Perpendicular relativistic shocks in magnetized pair plasma

Abstract

Perpendicular relativistic ($\\gamma_0=10$) shocks in magnetized pair plasmas\nare investigated using two dimensional Particle-in-Cell simulations. A\nsystematic survey, from unmagnetized to strongly magnetized shocks, is\npresented accurately capturing the transition from Weibel-mediated to\nmagnetic-reflection-shaped shocks. This transition is found to occur for\nupstream flow magnetizations $10^{-3}<\\sigma<10^{-2}$ at which a strong\nperpendicular net current is observed in the precursor, driving the so-called\ncurrent-filamentation instability. The global structure of the shock and shock\nformation time are discussed. The MHD shock jump conditions are found in good\nagreement with the numerical results, except for $10^{-4} < \\sigma < 10^{-2}$\nwhere a deviation up to 10\\% is observed. The particle precursor length\nconverges toward the Larmor radius of particles injected in the upstream\nmagnetic field at intermediate magnetizations. For $\\sigma>10^{-2}$, it leaves\nplace to a purely electromagnetic precursor following from the strong emission\nof electromagnetic waves at the shock front. Particle acceleration is found to\nbe efficient in weakly magnetized perpendicular shocks in agreement with\nprevious works, and is fully suppressed for $\\sigma > 10^{-2}$. Diffusive Shock\nAcceleration is observed only in weakly magnetized shocks, while a dominant\ncontribution of Shock Drift Acceleration is evidenced at intermediate\nmagnetizations. The spatial diffusion coefficients are extracted from the\nsimulations allowing for a deeper insight into the self-consistent particle\nkinematics and scale with the square of the particle energy in weakly\nmagnetized shocks. These results have implications for particle acceleration in\nthe internal shocks of AGN jets and in the termination shocks of Pulsar Wind\nNebulae.\n