Astrophysics Milestones For Pulsar Timing Array Gravitational Wave Detection
Abstract
The NANOGrav Collaboration found strong Bayesian evidence for a commonspectrum stochastic process in its 12.5yr pulsar timing array (PTA) dataset, with median characteristic strain amplitude at periods of a year of $A_{\rm yr} = 1.92^{+0.75}_{0.55} \times 10^{15}$. However, evidence for the quadrupolar Hellings & Downs interpulsar correlations, which are characteristic of gravitational wave (GW) signals, was not yet significant. We emulate and extend the NANOGrav dataset, injecting a wide range of stochastic gravitational wave background (GWB) signals that encompass a variety of amplitudes and spectral shapes. We then apply our standard detection pipeline and explore three key astrophysical milestones: (I) robust detection of the GWB; (II) determination of the source of the GWB; and (III) measurement of the properties of the GWB spectrum. 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 yrs of data. 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 blackhole binary origin from some models predicting primordial or cosmicstring origins. Similarly, the measured GWB amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive blackhole binaries. In general, however, powerlaw models are distinguishable from those having lowfrequency spectral turnovers once 20yrs 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 PTA datasets. Most notably, by combining individual PTA's data into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.
 Publication:

arXiv eprints
 Pub Date:
 October 2020
 arXiv:
 arXiv:2010.11950
 Bibcode:
 2020arXiv201011950P
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Astrophysics of Galaxies;
 General Relativity and Quantum Cosmology
 EPrint:
 14 pages, 7 figures. Abridged abstract presented due to arxiv char limit. Please refer to manuscript for full abstract. Submitted to Nature Astronomy