IGR J22517+2218=MG3 J225155+2217: a new gamma-ray lighthouse in the distant Universe

• Published in: arXiv.org 2007-09
• Main Authors: Bassani, L, Landi, R, Malizia, A, Fiocchi, M T, Bazzano, A, Bird, A J, Dean, A J, Gehrels, N, Giommi, P, Ubertini, P
• Format: Article
• Language: English
• Subjects: Absorption; Blazars; Curvature; Flux; Gamma rays; Integrals; Lighthouses; Quasars; Radio spectra; Spectra; Spectral energy distribution; Universe
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0709.3023

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 x10^-11 erg cm-2 s-1, is spatially coincident with MG3 J225155+2217, a quasar at z=3.668. The Swift/XRT 0.5-10 keV continuum is flat (Gamma=1.5) with evidence for a spectral curvature below 1-2 keV either due to intrinsic absorption (NH=3 +/- 2 x 10^22 cm-2) or to a change in slope (Delta Gamma= 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.