High Energy Ionic Charge State Composition in Large Solar Energetic Particle Events

Measurements of ionic charge states in solar energetic particle (SEP) events have been made at relatively high energies (> 15 MeV/nucleon) with the Mass Spectrometer Telescope (MAST) on board the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite using the Earth's magnetic field as a particle rigidity filter. We have examined the largest SEP events of solar cycle 23 and determined ionic charge states of Fe and other elements in several of these events. The mean charge state of Fe is often considerably higher (~20) in impulsive SEP events than in gradual events (~15). Surprisingly, in several cases, relatively high charge states of around 20 were found for Fe in very large events which are most likely gradual. Further, our measurements also show that Si in these events is not necessarily in thermal equilibrium with other elements.