Relativistic Jets in the Radio Reference Frame Image Database II: Blazar Jet Accelerations from the First 10 Years of Data (1994 - 2003)

摘要

(Abridged) We analyze blazar jet apparent speeds and accelerations from theRDV series of astrometric and geodetic VLBI experiments. From theseexperiments, we have produced and analyzed 2753 global VLBI images of 68sources at 8 GHz with a median beam size of 0.9 milliarcseconds (mas), and amedian of 43 epochs per source. From this sample, we analyze the motions of 225jet components in 66 sources. The distribution of the fastest measured apparentspeed in each source has a median of 8.3c and a maximum of 44c. Sources in the2FGL Fermi LAT catalog display higher apparent speeds than those that have notbeen detected. On average, components farther from the core in a given sourcehave significantly higher apparent speeds than components closer to the core.We measure accelerations of components in orthogonal directions parallel andperpendicular to their average velocity vector. Parallel accelerations havesignificantly larger magnitudes than perpendicular accelerations, implyingobserved accelerations are predominantly due to changes in the Lorentz factor(bulk or pattern) rather than projection effects from jet bending. Positiveparallel accelerations are significantly more common than negative ones, so theLorentz factor (bulk or pattern)tends to increase on the scales observed here.Observed parallel accelerations correspond to modest source frame increases inthe bulk or pattern Lorentz factor.