A Multi-instrument Analysis of a C4.1 Flare Occurring in a δ Sunspot
Journal
THE ASTROPHYSICAL JOURNAL
Date Issued
2016
Author(s)
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Cristaldi, A.
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Criscuoli, S.
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Zuccarello, F. P.
DOI
10.3847/0004-637X/819/2/157
Description
The research leading to these results has received fundingfrom the European Commissions Seventh Framework Pro-gramme under grant agreements no.606862 (F-CHROMA project), no.284461 (eHEROES project), and no.312495 (SOLARNET project). This work was also supported by theItalian MIUR-PRIN grant 2012P2HRCR onThe active Sun andits effects on space and Earth climate, by the Istituto Nazionale di Astrofisica (PRIN INAF 2010/2014), and by the Università degli Studi di Catania. The authors are gratefulto S. Jafarzadeh for his help in the SST/CRISP data reduction.S.L.G. and F.Z. thank Dr. L. Fletcher for a very useful discussion on this event. S.L.G. thanks Dr. J.M. Borrero for his help with the VFISV code and D.L. Distefano for his helpin editing the SST movie. The work of F.P.Z. is funded by a contract from the AXA Research Fund. F.P.Z. is a FondsWetenschappelijk Onderzoek (FWO) research fellow on leave.The Swedish 1 m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of Stockholm University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The authors wish to thank the SST staff for its support during the observing campaigns. The SDO/HMI data used in this paper are courtesy of NASA/SDO and the HMI science team. Hinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in co-operation with ESA and NSC (Norway). Use of NASA’s Astrophysical Data System is gratefully acknowledged.
Abstract
We present an analysis of multi-instrument space- and ground-based observations relevant to a C4.1 solar flare that occurred in the active region (AR) NOAA 11267 on 2011 August 6. Solar Dynamics Observatory observations indicate that at the flare’s beginning, it was localized in the preceding sunspot of the AR, which exhibits a δ configuration. Along the polarity inversion line between its opposite polarities we find a large shear angle of about 80°. The helicity accumulation shows that the AR does not obey the general hemispheric helicity rule. At the flare peak, unique observations taken with the X-Ray Telescope aboard Hinode reveal that the bulk of the X-ray emission takes place in the δ-spot region, where the plasma heats up to ≈ 1.9\cdot {10}7 K. During the gradual phase, we observe the development of a Y-shaped structure in the corona and in the high chromosphere. An extruding structure forms, being directed from the emitting region above the δ spot toward the following sunspot. This structure cools down in a few tens of minutes while moving eastward along a direction opposite to the flare ribbon expansion. Finally, remote brightenings are found at the easternmost footpoint of this structure, appearing as a third flare ribbon in the chromosphere. After some minutes, RHESSI measurements show that the X-ray emission is localized in the region close to the crossing point of the coronal Y-shaped structure. Simultaneously, high-resolution (0.″15) observations performed at the Swedish 1 m Solar Telescope indicate a decreasing trend of the Ca II H intensity in the flare ribbons with some transient enhancements. All these findings suggest that this event is a manifestation of magnetic reconnection, likely induced by an asymmetric magnetic configuration in a highly sheared region.
Volume
819
Issue
2
Start page
157
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