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Following the recent discovery of gamma rays from the radio-loud narrow-lineSeyfert 1 galaxy PMN J0948+0022 (z=0.5846), we started a multiwavelengthcampaign from radio to gamma rays, which was carried out between the end ofMarch and the beginning of July 2009. The source displayed activity at all theobserved wavelengths: a general decreasing trend from optical to gamma-rayfrequencies was followed by an increase of radio emission after less than twomonths from the peak of the gamma-ray emission. The largest flux change, abouta factor of about 4, occurred in the X-ray band. The smallest was atultraviolet and near-infrared frequencies, where the rate of the detectedphotons dropped by a factor 1.6-1.9. At optical wavelengths, where the samplingrate was the highest, it was possible to observe day-scale variability, withflux variations up to a factor of about 3. The behavior of PMN J0948+0022observed in this campaign and the calculated power carried out by its jet inthe form of protons, electrons, radiation and magnetic field are quite similarto that of blazars, specifically of flat-spectrum radio quasars. These resultsconfirm the idea that radio-loud narrow-line Seyfert 1 galaxies hostrelativistic jets with power similar to that of average blazars.

Multiwavelength monitoring of the enigmatic Narrow-Line Seyfert 1 PMN J0948+0022 in March-July 2009