The NANOGrav 15-year Data Set: Evidence for a Gravitational-wave Background
Creators: name: Afzal, Adeela
name: Agazie, Gabriella
name: Anumarlapudi, Akash
name: Archibald, Anne M.
name: Arzoumanian, Zaven
name: Baker, Paul T.
name: Bécsy, Bence
name: Blanco-Pillado, Jose Juan
name: Blecha, Laura
name: Boddy, Kimberly K.
name: Brazier, Adam
name: Brook, Paul R.
name: Burke-Spolaor, Sarah
name: Burnette, Rand
name: Case, Robin
name: Charisi, Maria
name: Chatterjee, Shami
name: Chatziioannou, Katerina
name: Cheeseboro, Belinda D.
name: Chen, Siyuan
name: Cohen, Tyler
name: Cordes, James M.
name: Cornish, Neil J.
name: Crawford, Fronefield
name: Cromartie, H. Thankful
name: Crowter, Kathryn
name: Cutler, Curt J.
name: DeCesar, Megan E.
name: DeGan, Dallas
name: Demorest, Paul B.
name: Deng, Heling
name: Dolch, Timothy
name: Drachler, Brendan
name: von Eckardstein, Richard
name: Ferrara, Elizabeth C.
name: Fiore, William
name: Fonseca, Emmanuel
name: Freedman, Gabriel E.
name: Garver-Daniels, Nate
name: Gentile, Peter A.
name: Gersbach, Kyle A.
name: Glaser, Joseph
name: Good, Deborah C.
name: Guertin, Lydia
name: Gültekin, Kayhan
name: Hazboun, Jeffrey S.
name: Hourihane, Sophie
name: Islo, Kristina
name: Jennings, Ross J.
name: Johnson, Aaron D.
name: Jones, Megan L.
name: Kaiser, Andrew R.
name: Kaplan, David L.
name: Kelley, Luke Zoltan
name: Kerr, Matthew
name: Key, Joey S.
name: Laal, Nima
name: Lam, Michael T.
name: Lamb, William G.
name: Lazio, T. Joseph W.
name: Lee, Vincent S. H.
name: Lewandowska, Natalia
name: Lino dos Santos, Rafael R.
name: Littenberg, Tyson B.
name: Liu, Tingting
name: Lorimer, Duncan R.
name: Luo, Jing
name: Lynch, Ryan S.
name: Ma, Chung-Pei
name: Madison, Dustin R.
name: McEwen, Alexander
name: McKee, James W.
name: McLaughlin, Maura A.
name: McMann, Natasha
name: Meyers, Bradley W.
name: Meyers, Patrick M.
name: Mingarelli, Chiara M. F.
name: Mitridate, Andrea
name: Nay, Jonathan
name: Natarajan, Priyamvada
name: Ng, Cherry
name: Nice, David J.
name: Ocker, Stella Koch
name: Olum, Ken D.
name: Pennucci, Timothy T.
name: Perera, Benetge B. P.
name: Petrov, Polina
name: Pol, Nihan S.
name: Radovan, Henri A.
name: Ransom, Scott M.
name: Ray, Paul S.
name: Romano, Joseph D.
name: Sardesai, Shashwat C.
name: Schmiedekamp, Ann
name: Schmiedekamp, Carl
name: Schmitz, Kai
name: Schröder, Tobias
name: Schult, Levi
name: Shapiro-Albert, Brent J.
name: Siemens, Xavier
name: Simon, Joseph
name: Siwek, Magdalena S.
name: Stairs, Ingrid H.
name: Stinebring, Daniel R.
name: Stovall, Kevin
name: Stratmann, Peter
name: Sun, Jerry P.
name: Susobhanan, Abhimanyu
name: Swiggum, Joseph K.
name: Taylor, Jacob
name: Taylor, Stephen R.
name: Trickle, Tanner
name: Turner, Jacob E.
name: Unal, Caner
name: Vallisneri, Michele
name: Verma, Sonali
name: Vigeland, Sarah J.
name: Wahl, Haley M.
name: Wang, Qiaohong
name: Witt, Caitlin A.
name: Wright, David
name: Young, Olivia
name: Zurek, Kathryn M.
name: NANOGrav Collaboration
Publisher: name: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Year: 2023
Subjects: subject: 520

description: 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$^{−3}$ (≈3σ) 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$^{−4}$ (≈3.5σ–4σ). Assuming a fiducial f$^{−2/3}$ characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is (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.