The non-ballistic superluminal motion in the plane of the sky

Gong, Biping

doi:10.1111/j.1365-2966.2008.13570.x

Cited by 21 publications

(31 citation statements)

References 14 publications

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“…In addition, we find a correlation with the morphological changes described as mode changes. Furthermore, we are able to explain the flux-density changes within the model by Gong et al (2008) of non-ballistically moving hotspots. Thus, it can be inferred that in PKS 0735+178 ejection of VLBI components from the core is not required to explain the observed (quasi-periodic) radio flaring.…”

Section: Timescales: Flux-density Variability and Mode Changementioning

confidence: 98%

“…Thus, conceivably, the non-ballistic model of Gong (2008) can provide a fairly simple explanation for the appearance of the staircase mode. Figure 6 shows the observation of the BL Lac object 0735+178 at 8.4 GHZ by Gómez et al (2001) as well as the curves fitted to the data.…”

Section: Helix or Pressure Gradients In The External Medium?mentioning

confidence: 99%

“…Figure 6 shows the observation of the BL Lac object 0735+178 at 8.4 GHZ by Gómez et al (2001) as well as the curves fitted to the data. The inner components K8, K6 and K5 -as defined in Gómez et al (2001) -are fitted within the nonballistic model (Gong 2008) by three solid curves (corresponding to ring 1, ring 2 and ring 3, respectively) at different distances to the core. The evolution of the three curves is clockwise, all of them start in 1988.…”

Section: Helix or Pressure Gradients In The External Medium?mentioning

confidence: 99%

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Understanding BL Lacertae objects

Britzen¹,

Witzel²,

Gong

et al. 2010

A&A

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Context. We present evidence that parsec-scale jets in BL Lac objects may be significantly distinct in kinematics from their counterparts in quasars. We argued this previously for the BL lac sources 1803+784 and 0716+714 and report here a similar pattern for another well-known BL Lac object, PKS 0735+178, whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. By analyzing the pc-scale jet morphology and its changes in 0735+178 we seek to understand the emission processes in BL Lac objects and to decipher their differences from quasars. A detailed study of the jet components' motion reveals that the standard AGN paradigm of apparent superluminal motion does not always describe the kinematics in BL Lac objects. We study 0735+178 here to augment and improve the understanding of the peculiar motions in the jets of BL Lac objects as a class. Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations (2 cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91. Multiple Gaussians were fitted to the derived VLBA data, to trace the kinematical and flux density evolution of the individual VLBI (Very Long Baseline Interferometry) components in the nuclear jet. We then compared the jet kinematics with the optical and radio light curves available for this BL Lac object and point out some striking correlations between the properties of the radio knots and the features in the light curves. Results. We found a drastic structural mode change in the VLBI jet of 0735+178, between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a linear shape. We further found that this jet had undergone a similar transition sometime between December 1981 and June 1983. A mode change, occurring in the reverse direction (between mid-1992 and mid-1995) has already been reported in the literature. These structural mode changes are found to be reflected in changed kinematical behavior of the nuclear jet, manifested as an apparent superluminal motion and stationarity of the radio knots. In addition, we found the individual mode changes to correlate in time with the maxima in the optical light curve. The last two transitions occurred before a (modest) radio flare. The behavior of this pc-scale jet appears to favor a scenario involving non-ballistic motions of the radio knots, produced by the precession of a continuous jet within the ambient medium. Conclusions. This is the third BL Lac object (after 1803+784 and 0716+714) analyzed by us, which reveals kinematic properties in the parsec-scale radio jet, which are atypical of quasars. For several years, the components in the jet are not found to be separating from the core but instead to be moving perpendicularly to the ridge line of the jet. In 0735+178 this unusual behavior has been particularly conspicuous. Curiously, however, fast apparent superluminal motion characteristic of quasars were present in this jet between the epochs ∼1995 and ∼2000. Thus we found for this BL Lac object a drastic change in the kinematics of the nucle...

