A Third Class of Gamma-Ray Bursts?

Two classes of gamma-ray bursts have been identified so far, characterized by T90 durations shorter and longer than approximately 2 s. We show here that the BATSE 3B data allow a good fit with three Gaussian distributions in log T90. The χ2 statistic indicates a 40% probability for two-Gaussian fits, whereas the three-Gaussian fit probability is 98%. Using another statistical method, it is argued that the probability that the third class is a random fluctuation is less than 0.02%.