Upper limit on the primary photon fraction from the Pierre Auger Observatory

Abstract

Based on observations of the depth of shower maximum performed with the hybrid detector of the Auger Observatory, an upper limit on the cosmic-ray photon fraction of 26% (at 95% confidence level) is derived for primary energies above 10^19 eV. Additional observables recorded with the surface detector array, available for a sub-set of the data sample, support the conclusion that a photon origin of the observed events is not favoured.

4 pages, 4 figures. To be presented at the 29th ICRC, Pune, August 2005. The Pierre Auger author list is given at http://www.auger.org/admin