Implications for the structure of the relativistic jet from
  multiwavelength observations of NGC 6251
  NGC 6251 is a luminous radio galaxy ~104 Mpc away that was detected
significantly with the Fermi Gamma-ray Space Telescope, and before that with
EGRET (onboard the Compton Gamma-ray Observatory). Different observational
constraints favor a nuclear origin for the gamma-ray emission. Here we present
a study of the spectral energy distribution (SED) of the core of NGC 6251, and
give results of modeling in the one-zone synchrotron/SSC framework. The SSC
model provides a good description of the radio to gamma-ray emission but, as
for other misaligned sources, predicts a lower Lorentz factor (\Gamma~2.4) than
typically found when modeling blazars. If the blazar unification scenario is
correct, this seems to point to the presence of at least two emitting regions
in these objects, one with a higher and one with a lower Lorentz factor. The
solution of a structured jet, with a fast moving spine surrounded by a slow
layer, is explored and the consequences of the two models for the jet
energetics and evolution are discussed.
