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 type of burst. 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. Using The First BAT Catalog
the maximum likelihood estimation was used to analyzed the duration
distribution of GRBs. The three log-normal fit is significantly (99.54 %
probability) better than the two for the duration distribution. Monte-Carlo
simulations also confirm this probability (99.2 %).Comment: NANJING GAMMA-RAY BURST CONFERENCE 200
