Gamma-ray burst is the highest energy phenomena found by people in cosmos so far.According to observatory
it can be divided into two classes.Mukherjee(1998)and Horvath(1999) respectively used different methods to reach the conclusion that gamma-ray bursts would be divided into three classes.People want to know the nature of the third class in the new classification of gamma-ray bursts and the difference from the other ones.The spectral hardness ratio of three classes is calculated and discussed.The physical mechanisms of the new third may be different from others.
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references
U. D. Desai. Morphological study of the time histories of gamma-ray bursts[J], 1981