Anisotropy as a Probe of the Galactic Cosmic Ray Propagation and the Galactic Halo Magnetic Field

TL;DR

This paper investigates cosmic ray anisotropy across the galaxy to understand GCR propagation and the Galactic halo magnetic field, proposing a new signature of GCR streaming and its magnetic effects.

Contribution

It introduces the concept of a GCR streaming loop as a new signature and links anisotropy observations to the Galactic halo magnetic field structure.

Findings

Large-scale anisotropy persists across a wide energy range.

A proposed GCR streaming loop aligns with observed magnetic field structures.

Qualitative consistency between GCR-induced magnetic fields and halo observations.

Abstract

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally at- tributed to the CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two dimensional large scale CR anisotropy has been measured by many experiments in TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large scale anisotropy structures in such a wide range of energy suggests that the anisotropy might be due to a global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistence with the observed structure of the halo magnetic field.