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Black Hole Astrophysics with VLBI: Past, Present, and Future
- Workshop in honor of Professor INOUE Makoto's retirement -
March 27-29, 2017
Mitaka Campus, NAOJ, Tokyo, Japan

Oral Presentation

Photon emission from the direct vicinity of black holes

Author(s): Kouichi Hirotani (ASIAA)

Presenter: Kouichi Hirotani (ASIAA)

In a BH magnetosphere, when the plasma accretion rate is low, the radiatively inefficient accretion flow (RIAF) can no longer 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 migratory 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. The created pairs polarize to partially screen the original acceleration electric field.
It is found that the gap emissions from M87 are detectable with CTA when the accretion rate is in a certain range. Moreover, such VHE gamma-ray fluxes are predicted to exhibit anti-correlation with the RIAF submillimeter fluxes, which enables us to discriminate the gap emission from the jet emission, using ALMA.

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