Detection of GW200105 with a targeted eccentric search

Abstract

The neutron star -- black hole (NSBH) binary GW200105 was recently found to have significant residual orbital eccentricity at a gravitational-wave frequency of 20 Hz~\cite{Morras:2025xfu}. The event was originally identified with moderate significance by matched-filter searches that employ non-eccentric templates. The neglect of relevant physical effects, such as orbital eccentricity, can severely reduce the sensitivity of the search and, consequently, also the significance of an event candidate. Here, we present a targeted eccentric search for GW200105. The eccentric search identifies GW200105 as the most significant event with a signal-to-noise ratio of $13.4$ and a false alarm rate of less than 1 in 1000 years. The best-matching template parameters are consistent with the Bayesian inference result, supporting the interpretation of GW200105 as an NSBH that formed through dynamical mechanisms including hierarchical triples and not via isolated binary evolution.