The gyro-synchrotron radiation from moving type IV sources in the solar corona

Calculations of the gyro-synchrotron emission are made for conditions which might be expected in moving type IV sources in the solar corona. Two simple models for an evolving source are treated: a uniform cube and an inhomogeneous sphere. The results suggest that most moving sources have the following features: (1) A rather strong magnetic field, 10 G, is carried out within the source. This is required to achieve the high degree of circular polarization often observed. (2) Synchrotron self-absorption causes the source to be optically thick at frequencies less than about 100 MHz, thus restricting the bandwidth of the radiation. The self-absorption decreases as the source moves outward and expands. The turnover frequency, which separates the optically thick and thin spectral regimes, moves rapidly to lower frequencies, accompanied by a change from low to high circular polarization. In the case of an inhomogeneous source, the source appears to be larger at the lower frequencies. (3) Razin-Tsytovich suppression cannot be an important factor in determining the characteristics of most sources.Exchange visitor from the Department of Astro-Geophysics, University of Colorado, Boulder, Colorado, U.S.A.