannekoek Institute for Astronomy, University of Amsterdam [Amsterdam] (UvA), University of Wisconsin - Milwaukee, Center for Gravitation, Cosmology and Astrophysics, Netherlands Institute for Radio Astronomy ( ASTRON ), Department of Physics and Astronomy, University of British Columbia, Department of Physics and Astronomy [Oberlin], Oberlin College, Department of Physics and Astronomy [Albuquerque], The University of New Mexico [Albuquerque], Birmingham City University (BCU), School of Physics [HUST], Huazhong University of Science and Technology [Wuhan] (HUST), School of Physics (University of Western Australia), Université, School of Physical Science and Technology, Southwest University [Chongqing], European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), Max-Planck-Institut für Radioastronomie, Cavendish Laboratory - University of Cambridge, University of Cambridge [UK] ( CAM ), CSIRO Astronomy and Space Science, PO BOX 76, NSW 1710, Australia, Jet Propulsion Laboratory ( JPL ), NASA-California Institute of Technology ( CALTECH ), National Radio Astronomy Observatory [Socorro] ( NRAO ), National Radio Astronomy Observatory ( NRAO ), Netherlands Institute for Radio Astronomy, Chinese Academy of Sciences [Beijing] ( CAS ), NASA Goddard Space Flight Center ( GSFC ), Albert Einstein Institute, Max-Planck-Institut für Gravitationsphysik, Curtin University, Perth, Australia, Cornell Center for Astrophysics and Planetary Science ( CCAPS ), Cornell University, MPI for Gravitational Physics (Albert Einstein Institute), INAF-Osservatorio di Cagliari, PennState University [Pennsylvania] ( PSU ), Center for Radiophysics and Space Research [Ithaca] ( CRSR ), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace ( LPC2E ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS ), Unité Scientifique de la Station de Nançay ( USN ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS ), University of British Columbia ( UBC ), University of Edimburgh, Kavli Institute for Astronomy and Astrophysics, National Radio Astronomy Observatory [Green Bank] ( NRAO ), Commonwealth Scientific and Industrial Research Organisation [Canberra] ( CSIRO ), TAPIR (Theoretical Astrophysics), California Institute of Technology, Texas Tech University [Lubbock] ( TTU ), Osservatorio Astronomico di Cagliari, Ist Nazl Astrofis, Osservatorio Astronomico di Cagliari, APC - Gravitation ( APC-Gravitation ), AstroParticule et Cosmologie ( APC - UMR 7164 ), Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Centre National de la Recherche Scientifique ( CNRS ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Observatoire de Paris-Université Paris Diderot - Paris 7 ( UPD7 ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), Max-Planck-Institut-Max-Planck-Institut, Centre for Astrophysics and Supercomputing [Swinburne] ( CAS ), Anton Pannekoek Institute for Astronomy, University of Amsterdam, Max Planck Institut für Gravitationsphysik, Albert Einstein Institut, Physics and Astronomy Department [Oberlin], Center for Gravitational Wave Astronomy, The University of Texas at Brownsville and Texas Southmost College, Birmingham City University ( BCU ), School of Physics, Huazhong University of Science and Technology, Huazhong University of Science and Technology, School of Physics ( University of Western Australia ), European Project : 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET ( 2014 ), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), California Institute of Technology (CALTECH), University of Virginia, Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI)
Subjects: data analysis, data analysis, pulsars: general [methods], FOS: Physical sciences, Methods: Data analysi, general [pulsars], 01 natural sciences, 7. Clean energy, Set (abstract data type), Pulsar timing array, Pulsar, 0103 physical sciences, data analysis [methods], Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, instrumentation, Physics, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], 010308 nuclear & particles physics, Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Pulsars: General, Astronomy, Astronomy and Astrophysics, methods: data analysis, Data set, European Pulsar Timing Array, Neutron star, gravitational waves, Space and Planetary Science, pulsars, Measurement uncertainty, Astrophysics - Instrumentation and Methods for Astrophysics, [ SDU.ASTR.SR ] Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Algorithm, astro-ph.IM
Abstract: The highly stable spin of neutron stars can be exploited for a variety of (astro-)physical investigations. In particular arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such "Pulsar Timing Arrays" (PTAs) have been set up around the world over the past decades and collectively form the "International" PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available online) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limits placed by individual PTAs by a factor of ~2 and provides a 2-sigma limit on the dimensionless amplitude of a stochastic GWB of 1.7x10^{-15} at a frequency of 1 yr^{-1}. This is 1.7 times less constraining than the limit placed by (Shannon et al. 2015), due mostly to the more recent, high-quality data they used., 25 pages, 6 tables, 5 figures. Accepted for publication in MNRAS
Published: 2016

26. On Frequency-dependent Dispersion Measures and Extreme Scattering Events

Author: Daniel R. Stinebring, Mayuresh Surnis, Megan L. Jones, Timothy Dolch, Michael T. Lam, Maura McLaughlin, and T. J. W. Lazio
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Line-of-sight, 010504 meteorology & atmospheric sciences, Scattering, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Electron, LOFAR, 01 natural sciences, Interstellar medium, Radio propagation, Pulsar, Space and Planetary Science, 0103 physical sciences, Dispersion (optics), Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract: Radio emission propagating over an Earth-pulsar line of sight provides a unique probe of the intervening ionized interstellar medium (ISM). Variations in the integrated electron column density along this line of sight, or dispersion measure (DM), have been observed since shortly after the discovery of pulsars. As early as 2006, frequency-dependent dispersion measures have been observed and attributed to several possible causes. Ray-path averaging over different effective light-cone volumes through the turbulent ISM contributes to this effect as will DM misestimation due to radio propagation across compact lensing structures such as those caused by "extreme scattering events". We present methods to assess the variations in frequency-dependent dispersion measures due to the turbulent ISM versus these compact lensing structures along the line of sight. We analyze recent Low-Frequency Array (LOFAR) observations of PSR J2219+4754 to test the underlying physical mechanism of the observed frequency-dependent DM. Previous analyses have indicated the presence of strong lensing due to compact overdensities halfway between the Earth and pulsar. Instead we find the frequency dependence of the DM timeseries for PSR J2219+4754 is consistent with being due solely to ISM turbulence and there is no evidence for any extreme scattering event or small-scale lensing structure. The data show possible deviations from a uniform turbulent medium, suggesting that there may be an enhanced scattering screen near one of the two ends of the line of sight. We present this analysis as an example of the power of low-frequency observations to distinguish the underlying mechanisms in frequency-dependent propagation effects., Comment: 16 pages, 7 figures, accepted by ApJ
Published: 2020

27. The NANOGrav 12.5-Year Data Set: The Frequency Dependence of Pulse Jitter in Precision Millisecond Pulsars

Author: Harsha Blumer, R. Spiewak, Peter A. Gentile, E. C. Ferrara, J. A. Ellis, Timothy Dolch, David J. Nice, Timothy T. Pennucci, N. Garver-Daniels, Scott M. Ransom, Chi-Yung Ng, Sarah J. Vigeland, H. T. Cromartie, M. E. DeCesar, Michael T. Lam, Paul Demorest, Joseph K. Swiggum, R. S. Lynch, W. W. Zhu, D. R. Lorimer, Zaven Arzoumanian, Robert D. Ferdman, Maura McLaughlin, Kevin Stovall, I. H. Stairs, Paul R. Brook, Emmanuel Fonseca, and M. L. Jones
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010504 meteorology & atmospheric sciences, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Radio telescope, Pulsar timing array, Amplitude, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Noise (radio), 0105 earth and related environmental sciences, Jitter
Abstract: Low-frequency gravitational-wave experiments require the highest timing precision from an array of the most stable millisecond pulsars. Several known sources of noise on short timescales in single radio-pulsar observations are well described by a simple model of three components: template-fitting from a finite signal-to-noise ratio, pulse phase/amplitude jitter from single-pulse stochasticity, and scintillation errors from short-timescale interstellar scattering variations. Currently template-fitting errors dominate, but as radio telescopes push towards higher signal-to-noise ratios, jitter becomes the next dominant term for most millisecond pulsars. Understanding the statistics of jitter becomes crucial for properly characterizing arrival-time uncertainties. We characterize the radio-frequency dependence of jitter using data on 48 pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) timing program. We detect significant jitter in 43 of the pulsars and test several functional forms for its frequency dependence; we find significant frequency dependence for 30 pulsars. We find moderate correlations of rms jitter with pulse width (R = 0.62) and number of profile components (R = 0.40); the single-pulse rms jitter is typically ~1% of pulse phase. The average frequency dependence for all pulsars using a power-law model has index -0.42. We investigate the jitter variations for the interpulse of PSR~B1937+21 and find no significant deviations from the main pulse rms jitter. We also test the time-variation of jitter in two pulsars and find that systematics likely bias the results for high-precision pulsars. Pulsar timing array analyses must properly model jitter as a significant component of the noise within the detector., 18 pages, 10 figures, submitted to ApJ
Published: 2018

