Evolution of the milliarcsecond total intensity and polarization structures of BL Lacertae objects

Gabuzda, D. C.; Mullan, C. M.; Cawthorne, T. V.; Wardle, J. F. C.; Roberts, D. H.

doi:10.1086/174801

Cited by 122 publications

(152 citation statements)

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“…The first 5 GHz image (observation epoch 1982.25) was presented by Weistrop et al (1985) and showed a core, emitting about one third of the total flux, and a multicomponent jet elongated in Position Angle (PA) ∼ 110 • . The same structure was confirmed by subsequent observations (Gabuzda et al 1992;Gabuzda et al 1994;Gabuzda & Cawthorne 1996). A recent image at 15 GHz can be found in Kellermann et al (1998) in which the jet can be tracked up to about 10 mas from the nucleus.…”

Section: Introductionsupporting

confidence: 75%

“…A weak component at 14 mas is visible in the 8.4 GHz image by Gabuzda & Cawthorne (1996) and a much farther one, at about 25 mas along the jet axis at PA ∼ 110 • , was reported by Gabuzda et al (1994). We found no evidence for emission at such long distances from the source centre.…”

Section: The Structure Of On 231 On the Parsec Scalecontrasting

confidence: 45%

“…The jet shows a multicomponent structure and the most relevant difference with respect to literature images (Gabuzda et al 1992(Gabuzda et al , 1994Gabuzda & Cawthorne 1996) is that the brightest component is no longer at the western extreme of the source, but rather in a central location. In fact, we clearly detect an extension on the western side of the brightest component at both frequencies.…”

Section: The Structure Of On 231 On the Parsec Scalementioning

confidence: 72%

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Two-sided radio emission in ON 231 (W Comae)

Massaro

Mantovani

Fanti

et al. 2001

A&A

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Abstract. Recent radio images of the BL Lac object ON 231 (W Com, 1219+285) show remarkable new features in the source structure compared to those previously published. The images were obtained from observations made with the European VLBI Network plus MERLIN at 1.6 GHz and 5 GHz after the exceptional optical outburst occurred in Spring 1998. The up-to-date B band historic light curve of ON 231 is also presented together with the R band luminosity evolution in the period 1994-1999. We identify the source core in the radio images with the brightest component having the flattest spectrum. A consequence of this assumption is the existence of a two-sided emission in ON 231 not detected in previous VLBI images. A further new feature is a large bend in the jet at about 10 mas from the core. The emission extends for about 20 mas after the bend, which might be due to strong interaction with the environment surrounding the nucleus. We suggest some possible interpretations to relate the changes in the source structure with the optical and radio flux density variation in the frame of the unification model.

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Section: Introductionsupporting

confidence: 75%

Section: The Structure Of On 231 On the Parsec Scalecontrasting

confidence: 45%

Section: The Structure Of On 231 On the Parsec Scalementioning

confidence: 72%

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Two-sided radio emission in ON 231 (W Comae)

Massaro

Mantovani

Fanti

et al. 2001

A&A

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“…If the underlying parallel field component is weak or absent, as appears to be the case in BL Lac objects (Gabuzda et al 1994), then the electric vectors in the shock are parallel to the jet, and the fractional polarization is higher in the knot than in the inter-knot regions (see 1055+018 , Attridge et al, these Proceedings, p. 159). If the parallel field component is strong, as in many quasars (Cawthorne et al 1993), then the electric vectors in the shock are orthogonal to the jet, and the fractional polarization is lower in the knot than in the inter-knot regions (see 3C345, Wardle et al 1994;and 3C273, Ojha et al, these Proceedings, p. 127).…”

Section: The "Shock In Jet" Paradigmmentioning

confidence: 99%

Magnetic Fields in AGN

Wardle

1998

International Astronomical Union Colloquium

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A b s t r a c t . We review VLBI polarization results. In particular, we discuss the a) "shock in jet paradigm", b) the orientation of the magnetic field in jets as a function of optical identification, c) rotation measure and Faraday dispersion measurements as a probe of the narrow line region, and d) future directions of polarization observations. Results we emphasize are i) there is still a strong correlation between optical L/C ratio or EW and magnetic field orientation in the jets of blazars, even for high redshift weak-lined objects, ii) observed rotation measures are much smaller than expected from the properties of the NLR, except for some CSS sources. Also iii) a faint boundary layer or sheath (with a parallel magnetic field) has been observed around the jet of the weak-lined blazar 1055+018, and iv) circular polarization has been detected for the first time in the jets of 3C 84 and 3C 279.

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“…There is evidence for a difference in the polarization properties of quasars and BL Lac objects, and the latter show significantly lower speeds, which argues for a physical and not merely an orientation difference between the two classes of source (Gabuzda et al, 1994). Wardle et al have studied the polarization structure at 5 GHz of 3C 345 and interpreted their results in terms of a comprehensive shock model.…”

Section: · Curved Trajectories and Variable Speedsmentioning

confidence: 99%

Parsec-Scale Structure of Compact Radio Sources

Zensus

1996

Symp. - Int. Astron. Union

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Abstract. High-dynamic range imaging and monitoring with Very Long Baseline Interferometry have considerably increased our knowledge of the parsec-scale properties of compact radio sources. I review some of the properties of individual sources in areas where particular progress has been made in the last few years. Imaging of Luminous ObjectsThe study of prominent flat-spectrum sources with Very Long Baseline Interferometry (VLBI) provides arguably the best opportunity for testing physical models of parsec-scale radio jets. Routine high-quality observations are possible with the Very Long Baseline Array (VLBA), the global VLBI campaigns with various other networks, and the "World Array" campaigns. At millimeter wavelengths, ad hoc arrays have been used to make images with highest resolution, albeit modest overall fidelity. Space VLBI missions in preparation bear the potential of imaging at yet higher resolution.For a review of the various VLBI surveys and for morphological classifications see Wilkinson (1995), and Vermeiden (these Proceedings) for a statistical analysis of superluminal motions. Here, I will focus on several recent results from various ongoing studies of individual objects. I will then review some of the results from detailed VLBI monitoring studies of specific sources.The high-luminosity VLBI sources typically have well collimated corejet structure at centimeter and millimeter wavelengths. The cores are identified based on compactness, flat radio spectra, and strong flux density variability. Stronger misalignment between the parsec-scale and the kiloparsec-

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Evolution of the milliarcsecond total intensity and polarization structures of BL Lacertae objects

Cited by 122 publications

References 0 publications

Two-sided radio emission in ON 231 (W Comae)

Two-sided radio emission in ON 231 (W Comae)

Magnetic Fields in AGN

Parsec-Scale Structure of Compact Radio Sources

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