Pair Cascades at the Edge of the Broad-line Region Shaping the Gamma-Ray Spectrum of 3C 279

The blazar 3C 279 emits a flux of gamma-rays that is variable on timescales as short the light-crossing time across event horizon its central black hole. It commonly reported spectral energy distribution (SED) does not show signs pair attenuation due to interactions gamma rays with ambient ultraviolet photons, concluding must originate from substructures in jet outside broad-line region (BLR). We address signature imprinted by atomic emission lines gamma-ray spectrum produced an inverse-Compton cascade photon field BLR. determine high precision SED using Fermi Large Area Telescope data MJD 58129 - 58150 and simulate for three different injection terms. Satisfactory fits observational are obtained. obtained shows features production line photons optically thick radiation transport, but lacking further exponential expected if would lie buried deep within consistent without external absorption. Our findings support view originates edge