Astron. Astrophys. 346, 397-406 (1999)

1. Introduction

The quasar 3C 273 (z=0.158; Schmidt 1963) is one of the most studied superluminal radio sources (e.g. Zensus et al. 1990). Due to its brightness and proximity (1 milliarcsecond corresponds to 1.85 parsec; =100 km s^-1 Mpc^{- 1}, =0.5), it has been the target of Very Long Baseline Interferometry (VLBI) observations over a wide range of radio frequencies.

The radio structure of 3C 273 shows a well defined core-jet morphology from the mas scale up to the arcsecond scale. The jet extends out to 20 arcseconds with the ridge line of emission showing a clear `wiggle' (Davis et al. 1985). VLBI imaging at frequencies from 5 to 100 GHz has shown that the ridge line of the jet is curved on a scale from 0.05 to 25 mas, oscillating around the main orientation of the jet (Båath et al. 1991; Krichbaum et al. 1990; Zensus et al. 1990). Zensus et al. (1990), examining the positions of the components at various epochs, pointed out that major bends apparently occur at about 0.2, 3-4, 10-11 and 15-17 mas from the core. They also suggest that discrepancy in the position angles of some of the components observed at different frequencies may represent a spectral index gradient across the jet which implies a frequency dependence of the jet ridge line in the evolution of parsec-scale jet. Krichbaum et al. (1990) investigated the jet structure and showed that there are clear indications that the jet bends along its entire length down to 1 mas. (There are too few observations interior to this). They also pointed out that the ridge line in the jet has a quasi-sinusoidal shape.

We present here VLBI observations of 3C 273 at 22 GHz and 43 GHz. They were performed as part of a multi-frequency campaign carried out from December 12, 1992 to January 24, 1993. Results from the X-ray observations can be found in Leach et al. (1995) and for the mm-band observations in McHardy et al. (1994). Hybrid maps at the two frequencies for four out of five epochs of observations will be shown. Model-fitting of the final data set obtained as a result of the imaging/self-calibration process had performed also. An analysis of the source structure in the first 8 mas of the jet and measurements for short time-scale structural variations in 3C 273 are presented and the results discussed.

© European Southern Observatory (ESO) 1999

Online publication: May 21, 1999
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