Latest results from the Pierre Auger Observatory

TL;DR

The Pierre Auger Observatory's recent findings include detailed measurements of ultra-high energy cosmic rays, revealing spectrum features, anisotropies, composition changes, and correlations with extragalactic sources, advancing understanding of cosmic ray origins.

Contribution

This paper reports new observational results on cosmic ray spectrum, composition, and anisotropies, including correlations with nearby extragalactic objects, using data from the Pierre Auger Observatory.

Findings

Spectrum ankle at 4×10^{18} eV and suppression above 3×10^{19} eV observed.

Correlation with nearby extragalactic objects above 5.5×10^{19} eV.

Composition shifts from light (protons) to heavier nuclei at higher energies.

Abstract

Recent results obtained with the Pierre Auger Observatory are described. These include measurements of the spectrum, anisotropies and composition of ultra-high energy cosmic rays. The ankle of the spectrum is measured at $4\times 10^{18}$~eV and a suppression above $3\times 10^{19}$~eV consistent with the GZK effect is observed. At energies above $5.5\times 10^{19}$~eV a correlation with the distribution of nearby extragalactic objects is found, including an excess around the direction of Centaurus~A, the nearest radio loud active galaxy. Measurements of the depth of shower maximum and its fluctuations suggest a gradual change in the average mass of the primary cosmic rays (under standard extrapolations of hadronic interaction models), being the results consistent with a light composition consisting mostly of protons at few$\times 10^{18}$~eV and approaching the expectations from iron nuclei at $4\times 10^{19}$~eV. Upper bounds on the photon fraction and the neutrino fluxes are also obtained.