학술논문
The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
Document Type
Working Paper
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.; Young, Olivia
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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
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