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Astron. Astrophys. 339, 1-6 (1998)

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Anisotropy of the sky distribution of gamma-ray bursts

L.G. Balázs 1, A. Mészáros 1, 2, 3 and I. Horváth 4

1 Konkoly Observatory, Budapest, Box 67, H-1505 Hungary (balazs@ogyalla.konkoly.hu)
2 Department of Astronomy, Charles University, V Holeovikách 2, CZ-180 00 Prague 8, Czech Republic (meszaros@mbox.cesnet.cz)
3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, Garching bei München, Germany
4 Department of Earth Science, Pusan National University, Pusan, 609-735, Republic of Korea (hoi@astrophys.es.pusan.ac.kr)

Received 31 March 1998 / Accepted 26 June 1998

Abstract

The isotropy of gamma-ray bursts collected in current BATSE catalog is studied. It is shown that the quadrupole term being proportional to [FORMULA] 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.

Key words: large-scale structure of Universe - gamma rays: bursts

Send offprint requests to: L.G. Balázs

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© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998
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