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Published 2001 | public
Book Section - Chapter

Ionizing Media and the Observed Charge States of Anomalous Cosmic Rays

Abstract

Singly-charged anomalous cosmic rays (ACRs) can give rise to multiply-charged ACR ions when they suffer further ionization during acceleration at or near the solar-wind termination shock. Measurements at 1 AU by SAMPEX have shown that above~ 25 MeV /nucleon ACR nitrogen, oxygen, and neon ions are multiply charged. These observations have also established that the transition from mostly singly-charged to mostly multiply-charged ACRs occurs at a total kinetic energy of~ 350 MeV. Recent simulations for ACR oxygen using ambient hydrogen as the only ionizing medium at or near the termination shock are able to successfully model this transition. The simulated oxygen intensity, however, appears deficient at high energies, where multiply-charged ACRs dominate. This paper presents further simulations that now include neutral helium as part of the ionizing medium in addition to the ambient, neutral hydrogen. The inclusion of helium helps reduce the deficiency, but appears to fall short of accounting fully for the observed spectrum. To that end, including heavier neutrals, e.g., oxygen, as well as taking multi-electron stripping into account, are suggested for more realistic modeling of the observed charge states of ACRs.

Additional Information

© 2001 COSPAR. Work is supported by NSF grant 9810653 and NASA-JOVE NAG8-1208 (A.F.B.) and by NASA NAS5-30704 and NAG5-6912 at Caltech. A.F.B. thanks Ed Stone, Alan Cummings, Rick Leske, Conrad Steenberg (Caltech), and Mark Weidenbeck (JPL) for stimulating discussions and insightful comments.

Additional details

Created:
August 19, 2023
Modified:
January 13, 2024