We study a truncated accretion disk using a well-resolved , semi-global magnetohydrodynamic simulation that is evolved for many dynamical times ( 6096 inner disk orbits ) .
The spectral properties of hard state black hole binary systems and low-luminosity active galactic nuclei are regularly attributed to truncated accretion disks , but a detailed understanding of the flow dynamics is lacking .
In these systems the truncation is expected to arise through thermal instability driven by sharp changes in the radiative efficiency .
We emulate this behavior using a simple bistable cooling function with efficient and inefficient branches .
The accretion flow takes on an arrangement where a “ transition zone ” exists in between hot gas in the inner most regions and a cold , Shakura \& Sunyaev thin disk at larger radii .
The thin disk is embedded in an atmosphere of hot gas that is fed by a gentle outflow originating from the transition zone .
Despite the presence of hot gas in the inner disk , accretion is efficient .
Our analysis focuses on the details of the angular momentum transport , energetics , and magnetic field properties .
We find that the magnetic dynamo is suppressed in the hot , truncated inner region of the disk which lowers the effective \alpha -parameter by 65 \% .