Shock structure and magnetic-field generation associated with relativistic jets in unmagnetized pair plasma

Abstract

Using 3D and 2.5D particle-in-cell simulations we investigate the shock structure, magneticfield generation, and particle acceleration associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized pair plasma. The simulations use long computational grids which allow us to study the complete dynamics of the system. We find for the first time a relativistic shock system comparable to the predicted magnetohydrodynamic shock structure consisting of leading and trailing shocks separated by a contact discontinuity. Strong electromagnetic fields resulting from the Weibel instability are generated in the trailing shock where jet matter is thermalized and decelerated. We analyze the formation and nonlinear development through saturation and dissipation of those fields and associated particle acceleration. In the AGN context the trailing shock corresponds to the jet shock at the head of a relativistic astrophysical jet. In the GRB context this trailing shock can be identified with the bow shock driven by relativistic ejecta. The strong electromagnetic field near the trailing shock provides the emission site for afterglow emission from GRBs and may correspond to the hot spot at the leading edge of AGN jets.