2020/12/22 by Christoph Wendel, J. Becerra González, Josefa Becerra González +4
Engineering · Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Blazar #Compton scattering #Context (archaeology) #Electron #Galaxy #Gamma ray #Luminosity #Nuclear physics #Optics #Particle Accelerators and Free-Electron Lasers #Photon #Physics #Radio Astronomy Observations and Technology #Spectral line #astro-ph.HE
paper · pdf · doi:10.1051/0004-6361/202038343
published as A&A 646, A115 (2021) · Accepted for publication in Astronomy and Astrophysics on 07.12.2020. Article comprises 15 pages including the appendices and six figures. Edition with corrected typos and clean grammar
openalex publication_date 2020/12/22 · arxiv created 2021/01/29 · arxiv updated 2021/02/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Context. An electron-positron beam escaping from the magnetospheric vacuum gap of an accreting black hole interacts with recombination-line photons from surrounding gas clouds. Inverse-Compton scattering and subsequent pair production initiate unsaturated electromagnetic cascades exhibiting a characteristic spectral energy distribution. Aims. By modelling the interactions of beam electrons (positrons) with hydrogen and helium recombination-line photons, we seek to describe the spectral signature of beam-driven cascades in the broad emission-line region of blazar jets. Methods. Employing coupled kinetic equations for electrons (positrons) and photons including an escape term, we numerically obtained their steady-state distributions and the escaping photon spectrum. Results. We find that cascade emission resulting from beam interactions can produce a narrow spectral feature at TeV energies. Indications of such an intermittent feature, which defies an explanation in the standard shock-in-jet scenario, have been found at ≈ 4 σ confidence level at an energy of ≈ 3 TeV in the spectrum of the blazar Mrk 501. Conclusions. The energetic requirements for explaining the intermittent 3 TeV bump with the beam-interaction model are plausible: Gap discharges that lead to multi-TeV beam electrons (positrons) carrying ≈ 0.1% of the Blandford-Znajek luminosity, which interact with recombination-line photons from gas clouds that reprocess ≈ 1% of the similar accretion luminosity are required.