A Chandra detection of the radio hotspot of 3C 123

Chandra X-ray Observatory observations of the powerful, peculiar radio gala xy 3C 123 have resulted in an X-ray detection of the bright eastern hotspot , with a 1-keV flux density of similar to 5nJy. The X-ray flux and spectrum of the hotspot are consistent with the X-rays being inverse-Compton scatte ring of radio synchrotron photons by the population of electrons responsibl e for the radio emission ('synchrotron self-Compton emission') if the magne tic fields in the hotspot are close to their equipartition values. 3C 123 i s thus the third radio galaxy to show X-ray emission from a hotspot which i s consistent with being in equipartition. Chandra also detects emission fro m a moderately rich cluster surrounding 3C 123, with L-X(2-10 keV) = 2 x 10 (44) egr s(-1) and kT similar to 5 keV, and absorbed emission from the acti ve 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) erg s(-1).