LEPTON ACCELERATION in the VICINITY of the EVENT HORIZON: HIGH-ENERGY and VERY-HIGH-ENERGY EMISSIONS from ROTATING BLACK HOLES with VARIOUS MASSES

Kouichi Hirotani, Hung Yi Pu, Lupin Chun Che Lin, Hsiang Kuang Chang, Makoto Inoue, Albert K.H. Kong, Satoki Matsushita, Pak Hin T. Tam

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

We investigate the electrostatic acceleration of electrons and positrons in the vicinity of the event horizon, applying the pulsar outer-gap model to black hole (BH) magnetospheres. During a low accretion phase, the radiatively inefficient accretion flow (RIAF) cannot emit enough MeV photons that are needed to sustain the force-free magnetosphere via two-photon collisions. In such a charge-starved region (or a gap), an electric field arises along the magnetic field lines to accelerate electrons and positrons into ultra-relativistic energies. These relativistic leptons emit copious gamma rays via curvature and inverse-Compton (IC) processes. Some of such gamma rays collide with the submillimeter-IR photons emitted from the RIAF to materialize as pairs, which polarize to partially screen the original acceleration electric field. It is found that the gap gamma-ray luminosity increases with decreasing accretion rate. However, if the accretion rate decreases too much, the diminished RIAF soft photon field can no longer sustain a stationary pair production within the gap. As long as a stationary gap is formed, the magnetosphere becomes force-free outside the gap by the cascaded pairs, irrespective of the BH mass. If a nearby stellar-mass BH is in quiescence, or if a galactic intermediate-mass BH is in a very low accretion state, its curvature and IC emissions are found to be detectable with Fermi/LAT and imaging atmospheric Cherenkov telescopes (IACT). If a low-luminosity active galactic nucleus is located within about 30 Mpc, the IC emission from its supermassive BH is marginally detectable with IACT.

Original languageEnglish
Article number142
JournalAstrophysical Journal
Volume833
Issue number2
DOIs
Publication statusPublished - 2016 Dec 20
Externally publishedYes

Keywords

  • acceleration of particles
  • gamma rays: stars
  • magnetic fields
  • methods: analytical
  • methods: numerical
  • stars: black holes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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