Evidence for Acceleration of Near-relativistic Electrons by Coronal Shocks

The time histories of near-relativistic impulsive electron beam events (38-315 keV, 0.4 < v/c < 0.8) measured at 1 AU provide unique information on their solar acceleration process. Nearly 80 such events have been identified by ACE/EPAM from 1997 through 2000. We have performed a detailed statistical analysis of the timing between the near-relativistic electron injection and the soft X-ray, microwave, metric type-III, and chromospheric Hα emission. We find that the 40-300 keV impulsive electron events observed at 1 AU are injected on average 10 minutes after the solar electromagnetic (EM) emissions. Consequently we rarely see 38-315 keV electron injections simultaneous with any solar electromagnetic emissions, including the metric typeIII bursts (which are known to be created by low energy electron beams escaping the corona). Therefore the electron populations escaping at the time of the EM emissions must have a much softer spectrum than the 38-315 keV electron events that are injected at a later time.