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dc.contributor.authorPage, M. J.-
dc.contributor.authorLehmann, I.-
dc.contributor.authorBoller, Th.-
dc.contributor.authorWatson, M. G.-
dc.contributor.authorDwelly, Tom-
dc.contributor.authorHess, S.-
dc.contributor.authorMatute, Israel-
dc.contributor.authorLoaring, N. S.-
dc.contributor.authorRosen, Simon-
dc.contributor.authorZiaeepour, H.-
dc.contributor.authorSchwope, A.-
dc.contributor.authorLamer, Georg-
dc.contributor.authorCarrera, Francisco J.-
dc.contributor.authorTedds, J. A.-
dc.contributor.authorDella Ceca, R.-
dc.contributor.authorSevergnini, P.-
dc.contributor.authorMcMahon, Richard G.-
dc.contributor.authorYuan, W.-
dc.identifierdoi: 10.1111/j.1365-2966.2007.11857.x-
dc.identifierissn: 0035-8711-
dc.identifiere-issn: 1365-2966-
dc.identifier.citationMonthly Notices of the Royal Astronomical Society 378(4): 1335-1355 (2007)-
dc.description.abstractWe present optical and X-ray data for a sample of serendipitous XMM-Newton sources that are selected to have 0.5-2 versus 2-4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2-4.5 keV X-ray flux ≥10-14 erg cm-2 s-1, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association rather than the correct identification of the X-ray source. The X-ray spectra of all the sources are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them, including the two sources with 2-10 keV intrinsic luminosities of <1042 erg s-1, appear to be absorbed active galactic nuclei (AGN). The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type 2 AGN. Three sources have 2-10 keV luminosities of >1044 erg s-1, and two of these sources have optical spectra which are dominated by narrow emission lines, that is, are type 2 QSOs. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 1023 cm-2. This implies that ratios of X-ray absorption to optical/ultraviolet extinction equivalent to >100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few per cent of the population), and may be restricted to broad absorption line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law; all seven are narrow emission-line objects with z < 0.3 and 2-10 keV intrinsic luminosities <1043 erg s-1. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that >4 per cent of broad-line AGN (BLAGN) have ionized absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray-absorbed BLAGN in our sample the X-ray spectrum requires an ionized absorber, consistent with this picture.-
dc.description.sponsorshipFJC acknowledges financial support from the Spanish Ministerio de Educacion Ciencia, under projects ESP2003-00812 and ESP2006-13608-C02-01. RDC and PS acknowledge partial financial support by the MIUR (Cofin-03-02-23) and INAF.-
dc.publisherRoyal Astronomical Society-
dc.publisherOxford University Press-
dc.relation.isversionofPublisher's version-
dc.subjectX-rays: galaxies-
dc.subjectGalaxies: active-
dc.titleThe XMM-SSC survey of hard-spectrum XMM-Newton sources - I. Optically bright sources-
dc.description.versionPeer Reviewed-
dc.contributor.funderIstituto Nazionale di Astrofisica-
dc.contributor.funderMinistero dell'Istruzione, dell'Università e della Ricerca-
dc.contributor.funderMinisterio de Educación y Ciencia (España)-
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