No Detectable Kilonova Counterpart is Expected for O3 Neutron Star–Black Hole Candidates

Abstract

We analyse the tidal disruption probability of potential neutron star-black hole (NSBH) merger gravitational wave (GW) events, including GW190426 152155, GW190814, GW200105 162426 and GW200115 042309, detected during the third observing run of the LIGO/Virgo Collaboration, and the detectability of kilonova emission in connection with these events. The posterior distributions of GW190814 and GW200105 162426 show that they must be plunging events and hence no kilonova signal is expected from these events. With the stiffest NS equation of state allowed by the constraint of GW170817 taken into account, the probability that GW190426 152155 and GW200115 042309 can make tidal disruption is ∼ 24% and ∼ 3%, respectively. However, the predicted kilonova brightness is too faint to be detected for present follow-up search campaigns, which explains the lack of electromagnetic (EM) counterpart detection after triggers of these GW events. Based on the best constrained population synthesis simulation results, we find that disrupted events account for only 20% of cosmological NSBH mergers since most of the primary BHs could have low spins. The associated kilonovae for those disrupted events are still difficult to be discovered by LSST after GW triggers in the future, because of their low brightness and larger distances. For future GW-triggered multi-messenger observations, potential short-duration gamma-ray bursts and afterglows are more probable EM counterparts of NSBH GW events.

4-OGC: Catalog of gravitational waves from compact-binary mergers

“…GW200105 162426 is observed only in LIGO Livingston data with an SNR ∼ 13.3. Whereas GW200115 042309 is observed in both Livingston and Hanford data with IFAR > 100 yr. We are unable to constrain the tidal deformability of the secondary component, which is consistent with previous results (Abbott et al 2021b;Zhu et al 2021b).…”

A Channel to Form Fast-spinning Black Hole–Neutron Star Binary Mergers as Multimessenger Sources

“…However, despite many efforts toward the follow-up observations, no confirmed EM counterpart candidate was identified (e.g., Coughlin et al 2020aCoughlin et al , 2020bGompertz et al 2020b;Kasliwal et al 2020;Page et al 2020;Anand et al 2021;Becerra et al 2021). The tidal disruption probability of NSBH mergers and the brightness of EM signals depend on NS mass, NS equation of state (EOS), BH mass, and especially BH projected aligned spin (e.g., Kyutoku et al 2015;Kawaguchi et al 2016;Foucart et al 2018;Barbieri et al 2019;Zhu et al 2020Zhu et al , 2021aZhu et al , 2021bZhu et al , 2021cRaaijmakers et al 2021). Disrupted events associated with brighter EM signals tend to occur only if an NSBH binary has a low-mass NS component with a stiff EOS and a low-mass BH component with a high projected aligned spin.…”

“…Disrupted events associated with brighter EM signals tend to occur only if an NSBH binary has a low-mass NS component with a stiff EOS and a low-mass BH component with a high projected aligned spin. The most promising explanation for the lack of EM counterparts is that these NSBH candidates were plunging events without forming any bright EM signals, mainly due to their near-zero BH projected aligned spins (D'Orazio et al 2022;Fragione 2021;Zhu et al 2021b).…”

Population Properties of Gravitational-Wave Neutron Star--Black Hole Mergers

“…Compared with BNS mergers which would definitely eject a certain amount of materials to produce EM signals, some NSBH binaries may not tidally disrupt the NS component and, hence, would not make bright EM counterparts such as sGRBs and kilonovae 2 . The tidal disruption probability of NSBH mergers and the brightness of NSBH EM signals are determined by BH mass, BH spin, NS mass, and NS equation of state (EoS; e.g., Kyutoku et al 2011Kyutoku et al , 2013Kyutoku et al , 2015Fernández et al 2015;Kawaguchi et al 2015Kawaguchi et al , 2016Foucart 2012;Foucart et al 2018;Barbieri et al 2019;Krüger & Foucart 2020;Fragione 2021;Zhu et al 2020Zhu et al , 2021cLi & Shen 2021). A NSBH merger tends to be a disrupted event and produces bright EM signals if it has a low massive BH with a high projected aligned-spin, and a low massive NS with a stiff EoS.…”

“…In spite of many efforts for follow-up observations of these three events, no confirmed EM counterpart candidate has been identified (e.g., Anand et al 2021;Alexander et al 2021;Coughlin et al 2020;Gompertz et al 2020;Kasliwal et al 2020;Kilpatrick et al 2021;Page et al 2020;Thakur et al 2020;Dobie et al 2021). Abbott et al (2021a); Zhu et al (2021c); Fragione (2021) showed that the parameter space of these GW candidates mostly lies outside the disrupted parameter region, so that these candidates are likely plunging events with a high probability. There have been many mysteries about NSBH binaries, such as the proportion of disrupted events in cosmological NSBH mergers, their cosmological contribution to the elements heavier than iron, the formation channel of NSBH binaries, and so on.…”