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Lookup NU author(s): Dr Anne ArchibaldORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2024. The Author(s). Published by the American Astronomical Society.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.
Author(s): Agazie G, Anumarlapudi A, Archibald AM, Arzoumanian Z, Baier J, Baker PT, Becsy B, Blecha L, Brazier A, Brook PR, Burke-Spolaor S, Burnette R, Case R, Casey-Clyde JA, Charisi M, Chatterjee S, Cohen T, Cordes JM, Cornish NJ, Crawford F, Cromartie HT, Crowter K, DeCesar ME, DeGan D, Demorest PB, Dolch T, Drachler B, Ferrara EC, Fiore W, Fonseca E, Freedman GE, Garver-Daniels N, Gentile PA, Glaser J, Good DC, Gultekin K, Hazboun JS, Jennings RJ, Johnson AD, Jones ML, Kaiser AR, Kaplan DL, Kelley LZ, Kerr M, Key JS, Laal N, Lam MT, Lamb WG, Lazio TJW, Lewandowska N, Liu T, Lorimer DR, Luo J, Lynch RS, Ma C-P, Madison DR, McEwen A, McKee JW, McLaughlin MA, McMann N, Meyers BW, Mingarelli CMF, Mitridate A, Natarajan P, Ng C, Nice DJ, Ocker SK, Olum KD, Pennucci TT, Perera BBP, Pol NS, Radovan HA, Ransom SM, Ray PS, Romano JD, Saffer A, Sardesai SC, Schmiedekamp A, Schmiedekamp C, Schmitz K, Shapiro-Albert BJ, Siemens X, Simon J, Siwek MS, Stairs IH, Stinebring DR, Stovall K, Sun JP, Susobhanan A, Swiggum JK, Taylor JA, Taylor SR, Turner JE, Unal C, Vallisneri M, Vigeland SJ, Wahl HM, Witt CA, Young O
Publication type: Article
Publication status: Published
Journal: Astrophysical Journal Letters
Year: 2024
Volume: 964
Issue: 1
Print publication date: 20/03/2024
Online publication date: 18/03/2024
Acceptance date: 16/02/2024
Date deposited: 10/04/2024
ISSN (print): 2041-8205
ISSN (electronic): 2041-8213
Publisher: American Astronomical Society
URL: https://doi.org/10.3847/2041-8213/ad2a51
DOI: 10.3847/2041-8213/ad2a51
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