Disambiguation of Cool and Hot Emission in SDO/AIA Channels and IRIS/Slit-Jaw Imager

Accurate temperature diagnostics of the solar corona are necessary for detecting the heating and cooling processes, and better understanding the conversion of the magnetic energy into thermal energy. A major obstacle in this enterprise is the multi-temperature emission contained in ultraviolet (UV) and extreme UV (EUV) passbands such as those of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) and the Slit-Jaw Imager (SJI) of the Interface Region Imaging Spectrograph (IRIS). In this work we extend the Response Fitting (RFit) method to disambiguate between cool, warm, and hot emission in the SDO/AIA and IRIS/SJI passbands. We improve previous results for AIA 304 Å and find very good cool/hot decomposition for AIA 94 Å allowing to improve previous empirical disambiguation methods for this passband. The hot temperature coverage of AIA allows RFit to be applied across instruments. This allows to disambiguate the hot flaring emission from Fe xxi contained within the SJI 1330 Å and SJI 1400 Å passbands, supported by IRIS spectrograph (SG) results. We further estimate that the SJI 1330 Å response function lacks
of emission at temperatures above
. Photospheric abundances help reduce this gap to
. The emission peak at
in the SJI response functions is greatly altered at different densities, which can be used, in principle, for density diagnostics. These results are basically identical to those with the Differential Emission Measure (DEM) method, with the advantage that RFit is instantaneous, unlocking the possibility of real-time measurements. We also provide lower bounds for the hot emission in AIA 211 Å, and the very hot (flaring) emission in AIA 131 Å and AIA 193 Å, which help constrain the overestimated emission from the DEM in the hot temperature range. We apply RFit to an AIA-IRIS co-observation that includes a flare, and calculate the average relative percentage contribution for the cool-hot emission to find 17/83, 96/4, 79/21, 10/90, 65/35, 65/35, respectively for AIA 94 Å, AIA 131 Å, AIA 211 Å, AIA 304 Å, SJI 1330 Å and SJI 1400 Å. We obtain a more coherent picture of the hot temperature evolution in the
 – 7.15 temperature range and its spatial localisation during the flare, and similarly for the cooling during the gradual phase. We further accurately detect and quantify the cool plasma from coronal rain, which is observed to increase seven-fold due to the flare-driven cooling.