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Astron. Astrophys. 322, 696-703 (1997)

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Electron acceleration at steepened magnetic field structures in the vicinity of quasi-parallel shock waves

H.-T. Claßen and G. Mann

Astrophysikalisches Institut Potsdam, Observatorium für solare Radioastronomie, Telegrafenberg A31, D-14473 Potsdam, Germany

Received 14 October 1996 / Accepted 5 December 1996


The acceleration of charged particles at shock waves plays an important role in many fields of astrophysics, but only a few shocks can be observed by in-situ measurements. Extraterrestrial measurements at Earth's bow shock and interplanetary shock waves show that supercritical, quasi-parallel shock waves are accompanied by large-amplitude magnetic field fluctuations (so-called steepened wave structures) in the upstream region. Test particle calculations with modelled electric and magnetic fields of such steepened wave structures yield the acceleration of thermal electrons up to nearly relativistic velocities (kinetic energy in the keV range). For smoothly varying magnetic fields an analytical treatment is possible in the framework of adiabatic theory. These analytical calculations show that the acceleration of electrons is caused by a particle drift in the direction of the electric field due to a noncoplanar component of the magnetic field at the steepened field structures. As an application of this result the generation of solar type II radio bursts - the radio signature of electrons accelerated at coronal shock waves - is briefly discussed.

Key words: shock waves: acceleration of particles – Sun: radio radiation

Send offprint requests to: H.-T. Claßen

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998