Abstract
The radio emission of a selected number of solar active regions has been investigated with high angular resolution at two frequencies: 10 and 17 GHz.
By comparing the results of the two observations the following conclusions can be drawn:
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(1)
The brightness temperature distribution of an active region is often composed of very bright cores of small dimension (angular extent θ≃20″) imbedded in extended halos of lower brightness.
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(2)
The radio emission of such structures as well as the degree of polarization can be explained with a thermal process. The halos can originate by pure thermal bremsstrahlung while in the case of the very bright cores found at 10 GHz (brightness temperature T b≃1–9 × 106K) the emission at the harmonics of the gyrofrequency is needed.
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Felli, M., Tofani, G., Fürst, E. et al. On the nature of some active regions in the microwave range. Sol Phys 42, 377–390 (1975). https://doi.org/10.1007/BF00149919
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DOI: https://doi.org/10.1007/BF00149919