Lensing, Not Luck! Detection Prospects of Strongly Lensed Gravitational Waves

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.