The influence of pickup, anomalous, and galactic cosmic-ray protons on the structure of the heliospheric shock: A self-consistent approach

A self-consistent time-dependent model is used to study the modification of the heliospheric shock in the upwind direction under the influence of three suprathermal particle populations, namely, pickup, anomalous, and Galactic cosmic-ray protons. By ensuring that the resulting modulated cosmic-ray proton spectra are consistent with those observed by the Voyager and Pioneer spacecraft during the solar activity minimum in 1987, two alternative modifications of the heliospheric shock can be identified. While the first is characterized by a low injection efficiency of pickup protons into the process of diffusive shock acceleration and is mainly determined by those particles, the second, resulting from a high injection efficiency, is clearly dominated by anomalous cosmic rays.