The Megaparsec-Scale X-ray Jet of the BL Lac Object OJ287
  We present an X-ray image of the BL Lacertae object OJ287 revealing a long
jet, curved by 55 degrees and extending 20", or 90 kpc from the nucleus. This
de-projects to >1 Mpc based on the viewing angle on parsec scales. Radio
emission follows the general X-ray morphology but extends even farther from the
nucleus. The upper limit to the isotropic radio luminosity, ~2E24 W/Hz, places
the source in the Fanaroff-Riley 1 (FR 1) class, as expected for BL Lac
objects. The spectral energy distribution indicates that the extended X-ray
emission is from inverse Compton scattering of cosmic microwave background
photons. In this case, the derived magnetic field is B ~ 5 microGauss, the
minimum electron energy is 7-40 m_e c^2, and the Doppler factor is delta ~ 8 in
a knot 8" from the nucleus. The minimum total kinetic power of the jet is
1-2E45 erg/s. Upstream of the bend, the width of the X-ray emission in the jet
is about half the projected distance from the nucleus. This implies that the
highly relativistic bulk motion is not limited to an extremely thin spine, as
has been proposed previously for FR 1 sources. The bending of the jet, the
deceleration of the flow from parsec to kiloparsec scales, and the knotty
structure can all be caused by standing shocks inclined by ~7 degrees to the
jet axis. Moving shocks resulting from major changes in the flow properties can
also reproduce the knotty structure, but such a model does not explain as many
of the observational details.
