Transverse streaming anisotropies of charged particles accelerated at the solar wind termination shock

We address the anisotropy, transverse to the heliographic radial direction, of energetic charged particles accelerated at the termination shock of the solar wind. We consider the transport of energetic charged particles both in the diffusion approximation and by directly integrating test particle trajectories in a turbulent magnetic field. We find that the nature and directions of the transverse anisotropies observed on Voyager 1 can be interpreted in terms of existing models of the heliosphere, if Voyager 1 were still upstream of the termination shock. In particular, the observations are consistent with recent models in which either the upstream heliospheric termination shock flares out from the nose of the heliosphere, so that its heliocentric radius increases away from the nose, or the heliosphere is offset from the direction of the incoming neutral wind, or both. In these pictures a Parker spiral magnetic field line from the Sun intersects the termination shock many times, not just once, and the closest intersection to Voyager 1 is on the direction along the field that leads back to the Sun, as is observed. We suggest that the recent Voyager 1 observations of energetic particle anisotropies, both radial and transverse, are expected in a scenario in which Voyager 1 did not cross the termination shock.