C. Fendt et E. Memola, Collimating, relativistic, magnetic jets from rotating disks - The axisymmetric field structure of relativistic jets and the example of the M 87 jet, ASTRON ASTR, 365(3), 2001, pp. 631-641
We investigate the axisymmetric structure of collimating, relativistic, str
ongly magnetized (force-free) jets. In particular, we include the different
ial rotation of the foot points of the held lines in our treatment. The mag
netic flux distribution is determined by the solution of the Grad-Shafranov
equation and the regularity condition along the light surface. With differ
ential rotation, i.e. the variation of the iso-rotation parameter Omega (F)
, the shape of the light surface is not known a priori and must be calculat
ed in an iterative way. For the first time, we have calculated the force-fr
ee magnetic structure of truly two-dimensional, relativistic jets, anchored
in a differentially rotating disk. Such an approach allows for a direct co
nnection between parameters of the central source (mass, rotation) and the
extension of the radio jet. In particular, this can provide a direct scalin
g of the location of the asymptotic jet light cylinder in terms of the cent
ral mass and the accretion disk magnetic flux distribution. We demonstrate
that differentially rotating jets must be collimated to a smaller radius in
terms of the light cylinder if compared to jets with rigid rotation. Also,
the opening angle is smaller. Further we present an analytical estimate fo
r the jet opening angle along the asymptotic branches of the light surface.
In general, differential rotation of the iso-rotation parameter leads to a
n increase of the jet opening angle. Our results are applicable for highly
magnetized, highly collimated, relativistic jets from active galactic nucle
i and Galactic superluminal jet sources. Comparison to the M 87 jet shows a
greement in the collimation distance. We derive a light cylinder radius of
the M 87 jet of 50 Schwarzschild radii.