Monday, July 22, 2013

1307.4988 (Yu. A. Fomin et al.)

Estimate of the fraction of primary photons in the cosmic-ray flux at
energies ~10^17 eV from the EAS-MSU experiment data

Yu. A. Fomin, N. N. Kalmykov, G. V. Kulikov, V. P. Sulakov, S. V. Troitsky
We reanalyze archival EAS-MSU data in order to search for events with anomalously low content of muons with energies E_mu>10 GeV in extensive air showers with number of particles N_e>2*10^7. We confirm the first evidence for nonzero flux of primary cosmic gamma rays at energies E~10^17 eV. The estimated fraction of primary gamma rays in the flux of cosmic particles with energies E>5.4*10^16 eV is (0.50 +0.14-0.13)%, which corresponds to the intensity of (9.7 +2.7-2.5)*10^{-16} cm^{-2} s^{-1} sr^{-1}. The study of arrival directions does not favour any particular mechanism of the origin of the photon-like events.
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