The Signature of an Anisotropic Distribution of Gamma-ray Bursts

Anomalies of the cosmic microwave background (CMB) map have been widely acquainted nowadays via the Wilkinson Microwave Anisotropy Probe (WMAP) satellite and the Planck satellite. One anomaly is the alignment of multipole moments from l = 2 to l = 5. In our work, we investigate the angular distribution of gamma-ray bursts (GRBs) to find whether there exists an anomaly similar to that of CMB. We perform the spherical-harmonic expansion on the GRB sample to derive the coefficients of a few foremost terms. It is found that a rough alignment of multipole moments from l = 2 to l = 4 exists, while the multipole moment of l = 5 points to a different direction. And that the quadrupole moment is obviously of planar distribution, while the other ones are normal.