You can’t always get what you want: the impact of prior assumptions on interpreting GW190412

Zevin, M., Berry, C. P.L. , Coughlin, S., Chatziioannou, K. and Vitale, S. (2020) You can’t always get what you want: the impact of prior assumptions on interpreting GW190412. Astrophysical Journal Letters, 899(1), L17. (doi: 10.3847/2041-8213/aba8ef)

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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 (gsim$20$: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 population-based priors in interpreting observations and considering their relative support from the data.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Berry, Dr Christopher
Authors: Zevin, M., Berry, C. P.L., Coughlin, S., Chatziioannou, K., and Vitale, S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal Letters
Publisher:IOP Publishing
ISSN (Online):2041-8213
Published Online:11 August 2020
Copyright Holders:Copyright © 2020 The American Astronomical Society
First Published:First published in Astrophysical Journal Letters 899(1): L17
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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