Non-linear Guiding Center Theory and Acceleration of Cosmic Rays at Supernova Remnant Shocks

Abstract

Supernova Remnant shocks have long been identified as the major site of cosmic ray acceleration. At the shock front, cosmic rays traverse upstream and downstream multiple times and gain energies up to 1013–14 eV and perhaps even reach 1018 eV. The maximum achievable energy at a SNR shock is decided by many factors. Among these, shock geometry is an important one. Using a simple quasi‐linear theory, Jokipii [1] showed that the acceleration rate at a perpendicular shock can be orders of magnitude faster than that at a quasi‐parallel shock. Consequently, high energy cosmic rays are produced at quasi‐perpendicular portion of a SNR shock. The perpendicular diffusion coefficient used in Jokipii [1], however, do not agree with careful numerical calculations. In this paper, we discuss cosmic ray acceleration at SNR shock using the Non Linear Guiding Center (NLGC) Theory for κ⊥. We show that at an oblique shock, the generation of Alfven waves along the upstream magnetic field direction will reduce κ‖, which is cou...