28. The NANOGrav 11-year Data Set: Solar Wind Sounding Through Pulsar Timing

Author: Timothy Dolch, Duncan R. Lorimer, Ryan S. Lynch, Cherry Ng, Elizabeth C. Ferrara, Kathryn Crowter, Paul S. Ray, David J. Nice, Chiara M. F. Mingarelli, Timothy T. Pennucci, Paul Demorest, J. A. Ellis, M. L. Jones, Renée Spiewak, Ingrid H. Stairs, James M. Cordes, Shami Chatterjee, J. K. Swiggum, Zaven Arzoumanian, Kevin Stovall, Peter A. Gentile, Glenn Jones, Robert D. Ferdman, D. R. Madison, Weiwei Zhu, Michael T. Lam, Megan E. DeCesar, Emmanuel Fonseca, Maura McLaughlin, Scott M. Ransom, and Lina Levin
Subjects: Physics, 010504 meteorology & atmospheric sciences, Total electron content, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Interstellar medium, Depth sounding, Solar wind, Pulsar, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, Observatory, Millisecond pulsar, 0103 physical sciences, Physics::Space Physics, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences
Abstract: The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has observed dozens of millisecond pulsars for over a decade. We have accrued a large collection of dispersion measure (DM) measurements sensitive to the total electron content between Earth and the pulsars at each observation. All lines of sight cross through the solar wind which produces correlated DM fluctuations in all pulsars. We develop and apply techniques for extracting the imprint of the solar wind from the full collection of DM measurements in the recently released NANOGrav 11-yr data set. We filter out long time scale DM fluctuations attributable to structure in the interstellar medium and carry out a simultaneous analysis of all pulsars in our sample that can differentiate the correlated signature of the wind from signals unique to individual lines of sight. When treating the solar wind as spherically symmetric and constant in time, we find the electron number density at 1 A.U. to be $7.9\pm0.2$ cm$^{-3}$. Our data shows little evidence of long-term variation in the density of the wind. We argue that our techniques paired with a high cadence, low radio frequency observing campaign of near-ecliptic pulsars would be capable of mapping out large-scale latitudinal structure in the wind., 15 pages, submitted to ApJ
Published: 2018

29. A second chromatic timing event of interstellar origin toward PSR J1713+0747

Author: Renée Spiewak, Harsha Blumer, Megan E. DeCesar, Paul Demorest, Emmanuel Fonseca, J. E. Turner, Elizabeth C. Ferrara, Robert D. Ferdman, James M. Cordes, Sarah J. Vigeland, P. A. Gentile, Justin A. Ellis, Joseph K. Swiggum, Megan L. Jones, Timothy Dolch, Maura McLaughlin, Wenbai Zhu, Ryan S. Lynch, Gianfranco Grillo, Nathan Garver-Daniels, Ingrid H. Stairs, V. Gupta, Zaven Arzoumanian, Cherry Ng, Michael T. Lam, H. T. Cromartie, Duncan R. Lorimer, Daniel R. Stinebring, T. J. W. Lazio, Shami Chatterjee, Jeffrey S. Hazboun, Kevin Stovall, Paul R. Brook, David J. Nice, Timothy T. Pennucci, Scott M. Ransom, and Dustin R. Madison
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Line-of-sight, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Electron, Astrophysics, 01 natural sciences, Pulse (physics), Interstellar medium, Pulsar, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Dispersion (optics), Chromatic scale, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Event (particle physics)
Abstract: The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. 2013 was the first to show a short-term (~100-200 days) reduction in the electron content along the line of sight to PSR J1713+0747 in data from 2008 (approximately MJD 54750) based on an apparent dip in the dispersion measure of the pulsar. We report on a similar event in 2016 (approximately MJD 57510), with average residual pulse-arrival times of approximately 3.0,-1.3, and -0.7 microseconds at 820, 1400, and 2300 MHz, respectively. Timing analyses indicate possible departures from the standard nu^-2 dispersive-delay dependence. We discuss and rule out a wide variety of potential interpretations. We find the likeliest scenario to be lensing of the radio emission by some structure in the interstellar medium, which causes multiple frequency-dependent pulse arrival-time delays., 9 pages, 3 figures, published in ApJ
Published: 2018

30. The NANOGrav 11 Year Data Set:Pulsar-timing Constraints on the Stochastic Gravitational-wave Background

Author: Megan E. DeCesar, Renée Spiewak, Timothy Dolch, Timothy T. Pennucci, Emmanuel Fonseca, Alexander Rasskazov, D. R. Madison, Elizabeth C. Ferrara, Jing Luo, Justin A. Ellis, David L. Kaplan, William M. Folkner, V. M. Kaspi, B. Christy, Maura McLaughlin, T. J. W. Lazio, Neil J. Cornish, Weiwei Zhu, Ryan S. Park, P. T. Baker, Sean T. McWilliams, Joseph Simon, Glenn Jones, Stephen Taylor, Ryan S. Lynch, David J. Nice, Jeffrey S. Hazboun, Kathryn Crowter, Michael T. Lam, Paul S. Ray, E. A. Huerta, Peter A. Gentile, K. Islo, Daniel R. Stinebring, Nihan Pol, M. L. Jones, Chiara M. F. Mingarelli, Sarah Burke-Spolaor, Andrea N. Lommen, Roland Haas, Sarah J. Vigeland, Lina Levin, Robert D. Ferdman, S. J. Chamberlin, Fronefield Crawford, Joseph K. Swiggum, Shami Chatterjee, Kevin Stovall, Ingrid H. Stairs, H. Thankful Cromartie, Michele Vallisneri, James M. Cordes, Scott M. Ransom, R. van Haasteren, Adam Brazier, Cherry Ng, Xavier Siemens, Paul Demorest, Zaven Arzoumanian, N. Garver-Daniels, and Duncan R. Lorimer
Subjects: Stellar mass, Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics, General Relativity and Quantum Cosmology (gr-qc), Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, 01 natural sciences, general [pulsars], General Relativity and Quantum Cosmology, Gravitational wave background, Pulsar timing array, Pulsar, 0103 physical sciences, data analysis [methods], ephemeredes, inflation, education, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), education.field_of_study, Supermassive black hole, 010308 nuclear & particles physics, Gravitational wave, supermassive black holes [quasars], Astronomy and Astrophysics, Quasar, 16. Peace & justice, Astrophysics - Astrophysics of Galaxies, gravitational waves, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena
Abstract: We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released $11$-year dataset from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). While we find no significant evidence for a GWB, we place constraints on a GWB from a population of supermassive black-hole binaries, cosmic strings, and a primordial GWB. For the first time, we find that the GWB upper limits and detection statistics are sensitive to the Solar System ephemeris (SSE) model used, and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first PTA constraints that are robust against SSE uncertainties. We thus place a $95\%$ upper limit on the GW strain amplitude of $A_\mathrm{GWB}, 21 pages, 12 figures, 9 tables. Published in The Astrophysical Journal. Please send any comments/questions to S. R. Taylor (srtaylor@caltech.edu)
Published: 2018

