Contraints on Galactic corona models of gamma-ray bursts imposed by Andromeda and the BATSE 3B catalog

Abstract

If our galaxy possesses a corona of neutron stars responsible for most or all currently observed gamma-ray bursts, then Andromeda (M31) should possess a similar corona. Bursts from the M31 corona are detectable by a sufficiently sensitive detector, and this places important constraints on Galactic corona models, in particular on the maximum distance out to which a detector like BATSE can see. We investigate the viability of coronal burst models by calculating the spatial distribution of bursts expected for a population of high-velocity neutron stars born in the disks of the Milky Way and Andromeda, and moving in a gravitational potential that includes the bulges, disks, and dark matter halos of both galaxies. We consider two burst emission scenarios, one in which the emission is isotropic and one in which it is beamed along the neutron star kick velocity. We constrain the models by comparing the resulting burst brightness and angular distributions with those of the BATSE 3B catalog. If bursts radiate isotropically, we find that the Galactic corona model can reproduce the BATSE data for kick velocities ≳800 km s−1, source turn-on ages ≳20 Myrs, and BATSE sampling distances 130 kpc≲dmax≲400 kpc. If bursts are instead beamed, kick velocities ≳800 km s−1 and BATSE sampling distance 100 kpc≲dmax≲400 kpc are still required, but a characteristic burst turn-on age is not.