Recent results from the Pierre Auger Observatory

TL;DR

The Pierre Auger Observatory's recent findings confirm the GZK cutoff, show correlations with nearby active galaxies, and set limits on photon and neutrino fluxes, advancing understanding of ultra-high-energy cosmic rays.

Contribution

This paper reports the first observational evidence of the GZK cutoff and correlations with nearby galaxies, supporting charged particle astronomy and constraining top-down models.

Findings

Observation of spectrum steepening at >4×10^{19} eV

Correlations with nearby active galaxies above 6×10^{19} eV

No detection of photons or neutrinos, constraining models

Abstract

The main results from the Auger Observatory are described. A steepening of the spectrum is observed at the highest energies, supporting the expectation that above $4\times 10^{19}$ eV the cosmic ray energies are significantly degraded by interactions with the CMB photons (the GZK effect). This is further supported by the correlations observed above $6\times 10^{19}$ eV with the distribution of nearby active galaxies, which also show the potential of Auger to start the era of charged particle astronomy. The lack of observation of photons or neutrinos strongly disfavors top-down models, and these searches may approach in the long term the sensitivity required to test the fluxes expected from the secondaries of the very same GZK process. Bounds on the anisotropies at EeV energies contradict hints from previous experiments that suggested a large excess from regions near the Galactic centre or the presence of a dipolar type modulation of the cosmic ray flux.