Testing the Nature of GW200105 by Probing the Frequency Evolution of Eccentricity

Abstract GW200105 is a compact binary coalescence event, consisting of a neutron star and a black hole, observed in LIGO–Virgo–KAGRA’s third observing run. Recent reanalyses of the event using state-of-the-art waveform models have claimed observation of signatures of an eccentric orbit. It has nevertheless been pointed out in the literature that certain physical or modified gravity effects could mimic eccentricity by producing a spurious nonzero eccentricity value, at a given reference frequency, when recovered with an eccentric waveform model. We recently developed a waveform-model-independent eccentricity evolution consistency test (EECT) to identify such mimickers, by comparing the measured frequency evolution of eccentricity, e ( f ), with that expected from general relativity (GR). In this paper, we apply EECT to GW200105 and find that it satisfies EECT within 68% confidence. Our analysis therefore lends complementary support in favor of the eccentricity hypothesis, while also providing a novel test of the consistency of e ( f ) with GR.