On the mediation of a shock front by Fermi-accelerated cosmic rays

Abstract

Fermi acceleration of high-energy cosmic ray particles by the convergingfluid flows on either side of a shock front is investigated. The effectof the preshock cosmic ray pressure in mediating the shock compressionand thereby the particle acceleration is studied for a shock in whichthis pressure can be regarded as a perturbation. The resulting spectraldistortions are dictated by the energy dependence of the spatialdiffusion coefficient and the Mach number of the shock. Examples arecomputed for diffusion coefficients independent of and proportional tothe particle momentum. The implications of these results for theefficiency of the particle acceleration mechanism are briefly discussed.