Paper detail

Eccentric or circular? A reanalysis of binary black hole gravitational wave events for orbital eccentricity signatures

We present a reanalysis of 17 gravitational-wave events detected with Advanced LIGO and Advanced Virgo in their first three observing runs, using the new IMRPhenomTEHM model -- a phenomenological time-domain multipolar waveform model for aligned-spin black-hole binaries in elliptical orbits with two eccentric parameters: eccentricity and mean anomaly. We also analyze all events with the underlying quasi-circular model IMRPhenomTHM to study the impact of including eccentricity and compare the eccentric and quasi-circular binary hypotheses. The high computational efficiency of IMRPhenomTEHM enables us to explore the impact of two different eccentricity priors -- uniform and log-uniform -- as well as different sampler and data settings. We find evidence for eccentricity in two publicly available LVK events, GW200129 and GW200208_22, with Bayes factors favoring the eccentric hypothesis over the quasi-circular aligned-spin scenario: $\log_{10}\mathcal{B}_{\mathrm{E/QC}}\in\left[1.30^{+0.15}_{-0.15}, 5.14^{+0.15}_{-0.15}\right]$ and $\log_{10}\mathcal{B}_{\mathrm{E/QC}}\in\left[0.49^{+0.08}_{-0.08}, 1.14^{+0.08}_{-0.08}\right]$, respectively. Additionally, the two high-mass events GW190701 and GW190929 exhibit potential eccentric features. For all four events, we conduct further analyses to study the impact of different sampler settings. We also investigate waveform systematics by exploring the support for spin precession using IMRPhenomTPHM and NRSur7dq4, offering new insights into the formation channels of detected binaries. Our results highlight the importance of considering eccentric waveform models in future observing runs, alongside precessing models, as they can help mitigate potential biases in parameter estimation studies. This will be particularly relevant with the expected increase in the diversity of the binary black hole population with new detectors.