Galactic magnetic fields and the large-scale anisotropy at MILAGRO

TL;DR

This paper suggests that the large-scale anisotropy in TeV cosmic rays observed by Milagro is caused by the combined effects of regular and turbulent galactic magnetic fields, with turbulence creating a preferred propagation direction.

Contribution

It introduces a novel approach by integrating Boltzmann's equation to explain cosmic-ray anisotropy due to magnetic turbulence, differing from traditional diffusion models.

Findings

The model explains Milagro's observed anisotropy.

Turbulence can create a preferred propagation direction.

The anisotropy is orthogonal to the local regular magnetic field.

Abstract

The air-shower observatory Milagro has detected a large-scale anisotropy of unknown origin in the flux of TeV cosmic rays. We propose that this anisotropy is caused by galactic magnetic fields, in particular, that it results from the combined effects of the regular and the turbulent (fluctuating) magnetic fields in our vicinity. Instead of a diffusion equation, we integrate Boltzmann's equation to show that the turbulence may define a preferred direction in the cosmic-ray propagation that is orthogonal to the local regular magnetic field. The approximate dipole anisotropy that we obtain explains well Milagro's data.