Solar flares in the Solar Orbiter era: Short-exposure EUI/FSI observations of STIX flares

¹ University of Applied Sciences and Arts Northwestern Switzerland (FHNW), Bahnhofstrasse 6, 5210 Windisch, Switzerland
² ETH Zürich, Rämistrasse 101, 8092 Zürich, Switzerland
³ European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ, Noordwijk, The Netherlands
⁴ Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
⁵ Space Sciences Laboratory, University of California, 7 Gauss Way, 94720 Berkeley, USA
⁶ Lockheed Martin Solar & Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA 94304, USA
⁷ Solar-Terrestrial Centre of Excellence (SIDC), Royal Observatory of Belgium, Ringlaan 3 Av. Circulaire, 1180 Brussels, Belgium
⁸ PMOD/WRC, Dorfstrasse 33, CH-7260 Davos Dorf, Switzerland
⁹ University College London, Mullard Space Science Laboratory, Holmbury Hill Rd, Dorking RH5 6NT, UK

^⋆ Corresponding author; hannah.collier@fhnw.ch

Received: 8 August 2024
Accepted: 7 November 2024

Abstract

Aims. This paper aims to demonstrate the importance of short-exposure extreme ultraviolet (EUV) observations of solar flares in the study of particle acceleration, heating, and energy partition in flares. This work highlights the observations now available from the Extreme Ultraviolet Imager (EUI) instrument suite on board Solar Orbiter while operating in short-exposure mode.

Methods. A selection of noteworthy flares observed simultaneously by the Spectrometer Telescope for Imaging X-rays (STIX) and the Full Sun Imager of EUI (EUI/FSI) are detailed. New insights are highlighted and potential avenues of investigation are demonstrated, including forward-modelling of the atmospheric response to a non-thermal beam of electrons using the RADYN 1D hydrodynamic code, in order to compare the predicted and observed EUV emission.

Results. The examples given in this work demonstrate that short-exposure EUI/FSI observations are providing important diagnostics during flares. A dataset of more than 9000 flares observed by STIX (from November 2022 until December 2023) with at least one short-exposure EUI/FSI 174 Å image is currently available. The observations reveal that the brightest parts of short-exposure observations consist of substructure in flaring ribbons that spatially overlap with the hard X-ray emission observed by STIX in the majority of cases. We show that these observations provide an opportunity to further constrain the electron energy flux required for flare modelling, among other potential applications.