An Efficient Dissipation Mechanism of Magnetic Field by Turbulence

Recently, the Poynting dominated Gamma Ray Burst (GRB) model has become more attractive. The central engine of GRB is considered to be a core collapse of a massive star. Some theoretical studies of this core collapse of a massive star report that generated relativistic jets are magnetically driven Poynting-dominated flows. Although this mechanism has many attractive points, this also generates a new difficult problem, that is, to find some efficient dissipate mechanisms of magnetic energy in Poynting-dominated flows. Since a MHD shock in Poynting-dominated flows is a weak shock, the dissipation of upstream magnetic energy is very inefficient; so finding other efficient dissipation mechanisms becomes one of the most important studies for GRB research. We report the enhancement of the dissipation of magnetic field due to decaying turbulence in the postshock region of a Poynting flux dominated flow. We find that the turbulence stretches the current sheet that substantially enhances the dissipation of magnetic field, and almost all the initial magnetic energy are dissipated within a few eddy turnover time. We also develop a simple theoretical model of turbulent dissipation of magnetic field that agrees well with the simulations. The theoretical model indicates that the dissipation rate does not depend on the resistivity. Our finding would alleviate the conversion of the magnetic energy into thermal energy.