31. PSR J2234+0611: A new laboratory for stellar evolution

Author: Renée Spiewak, Sarah J. Vigeland, Scott M. Ransom, Kevin Stovall, Timothy Dolch, Paul Demorest, Paulo C. C. Freire, M. L. Jones, P. A. Gentile, Manjari Bagchi, Julia Deneva, David J. Nice, Ryan S. Lynch, Weiwei Zhu, Timothy T. Pennucci, J. G. Martinez, Nathan Garver-Daniels, H. T. Cromartie, Megan E. DeCesar, J. K. Swiggum, Emmanuel Fonseca, Duncan R. Lorimer, Paul R. Brook, Elizabeth C. Ferrara, J. A. Ellis, Cherry Ng, Zaven Arzoumanian, Harsha Blumer, Ingrid H. Stairs, John Antoniadis, Robert D. Ferdman, Michael T. Lam, and Maura McLaughlin
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Solar mass, Proper motion, 010504 meteorology & atmospheric sciences, White dwarf, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Orbital inclination, Radial velocity, Orbit, Pulsar, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Stellar evolution, 0105 earth and related environmental sciences
Abstract: We report timing results for PSR J2234+0611, a 3.6-ms pulsar in a 32-day, eccentric (e = 0.13) orbit with a helium white dwarf companion discovered as part of the Arecibo Observatory 327 MHz drift scan survey. The precise timing and the eccentric nature of the orbit allow precise measurements of an unusual number of parameters: a) a precise proper motion of 27.10(3) mas/yr and a parallax of 1.05(4) mas resulting in a pulsar distance of 0.95(4) kpc; this allows a precise estimate of the transverse velocity, 123(5) km/s. Together with previously published spectroscopic measurements of the systemic radial velocity, this allows a full 3-D determination of the system's velocity; b) precise measurements of the rate of advance of periastron, which after subtraction of the contribution of the proper motion yields a total system mass of $1.6518^{+0.0033}_{-0.0035}$ solar masses; c) a Shapiro delay measurement, h_3 = $82 \pm 14$ ns despite the orbital inclination not being near 90 deg; combined with the measurement of the total mass, this yields a pulsar mass of $1.353^{+0.014}_{-0.017}$ solar masses and a companion mass of $0.298^{+0.015}_{-0.012}$ solar masses; d) we measure precisely the secular variation of the projected semi-major axis and detect significant annual orbital parallax; together these allow a determination of the full 3-D orbital geometry, including an unambiguous orbital inclination (i = $138.7^{+2.5}_{-2.2}$ deg) and a position angle for the line of nodes (Omega = $44^{+5}_{-4}$ deg). We discuss the component masses to investigate hypotheses previously advanced to explain the origin of eccentric MSPs. The unprecedented determination of the full 3-D position, motion and orbital orientation of the system, plus the precisely measured pulsar and WD mass and the latter's optical detection make this system an unique test of our understanding of white dwarfs and their atmospheres., Comment: 16 pages, 5 figures, accepted by ApJ
Published: 2018
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32. Studying the Solar system with the International Pulsar Timing Array

Author: R. S. Lynch, L. Toomey, Paul Demorest, J. K. Swiggum, X. Siemens, Gregory Desvignes, A. Possenti, T. J. W. Lazio, Gilles Theureau, D. R. Madison, Lucas Guillemot, Joseph Simon, Renée Spiewak, Kejia Lee, Alberto Sesana, Andrea N. Lommen, Gemma H. Janssen, Ramesh Karuppusamy, Xing-Jiang Zhu, Ismaël Cognard, Chiara M. F. Mingarelli, Benjamin Stappers, Stefan Oslowski, Sean T. McWilliams, Scott M. Ransom, S. A. Sanidas, David J. Nice, Kang Liu, G. Shaifullah, Marjorie Gonzalez, Y J Guo, Caterina Tiburzi, Robert D. Ferdman, James M. Cordes, P. Lazarus, N. D. R. Bhat, Jonathan R. Gair, Daniel R. Stinebring, George Hobbs, Sarah Burke-Spolaor, Nipuni Palliyaguru, Benetge Perera, Daniel J. Reardon, Richard N. Manchester, Shi Dai, Michael Kramer, Ryan Shannon, A. Brazier, R. van Haasteren, Joris P. W. Verbiest, Zaven Arzoumanian, M. Burgay, Timothy T. Pennucci, W. van Straten, Lina Levin, K. Plant, Ingrid H. Stairs, Peter A. Gentile, Duncan R. Lorimer, E. Graikou, Weiwei Zhu, N. Garver-Daniels, D. J. Champion, Matthew Bailes, S. J. Chamberlin, Delphine Perrodin, Sourav Chatterjee, Kevin Stovall, Michael Keith, Matthew Kerr, Timothy Dolch, J. B. Wang, R. N. Caballero, C. G. Bassa, Emmanuel Fonseca, Michael T. Lam, Stephen Taylor, Paul D. Lasky, J. W. McKee, Maura McLaughlin, Laboratoire de physique et chimie de l'environnement (LPCE), Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire Univers et Théories (LUTH (UMR_8102)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS), Caballero, R, Guo, Y, Lee, K, Lazarus, P, Champion, D, Desvignes, G, Kramer, M, Plant, K, Arzoumanian, Z, Bailes, M, Bassa, C, Bhat, N, Brazier, A, Burgay, M, Burke-Spolaor, S, Chamberlin, S, Chatterjee, S, Cognard, I, Cordes, J, Dai, S, Demorest, P, Dolch, T, Ferdman, R, Fonseca, E, Gair, J, Garver-Daniels, N, Gentile, P, Gonzalez, M, Graikou, E, Guillemot, L, Hobbs, G, Janssen, G, Karuppusamy, R, Keith, M, Kerr, M, Lam, M, Lasky, P, Lazio, T, Levin, L, Liu, K, Lommen, A, Lorimer, D, Lynch, R, Madison, D, Manchester, R, Mckee, J, Mclaughlin, M, Mcwilliams, S, Mingarelli, C, Nice, D, Osłowski, S, Palliyaguru, N, Pennucci, T, Perera, B, Perrodin, D, Possenti, A, Ransom, S, Reardon, D, Sanidas, S, Sesana, A, Shaifullah, G, Shannon, R, Siemens, X, Simon, J, Spiewak, R, Stairs, I, Stappers, B, Stinebring, D, Stovall, K, Swiggum, J, Taylor, S, Theureau, G, Tiburzi, C, Toomey, L, van Haasteren, R, van Straten, W, Verbiest, J, Wang, J, Zhu, X, and Zhu, W
Subjects: Solar System, Dwarf planet, FOS: Physical sciences, Astrophysics, Ephemeris, 01 natural sciences, Jovian, Pulsar, pulsars: general, 0103 physical sciences, Sensitivity (control systems), ephemerides, 010303 astronomy & astrophysics, Physics, Earth and Planetary Astrophysics (astro-ph.EP), methods: statistical, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Astronomy and Astrophysics, Planetary system, Ephemeride, methods: data analysis, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Methods: data analysi, Reference frame, Astrophysics - Earth and Planetary Astrophysics
Abstract: Pulsar-timing analyses are sensitive to errors in the solar-system ephemerides (SSEs) that timing models utilise to estimate the location of the solar-system barycentre, the quasi-inertial reference frame to which all recorded pulse times-of-arrival are referred. Any error in the SSE will affect all pulsars, therefore pulsar timing arrays (PTAs) are a suitable tool to search for such errors and impose independent constraints on relevant physical parameters. We employ the first data release of the International Pulsar Timing Array to constrain the masses of the planet-moons systems and to search for possible unmodelled objects (UMOs) in the solar system. We employ ten SSEs from two independent research groups, derive and compare mass constraints of planetary systems, and derive the first PTA mass constraints on asteroid-belt objects. Constraints on planetary-system masses have been improved by factors of up to 20 from the previous relevant study using the same assumptions, with the mass of the Jovian system measured at 9.5479189(3)$\times10^{-4}$ $M_{\odot}$. The mass of the dwarf planet Ceres is measured at 4.7(4)$\times10^{-10}$ $M_{\odot}$. We also present the first sensitivity curves using real data that place generic limits on the masses of UMOs, which can also be used as upper limits on the mass of putative exotic objects. For example, upper limits on dark-matter clumps are comparable to published limits using independent methods. While the constraints on planetary masses derived with all employed SSEs are consistent, we note and discuss differences in the associated timing residuals and UMO sensitivity curves., Comment: Accepted for publication by the Monthly Notices of the Royal Astronomical Society
Published: 2018

