Microwave plasma emission of a flare on AD Leo

¹ Pulkovo Observatory, 196140 St. Petersburg, Russia e-mail: stepanov@gao.spb.ru
² Astrophysikalisches Institut Potsdam, 14482 Potsdam, Germany
³ Institute of Applied Physics, 603600 Nizhny Novgorod, Russia e-mail: za130@appl.sci-nnov.ru
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: efuerst@mpifr-bonn.mpg.de
⁵ Universitätssternwarte Hamburg, 21029 Hamburg, Germany e-mail: jschmitt@hs.uni-hamburg.de

Corresponding author: B. Kliem, bkliem@aip.de

Received: 29 September 2000
Accepted: 6 April 2001

Abstract

An intense radio flare on the dMe star AD Leo, observed with the Effelsberg radio telescope and spectrally resolved in a band of 480 MHz centred at 4.85 GHz is analysed. A lower limit of the brightness temperature of the totally right handed polarized emission is estimated as K (with values K considered to be more probable), which requires a coherent radio emission process. In the interpretation we favour fundamental plasma radiation by mildly relativistic electrons trapped in a hot and dense coronal loop above electron cyclotron maser emission. This leads to densities and magnetic field strengths in the radio source of cm^-3 and G. Quasi-periodic pulsations during the decay phase of the event suggest a loop radius of cm. A filamentary corona is implied in which the dense radio source is embedded in hot thin plasma with temperature K and density . Runaway acceleration by sub-Dreicer electric fields in a magnetic loop is found to supply a sufficient number of energetic electrons.