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

¹ Max-Planck-Institut für Astronomie, 69117 Heidelberg, Germany
² SSTI, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Landessternwarte-Koenigstuhl, 69117 Heidelberg, Germany

Corresponding author: A. Hujeirat, hujeirat@mpia-hd.mpg.de

Received: 9 April 2003
Accepted: 30 June 2003

Abstract

The powerful and highly collimated jets observed in active galactic nuclei and μ-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  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 Alfvén 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 virial-temperature 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.