Propagation of extragalactic photons at ultra-high energy with the EleCa code

We provide an estimation of the survival probability for photons inducing electromagnetic cascades as a function of their distance from the observer and we calculate the distances within which we expect to observe UHE photons with energy between 1017 and 1019 eV. Furthermore, the flux of GZK photons at Earth is investigated in several astrophysical scenarios where we vary both the injection spectrum and composition, and the intensity of the intervening extragalactic magnetic field. Although the photon propagation depends on several astrophysical factors, our numerical predictions combined with future experimental observations (or non-observations) of UHE photons in the energy range between 1017.5 eV and 1020 eV can help to constrain these scenarios.