E_p − E_iso relations with differents assumptions for the model parameters; black dots: whole synthetic population, except (in cyan) bursts that are optically thick as a result of photon-photon annihilation; red dots: detected bursts assuming a threshold of 2.6 ph cm^-2 s^-1 between 15 and 150 keV; yellow dots: observed BAT6 sample (Salvaterra et al. 2012). Upper left panel: no correlation among model parameters. Upper right panel: . Bottom left panel: . Bottom right panel: .