Formation of GW230529 from Isolated Binary Evolution and Its Electromagnetic Counterparts

Kavli Affiliate: Lijing Shao

| First 5 Authors: Jin-Ping Zhu, Rui-Chong Hu, Yacheng Kang, Bing Zhang, Hui Tong

| Summary:

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.

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