Abstract
The Pierre Auger Observatory, located in Argentina, provides an unprecedented integrated aperture in the search for primary photons with energy above 10 17 eV over a large portion of the southern sky. Such photons can be detected in principle via the air showers they initiate at such energies, using the complement of Auger Observatory detectors. We discuss the results obtained in diffuse and directional searches for primary photons in the EeV energy range.
Highlights
Photons are possible primary cosmic messengers in the flux of particles with energy larger than 1018 eV
The GZK effect predicts that cosmic rays with energies above the threshold energy EGZK interact with cosmic microwave background photons, CMB, and produce pions via the resonance: CMB + p → + → p + 0; CMB + p → + → n + +
GZK photons come from the 0 decay, the observation of these Ultra High Energy (UHE) photons would be a proof of the GZK cut-off and a way to constrain source and propagation models
Summary
Photons are possible primary cosmic messengers in the flux of particles with energy larger than 1018 eV. The Pierre Auger Observatory and other experiments have observed a suppression in the cosmic ray energy spectrum at EGZK ∼ 6 × 1019 eV. This feature could be related to the GZK effect [1, 2], and to the photo-disintegration of heavy nuclei or to the maximum energy reached by the accelerating sources. C The Authors, published by EDP Sciences. Using these properties of photon-induced showers, several upper limits on the photon fraction and flux were published by the Pierre Auger Collaboration
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