  We report X-ray imaging of the powerful FR-II radio galaxy 3C353 using the
Chandra X-ray Observatory. 3C353's two 4"-wide and 2'-long jets allow us to
study in detail the internal structure of the large-scale relativistic outflows
at both radio and X-ray photon energies with the sub-arcsecond spatial
resolution. In a 90 ks Chandra observation, we have detected X-ray emission
from most radio structures in 3C353, including the nucleus, the jet and the
counterjet, the terminal jet regions (hotspots), and one radio lobe. We show
that the detection of the X-ray emission associated with the radio knots and
counterknots puts several crucial constraints on the X-ray emission mechanisms
in powerful large-scale jets of quasars and FR-II sources. In particular, we
show that this detection is inconsistent with the inverse-Compton model
proposed in the literature, and instead implies a synchrotron origin of the
X-ray jet photons. We also find that the width of the X-ray counterjet is
possibly narrower than that measured in radio bands, that the radio-to-X-ray
flux ratio decreases systematically downstream along the jets, and that there
are substantial (kpc-scale) offsets between the positions of the X-ray and
radio intensity maxima within each knot, whose magnitudes increase away from
the nucleus. We discuss all these findings in the wider context of the physics
of extragalactic jets, proposing some particular though not definitive
solutions or interpretations for each problem.
