Searches for Anisotropies in the Arrival Directions of the Highest Energy Cosmic Rays Detected by the Pierre Auger Observatory

TL;DR

This study analyzes 10 years of ultra-high energy cosmic ray data from the Pierre Auger Observatory, searching for anisotropies in arrival directions across various celestial structures and catalogs, but finds no statistically significant deviations from isotropy.

Contribution

It provides an extensive, updated analysis of cosmic ray anisotropies with a larger dataset and broader angular coverage than previous studies, including new correlation tests with multiple celestial catalogs.

Findings

No significant anisotropy detected in cosmic ray arrival directions.

Weakest anisotropy signals near Swift AGNs and Centaurus A, with post-trial probability ~1.4%.

Largest deviations observed for energies above 58 EeV in specific regions.

Abstract

We analyze the distribution of arrival directions of ultra-high energy cosmic rays recorded at the Pierre Auger Observatory in 10 years of operation. The data set, about three times larger than that used in earlier studies, includes arrival directions with zenith angles up to $80^\circ$, thus covering from $-90^\circ$ to $+45^\circ$ in declination. After updating the fraction of events correlating with the active galactic nuclei (AGNs) in the V\'eron-Cetty and V\'eron catalog, we subject the arrival directions of the data with energies in excess of 40 EeV to different tests for anisotropy. We search for localized excess fluxes and for self-clustering of event directions at angular scales up to $30^\circ$ and for different threshold energies between 40~EeV and 80~EeV. We then look for correlations of cosmic rays with celestial structures both in the Galaxy (the Galactic Center and Galactic Plane) and in the local Universe (the Super-Galactic Plane). We also examine their correlation with different populations of nearby extragalactic objects: galaxies in the 2MRS catalog, AGNs detected by Swift-BAT, radio galaxies with jets and the Centaurus~A galaxy. None of the tests shows a statistically significant evidence of anisotropy. The strongest departures from isotropy (post-trial probability ${\sim}1.4$\%) are obtained for cosmic rays with $E>58$~EeV in rather large windows around Swift AGNs closer than 130~Mpc and brighter than $10^{44}$~erg/s (18$^\circ$ radius) and around the direction of Centaurus~A (15$^\circ$ radius).