Strong gravitational lensing of gravitational waves from double compact binaries - perspectives for the Einstein Telescope

TL;DR

The paper assesses the potential of the Einstein Telescope to detect strongly gravitationally lensed gravitational waves from double compact binaries, predicting 50-100 such events annually, mainly from black hole mergers, over several years.

Contribution

It extends previous analyses by using detailed population synthesis models to predict lensed GW event rates for the Einstein Telescope.

Findings

ET could detect 50-100 lensed inspiral events per year.

Black hole mergers dominate the lensed event population.

Detection rates depend on the natal kick scenarios of black holes.

Abstract

Gravitational wave (GW) experiments are entering their advanced stage which should soon open a new observational window on the Universe. Looking into this future, the Einstein Telescope (ET) was designed to have a fantastic sensitivity improving significantly over the advanced GW detectors. One of the most important astrophysical GW sources supposed to be detected by the ET in large numbers are double compact objects (DCO) and some of such events should be gravitationally lensed by intervening galaxies. We explore the prospects of observing gravitationally lensed inspiral DCO events in the ET. This analysis is a significant extension of our previous paper. We are using the intrinsic merger rates of the whole class of DCO (NS-NS,BH-NS,BH-BH)located at different redshifts as calculated by Dominik et al. by using {\tt StarTrack} population synthesis evolutionary code. We discuss in details predictions from each evolutionary scenario. Our general conclusion is that ET would register about $50-100$ strongly lensed inspiral events per year. Only the scenario in which nascent BHs receive strong kick gives the predictions of a few events per year. Such lensed events would be dominated by the BH-BH merging binary systems. Our results suggest that during a few years of successful operation ET will provide a considerable catalog of strongly lensed events.