Fireball Heated by Neutrinos

The fireball, the promising model of the gamma-ray burst (GRB), is an opaqueradiation plasma, whose energy is significantly greater than its rest mass. Wenumerically simulate the evolution of the fireball heated by theneutrino-antineutrino annihilation process for the spherically symmetric case.We also derive analytical energy and momentum deposition rates via neutrinoscattering with thermalized electron-positron pairs in the fireball. In oursimulation the matter is provided around the neutrinosphere before neutrinosstart to be emitted, and the energy is injected during a finite period of time$t_{\rm dur}$. In the acceleration regime the matter shell is pushed frombehind by radiation pressure. The Lorentz factor of the shell reaches themaximum value $\eta$ at $r \simeq \eta^2 c t_{\rm dur}$. After the fireballenters the coasting regime, the velocity distribution in the shell becomes veryflat. The shell expansion rate $d W/dr$ can be much smaller than $\eta^{-2}$.The runaway of temperature of the fireball due to neutrino scattering withelectron-positron pairs does not occur in most cases. The energy deposition dueto scattering is not so significant.Comment: 26 pages, 11figures. To appear in ApJ Part 1, December 10, 200