Electron-beam interaction with emission-line clouds in blazars

Context: An electron-positron beam escaping from the magnetospheric vacuum gap of an accreting black hole interacts with recombination-line photons surrounding gas clouds. Inverse-Compton scattering and subsequent pair production initiate unsaturated electromagnetic cascades exhibiting a characteristic spectral energy distribution. Aims: By modelling interactions electrons (positrons) hydrogen helium photons, we seek to describe signature beam-driven in broad emission-line region blazar jets. Methods: Employing coupled kinetic equations for including escape term, numerically obtain their steady-state distributions, photon spectrum. Results: We find that cascade emission resulting can produce narrow feature at TeV energies. Indications such intermittent feature, which defies explanation standard shock-in-jet scenario, have been found $\approx\,4\,\sigma$ confidence level $\approx$ 3 spectrum Mrk 501. Conclusions: The energetic requirements explaining bump beam-interaction model are plausible: Gap discharges lead multi-TeV carrying 0.1 % Blandford-Znajek luminosity, interact clouds reprocess 1 similar accretion luminosity required.