R. S. Simon

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.

Superluminal variations in 3C 120, 3C 273, and 3C 345

The superluminal behavior of 3C 120, 3C 273, and 3C 345 has been reexamined in light of new hybrid maps of these objects. The maps of 3C 273 and 3C 345 are consistent with superluminal expansion. 3C 120 appeared to expand superluminally from 1972.6 to 1974.5, but the evidence has been inconclusive since 1974.5. It is suggested that the jetlike structure of these sources can be explained by a model in which all the components are approaching at a small angle to the line of sight. There is a range of ejection velocities for which components separate superluminally but still maintain comparable intensities.

Images of four compact steep-spectrum quasars with a resolution of 20 milliarcseconds at 329. 1 MHz

Four compact steep-spectrum quasars (3C 48, 3C 147, 3C 309.1, and 3C 380) have been mapped with a resolution of 20 mas at 329 MHz. The structures of all four objects are asymmetric and complex, but they are shown here to be consistent with a basic one-sided jet morphology. In this, they are quite similar to other classes of radio sources; however, their small scales and convoluted structures suggest that in these objects, other factors such as the interaction with the interstellar medium and/or variations in the initial jet direction significantly affect the morphology. 43 refs.

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.

Very long baseline interferometry observations of 3C 147 and 3C 286 at 329 megahertz

We present hybrid maps of two quasars, 3C 147 and 3C 286, made at 329 MHz from VLBI observations. Both objects consist of an unresolved core; an extended, asymmetric jet; and an even larger, completely resolved, halo. For 3C 147 it is possible to decompose the spectrum into individual component spectra; at 329 MHz the core of 3C 147 is found to be strongly self-adsorbed. For both sources, the spectral index decreases monotonically from core to jet to halo.

Low-frequency variability and predicted superluminal motion in 3C147

VLBI observations of 3C147 reveal that its core is a low-frequency variable radio source which has brightened by a factor of 2 in 6 years. In combination with X-ray observations, this implies that bulk relativistic motion is taking place within the core, and leads to the prediction that 3C147 is a member of the class of superluminal radio sources.