# Constraints on the amplitude of gravitational wave echoes from black hole ring-down using minimal assumptions

## TL;DR

This study searches for gravitational wave echoes following black hole mergers to test exotic compact object models, finding no evidence but setting upper limits on echo amplitudes using minimal assumptions.

## Contribution

It introduces a new search method with enhanced detection capabilities for gravitational wave echoes post-merger, applicable to generic echo models.

## Key findings

- No evidence of gravitational wave echoes was found.
- The loudest candidates are consistent with instrumental noise.
- Upper limits on echo amplitudes were established for individual mergers.

## Abstract

Gravitational wave echoes may appear following a compact binary coalescence if the remnant is an "exotic compact object" (ECO). ECOs are proposed alternatives to the black holes of Einstein's general relativity theory and are predicted to possess reflective boundaries. This work reports a search for gravitational wave transients (GWTs) of generic morphology occurring shortly after (<1s) binary black hole (BBH) mergers, therefore targeting all gravitational wave echo models. We investigated the times after the ringdown for the higher signal-to-noise ratio BBHs within the public catalog GWTC-3 by the LIGO-Virgo-KAGRA collaborations (LVK). Our search is based on the coherentWaveBurst pipeline, widely used in generic searches for GWTs by the LVK, and deploys new methods to enhance its detection performances at low signal-to-noise ratios. We employ Monte Carlo simulations for estimating the detection efficiency of the search and determining the statistical significance of candidates. We find no evidence of previously undetected GWTs and our loudest candidates are morphologically consistent with known instrumental noise disturbances. Finally, we set upper limits on the amplitude of GW echoes for single BBH mergers.