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

Abstract

Gamma-ray bursts (GRBs) have been phenomenologically divided into long- and short-duration populations, generally corresponding to collapsar and compact merger origins, respectively. Here, we collect three unique bursts, GRBs 060614, 211211A, and 211227A, all of which are characterized by a long-duration main emission (ME) phase and a rebrightening extended emission (EE) phase, to study their observed properties and their potential origins as neutron star–black hole (NSBH) mergers. NS-first-born (BH-first-born) NSBH mergers tend to contain fast-spinning (nonspinning) BHs that more easily (hardly) allow tidal disruption to occur, while (without) forming electromagnetic signals. We find that NS-first-born NSBH mergers can well interpret the origins of these three GRBs, supported by the following. (1) Their X-ray MEs and EEs show unambiguous fallback accretion signatures, decreasing as ∝ t −5/3, which might account for their long durations. The EEs could result from the fallback accretion of r-process heating materials, which is predicted to occur after NSBH mergers. (2) The beaming-corrected local event-rate density for these types of merger-origin long-duration GRBs is  0 ∼ 2.4 − 1.3 + 2.3 Gpc − 3 yr − 1 , consistent with that of NS-first-born NSBH mergers. (3) Our detailed analysis of the EE, afterglow, and kilonova of the recent high-impact event GRB 211211A reveals that it could be a merger between a ∼ 1.23 − 0.07 + 0.06 M ⊙ NS and a ∼ 8.21 − 0.75 + 0.77 M ⊙ BH, with an aligned spin of χ BH ∼ 0.62 − 0.07 + 0.06 , supporting an NS-first-born NSBH formation channel. A long-duration burst, with a rebrightening fallback accretion signature after the ME, and a bright kilonova, might be commonly observed features for on-axis NSBH mergers. We estimate the multimessenger detection rate between gravitational waves, GRBs, and kilonova emissions from NSBH mergers in O4 (O5) to be ∼0.1 yr−1 (∼1 yr−1).

Simulations of the Progenitors of Black Hole–Neutron Star Gravitational Wave Sources

“…The possibility to detect a gamma-ray burst (GRB) in connection with a BH+NS merger depends crucially on the spin rate of the BH, and thus on which compact object formed first (Fragione et al 2021;Román-Garza et al 2021;Hu et al 2022;Zhu et al 2022). Since the BH formed first in our Systems A, B, and C, it is anticipated to be relatively slowly spinning and therefore the subsequent BH+NS merger event would most likely prevent tidal disruption from occurring, and therefore not produce a GRB source.…”

GRB 211211A: A Neutron Star–White Dwarf Merger?

“…Until recently, a kilonova-like emission with similar luminosity, duration, and color to AT 2017gfo, associated with GRB 211211A and located in a nearby host galaxy SDSS J140910.47 + 275320.8 with a distance ∼350 Mpc, was reported and analyzed by Rastinejad et al (2022), Yang et al (2022), Mei et al (2022), Troja et al (2022), Gompertz et al (2023), and Xiao et al (2022). From the evidence of the host galaxy properties including the offset, the features of the kilonova-like emission, the modeling for the light curves of afterglows and kilonova-like emission, and the exponential decline phase and spectral features in GRB 211211A, most authors suggested or directly considered this association to arise from a compact star merger (Gao et al 2022;Gompertz et al 2023;Mei et al 2022;Rastinejad et al 2022;Troja et al 2022;Xiao et al 2022;Yang et al 2022;Zhang et al 2022;Zhu et al 2022;Chang et al 2023;Kunert et al 2023), while a few authors mainly discussed the explanation or possibility in a collapsar origin (Waxman et al 2022;Barnes & Metzger 2023). The final central engine either a black hole (BH) or magnetar is also under debate.…”

Kilonovae and Optical Afterglows from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational Wave Triggers

“…To date, except for AT2017gfo, other kilonova candidates were all detected in superposition with decaying sGRB afterglows (e.g., Berger et al 2013;Fan et al 2013;Tanvir et al 2013;Gao et al 2015Gao et al , 2017Jin et al 2015Jin et al , 2016Jin et al , 2020Yang et al 2015;Gompertz et al 2018;Ascenzi et al 2019;Rossi et al 2020;Fong et al 2021;Ma et al 2021;Wu et al 2021;Yuan et al 2021). Interestingly, a bright kilonova candidate was recently found to be associated with a longduration GRB 211211A (e.g., Rastinejad et al 2022;Troja et al 2022;Yang et al 2022b;Zhu et al 2022a). One possible reason why almost all kilonova candidates were detected in GRB afterglows is that most BNS and NSBH mergers are far away from us.…”