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

Abstract

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 (1 EeV equivalent to 10(18) eV), respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV.

Keywords

• Upper
• limit
• cosmic-ray
• photon
• fraction
• energies
• Pierre
• Auger
• Observatory