Magnetized Accretion Disks: Central Engine For High-Energy Radiation And Jets In Compact Objects

The existence of black holes is an important prediction of general relativity. It is widely believed that a super massive black holes lies in the center of every galaxy. And some extremely high-energy phenomena have been observed in some black-hole systems, including Active Galactic Nuclei and some X-Ray Binaries and Gamma-Ray Bursts.Black-hole accretion is the de facto standard model for the central engines of those compact objects. The accretion theory is well established, but there are still some essential problems, e.g., the physical viscosity process, the mechanism for launching outflow from disks. Recently, it is realized that both small-scale and large-scale magnetic fields might play important roles in the accretion physics. The small-scale magnetic fields are related closely to the internal viscosity which promotes accretion. And the larger-scale magnetic fields can give rise to "large-scale" transfers of energy and angular momentum, e.g., being in charge of accelerating and collimating jets.The rotation energy of a fast spinning black hole is also extractable. We discuss two main methods of extracting energy from a spinning black hole, i.e., Blandford-Znajeck (BZ) process and Magnetic Coupling (MC) process. The following aspects are investigated in details:(â…°) the energy budget and dissipation in the MC process, (â…±) the MC effects on disk radiation; (â…²) the derivation of inner edge of a thin disk from the innermost stable circular orbit due to the MC effects.We propose a magnetically induced disk-corona model, in which the closed field lines of MC process provide natural channels for corona matter falling onto the central black hole. We derive the boundaries of corona according to the configuration of large-scale magnetic fields. We obtained the global solution of the system numerically, taking into account the energy transfer among black hole, disk and corona and also its effects on the disk dynamics. Finally, the emerged spectra are simulated by using Monte-Carlo method. It turns out the disk-corona system naturally gives rise to hard spectra with low luminosity or soft spectra with high luminosity. This property could be used to explain the non-thermal hard X-ray spectra observed in black hole binaries.There are many observational implications for disk-jet connection. We discuss the coupling between magnetic outflow and disk accretion based on the balance of energy and angular momentum, trying to explain the correlation between the disk luminosity and jet power observed in dozens of radio quasars. We also discussed the contribution of magnetic outflow to the overall equilibrium of angular momentum in accretion disk.There are two key points related to our model, i.e., black hole spin and the configuration of large-scale magnetic fields. We give a general comment on these issues, expecting to do some new works based on the observations in future.