... Power-law seed photon spectra . ... We assume that due to radiative processes electrons convert all their kinetic energy into photons, and so are counted in . ... Noting that for flat seed photon spectra SOPHIA simulations give proton inelasticities about a factor of 2 larger than Mannheim (1993), we expect slightly lower maximum proton energies. ... FigureТљ3 shows the probability of photoproduction interaction at squared CMF energy s for a E -2 -proton spectrum with a photon spectrum with . ...