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Astron. Astrophys. 345, 298-306 (1999)

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Particle acceleration at oblique shocks and discontinuities of the density profile

U.D.J. Gieseler 1, J.G. Kirk 1, Y.A. Gallant 2 and A. Achterberg 2

1 Max-Planck-Institut für Kernphysik, Postfach 10 39 80, D-69029 Heidelberg, Germany
2 Sterrenkundig Instituut Utrecht, Postbus 80 000, 3508 TA Utrecht, The Netherlands

Received 28 October 1998 / Accepted 8 February 1999


In the theory of diffusive acceleration at oblique shock fronts the question of the existence of a discontinuity of energetic particle density is contentious. The resolution of this problem is interesting from a theoretical point of view, and potentially for the interpretation of observations of particle densities at heliospheric shocks and of high-resolution radio observations of the rims of supernova remnants. It can be shown analytically that an isotropic particle distribution at a shock front implies continuity of the particle density - whether or not the shock is oblique. However, if the obliquity of the shock induces an anisotropy, a jump is permitted. Both semi-analytic computations and Monte-Carlo simulations are used to show that, for interesting parameter ranges, a jump is indeed produced, with accelerated particles concentrated in a precursor ahead of the shock front.

Key words: acceleration of particles – shock waves – methods: numerical – ISM: cosmic rays – ISM: supernova remnants

Present address: University of Minnesota, Department of Astronomy, 116 Church St. S.E., Minneapolis, MN 55455, USA

Send offprint requests to: gieseler@msi.umn.edu

© European Southern Observatory (ESO) 1999

Online publication: April 12, 1999