Dual frequency observations of solar microwave bursts using the VLA

Abstract

Simultaneous observations at 2 and 6 cm wavelengths of a solar active region and of microwave bursts were carried out with the VLA. The quiescent 6 cm emission is strongly associated with photospheric sunspots and is dominated by gyroresonance radiation. The emission at 2 cm, on the other hand, is due to free-free mechanism, and it originates from the chromosphere-corona transition region. The bursts observed have multiple peaks. Two-dimensional snapshot maps have been produced at 6 and 2 cm. From the brightness temperature and the degree of circular polarization, the magnetic field in the microwave burst sources has been estimated. The generating mechanisms responsible for 6 and 2 cm radiation are discussed; it is concluded that the 6 cm radiation in the bursts studied here originates from the bulk heated plasma, whereas the 2 cm radiation is due to the nonthermal particles generated in the energy-release process.