A rapid method for preliminary identification of subthreshold strongly lensed counterparts to superthreshold gravitational-wave events

TL;DR

This paper introduces a rapid preliminary method to identify potential strongly lensed gravitational-wave counterparts to superthreshold events, enabling quicker follow-up analysis before detailed Bayesian parameter estimation.

Contribution

It presents a fast, approximate approach using Gaussian/Fisher likelihoods and sky localization comparison to flag promising candidate pairs for further investigation.

Findings

Identified candidate pairs involving sub-threshold and super-threshold GW events.

The method successfully prioritized pairs that were later analyzed with detailed Bayesian methods.

The most significant candidate was consistent with a potential lensing event, but not conclusively so.

Abstract

Gravitational waves (GWs) from stellar-mass compact binary coalescences (CBCs) are expected to be strongly lensed when encountering large agglomerations of matter, such as galaxies or clusters. Searches for strongly lensed GWs have been conducted using data from the first three observing runs of the LIGO-Virgo GW detector network. Although no confirmed detections have been reported, interesting candidate lensed pairs have been identified. In this work, we delineate a preliminary analysis that rapidly identifies pairs to be further analyzed by more sophisticated Bayesian parameter estimation (PE) methods. The analysis relies on the Gaussian/Fisher approximation to the likelihood and compares the corresponding approximate posteriors on the chirp masses of the candidate pair. It additionally cross-correlates the rapidly produced localization sky areas (constructed by Bayestar sky-localization software). The analysis was used to identify pairs involving counterparts from targeted sub-threshold searches to confidently detected super-threshold CBC events. The most significant candidate ``super-sub'' pair deemed by this analysis was subsequently found, by more sophisticated and detailed joint-PE analyses, to be among the more significant candidate pairs, but not sufficiently significant to suggest the observation of a lensed event [1].