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Monte Carlo Simulations of Particle Acceleration at Oblique Shocks

Published online by Cambridge University Press:  12 April 2016

Matthew G. Baring ,
Donald C. Ellison  and
Frank C. Jones
Matthew G. Baring
Affiliation:
Laboratory for High Energy Astrophysics, Code 665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771
Donald C. Ellison
Affiliation:
Department of Physics, North Carolina State University, Box 8202, Raleigh NC 27695
Frank C. Jones
Affiliation:
Laboratory for High Energy Astrophysics, Code 665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771

Abstract

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The Fermi shock acceleration mechanism may be responsible for the production of high-energy cosmic rays in a wide variety of environments. Modeling of this phenomenon has largely focused on plane-parallel shocks, and one of the most promising techniques for its study is the Monte Carlo simulation of particle transport in shocked fluid flows. One of the principal problems in shock acceleration theory is the mechanism and efficiency of injection of particles from the thermal gas into the accelerated population. The Monte Carlo technique is ideally suited to addressing the injection problem directly, and previous applications of it to the quasi-parallel Earth bow shock led to very successful modeling of proton and heavy ion spectra, as well as other observed quantities. Recently this technique has been extended to oblique shock geometries, in which the upstream magnetic field makes a significant angle ΘB1 to the shock normal. In this paper, spectral results from test particle Monte Carlo simulations of cosmic-ray acceleration at oblique, nonrelativistic shocks are presented. The results show that low Mach number shocks have injection efficiencies that are relatively insensitive to (though not independent of) the shock obliquity, but that there is a dramatic drop in efficiency for shocks of Mach number 30 or more as the obliquity increases above 15°. Cosmic-ray distributions just upstream of the shock reveal prominent bumps at energies below the thermal peak; these disappear far upstream but might be observable features close to astrophysical shocks.

Subject headings: acceleration of particles — cosmic rays — shock waves

Type
Planetary Environments
Information
International Astronomical Union Colloquium , Volume 142: Particle Acceleration Phenomena in Astrophysical Plasmas , 1994 , pp. 547 - 552
Copyright
Copyright © The American Astronomical Society 1994

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