Igr J22517+2218=mg3 J225155+2217: a New Gamma-ray Lighthouse in the Distant Universe

We report on the identification of a new soft gamma ray source, namely IGR J22517+2218, detected with IBIS/INTEGRAL. The source, which has an observed 20-100 keV flux of ∼4 × 10 erg cm s, is spatially coincident with MG3 J225155+2217, a quasar at z=3.668. The Swift/XRT 0.5-10 keV continuum is flat (Γ=1.5) with evidence for a spectral curvature below 1-2 keV either due to intrinsic absorption (NH=3±2 × 10 22 cm) or to a change in slope (∆Γ= 0.5). X-ray observations indicate flux variability over a 6 days period which is further supported by a flux mismatch between Swift and INTEGRAL spectra. IGR J22517+2218 is radio loud and has a flat radio spectrum; optically it is a broad line emitting quasar with the atypical property of hosting a narrow line absorption system. The Source Spectral Energy Distribution is unusual compared to blazars of similar type: either it has the synchrotron peak in the X/gamma-ray band (i.e. much higher than generally observed) or the Compton peak in the MeV range (i.e. lower than typically measured). IGR J22517+2218=MG3 J225155+2217 is the second most distant blazar detected above 20 keV and a gamma-ray lighthouse shining from the edge of our Universe. Subject headings: X-gamma-ray dataactive galactic nuclei