The luminous X-ray hotspot in 4C74.26: synchrotron or inverse-Compton emission?

Abstract

We report the discovery of an X-ray counterpart to the southern radio hotspot of the largest-known radio quasar 4C74.26 (whose redshift is z = 0.104). Both XMM-Newton and Chandra images reveal the same significant (10arcsec i.e. 19kpc) offset between the X-ray hotspot and the radio hotspot imaged with MERLIN. The peak of the X-ray emission may be either due to synchrotron emission or due to inverse-Compton emission. If synchrotron emission, the hotspot represents the site of particle acceleration and the offset arises from either the jet exhibiting Scheuer's `dentist's drill' effect or a fast spine having less momentum than the sheath surrounding it, which creates the radio hotspot. If the emission arises from the inverse-Compton process, it must be inverse-Compton scattering of the cosmic microwave background in a decelerating relativistic flow, implying that the jet is relativistic (Γ >= 2) out to a distance of at least 800kpc. Our analysis, including optical data from the Liverpool Telescope, rules out a background active galactic nucleus for the X-ray emission and confirms its nature as a hotspot, making it the most-X-ray-luminous hotspot detected at low redshift.