Latest results from the Pierre Auger Observatory

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.

Comments: Talk given at Quarks, Strings and the Cosmos, Hector Rubinstein Memorial Symposium, August 9-11 2010