Intrinsic time delay as a function of the energy. Upper panel: intrinsic time delay evolution for adiabatic expansion and compression effects, introduced with the variation of the blob’s radius R. Lower panel: illustration of delay evolution for decreasing external photon field effects, modelled as a blackbody emitted by an accretion disc, and further reprocessed by a BLR, varied by the increasing distance d between the central black hole and the emitting blob. For the SSC part, the simulations are based on the set of parameters given in Table 1. For both plots, the reference time for lag calculation is taken at 1 MeV (see the main text for further explanations).