Evidence for the Galactic origin of gamma-ray bursts

We investigate the angular distribution of the γ-ray bursts in the publicly available BATSE catalog, using the measures of burst brightness B and short-time-scale $$(\lesssim0.3 \text s)$$ variability V which we introduced earlier. We show that the 54 type I $$(\text {log}\enspace V\leq - 0.8)$$ bursts lying in the middle brightness range of $$490\leq B\leq 1250$$ count (corresponding to one-third of all type I bursts) exhibit a Galactic dipole moment of $$\langle \text {cos}\theta \rangle = 0.204\pm0.079$$and a deviation of the Galactic quadrupole moment from $$\langle \text {sin}^{2} b\rangle -1/3=-0.104\pm0.041$$. Using Monte Carlo simulations that include the BATSE sky exposure map, and taking into account division of the type I bursts into three equal samples, we find that the probability by chance of an isotropic distribution of 54 bursts exhibiting values of $$\langle \text {cos}\theta \rangle$$and the negative of $$\langle \text {sin}^{2}b\rangle-1/3$$ that equal or exceed the observed values is $$6.6\times{10}^{-5}$$. We conclude that γ-ray bursts are Galactic in origin.