A Novel Technique to Infer Ionic Charge States of Solar Energetic Particles

Abstract

In some large solar energetic particle (SEP) events, the intensities of higher energy SEPs decay more rapidly than at lower energies. This energy dependence varies with particle species, as would be expected if the decay timescale depended on a rigidity-dependent diffusion mean free path. By comparing the decay timescales of carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron, mean charge states are inferred for these (and other) elements in three SEP events between 1997 and 2002 at energies between 10 and 200 MeV nucleon?1. In a fourth event, upper limits for the charge states are inferred. The charge states of many different particle species are all consistent with a single source temperature; in two events in 1997 and 2002, the best-fit temperature is much higher than that of the corona, which could imply a contribution from solar flare material. However, comparison with lower energy iron charge states for the 1997 event implies that the observed high-energy charge state could also be understood as the result of stripping during shock acceleration in the corona.