Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra |
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Nataliia Meshalkina Submitted: 2020-09-22 23:03
On 23 July 2016 after 05:00 UTC, the first 48-antenna stage of the Siberian Radioheliograph detected two flares, M7.6 and M5.5, which occurred within half an hour in the same active region. Their multi-instrument analysis reveals the following. The microwave spectra were flattened at low frequencies and the spectrum of the stronger burst had a lower turnover frequency. Each flare was eruptive, emitted hard X-rays and γ -rays exceeding 800 keV, and had a rare three-ribbon configuration. An extended hard X-ray source associated with a longest middle ribbon was observed in the second flare. Unusual properties of the microwave spectra are accounted for by a distributed multi-loop system in an asymmetric magnetic configuration that our modeling supports. Microwave images did not resolve compact configurations in these flares, which may also be revealed incompletely in hard Xray images because of their limited dynamic range. Being apparently simple and compact, non-thermal sources corresponded to the structures observed in the extreme ultraviolet. In the scenario proposed for two successive eruptive flares in a configuration with a coronal magnetic null, the first filament eruption causes a flare and facilitates the second eruption that also results in a flare. Three persistent flare ribbons reflect magnetic reconnection at the coronal-null region forced by the filament motions.
Authors: V.V. Grechnev, N.S. Meshalkina, A.M. Uralov, A.A. Kochanov, S.V. Lesovoi, I.I. Myshyakov, V.I. Kiselev, D.A. Zhdanov, A.T. Altyntsev, M.V. Globa
Projects: None
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Publication Status: Accepted in Solar Physics
Last Modified: 2020-09-23 13:11
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