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

• Published in: Solar physics Vol. 295; no. 9
• Main Authors: Grechnev, V. V., Meshalkina, N. S., Uralov, A. M., Kochanov, A. A., Lesovoi, S. V., Myshyakov, I. I., Kiselev, V. I., Zhdanov, D. A., Altyntsev, A. T., Globa, M. V.
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01-09-2020; Springer Nature B.V
• Subjects: Astrophysics and Astroparticles; Atmospheric Sciences; Configurations; Flares; Hard X-rays; Magnetic reconnection; Microwave spectra; Physics; Physics and Astronomy; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; X ray sources; X-rays; Prominences, active; Magnetic reconnection; Radio bursts; X-ray bursts; Magnetic fields; Flares
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-020-01702-3

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 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 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.