Disk plus halo models of gamma‐ray burst sources

We show that, in principle, ≊70% of the γ‐ray bursts observed by BATSE can come from local (≲1 kpc), galactic disk neutron stars, with the rest in an extended galactic halo. We consider three possible forms for the distribution of the galactic halo sources: a Gaussian halo, an exponential halo, and a standard ‘‘dark matter’’ halo. We find that for the Gaussian halo the fraction of bursts that can come from the galactic disk can be ≊2/3, close to the maximum possible value; for exponential and dark matter halos the fraction can be ≊1/2 and ≊1/5 respectively. In each case, the values of 〈V/V_max〉, 〈sin²b〉, 〈cosθ〉, and the C_max/C_min distribution are all easily consistent with the BATSE observations. Dividing the bursts into three, equal‐sized groups of the brightest, intermediate, and weakest, there is little difference in the values of 〈sin²b〉 and 〈cosθ〉, agreeing with the BASTE observations. The disk sources have luminosities ≊10^36–37 ergs s⁻¹, while those in the halo have luminosities ≊10⁴¹–⁴² ergs s⁻¹. The brightest observed bursts must come from the halo; therefore, given current neutron star γ‐ray burst models, one might not expect to see cyclotron line features in the brightest γ‐ray bursts.