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Using three-dimensional general relativistic radiation magnetohydrodynamicssimulations of accretion flows around stellar mass black holes, we report thatthe relatively cold disk ($\gtrsim 10^{7}$K) is truncated near the black hole.Hot and less-dense regions, of which the gas temperature is $ \gtrsim 10^9$Kand more than ten times higher than the radiation temperature (overheatedregions), appear within the truncation radius. The overheated regions alsoappear above as well as below the disk, and sandwich the cold disk, leading tothe effective Compton upscattering. The truncation radius is $\sim 30 r_{\rmg}$ for $\dot{M} \sim L_{\rm Edd}/c^2$, where $r_{\rm g}, \dot M,L_\mathrm{Edd}, c$ are the gravitational radius, mass accretion rate, Eddingtonluminosity, and light speed. Our results are consistent with observations ofvery high state, whereby the truncated disk is thought to be embedded in thehot rarefied regions. The truncation radius shifts inward to $\sim 10 r_{\rmg}$ with increasing mass accretion rate $\dot{M} \sim 100 L_{\rm Edd}/c^2$,which is very close to an innermost stable circular orbit. This modelcorresponds to the slim disk state observed in ultra luminous X-ray sources.Although the overheated regions shrink if the Compton cooling effectivelyreduces the gas temperature, the sandwich-structure does not disappear at therange of $\dot{M} \lesssim 100L_{\rm Edd}/c^2$. Our simulations also revealthat the gas temperature in the overheated regions depends on black hole spin,which would be due to efficient energy transport from black hole to disksthrough the Poynting flux, resulting gas heating.

astrophysical journal/the astrophysical journal

Formation of Overheated Regions and Truncated Disks around Black Holes;  Three-dimensional General Relativistic Radiation-magnetohydrodynamics  Simulations