Estimate of the Fraction of Primary Photons in the Cosmic-Ray Flux at Energies ~10~(17) eV from the EAS–MSU Experiment Data~1

摘要

We reanalyze archival EAS–MSU data in order to search for events with an anomalously low content of muons with energies E_μ > 10 GeV in extensive air showers with the number of particles N_e approx. > 2 × 10~7. We confirm the first evidence for a 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 approx. > 5.4 × 10~(16) eV is ?_γ = (0.43_(-0.11)~(+0.12))%, which corresponds to the intensity I_γ = (1.2_(-0.3)~(+0.4)) × 10~(–16) cm~(–2) s~(–1) sr~(–1). The study of arrival directions does not favor any particular mechanism of the origin of the photon-like events.