Astron. Astrophys. 348, 249-250 (1999)

1. Introduction

The observation of millisecond microwave spikes from the Sun has been interpreted as gyrosynchrotron maser emission since the late 1970`s (Wu & Lee 1979; Holman et al. 1980). Melrose and Dulk (1982) have used the semi-relativistic approximation to derive approximate formulae for the frequency of the largest growth rate, and for the growth rate. Aschwanden (1990a,1990b) followed the evolution of the ECM numerically, and gives frequencies and angles of largest growth. All previous studies concentrated on the growth rate of the amplified wave, while we use the absorption coefficient approach of Ramaty (1969), and calculate the frequencies at which the absorption coefficient is negative.

© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999
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