On the identification of the Fermi/LAT source 0FGL J2001.0+4352 with a BL Lac

We report on the identification of the gamma-ray source 0FGL J20001.0+4352 listed in the Fermi bright source catalogue. This object, which has an observed 1-100 GeV flux of (7.8 +/- 1.2) x 10(-9) ph cm(-2) s(-1) and is located close to the Galactic plane, is not associated with any previously known high-energy source. We use archival XMM-Newton and Swift/X-ray Telescope (XRT) data to localize with arcsec accuracy the X-ray counterpart of this GeV emitter and to characterize its X-ray properties: the source is bright (the 0.2-12 keV flux is 1.9 x 10(-12) erg cm(-2) s(-1)), variable (by a factor of similar to 2) and with a steep power-law spectrum (Gamma = 2.7). It coincides with a radio bright (similar to 200 mJy at 8.4 GHz) and flat spectrum object [MG4 J200112+4352 in NASA/IPAC Extragalactic Database (NED)]. Broad-band optical photometry of this source suggests variability also in this waveband, while a spectroscopic follow-up observation provides the first source classification as a BL Lac object. The source SED, as well as the overall characteristics and optical classification, point to a high frequency peaked blazar identification for 0FGL J2001.0+4352.