You Can't Always Get What You Want: The Impact of Prior Assumptions on Interpreting GW190412
Abstract
GW190412 is the first observation of a black hole binary with definitively unequal masses. GW190412's mass asymmetry, along with the measured positive effective inspiral spin, allowed for inference of a component black hole spin: the primary black hole in the system was found to have a dimensionless spin magnitude between $0.17$ and $0.59$ (90% credible range). We investigate how the choice of priors for the spin magnitudes and tilts of the component black holes affect the robustness of parameter estimates for GW190412, and report Bayes factors across a suite of prior assumptions. Depending on the waveform family used to describe the signal, we find either marginal to moderate ( $2$ :1 $6$ :1) or strong (≳ $20$ :1) support for the primary black hole being spinning compared to cases where only the secondary is allowed to have spin. We show how these choices influence parameter estimates, and find the asymmetric masses and positive effective inspiral spin of GW190412 to be qualitatively, but not quantitatively, robust to prior assumptions. Our results highlight the importance of both considering astrophysically motivated or populationbased priors in interpreting observations and considering their relative support from the data.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 2020
 DOI:
 10.3847/20418213/aba8ef
 arXiv:
 arXiv:2006.11293
 Bibcode:
 2020ApJ...899L..17Z
 Keywords:

 Gravitational waves;
 LIGO;
 Gravitational wave sources;
 Binary stars;
 Bayesian statistics;
 Black holes;
 Stellar evolution;
 678;
 920;
 677;
 154;
 1900;
 162;
 1599;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Solar and Stellar Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 12 pages, 2 figures, 1 table, published in ApJL