Broad-band Jet Emission in Young and Powerful Radio Sources: the Case of the CSS Quasar 3C 186

摘要

We present the X-ray analysis of a deep ~200 ksec Chandra observation of thecompact steep spectrum radio-loud quasar 3C 186 (z=1.06) and investigate thecontribution of the unresolved radio jet to the total X-ray emission. Thespectral analysis is not conclusive on the origin of the bulk of the X-rayemission. In order to examine the jet contribution to the X-ray flux, we modelthe quasar spectral energy distribution (SED), adopting several scenarios forthe jet emission. For the values of the main physical parameters favored by theobservables, a dominant role of the jet emission in the X-ray band is ruled outwhen a single zone (leptonic) scenario is adopted, even including thecontribution of the external photon fields as seed photons for inverse Comptonemission. We then consider a structured jet, with the blazar component that-although not directly visible in the X-ray band - provides an intense field ofseed synchrotron photons Compton-scattered by electrons in a mildlyrelativistic knot. In this case the whole X-ray emission can be accounted forif we assume a blazar luminosity within the range observed from flat spectrumradio quasars. The X-ray radiative efficiency of such (structured) jet isintimately related to the presence of a complex velocity structure. The jetemission can provide a significant contribution in X-rays if it decelerateswithin the host galaxy, on kiloparsec scales. We discuss the implications ofthis model in terms of jet dynamics and interaction with the ambient medium.