Evidence for the Galactic Origin of Gamma-Ray Bursts

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Abstract
We propose a new criterion to divide the classical gamma-ray bursts into two classes on the basis of their distribution in the duration-hardness plane. We study the two proposed classes separately, dividing them into subsets of different hardness-ratio ranges. The intensity distribution (log N vs. log S) and the corresponding space distribution of the subsets provide us with a different scenario for each of the two classes. For the first time, in both cases, clear indications for a Galactic origin of gamma-ray bursts have been found. Two possibilities are favored: (1) two kinds of Galactic gamma-ray bursts coming from the disk and from the halo, respectively, and (2) two kinds of gamma-ray bursts deriving from two distinct source populations located at different positions in the Galactic disk.