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1. The NANOGrav 15 year Data Set: Removing pulsars one by one from the pulsar timing array

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Evidence has emerged for a stochastic signal correlated among 67 pulsars within the 15-year pulsar-timing data set compiled by the NANOGrav collaboration. Similar signals have been found in data from the European, Indian, Parkes, and Chinese PTAs. This signal has been interpreted as indicative of the presence of a nanohertz stochastic gravitational wave background. To explore the internal consistency of this result we investigate how the recovered signal strength changes as we remove the pulsars one by one from the data set. We calculate the signal strength using the (noise-marginalized) optimal statistic, a frequentist metric designed to measure correlated excess power in the residuals of the arrival times of the radio pulses. We identify several features emerging from this analysis that were initially unexpected. The significance of these features, however, can only be assessed by comparing the real data to synthetic data sets. After conducting identical analyses on simulated data sets, we do not find anything inconsistent with the presence of a stochastic gravitational wave background in the NANOGrav 15-year data. The methodologies developed here can offer additional tools for application to future, more sensitive data sets. While this analysis provides an internal consistency check of the NANOGrav results, it does not eliminate the necessity for additional investigations that could identify potential systematics or uncover unmodeled physical phenomena in the data., Comment: 21 pages, 11 figures, 2 tables

Published
2024

2. The NANOGrav 15 yr Data Set: Running of the Spectral Index

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Abstract

The NANOGrav 15-year data provides compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. The simplest model-independent approach to characterizing the frequency spectrum of this signal consists in a simple power-law fit involving two parameters: an amplitude A and a spectral index \gamma. In this paper, we consider the next logical step beyond this minimal spectral model, allowing for a running (i.e., logarithmic frequency dependence) of the spectral index, \gamma_run(f) = \gamma + \beta \ln(f/f_ref). We fit this running-power-law (RPL) model to the NANOGrav 15-year data and perform a Bayesian model comparison with the minimal constant-power-law (CPL) model, which results in a 95% credible interval for the parameter \beta consistent with no running, \beta \in [-0.80,2.96], and an inconclusive Bayes factor, B(RPL vs. CPL) = 0.69 +- 0.01. We thus conclude that, at present, the minimal CPL model still suffices to adequately describe the NANOGrav signal; however, future data sets may well lead to a measurement of nonzero \beta. Finally, we interpret the RPL model as a description of primordial GWs generated during cosmic inflation, which allows us to combine our results with upper limits from big-bang nucleosynthesis, the cosmic microwave background, and LIGO-Virgo-KAGRA., Comment: 17 pages, 4 figures, 2 tables

Published
2024

3. The NANOGrav 15 yr data set: Posterior predictive checks for gravitational-wave detection with pulsar timing arrays

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract

Pulsar-timing-array experiments have reported evidence for a stochastic background of nanohertz gravitational waves consistent with the signal expected from a population of supermassive--black-hole binaries. Those analyses assume power-law spectra for intrinsic pulsar noise and for the background, as well as a Hellings--Downs cross-correlation pattern among the gravitational-wave--induced residuals across pulsars. These assumptions are idealizations that may not be realized in actuality. We test them in the NANOGrav 15 yr data set using Bayesian posterior predictive checks: after fitting our fiducial model to real data, we generate a population of simulated data-set replications, and use them to assess whether the optimal-statistic significance, inter-pulsar correlations, and spectral coefficients assume extreme values for the real data when compared to the replications. We confirm that the NANOGrav 15 yr data set is consistent with power-law and Hellings--Downs assumptions. We also evaluate the evidence for the stochastic background using posterior-predictive versions of the frequentist optimal statistic and of Bayesian model comparison, and find comparable significance (3.2\ $\sigma$ and 3\ $\sigma$ respectively) to what was previously reported for the standard statistics. We conclude with novel visualizations of the reconstructed gravitational waveforms that enter the residuals for each pulsar. Our analysis strengthens confidence in the identification and characterization of the gravitational-wave background as reported by NANOGrav., Comment: 20 pages, 14 Figures

Published
2024

4. A Statistical Analysis of Crab Pulsar Giant Pulse Rates

Author

Doskoch, Graham M., Basuroski, Andrea, Halley, Kriisa, Sookram, Avinash, Rodriguez-Ramos, Iliomar, Nahata, Valmik, Rahman, Zahi, Zhang, Maureen, Uhlmann, Ashish, Lynch, Abby, Lewandowska, Natalia, Miranda, Nohely, Schmiedekamp, Ann, Schmiedekamp, Carl, McLaughlin, Maura A., Reichart, Daniel E., Haislip, Joshua B., Kouprianov, Vladimir V., White, Steve, Ghigo, Frank, and Heatherly, Sue Ann

