Electron acceleration by the reconnection outflow shock during solar flares

Abstract

During solar flares a large amount of nonthermal electromagnetic radiation up to the γ -ray range is emitted from the corona, which implies that energetic electrons are generated. Within the framework of the magnetic reconnection scenario, jets appear in the outflow region and can establish standing fast-mode shocks if they penetrate the surrounding plasma at super-Alfvenic speed. These shocks can be a source of energetic electrons. During the solar event on October 28, 2003, an enhanced flux of hard X- and γ -rays up to 10 MeV as observed by the INTEGRAL spacecraft indicates the generation of relativistic electrons. The radio signature of a standing shock wave appeared simultaneously with the enhanced hard X- and γ -ray fluxes. Here, we assume this shock is the source of the highly energetic electrons needed for the hard X- and γ -ray, as well as for the nonthermal radio radiation. The electrons are energized by shock drift acceleration, which is treated in a fully relativistic manner. After acceleration, the electrons travel along the magnetic field lines towards the denser chromosphere, where they emit hard X- and γ -ray radiation via bremsstrahlung. The observed photon fluxes in the range 7.5-10 MeV are explained by these theoretical results that adopt the coronal conditions found for the event on October 28, 2003.