Toward inference of overlapping gravitational-wave signals

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 and Virgo, are 16-130 Gpc-3 yr-1, 13-1900 Gpc-3 yr-1, and 7.4-320 Gpc-3 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 O(10 ms). We show that by 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 nonspinning 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 ∼1-2 s. Signals whose coalescence epochs lie within ∼0.5 s of each other suffer from significant biases in parameter inference, and new strategies and algorithms would be required to overcome such biases.