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Section: Timescales: Flux-density Variability and Mode Changementioning

confidence: 98%

Section: Helix or Pressure Gradients In The External Medium?mentioning

confidence: 99%

Section: Helix or Pressure Gradients In The External Medium?mentioning

confidence: 99%

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Understanding BL Lacertae objects

Britzen¹,

Witzel²,

Gong

et al. 2010

A&A

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“…We are currently working on a model to explain the quasistationarity within a model of non-ballistic motion (Gong 2008).…”

Section: Apparent Stationarity and Non-radial Motion Of Jet Componentsmentioning

confidence: 99%

Non-radial motion in the TeV blazar S5 0716+714

Britzen¹,

Kam²,

Witzel³

et al. 2009

A&A

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Context. Flat-spectrum radio sources often show a core-jet structure on pc-scales. Individual jet components reveal predominantly outward directed motion. For the BL Lac object S5 0716+714 conflicting apparent velocities have been reported in the literature. This object is an intra-day variable source and suited to investigate a possible correlation between kinematic properties and flux-density variability on different timescales. Aims. We study the kinematics in the pc-scale jet of S5 0716+714 to determine the apparent speeds of the jet components based on a much improved data set. In addition, we search for correlations between the radio flux-density light curves and the morphological changes detected along the VLBI jet. Methods. We (re-)analyze 50 VLBI observations obtained with the VLBA at 5 different frequencies (5-43 GHz) between 1992.73 and 2006.32. The data have been parameterized using circular Gaussian components. We analyze the jet component motion in detail taking care not only to account for motion in the radial but also in the orthogonal direction. We study the evolution of the jet ridge line and investigate the spectral properties of the individual components. We search for correlations between radio band light curves and the kinematic properties of the jet components. Results. We present an alternative kinematic scenario for jet component motion in S5 0716+714. We present evidence for the apparent stationarity of jet components (with regard to their core separation) with time. Jet components, however, do seem to move significantly non-radially with regard to their position angle and in a direction perpendicular to the major axis of the jet. We discuss a possible correlation between the long-term radio flux-density variability and apparent jet component motions. Conclusions. In S5 0716+714 an alternative motion scenario is proposed. With regard to the core separation, rather stationary components can fit the VLBI observations well. A new model to explain the observed motion with regard to the position angle is required. Based on the correlation between the longterm radio flux-density variability and the position angle evolution of a jet component, we conclude that a geometric contribution to the origin of the long-term variability might not be negligible. Subluminal motion has been reported for most of the TeV blazars. Our analysis also confirms this finding for the case of S5 0716+714. This result increases the number of TeV blazars showing apparent subluminal motion to 7.

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“…A recent merger of two supermassive black holes (SMBHs), where the wings constitute the relic emission of the past radio jets, is one of several scenarios proposed to explain this peculiar radio morphology (e.g., Rottmann 2001;Merritt & Ekers 2002;Komossa 2006;Gergely & Biermann 2009;Hodges-Kluck et al 2010b;Mezcua et al 2011). Alternative models employ jet-axis reorientation (e.g., Dennett-Thorpe et al 2002), two unresolved active galactic nuclei (AGN; Lal & Rao 2007), backflow of material from the main lobes into the wings (e.g., Leahy & Williams 1984;Capetti et al 2002;Hodges-Kluck et al 2010a;Landt et al 2010;Hodges-Kluck & Reynolds 2011), or non-ballistic precession assuming a pre-merger state of the two black holes (BHs; Gong 2008;Gong et al 2011). The existence of very few X-shaped sources with FRI edge-darkened radio lobes (Saripalli et al 2008;Saripalli & Subrahmanyan 2009) was initially used as a strong argument against the backflow scenario.…”

Section: Introductionmentioning

confidence: 99%

Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

Mezcua

Chavushyan

Lobanov

2012

A&A

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We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir, México. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.

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The non-ballistic superluminal motion in the plane of the sky

Cited by 21 publications

References 14 publications

Understanding BL Lacertae objects

Understanding BL Lacertae objects

Non-radial motion in the TeV blazar S5 0716+714

Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

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