GRB 211227A as a Peculiar Long Gamma-Ray Burst from a Compact Star Merger

Abstract

Long-duration gamma-ray bursts (GRBs) associated with supernovae (SNe) are believed to originate from massive star core-collapse events, whereas short-duration GRBs that are related to compact star mergers are expected to be accompanied by kilonovae. GRB 211227A, which lasted about 84 s, had an initial short/hard spike followed by a series of soft gamma-ray extended emission at redshift z = 0.228. We performed follow-up observations of the optical emission using BOOTES, LCOGT, and the Lijiang 2.4 m telescope, but we detected no associated supernova signature, even down to very stringent limits at such a low redshift. We observed the host galaxy within a large error circle and roughly estimated the physical offset of GRB 211227A as 20.47 ± 14.47 kpc from the galaxy center. These properties are similar to those of GRB 060614, and suggest that the progenitor of GRB 211227A is not favored to be associated with the death of massive stars. Hence, we propose that GRB 211227A originates from a compact star merger. Calculating pseudo-kilonova emission for this case by adopting the typical parameters, we find that any associated pseudo-kilonova is too faint to be detected. If this is the case, it explains naturally the characteristics of the prompt emission, the lack of SN and kilonova emission, and the large physical offset from the galaxy center.

Thermal and non-thermal emission from a peculiar long-duration GRB 211211A

“…GRB 211211A was observed by Fermi/GBM, Swift/BAT, and Insigt-HXMT to have a duration of ∼ 84 seconds at redshift z =0.076, but the light curve is characterized by an initial hard-main emission (with a duration ∼ 13 s) followed by a series of soft gamma-ray extended emission with a duration ∼ 55 s. The structure of lightcurve is similar to the cases of GRB 060614 and GRB 211227A which are believed to be from the compact star merger (Yang et al 2022;Xiao et al 2022;Lü et al 2022). The total isotropic-equivalent energy (E γ,iso ) and luminosity (L γ,iso ) are as high as 7.6 × 10 51 erg and 1.9 × 10 51 erg s −1 , respectively.…”

“…Most recently, a peculiar and nearby long-duration GRB 211211A that triggered Fermi Gamma-Ray Burst Monitor (GBM; Mangan et al 2021), Swift Burst Alert Telescope (BAT;D'Ai et al 2021), as well as Insigt-HXMT (Zhang et al 2021), is very excited for attention with redshift z=0.076. The lightcurve of prompt emission is composed of an initial hard-main emission (with a duration ∼ 13 s) followed by a series of soft gamma-ray extended emission (EE) with a duration ∼ 55 s, and the structure of lightcurve is similar to the particularly interesting case GRB 060614 (Yang et al 2022;Xiao et al 2022) and GRB 211227A (Lü et al 2022). More interestingly, no associated supernova signature is detected for GRB 211211A, even down to very stringent limits at such a low redshift, but associated with kilonova is observed by several optical telescopes (Rastinejad et al 2022).…”

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

“…We collect the observed data of three present zknown merger-origin lGRBs, including GRB 211221A (e.g., Rastinejad et al 2022;Yang et al 2022;Xiao et al 2022), GRB 060614 (Gal-Yam et al 2006Della Valle et al 2006;Zhang et al 2007), and GRB 211227A (Lü et al 2022), all characterized by a spiky long-duration ME phase, a rebrightening EE phase, and a temporal lull between these two phases, to study their similarities. Here, the EE phase is defined as the long-lasting lower level emission phase after the initial intense ME phase (Norris & Bonnell 2006;Lan et al 2020).…”

“…1 of Yang et al (2022). The data of GRB 211227A are collected from Lü et al (2022) and Tsvetkova et al (2022). The energy fluence of the ME for GRB 211227A is calculated by the HEASoft tool (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc) 2014) in the 15 − 1500 keV energy band.…”

“…Besides GRB 211211A, two other redshift-known (zknown) lGRBs, i.e., GRB 060614 and GRB 211227A, were proposed to derive from compact binary coalescences. GRB 060614 (Gal-Yam et al 2006;Della Valle et al 2006;Zhang et al 2007) were found to be associated with a kilonova candidate (Yang et al 2015), while GRB 211227A showed a large physical offset from the host center and lacked a supernova signature that should have been observed at the location of the burst (Lü et al 2022). In this Letter, we study the properties of these three merger-origin lGRBs, especially for GRB 211211A, and show that a single explosive population via the NS-first-born NSBH merger can account for their origin.…”