X-ray diagnostics of thermal flare emissions by Solar Orbiter/STIX and GOES

The Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter continuously measures the Sun in the energy range 4-150 keV. Due to the spacecraft’s peculiar orbit, around 50% of all STIX flares are backside flares and lack a corresponding GOES class. In Stiefel et al. (2025) we describe the correlation between the STIX background detector and GOES measurements where we found a power-law function between the two data sets. This function can be used to get a proxy of the GOES class for large backside flares.

Building up on the approach of using the background detector of STIX, we want to discuss how we can improve the spectral fitting of the thermal emission of large flares (> X1-class) observed by STIX and discuss the occurrence of “super-hot” components (e.g. Caspi et al. (2010)) in these flares. Using imaging and spectral analysis of STIX data, we want to understand the physical origin and the temporal evolution of the super-hot component. This talk will highlight the importance of understanding the thermal emission in solar flares and the richness of information we can gain regarding the thermal emission by combining spectral and spatial observations by various X-ray instruments.