A Chandra detection of the radio hotspot of 3C123

Chandra X-ray Observatory observations of the powerful, peculiar radio galaxy 3C123 have resulted in an X-ray detection of the bright eastern hotspot, with a 1-keV flux density of ~ 5 nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scattering of radio synchrotron photons by the population of electrons responsible for the radio emission (`synchrotron self-Compton emission') if the magnetic fields in the hotspot are close to their equipartition values. 3C123 is thus the third radio galaxy to show X-ray emission from a hotspot which is consistent with being in equipartition. Chandra also detects emission from a moderately rich cluster surrounding 3C123, with Lx (2-10 keV) = 2 x 10^44 ergs/s and kT ~ 5 keV, and absorbed emission from the active nucleus, with an inferred intrinsic column density of 1.7 x 10^22 cm^-2 and an intrinsic 2-10 keV luminosity of 10^44 ergs/s.