Anisotropy of TeV Cosmic Rays and the Outer Heliospheric Boundaries

TL;DR

This paper explores how scattering processes in the outer heliosphere influence the anisotropy and angular structure of TeV cosmic rays observed on Earth, highlighting the role of local interstellar magnetic field perturbations.

Contribution

It proposes that scattering in the outer heliosphere explains the observed non-dipolar anisotropy and small-scale features of TeV cosmic rays, challenging traditional diffusion models.

Findings

Scattering in the heliosphere affects cosmic ray anisotropy.

Outer heliospheric magnetic perturbations influence cosmic ray distribution.

Re-distribution of cosmic rays toward the heliotail observed.

Abstract

Cosmic rays in the energy range from about 10's GeV to several 100's TeV are observed on Earth with an energy-dependent anisotropy of order 0.01-0.1%, and a consistent topology that appears to significantly change at higher energy. The nearest and most recent galactic cosmic ray sources might stochastically dominate the observation and possibly explain a change in orientation of the anisotropy as a function of energy. However, the diffusion approximation is not able to explain its non-dipolar structure and, in particular, the significant contribution of small angular scale features. Particle propagation within the mean free path in the local interstellar medium might have a major role in determining the properties of galactic cosmic rays, such as their arrival distribution. In particular, scattering on perturbations induced in the local interstellar magnetic field by the heliosphere wake, may cause a re-distribution of anisotropic cosmic rays below about 100 TeV toward the direction of the elongated heliotail and of the local interstellar magnetic field in the outer heliosphere. Such scattering processes are considered responsible of the observed TeV cosmic ray global anisotropy and its fine angular structure.