Turbulent propagation of high-energy electrons in a solar coronal loop

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Abstract
Aims.We study the solar flare on 28 August 1999 observed by the Nobeyama Radioheliograph at 17 and 34 GHz and analyze the unusual behavior of microwave source (a coronal loop) after injections of high-energy electrons. The observations reveal a propagation velocity of the emission front along the loop of about 104 km s-1, which is 30 times less than the velocity of high-energy electrons generating gyrosynchrotron emission at 17 and 34 GHz. The main goal is to understand the physical origin of this electron propagation.Methods.We interpret this anomalous propagation in terms of the collective effects of relativistic electrons interacting with plasma turbulence. A cloud of highly energetic electrons responsible for microwave emission generates low-frequency whistler waves, and a turbulent “wall” in the loop is formed.Results.The electrons undergo strong resonant scattering due to wave-particle interaction, and the emission front propagates with the wave phase velocity, which is much lower than the particle velocity.