Mojave. X. Parsec-Scale Jet Orientation Variations and Superluminal Motion in Active Galactic Nuclei

Abstract

We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15 GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. We present new VLBA 15 GHz images of these and 59 additional AGNs from the MOJAVE and 2 cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12-16 yr interval, ranging from 10• to 150• on the sky, corresponding to intrinsic variations of ∼0.• 5 to ∼2• . The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5-12 yr), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (<0.1 mas yr −1 ), are more prevalent in BL Lac jets, and are typically found within 1 mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 10 26 W Hz −1 there is a fall-off in maximum speed with decreasing 15 GHz radio luminosity. The general shape of the envelope implies that the most intrinsically powerful AGN jets have a wide range of Lorentz factors up to ∼40, while intrinsically weak jets are only mildly relativistic.

Erratic Flaring of Bl Lac in 2012–2013: Multiwavelength Observations

“…Knot A2 is probably the same as knot "ID 7" in the 15 GHz VLBA imaging of Lister et al (2013). Another interesting feature apparent in Figure 17 is a region of low brightness ∼1 mas from the core.…”

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004−447

“…The one-sidedness of the radio jet is a strong indication of relativistic beaming, which often gives rise to apparent superluminal motion of distinct jet features (see, e.g., Lister et al 2013). SBS 0846+513 is the only source in this group, for which the apparent superluminal motion of β app = (9.3 ± 0.6)c (D'Ammando et al 2013b) has been reported so far.…”

“…We computed the mean T B -value at 15 GHz and ∼8 GHz for the northern γ-NLS1s based on available data from Doi et al (2012), Lister et al (2013), and Foschini et al (2015). In the case of [HB89] 1219+044, the T B value was taken directly from Pushkarev & Kovalev (2012).…”

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

“…In this model, the intrinsic brightness temperatures cannot exceed 10 11 -10 12 K (Kellermann & Pauliny-Toth 1969;Readhead 1994). Typical Doppler boosting is expected to be able to raise this temperature by a factor of ∼10 (see also Hovatta et al 2009;Lister et al 2013). For direct interferometric measurements, increasing the interferometer baseline length is the only way to measure higher brightness temperatures (see, e.g., Kovalev et al 2005), and hence, to place stringent observational constraints on the physics of the most energetic relativistic outflows.…”