Alfven wave transmission and particle acceleration in parallel shock waves

Abstract

We study Alfven wave transmission through parallel shocks. First, the paper corrects for mistakes made in a previous study by Campeanu & Schlickeiser on the same subject. It is shown, contrary to CS, that first-order Fermi acceleration by multiple shock crossings is generally more effective than stochastic acceleration in the downstream region. Moreover, we demonstrate that in a large region of the physical parameter space the scattering center compression ratio is much larger than the gas compression ratio. This leads to flat spectra for the cosmic rays accelerated by the first-order Fermi mechanism especially at low Alfvenic Mach number shocks.