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

Date

2023-07-01

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
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.
Gueltekin, 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.
Ünal, Caner
Vallisneri, Michele
van Haasteren, Rutger
Vigeland, Sarah J.
Wahl, Haley M.
Wang, Qiaohong
Witt, Caitlin A.
Young, Olivia

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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 1014, 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 (similar to 3s) 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 x 10-5 to 1.9 x 10-4 (similar to 3.5s-4s). Assuming a fiducial f -2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is 2.4 0.6 100.7 ' 15 -+ - (median + 90% credible interval) at a reference frequency of 1 yr-1. The inferred gravitationalwave 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.

URI

https://hdl.handle.net/11511/116553

Collections

Department of Physics, Article