Magnetic Coupling of a Rotating Black Hole with Advection-Dominated Accretion Flows

A model of magnetic coupling (MC) of a rotating black hole (BH) with advection- dominated accretion flow (MCADAF) is proposed. It turns out that MCADAF providers a natural explanation for the transition radius between ADAF and SSD, and could be used to interpret the highest luminosity of GX 339-4 in hard-state. A very steep emissivity index can be produced in the innermost part of the MCADAF,which is consistent with the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and with two X-ray binaries (XRBs): XTE J1655-500 and GX 339-4. In addition, we estimate the BH spins in Seyfert 1 galaxy MCG-6-30-15 and in the two XRBs based on this model.Comment: 18 pages, 9 figures,acceptted by New Astronom