GW190426_152155: a merger of neutron star-black hole or low mass binary black holes?

TL;DR

This paper reanalyzes GW190426_152155, a candidate gravitational wave event with uncertain origin, exploring whether it is a neutron star-black hole merger or low mass binary black holes, and estimates its merger rate.

Contribution

It systematically examines the event using different waveforms and priors, highlighting the ambiguity in its classification and providing a merger rate estimate.

Findings

Results depend on mass ratio priors.

Event could be either NSBH or low mass BBH.

Effective spin likely negative for BBH scenario.

Abstract

GW190426_152155 was recently reported as one of the 39 candidate gravitational wave (GW) events in \citet{2020arXiv201014527A}, which has an unusual source-frame chirp mass $\sim 2.4M_{\odot}$ and may be the first GW signal from a neutron star-black hole (NSBH) merger. Assuming an astrophysical origin, we reanalyze GW190426_152155 using several waveforms with different characteristics, and consider two different priors for the mass ratio of the binary (Uniform and LogUniform). We find that the results are influenced by the priors of mass ratio, and this candidate could also be from the merger of two low mass black holes (BH). In the case for a binary black hole (BBH) merger, the effective spin is likely negative and the effective precession spin is non-negligible. As for the NSBH merger, supposing the mass of the light object follow the distribution of current neutron stars (NSs) with a reasonably measured/constrained mass, the spin of the low mass BH is so small that is hard to generate bright electromagnetic emission. Finally, we estimate a merger rate of GW190426\_152155-like systems to be $59^{+137}_{-51}~{\rm Gpc}^{-3}~{\rm yr}^{-1}$.