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

It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the postmerger 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 O ( 10 − 5 ) and improving existing models by roughly 2 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.