Are Gamma-Ray Bursts Due to Rotation-powered High-Velocity Pulsars in the Halo?

Abstract

The BATSE experiment has now observed more than 1100 gamma-ray bursts. The observed angular distribution is isotropic, while the brightness distribution of bursts shows a reduced number of faint events. These observations favor a cosmological burst origin. Alternatively, very extended Galactic Halo (EGH) models have been considered. In the latter scenario, the currently favored source of gamma-ray bursts involves high velocity pulsars ejected from the Galactic disk. To be compatible with the observed isotropy, most models invoke a sampling distance of 300 kpc, a turn-on delay of 30 Myrs, and a source life time of about 1 Gyr. We consider the global energy requirements of such models and show that the largest known resource. rotational kinetic energy, is insufficient by orders of magnitude to provide the observed burst rate. More exotic energy sources or differently tuned pulsar models may be able to get around the global energy constraint but at the cost of becoming contrived. Thus, while extended halo models are not ruled out, our arguments place a severe obstacle for such models and we encourage proponents of EGH models to clearly address the issue of global energetics.