Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array

By S. Jorstad, A. Marscher, M. Lister, A. Stirling, T. Cawthorne, W. Gear, J. Gómez, J. Stevens, Paul S. Smith, J. Forster and 1 more. 2005

576 citations recorded by the source corpus.

We present total and polarized intensity images of 15 active galactic nuclei obtained with the Very Long Baseline Array at 7 mm wavelength at 17 epochs from 1998 March to 2001 April. At some epochs the images are accompanied by nearly simultaneous polarization measurements at 3 mm, 1.35/0.85 mm, and optical wavelengths. Here we analyze the 7 mm images to define the properties of the jets of two radio galaxies, five BL Lac objects, and eight quasars on angular scales ≳0.1 mas. We determine the apparent velocities of 106 features in the jets. For many of the features we derive Doppler factors using a new method based on a comparison of the timescale of decline in flux density with the light-travel time across the emitting region. This allows us to estimate the Lorentz factors (Γ), intrinsic brightness temperatures, and viewing angles of 73 superluminal knots, as well as the opening angle of the jet for each source. The Lorentz factors of the jet flows in the different blazars range from Γ ∼ 5 to 40 with the majority of the quasar components having Γ ∼ 16–18, while the values in the BL Lac objects are more uniformly distributed. The brightest knots in the quasars have the highest apparent speeds, while the more slowly moving components are pronounced in the BL Lac objects. The quasars in our sample have similar opening angles and marginally smaller viewing angles than the BL Lacs. The two radio galaxies have lower Lorentz factors and wider viewing angles than the blazars. Opening angle and Lorentz factor are inversely proportional, as predicted by gasdynamical models. The brightness temperature drops more abruptly with distance from the core in the BL Lac objects than in the quasars and radio galaxies, perhaps owing to stronger magnetic fields in the former resulting in more severe synchrotron losses of the highest energy electrons. In nine sources we detect statistically meaningful deviations from ballistic motion, with the majority of components accelerating with distance from the core. In six sources we identify jet features with characteristics of trailing shocks that form behind the primary strong perturbations in jet simulations. The apparent speeds of these components increase with distance from the core, suggestive of acceleration of the underlying jet.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

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Citations in the corpus

Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies (2008, methodology): “This would make ourDvar values even smaller, and the correspondence to Jorstad et al. (2005) would be worse.”
FLARING BEHAVIOR OF THE QUASAR 3C 454.3 ACROSS THE ELECTROMAGNETIC SPECTRUM (2010, methodology): “The majority of images show a brightness enhancement at 0.6-0.7 mas from the core, which is most likely associated with component C reported by Jorstad et al. (2005) as a stationary knot at position R ∼ 0.63 mas.”
BLACK HOLE SPIN AND THE RADIO LOUD/QUIET DICHOTOMY OF ACTIVE GALACTIC NUCLEI (2009, background): “Observations suggest a characteristic value for the Lorentz factor of AGN jets γAGN ∼ 25 (Jorstad et al. 2005).”
Multiwaveband Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Correlated Polarization Behavior (2007, background): “The knots usually separate from the core at apparent superluminal speeds, but roughly stationary knots are also present in many jets, perhaps representing standing shocks (e.g., Jorstad et al. 2001; Kellermann et al. 2004; Lister 2006; Jorstad et al. 2005, hereafter J05).”
LOCATION OF γ-RAY FLARE EMISSION IN THE JET OF THE BL LACERTAE OBJECT OJ287 MORE THAN 14 pc FROM THE CENTRAL ENGINE (2010, methodology): “The timescale for this decrease is the light-travel time across the shock times (1+ z)δ−1 ∼ 20(δ/19)−1(a/0.054mas) days, wherea is the cross-sectional angular size of the jet and the Doppler factor (δ) is that derived by Jorstad et al. (2005).”
Relativistic beaming and gamma-ray brightness of blazars (2009, background): “If one assumes that the variability timescale of the mm-wave flares seen in these sources corresponds to the light-travel time across the emis- sion region (Jorstad et al. 2005), and that the intrinsic brightness temperature of the source is limited to the equipartition value,Tb,int .”
FERMIGAMMA-RAY SPACE TELESCOPE OBSERVATIONS OF THE GAMMA-RAY OUTBURST FROM 3C454.3 IN NOVEMBER 2010 (2011, methodology): “From γγ -opacity constraints, a minimum Doppler factor δ min ≈ 13 was derived from the ﬂux variability time (Ackermann et al. 2010), and highest-energy photon measurements, in accord with independent measurements of δ from superluminal motion observations (Jorstad et al. 2005).”
Correlated Multi-Wave Band Variability in the Blazar 3C 279 from 1996 to 2007 (2008, methodology): “Very long baseline interferometry (VLBI) reveals a one-sided radio jet featuring bright knots (components) that are ‘‘ejected’’ from a bright, presumably stationary ‘‘core’’ (Jorstad et al. 2005).”
Magnetic field strength and spectral distribution of six parsec-scale active galactic nuclei jets (2009, methodology): “References: ∗Gabuzda et al. (1994); ∗∗Pushkarev & Gabuzda (1999); †Hovatta et al. (2009); ‡Jorstad et al. (2005).”
Simulations of ultrarelativistic magnetodynamic jets from gamma‐ray burst engines (2008, methodology): “In the case of accreting BHs in active galactic nuclei (AGN), accreting neutron stars and BHs in X-ray binaries, or accreting BHs for short GRBs (which presumably form as a result of a coalescence of a compact object binary system, Piran 2005; Meszaros 2006), there is no stellar envelope to confine ”
PROBING THE INNER JET OF THE QUASAR PKS 1510−089 WITH MULTI-WAVEBAND MONITORING DURING STRONG GAMMA-RAY ACTIVITY (2010, methodology): “The transverse radius of the jet at this point is ∼ 2 × 1017 cm, based on the opening angle of the jet ∼ 0.2◦ derived by Jorstad et al. (2005).”
Relativistic Jets in Active Galactic Nuclei (2006, methodology): “[16] have developed a technique for determining Γ, δ, and θ that is more precise and not so”
X-Ray Emission from Extragalactic Jets (2006, background): “Another VLBA monitoring project is described in Jorstad et al. (2005).”
Jet opening angles and gamma-ray brightness of AGN (2009, result): “Our results confirm those obtained earlier by Jorstad et al. (2005) using a smaller sample of 15 blazar jets.”
Magnetic acceleration of relativistic AGN jets (2007, methodology): “They further deduced that the maximum Lorentz factor in their sample of 119 AGN jets is ∼ 32, close to the value of ∼ 40 inferred for the jets observed by Jorstad et al. (2001, 2005).”
HIGH-RESOLUTION LINEAR POLARIMETRIC IMAGING FOR THE EVENT HORIZON TELESCOPE (2016, methodology): “…mm quasar observations from the Very Long Baseline Array obtained by the Boston University Blazar Research Group in 2013 (data reduction is described in Jorstad et al. 2005).6 We compared our polarimetric images with established CLEAN reconstructions that were convolved with the fitted clean beam.”