Charge States of Energetic Particles From Corotating Interaction Regions As Constraints On Their Source

Abstract

Since the discovery of large (factor of greater than 1000) enhancements of singly ionized helium in corotating interaction regions (CIRs), it has become clear that low charge state ions from interstellar neutrals or other heliospheric sources can be preferentially injected into the energetic particle population. The large enhancements in suprathermal and energetic He suggest that low charge state ions may likewise affect the composition of CIR-related heavy ions such as C or Ne. Therefore, a key observational test of the contribution of pickup ions to the energetic particles associated with CIRs is their ionization state. We have used instrumentation on board the low Earth orbiting SAMPEX satellite, along with the geomagnetic cutoff technique, to investigate the ionization states of CIR heavy ions in the energy range 0.5-1.0 MeV nucleon^(-1). In a sum of 14 CIR events, we find heavy-ion charge states similar to those of solar energetic particles from interplanetary shocks, with upper limits to the contribution of singly ionized particles on the order of a few percent of the total flux. We find that stripping in the interplanetary medium of singly ionized heavy ions energized in the CIR could not account for the observed high charge states. Thus, the high charge state material we observed must have originated in the bulk solar wind or its suprathermal tail.

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