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

By G. Agazie, A. Anumarlapudi, A. Archibald, Z. Arzoumanian, P. Baker, B. Bécsy, L. Blecha, A. Brazier, P. Brook, S. Burke-Spolaor and 104 more. Astrophysical Journal Letters, 2023

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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 (≈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 2.4−0.6+0.7×10−15 (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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/681a4dbd5cfc1548d52f81477e2765f714a688b4

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Citations in the corpus

The NANOGrav 15 yr Data Set: Observations and Timing of 68 Millisecond Pulsars (2023, methodology): “NG15detchar (Agazie et al. 2023a): the NANOGrav 15 yr detector characterization; 7.”
The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational-wave Background (2023, background): “The NANOGrav 15 yr data set shows that the common uncorrelated red-noise (CURN) signal discovered in Arzoumanian et al. (2020) persists with greater significance and is now detected in a larger number of pulsars (Agazie et al. 2023a, hereafter NG15gwb).”