Spectroscopic identification of ten faint hard X-ray sources discovered by Chandra

Abstract We report optical spectroscopic identifications of 10 hard (2–10 keV) X-ray selected sources discovered by Chandra. The X-ray flux of the sources ranges between 1.5 and 25 ×10−14 erg cm −2 s −1 , the lower value being 3 times fainter than in previous BeppoSAX and ASCA surveys. Their R band magnitudes are in the range 12.8–22. Six of the Chandra sources are broad line quasars with redshifts between 0.42 and 1.19, while the optical identification of the remaining four is quite varied: two are X-ray obscured, emission line AGN at z = 0.272 and z = 0.683, one is a starburst galaxy at z = 0.016 and one, most unusually, is an apparently normal galaxy at z = 0.158. These findings confirm and extend down to fainter X-ray fluxes the BeppoSAX results, in providing samples with a wide range of X-ray and optical properties. The ratio between the soft X-ray and the optical luminosity of the z = 0.158 galaxy is a factor at least 30 higher than that of normal galaxies, and similar to those of AGN. The high X-ray luminosity and the lack of optical emission lines suggest an AGN in which either continuum beaming dominates, or emission lines are obscured or not efficiently produced.