Strongly lensed gravitational waves from intrinsically faint double compact binaries - prediction for the Einstein Telescope

TL;DR

The paper predicts that the Einstein Telescope will detect a significant number of gravitationally lensed faint double compact binary mergers, extending the observable universe but with minimal impact on cosmological measurements.

Contribution

It provides a detailed prediction of the number of lensed gravitational wave events detectable by ET, highlighting the extended reach and minimal bias in cosmological studies.

Findings

ET can observe hundreds of thousands of inspirals annually.

Strong lensing can magnify faint sources, increasing detection at high redshifts.

Magnification bias is negligible for cosmological inferences.

Abstract

With a fantastic sensitivity improving significantly over the advanced GW detectors, Einstein Telescope (ET) will be able to observe hundreds of thousand inspiralling double compact objects per year. By virtue of gravitational lensing effect, intrinsically unobservable faint sources can be observed by ET due to the magnification by intervening galaxies. We explore the possibility of observing such faint sources amplified by strong gravitational lensing. Following our previous work, we use the merger rates of DCO (NS-NS,BH-NS,BH-BH systems) as calculated by Dominik et al.(2013). It turns out that tens to hundreds of such (lensed) extra events will be registered by ET. This will strongly broaden the ET's distance reach for signals from such coalescences to the redshift range z=2 - 8. However, with respect to the full inspiral event catalog this magnification bias is at the level of 0.001 and should not affect much cosmological inferences.