Understanding Energetic Electrons in the Inner Heliosphere

Solar Orbiter carries with it a full complement of remote-sensing and in-situ instruments. Understanding the physics underlying the acceleration, release, and transport of relativistic electrons requires such a suite of instruments. In this presentation, we describe the energy ranges, fields of view and temporal resolution of the measurements of the different detectors in the EPD suite by particularly focusing on the energetic electron measurements. In preparation for this mission, we have studied solar energetic electron events by using a Monte-Carlo interplanetary transport model combined with an inversion procedure to fit in-situ observations by Helios at different heliocentric radial distances from the Sun. We determined the mean free paths and release times at the Sun for 15 events measured by Helios. Remarkably, we found no dependence of the radial mean free path on the heliocentric distance of the observer. On the other hand we also found that strongly diffusive events observed by Helios at small radial distances would not be observable at 1 AU. In addition, we have modelled the angular response of the four fields of view of the EPT detector and compared it with the performance of the Helios/E6 instrument. W e will present a brief discussion of both different transport processes and instrument characteristics to be taken into account in future modeling efforts for such electron events, especially targeting to observations by Solar Orbiter and Parker Solar Probe. Directional information of the particle intensities gathered simultaneously from different spacecraft is of paramount importance in order to disentangle the radial and longitudinal dependencies of particle transport, and to infer the particle release time profiles at the Sun. In addition, remote observations of the source region and the evolving properties of the accelerated electrons will provide key constraints on models for such events.