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

A small number of pulsars are known to emit giant pulses, single pulses much brighter than average. Among these is PSR J0534+2200, also known as the Crab pulsar, a young pulsar with high giant pulse rates. Long-term monitoring of the Crab pulsar presents an excellent opportunity to perform statistical studies of its giant pulses and the processes affecting them, potentially providing insight into the behavior of other neutron stars that emit bright single pulses. Here, we present an analysis of a set of 24,985 Crab giant pulses obtained from 88 hours of daily observations at a center frequency of 1.55 GHz by the 20-meter telescope at the Green Bank Observatory, spread over 461 days. We study the effects of refractive scintillation at higher frequencies than previous studies and compare methods of correcting for this effect. We also search for deterministic patterns seen in other single-pulse sources, possible periodicities seen in several rotating radio transients and fast radio bursts, and clustering of giant pulses like that seen in the repeating fast radio burst FRB121102., Comment: 21 pages, 14 figures, accepted to ApJ

Published
2024
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5. The Anomalous Acceleration of PSR J2043+1711: Long-Period Orbital Companion or Stellar Flyby?

Author

Donlon II, Thomas, Chakrabarti, Sukanya, Lam, Michael T., Huber, Daniel, Hey, Daniel, Ramirez-Ruiz, Enrico, Shappee, Benjamin, Kaplan, David L., Agazie, Gabriella, Anumarlapudi, Akash, Archibald, Anne M., Arzoumanian, Zaven, Baker, Paul T., Brook, Paul R., Cromartie, H. Thankful, Crowter, Kathryn, DeCesar, Megan E., Demorest, Paul B., Dolch, Timothy, Ferrara, Elizabeth C., Fiore, William, Fonseca, Emmanuel, Freedman, Gabriel E., Garver-Daniels, Nate, Gentile, Peter A., Glaser, Joseph, Good, Deborah C., Hazboun, Jeffrey S., Huber, Mark, Jennings, Ross J., Jones, Megan L., Kerr, Matthew, Lorimer, Duncan R., Luo, Jing, Lynch, Ryan S., McEwen, Alexander, McLaughlin, Maura A., McMann, Natasha, Meyers, Bradley W., Ng, Cherry, Nice, David J., Pennucci, Timothy T., Perera, Benetge B. P., Pol, Nihan S., Radovan, Henri A., Ransom, Scott M., Ray, Paul S., Schmiedekamp, Ann, Schmiedekamp, Carl, Shapiro-Albert, Brent J., Stairs, Ingrid H., Stovall, Kevin, Susobhanan, Abhimanyu, Swiggum, Joseph K., Tucker, Michael A., and Wahl, Haley M.

Subjects
Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 $\pm$ 0.8 mm/s/yr, which deviates from the acceleration predicted by equilibrium Milky Way models at a $4\sigma$ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the Milky Way interacting with orbiting dwarf galaxies ($\sim$1 mm/s/yr), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in \textit{Gaia} DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6\%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 80 kyr, a companion mass of 0.3 $M_\odot$ (indicative of a white dwarf or low-mass star), and a semi-major axis of 2000 AU. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.

Published
2024

6. The NANOGrav 15 yr Data Set: Chromatic Gaussian Process Noise Models for Six Pulsars

Author

Larsen, Bjorn, Mingarelli, Chiara M. F., Hazboun, Jeffrey S., Chalumeau, Aurelien, Good, Deborah C., Simon, Joseph, Agazie, Gabriella, Anumarlapudi, Akash, Archibald, Anne M., Arzoumanian, Zaven, Baker, Paul T., Brook, Paul R., Cromartie, H. Thankful, Crowter, Kathryn, DeCesar, Megan E., Demorest, Paul B., Dolch, Timothy, Ferrara, Elizabeth C., Fiore, William, Fonseca, Emmanuel, Freedman, Gabriel E., Garver-Daniels, Nate, Gentile, Peter A., Glaser, Joseph, Jennings, Ross J., Jones, Megan L., Kaplan, David L., Kerr, Matthew, Lam, Michael T., Lorimer, Duncan R., Luo, Jing, Lynch, Ryan S., McEwen, Alexander, McLaughlin, Maura A., McMann, Natasha, Meyers, Bradley W., Ng, Cherry, Nice, David J., Pennucci, Timothy T., Perera, Benetge B. P., Pol, Nihan S., Radovan, Henri A., Ransom, Scott M., Ray, Paul S., Schmiedekamp, Ann, Schmiedekamp, Carl, Shapiro-Albert, Brent J., Stairs, Ingrid H., Stovall, Kevin, Susobhanan, Abhimanyu, Swiggum, Joseph K., Wahl, Haley M., Champion, David J., Cognard, Ismael, Guillemot, Lucas, Hu, Huanchen, Keith, Michael J., Liu, Kuo, McKee, James W., Parthasarathy, Aditya, Perrodin, Delphine, Possenti, Andrea, Shaifullah, Golam M., and Theureau, Gilles

