Lightning black holes as unidentified TeV sources

TL;DR

This paper proposes a new model where rapidly rotating black holes in gaseous clouds produce detectable TeV gamma-ray emissions via a magnetospheric accelerator, explaining some unidentified TeV sources with point-like images.

Contribution

It introduces a magnetospheric accelerator model near black holes that accounts for TeV gamma-ray emissions, contrasting with previous cosmic-ray hadron scenarios.

Findings

Gamma-ray spectra have two peaks at 0.1 GeV and 0.1 TeV.

Luminosity peaks at a mass accretion rate of about 0.01% of Eddington.

Emissions are point-like, near the event horizon.

Abstract

Imaging Atmospheric Cherenkov Telescopes have revealed more than 100 TeV sources along the Galactic Plane, around 45% of them remain unidentified. However, radio observations revealed that dense molecular clumps are associated with 67% of 18 unidentified TeV sources. In this paper, we propose that an electron-positron magnetospheric accelerator emits detectable TeV gamma-rays when a rapidly rotating black hole enters a gaseous cloud. Since the general-relativistic effect plays an essential role in this magnetospheric lepton accelerator scenario, the emissions take place in the direct vicinity of the event horizon, resulting in a point-like gamma-ray image. We demonstrate that their gamma-ray spectra have two peaks around 0.1 GeV and 0.1 TeV and that the accelerators become most luminous when the mass accretion rate becomes about 0.01% of the Eddington accretion rate. We compare the results with alternative scenarios such as the cosmic-ray hadron scenario, which predicts an extended morphology of the gamma-ray image with a single power-law photon spectrum from GeV to 100 TeV.