33. The NANOGrav 11-Year Data Set: Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author: David L. Kaplan, Adam Brazier, Sarah Burke-Spolaor, Megan E. DeCesar, Emmanuel Fonseca, R. van Haasteren, Joseph Simon, Joey Shapiro Key, Robert D. Ferdman, Cherry Ng, Zaven Arzoumanian, Lina Levin, Peter A. Gentile, N. Garver-Daniels, Neil J. Cornish, Ryan S. Lynch, Chiara M. F. Mingarelli, A. M. Holgado, Xavier Siemens, Kathryn Crowter, Justin A. Ellis, Stephen Taylor, J. E. Turner, Weiwei Zhu, Caitlin A. Witt, Ingrid H. Stairs, Paul Demorest, T. J. W. Lazio, Paul S. Ray, Michele Vallisneri, Ross J. Jennings, K. Islo, E. A. Huerta, J. Luo, Luke Zoltan Kelley, Sean T. McWilliams, David J. Nice, Maura McLaughlin, D. R. Madison, Daniel R. Stinebring, James M. Cordes, Renée Spiewak, P. T. Baker, M. R. Brinson, Kshitij Aggarwal, Elizabeth C. Ferrara, Nihan Pol, M. L. Jones, Glenn Jones, Paul R. Brook, Timothy Dolch, Jeffrey S. Hazboun, Scott M. Ransom, Michael T. Lam, Joseph K. Swiggum, H. T. Cromartie, Fronefield Crawford, Duncan R. Lorimer, Shami Chatterjee, Kevin Stovall, Andrew R. Kaiser, Timothy T. Pennucci, and Sarah J. Vigeland
Subjects: 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology (gr-qc), 01 natural sciences, General Relativity and Quantum Cosmology, Pulsar, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, Supermassive black hole, Solar mass, Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Virgo Cluster, Galaxy, Black hole, 13. Climate action, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Observations indicate that nearly all galaxies contain supermassive black holes (SMBHs) at their centers. When galaxies merge, their component black holes form SMBH binaries (SMBHBs), which emit low-frequency gravitational waves (GWs) that can be detected by pulsar timing arrays (PTAs). We have searched the recently-released North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set for GWs from individual SMBHBs in circular orbits. As we did not find strong evidence for GWs in our data, we placed 95\% upper limits on the strength of GWs from such sources as a function of GW frequency and sky location. We placed a sky-averaged upper limit on the GW strain of $h_0 < 7.3(3) \times 10^{-15}$ at $f_\mathrm{gw}= 8$ nHz. We also developed a technique to determine the significance of a particular signal in each pulsar using ``dropout' parameters as a way of identifying spurious signals in measurements from individual pulsars. We used our upper limits on the GW strain to place lower limits on the distances to individual SMBHBs. At the most-sensitive sky location, we ruled out SMBHBs emitting GWs with $f_\mathrm{gw}= 8$ nHz within 120 Mpc for $\mathcal{M} = 10^9 \, M_\odot$, and within 5.5 Gpc for $\mathcal{M} = 10^{10} \, M_\odot$. We also determined that there are no SMBHBs with $\mathcal{M} > 1.6 \times 10^9 \, M_\odot$ emitting GWs in the Virgo Cluster. Finally, we estimated the number of potentially detectable sources given our current strain upper limits based on galaxies in Two Micron All-Sky Survey (2MASS) and merger rates from the Illustris cosmological simulation project. Only 34 out of 75,000 realizations of the local Universe contained a detectable source, from which we concluded it was unsurprising that we did not detect any individual sources given our current sensitivity to GWs., 10 pages, 11 figures. Accepted by Astrophysical Journal. Please send any comments/questions to S. J. Vigeland (vigeland@uwm.edu)
Published: 2018
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34. The NANOGrav 11-year Data Set: High-precision timing of 45 Millisecond Pulsars

Author: Chiara M. F. Mingarelli, Megan E. DeCesar, Weiwei Zhu, Sean T. McWilliams, Emmanuel Fonseca, A. M. Matthews, David J. Nice, Fredrick A. Jenet, Paul Demorest, Joseph K. Swiggum, Andrea N. Lommen, Lina Levin, T. Joseph W. Lazio, Timothy T. Pennucci, Michael T. Lam, Renée Spiewak, Justin A. Ellis, Elizabeth C. Ferrara, Maura McLaughlin, Scott M. Ransom, Timothy Dolch, Ryan S. Lynch, D. R. Madison, Duncan R. Lorimer, Glenn Jones, Rutger van Haasteren, H. Thankful Cromartie, Michele Vallisneri, Ingrid H. Stairs, James M. Cordes, S. J. Chamberlin, Fronefield Crawford, Nathan Garver-Daniels, Stephen Taylor, Kathryn Crowter, Shami Chatterjee, Megan L. Jones, Paul S. Ray, Kevin Stovall, E. A. Huerta, Jing Luo, Robert D. Ferdman, B. Christy, Cherry Ng, Sarah J. Vigeland, Xavier Siemens, Cody Jessup, Daniel Halmrast, Daniel R. Stinebring, Peter A. Gentile, Sarah Burke-Spolaor, David L. Kaplan, Adam Brazier, Neil J. Cornish, Joseph Simon, and Zaven Arzoumanian
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Orbital elements, Physics, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Green Bank Telescope, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Shapiro delay, Pulsar, Space and Planetary Science, Observatory, Millisecond pulsar, 0103 physical sciences, Arecibo Observatory, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics
Abstract: We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, with six high--timing-precision pulsars observed weekly, and all were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and, if necessary, binary parameters, in addition to time-variable dispersion delays and parameters that quantify pulse-profile evolution with frequency. The new timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of large orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. Future papers will use these data to constrain or detect the signatures of gravitational-wave signals., Published in the Astrophysical Journal Supplement Series
Published: 2017

35. The NANOGrav nine-year data set: Measurement and analysis of variations in dispersion measures

Author: Sourav Chatterjee, G. Jones, Zaven Arzoumanian, Scott M. Ransom, Emmanuel Fonseca, Maura McLaughlin, Paul Demorest, Kathryn Crowter, Joseph K. Swiggum, Robert D. Ferdman, T. J. W. Lazio, Michael T. Lam, W. W. Zhu, Timothy T. Pennucci, Kevin Stovall, I. H. Stairs, D. R. Stinebring, J. A. Ellis, Lina Levin, David J. Nice, Timothy Dolch, M. E. Gonzalez, J. M. Cordes, and M. L. Jones
Subjects: Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Monotonic function, Astrophysics, Function (mathematics), 01 natural sciences, Measure (mathematics), Pulsar, 13. Climate action, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Dispersion (optics), Trajectory, Limit (mathematics), 010303 astronomy & astrophysics
Abstract: We analyze dispersion measure (DM) variations of 37 millisecond pulsars in the nine-year North American Nanohertz Observatory for Gravitational Waves (NANOGrav) data release and constrain the sources of these variations. DM variations can result from a changing distance between Earth and the pulsar, inhomogeneities in the interstellar medium, and solar effects. Variations are significant for nearly all pulsars, with characteristic timescales comparable to or even shorter than the average spacing between observations. Five pulsars have periodic annual variations, 14 pulsars have monotonically increasing or decreasing trends, and 14 pulsars show both effects. Of the four pulsars with linear trends that have line-of-sight velocity measurements, three are consistent with a changing distance and require an overdensity of free electrons local to the pulsar. Several pulsars show correlations between DM excesses and lines of sight that pass close to the Sun. Mapping of the DM variations as a function of the pulsar trajectory can identify localized interstellar medium features and, in one case, an upper limit to the size of the dispersing region of 4 au. Four pulsars show roughly Kolmogorov structure functions (SFs), and another four show SFs less steep than Kolmogorov. One pulsar has too large an uncertainty to allow comparisons. We discuss explanations for apparent departures from a Kolmogorov-like spectrum, and we show that the presence of other trends and localized features or gradients in the interstellar medium is the most likely cause.
Published: 2017

