Weibel Instability in Hot Plasma Flows with the Production of Gamma-Rays and Electron–Positron Pairs

We present the results of theoretical analysis and numerical simulations of the Weibel instability in two counter-streaming hot relativistic plasma flows, e.g. flows of electron-proton plasma having rest-mass density $\rho \sim 10^{-4}\; \text{g}\, \text{cm}^{-3}$, Lorentz factors $\Gamma \sim 10$ and proper temperature $T \sim 10^{13}\; \text{K}$. The instability growth rate and the filament size at the linear stage are found analytically, and are in qualitative agreement with results of three-dimensional particle-in-cell simulations. In the simulations, incoherent synchrotron emission and pair photoproduction in electromagnetic fields are taken into account. If the plasma flows are dense, fast and/or hot enough, the overall energy of synchrotron photons can be much larger than the energy of generated electromagnetic fields. Furthermore, a sizable number of positrons can be produced due to the pair photoproduction in the generated magnetic field. We propose a rough criterion for judging copious pair production and synchrotron losses. By means of this criterion we conclude that incoherent synchrotron emission and pair production during the Weibel instability can have implications for the collapsar model of gamma-ray bursts.