No abstract

X-ray flares are frequently detected in the X-ray afterglow light curves and are highly correlated with the prompt emission of gamma-ray bursts (GRBs). We compile a comprehensive sample of X-ray flares up to 2021 April, comprising 697 flares. We classify the total sample into four types: early flares (tp≤103 s), late flares (tp>103 s), long gamma-ray burst (LGRB) flares and short gamma-ray burst (SGRB) flares, and analyze the distributions and relationships of the flare parameters. It is found that the early flares have a higher frequency, shorter duration, and more asymmetrical structure. In addition, the distributions of the morphological parameters of the SGRB flares are similar to those of the LGRB flares. We also find that the durations and rising (decay) times of the early flares are positively correlated with the peak times, but the late flares follow the different dependent relations. There is a strong anti-correlation between the peak luminosities (LX,P) and the peak times of the flares, e.g., LX,p∝tp,z−1.45 for the LGRB flares, and LX,p∝tp,z−1.27 for the SGRB flares, respectively. Furthermore, the peak luminosity is highly dependent on the isotropic energy (EX,iso) for the early LGRB flares, the best fit is LX,p∝EX,iso1.06(r=0.89). We also find a tight three-parameter correlation, LX,p∝tp,z−1.03EX,iso0.92(r=0.96). All the late flares fall into the 3σ confidence region defined by the early flares. In terms of the point of kinematic arguments, both the SGRB and LGRB flares support a common scheme of internal origin. The SGRB flares have similar properties to the LGRB flares, suggesting that both of them share a similar physical mechanism from the late-time activity of central engine.

The intrinsic statistical properties and correlations of short gamma-ray bursts (SGRBs) have not been fully determined, due to the limitations of observations. In this paper, we compile a more extensive sample of 82 SGRBs with measured redshifts and present a comprehensive study of their intrinsic characteristics. We obtain the median values of the intrinsic duration (T 90,z), peak energy (E p,z), isotropic energy (E iso), and peak luminosity (L iso) as 0.47 s, 466 keV, 8.21 ×1050 erg, and 3.22 × 1051 erg s−1, respectively. We update the spectrum–energy correlations, and report E p , z ∝ E iso 0.36 ± 0.05 and E p , z ∝ L iso 0.33 ± 0.04 , which further confirm the previous results that the E p,z–E iso correlations of SGRBs and long gamma-ray bursts (LGRBs) are different and that this correlation can be used to distinguish GRB types. We report for the first time that there is a tighter correlation between the isotropic energy of the prompt emission of SGRBs and the star formation rate of their host galaxies, which reads sSFR ∝ E iso 0.38 ± 0.11 . Using the measured jet break time (t jet) of 11 SGRBs, we tentatively investigate the E iso–E p,z–t jet,z and L iso–E p,z–t jet,z correlations of SGRBs and find that three-parameter correlations of SGRBs also exist and are different from those of LGRBs. Based on the E iso–E p,z–t jet,z correlation, we estimate the t jet,z values of other SGRBs and calculate the opening angles of SGRBs. We find that the median value of the SGRB opening angle is 7.°5, which is larger than that of LGRBs.