Astrophysics Milestones for Pulsar Timing Array Gravitationalwave Detection
Abstract
The NANOGrav Collaboration reported strong Bayesian evidence for a commonspectrum stochastic process in its 12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of ${A}_{\mathrm{yr}}={1.92}_{0.55}^{+0.75}\times {10}^{15}$ . However, evidence for the quadrupolar Hellings & Downs interpulsar correlations, which are characteristic of gravitationalwave signals, was not yet significant. We emulate and extend the NANOGrav data set, injecting a wide range of stochastic gravitationalwave background (GWB) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones. (I) Given the amplitude measured in the 12.5 yr analysis and assuming this signal is a GWB, we expect to accumulate robust evidence of an interpulsarcorrelated GWB signal with 1517 yr of data, i.e., an additional 25 yr from the 12.5 yr data set. (II) At the initial detection, we expect a fractional uncertainty of 40% on the powerlaw strain spectrum slope, which is sufficient to distinguish a GWB of supermassive black hole binary origin from some models predicting more exotic origins. (III) Similarly, the measured GWB amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive black hole binaries. In addition, powerlaw models are distinguishable from those having lowfrequency spectral turnovers once 20 yr of data are reached. Even though our study is based on the NANOGrav data, we also derive relations that allow for a generalization to other pulsar timing array data sets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 2021
 DOI:
 10.3847/20418213/abf2c9
 arXiv:
 arXiv:2010.11950
 Bibcode:
 2021ApJ...911L..34P
 Keywords:

 Gravitational waves;
 Gravitational wave astronomy;
 Millisecond pulsars;
 Pulsar timing method;
 Astronomical simulations;
 678;
 675;
 1062;
 1305;
 1857;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Astrophysics of Galaxies;
 General Relativity and Quantum Cosmology
 EPrint:
 15 pages, 7 figures