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1. Erratum: 'The NANOGrav 15 yr Data Set: Search for Signals from New Physics' (2023, ApJL 951 L11)

Author

Adeela Afzal, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Jose Juan Blanco-Pillado, Laura Blecha, Kimberly K. Boddy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, Maria Charisi, Shami Chatterjee, Katerina Chatziioannou, Belinda D. Cheeseboro, Siyuan Chen, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Curt J. Cutler, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Heling Deng, Timothy Dolch, Brendan Drachler, Richard von Eckardstein, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Lydia Guertin, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Kristina Islo, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Vincent S. H. Lee, Natalia Lewandowska, Rafael R. Lino dos Santos, Tyson B. Littenberg, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Jonathan Nay, Priyamvada Natarajan, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Tobias Schröder, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Peter Stratmann, Jerry P. Sun, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Tanner Trickle, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sonali Verma, Sarah J. Vigeland, Haley M. Wahl, Qiaohong Wang, Caitlin A. Witt, David Wright, Olivia Young, Kathryn M. Zurek, and The NANOGrav Collaboration

Subjects
Astrophysics, QB460-466
Published
2024
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2. The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Jeremy Baier, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Priyamvada Natarajan, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Alexander Saffer, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob A. Taylor, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Pulsars, Scalar-tensor-vector gravity, Astrophysics, QB460-466
Abstract

Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors ∼2 when comparing HD to ST correlations, and ∼1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis.

Published
2024
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3. A Cyclic Spectroscopy Scintillation Study of PSR B1937+21. I. Demonstration of Improved Scintillometry

Author

Jacob E. Turner, Timothy Dolch, James M. Cordes, Stella K. Ocker, Daniel R. Stinebring, Shami Chatterjee, Maura A. McLaughlin, Victoria E. Catlett, Cody Jessup, Nathaniel Jones, and Christopher Scheithauer

Subjects
Millisecond pulsars, Pulsars, Radio pulsars, Interstellar medium, Intercloud medium, Interstellar plasma, Astrophysics, QB460-466
Abstract

We use cyclic spectroscopy to perform high-frequency resolution analyses of multihour baseband Arecibo observations of the millisecond pulsar PSR B1937+21. This technique allows for the examination of scintillation features in far greater detail than is otherwise possible under most pulsar timing array observing setups. We measure scintillation bandwidths and timescales in each of eight subbands across a 200 MHz observing band in each observation. Through these measurements we obtain intra-epoch estimates of the frequency scalings for scintillation bandwidth and timescale. Thanks to our high-frequency resolution and the narrow scintles of this pulsar, we resolve scintillation arcs in the secondary spectra due to the increased Nyquist limit, which would not have been resolved at the same observing frequency with a traditional filterbank spectrum using NANOGrav’s current time and frequency resolutions, and the frequency-dependent evolution of scintillation arc features within individual observations. We observe the dimming of prominent arc features at higher frequencies, possibly due to a combination of decreasing flux density and the frequency dependence of the plasma refractive index of the interstellar medium. We also find agreement with arc curvature frequency dependence predicted by Stinebring et al. in some epochs. Thanks to the frequency-resolution improvement provided by cyclic spectroscopy, these results show strong promise for future such analyses with millisecond pulsars, particularly for pulsar timing arrays, where such techniques can allow for detailed studies of the interstellar medium in highly scattered pulsars without sacrificing the timing resolution that is crucial to their gravitational-wave detection efforts.

Published
2024
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4. An Unusual Pulse Shape Change Event in PSR J1713+0747 Observed with the Green Bank Telescope and CHIME

Author

Ross J. Jennings, James M. Cordes, Shami Chatterjee, Maura A. McLaughlin, Paul B. Demorest, Zaven Arzoumanian, Paul T. Baker, Harsha Blumer, Paul R. Brook, Tyler Cohen, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Timothy Dolch, Elizabeth C. Ferrara, Emmanuel Fonseca, Deborah C. Good, Jeffrey S. Hazboun, Megan L. Jones, David L. Kaplan, Michael T. Lam, T. Joseph W. Lazio, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, James W. McKee, Dustin R. Madison, Bradley W. Meyers, Chiara M. F. Mingarelli, David J. Nice, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Scott M. Ransom, Paul S. Ray, Brent J. Shapiro-Albert, Xavier Siemens, Ingrid H. Stairs, Daniel R. Stinebring, Joseph K. Swiggum, Chia Min Tan, Stephen R. Taylor, Sarah J. Vigeland, and Caitlin A. Witt

Subjects
Pulsars, Millisecond pulsars, Radio astrometry, Astrophysics, QB460-466
Abstract

The millisecond pulsar J1713+0747 underwent a sudden and significant pulse shape change between 2021 April 16 and 17 (MJDs 59320 and 59321). Subsequently, the pulse shape gradually recovered over the course of several months. We report the results of continued multifrequency radio observations of the pulsar made using the Canadian Hydrogen Intensity Mapping Experiment and the 100 m Green Bank Telescope in a 3 yr period encompassing the shape change event, between 2020 February and 2023 February. As of 2023 February, the pulse shape had returned to a state similar to that seen before the event, but with measurable changes remaining. The amplitude of the shape change and the accompanying time-of-arrival residuals display a strong nonmonotonic dependence on radio frequency, demonstrating that the event is neither a glitch (the effects of which should be independent of radio frequency, ν ) nor a change in dispersion measure alone (which would produce a delay proportional to ν ^−2 ). However, it does bear some resemblance to the two previous “chromatic timing events” observed in J1713+0747, as well as to a similar event observed in PSR J1643−1224 in 2015.

Published
2024
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5. The NANOGrav 12.5 yr Data Set: A Computationally Efficient Eccentric Binary Search Pipeline and Constraints on an Eccentric Supermassive Binary Candidate in 3C 66B

Author

Gabriella Agazie, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Harsha Blumer, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Belinda D. Cheeseboro, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Lankeswar Dey, Timothy Dolch, Justin A. Ellis, Robert D. Ferdman, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Achamveedu Gopakumar, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Kai Schmitz, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Sophia V. Sosa Fiscella, Renée Spiewak, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Millisecond pulsars, Supermassive black holes, Astrophysics, QB460-466
Abstract

The radio galaxy 3C 66B has been hypothesized to host a supermassive black hole binary (SMBHB) at its center based on electromagnetic observations. Its apparent 1.05 yr period and low redshift (∼0.02) make it an interesting testbed to search for low-frequency gravitational waves (GWs) using pulsar timing array (PTA) experiments. This source has been subjected to multiple searches for continuous GWs from a circular SMBHB, resulting in progressively more stringent constraints on its GW amplitude and chirp mass. In this paper, we develop a pipeline for performing Bayesian targeted searches for eccentric SMBHBs in PTA data sets, and test its efficacy by applying it to simulated data sets with varying injected signal strengths. We also search for a realistic eccentric SMBHB source in 3C 66B using the NANOGrav 12.5 yr data set employing PTA signal models containing Earth term-only as well as Earth+pulsar term contributions using this pipeline. Due to limitations in our PTA signal model, we get meaningful results only when the initial eccentricity e _0 < 0.5 and the symmetric mass ratio η > 0.1. We find no evidence for an eccentric SMBHB signal in our data, and therefore place 95% upper limits on the PTA signal amplitude of 88.1 ± 3.7 ns for the Earth term-only and 81.74 ± 0.86 ns for the Earth+pulsar term searches for e _0 < 0.5 and η > 0.1. Similar 95% upper limits on the chirp mass are (1.98 ± 0.05) × 10 ^9 and (1.81 ± 0.01) × 10 ^9 M _☉ . These upper limits, while less stringent than those calculated from a circular binary search in the NANOGrav 12.5 yr data set, are consistent with the SMBHB model of 3C 66B developed from electromagnetic observations.

