Superluminal apparent velocities of relativistic electron beams in the solar corona

¹ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
² Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic

Corresponding author: A. Klassen, aklassen@aip.de

Received: 7 May 2003
Accepted: 16 July 2003

Abstract

We present spectral and imaging observations of high frequency type III bursts appearing in pairs: a primary fast drifting component and a secondary “normal" drifting component. The primary bursts have generally higher frequency drift and start at higher frequencies. They show superluminal velocities up to 2.5 c (c, speed of light), while the secondary component shows the usual <0.5 c velocity expected for type III burst exciters. These superluminal velocities are explained as apparent velocities of relativistic electron beams propagating nearly along the line of sight towards the observer with velocities close to the speed of light. A model of type III burst pairs consisting of subsequent fast drifting and “normal" drifting components is presented.