VLA observations of solar active regions. I - The slowly varying component

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In the considered investigation, it is argued that the substantial part of the radio flux from solar active regions at 6 cm wavelength is actually due to bremsstrahlung from plage-associated sources. A two-component model is needed in which only the sunspot-associated component is due to gyroresonant processes. Such a two-component model has been previously suggested by Pallavicini et al. (1979, 1980) on the basis of a comparison of 2.8 cm and X-ray observations. Very Large Array (VLA) synthesis maps of the active region AR 2032 at 6 cm wavelength are presented. The maps are compared with H-alpha photographs and magnetograms of the same region. The synthesis maps indicate that the radio emission is dominated by a small (approximately 30 seconds), bright (approximately 1 million K), circularly polarized (approximately 30%) source whose morphological features are correlated with the chromospheric plage seen as bright regions on the H-alpha photographs. A description is presented of radio wavelength observations of bursts which are composed of elementary events whose temporal evolution is very similar to that detected at hard X-ray wavelengths.