Multiepoch Very Long Baseline Array Observations of EGRET-detected Quasars and BL Lacertae Objects: Superluminal Motion of Gamma-Ray Bright Blazars

By S. Jorstad, A. Marscher, J. Mattox, A. Wehrle, S. Bloom, A. V. Yurchenko. 2001

312 citations recorded by the source corpus.

We present the results of a program to monitor the structure of the radio emission in 42 γ-ray bright blazars (31 quasars and 11 BL Lac objects) with the Very Long Baseline Array (VLBA) at 43, 22, and occasionally 15 and 8.4 GHz, over the period from 1993 November to 1997 July. We determine proper motions in 33 sources and find that the apparent superluminal motions in γ-ray sources are much faster than for the general population of bright compact radio sources. This follows the strong dependence of the γ-ray flux on the level of relativistic beaming for both external radiation Compton and synchrotron self-Compton emission. There is a positive correlation (correlation coefficient r = 0.45) between the flux density of the VLBI core and the γ-ray flux and a moderate correlation (partial correlation coefficient r = 0.31) between γ-ray apparent luminosity and superluminal velocities of jet components, as expected if the γ-ray emission originates in a very compact region of the relativistic jet and is highly beamed. In 43% of the sources the jet bends by more than 20° on parsec scales, which is consistent with amplification by projection effects of modest actual changes in position angle. In 27 of the sources in the sample there is at least one non-core component that appears to be stationary during our observations. Different characteristics of stationary features close to and farther from the core lead us to suggest two different classes of stationary components: those within about 2 mas of the core, probably associated with standing hydrodynamical compressions, and those farther down the jet, which tend to be associated with bends in the jet.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b489d2a1a9aca1c07c6f9dd10bc7fc505cee1439

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Citations in the corpus

Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations (2003, background): “10 (but exceeding 40 in some cases; e.g., Jorstad et al. 2001), most models to date have concentrated on the nonrelativistic regime.”
The Fermi blazar sequence (2017, background): “On the other hand, direct VLBI and VLBA measurements of superluminal knots in blazars (Jorstad et al. 2001; Lister et al. 2013), and modelling (Ghisellini & Tavecchio 2015) do not find strong differences in the bulk Lorentz factors of BL Lacs and FSRQs.”
FROM THE BLAZAR SEQUENCE TO THE BLAZAR ENVELOPE: REVISITING THE RELATIVISTIC JET DICHOTOMY IN RADIO-LOUD ACTIVE GALACTIC NUCLEI (2011, background): “…HSP BL Lacs which show that they are barely super-luminal, with average bulk Lorentz factors Γ ∼ 2−3 (Piner et al. 2001; Edwards & Piner 2002; Giroletti et al. 2004; Piner et al. 2008, 2010); however, several LSP BL Lacs show high velocities on VLBI scales (Jorstad et al. 2001; Cohen et al. 2007).”
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).”
Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies (2008, methodology): “We can find out theβapp from Very Long Baseline Interferometry (VLBI) observations, and i the past few years major progress has been made in this area (e.g. Jorstad et al. 2001; Homan et al. 2001; Kellermann et al. 2004; Jorstad et al. 2005; Piner et al. 2007; Britzen et al. 2008).”
General relativistic magnetohydrodynamic simulations of the jet formation and large-scale propagation from black hole accretion systems (2006, background): “That there can be two separate relativistic jet components makes it difficult to draw clear conclusions regarding the composition (Guilbert et al. 1983; Celotti & Fabian 1993; Levinson & Blandford 1996; Sikora & Madejski 2000).”
Total and Jet Blandford-Znajek Power in the Presence of an Accretion Disk (2005, background): “AGNs are observed to have jets withG 10 (Urry & Padovani 1995; Biretta et al. 1999), evenG ∼ 30 (Begelman et al. 1994; Ghisellini & Celotti 2001; Jorstad et al. 2001), while some observations implyG 200 (Ghisellini et al. 1993; Krawczynski et al. 2002; Konopelko et al. 2003).”
Optical and radio behaviour of the BL Lacertae object 0716+714 ⋆ (2003, unknown): “Old estimates of apparent velocity raised the issue of the existence of superluminal motion in this source (Gabuzda et al. 1998); however, a recent determination of proper motions by Jorstad et al. (2001) resulted in values greater than 11–15 h−1 c.”
Decelerating Flows in TeV Blazars: A Resolution to the BL Lacertae-FR I Unification Problem (2003, background): “Additional support for slow flows in sub-pc scales comes from Jorstad et al. (2001) that showed that in several cases VLBI components in BLs move with βapp ∼ 1−2.”
Relativistic Jets in Active Galactic Nuclei (2006, background): “of about 60% of the EGRET-detected sources identified as blazars, [19] reported apparent velocities as high as ~ 45c in PKS 1510−089, confirmed by [16] and by the data shown in Figure 2.”
Multiepoch Very Long Baseline Array Observations of EGRET-detected Quasars and BL Lacertae Objects: Connection between Superluminal Ejections and Gamma-Ray Flares in Blazars (2001, methodology): “The entire list of epochs of superluminal ejections for all components detected during our monitoring is given in Table 5 of Jorstad et al. 2001.”
Synchrotron Self-Compton Model for Rapid Nonthermal Flares in Blazars with Frequency-dependent Time Lags (2004, background): “In this scenario, stationary hot spots seen downstream of the core (Jorstad et al. 2001) may be explained by the oscillatory behavior of the jet producing multiple sets of stationary structures.”
BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THE FERMI LARGE AREA TELESCOPE ALL-SKY SURVEY (2009, background): “…& 100 MeV energies are also significant radio sources.68 This includes the 3EG and AGILE blazars, which are so far identified with flat spectrum (radio69 spectral index αr > −0.5 at GHz frequencies) radio-loud AGNs, and most show superluminal70 motion (Jorstad et al. 2001; Kellermann et al. 2004).”
Magnetic acceleration of relativistic AGN jets (2007, background): “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).”
Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array (2005, methodology): “For example, γ-ray blazars, which exhibit the highest apparent speeds (Jorstad et al. 2001a; Kellermann et al. 2004), do not possess more pronounced bends than sources not yet detected in γ-rays (Kellermann et al. 1998; Jorstad et al. 2001a).”
Dynamics and high-energy emission of the flaring HST-1 knot in the M 87 jet (2006, background): “We 3 For the possibility of stationary reconfinement shocks in the small-scale jets of blazar sources, see for example Jorstad et al. (2001). can also evaluate the energy density of the X-ray photons for the observed X-ray emission of the hot gas with the temperature k T G ≈ 1.5 keV in M 87.”