arXiv subjects
Publications and source records attributed to Shizuo Iwamoto.
We numerically calculate the energy and momentum transfer rates due to Coulomb scattering between two fluids moving with a relative velocity. The results are fitted by simple functions. The fitting formulae are useful to simulate outflows from active galactic nuclei and compact high energy sources.
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 $t_{\rm dur}$. In the acceleration regime the matter shell is pushed from behind by radiation pressure. The Lorentz factor of the shell reaches the maximum value $η$ at $r \simeq η^2 c t_{\rm dur}$. After the fireball enters the coasting regime, the velocity distribution in the shell becomes very flat. The shell expansion rate $d W/dr$ can be much smaller than $η^{-2}$. 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.