Gamma-Ray Burst Groups Observed by Different Satellites

Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third one. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore it is worth to reanalyze the durations and their distribution and also the classification of GRBs. In this paper we are going to analyze the bursts' duration distribution and also the duration-hardness bivariate distribution, published in The First BAT Catalog, whether it contains two, three or maybe more groups. Similarly to the BATSE data, to explain the BAT GRBs duration distribution three components are needed. Although, the relative frequencies of the groups are different than they were in the BATSE GRB sample, the difference in the instrument spectral sensitivities can explain this bias in a natural way. This means theoretical models may have to explain three different type of gamma-ray bursts.