Fireball Heated by Neutrinos

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 neutrinoantineutrino 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 tdur. In the acceleration regime the matter shell is pushed from behind by radiation pressure. The Lorentz factor of the shell reaches the maximum value η at r ≃ ηctdur. 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 η. 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. Subject headings: gamma rays: bursts—hydrodynamics—neutrinos