THE CHARGE STATE OF THE ANOMALOUS COMPONENT - RESULTS FROM THE TRAPPED IONS IN SPACE EXPERIMENT

We have used orbit-averaged fluxes observed with the TRapped Ions in Space (TRIS) experiment to investigate the geomagnetic transmission and hence the charge state of the anomalous component of cosmic rays. The observed oxygen flux below approximately 40 MeV per nucleon is more than an order of magnitude larger than what can be accounted for by contemporaneous Galactic cosmic-ray and solar energetic particle fluxes. Smaller excesses are observed in nitrogen and neon, while the fluxes of other elements are well accounted for by these two sources. The excess oxygen flux shows a strong change in slope at approximately 12 MeV per nucleon, indicating that two different sources may be primarily responsible for the excess above and below this energy. The excess flux above 12 MeV per nucleon is consistent in both normalization and shape with a singly ionized anomalous component. By comparing this excess with contemporaneous upper limits on the exomagnetospheric oxygen flux, a fully ionized charge state is ruled out at the 98% confidence level. Comparisons with earlier measurements in a nearly identical orbit suggest that the excess below 12 MeV per nucleon may be due to a trapped oxygen component.