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

¹ Pulkovo Observatory, Russian Academy of Sciences, 65 Pulkovo, 196140 St. Petersburg, Russia e-mail: stepanov@gao.spb.ru
² Department of Earth and Planetary Science, University of Tokyo, 113-0033, Japan
³ National Astronomical Observatory, Nobeyama, Minamimaki, Minamisaku, 384-1305 Nagano, Japan
⁴ Radiophysical Research Institute, 25 B. Pecherskaya, 603600 Nizhny Novgorod, Russia

Received: 16 October 2006
Accepted: 13 December 2006

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.