Eccentricity signatures in LIGO-Virgo-KAGRA's BNS and NSBH binaries

TL;DR

This study analyzes gravitational wave data from six low-mass binary systems to measure their eccentricities, using new waveform models and advanced inference techniques, revealing moderate eccentricity in one event and setting upper limits on others.

Contribution

Introduces the first application of the SEOBNRv5EHM eccentric waveform model to real GW data, improving eccentricity measurement accuracy and computational efficiency.

Findings

GW200105 shows moderate eccentricity with Bayes factor supporting eccentricity.

Five other sources are consistent with low eccentricity, with upper limits set.

First eccentricity constraints for GW190814 are provided.

Abstract

Measurement of eccentricity in low-mass binary systems through gravitational waves is crucial to distinguish between various formation channels. Detecting eccentricity in these systems is challenging due to a lack of accurate eccentric waveform models and the high computational cost of Bayesian inferences. We access the eccentricities of six previously observed low-mass gravitational wave events using publicly available data from the first four observing runs of the LIGO and Virgo collaboration. We analyze the events using the new eccentric waveform model, SEOBNRv5EHM, and compare our results with the existing model, TEOBResumS-Dali. We also present the first eccentricity constraints for GW190814. To improve accuracy, we include higher-order modes in both models and optimize inference using efficient marginalization and parallelization techniques. We find that GW200105 exhibits non-negligible eccentricity, with a measured eccentricity of $e=0.135^{+0.019}_{-0.088}$ at 20 Hz (90% credible level) for TEOBResumS-Dali and $e=0.125^{+0.029}_{-0.082}$ for SEOBNRv5EHM, given a uniform eccentricity prior from 0 to 0.2. This provides moderate support for the eccentric hypothesis, with a Bayes factor of $\sim6-7$ in favor of the eccentric model. With a uniform log prior on eccentricity, the Bayes factor is reduced to 2.35. The remaining five sources are consistent with low eccentricity, with 90% upper limits from $e \leq 0.011$ to $e \leq 0.066$. We find no support for non-negligible eccentricity in GW190814. Finally, we discuss the challenges of performing Bayesian inference in eccentric, multi-modal parameter spaces, including issues related to sampling efficiency and waveform systematics.