X-ray Observations of a Coronal Mass Ejection (CME) Core with Solar Orbiter/STIX

While the brightest X-ray emission from solar eruptive events originates from the flare arcades in the lower corona, the core of the associated Coronal Mass Ejection (CME) also emits X-rays. However, identifying this emission with current X-ray instruments can only readily be done when the flare arcade is occulted by the solar limb. Solar Orbiter and other spacecraft beyond Earth-orbit now enable us to study solar eruptive events from multiple vantage points. Here, we present observations of a CME core observed on 2022-02-15. We study its evolution by comparing images from Solar Orbiter’s Spectrometer/Telescope for Imaging X-rays (STIX) with those from EUV imagers including Solar Orbiter’s EUI/FSI large-field-of-view telescope, SDO/AIA and STEREO/EUVI. Using X-ray spectroscopy, we find that the escaping CME core not only shows a high temperature (>15MK), but the spectral fitting indicates the existence of non-thermal (>10 keV) electrons within the core. Our study showcases the unique capabilities of Solar Orbiter/STIX for probing the energetics of CME cores, and how multi-spacecraft observations from different vantage points provide a 3D approach to reveal energetically significant sources that are otherwise hidden.