36. Statistical analyses for NANOGrav 5-year timing residuals

Author: Fredrick A. Jenet, Yan Wang, X. Siemens, James M. Cordes, Dustin R. Madison, Shami Chatterjee, Paul Demorest, Michele Vallisneri, Timothy Dolch, Michael T. Lam, Joanna M. Rankin, Justin A. Ellis, Maura McLaughlin, Delphine Perrodin, ITA, USA, and CHN
Subjects: 010308 nuclear & particles physics, Gravitational wave, FOS: Physical sciences, Astronomy and Astrophysics, White noise, Geodesy, 01 natural sciences, Noise, Pulsar, Space and Planetary Science, Observatory, 0103 physical sciences, Outlier, Arecibo Observatory, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Mathematics, Statistical hypothesis testing
Abstract: In pulsar timing, timing residuals are the differences between the observed times of arrival and the predictions from the timing model. A comprehensive timing model will produce featureless residuals, which are presumably composed of dominating noise and weak physical effects excluded from the timing model (e.g. gravitational waves). In order to apply the optimal statistical methods for detecting the weak gravitational wave signals, we need to know the statistical properties of the noise components in the residuals. In this paper we utilize a variety of non-parametric statistical tests to analyze the whiteness and Gaussianity of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 5-year timing data which are obtained from the Arecibo Observatory and the Green Bank Telescope from 2005 to 2010 (Demorest et al. 2013). We find that most of the data are consistent with white noise; Many data deviate from Gaussianity at different levels, nevertheless, removing outliers in some pulsars will mitigate the deviations., Comment: 15 pages, 11 figures, 2 tables. Accepted by RAA
Published: 2017

37. THE NANOGRAV NINE-YEAR DATA SET:MASS and GEOMETRIC MEASUREMENTS of BINARY MILLISECOND PULSARS

Author: Kathryn Crowter, Scott M. Ransom, Joseph K. Swiggum, Paul Demorest, Michael T. Lam, Timothy Dolch, Ingrid H. Stairs, Zaven Arzoumanian, Kevin Stovall, Justin A. Ellis, Glenn Jones, Lina Levin, Maura McLaughlin, Emmanuel Fonseca, Weiwei Zhu, Robert D. Ferdman, David J. Nice, Timothy T. Pennucci, Megan L. Jones, and Marjorie Gonzalez
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Orbital elements, Physics, Mass distribution, close [binaries], 010308 nuclear & particles physics, Gravitational wave, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Shapiro delay, general [pulsars], Binary pulsar, Orbital inclination, neutron [stars], Pulsar, Space and Planetary Science, Millisecond pulsar, gravitation, evolution [stars], 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics
Abstract: We analyze 24 binary radio pulsars in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) nine-year data set. We make fourteen significant measurements of Shapiro delay, including new detections in four pulsar-binary systems (PSRs J0613$-$0200, J2017+0603, J2302+4442, and J2317+1439), and derive estimates of the binary-component masses and orbital inclination for these MSP-binary systems. We find a wide range of binary pulsar masses, with values as low as $m_{\rm p} = 1.18^{+0.10}_{-0.09}\text{M}_{\odot}$ for PSR J1918$-$0642 and as high as $m_{\rm p} = 1.928^{+0.017}_{-0.017}\text{M}_{\odot}$ for PSR J1614$-$2230 (both 68.3\% credibility). We make an improved measurement of the Shapiro timing delay in the PSR J1918$-$0642 and J2043+1711 systems, measuring the pulsar mass in the latter system to be $m_{\rm p} = 1.41^{+0.21}_{-0.18}\text{M}_{\odot}$ (68.3\% credibility) for the first time. We measure secular variations of one or more orbital elements in many systems, and use these measurements to further constrain our estimates of the pulsar and companion masses whenever possible. In particular, we used the observed Shapiro delay and periastron advance due to relativistic gravity in the PSR J1903+0327 system to derive a pulsar mass of $m_{\rm p} = 1.65^{+0.02}_{-0.02}\text{M}_{\odot}$ (68.3\% credibility). We discuss the implications that our mass measurements have on the overall neutron-star mass distribution, and on the "mass/orbital-period" correlation due to extended mass transfer., Comment: Fixed typos, added Table 5 and analysis of PSR J2145-0750. Accepted by ApJ on 24 September 2016
Published: 2016

38. The NANOGrav Nine-Year Data Set: Excess Noise in Millisecond Pulsar Arrival Times

Author: James M. Cordes, Robert D. Ferdman, Marjorie Gonzalez, David J. Nice, Paul Demorest, Timothy T. Pennucci, Ryan Shannon, Glenn Jones, Lina Levin, Kathryn Crowter, Megan L. Jones, X. Siemens, Joseph K. Swiggum, Scott M. Ransom, Shami Chatterjee, Kevin Stovall, Wei Zhu, Ingrid H. Stairs, Timothy Dolch, Dustin R. Madison, Emmanuel Fonseca, Michael T. Lam, Zaven Arzoumanian, Justin A. Ellis, and Maura McLaughlin
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Gravitational-wave astronomy, Pulsar timing array, Pulsar, Space and Planetary Science, Observatory, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Noise (radio)
Abstract: Gravitational wave astronomy using a pulsar timing array requires high-quality millisecond pulsars, correctable interstellar propagation delays, and high-precision measurements of pulse times of arrival. Here we identify noise in timing residuals that exceeds that predicted for arrival time estimation for millisecond pulsars observed by the North American Nanohertz Observatory for Gravitational Waves. We characterize the excess noise using variance and structure function analyses. We find that 26 out of 37 pulsars show inconsistencies with a white-noise-only model based on the short timescale analysis of each pulsar and we demonstrate that the excess noise has a red power spectrum for 15 pulsars. We also decompose the excess noise into chromatic (radio-frequency-dependent) and achromatic components. Associating the achromatic red-noise component with spin noise and including additional power-spectrum-based estimates from the literature, we estimate a scaling law in terms of spin parameters (frequency and frequency derivative) and data-span length and compare it to the scaling law of Shannon \& Cordes (2010). We briefly discuss our results in terms of detection of gravitational waves at nanohertz frequencies., 20 pages, 16 figures, to be published in ApJ
Published: 2016
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39. PSR J1024-0719: A Millisecond Pulsar in an Unusual Long-Period Orbit

Author: Adam A. Miller, P. A. Gentile, Cherry Ng, Weiwei Zhu, Elizabeth C. Ferrara, Ulrich Heber, Paul Demorest, Timothy T. Pennucci, Renée Spiewak, Scott M. Ransom, Kevin Stovall, Timothy Dolch, Joseph K. Swiggum, Duncan R. Lorimer, Michael T. Lam, Elif Beklen, Ryan S. Lynch, Simon Kreuzer, Thomas A. Prince, Justin A. Ellis, Thomas Kupfer, David L. Kaplan, Glenn Jones, Maura McLaughlin, Ingrid H. Stairs, Lina Levin, Kathryn Crowter, Megan L. Jones, Andreas Irrgang, Paul S. Ray, Megan E. DeCesar, Emmanuel Fonseca, David J. Nice, Zaven Arzoumanian, and Robert D. Ferdman
Subjects: Rotation period, Metallicity, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Pulsar, Millisecond pulsar, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Orbital elements, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy and Astrophysics, Orbit, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Globular cluster, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Halo orbit
Abstract: PSR J1024$-$0719 is a millisecond pulsar that was long thought to be isolated. However, puzzling results concerning its velocity, distance, and low rotational period derivative have led to reexamination of its properties. We present updated radio timing observations along with new and archival optical data that show PSR J1024$-$0719 is most likely in a long period (2$-$20 kyr) binary system with a low-mass ($\approx 0.4\,M_\odot$) low-metallicity ($Z \approx -0.9\,$ dex) main sequence star. Such a system can explain most of the anomalous properties of this pulsar. We suggest that this system formed through a dynamical exchange in a globular cluster that ejected it into a halo orbit, consistent with the low observed metallicity for the stellar companion. Further astrometric and radio timing observations such as measurement of the third period derivative could strongly constrain the range of orbital parameters., Comment: Accepted by ApJ. 14 pages, 8 figures
Published: 2016
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40. The NANOGrav 11-year Data Set: Pulse Profile Variability

