2-cm Observations of Quiescent and Flaring Emission from a Solar Active Region

Astronomy and Astrophysics – Astronomy

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Scientific paper

We present 2-cm images of a solar active region comprising a large leading spot and several smaller trailing spots, observed with the VLA on 1989 Dec 14 and 16. On both days, slowly-varying quiescent emission and impulsive flaring emission were detected. Comparisons of the radio images with white-light pictures and magnetograms obtained on Dec 13 and 17 revealed that the quiescent emission originated almost entirely from above the penumbra of large spots, whereas the flaring emission originated from regions of complex magnetic field topology near but not necessarily above magnetic neutral lines. The most intense source of quiescent emission had a relatively low brightness-temperature ( ~ 10(5) K), was highly circularly polarized (ranging from about 30\ trailing edge (i.e., limbward side) of the large leading spot. We discuss models for this emission, constrained by the low brightness temperature but high polarization. The weaker flare of Dec 14 showed a single resolved source, and was weakly circularly-polarized. The stronger flare of Dec 16 comprised a strong source with multiple peaks and several weaker compact sources, all with low degrees of circular polarization. Snapshot images of this flare showed an elongated feature moving rapidly away from the main region of emission and joining with the compact sources. We discuss likely mechanisms for this feature, and emission process(es) responsible for the flares.

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