Radiation Magnetohydrodynamic Simulations of Sub-Eddington Accretion Flows in AGNs: Origin of Soft X-Ray Excess and Rapid Time Variabilities
Radiation Magnetohydrodynamic Simulations of Sub-Eddington Accretion Flows in AGNs: Origin of Soft X-Ray Excess and Rapid Time Variabilities
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DOI：
10.3847/1538-4357/abb592
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发表时间：
2020-09
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影响因子：
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通讯作者：
T. Igarashi;Y. Kato;H. R. Takahashi;K. Ohsuga;Y. Matsumoto;R. Matsumoto
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文献类型：
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作者：
T. Igarashi;Y. Kato;H. R. Takahashi;K. Ohsuga;Y. Matsumoto;R. Matsumoto
我们研究了当塞弗特星系的光度超过爱丁顿光度的0.1%时观测到的软x射线过量成分的来源（）。应用辐射磁流体力学程序CANS+R模拟了辐射无效率吸积流（RIAF）中致密团块的演化过程。当黑洞的吸积速率超过爱丁顿吸积速率（其中c为光速）的10%时，密集的斑点由于辐射冷却而垂直收缩，形成一个汤姆逊厚、相对较冷（~ 107-8 K）的区域。冷区与黑洞附近光学薄的热RIAF共存。冷盘负责发射软x射线，而硬x射线是由热的内部吸积流发射的。这种冷热吸积流的混合结构与观测到的“变相”活动星系核（clagn）发出的硬x射线和软x射线是一致的。此外，我们还发现在软x射线发射区存在准周期振荡（QPOs）。这些振荡可能是在clagn中观察到的快速x射线时间变化的起源。
We investigate the origin of the soft X-ray excess component in Seyfert galaxies observed when their luminosity exceeds 0.1% of the Eddington luminosity ( ). The evolution of a dense blob in radiatively inefficient accretion flow (RIAF) is simulated by applying a radiation magnetohydrodynamic code, CANS+R. When the accretion rate onto a black hole exceeds 10% of the Eddington accretion rate ( , where c is the speed of light), the dense blob shrinks vertically because of radiative cooling and forms a Thomson thick, relatively cool (∼107–8 K) region. The cool region coexists with the optically thin, hot ( ) RIAF near the black hole. The cool disk is responsible for the soft X-ray emission, while hard X-rays are emitted from the hot inner accretion flow. Such a hybrid structure of hot and cool accretion flows is consistent with the observations of both hard and soft X-ray emissions from “changing-look” active galactic nuclei (CLAGNs). Furthermore, we find that quasi-periodic oscillations (QPOs) are excited in the soft X-ray-emitting region. These oscillations can be the origin of rapid X-ray time variabilities observed in CLAGNs.