Abstract
Two-dimensional maps of radio brightness temperature and polarization, computed assuming thermal emission with free-free and gyroresonance absorption, are compared with observations of active region 2502, performed at Westerbork at λ = 6.16 cm during a period of 3 days in June 1980. The computation is done assuming a homogeneous model in the whole field of view (5′ × 5′) and a force-free extrapolation of the photospheric magnetic field observed at MSFC with a resolution of 2″.34. The mean results are the following:
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(a)
A very good agreement is found above the large leading sunspot of the group, assuming a potential extrapolation of the magnetic field and a constant conductive flux in the transition region ranging from 2 × 106 to 107 erg cm−2s−1.
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(b)
A strong radio source, associated with a new-born moving sunspot, cannot be ascribed to thermal emission. It is suggested that this source may be due to synchrotron radiation by mildly relativistic electrons accelerated by resistive instabilities occurring in the evolving magnetic configuration. An order-of-magnitude computation of the expected number of accelerated particles seems to confirm this hypothesis.
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On leave from Universita di Firenze (Italy).
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Chiuderi Drago, F., Alissandrakis, C. & Hagyard, M. Microwave emission above steady and moving sunspots. Sol Phys 112, 89–105 (1987). https://doi.org/10.1007/BF00148490
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DOI: https://doi.org/10.1007/BF00148490