Jl. Gomez et al., SUBPARSEC POLARIMETRIC RADIO OBSERVATIONS OF 3C-120 - A CLOSE-UP LOOKAT SUPERLUMINAL MOTION, The Astrophysical journal, 499(1), 1998, pp. 221-226
We present two-epoch polarimetric images of the radio galaxy 3C 120 ob
tained with the Very Long Baseline Array at 22 and 43 GHz. Because of
the proximity of 3C 120 (z = 0.033), the 43 GHz observations allow us
to observe superluminal motions with the highest resolution achieved t
o date, 0.07 h(-1) pc. Up to ten different superluminal components, wi
th velocities between 2.3 and 5.4 h(-1)c, can be observed in this acti
ve source, with approximately monthly ejections of new components. Pol
arization is observed in several components and at both frequencies, w
ith peaks in the linearly polarized flux not always coincident with th
e peaks in total intensity. The orientation of the magnetic field is o
bserved to vary with respect to the jet flow direction as a function o
f frequency, epoch, and position along the jet. These observations are
in agreement with previous numerical simulations of superluminal sour
ces (Gomez et al. 1997). The classical association of lower frequency
components with single shocks does not appear to be valid, and multipl
e components may be the result of a single disturbance in the jet flow
. This is a consequence of the interaction of the shocked plasma with
the external medium and the underlying jet, as well as hydrodynamical
processes inside the shocked region, neglected in previous analytical
shock studies owing to the nonlinearity of the jet fluid dynamics.