Gamma-ray bursts from the interaction of degenerate disks with fast neutron stars (Part II)

Abstract

We describe a reasonable model of a galactic halo origin of gamma-ray bursts (GRBs). The observed isotropy of GRBs requires fast ∼108 cm s−1 neutron stars (NSs), with a finite delay period ∼30 My, before turn on and ∼×10 longer before turning off. The NSs might not be radio pulsars, despite a normal NS magnetic field, ∼1012 gauss because of slow rotation from tidal locking in a presupernova binary. The high velocity can be produced from a neutrino rocket effect from anisotropic accretion during the supernova event, which is expected to be aligned with the binary companion. Such a high-velocity NS will capture mass (∼10−5 M⊙) from a near miss of the companion or from the supernova debris. This mass is ×10 the mass required to power an initial soft gamma-ray repeater (SGR) phase for 104 y as well as later 105 GRBs in 3×108 y, (assuming one fast NS per 100 years). Following the SGR phase, the disk cools and condenses into a quiescent solar system type disk of grains, rocks and planetoids in ∼30 My. When the mass of one planetoid exceeds the critical scattering mass, ∼1022 to 23 g, some planetoids will be scattered into highly elliptic orbits and break up close to the NS. The orbits of the debris will decay forming a sequence of dense, degenerate, accretion disks, which evolve by radiation cooling and the internal friction of solidification. A disk mass of ∼1021 to 22 g results in a thin disk whose Alvén radius is close to that of the NS. The velocity of the disk crossed with the strong magnetic field creates high electric fields, large enough to cause vacuum break-down and electron-positron cascades. The displacement current from producing the electric field as well as the break-down current results in the torque of accretion. The break-down cascade process leads to both the characteristic soft spectrum of Iν∝ν1/3, and an observed log-normal distribution of the fluences of the peaks.