Towards inference of overlapping gravitational wave signals

Abstract

Merger rates of binary black holes, binary neutron stars, and neutron star-black hole binaries in the local Universe (i.e., redshift $z=0$), inferred from the Laser Interferometer Gravitational Wave Observatory (LIGO) and Virgo, are $16-130{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, $13-1900{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, and $7.4-320{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$, respectively. These rates suggest that there is a significant chance that two or more of these signals will overlap with each other during their lifetime in the sensitivity-band of future gravitational-wave detectors such as the Cosmic Explorer and Einstein Telescope. The detection pipelines provide the coalescence time of each signal with an accuracy $\mathcal{O}(10\mathrm{ms})$. We show that using a prior on the coalescence time from a detection pipeline, it is possible to correctly infer the properties of these overlapping signals with the current data-analysis infrastructure. We study different configurations of two overlapping signals created by non-spinning binaries, varying their time and phase at coalescence, as well as their signal-to-noise ratios. We conclude that, for the scenarios considered in this work, parameter inference is robust provided that their coalescence times in the detector frame are more than $\sim 1-2\mathrm{s}$. Signals whose coalescence epochs lie within $\sim 0.5\mathrm{s}$ of each other suffer from significant biases in parameter inference, and new strategies and algorithms would be required to overcome such biases.

13 pages, 5 figures, 1 table; accepted for publication in PRD