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arXiv · 2009.10350

Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra

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
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Abstract

On 23 July 2016 after 05:00\,UTC, the first 48-antenna stage of the Siberian Radioheliograph detected two flares of M7.6 and M5.5 GOES importance that 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 gamma-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. The unusual properties of the microwave spectra are accounted for by a distributed multi-loop system in an asymmetric magnetic configuration that our modeling confirms. Microwave images did not to resolve compact configurations in these flares that may also be revealed incompletely in hard X-ray 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 three-ribbon eruptive flares in a configuration with a coronal-null region, the first eruption causes a flare and facilitates the second eruption that also results in a flare.

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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. 2020-09-22. Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra. https://doi.org/10.1007/s11207-020-01702-3

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