Astrophysics Milestones For Pulsar Timing Array Gravitational Wave Detection
Creators: name: Pol, Nihan S.
name: Taylor, Stephen R.
name: Kelley, Luke Zoltan
name: Vigeland, Sarah J.
name: Simon, Joseph
name: Chen, Siyuan
name: Arzoumanian, Zaven
name: Baker, Paul T.
name: Bécsy, Bence
name: Brazier, Adam
name: Brook, Paul R.
name: Burke-Spolaor, Sarah
name: Chatterjee, Shami
name: Cordes, James M.
name: Cornish, Neil J.
name: Crawford, Fronefield
name: Cromartie, H. Thankful
name: DeCesar, Megan E.
name: Demorest, Paul B.
name: Dolch, Timothy
name: Ferrara, Elizabeth C.
name: Fiore, William
name: Fonseca, Emmanuel
name: Garver-Daniels, Nathan
name: Good, Deborah C.
name: Hazboun, Jeffrey S.
name: Jennings, Ross J.
name: Jones, Megan L.
name: Kaiser, Andrew R.
name: Kaplan, David L.
name: Key, Joey Shapiro
name: Lam, Michael T.
name: Lazio, T. Joseph W.
name: Luo, Jing
name: Lynch, Ryan S.
name: Madison, Dustin R.
name: McEwen, Alexander
name: McLaughlin, Maura A.
name: Mingarelli, Chiara M. F.
name: Ng, Cherry
name: Nice, David J.
name: Pennucci, Timothy T.
name: Ransom, Scott M.
name: Ray, Paul S.
name: Shapiro-Albert, Brent J.
name: Siemens, Xavier
name: Stairs, Ingrid H.
name: Stinebring, Daniel R.
name: Swiggum, Joseph K.
name: Vallisneri, Michele
name: Wahl, Haley
name: Witt, Caitlin A.
Publisher: name: arXiv
Year: 2020
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its 12.5-yr pulsar timing array 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 \&amp; Downs interpulsar correlations, which are characteristic of gravitational wave 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, 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 interpulsar-correlated GWB signal with 15--17 yrs of data, i.e., an additional 2--5 yrs from the 12.5 yr dataset; (II) At the initial detection, we expect a fractional uncertainty of $40\%$ on the power-law 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, power-law models are distinguishable from those having low-frequency spectral turnovers once 20~yrs 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 datasets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.
description: 15 pages, 7 figures