Radio and X-ray emission from disc winds in radio-quiet quasars
  It has been proposed that the radio spectra of radio-quiet quasars is
produced by free-free emission in the optically thin part of an accretion disc
wind. An important observational constraint on this model is the observed X-ray
luminosity. We investigate this constraint using a sample of PG radio-quiet
quasars for which XMM-Newton EPIC spectra are available. Comparing the
predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all
of the studied PG quasars require a large hydrogen column density absorber,
requiring these quasars to be close to or Compton-thick. Such a large column
density can be directly excluded for PG 0050+124, for which a high-resolution
RGS spectrum exists. Further constraint on the column density for a further 19
out of the 21 studied PG quasars comes from the EPIC spectrum characteristics
such as hard X-ray power-law photon index and the equivalent width of the Fe
Kalpha line; and the small equivalent width of the C IV absorber present in UV
spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they
are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind
originating close to the super-massive black hole. We conclude that for 20 out
of 22 PG quasars studied free-free emission from a wind emanating from the
accretion disc cannot mutually explain the observed radio and X-ray luminosity.
