An optical inverse - Compton hotspot in 3 C 196 ?

Several hotspots of FRII radio sources have previously been detected in the X-ray at a flux level consistent with the X-rays being due to inverse-Compton scattering of radio “synchrotron photons synchrotron self-Compton”, if the magnetic fields in the hotspots are close to their equipartition values. However, the number of hotspots compact and bright enough to exhibit detectable X-ray emission is small, so it is worth searching for synchrotron self-Compton emission in the optical, in spite of the obvious observational difficulties of such an approach. In this note I report on a possible detection of an optical inverse-Compton hotspot in a deep Hubble Space Telescope observation of the distant quasar 3C 196, at a level which implies a hotspot magnetic field strength close to equipartition if the electrons have a low-energy cutoff around γ ∼ 500.