First Eccentric Inspiral–Merger–Ringdown Analysis of Neutron Star–Black Hole Mergers

Abstract The gravitational wave event GW200105 was the first confident neutron star–black hole (NSBH) merger identified by the LIGO–Virgo–KAGRA collaboration. A recent analysis with an eccentric precessing waveform model that describes the inspiral phase of the l = 2 and m = {0, ±2} modes has identified this event as the first NSBH merger with strong evidence of orbital eccentricity. In this paper we perform the first analysis of this event with an aligned-spin eccentric waveform model that describes the full inspiral, merger, and ringdown, includes subdominant harmonics, and is partially calibrated to numerical relativity simulations. This analysis confirms the results and finds evidence in favor of eccentricity even with a log-uniform prior in eccentricity. We also analyze the NSBH events GW200115 and GW230529, completing the analysis of all NSBHs with IMRPhenomTEHM , and find that these signal are consistent with vanishing eccentricity. Finally, we briefly discuss computational challenges when performing the analysis with time-domain eccentric waveform models.