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X-ray spectra of XMM-Newton serendipitous medium flux sources

By S. Mateos, X. Barcons, F.J. Carrera, M.T. Ceballos, A. Caccianiga, G. Lamer, T. Maccacaro, M.J. Page, A. Schwope and Michael G. Watson


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.Peer-reviewedPublisher Versio

Publisher: EDP Sciences for European Southern Observatory (ESO)
Year: 2005
DOI identifier: 10.1051/0004-6361:20041340
OAI identifier:

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