Study of cosmic ray sources using data on extragalactic diffuse gamma-ray emission

We discuss ultra-high energy cosmic rays from minor sources and their possible contribution to the extragalactic diffuse gamma-ray emission. As an illustration of minor sources we consider the possible specific type of active galactic nuclei in which supermassive black hole is surrounded by a super strong magnetic field of 10(10)-10(11) Gs. In this model we have calculated cosmic ray energy spectra at the Earth and intensity of cascade quanta produced by cosmic rays in extragalactic space. Proceeding from numerical results and the data by Pierre Auger Observatory and Telescope Array it is shown that these active galactic nuclei make a negligible contribution to the cosmic ray flux at the Earth. However cosmic rays from these active galactic nuclei produce significant gamma-ray flux as compared to extragalactic diffuse gamma-ray emission measured by Fermi LAT. We conclude that ultra-high energy cosmic rays from minor sources contribute noticeably to extragalactic diffuse gamma-ray emission.