Local Magnetic Turbulence and TeV-PeV Cosmic Ray Anisotropies

TL;DR

This paper explores how local magnetic turbulence causes small-scale anisotropies in cosmic ray fluxes between 10^12 and 10^15 eV, explaining observations that deviate from simple diffusion models.

Contribution

It demonstrates that local magnetic turbulence naturally produces small-scale cosmic ray anisotropies and proposes a method to calculate these anisotropies based on local magnetic field structures.

Findings

Small-scale anisotropies arise from local magnetic turbulence.

Diffusion models predict larger, dipolar anisotropies, but not smaller scales.

Local magnetic field structure influences cosmic ray anisotropy patterns.

Abstract

In the energy range from ~ 10^12 eV to ~ 10^15 eV, the Galactic cosmic ray flux has anisotropies both on large scales, with an amplitude of the order of 0.1%, and on scales between ~ 10 and ~ 30 degrees, with amplitudes smaller by a factor of a few. With a diffusion coefficient inferred from Galactic cosmic ray chemical abundances, the diffusion approximation predicts a dipolar anisotropy of comparable size, but does not explain the smaller scale anisotropies. We demonstrate here that energy dependent smaller scale anisotropies naturally arise from the local concrete realization of the turbulent magnetic field within the cosmic ray scattering length. We show how such anisotropies could be calculated if the magnetic field structure within a few tens of parsecs from Earth were known.