A Comparative Analysis of Two Peculiar Gamma-Ray Bursts: GRB 230307A and GRB 211211A

GRB 211211A is a peculiar long gamma-ray burst (GRB) with very high brightness and short burst properties. Its full light curve consists of three emission episodes, i.e., a precursor, a main burst, and an extended emission. We find that a recently detected long-duration GRB 230307A also includes the three consistent emission episodes. Furthermore, the two bursts have similar redshifts, 0.076 and 0.065, respectively. We perform a detailed 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 predicted by the model; (7) there are strong correlations between thermal flux and total flux and the correlation coefficients, and the slopes for the corresponding stages are very consistent; and (8) the photosphere emission properties are very consistent. Other investigations and observations suggest that the two GRBs indeed belong to a short burst with a compact star merger origin. Therefore, we think that GRB 230307A and GRB 211211A are rare and similar GRBs, and the photospheric radiation can interpret their radiation mechanisms.