Disentangling Spin-induced Precession vs. Eccentricity in GW190521 and GW231123

Abstract

We use the more than 2000 full numerical-relativity simulations included in the fifth release of the RIT binary-black-hole waveform catalog to perform Bayesian parameter estimation, via the rapid iterative fitting algorithm (RIFT), for the gravitational-wave events GW190521 and GW231123. We revisit GW190521, which has previously been identified as potentially possessing large eccentricity upon entering the detector band at $20~\mathrm{Hz}$, and confirm this finding: the highest likelihood is obtained from waveforms that are simultaneously eccentric and spin-precessing, yielding $e_{20} =0.207_{-0.147}^{+0.192}$ and $χ_{1,\perp}=0.717_{-0.406}^{+0.194}$. Applying the same simulation pool to GW231123, we likewise find a preference for spin precession where at 20 Hz $χ_{1,\perp}=0.678_{-0.462}^{+0.218}$, but in this case with negligible eccentricity at both $10~\mathrm{Hz}$ and $20~\mathrm{Hz}$, with $e_{10}=0.097_{-0.073}^{+0.124}$ and $e_{20}=0.056_{-0.045}^{+0.059}$. For comparison, both events are also analyzed using exclusively non-precessing (eccentric and quasi-circular) simulations, which yield lower likelihoods in each case. These results indicate that our approach is capable of discriminating between the effects of eccentricity and spin precession in current gravitational-wave signals. The singled out top peak likelihood NR simulations give estimates of the recoil velocities of the merged final holes of 3965km/s for GW190521, and of 2059km/s for GW231123.