Energetic Electrons Accelerated in Solar Particle Events
Robert P. Lin
Physics Dept & Space Sciences Laboratory, University of California, 
Berkeley, California, USA

New measurements of energetic solar electrons from the WIND spacecraft are reviewed, and the implications for particle acceleration mechanisms discussed. The electron energy spectrum in solar impulsive events is often found to extend below ~1 keV, indicating that acceleration occurs high in the corona. Two types of impulsive events are found, those where the electrons are released from the Sun at the onset of the solar type III radio burst, and those where they are released up to ~0.5 hour later. The latter events are proton-rich, and coronal transient waves are usually detected traveling across the Sun by the SOHO EIT instrument. Timing analyses show that in some events the first arriving ions (assumed protons) are released ~0.5 - 2 hours after the electrons and travel a path length of ~1.2 AU (essentially scatter-free), while in other events the ions are released at the same time as the electrons but travel ~2 AU. Solar hard X-ray and gamma-ray observations (which provide information on energetic electrons and ions, respectively, at the Sun) are compared with the energetic particle measurements made in the interplanetary medium. In mid-2000 the High Energy Solar Spectroscopic Imager (HESSI) mission will be launched to provide detailed X-ray and gamma-ray imaging and spectroscopy observations to study particle acceleration and energy release processes at the Sun. Comparisons between HESSI and ACE/WIND will provide new insights into the origins of energetic solar particles.