Tracking a solar energetic eruption and associated energetic particles from the Sun to spacecraft

Solar energetic particles (SEPs) in the heliosphere are produced by flaring processes on the Sun or shocks driven by coronal mass ejections (CMEs). Electrons in particular are regularly detected remotely as electromagnetic radiation (X-rays or radio emission) --- which they generate through various processes --- as well as in situ by spacecraft monitoring the Sun and the heliosphere. We aim to combine remote-sensing and in situ observations of an energetic solar eruption to link energetic processes in the solar corona to energetic particles observed in situ in the heliosphere. This will be done using the tools developed in the Horizon Europe SOLER project. We investigated a solar energetic eruption at the Sun together with its associated signatures of accelerated electrons observed at radio and X-ray wavelengths and combined these remote observations to in situ particles observed by spacecraft on 10 March 2024. These observations were combined with a magneto-hydrodynamic (MHD) model of the solar corona in order to make the remote to in situ connections. We observe a high-energy SEP event at multiple spacecraft (>25 MeV protons and 1 MeV electrons), despite the event being associated with a slow white-light CME. Remote observations of the Sun show that the event was associated with a fast, large-scale coronal wave (1400 km/s) and multiple regions where electrons are accelerated around this large-scale wave observed as type II radio bursts. In addition, we observe a strong coronal dimming away from the main flaring region, providing evidence of field lines being opened onto interplanetary space and dislocated from the flare site. Although we observe a slow, co-temporal CME in white light, we show that an expanding extreme-ultraviolet (EUV) dome corresponding to the upper portions of the large-scale coronal wave is likely to steepen into a shock, as shown by the presence of multiple type II radio bursts on the surface of the dome. The EUV dome, and thus a coronal shock, is a likely source of energetic particles since it is the main feature intersecting magnetic field lines connecting to spacecraft. The SEPs observed in this study also have consistently hard spectral indices at two different locations.