2010MNRAS.404..629E

New Chandra observations have resolved the structure of the X-ray luminous southern hotspot in the giant radio quasar 4C74.26 into two distinct features. The nearer one to the nucleus is an extremely luminous peak, extended some 5kpc perpendicular to the orientation of the jet; 19kpc projected further away from the central nucleus than this is an arc having similar symmetry. This X-ray arc is cospatial with near-infrared (near-IR) and optical emission imaged with Gemini and radio emission imaged with Multi-Element Radio-Linked Interferometer Network (MERLIN). We explore how this double feature corresponds to two shocks having very different characteristics in spectral energy distribution. We present the case that these observations are explained by the luminous X-ray peak being synchrotron emission with a flux density of ∼7nanoJy. There is no steep spectrum radio, optical or near-IR emission directly associated with this shock. Beyond this point in the jet's flow, and following adiabatic losses, at least 19kpc further downstream where the flow impinges on the intergalactic medium, the arc structure seen in sharp focus at radio wavelengths appears to be approximately mimicked at near-IR, optical and X-ray wavelengths. The radio emission is most naturally explained as synchrotron emission, but it would be unnatural to explain the X-rays as arising from the same emission mechanism since they show a non-monotonic spectrum. They are, however, explicable as inverse Compton scattering of photons in the cosmic microwave background, though this requires that the magnetic field strength in this slender arc/shock region responsible for the associated synchrotron radio emission is just a few per cent of the minimum energy value. The angular separation of the double shock structure (itself ≳19kpc or 10arcsec in size) from the active nucleus which fuels them of ∼550kpc could present a challenge for connecting `unidentified' hard X-ray or Fermi sources with their origins.