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تسجيل مستخدم جديدRadiation Magnetohydrodynamic Simulations of Sub-Eddington accretion Flows in AGN: Origin of Soft X-ray Excess and Rapid Time Variabilities
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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 ($L_{mathrm{Edd}}$). 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 $10^7M_{odot}$ black hole exceeds 10% of the Eddington accretion rate ($dot M_{rm Edd}=L_{rm Edd}/c^2$, where $c$ is the speed of light)}, the dense blob shrinks vertically because of radiative cooling and forms a Thomson thick, relatively cool ($sim10^{7-8}$ K) region. The cool region coexists with the optically thin, hot ($Tsim10^{11}~mathrm{K}$) 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. The soft X-ray emitting region coexists with the optically thin, hot ($T sim 10^{11}~mathrm{K}$), radiatively inefficient accretion flow (RIAF) near the black hole. 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 (CLAGN). 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 CLAGN.
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