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

Understand

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 of the shower front.
• Applying this method to the data, upper limits on the flux of photons of 3.8*10^-3, 2.5*10^-3, and 2.2*10^-3 km^-2 sr^-1 yr^-1 above 10^19 eV, 2*10^19 eV, and 4*10^19 eV are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.).
• These photon limits disfavor certain exotic models of sources of cosmic rays.