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DRAGN, from ‘double radio source associated with a galactic nucleus’, is my proposed name for the hitherto anonymous phenomenon with which we are concerned at this meeting. This includes the radio sources associated with radio galaxies, radio-loud quasars and some Seyfert galaxies. Two aspects of this phenomenon are reviewed. One is recent evidence that the host galaxies of such radiosources are gas-rich...
An overview is given of the morphological properties of jets and hot spots in a sample of 30 nearby FR II radio galaxies, following extensive observations at 8 GHz using the VLA. Jets are found to be common (in more than 57%) and predominantly 1-sided; their detection requires high dynamic-range imaging. The hot spots are strikingly different in detail; it is argued that this dissimilarity reflects...
A progress report is given on further radio studies of the B2 sample of low luminosity radio galaxies. We present results on the polarization at 20 cm and compare our results with the Laing-Garrington effect. We also discuss new results on the so called naked jets.
The properties of Compact Steep-Spectrum radio sources are reviewed. Particular analysis is placed on radio distortions, which are considered as indicators of strong interaction between jets and ambient medium.
It is evident from this review that the mathematical and physical models which are applied to class I and class II jets are quite different. As stated in the introduction, this reflects very much the quite different mode of energy transport in the two classes of source. Another parameter which also highlights the differences between the two types of jet is the velocity. This can be written in the...
Numerical calculations are used to study the properties of stationary pressure-matched supersonic jets with boundary layers, propagating through interstellar and intergalactic mediums. It is shown that for low initial Mach numbers, M = 1 − 2, the jets become slow, fully turbulent, wide, and subsonic on a scale typical of FRI radio sources. These slow, distant parts of the jets could be identified...
VLBI images of compact radio sources show parsec-scale jets that extend continuously from the central radio core to the jets and extended emission found on arcsecond scales. Detailed imaging and monitoring show that these jets are curved and complex, and that superluminal motion is prominent in core-dominated objects.
We present new VLBI observations obtained with the European VLBI network (EVN) and US network (USN) of the two FRI radio galaxies NGC315 and 3C338. They belong to a complete sample of low-intermediate power radio galaxies selected at 6 cm, which is presently under study on the parsec scale. NGC315 shows a one-sided parsec scale jet, while 3C338 is two-sided. We present these new data and briefly summarize...
Global VLBI observations at 7 mm wavelength provide images of extragalactic radio jets with an angular resolution of ∼ 100μas. The objects observed so far show enhanced jet-curvature in the vicinity of their ‘VLBI-cores’. Monitoring the structural evolution reveals in many cases strong evidence for motion along curved paths and flux density outburst preceding the ejection of new components.
We have identified a new class of active galactic nucleus, with symmetric nuclear radio structure (two opposed jets, and little evidence for relativistic effects. These objects are most readily explained as young (or rejuvenated) radio galaxies, less than 104 years old. Study of these and similar objects is likely to lead to a better understanding of the formation of double-lobed radio galaxies and...
For radio-loud active galactic nuclei, and blazars in particular, the nonthermal radio continuum shows slow variation (months) that is successfully modeled by a shock propagating down a partially opaque jet. At frequencies above the millimeter band, the plasma is transparent to synchrotron radiation and the entire broadband continuum responds to brightness fluctuations together, suggesting that this...
We present a series of lightcurves of the quasar 3C 273 from the infrared to centimetre wavelengths. Correlation analysis reveals that the synchrotron emission from the infrared to around 2 mm is from a single component, while the 3 mm to centimetre wavelength emission is most probably a secondary emission component from further down the jet. This is in agreement with the findings from our multifrequency...
Recently it has been suggested that a class of compact flat-spectrum sources varies both in the radio and optical waveband regimes in a correlated fashion on very short timescales. In this note further properties of this rapid variability are described. The short lag observed between the various waveband regimes argues in favour of a close spatial and physical correlation of the regions dominating...
There is now a fairly clear indication that not all extragalactic jets are relativistic. The fundamental parameters of the parsec-scale jets (radius, speed, density, magnetic fields, collimation) must be related in a way to the properties of the very central object and its accretion disk. Early models of jet formation were based on pure hydrodynamic acceleration in the funnels of geometrically thick...
Turbulence in radio jets will amplify any initial magnetic field to a level comparable to the energy density in the turbulence. If the turbulence is helical, as could be the case in a jet arising from a rotating accretion flow, magnetic flux as well as energy will be generated, and magnetic fields will be maintained which are ordered on scales comparable to the jet radius. This paper presents large-scale...
I consider several issues connected with the velocities and confinement properties of kpc-scale jets in FRII sources. There is considerable evidence that large-scale jets are at least mildly relativistic. I discuss whether the Doppler-beaming interpretation of one-sidedness can be reconciled with Barthel's unified scheme, and consider modifications to the Doppler beaming formula due to the directionality...
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