Fireball Heated by Neutrinos

Abstract

The fireball, the promising model of the gamma-ray burst (GRB), is an opaque radiation plasma, whose energy is significantly greater than its rest mass. We numerically simulate the evolution of the fireball heated by the neutrino-antineutrino annihilation process for the spherically symmetric case. We also derive analytical energy and momentum deposition rates via neutrino scattering with thermalized electron-positron pairs in the fireball. In our simulation the matter is provided around the neutrinosphere before neutrinos start to be emitted, and the energy is injected during a finite period of time $t_{\mathrm{dur}}$. In the acceleration regime the matter shell is pushed from behind by radiation pressure. The Lorentz factor of the shell reaches the maximum value $\eta$ at $r\simeq {\eta }^{2}c{t}_{\mathrm{dur}}$. After the fireball enters the coasting regime, the velocity distribution in the shell becomes very flat. The shell expansion rate $dW/dr$ can be much smaller than ${\eta }^{-2}$. The runaway of temperature of the fireball due to neutrino scattering with electron-positron pairs does not occur in most cases. The energy deposition due to scattering is not so significant.

26 pages, 11figures. To appear in ApJ Part 1, December 10, 2002