On Speeds of Exciter Beams of Interplanetary Type III Radio Bursts

Vratislav Krupar, Paris Observatory, Paris, France, Eduard Kontar, University of Glasgow, Glasgow, G12, United Kingdom, Jan Soucek, Academy of Sciences of the Czech Republic, Prague, Czech Republic, Ondrej Santolik, Institute of Atmospheric Physics ASCR, Department of Space Physics, Prague, Czech Republic, Milan Maksimovic, LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, Meudon, France, Meudon, France and Oksana Kruparova, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
Abstract:
Type III radio bursts are intense radio emissions triggered by beams of energetic electrons often associated with solar flares. These exciter beams propagate outward the Sun along an open magnetic field line in the corona and the interplanetary medium at large distances beyond 1 AU, where energetic electrons can be detected in situ by spacecraft. We performed a statistical survey of 20 simple and isolated interplanetary Type III radio bursts observed by STEREO/Waves between January 2013 and June 2014. We investigated time – frequency profiles to derive speeds of exciter electron beams. We present evidence that these beams decelerate in the solar wind. Obtained beam speeds range from 0.05c up to 0.55c depending on initial assumptions. It corresponds to electron energies between tens of eV and hundreds of keV.
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