SIMBAD references

In this paper, we randomly selected a sample (sample 1) of long gamma-ray bursts, with its size being the same as that of the short-burst group (sample 2) (N= 500), from the Current BATSE Bursts Catalog. We randomly selected a short burst and assigned its T₉₀to each of these long bursts. We thus constructed a long-burst sample with both the sample size and the distribution of T₉₀being the same as those of the short-burst sample obtained from the Current BATSE Bursts Catalog. Then we calculated the hardness ratio (hr_t) over the assigned T₉₀for the long bursts and over their own T₉₀for the short bursts, and studied the relation between the hardness ratio and the corresponding T₉₀for these two samples. We also calculated the hardness ratio (hr_t) over the randomly selected 64-ms time intervals within the T₉₀, and investigated the relation between this hardness ratio and the selected 64-ms time interval. In addition, the hr_Twithin and beyond the first two seconds for all the long bursts (sample 3; N= 1541) were also investigated. We found that the Kolmogorov-Smirnov (KS) probabilities of the distributions of hr_T(7.15337E-15) and hr_t(9.54833E-10) for samples 1 and 2 are very small, and the average values of hr_Tand hr_t for short bursts are obviously larger than those of the long bursts. The correlations between loghr_Tand logT₉₀, and between loghr_t_and logt, are different for samples 1 and 2. These show that short and long bursts in the first two seconds have different characters and they probably originate from different progenitors. For sample 3, for the two time intervals, the KS probability is 5.35828E-5, which suggests that the hardness ratios in different time intervals for long bursts are also different.