How to Detect an Astrophysical Nanohertz Gravitational Wave Background
Abstract
Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a powerlaw spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The dataset length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them.
 Publication:

The Astrophysical Journal
 Pub Date:
 December 2023
 DOI:
 10.3847/15384357/ad09e4
 arXiv:
 arXiv:2309.04443
 Bibcode:
 2023ApJ...959....9B
 Keywords:

 Gravitational waves;
 Gravitational wave sources;
 Gravitational wave astronomy;
 Supermassive black holes;
 Astronomy data analysis;
 Bayesian statistics;
 Millisecond pulsars;
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 General Relativity and Quantum Cosmology;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 14 pages, 8 figures, version matching published paper