Mediation of the heliospheric termination shock by termination-shock-accelerated particles

Energetic particle measurements made by Voyager 2 during its crossing of the heliospheric termination shock had distinctive features of a locally shock-accelerated component in the energy range between 1 and 3.5 MeV. Intensities of energetic ions rose exponentially upstream of the shock and were accompanied by a deceleration of the bulk plasma flow. Our analysis of the Voyager 2 shock precursor shows that the termination shock was in a rare state known as a cosmic-ray-mediated shock, where plasma slowdown in the precursor is produced by a positive energetic particle radial pressure gradient. The amount of deceleration in the last 40 days of the precursor was about 13% (by dynamic pressure), which is consistent with earlier model predictions. However, the precursor was narrower than predicted by these models, which assumed dominance of a high-energy anomalous cosmic-ray component.