Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...324..857h&link_type=abstract
Astronomy and Astrophysics, v.324, p.857-869
Astronomy and Astrophysics
Astrophysics
14
Galaxies: Jets, Quasars: General, Quasars: Individual: Qso 0153+744
Scientific paper
We present new high resolution VLBI images of the radio structure of quasar 0153+744 (z=2.338) at λλ 13cm, 6cm, 3.6cm, and 1.3cm, 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 0.7c (H_0_=100km/s/Mpc, q_0_=0.5) 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 1.3cm 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 1.3cm and at 6cm. 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 6cm and 3.6cm. No extended emission is found on scales larger than about 1 arcsecond in new VLA images made at 20cm 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 λ=1.3cm 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.
Alef Walter
Fey Alan
Hummel Christian A.
Krichbaum Thomas P.
Steffen Will
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