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The XMM-SSC survey of hard-spectrum XMM-Newton sources - I. Optically bright sources

AuthorsPage, M. J.; Lehmann, I.; Boller, Th.; Watson, M. G.; Dwelly, Tom; Hess, S.; Matute, Israel; Loaring, N. S.; Rosen, Simon; Ziaeepour, H.; Schwope, A.; Lamer, Georg; Carrera, Francisco J. ; Tedds, J. A.; Della Ceca, R.; Severgnini, P.; McMahon, Richard G.; Yuan, W.
KeywordsX-rays: galaxies
Galaxies: active
Issue Date2007
PublisherRoyal Astronomical Society
Oxford University Press
CitationMonthly Notices of the Royal Astronomical Society 378(4): 1335-1355 (2007)
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.
Publisher version (URL)https://doi.org/10.1111/j.1365-2966.2007.11857.x
Identifiersdoi: 10.1111/j.1365-2966.2007.11857.x
issn: 0035-8711
e-issn: 1365-2966
Appears in Collections:(IFCA) Artículos
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