Solar origin of in-situ near-relativistic electron spikes observed with SEPT/STEREO

Abstract

During 2010–2011 the Solar Electron Proton Telescope (SEPT) onboard the twin STEREO spacecraft detected a number of typical impulsive electron events showing a prompt intensity onset followed by a long decay, as well as several near-relativistic so-called electron spike events. These spikes are characterized by a very short duration of below 10–20 min at FWHM, almost symmetric time profiles, velocity dispersion and strong anisotropy, revealing a very weak scattering during particle propagation from the Sun to STEREO. Spikes are detected at energies below 300 keV and appear simulateneously with type III radio bursts detected by SWAVES/STEREO and narrow EUV jets in active regions. Using particle, EUV and radio imaging observations we found that near-relativistic electrons were accelerated simultaneously and at the same location as the electrons emitting the accompanying type III radio bursts and together with coronal EUV jets. Furthermore, the sources of type III radio bursts match very well the locations and the trajectories of the associated EUV jet. Applying a particle propagation model we demonstrate that the spike characteristics reflect both, properties of the accelerator and effects of interplanetary propagation.