Published
2024
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6. The NANOGrav 12.5 yr Data Set: Search for Gravitational Wave Memory

Author

Gabriella Agazie, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Harsha Blumer, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Justin A. Ellis, Robert D. Ferdman, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Nihan S. Pol, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Kai Schmitz, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Sophia V. Sosa Fiscella, Renée Spiewak, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Gravitational wave astronomy, Astrophysics, QB460-466
Abstract

We present the results of a Bayesian search for gravitational wave (GW) memory in the NANOGrav 12.5 yr data set. We find no convincing evidence for any gravitational wave memory signals in this data set. We find a Bayes factor of 2.8 in favor of a model that includes a memory signal and common spatially uncorrelated red noise (CURN) compared to a model including only a CURN. However, further investigation shows that a disproportionate amount of support for the memory signal comes from three dubious pulsars. Using a more flexible red-noise model in these pulsars reduces the Bayes factor to 1.3. Having found no compelling evidence, we go on to place upper limits on the strain amplitude of GW memory events as a function of sky location and event epoch. These upper limits are computed using a signal model that assumes the existence of a common, spatially uncorrelated red noise in addition to a GW memory signal. The median strain upper limit as a function of sky position is approximately 3.3 × 10 ^−14 . We also find that there are some differences in the upper limits as a function of sky position centered around PSR J0613−0200. This suggests that this pulsar has some excess noise that can be confounded with GW memory. Finally, the upper limits as a function of burst epoch continue to improve at later epochs. This improvement is attributable to the continued growth of the pulsar timing array.

Published
2024
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7. A Simultaneous Dual-frequency Scintillation Arc Survey of Six Bright Canonical Pulsars Using the Upgraded Giant Metrewave Radio Telescope

Author

Jacob E. Turner, Bhal Chandra Joshi, Maura A. McLaughlin, and Daniel R. Stinebring

Subjects
Interstellar medium, Interstellar plasma, Radio pulsars, Pulsars, Interstellar scintillation, Radio astronomy, Astrophysics, QB460-466
Abstract

We use the upgraded Giant Metrewave Radio Telescope (uGMRT) to measure scintillation arc properties in six bright canonical pulsars with simultaneous dual-frequency coverage. These observations, at frequencies from 300 to 750 MHz, allowed for detailed analysis of arc evolution across frequency and epoch. We perform more robust determinations of frequency dependence for arc curvature, scintillation bandwidth, and scintillation timescale, and comparison between arc curvature and pseudo-curvature than allowed by single-frequency-band-per-epoch measurements, which we find to agree with theory and previous literature. We find a strong correlation between arc asymmetry and arc curvature, which we have replicated using simulations, and attribute to a bias in the Hough transform approach to scintillation arc analysis. Possible evidence for an approximately week-long timescale over which a given scattering screen dominates signal propagation was found by tracking visible scintillation arcs in each epoch in PSR J1136+1551. The inclusion of a 155-minute observation allowed us to resolve the scale of scintillation variations on short timescales, which we find to be directly tied to the amount of interstellar medium sampled over the observation. Some of our pulsars showed either consistent or emerging asymmetries in arc curvature, indicating instances of refraction across their lines of sight. Significant features in various pulsars, such as multiple scintillation arcs in PSR J1136+1551 and flat arclets in PSR J1509+5531, that have been found in previous works, were also detected. The simultaneous multiple-band observing capability of the upgraded GMRT shows excellent promise for future pulsar scintillation work.

Published
2024
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8. The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko Gardiner, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, and Olivia Young

Subjects
Gravitational waves, Gravitational wave astronomy, Supermassive black holes, Pulsars, Astrophysics, QB460-466
Abstract

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if the GWB is produced by a population of inspiraling supermassive black hole binary (SMBHB) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local Universe and the statistical properties of the SMBHB population. In this work, we search for anisotropy in the GWB using multiple methods and bases to describe the distribution of the GWB power on the sky. We do not find significant evidence of anisotropy. By modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the Bayesian 95% upper limit on the level of dipole anisotropy is ( C _l _=1 / C _l _=0 ) < 27%. This is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. By contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. We also derive conservative estimates on the anisotropy expected from a random distribution of SMBHB systems using astrophysical simulations conditioned on the isotropic GWB inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. We end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data.

Published
2023
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9. The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Paul T. Baker, Bence Bécsy, Laura Blecha, Alexander Bonilla, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Katerina Chatziioannou, Belinda D. Cheeseboro, Siyuan Chen, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Curt J. Cutler, Daniel J. D’Orazio, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Heling Deng, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko Gardiner, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Kristina Islo, Ross J. Jennings, Aaron Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tyson B. Littenberg, Tingting Liu, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Priyamvada Natarajan, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Jessie C. Runnoe, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Jeremy M. Wachter, Haley M. Wahl, Qiaohong Wang, Caitlin A. Witt, David Wright, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Supermassive black holes, Galaxy evolution, Astrophysics, QB460-466
Abstract

The NANOGrav 15 yr data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such low-frequency gravitational waves, here we analyze the signal as coming from a population of supermassive black hole (SMBH) binaries distributed throughout the Universe. We show that astrophysically motivated models of SMBH binary populations are able to reproduce both the amplitude and shape of the observed low-frequency gravitational-wave spectrum. While multiple model variations are able to reproduce the GWB spectrum at our current measurement precision, our results highlight the importance of accurately modeling binary evolution for producing realistic GWB spectra. Additionally, while reasonable parameters are able to reproduce the 15 yr observations, the implied GWB amplitude necessitates either a large number of parameters to be at the edges of expected values or a small number of parameters to be notably different from standard expectations. While we are not yet able to definitively establish the origin of the inferred GWB signal, the consistency of the signal with astrophysical expectations offers a tantalizing prospect for confirming that SMBH binaries are able to form, reach subparsec separations, and eventually coalesce. As the significance grows over time, higher-order features of the GWB spectrum will definitively determine the nature of the GWB and allow for novel constraints on SMBH populations.

