Acceleration of the anomalous component of cosmic rays revisited

Abstract

In the years 2004 and 2007, the instruments onboard the Voyager 1 and 2 spacecraft delivered unprecedented data on the structure of the solar wind termination shock. This shock has been assumed to be responsible for the acceleration of the anomalous component of cosmic rays from a pick-up ion seed population derived from the interstellar neutral gas penetrating the heliosphere. In expectation of the Voyager observations near the termination shock and in the heliosheath region, detailed models have been developed on the acceleration mechanism for the anomalous cosmic rays and on the structure of the termination shock. Here, an overview on the models on injection mechanisms into first-order Fermi acceleration, stochastic acceleration in the supersonic and subsonic solar wind, shock mediation by suprathermal ions, and on shock reformation by ions reflected at the shock is given. Comparing the results of these models to the Voyager observations, we try to synthesize an updated picture on the acceleration process of the anomalous cosmic rays.