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Astron. Astrophys. 324, 857-869


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The radio jet of quasar 0153+744

C.A. Hummel1,2 and T.P. Krichbaum3, and A. Witzel3, and K.H. Wüllner4, and W. Steffen3,5, and W. Alef3, and A. Fey2

1Universities Space Research Association, 300 D Street SW, Suite 801, Washington, DC 20024, USA
2U.S. Naval Observatory, AD5, 3450 Massachusetts Avenue NW, Washington, DC 20392, USA
3Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69; D-53121 Bonn, Germany
4on leave from the Max-Planck-Institut für Radioastronomie
5Dept. of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

Received 8 July 1996 / Accepted 14 January 1997

Abstract

We present new high resolution VLBI images of the radio structure of quasar 0153+744 (z = 2.338) at FORMULA 13 cm, 6 cm, 3.6 cm, and 1.3 cm, and show that its jet as projected on the sky changes direction by a full 180 degrees between the core-jet component (A) and the bright secondary component (B) located only 10 milliarcseconds away from the core. Using images published for earlier epochs, we conclude that component B is stationary with respect to A and place an upper limit of 0.7 c ( FORMULA km s-1 Mpc-1, FORMULA ) on any apparent motion. No component motions are found in the jet either, albeit with a less stringent upper limit. This is in contrast to the superluminal motion typically found in flat-spectrum radio sources, of which class 0153+744 is a member. Component A is resolved at a wavelength of 1.3 cm into a core-jet structure with four distinct components, whereas B shows complex structure consisting of resolved steep-spectrum emission. At lower resolution, the structure of B is very similar at 1.3 cm and at 6 cm. Using B as a reference position, we measure a dependence of the core peak brightness position on the observing frequency in accordance with models for inhomogeneous synchrotron components. We find the spectral index of the optically thin emission of B to be close to the one of the steep-spectrum jet components between 6 cm and 3.6 cm. No extended emission is found on scales larger than about 1 arcsecond in new VLA images made at 20 cm in A and C configuration. We discuss a model of a precessing mildly relativistic jet for 0153+744, and show that a reasonable fit to the observed properties of the radio structure is achieved. In this model, component B is the result of jet components superposed along the line-of-sight (LOS) and enhanced Doppler boosting due to their moving close to the LOS. The new components found close to the core with VLBI at FORMULA cm are sufficiently well-defined so that they may be studied in future VLBI experiments to detect motion, if any, which would further constrain, or perhaps falsify, the precessing beam model.

Key words: galaxies: jets - quasars: general - quasars: individual: 0153+744

Send offprint requests to: C.A. Hummel (USNO)


© European Southern Observatory (ESO) 1997

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