Magnetic fields and cosmic ray anisotropies at TeV energies

TL;DR

This paper models TeV cosmic-ray anisotropies using Boltzmann's equation, linking observed anisotropy features to local magnetic fields, cosmic-ray sources, and turbulence effects.

Contribution

It provides a theoretical framework connecting cosmic-ray anisotropies at TeV energies with magnetic field configurations and source distributions, explaining observed features.

Findings

Anisotropies depend on local and galactic magnetic fields.

Dipole anisotropy can be modulated by cosmic-ray wind variations.

Turbulence acts as a magnetic lens creating small-scale anisotropies.

Abstract

Several cosmic-ray observatories have provided a high accuracy map of the sky at TeV--PeV energies. The data reveals an O(0.1%) deficit from north galactic directions that peaks at 10 TeV and then evolves with the energy, together with other anisotropies at smaller angular scales. Using Boltzmann's equation we derive expressions for the cosmic-ray flux that fit most of these features. The anisotropies depend on the local interstellar magnetic field B_{IS}, on the average galactic field B_{R} in our vicinity, and on the distribution of dominant cosmic-ray sources. We show that the initial dipole anisotropy along B_{IS} can be modulated by changes in the global cosmic ray wind, and that a variation in the dipole direction would imply a given radius of coherence for B_{IS}. We also show that small and medium-scale anisotropies may appear when the full-sky anisotropy finds a turbulence acting as a magnetic lens.