Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory

GARCIA, B. ( 400 AUTORES DE LA COL. INTERNACIONAL PIERRE AUGER)

ASTROPARTICLE PHYSICS

Elsevier

Lugar: Amsterdam; Año: 2009 vol. 31 p. 399 - 406

0927-6505

From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV ð1 EeV 1018 eVÞ, respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top?down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.