Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS and RHESSI
Paulo Simões
University of Glasgow
David Graham (INAF-Ossevatorio Astrofisico di Arcetri), Lyndsay Fletcher (University of Glasgow)
We present direct evidence of the detection of the main energy release site in a non-eruptive solar flare, SOL2013-11-09T06:38~UT. The focus of our study is a compact, bright coronal source located between the flare ribbons. We use imaging from SDO/AIA, and RHESSI X-ray data to characterise the thermal and non-thermal emission from the coronal source, and EUV spectroscopy from the Hinode/EIS to analyse Doppler shifts in several Fe emission lines. The coronal source exhibited an impulsive emission lightcurve in all SDO/AIA filters during the impulsive phase. RHESSI images indicate both thermal and non-thermal emission at the coronal source, and its plasma temperature shows an impulsive rise, reaching a maximum at 12–13 MK about 10 seconds prior to the X-ray peak. High red-shifts associated with this bright source indicate downflows of 40–250 km/s at a broad range of temperatures, interpreted as loop shrinkage and/or outflows along the magnetic field. The electron density of the source obtained from a Fe XIV line pair is log n = 11.50 cm^-3 which is collisionally thick to electrons with energy up to 45-65 keV, responsible for the source's non-thermal X-ray emission. Given the rich observational evidence, we conclude that the bright coronal source is the location of the main release of magnetic energy in this flare, with a geometry consistent with component reconnection between crossing, current-carrying loops. We argue that the energy that can be released via reconnection, based on observational estimates, can plausibly account for the non-thermal energetics of the flare.