Published
2023
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10. The NANOGrav 15 yr Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Robin Case, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Matthew C. Digman, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Rutger van Haasteren, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational wave astronomy, Astrophysics, QB460-466
Abstract

Evidence for a low-frequency stochastic gravitational-wave background has recently been reported based on analyses of pulsar timing array data. The most likely source of such a background is a population of supermassive black hole binaries, the loudest of which may be individually detected in these data sets. Here we present the search for individual supermassive black hole binaries in the NANOGrav 15 yr data set. We introduce several new techniques, which enhance the efficiency and modeling accuracy of the analysis. The search uncovered weak evidence for two candidate signals, one with a gravitational-wave frequency of ∼4 nHz, and another at ∼170 nHz. The significance of the low-frequency candidate was greatly diminished when Hellings–Downs correlations were included in the background model. The high-frequency candidate was discounted due to the lack of a plausible host galaxy, the unlikely astrophysical prior odds of finding such a source, and since most of its support comes from a single pulsar with a commensurate binary period. Finding no compelling evidence for signals from individual binary systems, we place upper limits on the strain amplitude of gravitational waves emitted by such systems. At our most sensitive frequency of 6 nHz, we place a sky-averaged 95% upper limit of 8 × 10 ^−15 on the strain amplitude. We also calculate an exclusion volume and a corresponding effective radius, within which we can rule out the presence of black hole binaries emitting at a given frequency.

Published
2023
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11. The NANOGrav 12.5 yr Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author

Zaven Arzoumanian, Paul T. Baker, Laura Blecha, Harsha Blumer, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Bence Bécsy, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Siyuan Chen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Justin A. Ellis, E. C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nathan Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Joey Shapiro Key, Nima Laal, Michael T. Lam, William G Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Dustin R. Madison, Alexander McEwen, Maura A. McLaughlin, Chiara M. F. Mingarelli, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Nihan S. Pol, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena Siwek, Renée Spiewak, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Joseph K. Swiggum, Jessica Sydnor, Stephen R. Taylor, Jacob E. Turner, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Gregory Walsh, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Astronomy data analysis, Millisecond pulsars, Supermassive black holes, Astrophysics, QB460-466
Abstract

Pulsar timing array collaborations, such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), are seeking to detect nanohertz gravitational waves emitted by supermassive black hole binaries formed in the aftermath of galaxy mergers. We have searched for continuous waves from individual circular supermassive black hole binaries using NANOGrav’s recent 12.5 yr data set. We created new methods to accurately model the uncertainties on pulsar distances in our analysis, and we implemented new techniques to account for a common red-noise process in pulsar timing array data sets while searching for deterministic gravitational wave signals, including continuous waves. As we found no evidence for continuous waves in our data, we placed 95% upper limits on the strain amplitude of continuous waves emitted by these sources. At our most sensitive frequency of 7.65 nHz, we placed a sky-averaged limit of h _0 < (6.82 ± 0.35) × 10 ^−15 , and h _0 < (2.66 ± 0.15) × 10 ^−15 in our most sensitive sky location. Finally, we placed a multimessenger limit of ${ \mathcal M }\lt (1.41\pm 0.02)\times {10}^{9}\,{M}_{\odot }$ on the chirp mass of the supermassive black hole binary candidate 3C 66B.

Published
2023
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12. The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, Maria Charisi, Shami Chatterjee, Katerina Chatziioannou, Belinda D. Cheeseboro, Siyuan Chen, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Curt J. Cutler, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Heling Deng, Timothy Dolch, Brendan Drachler, Justin A. Ellis, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Kristina Islo, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Tonia C. Klein, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tyson B. Littenberg, Tingting Liu, Andrea Lommen, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Margaret A. Mattson, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Priyamvada Natarajan, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Jerry P. Sun, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Rutger van Haasteren, Sarah J. Vigeland, Haley M. Wahl, Qiaohong Wang, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Gravitational waves, Gravitational wave astronomy, Millisecond pulsars, Radio pulsars, Supermassive black holes, Astrophysics, QB460-466
Abstract

We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings–Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 10 ^14 , and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200–1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10 ^−3 (≈3 σ ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10 ^−5 to 1.9 × 10 ^−4 (≈3.5 σ –4 σ ). Assuming a fiducial f ^−2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is ${2.4}_{-0.6}^{+0.7}\times {10}^{-15}$ (median + 90% credible interval) at a reference frequency of 1 yr ^−1 . The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings–Downs correlations points to the gravitational-wave origin of this signal.

Published
2023
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13. The NANOGrav 15 yr Data Set: Observations and Timing of 68 Millisecond Pulsars

Author

Gabriella Agazie, Md Faisal Alam, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Laura Blecha, Victoria Bonidie, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Bence Bécsy, Christopher Chapman, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Cody Jessup, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Anastasia Kuske, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Ye Lin, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Kaleb Maraccini, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Elisa Panciu, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Laura Salo, Shashwat C. Sardesai, Carl Schmiedekamp, Ann Schmiedekamp, Kai Schmitz, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Qiaohong Wang, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Millisecond pulsars, Pulsar timing method, Time series analysis, Pulsars, Gravitational waves, Astrophysics, QB460-466
Abstract

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA) experiment that is sensitive to low-frequency gravitational waves (GWs). This is NANOGrav’s fifth public data release, including both “narrowband” and “wideband” time-of-arrival (TOA) measurements and corresponding pulsar timing models. We have added 21 MSPs and extended our timing baselines by 3 yr, now spanning nearly 16 yr for some of our sources. The data were collected using the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between frequencies of 327 MHz and 3 GHz, with most sources observed approximately monthly. A number of notable methodological and procedural changes were made compared to our previous data sets. These improve the overall quality of the TOA data set and are part of the transition to new pulsar timing and PTA analysis software packages. For the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. Our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. We find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. In this data set, we find evidence for a stochastic GW background.

Published
2023
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14. The NANOGrav 15 yr Data Set: Detector Characterization and Noise Budget

Author

Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Brendan Drachler, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Lydia Guertin, Kayhan Gültekin, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, Olivia Young, and The NANOGrav Collaboration

Subjects
Millisecond pulsars, Pulsar timing method, Gravitational wave astronomy, Gravitational wave detectors, Radio astronomy, Astrophysics, QB460-466
Abstract

Pulsar timing arrays (PTAs) are galactic-scale gravitational wave (GW) detectors. Each individual arm, composed of a millisecond pulsar, a radio telescope, and a kiloparsecs-long path, differs in its properties but, in aggregate, can be used to extract low-frequency GW signals. We present a noise and sensitivity analysis to accompany the NANOGrav 15 yr data release and associated papers, along with an in-depth introduction to PTA noise models. As a first step in our analysis, we characterize each individual pulsar data set with three types of white-noise parameters and two red-noise parameters. These parameters, along with the timing model and, particularly, a piecewise-constant model for the time-variable dispersion measure, determine the sensitivity curve over the low-frequency GW band we are searching. We tabulate information for all of the pulsars in this data release and present some representative sensitivity curves. We then combine the individual pulsar sensitivities using a signal-to-noise ratio statistic to calculate the global sensitivity of the PTA to a stochastic background of GWs, obtaining a minimum noise characteristic strain of 7 × 10 ^−15 at 5 nHz. A power-law-integrated analysis shows rough agreement with the amplitudes recovered in NANOGrav’s 15 yr GW background analysis. While our phenomenological noise model does not model all known physical effects explicitly, it provides an accurate characterization of the noise in the data while preserving sensitivity to multiple classes of GW signals.