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Pulsar timing arrays (PTAs) are designed to detect low-frequency gravitational waves (GWs). GWs induce achromatic signals in PTA data, meaning that the timing delays do not depend on radio-frequency. However, pulse arrival times are also affected by radio-frequency dependent "chromatic" noise from sources such as dispersion measure (DM) and scattering delay variations. Furthermore, the characterization of GW signals may be influenced by the choice of chromatic noise model for each pulsar. To better understand this effect, we assess if and how different chromatic noise models affect achromatic noise properties in each pulsar. The models we compare include existing DM models used by NANOGrav and noise models used for the European PTA Data Release 2 (EPTA DR2). We perform this comparison using a subsample of six pulsars from the NANOGrav 15 yr data set, selecting the same six pulsars as from the EPTA DR2 six-pulsar dataset. We find that the choice of chromatic noise model noticeably affects the achromatic noise properties of several pulsars. This is most dramatic for PSR J1713+0747, where the amplitude of its achromatic red noise lowers from $\log_{10}A_{\text{RN}} = -14.1^{+0.1}_{-0.1}$ to $-14.7^{+0.3}_{-0.5}$, and the spectral index broadens from $\gamma_{\text{RN}} = 2.6^{+0.5}_{-0.4}$ to $\gamma_{\text{RN}} = 3.5^{+1.2}_{-0.9}$. We also compare each pulsar's noise properties with those inferred from the EPTA DR2, using the same models. From the discrepancies, we identify potential areas where the noise models could be improved. These results highlight the potential for custom chromatic noise models to improve PTA sensitivity to GWs.

Published
2024

7. The NANOGrav 15 yr Data Set: Looking for Signs of Discreteness in the Gravitational-wave Background

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

The cosmic merger history of supermassive black hole binaries (SMBHBs) is expected to produce a low-frequency gravitational wave background (GWB). Here we investigate how signs of the discrete nature of this GWB can manifest in pulsar timing arrays through excursions from, and breaks in, the expected $f_{\mathrm{GW}}^{-2/3}$ power-law of the GWB strain spectrum. To do this, we create a semi-analytic SMBHB population model, fit to NANOGrav's 15 yr GWB amplitude, and with 1,000 realizations we study the populations' characteristic strain and residual spectra. Comparing our models to the NANOGrav 15 yr spectrum, we find two interesting excursions from the power-law. The first, at $2 \; \mathrm{nHz}$, is below our GWB realizations with $p$-value significance $p = 0.05$ to $0.06$ ($\approx 1.8 \sigma - 1.9 \sigma$). The second, at $16 \; \mathrm{nHz}$, is above our GWB realizations with $p = 0.04$ to $0.15$ ($\approx 1.4 \sigma - 2.1 \sigma$). We explore the properties of a loud SMBHB which could cause such an excursion. Our simulations also show that the expected number of SMBHBs decreases by three orders of magnitude, from $\sim 10^6$ to $\sim 10^3$, between $2\; \mathrm{nHz}$ and $20 \; \mathrm{nHz}$. This causes a break in the strain spectrum as the stochasticity of the background breaks down at $26^{+28}_{-19} \; \mathrm{nHz}$, consistent with predictions pre-dating GWB measurements. The diminished GWB signal from SMBHBs at frequencies above the $26~\mathrm{nHz}$ break opens a window for PTAs to detect continuous GWs from individual SMBHBs or GWs from the early universe., Comment: 13 pages, 8 figures, 2 appendices, in press at ApJ

Published
2024
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8. The NANOGrav 15-year data set: Search for Transverse Polarization Modes in the Gravitational-Wave Background

