Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes
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.
- Publication:
-
Galaxies
- Pub Date:
- November 2018
- DOI:
- 10.3390/galaxies6040122
- arXiv:
- arXiv:1811.09349
- Bibcode:
- 2018Galax...6..122H
- Keywords:
-
- gamma-rays: observation;
- gamma-rays: theory;
- general relativity;
- particle acceleration;
- stars: black holes;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Invited review article, published in Radio Galaxies at TeV Energies, special issue of Galaxies