Energy spectra of Solar Energetic Electron Events Observed with Solar Orbiter

The identification of the phenomena responsible for the acceleration of solar energetic particles (SEP) still challenges current research and limits our forecasting abilities of SEP events. Even the most recent space missions, such as Solar Orbiter and Parker Solar Probe, are still not reaching close enough distances to the Sun to be able to make direct measurements of the acceleration processes without the effects of transport mechanisms.

The analysis of SEP spectra is crucial to infer the underlying acceleration mechanisms of SEPs as different mechanisms are characterised by different spectral shapes and features. Making this connection can, however, be challenging as transport effects are also known for altering spectral shapes, and these processes are not fully understood either.

Our analysis focuses on solar energetic electrons (SEEs). The acceleration of SEEs, especially by shocks, still raises multiple questions in our field. In our analysis we use the novel measurements of the Energetic Particle Detector (EPD) on board
the Solar Orbiter spacecraft. EPD detects energetic particles with unprecedented time and energy-resolution (1-second resolution covering energies from the suprathermal to relativistic range). This data product, together with Solar Orbiter’s varying distances to the Sun, allows us to characterise features of the energy spectra of SEEs better than ever before and to pin down transport effects.

We determine the peak intensity spectra of more than 200 SEE events using newly developed techniques, taking into account velocity dispersion as well as the pitch angle coverage of the instruments. We determine and characterise the spectral features of each event by fitting the spectra with multiple mathematical models.

We will present the results of our statistical analysis and discuss which spectral features can be associated with acceleration or transport effects.