Published
2023
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15. The NANOGrav 15 yr Data Set: Search for Signals from New Physics

Author

Adeela Afzal, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Jose Juan Blanco-Pillado, Laura Blecha, Kimberly K. Boddy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, Maria Charisi, Shami Chatterjee, Katerina Chatziioannou, Belinda D. Cheeseboro, Siyuan Chen, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Curt J. Cutler, Megan E. DeCesar, Dallas DeGan, Paul B. Demorest, Heling Deng, Timothy Dolch, Brendan Drachler, Richard von Eckardstein, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Lydia Guertin, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Kristina Islo, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Vincent S. H. Lee, Natalia Lewandowska, Rafael R. Lino dos Santos, Tyson B. Littenberg, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Jonathan Nay, Priyamvada Natarajan, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Tobias Schröder, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Peter Stratmann, Jerry P. Sun, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Tanner Trickle, Jacob E. Turner, Caner Unal, Michele Vallisneri, Sonali Verma, Sarah J. Vigeland, Haley M. Wahl, Qiaohong Wang, Caitlin A. Witt, David Wright, Olivia Young, Kathryn M. Zurek, and The NANOGrav Collaboration

Subjects
Gravitational waves, Cosmology, Particle astrophysics, Gravitational wave sources, Astrophysics, QB460-466
Abstract

The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence for the presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations of this signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, cosmic strings, and domain walls. We find that, with the exception of stable cosmic strings of field theory origin, all these models can reproduce the observed signal. When compared to the standard interpretation in terms of inspiraling supermassive black hole binaries (SMBHBs), many cosmological models seem to provide a better fit resulting in Bayes factors in the range from 10 to 100. However, these results strongly depend on modeling assumptions about the cosmic SMBHB population and, at this stage, should not be regarded as evidence for new physics. Furthermore, we identify excluded parameter regions where the predicted GW signal from cosmological sources significantly exceeds the NANOGrav signal. These parameter constraints are independent of the origin of the NANOGrav signal and illustrate how pulsar timing data provide a new way to constrain the parameter space of these models. Finally, we search for deterministic signals produced by models of ultralight dark matter (ULDM) and dark matter substructures in the Milky Way. We find no evidence for either of these signals and thus report updated constraints on these models. In the case of ULDM, these constraints outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons.

Published
2023
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16. How to Detect an Astrophysical Nanohertz Gravitational Wave Background

Author

Bence Bécsy, Neil J. Cornish, Patrick M. Meyers, Luke Zoltan Kelley, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Paul T. Baker, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Katerina Chatziioannou, Tyler Cohen, James M. Cordes, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Jeffrey S. Hazboun, Sophie Hourihane, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, T. Joseph W. Lazio, Natalia Lewandowska, Tyson B. Littenberg, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Stella Koch Ocker, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, Sophia V. Sosa Fiscella, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Caner Unal, Michele Vallisneri, Rutger van Haasteren, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt, and Olivia Young

Subjects
Gravitational waves, Gravitational wave sources, Gravitational wave astronomy, Supermassive black holes, Astronomy data analysis, Bayesian statistics, Astrophysics, QB460-466
Abstract

Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a power-law spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The data-set length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them.

Published
2023
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17. Scattering Delay Mitigation in High-accuracy Pulsar Timing: Cyclic Spectroscopy Techniques

Author

Jacob E. Turner, Daniel R. Stinebring, Maura A. McLaughlin, Anne M. Archibald, Timothy Dolch, and Ryan S. Lynch

Subjects
Interstellar medium, Pulsar timing method, Radio pulsars, Interstellar scattering, Astrophysics, QB460-466
Abstract

We simulate scattering delays from the interstellar medium to examine the effectiveness of three estimators in recovering these delays in pulsar timing data. Two of these estimators use the more traditional process of fitting autocorrelation functions to pulsar dynamic spectra to extract scintillation bandwidths, while the third estimator uses the newer technique of cyclic spectroscopy on baseband pulsar data to recover the interstellar medium’s impulse response function. We find that either fitting a Lorentzian or Gaussian distribution to an autocorrelation function or recovering the impulse response function from the cyclic spectrum are, on average, accurate in recovering scattering delays, although autocorrelation function estimators have a large variance, even at high signal-to-noise ratio (S/N). We find that, given sufficient S/N, cyclic spectroscopy is more accurate than both Gaussian and Lorentzian fitting for recovering scattering delays at specific epochs, suggesting that cyclic spectroscopy is a superior method for scattering estimation in high-quality data.

Published
2023
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18. 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, Renee Spiewak, Ingrid H Stairs, Kevin Stovall, Joseph K Swiggum, and Sarah J Vigeland

Subjects
Astronomy
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 at1500 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 at820 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 are 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 nanoseconds or less.

Published
2021
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19. The NANOGrav 11yr Data Set: Limits on Supermassive Black Hole Binaries in Galaxies within 500 Mpc

Author

Zaven Arzoumanian, Paul T. Baker, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Bence Bécsy, Maria Charisi, Shami Chatterjee, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Rodney D. Elliott, Justin A. Ellis, Elizabeth C. Ferrara, Emmanuel Fonseca, Nathan Garver-Daniels, Peter A. Gentile, Deborah C. Good, Jeffrey S. Hazboun, Kristina Islo, Ross J. Jennings, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Luke Zoltan Kelley, Joey Shapiro Key, Michael T. Lam, T. Joseph W. Lazio, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Maura A. McLaughlin, Chiara M. F. Mingarelli, Cherry Ng, David J. Nice, Timothy T. Pennucci, Nihan S. Pol, Scott M. Ransom, Paul S. Ray, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Renée Spiewak, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Joseph K. Swiggum, Stephen R. Taylor, Michele Vallisneri, Sarah J. Vigeland, and Caitlin A. Witt

Subjects
Astrophysics, Astronomy
Abstract

Supermassive black hole binaries (SMBHBs) should form frequently in galactic nuclei as a result of galaxy mergers. At subparsec separations, binaries become strong sources of low-frequency gravitational waves (GWs), targeted by Pulsar Timing Arrays. We used recent upper limits on continuous GWs from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11 yr data set to place constraints on putative SMBHBs in nearby massive galaxies. We compiled a comprehensive catalog of ∼44,000 galaxies in the local universe (up to redshift ∼0.05) and populated them with hypothetical binaries, assuming that the total mass of the binary is equal to the SMBH mass derived from global scaling relations. Assuming circular equal-mass binaries emitting at NANOGrav's most sensitive frequency of 8 nHz, we found that 216 galaxies are within NANOGrav's sensitivity volume. We ranked the potential SMBHBs based on GW detectability by calculating the total signal-to-noise ratio such binaries would induce within the NANOGrav array. We placed constraints on the chirp mass and mass ratio of the 216 hypothetical binaries. For 19 galaxies, only very unequal-mass binaries are allowed, with the mass of the secondary less than 10% that of the primary, roughly comparable to constraints on an SMBHB in the Milky Way. However, we demonstrated that the (typically large) uncertainties in the mass measurements can weaken the upper limits on the chirp mass. Additionally, we were able to exclude binaries delivered by major mergers (mass ratio of at least 1/4) for several of these galaxies. We also derived the first limit on the density of binaries delivered by major mergers purely based on GW data.

