The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

Gabriella Agazie(University of Wisconsin–Milwaukee), Akash Anumarlapudi(University of Wisconsin–Milwaukee), Anne M. Archibald(Newcastle University), Zaven Arzoumanian(Goddard Space Flight Center), P. T. Baker(Widener University), B. Bécsy(Oregon State University), Laura Blecha(University of Florida), Adam Brazier(Cornell University), Paul R. Brook(University of Birmingham), Sarah Burke-Spolaor(West Virginia University), Rand Burnette(Oregon State University), Robin Case(Oregon State University), Maria Charisi(Vanderbilt University), Shami Chatterjee(Cornell University), Katerina Chatziioannou(California Institute of Technology), B. D. Cheeseboro(West Virginia University), Siyuan Chen(Peking University), Tyler Cohen(New Mexico Institute of Mining and Technology), J. M. Cordes(Cornell University), Neil J. Cornish(Montana State University), F. Crawford(Franklin & Marshall College), H. Thankful Cromartie(Cornell University), Kathryn Crowter(University of British Columbia), Curt Cutler(California Institute of Technology), Megan E. DeCesar(United States Naval Research Laboratory), Dallas DeGan(Oregon State University), Paul B. Demorest(National Radio Astronomy Observatory), Heling Deng(Oregon State University), Timothy Dolch(Hillsdale College), Brendan Drachler(Rochester Institute of Technology), Justin A. Ellis, E. C. Ferrara(Goddard Space Flight Center), William Fiore(West Virginia University), Emmanuel Fonseca(West Virginia University), Gabriel E. Freedman(University of Wisconsin–Milwaukee), Nate Garver-Daniels(West Virginia University), Peter A. Gentile(West Virginia University), Kyle A. Gersbach(Vanderbilt University), Joseph Glaser(West Virginia University), Deborah C. Good(University of Connecticut), Kayhan Gültekin(University of Michigan), Jeffrey S. Hazboun(Oregon State University), Sophie Hourihane(California Institute of Technology), Kristina Islo(University of Wisconsin–Milwaukee), Ross J. Jennings(West Virginia University), Aaron D. Johnson(California Institute of Technology), Megan L. Jones(University of Wisconsin–Milwaukee), Andrew R. Kaiser(West Virginia University), D. L. Kaplan(University of Wisconsin–Milwaukee), Luke Zoltan Kelley(University of California, Berkeley), M. Kerr(United States Naval Research Laboratory), J. S. Key(University of Washington Bothell), Tonia C. Klein(University of Wisconsin–Milwaukee), Nima Laal(Oregon State University), Michael T. Lam(Rochester Institute of Technology), William G. Lamb(Vanderbilt University), T. Joseph W. Lazio(Jet Propulsion Laboratory), N. Lewandowska(State University of New York at Oswego), T. B. Littenberg(Marshall Space Flight Center), Tingting Liu(West Virginia University), A. N. Lommen(Haverford College), D. R. Lorimer(West Virginia University), Jing Luo(University of Toronto), Ryan S. Lynch, Chung‐Pei Ma(University of California, Berkeley), Dustin R. Madison(University of the Pacific), M. A. Mattson(West Virginia University), Alexander McEwen(University of Wisconsin–Milwaukee), James W. McKee(University of Hull), M. A. McLaughlin(West Virginia University), Natasha McMann(Vanderbilt University), Bradley W. Meyers(University of British Columbia), P. M. Meyers(California Institute of Technology), Chiara M. F. Mingarelli(University of Connecticut), Andrea Mitridate(Deutsches Elektronen-Synchrotron DESY), Priyamvada Natarajan(Woodwell Climate Research Center), Cherry Ng(University of Toronto), David J. Nice(Lafayette College), Stella Koch Ocker(Cornell University), Ken D. Olum(Tufts University), Timothy T. Pennucci(Eötvös Loránd University), Benetge B. P. Perera(University of Puerto Rico at Arecibo), Polina Petrov(Vanderbilt University), Nihan S. Pol(Vanderbilt University), H. A. Radovan(University of Puerto Rico-Mayaguez), S. M. Ransom(National Radio Astronomy Observatory), Paul S. Ray(United States Naval Research Laboratory), Joseph D. Romano(Texas Tech University), Shashwat C. Sardesai(University of Wisconsin–Milwaukee), Ann Schmiedekamp(Pennsylvania State University), Carl Schmiedekamp(Pennsylvania State University), Kai Schmitz(University of Münster), Levi Schult(Vanderbilt University), Brent J. Shapiro-Albert(West Virginia University), Xavier Siemens(Oregon State University), Joseph Simon(University of Colorado Boulder), Magdalena S. Siwek(Harvard University), I. H. Stairs(University of British Columbia), Daniel R. Stinebring(Oberlin College), Kevin Stovall(National Radio Astronomy Observatory), Jerry P. Sun(Oregon State University), Abhimanyu Susobhanan(University of Wisconsin–Milwaukee), Joseph K. Swiggum(Lafayette College), Jacob Taylor(Oregon State University), Stephen R. Taylor(Vanderbilt University), Jacob E. Turner(West Virginia University), Caner Ünal(Ben-Gurion University of the Negev), Michele Vallisneri(California Institute of Technology), Rutger van Haasteren(Max Planck Institute for Gravitational Physics), Sarah J. Vigeland(University of Wisconsin–Milwaukee), Haley M. Wahl(West Virginia University), Qiaohong Wang(Vanderbilt University), Caitlin A. Witt(Northwestern University), Olivia Young(Rochester Institute of Technology)
The Astrophysical Journal Letters
June 29, 2023
10.3847/2041-8213/acdac6
Cited by 1,432Open Access
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Abstract

Abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings–Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 10 14 , and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200–1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10 −3 (≈3 σ ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10 −5 to 1.9 × 10 −4 (≈3.5 σ –4 σ ). Assuming a fiducial f −2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>2.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.7</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15</mml:mn> </mml:mrow> </mml:msup> </mml:math> (median + 90% credible interval) at a reference frequency of 1 yr −1 . The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings–Downs correlations points to the gravitational-wave origin of this signal.

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