JOINT HIGH TEMPERATURE OBSERVATION OF A SMALL C6.5 SOLAR FLARE WITH IRIS/EIS/AIA

Abstract

We present the observation of a C6.5 class flare on 2014 February 3, obtained with the Interface Region Imaging Spectrograph (IRIS) and the EUV Imaging Spectrometer (EIS) on board HINODE. We follow the details of the impulsive phase with IRIS and the gradual decay phase with both IRIS and EIS. The IRIS Slit-Jaw Imager and Atmospheric Imaging Assembly (AIA) are used to precisely co-align the two sets of spectroscopic observations. Of particular interest is the Fe xxi 1354.08 Å spectral line, which is the highest temperature emission (∼10 MK) observed in the IRIS wavelength range. We show the evolution of the Fe xxi profiles during the impulsive phase of the flare at the same ribbon location with a 75 s temporal cadence. Totally blueshifted (∼82 km ) profiles are found at the very early phase of the flare and gradually decrease in about 6 minutes. This result is consistent with 1D model predictions during chromospheric evaporation in flares. The blueshifted components also exhibit large non-thermal broadening, which decreases simultaneously with the blueshifted velocity. After the evaporation first occurs, the Fe xxi intensity progressively moves from the footpoints to the top of the hot flare loops seen in the AIA 131 Å images, where the emission is observed to be at rest and thermal. Emission measure estimates from IRIS/EIS/AIA observations during the gradual phase show isothermal loop top structures cooling from about 13.5 to 12 MK with electron densities of the order of .