Frequency-Dependent Responses in 3rd Generation Gravitational-Wave Detectors

TL;DR

This paper investigates how frequency-dependent effects in third-generation gravitational-wave detectors influence their response, showing that neglecting these effects can cause significant biases in source localization, especially for neutron star mergers.

Contribution

It demonstrates the importance of accounting for frequency-dependent responses in third-generation detectors to avoid systematic biases in gravitational-wave source localization.

Findings

Neglecting frequency dependence causes large localization biases.

Effects are significant for neutron star mergers at z<1.7.

Third-generation detectors must incorporate these effects in analysis.

Abstract

Interferometric gravitational wave detectors are dynamic instruments. Changing gravitational-wave strains influence the trajectories of null geodesics and therefore modify the interferometric response. These effects will be important when the associated frequencies are comparable to the round-trip light travel time down the detector arms. The arms of advanced detectors currently in operation are short enough that the strain can be approximated as static, but planned 3$^\mathrm{rd}$ generation detectors, with arms an order of magnitude longer, will need to account for these effects. We investigate the impact of neglecting the frequency-dependent detector response for compact binary coalescences and show that it can introduce large systematic biases in localization, larger than the statistical uncertainty for 1.4-1.4$M_\odot$ neutron star coalescences at $z\lesssim1.7$. Analysis of $3^\mathrm{rd}$ generation detectors therefore must account for these effects.