High-frequency very long baseline interferometry studies of NRAO 530
  NRAO 530 is an optically violent variable source and has been studied with
multi-epoch multi-frequency high-resolution VLBI observations. NRAO 530 was
monitored with the VLBA at three frequencies (22, 43 and 86 GHz) on 10
consecutive days in 2007 May during observations of the Galactic Center (Sgr
A*). Furthermore, analysis of archival data of NRAO 530 at 15 GHz over the last
ten years allows us to study its detailed jet kinematics. We identified the
compact component located at the southern-end of the jet as the VLBI core,
consistent with previous studies. The 10-d monitoring data at the 3 high
frequencies were shown to produce high quality and self-consistent measurements
of the component positions, from which we detected for the first time a
two-dimensional frequency-dependent position shift. In addition, the repeated
measurements also permit us to investigate the interday flux density and
structure variability of NRAO 530. We find that it is more variable for the
inner jet components than those further out. We obtained apparent velocities
for eight jet components with $\beta_{\rm app} ranging from 2 to 26 c.
Accordingly, we estimated physical jet parameters with the minimum Lorentz
factor of 14 and Doppler factors in the range of 14--28 (component f). The
changes in the morphology of NRAO 530 were related to the motion of separate
jet components with the most pronounced changes occurring in the regions close
to the core. For NRAO 530, we estimated a P.A. swing of $3^{\circ}.4$ per year
for the entire inner jet (components d and e). The non-ballistic motion and
change of jet orientation makes this source another prominent example of a
helical and possibly `swinging' jet.
