Contribution
X-ray spectral structure in Centaurus A's inner jet
Presenter: Diana Worrall (University of Bristol)
Abstract: Chandra data taken as part of the Very Large Program (VLP) show that the X-ray spectrum in Centaurus A's jet steepens with increasing distance from the jet axis. This transverse spectral steepening predominantly arises from a change in the average spectrum of the most knotty emission. Electrons with sufficient energy to emit synchrotron X-rays must be accelerated locally to the knots, since their energy loss timescale is short compared with any dynamical timescale associated with fluid motion. Thus the observed X-ray spectral changes imply that the conditions for particle acceleration differ across the jet. If the knots are predominantly a surface feature residing in a shear layer between faster and slower flows we would have expected a harder spectrum towards the edge of the jet, the opposite to what is found. Thus we conclude that the knots reside throughout the jet and that particle acceleration is more efficient near the jet axis, presumably because the kinetic energy density of the flow is higher here. The knots themselves may result from internal flow irregularities, or from gas clouds or high-mass stars intruding into the jet, with different and potentially testable predictions for the speed of knot migration across the jet.