Cosmic ray diffusive acceleration at shock waves with finite upstream and downstream escape boundaries

M. Ostrowski; R. Schlickeiser

doi:10.1007/bf00146347

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arXiv · astro-ph/9604112

Cosmic ray diffusive acceleration at shock waves with finite upstream and downstream escape boundaries

M. Ostrowski·R. Schlickeiser

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Abstract

In the present paper we discuss the modifications introduced into the first-order Fermi shock acceleration process due to a finite extent of diffusive regions near the shock or due to boundary conditions leading to an increased particle escape upstream and/or downstream the shock. In the considered simple example of the planar shock wave we idealize the escape phenomenon by imposing a particle escape boundary at some distance from the shock. Presence of such a boundary (or boundaries) leads to coupled steepening of the accelerated particle spectrum and decreasing of the acceleration time scale. It allows for a semi-quantitative evaluation and, in some specific cases, also for modelling of the observed steep particle spectra as a result of the first-order Fermi shock acceleration. We also note that the particles close to the upper energy cut-off are younger than the estimate based on the respective acceleration time scale. In Appendix A we present a new time-dependent solution for infinite diffusive regions near the shock allowing for different constant diffusion coefficients upstream and downstream the shock.

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M. Ostrowski, R. Schlickeiser. 1996-04-18. Cosmic ray diffusive acceleration at shock waves with finite upstream and downstream escape boundaries. https://doi.org/10.1007/bf00146347

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