Author: Zaven Arzoumanian, Wenbai Zhu, Duncan R. Lorimer, Megan E. DeCesar, Timothy Dolch, Emmanuel Fonseca, Renée Spiewak, Scott M. Ransom, Michael T. Lam, Daniel R. Stinebring, Paul R. Brook, Ingrid H. Stairs, Kathryn Crowter, Justin A. Ellis, Cherry Ng, Megan L. Jones, Paul S. Ray, P. A. Gentile, Maura McLaughlin, Ryan S. Lynch, G. Jones, Robert D. Ferdman, Aris Karastergiou, Lina Levin, Paul Demorest, T. J. W. Lazio, David J. Nice, Timothy T. Pennucci, Joseph K. Swiggum, James M. Cordes, Shami Chatterjee, Kevin Stovall, and Elizabeth C. Ferrara
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Scintillation, 010308 nuclear & particles physics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Pulsar, Space and Planetary Science, Millisecond pulsar, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics
Abstract: Access to 50 years of data has led to the discovery of pulsar emission and rotation variability on timescales of months and years. Most of this long-term variability has been seen in long-period pulsars, with relatively little focus on recycled millisecond pulsars. We have analyzed a 38-pulsar sub-set of the 45 millisecond pulsars in the NANOGrav 11-year data set, in order to review their pulse profile stability. The most variability, on any timescale, is seen in PSRs J1713+0747, B1937+21 and J2145-0750. The strongest evidence for long-timescale pulse profile changes is seen in PSRs B1937+21 and J1643-1224. We have focused our analyses on these four pulsars in an attempt to elucidate the causes of their profile variability. Effects of scintillation seem to be responsible for the profile modifications of PSR J2145-0750. We see evidence that imperfect polarization calibration contributes to the profile variability of PSRs J1713+0747 and B1937+21, along with radio frequency interference around 2 GHz, but find that propagation effects also have an influence. The changes seen in PSR J1643-1224 have been reported previously, yet elude explanation beyond their astrophysical nature. Regardless of cause, unmodeled pulse profile changes are detrimental to the accuracy of pulsar timing and must be incorporated into the timing models where possible., Comment: 38 pages, 25 figures
Published: 2018

41. Optimizing Pulsar Timing Array Observational Cadences for Sensitivity to Low-frequency Gravitational-wave Sources

Author: Michael T. Lam
Subjects: Physics, Supermassive black hole, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Pulsar timing array, Amplitude, Pulsar, 13. Climate action, Space and Planetary Science, Colors of noise, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Noise (radio)
Abstract: Observations of low-frequency gravitational waves (GWs) will require the highest possible timing precision from an array of the most spin-stable pulsars. We can improve the sensitivity of a pulsar timing array (PTA) to different GW sources by observing pulsars with low timing noise over years to decades and distributed across the sky. We discuss observing strategies for a PTA focused on a stochastic GW background such as from unresolved supermassive black hole binaries as well as focused on single continuous-wave sources. First, we describe the method to calculate a PTA's sensitivity to different GW-source classes. We then apply our method to the 45 pulsars presented in the North American Nanohertz Observatory for the GW 11 year data set. For expected amplitudes of the stochastic background, we find that all pulsars contribute significantly over the timescale of decades; the exception is for very pessimistic values of the stochastic-background amplitude. For individual single sources, we find that a number of pulsars contribute to the sensitivity of a given source, but that which pulsars contribute is different depending on the source, or versus an all-sky metric. Our results seem robust to the presence of red noise in pulsar arrival times. It is critical to obtain more robust pulsar-noise parameters as they heavily affect our results. Our results show that it is also imperative to locate and time as many high-precision pulsars as possible, as quickly as possible, to maximize the sensitivity of next-generation PTA detectors.
Published: 2018

42. The NANOGrav 11 yr Data Set: Arecibo Observatory Polarimetry and Pulse Microcomponents

Author: Paul Demorest, Zaven Arzoumanian, Renée Spiewak, Glenn Jones, Duncan R. Lorimer, Timothy T. Pennucci, Cherry Ng, Lina Levin, Marjorie Gonzalez, Ryan S. Lynch, Joseph K. Swiggum, Kathryn Crowter, Megan L. Jones, Paul S. Ray, Weiwei Zhu, Scott M. Ransom, Ingrid H. Stairs, Timothy Dolch, David J. Nice, Robert D. Ferdman, Megan E. DeCesar, Emmanuel Fonseca, Elizabeth C. Ferrara, Kevin Stovall, Peter A. Gentile, Michael T. Lam, Justin A. Ellis, and Maura McLaughlin
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Polarimetry, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Pulse (physics), Data set, Space and Planetary Science, 0103 physical sciences, Arecibo Observatory, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract: We present the polarization pulse profiles for 28 pulsars observed with the Arecibo Observatory by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) timing project at 2.1 GHz, 1.4 GHz, and 430 MHz. These profiles represent some of the most sensitive polarimetric millisecond pulsar profiles to date, revealing the existence of microcomponents (that is, pulse components with peak intensities much lower than the total pulse peak intensity). Although microcomponents have been detected in some pulsars previously, we present microcomponents for PSRs B1937+21, J1713+0747, and J2234+0944 for the first time. These microcomponents can have an impact on pulsar timing, geometry, and flux density determination. We present rotation measures for all 28 pulsars, determined independently at different observation frequencies and epochs, and find the Galactic magnetic fields derived from these rotation measures to be consistent with current models. These polarization profiles were made using measurement equation template matching, which allows us to generate the polarimetric response of the Arecibo Observatory on an epoch-by-epoch basis. We use this method to describe its time variability, and find that the polarimetric responses of the Arecibo Observatory's 1.4 and 2.1 GHz receivers vary significantly with time., Comment: 41 pages, 20 figures
Published: 2018

43. Optimal Frequency Ranges for Submicrosecond Precision Pulsar Timing

Author: T. J. W. Lazio, Shami Chatterjee, Michael T. Lam, Maura McLaughlin, and James M. Cordes
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Methods observational, Pulsar, Space and Planetary Science, 0103 physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics
Abstract: Precision pulsar timing requires optimization against measurement errors and astrophysical variance from the neutron stars themselves and the interstellar medium. We investigate optimization of arrival time precision as a function of radio frequency and bandwidth. We find that increases in bandwidth that reduce the contribution from receiver noise are countered by the strong chromatic dependence of interstellar effects and intrinsic pulse-profile evolution. The resulting optimal frequency range is therefore telescope and pulsar dependent. We demonstrate the results for five pulsars included in current pulsar timing arrays and determine that they are not optimally observed at current center frequencies. For those objects, we find that better choices of total bandwidth as well as center frequency can improve the arrival-time precision. Wideband receivers centered at somewhat higher frequencies with respect to the currently adopted receivers can reduce required overall integration times and provide significant improvements in arrival time uncertainty by a factor of ~sqrt(2) in most cases, assuming a fixed integration time. We also discuss how timing programs can be extended to pulsars with larger dispersion measures through the use of higher-frequency observations., Comment: 13 pages, 8 figures, published in ApJ
Published: 2018

