Observation of Small-scale Anisotropy in the Arrival Direction Distribution of TeV Cosmic Rays with HAWC

TL;DR

This paper reports the detection of small-scale anisotropy in TeV cosmic rays using HAWC data, revealing three regions of enhanced flux and analyzing their angular power spectrum.

Contribution

First observation of small-scale anisotropy in TeV cosmic rays with HAWC, confirming previous findings and providing detailed angular power spectrum analysis.

Findings

Identified three regions of enhanced cosmic-ray flux.

Confirmed two regions previously reported by Milagro.

Detected significant contributions up to angular scale b115 in the power spectrum.

Abstract

The High-Altitude Water Cherenkov (HAWC) Observatory is sensitive to gamma rays and charged cosmic rays at TeV energies. The detector is still under construction, but data acquisition with the partially deployed detector started in 2013. An analysis of the cosmic-ray arrival direction distribution based on $4.9\times 10^{10}$ events recorded between June 2013 and February 2014 shows anisotropy at the $10^{-4}$ level on angular scales of about $10^\circ$. The HAWC cosmic-ray sky map exhibits three regions of significantly enhanced cosmic-ray flux; two of these regions were first reported by the Milagro experiment. A third region coincides with an excess recently reported by the ARGO-YBJ experiment. An angular power spectrum analysis of the sky shows that all terms up to $\ell=15$ contribute significantly to the excesses.