The Self-Inversion of the Sign of Circular Polarization in “Halo” Microwave Sources |
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Authors: | T I Kaltman A N Korzhavin N G Peterova |
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Institution: | (1) SAO RAS, St. Petersburg, Russia |
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Abstract: | The large active region AR NOAA 5200 from October 1988 is used to investigate the concept of the “halo,” a magnetosphere-like
structure above the active region. This structure is studied by using radio spectral polarization observations with high spatial
resolution obtained mainly with the radio telescope RATAN-600. In the case of AR 5200 the halo emission accounted for >50%
of the total AR emission. The results of the analysis of the observational data and of the model calculations allow us to
reach the following conclusions: (1) The halo is a large, nonstructured, source of emission with a size of the total AR, with
the emission centered at the dividing (neutral) line of polarities of the bipolar sunspot group. (2) The emission spectrum
allows us to distinguish two components: a thermal part and a nonthermal part. The presence of two components implies that
there are two populations of particles with different energy levels in the emission region. The phenomenon of inversion of
the polarized halo radio emission could be explained by the influence of propagation conditions inside the source. The term
“self-inversion” is introduced. The maximum in the halo density flux spectrum at wavelengths of 5 –10 cm may be explained
by scattering resulting from the strong suppression of the emissivity of nonthermal electrons at these and longer wavelengths. |
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Keywords: | Sun Circular polarization Microwave sources |
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