An intrinsic anisotropy in the angular distribution of gamma-ray bursts

¹ Konkoly Observatory, Budapest, Box. 67, H-1505 Hungary
² Department of Astronomy, Charles University, V Holešovičkách 2, CZ-180 00 Prague 8, Czech Republic
³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, Garching bei München, Germany
⁴ Department of Physics, BJKMF, Budapest POB.12, H-1456 Hungary

Send offprint request to: L.G. Balázs

Received: 18 December 1998
Accepted: 10 March 1999

Abstract

The anisotropy of the sky distribution of 2025 gamma-ray bursts (GRBs) collected in Current BATSE catalog is confirmed. It is shown that the quadrupole term being proportional to is non-zero with a probability 99.9%. The occurrence of this ani sot ropy term is then supported by the binomial test even with the probability 99.97%. It is also argued that this anisotropy cannot be caused exclusively by instrumental effects due to the non-uniform sky exposure of BATSE instrument; there should exist also some intrinsic anisotropy in the angular distribution of GRBs. Separating GRBs into short and long subclasses, it is shown that the 251 short ones are distributed anisotropically, but the 681 long ones seem to be distributed still isotropically. The 2-sample Kolmogorov-Smirnov test shows that they are distributed differently with a 98.7% probability. The character of anisotropy suggests that the cosmological origin of short GRBs further holds, and there is no evidence for their Galactical origin. The work in essence contains the key ideas and results of a recently published paper (Balázs et al. 1998), to which the new result following from the 2-sample Kolmogorov-Smirnov test is added, too.