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

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] 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

Searching for absorbed AGN in the 2XMM-Newton pre-release EPIC Serendipitous Source Catalogue

Aims.We aim to test a method of efficiently selecting X-ray obscured AGN in the 2XMM-Newton EPIC Serendipitous Source Catalogue. Methods.By means of a strong correlation established using the XMM-Newton Hard Bright Sample between the intrinsic absorption and the hardness ratio to the 0.5-2.0 keV and 2.0-4.5 keV bands, an efficient way of selecting absorbed sources has been worked out. A hardness ratio selection based on the 2XMM-Newton pre-release Source Catalogue led us to the definition of candidates likely to be obscured in X-rays. Results.X-ray and optical spectral analysis were performed for three objects. Strong absorption ($N_{\rm H} > 10^{22}$ cm-2) was detected from the X-ray analysis, confirming the efficiency of the method used to select obscured sources. The presence of absorption is also revealed in the optical band, although at a significantly lower level than inferred from the X-ray band

An X-ray bright ERO hosting a type 2 QSO

We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray ( $F_{2{-}10~\rm keV}\sim10^{-13}$ erg s-1 cm-2) extremely red objects ($R-K\ge5$) discovered so far. The source, XBS J0216-0435, belongs to the XMM-Newton Bright Serendipitous Survey and it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured ( $N_{\rm H}>10^{22}$ cm-2) QSO ( $L_{2{-}10~\rm keV}=4\times10^{45}$ erg s-1) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron K$\alpha$ line at 6.4 keV, a first estimate of the redshift of the source is derived ( $z_{\rm X}\sim2$). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations ( $z_{\rm O}=1.985\pm0.002$). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBS J0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-z between massive galaxies and powerful QSOs

The cosmological properties of AGN in the XMM-Newton Hard Bright Survey

Aims. We investigate here the X-ray luminosity function (XLF) of absorbed ($N_{\rm H}$ between 4 $\times$ 1021 and 1024 cm-2) and unabsorbed ($N_{\rm H}$ 1024 cm-2) AGN. Methods. To carry out this investigation, we have used the XMM-Newton Hard Bright Serendipitous Sample (HBSS), a complete sample of bright X-ray sources ($f_{\rm x}$ \ga 7 $\times$ 10-14 erg cm-2 s-1) at high galactic latitude (|b| > 20°) selected in the 4.5-7.5 keV energy band. The HBSS sample is now almost completely identified (97% spectroscopic identifications) and it can be safely used for a statistical investigation. The HBSS contains 62 AGN out of which 40 are unabsorbed (or marginally absorbed; $N_{\rm H}$ < 4 $\times$ 1021 cm-2) and 22 are absorbed ($N_{\rm H}$ between 4 $\times$ 1021 and ~1024 cm-2). Results. Absorbed and unabsorbed AGN are characterised by two different XLF with the absorbed AGN population being described by a steeper XLF, if compared with the unabsorbed ones, at all luminosities. The intrinsic fraction F of absorbed AGN (i.e., the fraction of sources with $N_{\rm H}$ between 4 $\times$ 1021 and 1024 cm-2 divided the sources with $N_{\rm H}$ below 1024 cm-2, corrected for the bias due to the photoelectric absorption) with $L_{2{-}10~{\rm keV}}$ \ga 3 $\times$ 1042 erg s-1 is 0.57 $\pm$ 0.11; we find that F decreases with the intrinsic luminosity, and probably, increases with the redshift. Our data are consistent with a flat Log $N_{\rm H}$ distribution for $N_{\rm H}$ between 1020 and 1024 cm-2. Finally, by comparing the results obtained here with those obtained using an optically-selected sample of AGN we derive, in an indirect way, the XLF of Compton thick AGN; the latter is well described by a XLF similar, in shape, to that of absorbed AGN, but having a normalization of about a factor of 2 above. The density ratio between Compton thick AGN ($N_{\rm H}$ $\geq$ 1024 cm-2) and Compton thin AGN ($N_{\rm H}$ $\leq$ 1024 cm-2) decreases from 1.08 $\pm$ 0.44 at ~1043 erg s-1 to 0.57 $\pm$ 0.22 at ~1044 erg s-1 to 0.23 $\pm$ 0.15 at ~1045 erg s-1. Conclusions. The results presented here on the anti-correlation between F and $-L_{\rm x}$ are fully consistent with the hypothesis of a reduction of the covering factor of the gas as a function of the luminosity and are clearly inconsistent with the simplest unified scheme of AGN. These results strongly support the recently proposed radiation-limited clumpy dust torus model although alternative physical models are also consistent with the observations

The XMM-Newton bright serendipitous survey - Identification and optical spectral properties

Aims.We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS), which contains a total of 400 objects (identification level = 87%). About 240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the active galactic nuclei (AGNs) population. Methods.By means of systematic spectroscopic campaigns using various telescopes and through the literature search, we have collected an optical spectrum for the large majority of the sources in the XBS survey and applied a well-defined classification "flow chart". Results.We find that the AGNs represent the most numerous population at the flux limit of the XBS survey (~10-13 erg cm-2 s-1) constituting 80% of the XBS sources selected in the 0.5-4.5 keV energy band and 95% of the "hard" (4.5-7.5 keV) selected objects. Galactic sources populate the 0.5-4.5 keV sample significantly (17%) and only marginally (3%) the 4.5-7.5 keV sample. The remaining sources in both samples are clusters/groups of galaxies and normal galaxies (i.e. probably not powered by an AGN). Furthermore, the percentage of type 2 AGNs (i.e. optically absorbed AGNs with $A_{\rm V}>2$ mag) dramatically increases going from the 0.5-4.5 keV sample ( $f=N_{\rm AGN 2}/N_{\rm AGN}=7$%) to the 4.5-7.5 keV sample (f=32%). We finally propose two simple diagnostic plots that can be easily used to obtain the spectral classification for relatively low-redshift AGNs even if the quality of the spectrum is not good

The XMM-Newton Serendipitous Survey: I - The role of XMM-Newton Survey Science Centre

This paper describes the performance of XMM-Newton for serendipitous surveys and summarises the scope and potential of the XMM-Newton Serendipitous Survey. The role of the Survey Science Centre (SSC) in the XMM-Newton project is outlined. The SSC's follow-up and identification programme for the XMM-Newton serendipitous survey is described together with the presentation of some of the first results