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Title: X-ray spectra of XMM-Newton serendipitous medium flux sources
Authors: Mateos, S.
Barcons, X.
Carrera, F.J.
Ceballos, M.T.
Caccianiga, A.
Lamer, G.
Maccacaro, T.
Page, M.J.
Schwope, A.
Watson, Michael G.
First Published: Apr-2005
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy and Astrophysics, 2005, 433 (3), pp.855-873
Abstract: We report on the results of a detailed analysis of the X-ray spectral properties of a large sample of sources detected serendipitously with the XMM-Newton observatory in 25 selected fields, for which optical identification is in progress. The survey covers a total solid angle of ~3.5 deg[superscript 2] and contains 1137 sources with ~10[superscript -15] < S[subscript 0.5-10] < 10[superscript -12] erg cm[superscript -2] s[superscript -1] with good enough spectral quality as to perform a detailed X-ray spectral analysis of each individual object. We find evidence for hardening of the average X-ray spectra of the sources towards fainter fluxes, and we interpret this as indicating a higher degree of photoelectric absorption amongst the fainter population. Absorption is detected at 95% confidence in 20% of the sources, but it could certainly be present in many other sources below our detection capabilities. For Broad Line AGNs (BLAGNs), we detect absorption in ~10% of the sources with column densities in the range 10[superscript 21] – 10[superscript 22] cm[superscript -2]. The fraction of absorbed Narrow Emission Line galaxies (NELGs, most with intrinsic X-ray luminosities >10[superscript 43] erg s[superscript -1], and therefore classified as type 2 AGNs) is significantly higher (40%), with a hint of moderately higher columns. After correcting for absorption, we do not find evidence for a redshift evolution of the underlying power law index of BLAGNs, which stays roughly constant at Γ ~ 1.9, with intrinsic dispersion of 0.4. A small fraction (~7%) of BLAGNs and NELGs require the presence of a soft excess, that we model as a black body with temperature ranging from 0.1 to 0.3 keV. Comparing our results on absorption to popular X-ray background synthesis models, we find absorption in only ~40% of the sources expected. This is due to a deficiency of heavily absorbed sources (with N[subscript H] ~ 10[superscript 22] – 10[superscript 24] cm[superscript -2]) in our sample in comparison with the models. We therefore conclude that the synthesis models require some revision in their specific parameters.
DOI Link: 10.1051/0004-6361:20041340
ISSN: 0004-6361
eISSN: 1432-0746
Version: Publisher Version
Status: Peer-reviewed
Type: Article
Rights: © ESO 2005. Reproduced with permission from Astronomy & Astrophysics.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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