S. C. Unwin

Radio morphology of 3C 120 on scales from 0. 5 parsecs to 400 kiloparsecs

VLA observations of the radio source 3C 120 on scales from 0.1 arcsec to over 14 arcmin were made, and the resulting maps are presented and discussed. The radio emission shows structure on all scales from less than a pc to greater than 400 kpc. A continuously connected jet is visible from less than a parsec from the central engine to over 100 kpc, well outside the galaxy. There is a lobe in the counterjet direction and diffuse emission in several directions. The three-dimensional morphology is not clear but might resemble some of the large double or wide-angle head-tail sources seen along the axis of the jet. The polarization observations imply a longitudinal magnetic field throughout nearly all of the jet. The brightness of the jet decreases following a simple power law with width, implying that the physical parameters also follow simple power laws. These results are interpreted in the context of the incoherent synchrotron model for radio emission. 60 references.

Superluminal motion in the quasar 3C 279

VLBI maps of the quasar 3C 279 have been made at 5, 11, and 22 GHz, at several epochs between 1981 and 1985, to study the varying structure of the compact radio source. Spectra derived from the maps show that the NE component has the highest turnover frequency, and thus probably represents the core of the source. By comparing the predicted inverse-Compton X-ray emission with the measured X-ray flux, lower limits to the Doppler factor are derived for the compact components. A simple model of a jet which is mildly relativistic explains both the superluminal motion and the X-ray flux. 48 refs.

High dynamic range VLBI observations of NGC 6251

The large radio galaxy NGC 6251 has been observed with an 11-telescope VLBI array, including the full VLA, at 18 cm. High-dynamic-range maps of both the VLBI-scale and VLA-scale radio structure from these observations, as well as hybrid maps from earlier VLBI experiments at 6 and 13 cm, are presented. The 18-cm VLBI hybrid map has an unusually high dynamic range of about 300 to 1 (ratio of the peak brightness to five times the rms noise level) and is limited by thermal noise rather than calibration errors. A lower limit of 80 to 1 for the ratio of jet/counterjet brightness at parsec scales can be set. This is the strongest such limit produced by VLBI observations of any source to date. If the absence of a detectable counterjet is caused by relativistic beaming, then the jet must be aligned within 45 deg of the line of sight. The VLA map shows a complex structure along the previously detected kiloparsec-scale counterjet. The physical conditions in the inner few parsecs of the NGC 6251 jet and their relation to the conditions in the extraordinarily long and well collimated kiloparsec-scale jets are discussed, and it is shown that both small-scale and large-scalemorexa0» morphology can be explained in terms of a simple model and relativistic beaming. 43 references.«xa0less

VLBI monitoring of the superluminal quasar 3C 273, 1977-1982

The compact ratio structure of the quasar 3C 273 has been monitored with a VLBI array at 5.0 and 10.7 GHz at six-month intervals during 1977-1982. THe VLBI monitoring observations, data reduction, calibration, and mapping techniques are described, and hybrid maps from the monitoring program are presented along with a brief discussion of the main features. Results on the source kinematics (superluminal motion of the knots and their time evolution) are given, and synchro-Compton models of the knots are presented and limits to their Doppler factors (delta) derived from X-ray measurements. The constraints on jet geometry provided by the combined measurements of delta and v/c are considered. For the core, the inhomogeneous jet model of Koenigl (1981) is compared with the available data. The relation between 3C 273 and the similar superluminal source 3C 345 is discussed.

The Structure and Motions of the 3C 120 Radio Jet on Scales of 0.6-300 Parsecs

Results are presented from long-term very long baseline interferometry monitoring of the parsec-scale radio jet in 3C 120 at 5 and 1.7 GHz. The 5 GHz sequence includes a few early epochs at 10.7 GHz. Superluminal features are seen leaving the core at intervals of less than a year, about as often as new features could be distinguished with the 0.6 pc resolution of the observations. The underlying jet is continuous but not smooth, and the measured features are simply the bright points in the convolution of the observing beam with brightness fluctuations that occur on many scales. The velocity of different features varies, but not by more than about a factor of 2. Clear variations in the velocity of an individual feature are not seen. Some features that were observed leaving the core in the 5 GHz observations with 0.6 pc resolution are followed at 1.7 GHz with 2.4 pc resolution to projected distances in excess of 25 pc from the core. Older features up to at least 150 pc in projection from the core are still moving at superluminal apparent speeds and are therefore presumed to be relativistic. Beyond that, the data are inadequate for motion measurements. The region where the jet slows to nonrelativistic speeds has not been found. There are suggestions of stationary features, or brightening and dimming regions, through which the moving features pass. These may be locations where there is interaction with the external medium, or they may simply be the result of variations in the jet angle to the line of sight. The observation of stationary features in an otherwise moving jet reinforces the idea that the lack of motion of the knot at 4 (2 kpc), which has been found not to be superluminal in other observations, might not actually imply that the jet has slowed by that position. The structure of the jet in the vicinity of the most likely stationary feature is suggestive of a helical pattern seen in projection. The deprojected wavelength of the pattern is very long relative to the jet radius, unlike the situation in sources such as M87 (Owen and coworkers). If the 3C 120 jet does contain a slowly moving, helical structure, then theory suggests that the jet resides in a relatively cool medium, not in a relativistically hot cocoon or lobe.

The compact triples 0710+439 and 2352+495 : a new morphology of radio galaxy nuclei

The compact radio sources 0710+439 and 2352+495 have each been mapped using intercontinental VLBI arrays at frequencies of 5.0 and 10.7 GHz. The source 0710+439 has also been mapped at 1.7 GHz. Both sources consist of three principal components that lie almost on a straight line. Except for the existence of three VLBI components instead of two they both seem to have similar properties to members of the compact double class. Multi-epoch observations show that apparent velocities between the components in both sources are below c

VLBI and Merlin observations of 3C 120 at 1. 7 GHz - superluminal motions beyond 0. 05 arcsec

The radio galaxy 3C 120 was observed at 1.7 GHz in 1982 and 1984 with VLBI arrays, and the results are reported. Significant changes in the radio structure are seen on scales out to 100 mas between two observations separated by 1.5 yr. The changes indicate the presence of superluminal motions at 50 mas and probably at 90 mas from the core. These are the largest angular scales on which superluminal motions have been observed. The continuity of the 3C 120 jet on scales of a fraction of an arcsec is established. The observations that the jet does not slow down over an order of magnitude in core distance, combined with the continuity of the physical parameters deduced from observations over many orders of magnitude in core distance, suggests that the jet remains relativistic on even larger scales. This supports the concept that the powerful, one-sided jets are relativistic on all scales and that the one-sidedness is the result of relativistic beaming. 31 references.

Rapid structural variations in 3C 120

VLBI observations of the radio galaxy 3C 120 at 2.8 and 6.0 cm between 1978.24 and 1980.27 are presented. The source consists of a highly variable linear emission region with a relatively stable, compact component at one end, suggestive of a core-jet morphology. The observations were not frequent enough and did not have sufficient dynamic range to clearly show the evolution of individual components, with the probable exception of one bright component which appeared to separate from the core at an apparent rate of 3.7 +- 0.8 times the speed of light (H/sub 0/ = 55 km s/sup -1/ Mpc/sup -1/) during 1979.