Observations of Energy-Dependent Charge States in Solar Energetic Particles

Abstract

Ionic charge states of solar energetic particles (SEPs) provide information about their source environment and acceleration process. For example, SEPs in flare-associated events typically have higher charge states than those in large, interplanetary shock-associated events. This may be explained by the dierent temperatures of the ion populations undergoing acceleration. Recently, some large SEP events have been observed with energy dependent charge states. In these cases, higher energy ions have higher charge states. This phenomenon may be a result of acceleration by shocks or flares in a collisional plasma close to the Sun. In the interplanetary medium, a moderate energy dependence may be created by rigidity-dependent shock acceleration. We present observations of energy dependent charge states for three large SEP events, using data from the ACE, SAMPEX and SOHO spacecraft. The energy range for these data extend from 0.1 MeV/nuc up to as high as 20 MeV/nuc. In each event, the iron charge states increase by at least 9 units over this energy range. These results will be discussed with respect to the cited models for energy dependent charge states.