  IIIZw2 was observed with XMM-Newton in July 2000. Its X-ray spectrum can be
described by a powerlaw of photon index Gamma = 1.7 with a Gaussian line at 6.7
keV. There is no significant evidence of intrinsic absorption within the source
or of a soft X-ray excess.
  Multi-wavelength light curves over a period of 25 years show related
variations from the radio to the X-rays. We interpret the radio to optical
emission as synchrotron radiation, self-absorbed in the radio/millimeter
region, and the X-rays as mainly due to Compton up-scattering of low-energy
photons by the population of high-energy electrons that give rise to the
synchrotron radiation.
