The Origin of the X-ray Emission in Two Well-Aligned Extragalactic Jets:
  The Case for IC/CMB
  Over the past two decades, the most commonly adopted explanation for high and
hard X-ray emission in resolved quasar jets has been inverse Compton
upscattering of the Cosmic Microwave Background (IC/CMB), which requires jets
which remain highly relativistic on 10-1000 kpc scales. In more recent years
various lines of observational evidence, including gamma-ray upper limits, have
disfavored this explanation in favor of a synchrotron origin. While the IC/CMB
model generally predicts a high level of gamma-ray emission, it has never been
detected. Here we report the detection of a low-state Fermi/LAT gamma-ray
spectrum associated with two jetted AGN which is consistent with the
predictions of the IC/CMB model for their X-ray emission. We have used archival
multiwavelength observations to make precise predictions for the expected
minimum flux in the GeV band, assuming that the X-ray emission from the
kpc-scale jet is entirely due to the IC/CMB process. In both sources -- OJ 287
and PKS 1510-089 -- the minimum-detected gamma-ray flux level agrees with
predictions. Both sources exhibit extreme superluminal proper motions relative
to their jet power, which argues for the well-aligned jets required by the
IC/CMB model. In the case of PKS~1510-089, it cannot be ruled out that the
minimum gamma-ray flux level is due to a low state of the variable core which
only matches the IC/CMB prediction by chance. Continued long-term monitoring
with the Fermi/LAT could settle this issue by detecting a plateau signature in
the recombined light-curve which would clearly signal the presence of a
non-variable emission component.
