  Two classes of gamma-ray bursts were identified in the BATSE catalogs
characterized by their durations. There were also some indications for the
existence of a third type of gamma-ray bursts. Swift satellite detectors have
different spectral sensitivity than pre-Swift ones for GRBs. Therefore in this
paper we analyze the bursts' duration distribution and also the
duration-hardness bivariate distribution, published in The First BAT Catalog.
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.
