An Isotropy Measurement with Gravitational Wave Observations

Abstract

We constrain the distribution of merging compact binaries across the celestial sphere using the GWTC-3 catalog from the LIGO-Virgo-KAGRA Collaborations' (LVK) third observing run. With 63 confident detections from O3, we constrain the relative variability (standard deviation) of the rate density across the sky to be $\lesssim 16\%$ at 90\% confidence assuming the logarithm of the rate density is described by a Gaussian random field with correlation length $\ge 10^{\circ }$. This tightens to $\lesssim 3.5\%$ when the correlation length is $\ge 20^{\circ }$. While the new O3 data provides the tightest constraints on anisotropies available to-date, we do not find overwhelming evidence in favor of isotropy, either. A simple counting experiment favors an isotropic distribution by a factor of ${\mathcal{B}}_{\mathrm{ani}}^{\mathrm{iso}}=3.7$, which is nonetheless an improvement of more than a factor of two compared to analogous analyses based on only the first and second observing runs of the LVK.

main text: 12 pages, 6 figures, 2 tables