Characteristics of geomagnetic cascading of ultra-high energy photons at the southern and northern sites of the Pierre Auger Observatory

Abstract

Cosmic-ray photons above 10^19 eV can convert in the geomagnetic field and initiate a preshower, i.e. a particle cascade before entering the atmosphere. We compare the preshower characteristics at the southern and northern sites of the Pierre Auger Observatory. In addition to a shift of the preshower patterns on the sky due to the different pointing of the local magnetic field vectors, the fact that the northern Auger site is closer to the geomagnetic pole results in a different energy dependence of the preshower effect: photon conversion can start at smaller energies, but large conversion probabilitites (>90%) are reached for the whole sky at higher energies compared to the southern Auger site. We show how the complementary preshower features at the two sites can be used to search for ultra-high energy photons among cosmic rays. In particular, the different preshower characteristics at the northern Auger site may provide an elegant and unambiguous confirmation if a photon signal is detected at the southern site.

25 pages, 14 figures, minor changes, conclusions unchanged, Appendix A replaced, accepted by Astroparticle Physics

References in corpus (3)

• Upper limit on the ultra-high-energy photon flux from AGASA and Yakutsk data
• Upper limit on the photon fraction in highest-energy cosmic rays from AGASA data
• Was the Highest Energy Cosmic Ray a Photon?

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• Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory
• Search for ultra-high energy photons through preshower effect with gamma-ray telescopes: Study of CTA-North efficiency
• Extreme high energy proton-gamma discrimination from space observations
• An upper limit to photons from first data taken by the Pierre Auger Observatory