A model for the jet-disk connection in BH accreting systems

The powerful and highly collimated jets observed in active galactic nuclei and (mu)quasars are likely to be connected to the accretion phenomenon via disks. Based on theoretical arguments and quasi-stationary radiative MHD calculations, a model for an accretion-powered jet is presented. It is argued that accretion disks around black holes consist of 1) a cold, Keplerian-rotating and weakly magnetized medium in the outer part, 2) a highly advective and turbulent-free plasma inside r tr = 10-20 Schwarzschild radii, where magnetic fields are predominantly of large scale topology and in excess of thermal equipartition, and 3) an ion-dominated torus in the vicinity of the hole, where magnetic fields undergo a topological change into a monopole like-configuration. The action of magnetic fields interior to r tr is to initiate torsional Alfven waves that extract angular momentum from the disk-plasma and deposit it into the transition layer between the disk and the overlying corona, where the plasma is dissipative and tenuous. A significant fraction of the shear-generated toroidal magnetic field reconnects in the transition layer, thereby heating the plasma up to the virialtemperature and forming a super-Keplerian rotating, and hence centrifugally accelerated outflow. The strong magnetic field in the transition layer forces the electrons to cool rapidly which, in combination with the fast outward-oriented motion, yields a two-temperature ion-dominated outflow. The toroidal magnetic field in the transition layer is in thermal equipartition with the ions, whereas the poloidal component is in equipartition with the electrons. Such a strong toroidal magnetic field is essential for increasing the jet-disk luminosity in the radio regime. These gravitationally unbound outflows serve as seeds, possibly, for all the powerful electron-proton jets observed in accreting systems containing black holes.