RELATIVISTIC POYNTING JETS FROM ACCRETION DISKS Authors: R.V.E. Lovelace, M.M. Romanova 2003, ApJ 596: L159L162 A model is derived for relativistic Poynting jets from the inner region of a disk around a rotating black hole that is initially threaded by a dipolelike magnetic field. The model is derived from the special relativistic equation for a forcefree electromagnetic field. The "head" of the Poynting jet is found to propagate outward with a velocity that may be relativistic. The Lorentz factor of the head is G = [B_{0}^{2} / (8pR)^{2} r_{ext }c^{2}] ^{1/6} if this quantity is much larger than unity. For conditions pertinent to an active galactic nuclei, G ~ 8(10/R)^{1/3} (B_{0}/10^{3} G)^{1/3} (n_{ext}/1 cm^{3} )^{1/6}, where B_{0} is the magnetic field strength close to the black hole, r_{ext} = mn_{ext} is the mass density of the ambient medium into which the jet propagates R = r_{0}/r_{g} >1, where r_{g} is the gravitational radius of the black hole, and r_{0} is the radius of the Opoint of the initial dipole field. This model offers an explanation for the observed Lorentz factors of ~10 of parsecscale radio jets measured with very long baseline interferometry.

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