A comparative analysis of two peculiar long Gamma-ray bursts: GRB 230307A and GRB 211211A

TL;DR

This study compares two peculiar long gamma-ray bursts, GRB 230307A and GRB 211211A, revealing their remarkable similarities in emission phases, spectral properties, and potential common origin from compact star mergers, with photospheric radiation explaining their mechanisms.

Contribution

The paper provides a detailed temporal and spectral comparison of two similar long GRBs, highlighting their shared properties and suggesting a common origin from compact star mergers, which is a novel insight.

Findings

Both GRBs have similar redshifts and emission phase structures.

They exhibit near-zero spectral lag and short variability timescales.

Their spectral and flux properties are highly consistent across phases.

Abstract

GRB 211211A is a peculiar long Gamma-ray burst (GRB) with very high brightness and short burst properties. It's full lightcurve consists of three emission episodes, i.e. a precursor, a main burst and a extended emission. We find a recently detected long-duration GRB 230307A also includes the three consistent emission episodes. Furthermore, the two bursts have similar redshift 0.076 and 0.065, respectively. We perform a detail temporal and spectral analysis of the two GRBs to compare their temporal and spectral properties. Our analysis shows that the two bursts share great similarities for both the whole emission and the three corresponding emission phases, which are listed as follows: (1) they have near zero spectral lag, (2) they have very short minimum variability timescale (MVT), (3) they lie in the same region of in the MVT-$T_{90}$, Amati relation, and hardness-$T_{90}$ planes, (4) the three phases are quasi-thermal spectra, (5) both the peak energy and the low-energy index track the flux, (6) the time-resolved spectra are much wider than those of the blackbody prediced by theory model, (7) there are strong correlations between thermal flux and total flux and the correlation coefficients as well as the slopes for the corresponding stages are very consistent, (8) the photosphere emission properties are very consistent. Other investigations and observations suggest the two GRBs indeed belong to short burst with a compact star merger origin. Therefore, we think that GRB 230307A and GRB 211211A are the rare and similar GRBs and the photospheric radiation can interpret their radiation mechanisms.