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Astron. Astrophys. 331, 793-799 (1998)

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Alfvén wave transmission and particle acceleration in parallel shock waves

R. Vainio 1 and R. Schlickeiser 2

1 Space Research Laboratory, Department of Physics, FIN-20014 Turku University, Finland *
2 Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 25 September 1997 / Accepted 10 November 1997


We study Alfvén 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 Alfvénic Mach number shocks.

Key words: acceleration of particles – shock waves – turbulence – cosmic rays

* SRL is financially supported by the Academy of Finland

Send offprint requests to: R. Vainio

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998