Modeling the frequency-domain ringdown amplitude of comparable-mass mergers with greybody factors

TL;DR

This paper introduces a simple four-parameter model based on greybody factors that accurately reproduces the frequency-domain amplitude of black hole merger ringdowns, significantly improving previous models.

Contribution

The authors develop and validate a new model for black hole ringdown amplitudes using greybody factors, enhancing accuracy and enabling new tests of black hole physics.

Findings

Achieved mismatches of order 10^{-5} with numerical relativity waveforms.

Improved existing models by roughly two orders of magnitude.

Provided analytical fits for model parameters based on progenitor properties.

Abstract

It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the post-merger ringdown signal. In this work, we demonstrate that a simple four-parameter model based on the greybody factor accurately reproduces the frequency-domain amplitude of a large set of comparable-mass, aligned-spin numerical relativity waveforms from the SXS catalog, achieving mismatches of order ${\cal O}(10^{-5})$ and improving existing models by roughly two orders of magnitude. We also identify the optimal initial frequency for applying the model in the frequency domain and provide analytical fits of the model parameters in terms of the progenitor masses and aligned spins. Our results pave the way for new consistency tests of the ringdown phase, complementary to traditional black hole spectroscopy.