Understanding TeV-band cosmic-ray anisotropy

TL;DR

This paper analyzes TeV cosmic-ray anisotropy, comparing theoretical models with IceCube data, and finds that conventional source distributions predict higher anisotropy than observed, suggesting the need for alternative explanations.

Contribution

It provides a detailed comparison of cosmic-ray anisotropy models with recent IceCube observations, highlighting discrepancies and the influence of source distribution and halo size.

Findings

Conventional source models overpredict anisotropy levels.

Source discreteness fluctuations have limited probability to match observations.

Large halo sizes increase the likelihood of matching observed anisotropy.

Abstract

We investigate the temporal and spectral correlations between flux and anisotropy fluctuations of TeV-band cosmic rays in the light of recent data taken with IceCube. We find that for a conventional distribution of cosmic-ray sources the dipole anisotropy is higher than observed, even if source discreteness is taken into account. Moreover, even for a shallow distribution of galactic cosmic-ray sources and a reacceleration model, fluctuations arising from source discreteness provide a probability only of the order of 10% that the cosmic-ray anisotropy limits of the recent IceCube analysis are met. This probability estimate is nearly independent of the exact choice of source rate, but generous for a large halo size. The location of the intensity maximum far from the Galactic Center is naturally reproduced.