伽马射线暴的各向异性分布的特征

The Signature of an Anisotropic Distribution of Gamma-ray Bursts

从过去的威尔金森微波各向异性探测器(Wilkinson MicrowaveAnisotropy Probe)到现在的普朗克卫星(Planck satellite),宇宙微波背景辐射图的反常现象已经被广泛地认知.其中一个反常是:从l=2到l=5的多极矩存在耦合现象.为了考察伽马射线暴中是否存在与微波背景辐射相同的反常现象,研究了伽马射线暴的角分布.对伽玛暴样本的角分布进行球谐函数展开,得到前几项展开项的系数,发现从l=2到l=4有一定程度的耦合,而l=5与前面几个极矩相距较远.而且,四极矩分布是趋近平面化的,而其他几个极矩没有这样的特征.

Anomalies of the cosmic microwave background （CMB） maps have been widely acquainted nowadays via the Wilkinson Microwave Anisotropy Probe （WMAP） satellite and the Planck satellite. One anomaly 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 exists an anomaly similar to that of CMB. We perform a spherical harmonics expansion on the GRB samples to derive coefficients of a few multipole terms. A rough alignment from l = 2 to l = 4 exists, while the l = 5 multipole points to a different direction. The quadrupole is obviously planar, while the other ones are normal.