High Precision Multimode Ringdown Fitting*

Binary black hole ringdown studies are crucial in understanding astrophysical black holes and provide a consistency check between perturbation theory and numerical relativity. Third generation gravitational-wave detectors will be much more sensitive to multiple ringdown frequencies, thereby requiring high precision ringdown models. In this talk, I will introduce a new multimode ringdown fitting model which incorporates spherical-spheroidal mixing, retrograde modes, and overtones. In addition, the numerical relativity waveforms used to fit for the mode amplitudes are mapped to the Bondi-van der Burg-Metzner-Sachs super rest frame, the canonical frame to use in ringdown analyses resulting from the Teukolsky formalism. Working in this correct frame allows us to get up to a 10⁵ order of magnitude improvement in the mismatches between numerical relativity simulations and our analytical ringdown model.