A Comparative Study on the Characteristics of X-ray Afterglow Variation in Two Types of Gamma Bursts

The classification of gamma-ray bursts (GRBs) is an unsolved hot issue in the field of GRBs. To solve this problem, we collected a samples of X-ray afterglow curves including 180 known redshift GRBs observed by Swift with slow attenuation and subsequent attenuation characteristics, in which there are 172 Long GRBs and 8 Short GRBs. We adopt the smooth broken power law function and the Markov chain Monte Carlo (MCMC) method to fit these X-ray afterglow light curves. After obtaining these light curve characteristic parameters α₁ (slow decay index), α₂ (normal attenuation index), and T_a (slow attenuation end time in rest frame), we analyze the characteristic parameters of the two types of bursts to check whether there are differences in the distribution of these parameters and whether the two types of storms follow the same correlation. Our research findings are as follows:(1) The distribution range, median value, and average value of the characteristic parameters (α₁、α₂, T_a) of two types of bursts are very close, and there is no significant difference. The subsequent K-S test further indicates that there is no significant difference in the distribution of parameters between the two types of bursts. (2) The two types of bursts we selected follow the following correlation:L_x-T_a, L_x-E_γ,iso、S-T₉₀、E_γ,iso-T₉₀, and they are not distinguishable on a scatter chart. These statistical results indicate that the optical variability characteristics of the two types of bursts are similar. Therefore, we infer that the two types of GRBs have the same physical origin, and their jet structures may also be the same.