Characterization of low-significance gravitational-wave compact binary sources

TL;DR

This paper investigates the parameter estimation accuracy for weak gravitational-wave signals from compact binary coalescences, highlighting challenges in measuring extrinsic parameters at low SNRs and the potential for precise intrinsic parameter measurements.

Contribution

It provides a detailed simulation-based analysis of how well advanced LIGO and Virgo can measure parameters of marginal gravitational-wave sources in their third observing run.

Findings

Sky localization uncertainties exceed 400 deg^2 for SNRs below 12.

Luminosity distance uncertainties are larger than 40% for BNSs at low SNRs.

Intrinsic parameters like chirp mass can be measured with sub-1% uncertainty at SNR 6.

Abstract

Advanced LIGO and Virgo have so far detected gravitational waves from 10 binary black hole mergers (BBH) and 1 binary neutron star merger (BNS). In the future, we expect the detection of many more marginal sources, since compact binary coalescences detectable by advanced ground-based instruments are roughly distributed uniformly in comoving volume. In this paper we simulate weak signals from compact binary coalescences of various morphologies and optimal network signal-to-noise ratios (henceforth SNRs), and analyze if and to which extent their parameters can be measured by advanced LIGO and Virgo in their third observing run. We show that subthreshold binary neutron stars, with SNRs below 12 (10) yield uncertainties in their sky position larger than 400 (700) $\mathrm{deg}^2$ (90% credible interval). The luminosity distance, which could be used to measure the Hubble constant with standard sirens, has relative uncertainties larger than 40% for BNSs and neutron star black hole mergers. For sources with SNRs below 8, it is not uncommon that the extrinsic parameters, sky position and distance, cannot be measured. Next, we look at the intrinsic parameters, masses and spins. We show that the detector-frame chirp mass can sometimes be measured with uncertainties below 1% even for sources at SNRs of 6, although multimodality is not uncommon and can significantly broaden the posteriors. The effective inspiral spin is best measured for neutron star black hole mergers, for which the uncertainties can be as low as $\sim0.08$ ($\sim 0.2$) at SNR 12 (8). The uncertainty is higher for systems with comparable component masses or lack of spin precession.