Author

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

Subjects
General Relativity and Quantum Cosmology, Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Recently we found compelling evidence for a gravitational wave background with Hellings and Downs (HD) correlations in our 15-year 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-year data set for evidence of a gravitational wave background with quadrupolar Hellings and Downs (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 $\sim 2$ when comparing HD to ST correlations, and $\sim 1$ 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., Comment: 11 pages, 5 figures

Published
2023

9. How to Detect an Astrophysical Nanohertz Gravitational-Wave Background

Author

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

Subjects
General Relativity and Quantum Cosmology, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Analysis of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nHz frequency band. The most plausible source of such a background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for such a 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 datasets. The dataset length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15-year dataset. 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 datasets, despite their fundamental assumptions not being 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., Comment: 14 pages, 8 figures, version matching published paper

Published
2023
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10. The NANOGrav 15-year Gravitational-Wave Background Analysis Pipeline

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology
Abstract

This paper presents rigorous tests of pulsar timing array methods and software, examining their consistency across a wide range of injected parameters and signal strength. We discuss updates to the 15-year isotropic gravitational-wave background analyses and their corresponding code representations. Descriptions of the internal structure of the flagship algorithms \texttt{Enterprise} and \texttt{PTMCMCSampler} are given to facilitate understanding of the PTA likelihood structure, how models are built, and what methods are currently used in sampling the high-dimensional PTA parameter space. We introduce a novel version of the PTA likelihood that uses a two-step marginalization procedure that performs much faster when the white noise parameters remain fixed. We perform stringent tests of consistency and correctness of the Bayesian and frequentist analysis software. For the Bayesian analysis, we test prior recovery, injection recovery, and Bayes factors. For the frequentist analysis, we test that the cross-correlation-based optimal statistic, when modified to account for a non-negligible gravitational-wave background, accurately recovers the amplitude of the background. We also summarize recent advances and tests performed on the optimal statistic in the literature from both GWB detection and parameter estimation perspectives. The tests presented here validate current and future analyses of PTA data., Comment: 30 pages, 10 figures, 1 table; Companion paper to "The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background"; For questions or comments, please email comments@nanograv.org

Published
2023

11. The NANOGrav 15-year Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
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 datasets. Here we present the search for individual supermassive black hole binaries in the NANOGrav 15-year dataset. 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 $\sim$4 nHz, and another at $\sim$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., Comment: 23 pages, 13 figures, 2 tables. Accepted for publication in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023
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12. The NANOGrav 15-year Data Set: Search for Anisotropy in the Gravitational-Wave Background

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
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 dataset. 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, and place a Bayesian $95\%$ upper limit on the level of broadband anisotropy such that $(C_{l>0} / C_{l=0}) < 20\%$. 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 dataset, and show that this dataset 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., Comment: 19 pages, 11 figures; submitted to Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023

13. The NANOGrav 15-year Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology
Abstract

The NANOGrav 15-year 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-year 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 sub-parsec 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., Comment: Accepted by Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org. Edited to fix two equation typos (Eq.13 & 21), and minor text typos

Published
2023
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14. The NANOGrav 15-year Data Set: Search for Signals from New Physics

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Abstract

The 15-year 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., Comment: 74 pages, 31 figures, 4 tables; published in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023
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15. The NANOGrav 15-Year Data Set: Detector Characterization and Noise Budget

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics, General Relativity and Quantum Cosmology
Abstract

Pulsar timing arrays (PTAs) are galactic-scale gravitational wave 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 gravitational wave (GW) signals. We present a noise and sensitivity analysis to accompany the NANOGrav 15-year 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 $7\times 10^{-15}$ at 5 nHz. A power law-integrated analysis shows rough agreement with the amplitudes recovered in NANOGrav's 15-year 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., Comment: 67 pages, 73 figures, 3 tables; published in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023
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16. The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15-year 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. 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 three years, now spanning nearly 16 years 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 gravitational-wave background., Comment: 90 pages, 74 figures, 6 tables; published in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023
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17. The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background

Author

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

Subjects
Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract

We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15-year 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 these latter Bayes factors using a method that removes inter-pulsar correlations from our data set, finding $p = 10^{-3}$ (approx. $3\sigma$) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of inter-pulsar correlations yields $p = 5 \times 10^{-5} - 1.9 \times 10^{-4}$ (approx. $3.5 - 4\sigma$). Assuming a fiducial $f^{-2/3}$ characteristic-strain spectrum, as appropriate for an ensemble of binary supermassive black-hole inspirals, the strain amplitude is $2.4^{+0.7}_{-0.6} \times 10^{-15}$ (median + 90% credible interval) at a reference frequency of 1/(1 yr). 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., Comment: 30 pages, 18 figures. Published in Astrophysical Journal Letters as part of Focus on NANOGrav's 15-year Data Set and the Gravitational Wave Background. For questions or comments, please email comments@nanograv.org

