Ringdown amplitudes of nonspinning eccentric binaries

TL;DR

This paper provides closed-form expressions for the ringdown amplitudes of nonspinning eccentric binary black hole mergers, based on extensive numerical simulations, enhancing gravitational wave modeling beyond circular orbits.

Contribution

It introduces new analytical formulas for ringdown amplitudes of eccentric binaries, derived from a large simulation dataset, applicable to existing quasi-circular models.

Findings

Ringdown amplitudes increase by over 50% at high impact parameters.

Amplitude suppression occurs in highly eccentric (low impact parameter) cases.

Fitting accuracy is within a few percent, comparable to current models.

Abstract

Closed-form expressions for the ringdown complex amplitudes of nonspinning unequal-mass binaries in arbitrarily eccentric orbits are presented. They are built upon 237 numerical simulations contained within the RIT catalog, through the parameterisation introduced in [Phys. Rev. Lett. 132, 101401]. Global fits for the complex amplitudes, associated to linear quasinormal mode frequencies of the dominant ringdown modes, are obtained in a factorised form immediately applicable to any existing quasi-circular model. Similarly to merger amplitudes, ringdown ones increase by more than 50% compared to the circular case for high impact parameters (medium eccentricities), while strongly suppressed in the low impact parameter (highly eccentric) limit. Such reduction can be explained by a transition between an "orbital-type" and an "infall-type" dynamics. The amplitudes (phases) fits accuracy lies around a few percent (deciradians) for the majority of the dataset, comparable to the accuracy of current state-of-the-art quasi-circular ringdown models, and well within current statistical errors of current LIGO-Virgo-Kagra ringdown observations. These expressions constitute another building block towards the construction of complete general-relativistic inspiral-merger-ringdown semi-analytical templates, and allow to extend numerically-informed spectroscopic analyses beyond the circular limit. Such generalisations are key to achieve accurate inference of compact binaries astrophysical properties, and tame astrophysical systematics within observational investigations of strong-field general relativistic dynamics.