Long-duration Gamma-ray Burst and Associated Kilonova Emission from Fast-spinning Black Hole–Neutron Star Mergers

Kavli Affiliate: Zhuo Li

| First 5 Authors: Jin-Ping Zhu, Xiangyu Ivy Wang, Hui Sun, Yuan-Pei Yang, Zhuo Li

| Summary:

Here we collect three unique bursts, GRBs,060614, 211211A and 211227A, all
characterized by a long-duration main emission (ME) phase and a rebrightening
extended emission (EE) phase, to study their observed properties and the
potential origin as neutron star-black hole (NSBH) mergers. NS-first-born
(BH-first-born) NSBH mergers tend to contain fast-spinning (non-spinning) BHs
that more easily (hardly) allow tidal disruption to happen with (without)
forming electromagnetic signals. We find that NS-first-born NSBH mergers can
well interpret the origins of these three GRBs, supported by that: (1) Their
X-ray MEs and EEs show unambiguous fall-back accretion signatures, decreasing
as $propto{t}^{-5/3}$, which might account for their long duration. The EEs
can result from the fall-back accretion of $r$-process heating materials,
predicted to occur after NSBH mergers. (2) The beaming-corrected local event
rate density for this type of merger-origin long-duration GRBs is
$mathcal{R}_0sim2.4^{+2.3}_{-1.3},{rm{Gpc}}^{-3},{rm{yr}}^{-1}$,
consistent with that of NS-first-born NSBH mergers. (3) Our detailed analysis
on the EE, afterglow and kilonova of the recently high-impact event
GRB,211211A reveals it could be a merger between a
$sim1.17^{+0.13}_{-0.04},M_odot$ NS and a $sim9.3^{+1.6}_{-1.6},M_odot$
BH with an aligned-spin of $chi_{rm{BH}}sim0.67^{+0.08}_{-0.10}$, supporting
an NS-first-born NSBH formation channel. Long-duration burst with rebrightening
fall-back accretion signature after ME, and bright kilonova might be commonly
observed features for on-axis NSBHs. We estimate the multimessenger detection
rate between gravitational waves, GRBs and kilonovae from NSBH mergers in O4
(O5) is $sim0.1,{rm{yr}}^{-1}$ ($sim1,{rm{yr}}^{-1}$).

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