The signature of an anisotropic distribution of gamma-ray bursts

TL;DR

This paper investigates the angular distribution of gamma-ray bursts to identify anisotropic patterns similar to known anomalies in the cosmic microwave background, revealing multipole alignments and planar structures.

Contribution

It introduces an analysis of gamma-ray burst distributions using spherical harmonics to detect anisotropic features comparable to CMB anomalies.

Findings

Rough multipole alignment from l=2 to l=4 in GRB distribution

Dipole and l=5 multipole are oriented differently

Quadrupole is distinctly planar

Abstract

Anomalies of the cosmic microwave background (CMB) maps have been widely acquainted nowadays from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite to the Planck satellite. One of the anomalies is a multipole alignment from $l=2$ to $l=5$. In our work, we investigate the angular distribution of gamma-ray bursts (GRBs) to find whether there is the same anomaly of GRB as CMB. We perform spherical harmonics expansion on GRB samples to derive coefficients of a few first terms of the expansion terms and find that there is rough multipole alignment from $l=2$ to $l=4$ while the dipole and $l=5$ multipole is in a distant direction, and that the quadrupole is obviously planar and the other ones are normal.