Published
2021
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20. Astrophysics Milestones for Pulsar Timing Array Gravitational-wave Detection

Author

Nihan S. Pol, Stephen R. Taylor, Luke Zoltan Kelley, Sarah J. Vigeland, Joseph Simon, Siyuan Chen, Zaven Arzoumanian, Paul T. Baker, Bence Bécsy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Shami Chatterjee, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Megan E. DeCesar, Paul B. Demorest, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Nathan Garver-Daniels, Deborah C. Good, Jeffrey S. Hazboun, Ross J. Jennings, Megan L. Jones, Andrew R. Kaiser, David L. Kaplan, Joey Shapiro Key, Michael T. Lam, T. Joseph W. Lazio, Jing Luo, Ryan S. Lynch, Dustin R. Madison, Alexander McEwen, Maura A. McLaughlin, Chiara M. F. Mingarelli, Cherry Ng, David J. Nice, Timothy T. Pennucci, Scott M. Ransom, Paul S. Ray, Brent J. Shapiro-Albert, Xavier Siemens, Ingrid H. Stairs, Daniel R. Stinebring, Joseph K. Swiggum, Michele Vallisneri, Haley Wahl, and Caitlin A. Witt

Subjects
Astrophysics, Physics Of Elementary Particles And Fields
Abstract

The NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of A(yr) = 1.92(+0.75,-0.55) x 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 data set, 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 yr of data, i.e., an additional 2–5 yr from the 12.5 yr data set.(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 yr 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 data sets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.

Published
2021
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21. Multimessenger Gravitational-wave Searches with Pulsar Timing Arrays: Application to 3C 66B Using the NANOGrav 11-year Data Set

Author

Zaven Arzoumanian, Paul T Baker, Adam Brazier, Paul R Brook, Sarah Burke-Spolaor, Bence Becsy, Maria Charisi, Shami Chatterjee, James M Cordes, Neil J Cornish, Fronefield Crawford, H Thankful Cromartie, Kathryn Crowter, Megan E DeCesar, Paul B Demorest, Timothy Dolch, Rodney D Elliott, Justin A Ellis, Robert D Ferdman, Elizabeth C Ferrara, Emmanuel Fonseca, Nathan Garver-Daniels, Peter A Gentile, Deborah C Good, Jeffrey S Hazboun, Kristina Islo, Ross J Jennings, Megan L Jones, Andrew R Kaiser, David L Kaplan, Luke Zoltan Kelley, Joey Shapiro Key, Michael T Lam, T Joseph W Lazio, Lina Levin, Jing Luo, Ryan S Lynch, Dustin R Madison, Maura A McLaughlin, Chiara M F Mingarelli, Cherry Ng, David J Nice, Timothy T Pennucci, Nihan S Pol, Scott M Ransom, Paul S Ray, Brent J Shapiro-Albert, Xavier Siemens, Joseph Simon, Renee Spiewak, Ingrid H Stairs, Daniel R Stinebring, Kevin Stovall, Joseph K Swiggum, Stephen R Taylor, Michele Vallisneri, Sarah J Vigeland, Caitlin A Witt, and Weiwei Zhu

Subjects
Astronomy
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Me 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
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22. Evidence for three-dimensional spin–velocity alignment in a pulsar

Author

William A. Coles, Jiguang Lu, Yi Feng, Weiwei Zhu, Chenchen Miao, Richard N. Manchester, W. M. Yan, Daniel R. Stinebring, Jumei Yao, Pei Wang, Di Li, Na Wang, Mao Yuan, and Michael Kramer

Subjects
Physics, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Radial velocity, Radio telescope, Neutron star, Supernova, Pulsar, 0103 physical sciences, Neutrino, Ejecta, Supernova remnant, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences
Abstract

More than 50 years after the discovery of pulsars1 and confirmation of their association with supernova explosions2–4, the origin of the initial spin and velocity of pulsars remains largely a mystery. The typical space velocities of several hundred km s−1 have been attributed to ‘kicks’ resulting from asymmetries either in the supernova ejecta or in the neutrino emission5–7. Observations have shown a strong tendency for alignment between the pulsar space velocity and the spin axis in young pulsars, but until now these comparisons have been restricted to two dimensions. Here, we report evidence for three-dimensional alignment between the spin and velocity vectors, largely based on observations made with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) of the pulsar PSR J0538+2817 and its associated supernova remnant S147. Analysis of these and related observations has enabled us to determine the location of the pulsar within the supernova remnant and hence its radial velocity. Current simulations of supernova explosions have difficulty producing such three-dimensional alignment7–9. Our results, which depend on the unprecedented sensitivity of the observations, add another dimension to the intriguing correlation between pulsar spin-axis and birth-kick directions, thereby deepening the mysteries surrounding the birth of neutron stars. Fast-moving pulsars and neutron stars in general may have received a kinetic ‘kick’ from an asymmetric element in the supernova explosion that formed them. Here, the spin axis of a pulsar is determined to lie along the three-dimensional direction of the pulsar’s motion, providing a challenging constraint on supernova explosion modelling.

