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

• Published in: arXiv.org
• 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: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 22.09.2020
• Subjects: Configurations; Flares; Gamma rays; Microwave spectra; Physics - Solar and Stellar Astrophysics; X ray sources; X-rays
• DOI: 10.48550/arxiv.2009.10350

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.