X-ray constraints on the acceleration of electrons at a coronal shock wave

Karl-Ludwig Klein

Abstract

Large scale coronal shock waves associated with type II radio bursts are frequently considered to accelerate transient energetic particle populations in the corona and in interplanetary space. Since type II bursts usually occur together with other types of emission, the distinction between shock-accelerated particles and other populations is difficult. Only a few limb-occulted events allow us to analyse separately and specifically the electrons accelerated by the coronal shock. On 1996 August 19 a coronal shock wave was generated during a flare on the backside of the Sun. No signal was observed at photon energies above 1~keV by the X-ray instruments aboard the GOES and Compton-GRO satellites. From the non detection of X-ray signatures upper limits of the number and energy content of shock-accelerated electrons are inferred. These are comparable to electrons during small hard X-ray flares produced in dense chromospheric plasma. It is argued that the coronal shock is a less efficient accelerator of electrons than the yet unidentified processes which produce superthermal electron populations during flares.

     Authors: Karl-Ludwig Klein, Richard A. Schwartz

  Organization: Observatoire de Paris-Meudon
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