The Anisotropy of Anomalous Cosmic Rays Observed by Voyager 2 in the Heliosheath
E. Stone, A.C. Cummings, B.C. Heikkila, N. Lal, W.R. Webber
Voyager 2 (V2) has been observing anomalous cosmic rays (ACRs) in the heliosheath
since August 2007 when V2 crossed the termination shock of the supersonic solar wind.
We use the counting rate of ~0.5-35 MeV protons collected during periods when the
spacecraft was rolling about the axis pointed to the Earth to infer
their direction of flow.
The observed flow velocity is the combination of the flow due to motion of
heliosheath plasma and a diffusive flow due to a gradient in the ACR intensity.
The latitudinal component of the flow (N component) agrees with the convective flow due to
the heliospheric plasma flow as determined by the plasma instrument on V2.
However, the tangential component of the flow (T component) is smaller than the
predicted convective flow, consistent with an intensity gradient in the +T direction
and a diffusive flow of ACRs from a source located in the +T direction.
This would be consistent with models predicting that the acceleration of higher energy
ACRs occurs along the flanks or tail of the heliosphere. A similar result was
obtained by analysis of the V1 magrol data during V1's journey through
the heliosheath .