Published
2021
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23. Interstellar Scintillation and Polarization of PSR B0656+14 in the Monogem Ring

Author

Jumei Yao, William A. Coles, Richard N. Manchester, Daniel R. Stinebring, Michael Kramer, Na Wang, Di Li, Weiwei Zhu, Yi Feng, Jianping Yuan, and Pei Wang

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

High sensitivity interstellar scintillation and polarization observations of PSR~B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the space velocity are significantly different, with a separation of $19\fdg3\pm$0\fdg8, inconsistent with a previously published near-perfect alignment of $1\degr\pm 2\degr$. The two independent scattering regions are clearly defined in the secondary spectra which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28~pc from PSR B0656+14 and 185~pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy $A_R$ to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this., 21 pages, 11 figures, accepted for publication in the Astronomical Journal

Published
2022
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24. 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
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25. Probing the local interstellar medium with scintillometry of the bright pulsar B1133+16

Author

James W. McKee, Hengrui Zhu, Daniel R. Stinebring, and James M. Cordes

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

The interstellar medium hosts a population of scattering screens, most of unknown origin. Scintillation studies of pulsars provides a sensitive tool for resolving these scattering screens and a means of measuring their properties. In this paper, we report our analysis of 34 years of Arecibo observations of PSR B1133+16, from which we have obtained high-quality dynamic spectra and their associated scintillation arcs, arising from the scattering screens located along the line of sight to the pulsar. We have identified six individual scattering screens that are responsible for the observed scintillation arcs, which persist for decades. Using the assumption that the scattering screens have not changed significantly in this time, we have modeled the variations in arc curvature throughout the Earth's orbit and extracted information about the placement, orientation, and velocity of five of the six screens, with the highest-precision distance measurement placing a screen at just $5.46^{+0.54}_{-0.59}$ pc from the Earth. We associate the more distant of these screens with an under-dense region of the Local Bubble., Comment: 16 pages, 9 figures, accepted for publication in ApJ

Published
2021
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26. 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
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27. 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

28. 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

29. 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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30. 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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31. 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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32. Scintillation Arcs Shed Light on Scattering from Planar Plasma Sheets

Author

Daniel R. Stinebring

Subjects
Physics, Scintillation, Optics, Planar, Space and Planetary Science, business.industry, Scattering, Astronomy and Astrophysics, Plasma, business
Abstract

Scintillation arcs provide an unprecedented degree of detail into the scattering of radio waves from pulsars. We review evidence that has emerged over the last fifteen years that: a) the scattering of many nearby pulsars is dominated by one or several relatively thin “screens” of material, b) the resulting image on the sky is highly linear, with axial ratios at least as high as 10:1, and c) this arrangement is persistent for at least one source (B1133+16) for at least 25 years. We expand on the idea of Pen and Levin (2014) and previous authors that such scattering may be caused by linear sheets of plasma seen nearly edge-on. Further analysis of such scintillation arcs, including new work on multi-frequency, multi-epoch observations, should help elucidate the astrophysical nature of these ubiquitous scattering entities, which are currently not convincingly linked with any known structures.

Published
2017
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33. 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
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34. 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
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35. 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
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36. 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
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37. Scattering features and variability of the Crab pulsar

Author

C. G. Bassa, Benjamin Stappers, Daniel R. Stinebring, Gemma H. Janssen, and Laura Driessen

Subjects
Astronomy, Gaussian, Astrophysics::High Energy Astrophysical Phenomena, Phase (waves), FOS: Physical sciences, Astrophysics, Expected value, 01 natural sciences, Radio telescope, symbols.namesake, 0103 physical sciences, 010303 astronomy & astrophysics, Scaling, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, interstellar medium, 010308 nuclear & particles physics, Crab Pulsar, Scattering, Astronomy and Astrophysics, Pulse (physics), Space and Planetary Science, Crab pulsar, symbols, pulsars, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report on Westerbork Synthesis Radio Telescope observations of the Crab pulsar at 350 MHz from 2012 November 24 until 2015 June 21. During this period we consistently observe variations in the pulse profile of the Crab. Both variations in the scattering width of the pulse profile as well as delayed copies, also known as echoes, are seen regularly. These observations support the classification of two types of echoes: those that follow the truncated exponential shape expected for the thin-screen scattering approximation, and echoes that show a smoother, more Gaussian shape. During a sequence of high-cadence observations in 2015, we find that these non-exponential echoes evolve in time by approaching the main pulse and interpulse in phase, overlapping the main pulse and interpulse, and later receding. We find a pulse scatter-broadening time scale, $\tau$, scaling with frequency as $\nu^{\alpha}$, with $\alpha=-3.9\pm0.5$, which is consistent with expected values for thin-screen scattering models, Comment: 10 pages, 7 figures

Published
2018

38. 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

39. Evolution of the low-frequency pulse profile of PSR B2217+47

Author

J. Y. Donner, Michael Kramer, L. Bondonneau, Stefan Oslowski, J.-M. Grießmeier, M. Serylak, Aris Karastergiou, M. Pilia, M. Geyer, S. Sanidas, Jason W. T. Hessels, Daniele Michilli, Benjamin Stappers, Adam Deller, Joris P. W. Verbiest, Matthias Hoeft, Daniel R. Stinebring, L.N. Driessen, Patrick Weltevrede, B. Shaw, and High Energy Astrophys. & Astropart. Phys (API, FNWI)

Subjects
Physics, Scintillation, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Magnetosphere, Astronomy and Astrophysics, Astrophysics, LOFAR, 01 natural sciences, Pulse (physics), law.invention, Interstellar medium, Telescope, Pulsar, Space and Planetary Science, law, 0103 physical sciences, Precession, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics
Abstract

An evolution of the low-frequency pulse profile of PSR B2217+47 is observed during a six-year observing campaign with the LOFAR telescope at 150 MHz. The evolution is manifested as a new component in the profile trailing the main peak. The leading part of the profile, including a newly-observed weak component, is steady during the campaign. The transient component is not visible in simultaneous observations at 1500 MHz using the Lovell telescope, implying a chromatic effect. A variation in the dispersion measure of the source is detected in the same timespan. Precession of the pulsar and changes in the magnetosphere are investigated to explain the profile evolution. However, the listed properties favour a model based on turbulence in the interstellar medium (ISM). This interpretation is confirmed by a strong correlation between the intensity of the transient component and main peak in single pulses. Since PSR B2217+47 is the fourth brightest pulsar visible to LOFAR, we speculate that ISM-induced pulse profile evolution might be relatively common but subtle and that SKA-Low will detect many similar examples. In this scenario, similar studies of pulse profile evolution could be used in parallel with scintillation arcs to characterize the properties of the ISM.

Published
2018

40. 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
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41. Low-frequency pulse profile variation in PSR B2217+47: evidence for echoes from the interstellar medium

Author

J. Y. Donner, Benjamin Stappers, Daniel R. Stinebring, Patrick Weltevrede, B. Shaw, Daniele Michilli, Jason W. T. Hessels, J.-M. Grießmeier, Adam Deller, Maura Pilia, Joris P. W. Verbiest, Matthias Hoeft, Aris Karastergiou, Laura Driessen, M. Serylak, L. Bondonneau, M. Geyer, S. Sanidas, Stefan Oslowski, Michael Kramer, 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), 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), High Energy Astrophys. & Astropart. Phys (API, FNWI), 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 ), and Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS )

Subjects
Electron density, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics, Low frequency, 01 natural sciences, Pulsar, 0103 physical sciences, education, 010303 astronomy & astrophysics, ISM: general, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, education.field_of_study, pulsars: individual: PSR B2217+47, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Interstellar medium, radio continuum: ISM, 13. Climate action, Space and Planetary Science, Circular symmetry, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Order of magnitude
Abstract