Published
2023
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18. The Green Bank Northern Celestial Cap Pulsar Survey. VI. Timing and Discovery of PSR J1759+5036: A Double Neutron Star Binary Pulsar

Author

Agazie, Gabriella, Mingyar, Michael, McLaughlin, Maura, Swiggum, Joseph, Kaplan, David, Blumer, Harsha, Chawla, Pragya, DeCesar, Megan, Demorest, Paul, Fiore, William, Fonseca, Emmanuel, Gelfand, Joseph, Kaspi, Victoria, Kondratiev, Vladislav, LaRose, Malcolm, van Leeuwen, Joeri, Levin, Lina, Lewis, Evan, Lynch, Ryan, McEwen, Alexander, Noori, Hind Al, Parent, Emilie, Ransom, Scott, Roberts, Mallory, Schmiedekamp, Ann, Schmiedekamp, Carl, Siemens, Xavier, Spiewak, Renée, Stairs, Ingrid, and Surnis, Mayuresh

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract

The Green Bank North Celestial Cap (GBNCC) survey is a 350-MHz all-sky survey for pulsars and fast radio transients using the Robert C. Byrd Green Bank Telescope. To date, the survey has discovered over 190 pulsars, including 33 millisecond pulsars (MSPs) and 24 rotating radio transients(RRATs). Several exotic pulsars have been discovered in the survey, including PSR J1759+5036, a binary pulsar with a 176-ms spin period in an orbit with a period of 2.04 days, an eccentricity of 0.3,and a projected semi-major axis of 6.8 light seconds. Using seven years of timing data, we are able to measure one post-Keplerian parameter, advance of periastron, which has allowed us to constrain the total system mass to 2.62(3) solar masses. This constraint, along with the spin period and orbital parameters, suggests that this is a double neutron star system, although we cannot entirely rule out a pulsar-white dwarf binary. This pulsar is only detectable in roughly 45% of observations, most likely due to scintillation. However, additional observations are required to determine whether there may be other contributing effects., Comment: 11 pages, 13 figures, Accepted to APJ

Published
2021
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19. How to Detect an Astrophysical Nanohertz Gravitational Wave Background

Author

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

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

Author

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

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

Author

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

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

Author

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

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

Author

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

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

Author

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

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

Author

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

Published
2023
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29. Synthesis and characterization of homo- and heterodinuclear M(ii)-M′(iii) (M(ii) = Mn or Fe, M′(iii) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(ii)

Author

Brewer, Cynthia T., primary, Brewer, Greg, additional, Butcher, Ray J., additional, Carpenter, Everett E., additional, Schmiedekamp, Ann M., additional, Schmiedekamp, Carl, additional, Straka, Alison, additional, Viragh, Carol, additional, Yuzefpolskiy, Yevgeniy, additional, and Zavalij, Peter, additional

Published
2011
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30. Toward the MIL-STD and MIL-HDBK for Project Support Environment Interfaces

Author

NAVAL COMMAND CONTROL AND OCEAN SURVEILLANCE CENTER RDT AND E DIV SAN DIEGO CA, Schmiedekamp, Carl, Shapiro, Michael D., NAVAL COMMAND CONTROL AND OCEAN SURVEILLANCE CENTER RDT AND E DIV SAN DIEGO CA, Schmiedekamp, Carl, and Shapiro, Michael D.

Abstract

This document provides the necessary background information to create a military standard (MIL-STD) and military handbook (MIL-HDBK) for the project support environment interfaces (PSEI). Preliminary incomplete drafts of the MIL- STD and MIL-HDBK are included as appendices A and B respectively. Project Support Environment (PSE), Interfaces, Military standard (MIL-STD), Military handbook (MIL-HDBK), Standards.

