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Astron. Astrophys. 356, 377-388 (2000)


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Electron acceleration due to high frequency instabilities at supernova remnant shocks

M.E. Dieckmann  *  1, K.G. McClements 2, S.C. Chapman 1, R.O. Dendy 2,1 and L.O'C. Drury 3

1 Space and Astrophysics Group, Department of Physics, University of Warwick, Coventry CV4 7AL, UK
2 EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
3 Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland

Received 20 August 1999 / Accepted 15 February 2000

Abstract

Observations of synchrotron radiation across a wide range of wavelengths provide clear evidence that electrons are accelerated to relativistic energies in supernova remnants (SNRs). However, a viable mechanism for the pre-acceleration of such electrons to mildly relativistic energies has not yet been established. In this paper an electromagnetic particle-in-cell (PIC) code is used to simulate acceleration of electrons from background energies to tens of keV at perpendicular collisionless shocks associated with SNRs. Free energy for electron energization is provided by ions reflected from the shock front, with speeds greater than the upstream electron thermal speed. The PIC simulation results contain several new features, including: the acceleration, rather than heating, of electrons via the Buneman instability; the acceleration of electrons to speeds exceeding those of the shock-reflected ions producing the instability; and strong acceleration of electrons perpendicular to the magnetic field. Electron energization takes place through a variety of resonant and non-resonant processes, of which the strongest involves stochastic wave-particle interactions. In SNRs the diffusive shock process could then supply the final step required for the production of fully relativistic electrons. The mechanisms identified in this paper thus provide a possible solution to the electron pre-acceleration problem.

Key words: acceleration of particles – instabilities – shock waves – stars: supernovae: general

* Present address: Institutet för teknik och naturvetenskap, Linköpings Universitet, Campus Norrköping, 601 74 Norrköping, Sweden

Send offprint requests to: K.G. McClements (k.g.mcclements@ukaea.org.uk)

© European Southern Observatory (ESO) 2000

Online publication: March 28, 2000

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