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Astron. Astrophys. 354, 1-6 (2000)


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On the existence of the intrinsic anisotropies in the angular distributions of gamma-ray bursts

A. Mészáros 1, Z. Bagoly 2 and R. Vavrek 3,4

1 Department of Astronomy, Charles University, V Holeovikách 2, 180 00 Prague 8, Czech Republic (meszaros@mbox.cesnet.cz)
2 Laboratory for Information Technology, Eötvös University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary (bagoly@ludens.elte.hu)
3 Konkoly Observatory, Box 67, 1505 Budapest, Hungary (vavrek@ogyalla.konkoly.hu)
4 Observatoire de Paris, 92195 Meudon Cedex, France

Received 5 July 1999 / Accepted 21 September 1999

Abstract

This article is concerned primarily with the intrinsic anisotropy in the angular distribution of 2281 gamma-ray bursts (GRBs) collected in Current BATSE Gamma-Ray Burst Catalog until the end of year 1998, and, second, with intrinsic anisotropies of three subclasses ("short", "intermediate", "long") of GRBs. Testing based on spherical harmonics of each class, in equatorial coordinates, is presented. Because the sky exposure function of BATSE instrument is not dependent on the right ascension [FORMULA], any non-zero spherical harmonic proportional either to [FORMULA] or to [FORMULA] with [FORMULA] ([FORMULA] is the declination), immediately indicates an intrinsic non-zero term. It is a somewhat surprising result that the "intermediate" subclass shows an intrinsic anisotropy at the [FORMULA] significance level caused by the high non-zero [FORMULA] harmonic. The remaining two subclasses, and the full sample of GRBs, remain isotropic.

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

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© European Southern Observatory (ESO) 2000

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