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The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

2024; IOP Publishing; Volume: 964; Issue: 1 Linguagem: Inglês

10.3847/2041-8213/ad2a51

2041-8213

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

Black Holes and Theoretical Physics

Abstract Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr 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 yr data set for evidence of a gravitational-wave background with quadrupolar 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 ∼2 when comparing HD to ST correlations, and ∼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.