SED of photons obtained for a GRB with Γ = 100 (top panels) and with Γ = 300 (bottom panels) originated in both the acceleration zone (solid lines with circles) and in the cooling zone at different times (solid lines). A typical GRB photon field is shown for comparison in a thick dashed grey line. The dominant processes are included: electron synchrotron (blue), inverse Compton (black), muon synchrotron (cyan), secondary e + e − synchrotron (green), pγ (purple), and pp (orange). The different values adopted for ξ_esc are indicated.