Energetic Gamma Radiation from Rapidly Rotating Black Holes

TL;DR

This paper models gamma-ray emission from rapidly rotating black holes using a magnetospheric particle acceleration mechanism, explaining observed VHE gamma-ray fluxes and spectra in active galactic nuclei like IC 310.

Contribution

It introduces a gap model around black hole horizons that accounts for gamma-ray production via curvature and inverse-Compton processes, linking black hole spin and accretion rate to gamma-ray luminosity.

Findings

The gap forms near the null charge surface due to frame-dragging effects.

Gamma-ray luminosity increases as plasma accretion decreases.

The model reproduces the VHE gamma-ray flux observed from IC 310.

Abstract

Supermassive black holes are believed to be the central power house of active galactic nuclei. Applying the pulsar outer-magnetospheric particle accelerator theory to black-hole magnetospheres, we demonstrate that an electric field is exerted along the magnetic field lines near the event horizon of a rotating black hole. 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 black hole, 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.