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

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 α, any non-zero spherical harmonic proportional either to P n (sin δ) sinmα or to P m n (sin δ) cosmα with m 6= 0 (δ 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 97% significance level caused by the high non-zero P 1 3 (sin δ) sinα harmonic. The remaining two subclasses, and the full sample of GRBs, remain isotropic.