We have observed a complex and continuous change in the integrated pulse profile of PSR B2217+47, manifested as additional components trailing the main peak. These transient components are detected over 6 years at $150$ MHz using the LOw Frequency ARray (LOFAR), but they are not seen in contemporaneous Lovell observations at $1.5$ GHz. We argue that propagation effects in the ionized interstellar medium (IISM) are the most likely cause. The putative structures in the IISM causing the profile variation are roughly half-way between the pulsar and the Earth and have transverse radii $R \sim 30$ AU. We consider different models for the structures. Under the assumption of spherical symmetry, their implied average electron density is $\overline{n}_e \sim 100$ cm$^{-3}$. Since PSR B2217+47 is more than an order of magnitude brighter than the average pulsar population visible to LOFAR, similar profile variations would not have been identified in most pulsars, suggesting that subtle profile variations in low-frequency profiles might be more common than we have observed to date. Systematic studies of these variations at low frequencies can provide a new tool to investigate the proprieties of the IISM and the limits to the precision of pulsar timing., to be published in MNRAS

Published
2018
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42. 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
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43. Noise Budget and Interstellar Medium Mitigation Advances in the NANOGrav Pulsar Timing Array

Author

Justin A. Ellis, Timothy Dolch, J. M. Cordes, Maura McLaughlin, T. J. W. Lazio, Lina Levin, Daniel R. Stinebring, Paul Demorest, Michael T. Lam, Nipuni Palliyaguru, Shami Chatterjee, and Megan L. Jones

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), History, 010308 nuclear & particles physics, Gravitational wave, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, FOS: Physical sciences, White noise, 01 natural sciences, 7. Clean energy, Computer Science Applications, Education, Interstellar medium, Pulsar timing array, Pulsar, Millisecond pulsar, 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), Noise (radio), Astrophysics::Galaxy Astrophysics, Radio wave
Abstract

Gravitational wave (GW) detection with pulsar timing arrays (PTAs) requires accurate noise characterization. The noise of our Galactic-scale GW detector has been systematically evaluated by the Noise Budget and Interstellar Medium Mitigation working groups within the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration. Intrinsically, individual radio millisecond pulsars (MSPs) used by NANOGrav can have some degree of achromatic red spin noise, as well as white noise due to pulse phase jitter. Along any given line-of-sight, the ionized interstellar medium contributes chromatic noise through dispersion measure (DM) variations, interstellar scintillation, and scattering. These effects contain both red and white components. In the future, with wideband receivers, the effects of frequency-dependent DM will become important. Having anticipated and measured these diverse sources of detector noise, the NANOGrav PTA remains well-poised to detect low-frequency GWs., 5 pages, 3 figures, submitted to Journal of Physics: Conference Series as Proceedings of Amaldi 12

Published
2017

44. 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

45. 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
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46. Time Variability of Interstellar Scattering and Improvements to Pulsar Timing

Author

Daniel A. Hemberger and Daniel R. Stinebring

Subjects
Physics, Gravitational wave, Scattering, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, Detector, Astronomy, Astronomy and Astrophysics, Astrophysics, law.invention, Interstellar medium, Telescope, Pulsar timing array, Pulsar, Space and Planetary Science, Sky, law, Astrophysics::Galaxy Astrophysics, media_common
Abstract

Delay due to multipath scattering in the interstellar medium is a concern for high-precision pulsar timing, particularly if it is not constant over time. We report on 36 weekly observations of the pulsar PSR B1737+13 with the Arecibo telescope that monitored the time variability of the scattering delay. At a frequency of 1380 MHz, the interstellar delay varied between 0.2 and 2.1 μ s (±0.1 μ s ) over 270 days of observation. The delay was consistent over four observing bands with center frequencies from 1175 to 1470 MHz and scaled as τ ∝ ν−3.6 ± 0.2, which differs from the ν−4.4 scaling expected for Kolmogorov turbulence. We show that another estimation technique is feasible for weaker pulsars or smaller telescopes, although it underestimates the delay during episodes of extra scattering detectable through a full secondary spectrum analysis. An array of pulsars distributed around the sky can be used as a sensitive detector of long-wavelength (~ several light-years) gravitational radiation, and such pulsar timing array observations have been initiated by several groups worldwide. To reach interesting sensitivity levels it is necessary to reduce the sources of error to below 1 μ s , and 100 ns is a target precision level. Correction for interstellar scattering delay will be an important step in achieving long-term, submicrosecond timing precision.

Published
2008
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47. Frequency-Dependent Dispersion Measures and Implications for Pulsar Timing

Author

Ryan Shannon, J. M. Cordes, and Daniel R. Stinebring

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Observational error, 010308 nuclear & particles physics, Gravitational wave, Spectral density, FOS: Physical sciences, Astronomy and Astrophysics, 01 natural sciences, Computational physics, Pulsar, Astrophysics - Solar and Stellar Astrophysics, 13. Climate action, Space and Planetary Science, 0103 physical sciences, Dispersion (optics), Chromatic scale, Radio frequency, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Noise (radio), Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

We analyze the frequency dependence of the dispersion measure (DM), the column density of free electrons to a pulsar, caused by multipath scattering from small scale electron-density fluctuations. The DM is slightly different along each propagation path and the transverse spread of paths varies greatly with frequency, yielding time-of-arrival (TOA) perturbations that scale differently than the inverse square of the frequency, the expected dependence for a cold, unmagnetized plasma. We quantify DM and TOA perturbations analytically for thin phase screens and extended media and verify the results with simulations of thin screens. The rms difference between DMs across an octave band near 1.5~GHz $\sim 4\times10^{-5}\,{\rm pc\ cm^{-3}}$ for pulsars at $\sim 1$~kpc distance. TOA errors from chromatic DMs are of order a few to hundreds of nanoseconds for pulsars with DM $\lesssim 30$~pc~cm$^{-3}$ observed across an octave band but increase rapidly to microseconds or larger for larger DMs and wider frequency ranges. Frequency-dependent DMs introduce correlated noise into timing residuals whose power spectrum is `low pass' in form. The correlation time is of order the geometric mean of the refraction times for the highest and lowest radio frequencies used and thus ranges from days to years, depending on the pulsar. We discuss the implications for methodologies that use large frequency separations or wide bandwidth receivers for timing measurements. Chromatic DMs are partially mitigable by using an additional chromatic term in arrival time models. Without mitigation, our results provide an additional term in the noise model for pulsar timing; they also indicate that in combination with measurement errors from radiometer noise, an arbitrary increase in total frequency range (or bandwidth) will yield diminishing benefits and may be detrimental to overall timing precision., 19 pages, 13 figures; submitted to the Astrophysical Journal

