Large-scale motion, oscillations and a possible halo on the counter-jet side in 1803+784

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53 121 Bonn, Germany e-mail: sbritzen@mpifr-bonn.mpg.de
² Landessternwarte, Königstuhl, 69117 Heidelberg, Germany
³ ASTRON, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁴ Astronomical Institute `A. Pannekoek', University of Amsterdam, The Netherlands
⁵ The University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire SK11 9DL, UK
⁶ Space Research Institute, Profsojuznaja 84/32, Moscow 117997, Russia
⁷ Joint Institute for VLBI in Europe, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁸ U.S. Naval Observatory, 3450 Massachusetts Avenue NW, Washington, DC 20392, USA
⁹ European Southern Observatory, Casilla 19001, Santiago 19, Chile

Received: 10 August 2004
Accepted: 23 August 2005

Abstract

We present world-array VLBI observations of the blazar 1803+784 performed on May 29, 1993 at  cm. A 17-station VLBI array, the phased VLA and the 7-station MERLIN array observed the source simultaneously for 11 h. We present the global VLBI map, the MERLIN map, and combined-array maps at different resolutions giving an overview of the morphology of 1803+784 from the inner 10 mas to ~2 arcsec. We show that the jet bends by around 90° at a core separation of about 0.5 arcsec towards the South. On larger scales, a Westerbork Synthesis Radio Telescope (WSRT) map made at a wavelength of 6 cm resolves the bridge connecting the core with the secondary component some 45'' to the south. Wiggles in the ridge of this emission suggest that, as on the 100-pc scale, the jet may also oscillate on 50-100 kpc scales. In addition to improved imaging of the southern component, the 6 cm map provides evidence for amorphous emission to the north, as well as an extended, halo-like component about the nucleus. We compare the source structure at 6 and 18 cm with the structure at 2 cm in a VLBA image obtained on November 6, 1999. Jet wiggling is clearly seen on all scales between 1 mas and 50 arcsec. We find some indication for apparent superluminal motion between ~5c and 7c for the 25 mas jet component in model-fit results for five epochs of VLBI observations performed at 6 and 18 cm. In addition, we find some evidence for further so-called stationary components in the jet of this source which will have to be confirmed in future observations spaced more densely in time. We discuss the self-similar source morphology observed from mm to cm wavelengths – namely the wiggling on all observed scales – and the implications of the deviations from self-similarity. This is the second of two papers describing the radio structure of S5 1803+784. The first presented the results of 6 years of VLBI monitoring in the X-band (Britzen et al. 2005, MNRAS, in press).