Identification of Two Distinct Electron Populations in an Impulsive Solar Energetic Electron Event

We examine the release times of energetic electrons in the 2001 April 25 event. An M2.7 flare occurred on 2001 April 25, from AR 09433, located at N18W09. The flare was observed in X-rays by GOES and the Yohkoh spacecraft. The Yohkoh observation also included hard X-ray (HXR) images for all four energy channels: L, M1, M2, and H. We use Yohkoh observation times as a proxy for the release time of energetic electrons that propagated downward, which are responsible for the HXRs. In situ >∼25 keV electrons were observed by the Wind spacecraft. For these electrons, we obtain the release time at the Sun using the recently developed Fractional Velocity Dispersion Analysis method. We find that the release times of outward-propagating energetic electrons are clearly delayed from those that propagated downward. Furthermore, these delayed releases are energy dependent. The implication of this delay on the underlying acceleration and trapping process of the >∼25 keV electrons at solar flares is discussed.