RELATIVISTIC POYNTING JETS FROM ACCRETION DISKS

Authors: R.V.E. Lovelace, M.M. Romanova

2003, ApJ  596: L159-L162

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 dipole-like magnetic field. The model is derived from the special relativistic equation for a force-free 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 = [B02 / (8pR)2 rext c2] 1/6  if this quantity is much larger than unity. For conditions pertinent to an active galactic nuclei, G ~ 8(10/R)1/3 (B0/103 G)1/3 (next/1 cm-3 )-1/6, where  B0 is the magnetic field strength close to the black hole, rext = mnext  is the mass density of the ambient medium  into which the jet propagates R = r0/rg >1, where rg is the gravitational radius of the black hole, and r0 is the  radius of the O-point of the initial dipole field. This model offers an explanation for the observed Lorentz factors of ~10 of parsec-scale radio jets measured with very long baseline interferometry.

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