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

TL;DR

This study analyzes a decade of VLBI data to measure blazar jet speeds and accelerations, revealing that jets tend to accelerate and that faster components are farther from the core, with implications for jet physics.

Contribution

It provides the first detailed analysis of blazar jet accelerations over 10 years, highlighting the predominance of acceleration due to Lorentz factor changes rather than jet bending.

Findings

Median apparent speed of 8.3c with a maximum of 44c.

Faster jet components are located farther from the core.

Parallel accelerations dominate, indicating increasing Lorentz factors.

Abstract

(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.