Heliospheric Pickup Ions and Favored Acceleration Locations at the Termination Shock (FALTS): Are Voyager observations really inconsistent?

摘要

Pickup ions (PUIs) are created from a number of neutral sources both inside and outside the heiosphere. The combination of recent observational and theoretical work has completed the catalog of at least the major sources of Heliospheric PUIs. These PUIs are the seed population for anomalous cosmic rays (ACRs), which are accelerated to high energies at the termination shock (TS). Recently, Voyager 1 (V1) encountered strong intensity enhancements in the energy range where pickup ions are energized into ACRs. These observations may indicate that V1 has already passed beyond the TS into the bath of accelerated pickup ions in the inner heliosheath. However, opposing this conclusion, V1 magnetic field and higher energy particle observations appear very typical. Here, we advance the concept that V1 was in a special region in the heliosphere where the magnetic field is highly distorted due to solar wind shearing and footpoint motions at the Sun. These Favored Acceleration Locations at the Termination Shock (FALTS) efficiently inject pickup ions into diffusive shock acceleration due to slightly increased radial field components in the FALTS field regions. Such regions provide much more direct field-line connection to the TS than along strongly wound Parker field lines found outside of FALTS. Inside the TS, FALTS naturally enhance fluxes of accelerated pickup ions. Thus, FALTS may be responsible for the V1 observations of energetic particle enhancements. Further, FALTS provide a conduit for an inward electron heat flux from hot electrons beyond the TS, thereby heating the plasma and increasing the electron impact ionization rate. This additional ionization causes mass loading that locally weakens the TS and draws it in toward the Sun. Thus, FALTS can cause both energetic particle intensity enhancements and a weaker, locally drawn in TS; these effects may help explain the otherwise contradictory V1 observations.