Upper limit on the cosmic-ray photon flux above 10^19 eV using the surface detector of the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION, A. TAMASHIRO

ASTROPARTICLE PHYSICS

Año: 2008 vol. 29 p. 243 - 260

0927-6505

 A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature ofthe shower front. Applying this method to the data, upper limits on the flux of photons of 3.8 x 10^-3 , 2.5 x 10^-3 ; and 2.2 10^-3 km^-2 sr^-1 yr^-1 above 10^19 eV, 2x10^19 eV; and 4x10^19 eV are derived, with corresponding limits on the fraction of photons being2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results alsoshow that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination fromphotons.