Formation of GW230529 from Isolated Binary Evolution

TL;DR

This study models the formation of a mass-gap black hole-neutron star merger, GW230529, via isolated binary evolution, and predicts its electromagnetic signatures, supporting its detectability and multimessenger potential.

Contribution

It demonstrates that GW230529 can be explained by isolated binary evolution and predicts its electromagnetic counterparts, highlighting the significance of mgBHNS mergers in multimessenger astronomy.

Findings

GW230529 can be explained by isolated binary evolution.

Predicted kilonova magnitude is 23-24 mag, detectable by current surveys.

High likelihood (63.2%) of tidal disruption under certain conditions.

Abstract

In this {\em{Letter}}, we explore the formation of the mass-gap black hole-neutron star (mgBHNS) merger detected in gravitational wave (GW) event, i.e., GW230529, from the isolated binary evolution channel, and study potential signatures of its electromagnetic counterparts. By adopting the `delayed' supernova prescription and reasonable model realizations, our population synthesis simulation results can simultaneously match the rate densities of mgBHNS and total BHNS mergers inferred from the population analyses, along with the population distribution of the BH mass in BHNS mergers reported by the LIGO-Virgo-KAGRA Collaboration. Because GW230529 contributes significantly to the inferred mgBHNS rate densities, we suggest that GW230529 can be explained through the isolated binary evolution channel. Considering the AP4 (DD2) equation of state, the probability that GW230529 can make tidal disruption is $12.8\%$ ($63.2\%$). If GW230529 is a disrupted event, its kilonova peak apparent magnitude is predicted $\sim23-24\,{\rm{mag}}$, and hence, can be detected by the present survey projects and LSST. Since GW230529 could be an off-axis event inferred from the GW observation, its associated gamma-ray burst (GRB) might be too dim to be observed by $\gamma$-ray detectors, interpreting the lack of GRB observations. Our study suggests the existence of mgBHNS mergers formed through the isolated binary evolution channel due to the discovery of GW230529, indicating that BHNS mergers are still likely to be multimessenger sources that emit GWs, GRBs, and kilonovae. Although mgBHNS mergers account for $\sim50\%$ cosmological BHNS population, we find that $\gtrsim90\%$ disrupted BHNS mergers are expected to originate from mgBHNS mergers.