2D MHD Simulations of the State Transitions of X-Ray Binaries Taking into Account Thermal Conduction

Thermal conduction plays an important role in bimodal accretion flows consisting of high-temperature flow and cool flow, especially when the temperature is high and/or has a steep gradient. For example, in hard-to-soft transitions of black hole accretion flows, thermal conduction between the high-temperature region and the low-temperature region is appropriately considered. We conducted two-dimensional magnetohydrodynamic (MHD) numerical simulations considering anisotropic heat conduction to study condensation of geometrically thick hot accretion flows driven by radiative cooling during state transitions. Numerical results show that the intermediate region appears between the hot corona and the cool accretion disk when we consider heat conduction. The typical temperature and number density of the intermediate region of the 10 M ⊙ black hole at 10 ？ R g ( ？ R g = 3.0 × 10 6 cm is the Schwarzschild radius) are 4 × 10 10 < T ？ [ K ] < 4 × 10 12 and 5 × 10 15 < n ？ [ cm ？ 3 ] < 5 × 10 17 , respectively. The thickness of intermediate region is about half of the radius. By comparing two models with or without thermal conduction, we demonstrate the effects of thermal conduction. View Full-Tex