Speaker
Description
We found by three-dimensional global radiation magnetohydrodynamic simulations that during the hard-to-soft state transition observed in stellar mass black hole candidates and in active galactic nuclei, toroidal magnetic field is amplified around the interface between the hard X-ray emitting hot accretion flow near the black hole and the radiatively cooled outer disk. Since the magnetic pressure supports the disk around the interface, the thermal and dynamical state of the region are distinct from the geometrically thin, standard accretion disk.
The magnetically supported toroidally magnetized accretion disk (Toroidal MAD) can explain why black hole candidates stay in the intermediate state between X-ray hard state and X-ray soft state for time scale much longer than the thermal time scale. We found that counter helicity toroidal flux tubes formed around the interface are injected into the radiatively cooled outer region, and keeps this region warm by releasing the magnetic energy through magnetic reconnection.
