  We present results from a 49.4 ks Chandra/ACIS-S observation of the nearby
($z$=0.059) X-shaped FRII radio galaxy 3C~403. This is the first Chandra
observation of an X-shaped radio galaxy, and one of the goals of this
pioneering study is to determine the relationship between the X-ray emitting
gas and the X-shaped radio morphology. The X-ray isophotes of the hot gas
within $\sim3.5''$ of the central galaxy are highly elliptical
(eccentricity$\sim$0.57) and co-aligned with the elliptical optical isophotes.
This supports the hypothesis that X-shaped radio sources are created by
propagation of jets through asymmetric density distributions. Within large
uncertainties, there is no evidence that the lobes or wings are overpressurized
relative to the ISM. We have detected X-ray emission from several of the radio
knots to the E of the active nucleus, and diffuse emission from the radio lobe
to the W. The X-ray emission from the eastern knots cannot be explained by an
inverse Compton model unless they are far from equipartition. Using archival
HST data, optical emission is detected from two knots, and the
radio/optical/X-ray spectra are well fitted by simple synchrotron models. This
is one of the strongest examples to date of X-ray synchrotron emission from
multiple knots in the jet of an FR II radio galaxy. X-ray emission is also
detected from the radio wings at a flux consistent with inverse Compton
scattering of CMB photons from relativistic electrons if the wings are near
equipartition. The nuclear spectrum is well described by a multi-component
model that includes a heavily absorbed power law and a bright, broadened Fe
line. A second, less absorbed, power-law component, likely to represent
unresolved emission from a pc-scale jet, is also required.