44. Testing theories of gravitation using 21-year timing of Pulsar Binary J1713+0747

Author: Timothy Dolch, Kathryn Crowter, Megan L. Jones, Joseph K. Swiggum, Marjorie Gonzalez, Scott M. Ransom, Justin A. Ellis, Lina Levin, Emmanuel Fonseca, Maura McLaughlin, Paul Demorest, Zaven Arzoumanian, Glenn Jones, Weiwei Zhu, Michael T. Lam, Ingrid H. Stairs, Kevin Stovall, Timothy T. Pennucci, David J. Nice, and Robert D. Ferdman
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, White dwarf, Astronomy and Astrophysics, General Relativity and Quantum Cosmology (gr-qc), Astrophysics, Orbital period, General Relativity and Quantum Cosmology, Gravitational constant, Gravitation, Neutron star, Pulsar, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Circular orbit, Astrophysics - High Energy Astrophysical Phenomena, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics
Abstract: We report 21-yr timing of one of the most precise pulsars: PSR J1713+0747. Its pulse times of arrival are well modeled by a comprehensive pulsar binary model including its three-dimensional orbit and a noise model that incorporates correlated noise such as jitter and red noise. Its timing residuals have weighted root mean square $\sim 92$ ns. The new dataset allows us to update and improve previous measurements of the system properties, including the masses of the neutron star ($1.31\pm0.11$ $M_{\odot}$) and the companion white dwarf ($0.286\pm0.012$ $M_{\odot}$) and the parallax distance $1.15\pm0.03$ kpc. We measured the intrinsic change in orbital period, $\dot{P}^{\rm Int}_{\rm b}$, is $-0.20\pm0.17$ ps s$^{-1}$, which is not distinguishable from zero. This result, combined with the measured $\dot{P}^{\rm Int}_{\rm b}$ of other pulsars, can place a generic limit on potential changes in the gravitational constant $G$. We found that $\dot{G}/G$ is consistent with zero [$(-0.6\pm1.1)\times10^{-12}$ yr$^{-1}$, 95\% confidence] and changes at least a factor of $31$ (99.7\% confidence) more slowly than the average expansion rate of the Universe. This is the best $\dot{G}/G$ limit from pulsar binary systems. The $\dot{P}^{\rm Int}_{\rm b}$ of pulsar binaries can also place limits on the putative coupling constant for dipole gravitational radiation $\kappa_D=(-0.9\pm3.3)\times10^{-4}$ (95\% confidence). Finally, the nearly circular orbit of this pulsar binary allows us to constrain statistically the strong-field post-Newtonian parameters $\Delta$, which describes the violation of strong equivalence principle, and $\hat{\alpha}_3$, which describes a breaking of both Lorentz invariance in gravitation and conservation of momentum. We found, at 95\% confidence, $\Delta, Comment: 14 pages, 6 figures. Published on ApJ, 809, 41 (2015)
Published: 2015

45. The NANOGrav Nine-year Data Set: Observations, Arrival Time Measurements, and Analysis of 37 Millisecond Pulsars

Author: Fredrick A. Jenet, Justin A. Ellis, V. M. Kaspi, Sarah Burke-Spolaor, Adam Brazier, Maura McLaughlin, Glenn Jones, R. van Haasteren, D. R. Madison, T. J. W. Lazio, Paul Demorest, B. Christy, Andrea N. Lommen, Michael T. Lam, Joseph K. Swiggum, Lina Levin, Timothy Dolch, Michele Vallisneri, D. R. Lorimer, James M. Cordes, Scott M. Ransom, Neil J. Cornish, R. S. Lynch, S. J. Chamberlin, Nipuni Palliyaguru, Zaven Arzoumanian, Shami Chatterjee, Jing Luo, M. Koop, Weiwei Zhu, Kevin Stovall, M. L. Jones, D. R. Stinebring, Robert D. Ferdman, Xavier Siemens, Timothy T. Pennucci, Yan Wang, M. E. Gonzalez, Kathryn Crowter, Sean T. McWilliams, David J. Nice, Ingrid H. Stairs, Emmanuel Fonseca, and N. Garver-Daniels
Subjects: 010308 nuclear & particles physics, Gravitational wave, FOS: Physical sciences, Astronomy and Astrophysics, Geodesy, 01 natural sciences, Radio telescope, European Pulsar Timing Array, Pulsar timing array, Time of arrival, Pulsar, Space and Planetary Science, Millisecond pulsar, Observatory, 0103 physical sciences, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Geology
Abstract: We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or "red," timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals., 37 pages, 43 figures, this revision matches the final ApJ accepted version
Published: 2015

46. The NANOGrav Nine-Year Data Set: Noise Budget for Pulsar Arrival Times on Intraday Timescales

Author: Paul Demorest, Robert D. Ferdman, Lina Levin, Timothy Dolch, Justin A. Ellis, Zaven Arzoumanian, Glenn Jones, Marjorie Gonzalez, Scott M. Ransom, Maura McLaughlin, Joseph K. Swiggum, Ingrid H. Stairs, Shami Chatterjee, Emmanuel Fonseca, Kevin Stovall, Michael T. Lam, Kathryn Crowter, Megan L. Jones, J. M. Cordes, X. Siemens, Timothy T. Pennucci, Weiwei Zhu, Dustin R. Madison, and David J. Nice
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Line-of-sight, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, 7. Clean energy, Pulse (physics), Amplitude, Pulsar, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Impulse response, Noise (radio), Jitter
Abstract: The use of pulsars as astrophysical clocks for gravitational wave experiments demands the highest possible timing precision. Pulse times of arrival (TOAs) are limited by stochastic processes that occur in the pulsar itself, along the line of sight through the interstellar medium, and in the measurement process. On timescales of seconds to hours, the TOA variance exceeds that from template-fitting errors due to additive noise. We assess contributions to the total variance from two additional effects: amplitude and phase jitter intrinsic to single pulses and changes in the interstellar impulse response from scattering. The three effects have different dependencies on time, frequency, and pulse signal-to-noise ratio. We use data on 37 pulsars from the North American Nanohertz Observatory for Gravitational Waves to assess the individual contributions to the overall intraday noise budget for each pulsar. We detect jitter in 22 pulsars and estimate the average value of RMS jitter in our pulsars to be $\sim 1\%$ of pulse phase. We examine how jitter evolves as a function of frequency and find evidence for evolution. Finally, we compare our measurements with previous noise parameter estimates and discuss methods to improve gravitational wave detection pipelines., Comment: 22 pages, 11 figures, published in ApJ
Published: 2015
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47. The NANOGrav Nine-year Data Set: Astrometric Measurements of 37 Millisecond Pulsars

Author: Paul Demorest, Lina Levin, Weiwei Zhu, Michael T. Lam, Scott M. Ransom, Marjorie Gonzalez, Justin A. Ellis, Maura McLaughlin, Zaven Arzoumanian, Timothy Dolch, Glenn Jones, Kathryn Crowter, Emmanuel Fonseca, Joseph K. Swiggum, Kevin Stovall, Robert D. Ferdman, Ingrid H. Stairs, Timothy T. Pennucci, David J. Nice, Megan L. Jones, and A. M. Matthews
Subjects: Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics, 01 natural sciences, Pulsar, Millisecond pulsar, 0103 physical sciences, Arecibo Observatory, education, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), education.field_of_study, 010308 nuclear & particles physics, Gravitational wave, Green Bank Telescope, Astrophysics::Instrumentation and Methods for Astrophysics, Velocity dispersion, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Neutron star, 13. Climate action, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - High Energy Astrophysical Phenomena
Abstract: Using the nine-year radio-pulsar timing data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), collected at Arecibo Observatory and the Green Bank Telescope, we have measured the positions, proper motions, and parallaxes for 37 millisecond pulsars. We report twelve significant parallax measurements and distance measurements, and eighteen lower limits on distance. We compare these measurements to distances predicted by the NE2001 interstellar electron density model and find them to be in general agreement. We use measured orbital-decay rates and spin-down rates to confirm two of the parallax distances and to place distance upper limits on other sources; these distance limits agree with the parallax distances with one exception, PSR J1024-0719, which we discuss at length. Using the proper motions of the 37 NANOGrav pulsars in combination with other published measurements, we calculate the velocity dispersion of the millisecond pulsar population in Galactocentric coordinates. We find the radial, azimuthal, and perpendicular dispersions to be 46, 40, and 24 km s-1, respectively, in a model that allows for high-velocity outliers; or 81, 58, and 62 km s-1 for the full population. These velocity dispersions are far smaller than those of the canonical pulsar population, and are similar to older Galactic disk populations. This suggests that millisecond pulsar velocities are largely attributable to their being an old population rather than being artifacts of their birth and evolution as neutron star binary systems. The components of these velocity dispersions follow similar proportions to other Galactic populations, suggesting that our results are not biased by selection effects., Comment: Accepted by ApJ
Published: 2015
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48. Systematic and Stochastic Variations in Pulsar Dispersion Measures

