The milliarcsecond-scale jet of PKS 0735+178 during quiescence

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: iagudo@mpifr-bonn.mpg.de
² Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain
³ Physics Department, University College Cork, Cork, Ireland
⁴ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
⁵ Sobolev Astronomical Institute, St. Petersburg State University, Universitetskij Pr. 28, 198504 St. Petersburg, Russia

Received: 14 November 2005
Accepted: 30 January 2006

Abstract

We present polarimetric 5 GHz to 43 GHz VLBI observations of the BL Lacertae object PKS 0735+178, spanning March 1996 to May 2000. Comparison with previous and later observations suggests that the overall kinematic and structural properties of the jet are greatly influenced by its activity. Time intervals of enhanced activity, as reported before 1993 and after 2000 by other studies, are followed by highly superluminal motion along a rectilinear jet. In contrast the less active state in which we performed our observations, shows subluminal or slow superluminal jet features propagating through a twisted jet with two sharp bends of about 90° within the innermost three-milliarcsecond jet structure. Proper motion estimates from the data presented here allow us to constrain the jet viewing angle to values ≤, and the bulk Lorentz factor to be between 2 and 4.