# Black hole ringdown echoes and howls

## TL;DR

This paper proposes advanced gravitational wave templates for black hole ringdown echoes, potentially improving detection sensitivity by about 10% by modeling reflections near the horizon.

## Contribution

It introduces more sophisticated templates based on solving the linear perturbation equations with reflecting boundary conditions around Kerr black holes.

## Key findings

- Templates can improve signal-to-noise ratio by 10%.
- Reflecting boundary conditions model black hole echoes more accurately.
- Enhanced templates aid in detecting gravitational wave echoes.

## Abstract

Recently the possibility of detecting echoes of ringdown gravitational waves from binary black hole mergers was shown. The presence of echoes is expected if the black hole is surrounded by a mirror that reflects gravitational waves near the horizon. Here, we present slightly more sophisticated templates motivated by a waveform which is obtained by solving the linear perturbation equation around a Kerr black hole with a complete reflecting boundary condition in the stationary traveling wave approximation. We estimate that the proposed template can bring about $10\%$ improvement in the signal-to-noise ratio.