Constraining sources of ultra high energy cosmic rays using high energy observations with the Fermi satellite

We analyze the conditions that enable acceleration of particles to ultra-high energies, similar to 10(20) eV (UHECRs). We show that broad band photon data recently provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the ability of active galacticnuclei (AGN) to produce UHECRs. The high energy (MeV-GeV) photons are produced by Compton scattering of the emitted low energy photons and the cosmic microwave background or extra-galactic background light. The ratio of the luminosities at high and low photon energies can therefore be used as a probe of the physical conditions in the acceleration site. We find that existing data excludes core regions of nearby radio-loud AGN as possible acceleration sites of UHECR protons. However, we show that giant radio lobes are not excluded. We apply our method to Cen A, and show that acceleration of protons to similar to 10(20) eV can only occur at distances greater than or similar to 100kpc from the core.