We investigate how the extragalactic proton component derived within the “ escape model ” can be explained by astrophysical sources .
We consider as possible cosmic ray ( CR ) sources normal/starburst galaxies and radio-loud active galactic nuclei ( AGN ) .
We find that the contribution to the total extragalactic proton flux from normal and starburst galaxies is only subdominant and does not fit the spectral shape deduced in the escape model .
In the case of radio-loud AGN , we show that the complete extragalactic proton spectrum can be explained by a single source population , BL Lac/FR I , for any of the potential acceleration sites in these sources .
We calculate the diffuse neutrino and \gamma -ray fluxes produced by these CR protons interacting with gas inside their sources .
For a spectral slope of CRs close to \alpha = 2.1 - 2.2 as suggested by shock acceleration , we find that these UHECR sources contribute the dominant fraction of both the isotropic \gamma -ray background and of the extragalactic part of the astrophysical neutrino signal observed by IceCube .