Precursor Wave Amplification by Ion–Electron Coupling through Wakefield in Relativistic Shocks

We investigated electromagnetic precursor wave emission in relativistic shocks by using two-dimensional particle-in-cell simulations. We found that the wave amplitude is significantly enhanced by a positive feedback process associated with ion–electron coupling through the wakefields for high magnetization. The wakefields collapse during the nonlinear process of the parametric decay instability in the near-upstream region, where nonthermal electrons and ions are generated. The intense coherent emission and the particle acceleration may operate in high-energy astrophysical objects.