Interaction between Alternating Magnetic Fields and a Relativistic Collisionless Shock

Abstract

We investigate the interaction between alternating magnetic fields with cold current sheets and a relativistic collisionless shock wave. Many kinds of high-energy astrophysical objects may involve such alternating magnetic fields and a relativistic shock. They can be potent sources for the generation of high-energy particles. We found that a precursor wave, propagating upstream from the shock front, accelerates a dense current sheet plasma upstream. In the case that the width of the respective magnetic field reversal is larger than the downstream gyroradius, the current sheet generates a large-amplitude magnetosonic wave downstream by the collision with a shock front. The motional electric field accompanied by the magnetosonic wave can further accelerate the preaccelerated particles, forming a nonthermal energy spectrum. In addition, the current sheet structure is stable against not only the collision but also compression by other current sheets. In the thin current sheet case, which means the case that the width of the alternating magnetic field reversal is smaller than the downstream gyroradius, the magnetic field dissipates and the magnetosonic wave excitation is absent. This result is applied to pulsar wind nebulae. The result of the dissipation could solve the σ problem.