Energetic Electrons in ³He-Enhanced Solar Energetic Particle Events

Using both the Electron, Proton, and Alpha Monitor and Ultra Low Energy Isotope Spectrometer instruments on board the Advanced Composition Explorer, we investigated from 1997 September to 1999 December a total of 27 ³He-rich solar energetic particle (SEP) ion events. The majority of these events (16 out of 27) have a clear association with impulsive injections of energetic electrons (38-53 keV). However, we find that the maximum electron intensity is statistically uncorrelated with the ³He/⁴He ratio (at 0.4-2.0 MeV nucleon^-1). We therefore examined the electron associations in the general class of impulsive ⁴He ion SEP events over the same time period. The general class is statistically indistinguishable from the ³He-enhanced subclass: 43 out of 97 impulsive ⁴He ion events were associated with impulsive electron events. The weak correlations between maximum electron intensities and maximum helium intensities (either ³He or ⁴He) are statistically indistinguishable between the general class of impulsive He events and the special class that was ³He enriched. Consequently, we have found no evidence (at the energies we studied) that the energetic electron population that escapes into interplanetary space is causally involved in the preferential enrichment of ³He. However, this does not rule out the possibility that a separate (nonescaping) population of electrons in the corona participates in the preferential acceleration of ³He.