Abstract
We studied the complete randomness of the angular distribution of BATSE gamma-ray bursts (GRBs). Based on their durations and peak fluxes, we divided the BATSE sample into 5 subsamples (short1, short2, intermediate, long1, long2) and studied the angular distributions separately. We used three methods to search for non-randomness in the subsamples: Voronoi tesselation, minimal spanning tree, and multifractal spectra. To study any non-randomness in the subsamples we defined 13 test-variables (9 from Voronoi tesselation, 3 from the minimal spanning tree and one from the multifractal spectrum). We made Monte Carlo simulations taking into account the BATSE’s sky-exposure function. We tested therandomness by introducing squared Euclidean distances in the parameter space of the test-variables. We recognized that the short1, short2 groups deviate significantly (99.90%, 99.98%) from the fully random case in the distribution of the squared Euclidean distances but this is not true for the long samples. In the intermediate group, the squared Euclidean distances also give significant deviation (98.51%).
Highlights
The cosmological origin of gamma-ray bursts has been widely accepted [24, 49, 75]
To characterize the statistical properties of the point patterns given by the samples, we defined 13 test-variables based on Voronoi tesselation (VT), a minimal spanning tree (MST) and a multifractal spectra
The numerical simulations enabled us to define the empirical probabilities for testing the null hypothesis, i.e. the assumption that the angular distributions of the BATSE samples are fully random
Summary
The cosmological origin of gamma-ray bursts (hereafter GRBs) has been widely accepted [24, 49, 75]. There is an increasing amount of evidence that all GRBs do not all form a physically homogeneous group [5, 27,28,29,30,31, 39, 50] It is worth investigating whether physically different subgroups are different in their angular distributions. The authors have carried out several different tests in recent years [3, 4, 45, 46] probing the intrinsic isotropy in the angular sky-distribution of the GRBs collected in BATSE Catalog [44]. For the short subgroup (T90 < 2s) the assumption of isotropy is rejected only on the 92 % significance level; D. The long and short subclasses, respectively, are distributed differently on the 99.3 % significance level. The long and short subclasses, respectively, are distributed differently on the 99.3 % significance level. (For a definition of the subclasses see [29,30,31,32,33, 69].)
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