Author: John W. Armstrong, Shami Chatterjee, Megan L. Jones, James M. Cordes, Michael T. Lam, and Maura McLaughlin
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Solar System, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Solar cycle, Interstellar medium, Solar wind, Amplitude, Pulsar, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Ionosphere, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Heliosphere, Astrophysics::Galaxy Astrophysics
Abstract: We analyze deterministic and random temporal variations in dispersion measure (DM) from the full three-dimensional velocities of pulsars with respect to the solar system, combined with electron-density variations on a wide range of length scales. Previous treatments have largely ignored the pulsar's changing distance while favoring interpretations involving the change in sky position from transverse motion. Linear trends in pulsar DMs seen over 5-10~year timescales may signify sizable DM gradients in the interstellar medium (ISM) sampled by the changing direction of the line of sight to the pulsar. We show that motions parallel to the line of sight can also account for linear trends, for the apparent excess of DM variance over that extrapolated from scintillation measurements, and for the apparent non-Kolmogorov scalings of DM structure functions inferred in some cases. Pulsar motions through atomic gas may produce bow-shock ionized gas that also contributes to DM variations. We discuss possible causes of periodic or quasi-periodic changes in DM, including seasonal changes in the ionosphere, annual variation of the solar elongation angle, structure in the heliosphere-ISM boundary, and substructure in the ISM. We assess the solar cycle's role on the amplitude of ionospheric and solar-wind variations. Interstellar refraction can produce cyclic timing variations from the error in transforming arrival times to the solar system barycenter. We apply our methods to DM time series and DM gradient measurements in the literature and assess consistency with a Kolmogorov medium. Finally, we discuss the implications of DM modeling in precision pulsar timing experiments., Comment: 24 pages, 17 figures, published in ApJ
Published: 2015
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49. A 24 HR GLOBAL CAMPAIGN TO ASSESS PRECISION TIMING OF THE MILLISECOND PULSAR J1713+0747

Author: Sourav Chatterjee, Gemma H. Janssen, G. Jones, Fredrick A. Jenet, Christine Jordan, J. W. T. Hessels, I. H. Stairs, Ryan Shannon, T. J. W. Lazio, L. Guillemot, Kang Liu, C. G. Bassa, P. Lazarus, Nipuni Palliyaguru, Michael Kramer, D. R. Madison, E. Petroff, M. A. McLaughlin, J. M. Cordes, Bhaswati Bhattacharyya, Joanna M. Rankin, D. J. Champion, Benjamin Stappers, Kevin Stovall, Michael Keith, Kuan Jin Lee, Joris P. W. Verbiest, Timothy Dolch, Shi Dai, W. W. Zhu, V. I. Kondratiev, A. G. Lyne, Kathryn Crowter, Delphine Perrodin, R. Smits, G. Desvignes, Ramesh Karuppusamy, Benetge Perera, Ismaël Cognard, Paul Demorest, Scott M. Ransom, Jayashree Roy, Michael T. Lam, Oberlin College, Cornell University, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Inter-University Centre for Astronomy and Astrophysics, Max-Planck-Institut für Radioastronomie (MPIFR), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), University of British Colombia, National Radio Astronomy Observatory [Socorro] (NRAO), National Radio Astronomy Observatory (NRAO), Netherlands Institute for Radio Astronomy (ASTRON), University of Amsterdam [Amsterdam] (UvA), Center for Advanced Radio Astronomy (CARA), University of Texas Rio Grande Valley [Brownsville, TX] (UTRGV), ARC Centre of Excellence for Coral Reef Studies (CoralCoE), James Cook University (JCU), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Vrije Universiteit Medical Centre (VUMC), Vrije Universiteit Amsterdam [Amsterdam] (VU), Max-Planck-Institut für Gravitationsphysik ( Albert-Einstein-Institut ) (AEI), Max-Planck-Gesellschaft, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), School of Medical Sciences - Institute of Medical Sciences, University of Aberdeen, Department of Physics, West Virginia University, West Virginia University, Department of Physics and Astronomy, University of British Columbia, University of British Columbia (UBC), Center for Gravitational Wave Astronomy (CGWA), Department of Physics [Rolla], Missouri University of Science and Technology (Missouri S&T), University of Missouri System-University of Missouri System, INAF - Osservatorio Astronomico di Cagliari (OAC), Istituto Nazionale di Astrofisica (INAF), Laboratory of Infrared Material and Devices, Ningbo University, Centre de Physique des Particules de Marseille (CPPM), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Aix Marseille Université (AMU), University of Vermont [Burlington], European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), European Project: 227947,EC:FP7:ERC,ERC-2008-AdG,LEAP(2009), Cornell University [New York], Inter-University Centre for Astronomy and Astrophysics [Pune] (IUCAA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Jodrell Bank Centre for Astrophysics (JBCA), Ningbo University (NBU), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, ISM: structure, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Radio telescope, Pulsar, Millisecond pulsar, Instrumentation and Methods for Astrophysics (astro-ph.IM), Astrophysics::Galaxy Astrophysics, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Scintillation, Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, LOFAR, gravitational waves, Space and Planetary Science, Sky, [SDU]Sciences of the Universe [physics], pulsars: individual: PSR J1713+0747, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Noise (radio)
Abstract: The radio millisecond pulsar J1713+0747 is regarded as one of the highest-precision clocks in the sky, and is regularly timed for the purpose of detecting gravitational waves. The International Pulsar Timing Array collaboration undertook a 24-hour global observation of PSR J1713+0747 in an effort to better quantify sources of timing noise in this pulsar, particularly on intermediate (1 - 24 hr) timescales. We observed the pulsar continuously over 24 hr with the Arecibo, Effelsberg, GMRT, Green Bank, LOFAR, Lovell, Nancay, Parkes, and WSRT radio telescopes. The combined pulse times-of-arrival presented here provide an estimate of what sources of timing noise, excluding DM variations, would be present as compared to an idealized root-N improvement in timing precision, where N is the number of pulses analyzed. In the case of this particular pulsar, we find that intrinsic pulse phase jitter dominates arrival time precision when the S/N of single pulses exceeds unity, as measured using the eight telescopes that observed at L-band/1.4 GHz. We present first results of specific phenomena probed on the unusually long timescale (for a single continuous observing session) of tens of hours, in particular interstellar scintillation, and discuss the degree to which scintillation and profile evolution affect precision timing. This paper presents the data set as a basis for future, deeper studies., Published in the Astrophysical Journal
Published: 2014

50. Pulsar Timing Errors from Asynchronous Multi-Frequency Sampling of Dispersion Measure Variations

Author: Shami Chatterjee, Timothy Dolch, J. M. Cordes, and Michael T. Lam
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Line-of-sight, 010308 nuclear & particles physics, Gravitational wave, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, 01 natural sciences, Computational physics, Interstellar medium, Data acquisition, Pulsar, Space and Planetary Science, Asynchronous communication, 0103 physical sciences, Wavenumber, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM)
Abstract: Free electrons in the interstellar medium cause frequency-dependent delays in pulse arrival times due to both scattering and dispersion. Multi-frequency measurements are used to estimate and remove dispersion delays. In this paper, we focus on the effect of any non-simultaneity of multi-frequency observations on dispersive delay estimation and removal. Interstellar density variations combined with changes in the line-of-sight from pulsar and observer motions cause dispersion measure variations with an approximately power-law power spectrum, augmented in some cases by linear trends. We simulate time series, estimate the magnitude and statistical properties of timing errors that result from non-simultaneous observations, and derive prescriptions for data acquisition that are needed in order to achieve a specified timing precision. For nearby, highly stable pulsars, measurements need to be simultaneous to within about one day in order that the timing error from asynchronous DM correction is less than about 10 ns. We discuss how timing precision improves when increasing the number of dual-frequency observations used in dispersion measure estimation for a given epoch. For a Kolmogorov wavenumber spectrum, we find about a factor of two improvement in precision timing when increasing from two to three observations but diminishing returns thereafter., Comment: 8 pages, 6 figures, accepted for publication in the Astrophysical Journal
Published: 2014
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52 results on '"Michael T. Lam"'

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