Relativistic Jets in the Radio Reference Frame Image Database II: Blazar   Jet Accelerations from the First 10 Years of Data (1994 - 2003)
  (Abridged) We analyze blazar jet apparent speeds and accelerations from the RDV series of astrometric and geodetic VLBI experiments. From these experiments, we have produced and analyzed 2753 global VLBI images of 68 sources at 8 GHz with a median beam size of 0.9 milliarcseconds (mas), and a median of 43 epochs per source. From this sample, we analyze the motions of 225 jet components in 66 sources. The distribution of the fastest measured apparent speed in each source has a median of 8.3c and a maximum of 44c. Sources in the 2FGL Fermi LAT catalog display higher apparent speeds than those that have not been detected. On average, components farther from the core in a given source have significantly higher apparent speeds than components closer to the core. We measure accelerations of components in orthogonal directions parallel and perpendicular to their average velocity vector. Parallel accelerations have significantly larger magnitudes than perpendicular accelerations, implying observed accelerations are predominantly due to changes in the Lorentz factor (bulk or pattern) rather than projection effects from jet bending. Positive parallel accelerations are significantly more common than negative ones, so the Lorentz factor (bulk or pattern)tends to increase on the scales observed here. Observed parallel accelerations correspond to modest source frame increases in the bulk or pattern Lorentz factor. 
B. G. Piner, A. B. Pushkarev, Y. Y. Kovalev, C. J. Marvin, J. G.   Arenson, P. Charlot, A. L. Fey, A. Collioud, and P. A. Vo...
astro-ph.CO astro-ph.HE