Published
2015

48. Single-Source Gravitational Wave Limits from the J1713+0747 24-hr Global Campaign

Author

Ramesh Karuppusamy, Ryan Shannon, Ismaël Cognard, Glenn Jones, Timothy Dolch, Duncan R. Lorimer, C. G. Bassa, J. M. Cordes, Kevin Stovall, Paul Demorest, Gemma H. Janssen, T. J. W. Lazio, Jason W. T. Hessels, Fredrick A. Jenet, Christine Jordan, Jayanta Roy, Dustin R. Madison, Joris P. W. Verbiest, P. Lazarus, D. J. Champion, Kathryn Crowter, R. Smits, Nipuni Palliyaguru, Maura McLaughlin, Delphine Perrodin, Bhaswati Bhattacharyya, J. A. Ellis, Daniel R. Stinebring, Michael Kramer, Ingrid H. Stairs, Scott M. Ransom, S. Chatterjee, Michael Keith, Wei Zhu, Michael T. Lam, V. I. Kondratiev, Benjamin Stappers, Department of Physics, Hillsdale College, Jet Propulsion Laboratory ( JPL ), NASA-California Institute of Technology ( CALTECH ), Department of Astronomy [Ithaca], Cornell University, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Max-Planck-Institut für Radioastronomie ( MPIFR ), 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 ), Department of Physics and Astronomy [Vancouver], University of British Columbia ( UBC ), National Radio Astronomy Observatory [Socorro] ( NRAO ), National Radio Astronomy Observatory ( NRAO ), Netherlands Institute for Radio Astronomy ( ASTRON ), Center for Gravitational Wave Astronomy, The University of Texas at Brownsville and Texas Southmost College, Columbia Astrophysics Laboratory ( COLUMBIA UNIVERSITY ), Columbia University [New York], Max-Planck-Institut für Radioastronomie, Department of Physics and Astronomy, West Virginia University, West Virginia University [Morgantown], Department of Physics, West Virginia University, West Virginia University, INAF - Osservatorio Astronomico di Cagliari, National Radio Astronomy Observatory [Green Bank] ( NRAO ), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] ( CSIRO ), Department of Physics and Astronomy, University of British Columbia, Physics and Astronomy Department [Oberlin], Oberlin College, Sponsors : int Union Pure & Appl Phys, Korean Astron Soc, Korean Phys Soc, Korean Federat Sci & Technol, Natl Res Fdn, Korea Tourism Organism, Gwangju Convent Bur, ITA, USA, GBR, FRA, DEU, AUS, CAN, IND, NLD, RUS, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Cornell University [New York], 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, 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), University of British Columbia (UBC), National Radio Astronomy Observatory [Socorro] (NRAO), National Radio Astronomy Observatory (NRAO), Netherlands Institute for Radio Astronomy (ASTRON), Center for Gravitational Wave Astronomy (CGWA), University of Texas Rio Grande Valley [Brownsville, TX] (UTRGV), Columbia Astrophysics Laboratory (CAL), INAF - Osservatorio Astronomico di Cagliari (OAC), Istituto Nazionale di Astrofisica (INAF), National Radio Astronomy Observatory [Green Bank] (NRAO), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Department of Physics and Astronomy [Oberlin], Department of Physics and Astronomy [Albuquerque], and The University of New Mexico [Albuquerque]

Subjects
History, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, BLACK-HOLE BINARIES, 01 natural sciences, Education, Pulsar timing array, Pulsar, Millisecond pulsar, Observatory, 0103 physical sciences, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), [ SDU.ASTR ] Sciences of the Universe [physics]/Astrophysics [astro-ph], astro-ph.HE, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], 010308 nuclear & particles physics, Gravitational wave, DATA SET, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, PULSAR TIMING ARRAY, Computer Science Applications, European Pulsar Timing Array, Intermediate frequency, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Noise (radio), SYSTEM, astro-ph.IM
Abstract

Dense, continuous pulsar timing observations over a 24-hr period provide a method for probing intermediate gravitational wave (GW) frequencies from 10 microhertz to 20 millihertz. The European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the Parkes Pulsar Timing Array (PPTA), and the combined International Pulsar Timing Array (IPTA) all use millisecond pulsar observations to detect or constrain GWs typically at nanohertz frequencies. In the case of the IPTA's nine-telescope 24-Hour Global Campaign on millisecond pulsar J1713+0747, GW limits in the intermediate frequency regime can be produced. The negligible change in dispersion measure during the observation minimizes red noise in the timing residuals, constraining any contributions from GWs due to individual sources. At 10$^{-5}$Hz, the 95% upper limit on strain is 10$^{-11}$ for GW sources in the pulsar's direction., Comment: 4 pages, 2 figures, published in the proceedings of Amaldi 11

Published
2015
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49. Multiple Scintillation Arcs in Six Pulsars

Author

Daniel R. Stinebring and Margaret L. Putney

Subjects
Sight, Physics, Scintillation, Transverse plane, Line-of-sight, Pulsar, Space and Planetary Science, Scattering, Astronomy, Astronomy and Astrophysics, Astrophysics, Curvature, Spectral line
Abstract

Low-intensity scattering in discrete screens gives rise to parabolic scintillation arcs in pulsar secondary spectra. The curvature of the arc boundary is uniquely determined by the location of the screen along the line of sight, the distance to the pulsar, and the relative velocity of pulsar and Earth (assuming the transverse screen velocity to be small). This information is usually available for the strong pulsars needed to exhibit clear scintillation arcs. Early studies reported single arcs along most lines of sight. This seemed puzzling given the variety of distances and sight lines being probed. We report new, higher sensitivity observations that show up to four scintillation arcs for a particular sight line.

Published
2006
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50. The interstellar turbulent plasma spectrum in the direction to PSR B1642-03 from multi-frequency observations of interstellar scintillation

Author

S. A. Tyul'bashev, W. Sieber, Richard Wielebinski, T. V. Smirnova, Daniel R. Stinebring, V. A. Potapov, V. I. Shishov, Axel Jessner, and V. M. Malofeev

Subjects
Physics, Scintillation, Line-of-sight, Turbulence, Astrophysics::High Energy Astrophysical Phenomena, Astronomy and Astrophysics, Astrophysics, Plasma, Power law, Interstellar medium, Solar wind, Pulsar, Space and Planetary Science, Astrophysics::Galaxy Astrophysics
Abstract

Multi-frequency observations of interstellar scintillation toward the pulsar PSR B1642-03 were analyzed to estimate the spectrum of interstellar plasma inhomogeneities in the direction of this pulsar. Using data over the frequency range from 103 MHz to 5 GHz, we constructed the composite structure function (SF) of phase fluctuations, which covers a corresponding wide range of turbulence scales. The structure function shows that the interstellar plasma spectrum in the direction to this pulsar follows a piecewise power law. The power law is well described by two exponents: $n = 3. 7$ for scales from 10 9 to 10 15 cm (Kolmogorov spectrum) and $n = 3.35$ for scales less than 10 9 cm. We interpret the unusual behaviour of the spectrum to be caused by the line of sight passing through the North Polar Spur, which may have plasma properties similar to the anisotropic plasma of the solar wind, although at a very different density.

Published
2006
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