Gamma Ray Jets and Black Hole Magnetospheres in Active Galactic Nuclei

Abstract

Recent observational evidence pertaining to putative black holes, accretion disks and outflowing jets in active galactic nuclei is summarised. It is argued that, although equatorial inflows are observed on scales ≳ 10 pc, the gas flow at smaller radii must be more complex. The recent discovery of powerful gamma ray emission from bright, flat-spectrum radio sources suggests that most of the power from relativistic jets is emitted through inverse Compton scattering of optical-X-ray photons. It is argued that the jet power must originate in an electromagnetic form close to a massive black hole which is collimated by a super-Alfvenic disk wind extending over several decades of disk radius. The extraction of the rotational energy of a spinning black hole by electromagnetic torques is described and some recent formal developments are reviewed. It is suggested that AGN are only radio-loud when the nuclear stellar mass loss rate is low enough to allow this wind to collimate.