Published
1992

31. General Goals and Characteristic for PSEI Standards.

Author

NAVAL AIR WARFARE CENTER AIRCRAFT DIV WARMINSTER PA SYSTEMS AND SOFTWARE TECH NOLOGY DEPT, Schmiedekamp, Carl, Shields, Thomas, NAVAL AIR WARFARE CENTER AIRCRAFT DIV WARMINSTER PA SYSTEMS AND SOFTWARE TECH NOLOGY DEPT, Schmiedekamp, Carl, and Shields, Thomas

Abstract

This document describes the Department of the Navy's goals and general characteristics for the definition and specification of Project Support Environment (PSE) Interface (PSEI) standards for the Next Generation Computer Resources (NGCR) Program. These goals and characteristics provide general guidance to the NGCR Project Support Environment Standards Working Group (PSESWG) in the selection of PSEI standards. It is expected that more specific goals and characteristics will be defined within particular PSE service areas to guide the selection of individual PSEI standards. Each general goal and characteristic is described in a subsection of this document. In addition, each general characteristic description includes evaluation criteria with a scoring scheme. It is intended that these evaluation criteria be used for subjective scoring and analysis of competing standards.

Published
1992

32. Synthesis and characterization of homo- and heterodinuclear M(ii)-M′(iii) (M(ii) = Mn or Fe, M′(iii) = Fe or Co) mixed-valence supramolecular pseudo-dimers. The effect of hydrogen bonding on spin state selection of M(ii)Electronic supplementary information (ESI) available: Additional figures. CCDC reference numbers: [MnH3L1](ClO4)2(609761), [FeH3L1](BF4)2(766398), {[FeH1.5L1](BF4)}2(766394 @ 295 K, 766397 @ 110 K), {[Fe(ii)0.5Co(iii)0.5H1.5L1](BF4)}2(766395 @ 295 K, 766396 @ 110 K), {[Mn(ii)0.5Co(iii)0.5H1.5L1](ClO4)}2(785615), [MnH3L1][CoL1](ClO4)2(785614) and [FeH3L1][FeL1](PF6)2(661178). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c0dt01098g

Author

Brewer, Cynthia T., Brewer, Greg, Butcher, Ray J., Carpenter, Everett E., Schmiedekamp, Ann M., Schmiedekamp, Carl, Straka, Alison, Viragh, Carol, Yuzefpolskiy, Yevgeniy, and Zavalij, Peter

Subjects
ORGANOMETALLIC compounds, CONDUCTION electrons, SUPRAMOLECULAR chemistry, DIMERS, HYDROGEN bonding, NUCLEAR spin, SCHIFF bases, ORGANIC synthesis
Abstract

Reaction of H3L1, the Schiff base condensate of tris(2-aminoethyl)amine with three equivalents of 5-methyl-1H-pyrazole-3-carboxaldehyde, with manganese(ii)perchlorate or iron(ii)tetrafluoroborate results in the isolation of [MH3L1]X2(M = Mn and X = ClO4and M = Fe and X = BF4). These complexes are high spin d5and d6, respectively, as inferred from the long M–N bond distances obtained by single crystal X-ray diffraction for both and variable temperature magnetic susceptibility and Mössbauer spectroscopy for the iron complex. Aerobic treatment of a solution of [CoH3L1]2+with three equivalents of potassium hydroxide produced [CoL1]. Homonuclear pseudo-dimers were prepared by the aerobic reaction of [FeH3L1](BF4)2with 1.5 equivalents of potassium hydroxide to give {[FeH1.5L1](BF4)}2or by the metathesis reaction of [FeH2L1][FeHL1](ClO4)2with sodium hexafluorophosphate to give [FeH3L1][FeL1](PF6)2. The complexes were characterized by EA, IR, ESI-MS, variable temperature single crystal xray diffraction and Mössbauer spectroscopy. The iron(iii) atom is low spin while the iron(ii) atom is spin crossover. Heteronuclear pseudo-dimers were prepared by the 1 : 1 reaction of [FeH3L1](BF4)2or [MnH3L1](ClO4)2with [CoL1]. [MH3L1][CoL1](X)2(M = Fe and X = BF4or M = Mn and X = ClO4), were characterized by IR, EA, variable temperature single crystal X-ray diffraction and Mössbauer spectroscopy in the iron case. The data support a spin crossover and high spin assignment for the iron(ii) and manganese(ii), respectively. DFT calculations demonstrate that the spin state of the iron(ii) atom in {[FeH3L1][FeL1]}2+changes from high spin to low spin as the iron(ii)-iron(iii) distance decreases. This is supported by experimental results and is a result of hydrogen bonding interactions which cause a significant compression of the M(ii)-Npyrazolebond distances. [ABSTRACT FROM AUTHOR]

Published
2010

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