Study on Spectral Variability of Black-Hole MHO Accretion Flow

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Magnetohydrodynamical Accretion Flows and Jet around a Black HoleWe performed three-dimensional (3D) magnetohydrodynamical (MHD) simulations of radiatively inefficient accretion flow around black holes, and, for the first time, succeeded in producing a jet from a rotating torus threaded by weak, localized poloidal, magnetic fields. This jet is derived by vertically inflating toroidal fields ('magnetic tower') and has a two-component structure: weakly magnetized plasmas threaded with poloidal (vertical) fields are surrounded by strongly magnetized plasmas with toroidal fields. We also calculated the emergent spectra of the MHD flows, finding that the simulated MHD flows can account for the observed spectrum of Sagittarius A^* in the flaring state, although we need to restrict the emission region to be compact.Photon Trapping in Black-Hole Accretion FlowsSome Ultra-Luminous X-ray sources (ULXs} and narrow-line Seyfert 1 galaxies (NLS1s) show rather peculiar behavior in the X-ray H-R diagram (diagram on the disk temperature, and disk luminosity plane); namely, flow temperature decreases as luminosity increases. We carefully solved the radiative transfer equation in the accretion flow, finding that the behavior of ULXs and NLS1s can be understood. The reason is that hard photons originating from deep inside the flow are more effectively trapped and only soft photons can go out, when accretion rate exceeds the critical rate.