Distributions of the Hardness Ratio of short and Long Gamma-Ray Bursts in Different Time Intervals within the First 2 Seconds

Abstract

In the present paper, we investigated the distribution of hardness ratio (HR) for short and long gamma-ray bursts (GRBs) in different time scales for the first two seconds. After including and subtracting the background count, we performed a Kolmogorov--Smirnov (K-S) test to the HR distributions of the two classes of GRBs in each time interval. Our analysis shows that the probabilities of the KS test to the distributions are very small, suggesting that the two classes of bursts are unlikely to arise from the same HR distributions, and indicating that they probably originate from the different physical processes and central engine. In addition, we found that the hardness ratio of short bursts within the time interval of 0$-$0.96 seconds changes hard-to-soft, on the other hand long bursts do not. The two kinds of bursts have different characteristics in the first 2 seconds which might be associated with different physical mechanisms.