High velocity neutron stars and γ-ray bursts

Abstract

The observations of the BATSE instrument on the Compton Gamma-Ray Observatory show that the spatial distribution of γ-ray burst sources is isotropic but radially non-uniform. As is well known, the spectral features, the time histories and the X-ray tails present in some γ-ray bursts suggest that they may arise from galactic neutron stars. But, low velocity neutron stars born in the Galactic disk would concentrate toward the galactic plane and center, and could not fit the BATSE results. However, the high velocity neutron stars with velocity ∼1000 km s⁻¹ may escape from the Galactic gravitational field and form a nearly isotropic distribution. Here we calculate the three statistical values of 〈V/V _max〉, 〈sin² b〉 and 〈cos θ〉 as functions of the intensitiesC _max/C _min and find that they could be fitted by the distribution of high velocity neutron stars under the assumption that the high velocity neutron stars should turn on as γ-ray burst sources only after some time (perhaps after they have ceased to be radio pulsars). Our calculation shows that the statistical value of 〈cos θ〉 is more sensitive than 〈sin² b〉 to the angular distribution of high velocity neutron stars, i.e. the deviation of 〈cos θ〉 from 0 is more readily detected than the deviation of sin² b from 1/3, so we expect that with the increasing sensitivity of instrument and the more exact value of 〈cos θ〉, it is possible to determine whether this high velocity neutron star model is correct. Some results are discussed in the text.