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Galaxies 2018, 6(4), 122; https://doi.org/10.3390/galaxies6040122

Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Academia Sinica, Institute of Astronomy and Astrophysics, AS/NTU Astronomy-Mathematics Building, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
Received: 31 October 2018 / Revised: 19 November 2018 / Accepted: 19 November 2018 / Published: 22 November 2018
(This article belongs to the Special Issue Radio Galaxies at TeV Energies)
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Abstract

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. View Full-Text
Keywords: gamma-rays: observation; gamma-rays: theory; general relativity; particle acceleration; stars: black holes gamma-rays: observation; gamma-rays: theory; general relativity; particle acceleration; stars: black holes
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Hirotani, K. Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes. Galaxies 2018, 6, 122.

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