Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra
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Twin Null-Point-Associated Major Eruptive Three-Ribbon Flares with Unusual Microwave Spectra V.V. Grechnev1 · N.S. Meshalkina1 · A.M. Uralov1 · A.A. Kochanov1 · S.V. Lesovoi1 · I.I. Myshyakov1 · V.I. Kiselev1 · D.A. Zhdanov1 · A.T. Altyntsev1 · M.V. Globa1
Received: 10 May 2020 / Accepted: 7 September 2020 / Published online: 22 September 2020 © Springer Nature B.V. 2020
Abstract 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 assoElectronic supplementary material The online version of this article (https://doi.org/10.1007/s11207-020-01702-3) contains supplementary material, which is available to authorized users.
B V.V. Grechnev
[email protected] N.S. Meshalkina [email protected] A.M. Uralov [email protected] A.A. Kochanov [email protected] S.V. Lesovoi [email protected] I.I. Myshyakov [email protected] V.I. Kiselev [email protected] D.A. Zhdanov [email protected] A.T. Altyntsev [email protected] M.V. Globa [email protected]
1
Institute of Solar-Terrestrial Physics SB RAS, Lermontov St. 126A, Irkutsk 664033, Russia
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ciated 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. Keywords Flares · Magnetic fields · Magnetic reconnection · Prominences, active · Radio bursts · X-ray bursts
1. Introduction Solar eruptions, flares, and similar weaker events draw energy from coronal magnetic fields. Such events span a vast range of energy and time scales and spatial extent and manifest in various associated phenomena. The way in which an eruption (flare) develops, its manifestations and particularities depend on the magnetic configuration that hosts the event and magnetic-field transformations that occur in its course. Magnetic reconnection is considered as the key process that governs solar
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