  Chandra ACIS observations of PKS 0521-365 find that the X-ray emission of
this BL Lac object consists of emission from an unresolved core, a diffuse
halo, and a 2 arcsec jet feature coincident with the inner radio/optical jet. A
comparison with a new ATCA 8.6-GHz map also finds X-ray emission from the
bright hotspot south-east of the nucleus. The jet spectrum, from radio to
X-ray, is probably synchrotron emission from an electron population with a
broken power-law energy distribution, and resembles the spectra seen from the
jets of low-power (FR I) radio galaxies. The hotspot X-ray flux is consistent
with the expectations of synchrotron self-Compton emission from a plasma close
to equipartition, as seen in studies of high-power (FR II) radio galaxies.
While the angular structure of the halo is similar to that found by an analysis
of the ROSAT HRI image, its brightness is seen to be lower with Chandra, and
the halo is best interpreted as thermal emission from an atmosphere of similar
luminosity to the halos around FR I radio galaxies. The X-ray properties of PKS
0521-365 are consistent with it being a foreshortened, beamed, radio galaxy.
