Long Term Monitoring of the Dynamics and Particle Acceleration of Knots
  in the Jet of Centaurus A
  We present new and archival multi-frequency radio and X-ray data for
Centaurus A obtained over almost 20 years at the VLA and with Chandra, with
which we measure the X-ray and radio spectral indices of jet knots, flux
density variations in the jet knots, polarization variations, and proper
motions. We compare the observed properties with current knot formation models
and particle acceleration mechanisms. We rule out impulsive particle
acceleration as a formation mechanism for all of the knots as we detect the
same population of knots in all of the observations and we find no evidence of
extreme variability in the X-ray knots. We find the most likely mechanism for
all the stationary knots is a collision resulting in a local shock followed by
a steady state of prolonged, stable particle acceleration and X-ray synchrotron
emission. In this scenario, the X-ray-only knots have radio counterparts that
are too faint to be detected, while the radio-only knots are due to weak shocks
where no particles are accelerated to X-ray emitting energies. Although the
base knots are prime candidates for reconfinement shocks, the presence of a
moving knot in this vicinity and the fact that there are two base knots are
hard to explain in this model. We detect apparent motion in three knots;
however, their velocities and locations provide no conclusive evidence for or
against a faster moving `spine' within the jet. The radio-only knots, both
stationary and moving, may be due to compression of the fluid.
