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We investigate the origin of the soft X-ray excess component in Seyfertgalaxies observed when their luminosity exceeds 0.1% of the Eddingtonluminosity ($L_{\mathrm{Edd}}$). The evolution of a dense blob in radiativelyinefficient accretion flow (RIAF) is simulated by applying a radiationmagnetohydrodynamic code, CANS+R. When the accretion rate onto a$10^7M_{\odot}$ black hole exceeds 10% of the Eddington accretion rate ($\dotM_{\rm Edd}=L_{\rm Edd}/c^2$, where $c$ is the speed of light)}, the dense blobshrinks vertically because of radiative cooling and forms a Thomson thick,relatively cool ($\sim10^{7-8}$ K) region. The cool region coexists with theoptically thin, hot ($T\sim10^{11}~\mathrm{K}$) RIAF near the black hole. Thecool disk is responsible for the soft X-ray emission, while hard X-rays areemitted from the hot inner accretion flow. The soft X-ray emitting regioncoexists with the optically thin, hot ($T \sim 10^{11}~\mathrm{K}$),radiatively inefficient accretion flow (RIAF) near the black hole. Such ahybrid structure of hot and cool accretion flows is consistent with theobservations of both hard and soft X-ray emissions from `changing-look' activegalactic nuclei (CLAGN). Furthermore, we find that quasi-periodic oscillations(QPOs) are excited in the soft X-ray emitting region. These oscillations can bethe origin of rapid X-ray time variabilities observed in CLAGN.

Radiation Magnetohydrodynamic Simulations of Sub-Eddington accretion Flows in AGN: Origin of Soft X-ray Excess and Rapid Time Variabilities