Lensing, not luck! Detection prospects of strongly lensed gravitational waves

TL;DR

Detecting strongly lensed gravitational waves is challenging due to false alarms, but improved measurement precision and advanced methods like Posterior Overlap 2.0 can enable confident identification in future observations.

Contribution

This paper demonstrates that enhanced parameter measurement accuracy and the Posterior Overlap 2.0 method can effectively distinguish true lensed GW signals from false alarms.

Findings

First confident detection possible in fifth LIGO/Virgo/KAGRA run

Measurement precision significantly reduces false alarms

Posterior Overlap 2.0 offers an efficient detection approach

Abstract

A small fraction of gravitational-wave (GW) signals detected by ground-based observatories will be strongly lensed by intervening galaxies or clusters. This may produce multiple copies of the signals (i.e., lensed images) arriving at different times at the detector. These, if observed, could offer new probes of astrophysics and cosmology. However, identification of lensed image pairs among a large number of unrelated GW events is challenging. Though the number of lensed events increases with improved detector sensitivity, the false alarms increase quadratically faster. While this "lensing or luck" problem would appear to be insurmountable, we show that the expected increase in measurement precision of source parameters will efficiently weed out false alarms. Based on current astrophysical models and anticipated sensitivities, we predict that the first confident detection could occur in the fifth observing run of LIGO, Virgo, and KAGRA. We expect computational costs to be a major hurdle in achieving such a detection, and show that the Posterior Overlap 2.0 method may offer a near-optimal solution to this challenge.