  We report on radio-to-gamma-ray observations during 2011 May-September of PMN
J0948+0022, the first narrow-line Seyfert 1 (NLSy1) galaxy detected in
gamma-rays by Fermi-LAT. Strong variability was observed in gamma-rays, with
two flaring periods peaking on 2011 June 20 and July 28. The variability
observed in optical and near-infrared seems to have no counterpart in
gamma-rays. This different behaviour could be related to a bending and
inhomogeneous jet or a turbulent extreme multi-cell scenario. The radio spectra
showed a variability pattern typical of relativistic jets.
  The XMM spectrum shows that the emission from the jet dominates above 2 keV,
while a soft X-ray excess is evident in the low-energy part of the X-ray
spectrum. Models where the soft emission is partly produced by blurred
reflection or Comptonisation of the thermal disc emission provide good fits to
the data. The X-ray spectral slope is similar to that found in radio-quiet
NLSy1, suggesting that a standard accretion disc is present, as expected from
the high accretion rate. Except for the soft X-ray excess, unusual in
jet-dominated AGNs, PMN J0948+0022 shows all characteristics of the blazar
class.
