Particle acceleration at a blunt termination shock

Voyager 1's recent and long anticipated passage into the heliosheath contradicted the prediction that we would observe the source of anomalous cosmic rays (ACRs) accelerated at the termination shock (TS). McComas and Schwadron suggested a simple resolution to this paradox. Because of the TS's blunt structure, the azimuthal magnetic field lines frozen into the solar wind first make contact with the TS at its nose where ions have very little time to be accelerated prior to being swept toward the shock's flanks. Ions achieve high ACR energies not near the nose, but off on the flanks of the termination shock. Here, we describe an important consequence that follows naturally from this scenario concerning the modulation of ACRs. ACRs are produced on the flanks of the termination shock, which are beyond Voyager. Thus, fluctuations caused by modulation of ACRs should be correlated with GCR fluctuations because both populations must drift in against the modulating effects of solar wind in the heliosheath. McDonald et al. [this volume] show striking evidence of this correlation, demonstrating clearly that the ACR source should be beyond Voyager.