X-ray Emission from the Radio Jet in 3c 120

We report the discovery of X-ray emission from a radio knot at a projected distance of 25′′ from the nucleus of the Seyfert galaxy, 3C 120. The data were obtained with the ROSAT High Resolution Imager (HRI). Optical upper limits for the knot preclude a simple power law extension of the radio spectrum and we calculate some of the physical parameters for thermal bremsstrahlung and synchrotron self-Compton models. We conclude that no simple model is consistent with the data but if the knot contains small regions with flat spectra, these could produce the observed X-rays (via synchrotron emission) without being detected at other wavebands. Subject headings: galaxies: active—galaxies: individual (3C 120)—galaxies: jets—galaxies: Seyfert—radiation mechanisms: non-thermal—radio continuum: galaxies