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國立清華大學天文研究所 NTHU Institute of Astronomy

Time Coordinate: 3:30 pm 28th Oct. 2016 (Friday)

Space Coordinate: NTHU General Building II, R521

Speaker: Dr. Kouichi Hirotani (TIARA/ASIAA)

High-energy and very-high-energy emissions from the direct vicinity of rotating black holes

In a black hole 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 several nearby black hole transients are detectable with Fermi/LAT and and future ground-based atmospheric Cherenkov telescopes like CTA. Since their HE/VHE gamma-ray fluxes are predicted to exhibit anti-correlation with the IR/optical fluxes, it is possible to discriminate the gap emission from the jet.