Fireballs in the Galactic halo and gamma-ray bursts

If gamma ray burst sources are in the galactic halo they inevitably involve a creation of an opaque pair plasma fireball, just like in cosmological sources. We find that the typical physical conditions in a galactic halo fireball are: optical depth $ap 10^8$, thermal energy $ap 100 KeV$, maximal relativstic expansion $G ap 300 $ and a maximal baryonic load of $ap 10^{-15} M_odot$. This does not rule out galctic halo models but it poses an addtional severe constraint on all such sources. A comparison of these conditions with the physical conditions at cosmological fireballs reveal that galactic halo fireballs are less favorable than cosmological ones as sources of gamma ray bursts.Comment: 11 page