Heliosheath particles, anomalous cosmic rays and a possible “third source” of energetic ions

The evolving 40 keV–1 GeV ion spectrum observed in the inner heliosheath by Voyager 1 in 2005 can be understood as either (1) an intensifying local inner heliosheath particle spectrum, with a roughly constant form, superposed with an “unfolding” anomalous cosmic ray component, or (2) a slowly changing anomalous cosmic ray spectrum overcome by an “unrolling” and intensifying inner heliosheath particle spectrum. We demonstrate the latter by subtracting the anomalous cosmic ray component to produce an estimated local inner heliosheath spectrum, which, during days 30–110 of 2005, has an exponential cutoff at ∼45±5 MeV and a spectral power‐law index of −1.70±0.02, and during days 220–320 of 2005, has no measured cutoff and a spectral index of −1.75±0.03. This method also indicates that there is a ∼1–10 MeV low‐energy enhancement that is not accounted for in the simple two‐source (i.e., inner heliosheath particles plus anomalous cosmic rays) model. We have observed similar, unusual, low‐energy spectral features in the termination foreshock at Voyager 1 since 2002 and we discuss the possibility that these features are related to one another, comprising a possible “third source” of energetic particles in the vicinity of the termination shock.