Spatial variation of accelerated pickup ions at co-rotating interaction regions

The spatial distribution of accelerated particles at corotating interaction regions (CIR's) provides constraints on possible acceleration mechanisms. We point out some previously unrecognized aspects of acceleration at the forward and reverse shocks bounding CIRs, which support the idea that acceleration of pickup ions at these shocks is an important contributor to energetic ions in the inner heliosphere. We find that the acceleration of pickup ions is strongly favored at the reverse shock over the forward shock. Also, the scaling of the pickup-ion velocity distribution with respect to local solar wind speed is not necessarily useful within the CIR.