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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
The XMM-SSC survey of hard-spectrum XMM-Newton sources - I. Optically bright sources
Monthly Notices of the Royal Astronomical Society, Volume 378, No. 4, Year 2007
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Description
We 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. © 2007 RAS.
Authors & Co-Authors
Page, Mathew J.
United Kingdom, Dorking
Ucl Mullard Space Science Laboratory
Lehmann, I.
Germany, Garching Bei Munchen
Max Planck Institute for Extraterrestrial Physics
Boller, Th
Germany, Garching Bei Munchen
Max Planck Institute for Extraterrestrial Physics
Watson, Mike G.
United Kingdom, Leicester
University of Leicester
Dwelly, Tom
United Kingdom, Dorking
Ucl Mullard Space Science Laboratory
United Kingdom, Southampton
University of Southampton
Hess, S.
Germany, Garching Bei Munchen
Max Planck Institute for Extraterrestrial Physics
Matute, I.
Germany, Garching Bei Munchen
Max Planck Institute for Extraterrestrial Physics
Loaring, Nicola S.
United Kingdom, Dorking
Ucl Mullard Space Science Laboratory
South Africa, Cape Town
South African Astronomical Observatory
Rosen, Simon R.
United Kingdom, Dorking
Ucl Mullard Space Science Laboratory
Ziaeepour, Houri
United Kingdom, Dorking
Ucl Mullard Space Science Laboratory
Schwope, Axel D.
Germany, Potsdam
Leibniz Institute for Astrophysics Potsdam
Lamer, Georg
Germany, Potsdam
Leibniz Institute for Astrophysics Potsdam
Carrera, Francisco J.
Spain, Santander
Universidad de Cantabria
Tedds, Johnathan A.
United Kingdom, Leicester
University of Leicester
Della Ceca, Roberto
Italy, Milan
Inaf Istituto Di Astrofisica Spaziale e Fisica Cosmica, Milan
Severgnini, Paola
Italy, Milan
Inaf Istituto Di Astrofisica Spaziale e Fisica Cosmica, Milan
McMahon, R. G.
United Kingdom, Cambridge
Institute of Astronomy
Yuan, W.
United Kingdom, Cambridge
Institute of Astronomy
China, Kunming
Yunnan Observatories
Statistics
Citations: 18
Authors: 18
Affiliations: 10
Identifiers
Doi:
10.1111/j.1365-2966.2007.11857.x
ISSN:
00358711
e-ISSN:
13652966
Research Areas
Environmental
Study Design
Cross Sectional Study
Study Approach
Quantitative