Study on Spectral Variability of Black-Hole MHO Accretion Flow

黑洞周围的磁流体动力学吸积流和喷流我们对黑洞周围的辐射低效吸积流进行了三维（3D）磁流体动力学（MHD）模拟，并首次成功地从旋转环面中产生了喷流。这种射流是由垂直膨胀的环形场（“磁塔”），并有一个两个组成部分的结构：弱磁化等离子体线程极向（垂直）场被强磁化等离子体与环形场包围。我们还计算了MHD流的出射光谱，发现模拟的MHD流可以解释人马座A^* 在耀斑状态下的观测光谱，尽管我们需要将发射区域限制得紧凑。黑洞吸积流中的光子俘获--某些超亮X射线源（ULXs）和窄线塞弗特1星系（NLS 1 s）在X射线H-R图（盘温度和盘光度平面图）中表现出相当特殊的行为，即流动温度随着光度的增加而降低。我们仔细求解了吸积流中的辐射传输方程，发现ULX和NLS 1的行为可以理解。原因在于，当吸积速率超过临界速率时，来自流内部深处的硬光子被更有效地捕获，并且只有软光子可以出去。

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.