Non-thermal radio sources in solar active regions
Abstract
High-resolution observations of solar active regions performed at 6 cm have often shown the presence of high-temperature sources (brightness temperature greater than 2 x 10 to the 6th K) which cannot be explained simply by increasing the opacity of the coronal plasma with thermal free-free or gyroresonance absorption. These sources are explained by synchrotron emission of mildly relativistic electrons following a power-law distribution in a field of about 100 G. A type-III burst-like mechanism for the electron acceleration is proposed, and it is shown that electrons trapped in regions of low pressure can survive for about 1 h, a time longer than the average interval between two consecutive bursts in some active regions. The emissivity and the absorption coefficient in the ordinary and extraordinary waves are computed with an approximate method which gives a perfect agreement with the exact equation after the seventh harmonic. The computed brightness temperature and polarization, which perfectly agree with the observed ones at 6 cm, present a maximum at 10-15 cm.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- February 1984
- Bibcode:
- 1984A&A...131..103C
- Keywords:
-
- Nonthermal Radiation;
- Solar Activity;
- Solar Electrons;
- Solar Radio Emission;
- Synchrotron Radiation;
- Brightness Temperature;
- Magnetically Trapped Particles;
- Polarized Electromagnetic Radiation;
- Relativistic Electron Beams;
- Solar Spectra;
- Type 3 Bursts;
- Solar Physics