ENERGETIC GAMMA RADIATION FROM RAPIDLY ROTATING BLACK HOLES

ABSTRACT Supermassive black holes (BHs) are believed to be the central powerhouse of active galactic nuclei. Applying the pulsar outer-magnetospheric particle accelerator theory to BH magnetospheres, we demonstrate that an electric field is exerted along the magnetic field lines near the event horiz...

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Bibliographic Details
Published in:The Astrophysical journal 2016-02, Vol.818 (1), p.50
Main Authors: Hirotani, Kouichi, Pu, Hung-Yi
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
black hole physics
BLACK HOLES
Black holes (astronomy)
COSMIC ELECTRONS
COSMIC PHOTONS
COSMIC POSITRONS
Curvature
ELECTRIC FIELDS
Flux
galaxies: individual (IC 310)
GALAXY NUCLEI
GAMMA RADIATION
Gamma rays
gamma-rays: stars
LUMINOSITY
MAGNETIC FIELDS
Mathematical analysis
methods: analytical
methods: numerical
Particle accelerators
PHOTON COLLISIONS
PLASMA
PULSARS
RADIO GALAXIES
Rotating
STAR ACCRETION
STARS
STELLAR MAGNETOSPHERES
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Summary:ABSTRACT Supermassive black holes (BHs) are believed to be the central powerhouse of active galactic nuclei. Applying the pulsar outer-magnetospheric particle accelerator theory to BH magnetospheres, we demonstrate that an electric field is exerted along the magnetic field lines near the event horizon of a rotating BH. In this particle accelerator (or a gap), electrons and positrons are created by photon-photon collisions and accelerated in the opposite directions by this electric field, efficiently emitting gamma-rays via curvature and inverse-Compton processes. It is shown that a gap arises around the null-charge surface formed by the frame-dragging effect, provided that there is no current injection across the gap boundaries. The gap is dissipating a part of the hole's rotational energy, and the resultant gamma-ray luminosity increases with decreasing plasma accretion from the surroundings. Considering an extremely rotating supermassive BH, we show that such a gap reproduces the significant very-high-energy (VHE) gamma-ray flux observed from the radio galaxy IC 310, provided that the accretion rate becomes much less than the Eddington rate particularly during its flare phase. It is found that the curvature process dominates the inverse-Compton process in the magnetosphere of IC 310, and that the observed power-law-like spectrum in VHE gamma-rays can be explained to some extent by a superposition of the curvature emissions with varying curvature radius. It is predicted that the VHE spectrum extends into higher energies with increasing VHE photon flux.
ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/818/1/50