Multiwavelength monitoring of the enigmatic Narrow-Line Seyfert 1 PMN
  J0948+0022 in March-July 2009
  Following the recent discovery of gamma rays from the radio-loud narrow-line
Seyfert 1 galaxy PMN J0948+0022 (z=0.5846), we started a multiwavelength
campaign from radio to gamma rays, which was carried out between the end of
March and the beginning of July 2009. The source displayed activity at all the
observed wavelengths: a general decreasing trend from optical to gamma-ray
frequencies was followed by an increase of radio emission after less than two
months from the peak of the gamma-ray emission. The largest flux change, about
a factor of about 4, occurred in the X-ray band. The smallest was at
ultraviolet and near-infrared frequencies, where the rate of the detected
photons dropped by a factor 1.6-1.9. At optical wavelengths, where the sampling
rate was the highest, it was possible to observe day-scale variability, with
flux variations up to a factor of about 3. The behavior of PMN J0948+0022
observed in this campaign and the calculated power carried out by its jet in
the form of protons, electrons, radiation and magnetic field are quite similar
to that of blazars, specifically of flat-spectrum radio quasars. These results
confirm the idea that radio-loud narrow-line Seyfert 1 galaxies host
relativistic jets with power similar to that of average blazars.
