Microwave plasma emission of a flare on AD Leo

An intense radio flare on the dMe star AD Leo, observed with the Eelsberg 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 Tb 5 10 10 K( with valuesTb > 310 13 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 eld strengths in the radio source of n 2 10 11 cm 3 and B 800 G. Quasi-periodic pulsations during the decay phase of the event suggest a loop radius of r 7 10 8 cm. A lamentary corona is implied in which the dense radio source is embedded in hot thin plasma with temperature T 2 10 7 K and density next 10 2 n. Runaway acceleration by sub-Dreicer