2018/11/22 by Kouichi Hirotani · 1 citation
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Black hole (networking) #Bremsstrahlung #Cherenkov radiation #Electron #Galaxies: Formation, Evolution, Phenomena #Galaxy #Lepton #Luminosity #Magnetosphere #Nuclear physics #Physics #Plasma #astro-ph.HE
paper · pdf · doi:10.3390/galaxies6040122
published as Galaxies 2018, 6, 122 · Invited review article, published in Radio Galaxies at TeV Energies, special issue of Galaxies; 37 pages, 18 figures
openalex publication_date 2018/11/22 · arxiv created 2018/11/23 · arxiv updated 2018/11/26 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.