Analytical template for gravitational-wave echoes: signal characterization and prospects of detection with current and future interferometers

TL;DR

This paper develops an analytical template for gravitational-wave echoes from ultracompact objects, enabling parameter estimation and prospects for detecting near-horizon quantum structures with current and future interferometers.

Contribution

It introduces a new analytical template for gravitational-wave echoes characterized by reflectivity and redshift, and assesses detection prospects with current and future detectors.

Findings

Constraints on model parameters depend strongly on reflectivity.

Possible to detect or rule out Planckian corrections at horizon scale with Advanced LIGO/Virgo.

Future interferometers can probe near-horizon quantum structures with high confidence.

Abstract

Gravitational-wave echoes in the post-merger ringdown phase are under intense scrutiny as probes of near-horizon quantum structures and as signatures of exotic states of matter in ultracompact stars. We present an analytical template that describes the ringdown and the echo signal for nonspinning objects in terms of two physical parameters: the reflectivity and the redshift at the surface of the object. We characterize the properties of the template and adopt it in a preliminary parameter estimation with current (aLIGO) and future (Cosmic Explorer, Einstein Telescope, LISA) gravitational-wave detectors. For fixed signal-to-noise ratio in the post-merger phase, the constraints on the model parameters depend only mildly on the details of the detector sensitivity curve, but depend strongly on the reflectivity. Our analysis suggests that it might be possible to detect or rule out Planckian corrections at the horizon scale for perfectly-reflecting ultracompact objects at $5\sigma$ confidence level with Advanced LIGO/Virgo. On the other hand, signal-to-noise ratios in the ringdown phase equal to $\approx 100$ (as achievable with future interferometers) might allow us to probe near-horizon quantum structures with reflectivity $\gtrsim30\%$ ($\gtrsim85\%$) at $2\sigma$ ($3\sigma$) level.