Imprint of a 2 Myr old source on the cosmic ray anisotropy

TL;DR

This paper demonstrates that the anisotropy of cosmic rays from a single source depends mainly on its contribution, age, and distance, explaining observed anisotropy features with a nearby 2 Myr old source.

Contribution

It provides a numerical analysis showing the dominance of a single source in cosmic ray anisotropy and links it to a nearby source around 200 pc, challenging the smooth source distribution assumption.

Findings

Constant dipole anisotropy indicates a single dominant source.

A 2 Myr old source at ~200 pc explains the observed plateau in anisotropy.

The local source contribution can account for the data between 200 GeV and 1 PeV.

Abstract

We study numerically the anisotropy of the cosmic ray (CR) flux emitted by a single source calculating the trajectories of individual CRs. We show that the contribution of a single source to the observed anisotropy is instead determined solely by the fraction the source contributes to the total CR intensity, its age and its distance,and does not depend on the CR energy at late times. Therefore the observation of a constant dipole anisotropy indicates that a single source dominates the CR flux in the corresponding energy range. A natural explanation for the plateau between 2--20 TeV observed in the CR anisotropy is thus the presence of a single, nearby source. For the source age of 2 Myr, as suggested by the explanation of the antiproton and positron data from PAMELA and AMS-02 through a local source [arXiv:astro-ph/1504.06472], we determine the source distance as $\sim 200$ pc. Combined with the contribution of the global CR sea calculated in the escape model, we can explain qualitatively the data for the dipole anisotropy. Our results suggest that the assumption of a smooth CR source distribution should be abandoned between 200 GeV and 1 PeV.