Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-04-24
Astrophys.J.593:169,2003; Astrophys.J.593:169-183,2003
Astronomy and Astrophysics
Astrophysics
35 pages, 11 figures. Accepted for publication in ApJ. Figure quality reduced: for version with full-quality figures (gzipped
Scientific paper
10.1086/376519
We present new, high dynamic range VLA images of the inner jet of the closest radio galaxy, Centaurus A. Over a ten-year baseline we detect apparent sub-luminal motions (v ~ 0.5c) in the jet on scales of hundreds of pc. The inferred speeds are larger than those previously determined using VLBI on smaller scales, and provide new constraints on the angle made by the jet to the line of sight if we assume jet-counterjet symmetry. The new images also allow us to detect faint radio counterparts to a number of previously unidentified X-ray knots in the inner part of the jet and counterjet, showing conclusively that these X-ray features are genuinely associated with the outflow. However, we find that the knots with the highest X-ray to radio flux density ratios do not have detectable proper motions, suggesting that they may be related to standing shocks in the jet; we consider some possible internal obstacles that the jet may encounter. Using new, high-resolution Chandra data, we discuss the radio to X-ray spectra of the jet and the discrete features that it contains, and argue that the compact radio and X-ray knots are privileged sites for the in situ particle acceleration that must be taking place throughout the jet. We show that the offsets observed between the peaks of the radio and X-ray emission at several places in the Cen A jet are not compatible with the simplest possible models involving particle acceleration and downstream advection together with synchrotron and expansion losses.
Forman William R.
Hardcastle Martin J.
Jones Christine
Kraft Ralph Porter
Murray Stephen S.
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