Gamma-ray Burst Classification And Light Curve Study

The history and actuality of the observational and theoretical studies on gamma-ray bursts (GRB) and their afterglows are reviewed, the theoretical models of this field are introduced in detail, and some problems of these models are discussed. The statistical properties of the light curves and the classification of GRBs are investigated.The widely accepted classification of gamma-ray bursts are classifying the gamma-ray bursts into two classes with T90, while few people think about the role of T50 which includes the duration of the dominant part of a gamma-ray burst when classifying. We make the distribution of T50 with the data of the Current BATSE Catalog and following the distribution of clearly bimodal, we also classify all the bursts into two classes with T50. Compared with the two types classified with T90 and T50, we find 27 bursts belong to long bursts classifying with T90, while become short bursts when classifying with T50. We analyze the light curves of the 27 bursts, and reach the following conclusion: these bursts should belong to short bursts viewing from the proccess of the burst, but because the background counts are not sufficiently substracted, which make the T90 become longer than it should be, these bursts become long bursts. We think the T50 of these bursts should play an important role in the classification for this type of bursts.