Anisotropy of the sky distribution of gamma-ray bursts

Balázs, Lajos György and Mészáros, A. and Horváth, István (1998) Anisotropy of the sky distribution of gamma-ray bursts. Astronomy and Astrophyics, 339 (1). pp. 1-6. ISSN 0365-0138

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Abstract

The isotropy of gamma-ray bursts collected in current BATSE catalog is studied. It is shown that the quadrupole term being proportional to \sim sin 2b sin l is non-zero with a probability of 99.9%. The occurrence of this anisotropy term is then confirmed by the binomial test even with the probability of 99.97 %. Hence, the sky distribution of all known gamma-ray bursts is anisotropic. It is also argued that this anisotropy cannot be caused exclusively by instrumental effects due to the nonuniform sky exposure of BATSE instrument. Separating the GRBs into short and long subclasses, it is shown that the short ones are distributed anisotropically, but the long ones seem to be distributed still isotropically. The character of anisotropy suggests that the cosmological origin of short GRBs further holds, and there is no evidence for their Galactical origin.

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