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High dynamic range multifrequency radio observations of a solar active region
White, S. M.; Kundu, M. R.; Gopalswamy, N.
AA(Maryland, University, College Park), AB(Maryland, University, College Park), AC(Maryland, University, College Park)
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 78, Feb. 1992, p. 599-617. (ApJS Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Solar Activity, Solar Radio Emission, Brightness Temperature, Solar Magnetic Field, Thermal Emission, Very Large Array (Vla)
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High-dynamic-range multifrequency radio observations of a solar active region are presented. The evolution of the region is followed at 5 GHz as it rotates from the limb to disk center, and when it is at disk center, observations at 0.33, 1.5, 5, 8.4, and 15 GHz are used to analyze the distribution of density and magnetic field within the active region. A dynamic range of up to 1500 (at 8.4 GHz) was achieved because these data were well suited to the self-calibration technique. The signatures of both optically thick gyroresonance emission are unambiguously identified, and magnetic fields and optically thin thermal free-free emission are outlined. Images are compared at 5 and 8.4 GHz in order to identify regions in the trailing part of the active region where optically thin four-harmonic gyroresonance emission is contributing to the observed brightness temperatures at 5 GHz, indicating the presence of 450 G fields.

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