Large-scale cosmic ray anisotropies with 19 years of data from the Pierre Auger Observatory

TL;DR

This study analyzes 19 years of Pierre Auger Observatory data to measure large-scale anisotropies in ultra-high-energy cosmic rays, confirming a dipolar anisotropy above 8 EeV and exploring lower energies with new data sets.

Contribution

It provides the first measurement of the equatorial dipole component down to 0.03 EeV using an optimized trigger, and compares observations with source emission models.

Findings

Confirmed dipolar anisotropy above 8 EeV

Detected significant Fourier amplitude in 8-16 EeV range

No significant time variation in dipole moment

Abstract

Results are presented for the measurement of large-scale anisotropies in the arrival directions of ultra-high-energy cosmic rays detected at the Pierre Auger Observatory during 19 years of operation, prior to AugerPrime, the upgrade of the Observatory. The 3D dipole amplitude and direction are reconstructed above $4\,$EeV in four energy bins. Besides the established dipolar anisotropy in right ascension above $8\,$EeV, the Fourier amplitude of the $8$ to $16\,$EeV energy bin is now also above the $5\sigma$ discovery level. No time variation of the dipole moment above $8\,$EeV is found, setting an upper limit to the rate of change of such variations of $0.3\%$ per year at the $95\%$ confidence level. Additionally, the results for the angular power spectrum are shown, demonstrating no other statistically significant multipoles. The results for the equatorial dipole component down to $0.03\,$EeV are presented, using for the first time a data set obtained with a trigger that has been optimized for lower energies. Finally, model predictions are discussed and compared with observations, based on two source emission scenarios obtained in the combined fit of spectrum and composition above $0.6\,$EeV.