Journal
ASTROPHYSICAL JOURNAL
Volume 827, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/0004-637X/827/1/27
Keywords
Sun: chromosphere; Sun: corona; Sun: flares; Sun: X-rays, gamma-rays; techniques: spectroscopic
Categories
Funding
- Norwegian Space Center (NSC, Norway)
- NSFC [11303101, 11333009, 11573072, 11473071]
- open research program of Key Laboratory of Solar Activity, National Astronomical Observatories, CAS [KLSA201510]
- Strategic Priority Research Program-The Emergence of Cosmological Structures of the CAS [XDB09000000]
- Youth Fund of Jiangsu [BK20141043]
- One Hundred Talent Program of Chinese Academy of Sciences
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In this paper, we report our multiwavelength observations of the C4.2 circular-ribbon flare in active region (AR) 12434 on 2015 October 16. The short-lived flare was associated with positive magnetic polarities and a negative polarity inside, as revealed by the photospheric line-of-sight magnetograms. Such a magnetic pattern is strongly indicative of a magnetic null point and spine-fan configuration in the corona. The flare was triggered by the eruption of a mini-filament residing in the AR, which produced the inner flare ribbon (IFR) and the southern part of a closed circular flare ribbon (CFR). When the eruptive filament reached the null point, it triggered null point magnetic reconnection with the ambient open field and generated the bright CFR and a blowout jet. Raster observations of the Interface Region Imaging Spectrograph show plasma upflow at speeds of 35-120 km s(-1) in the Fe XXI lambda 1354.09 line (log T approximate to 7.05) and downflow at speeds of 10-60 km s(-1) in the Si IV lambda 1393.77 line (log T approximate to 4.8) at certain locations of the CFR and IFR during the impulsive phase of the flare, indicating explosive chromospheric evaporation. Coincidence of the single hard X-ray source at 12-25 keV with the IFR and calculation based on the thick-target model suggest that the explosive evaporation was most probably driven by nonthermal electrons.
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