Arrival Directions of Cosmic Rays above 32 EeV from Phase One of the Pierre Auger Observatory

Abstract

A promising energy range to look for angular correlation between cosmic rays of extragalactic origin and their sources is at the highest energies, above few tens of EeV ($1\mathrm{EeV}\equiv 10^{18}$eV). Despite the flux of these particles being extremely low, the area of $\sim 3,000{\text{km}}^2$ covered at the Pierre Auger Observatory, and the 17-year data-taking period of the Phase 1 of its operations, have enabled us to measure the arrival directions of more than 2,600 ultra-high energy cosmic rays above $32\text{EeV}$. We publish this data set, the largest available at such energies from an integrated exposure of $122,000{\text{km}}^2\text{sr}\text{yr}$, and search it for anisotropies over the $3.4\pi$ steradians covered with the Observatory. Evidence for a deviation in excess of isotropy at intermediate angular scale, with $\sim 15^{\circ }$ Gaussian spread or $\sim 25^{\circ }$ top-hat radius, is obtained at the $4\sigma$ significance level for cosmic-ray energies above $\sim 40\text{EeV}$.

Published version, 33 pages, 10 figures. Dataset and analysis software available at https://doi.org/10.5281/zenodo.6504276

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