STEREO observations of non-thermal electrons in the heliosphere
Nina Dresing, IEAP, University of Kiel, Germany
The two STEREO spacecraft have accumulated a vast database of solar energetic particle (SEP) events since their launch in 2006. We use data of the Solar Electron and Proton Telescope (SEPT) providing directional measurements of near-relativistic electrons in 15 energy channels to study the energy spectra of solar energetic electron events.
From 2007 to 2017 we collect in total 765 events with sufficiently high signal to noise ratio for a statistical analysis including all types of events, e.g. impulsive, gradual, accompanied by large CMEs or not. A mean spectral index of -2.7 at 70 keV is found for the whole sample where about half of the events show a broken power law shape.
A spectral difference is observed when comparing the spectra detected in the sunward and anti-sunward pointing telescopes. On average harder spectra are observed from the backside direction, which we attribute to transport effects. We further analyze the electron spectra with respect to anisotropies, event rise times, longitudinal separations to the parent flaring active regions, and presence of high energy SEPs to gain further insight on acceleration, injection, and transport effects.