G. C. Stewart

The XMM-Newton serendipitous survey: V - The Second XMM-Newton serendipitous source catalogue

Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods. The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results. The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg(2). The non-overlapping sky area is similar to 360 deg(2) (similar to 1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties

The XMM-Newton serendipitous survey - IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)

Aims. X-ray sources at intermediate fluxes (a few x 10(-14) erg cm(-2) s(-1)) with a sky density of similar to 100 deg(-2) are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods. We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. Results. We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (similar to 35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.

X-ray groups and clusters of galaxies in the Subaru-XMM Deep Field

We present the results of a search for galaxy clusters in the Subaru–XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5–2 keV band of 2 × 10^(−15) erg cm^(−2) s^(−1) over one of the widest XMM–Newton contiguous raster surveys, covering an area of 1.3 deg^2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) − log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance σ_8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg^2) survey is needed.

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 SSCs follow-up and identification programme for the XMM-Newton serendipitous survey is described together with the presentation of some of the first results.

The X-ray spectra of high-luminosity active galactic nuclei observed by Ginga

Results are presented on the X-ray emission from 13 objects, observed by Ginga as part of a spectral survey of bright quasars in the energy range 2-20 keV. The distribution of the power-law energy index for this sample has a mean of 0.81 and shows significant intrinsic dispersion, σ = 0.31, values which are broadly compatible with those from samples of lower luminosity active galactic nuclei. The mean spectral slope is clearly too sleep to fit the spectrum of the cosmic diffuse X-ray background (CXB) at energies less than 20 keV, confirming the spectral paradox in the discrete-source explanation of the CXB

The mass profile and gas content of M87

X-ray images and spectroscopic observations, in particular of the Fe L lines, are used to constrain the structure of the hot gas and gravitating matter around M87 with respect to allowable temperature gradient, and therefore gravitational potential, over the 1-10 arcmin radius range. Models in which the gravitating mass has a core radius of about 25 kpc are favored, suggesting that the material is associated with M87 rather than with the Virgo cluster as a whole. The gas temperature is noted to vary slowly beyond 5 arcmin, while the variation in the inner regions is not consistent with thermal conduction models for powering the central X-ray emission.

High precision X-ray log N - Log S distributions: Implications for the obscured AGN population

Context. Our knowledge of the properties of AGN, especially those of optical type-2 objects, is very incomplete. Because extragalactic source count distributions are dependent on the cosmological and statistical properties of AGN, they provide a direct method of investigating the underlying source populations. Aims. We aim to constrain the extragalactic source count distributions over a broad range of X-ray fluxes and in various energy bands to test whether the predictions from X-ray background synthesis models agree with the observational constraints provided by our measurements. Methods. We have used 1129 XMM-Newton observations at |b| > 20 ◦ covering a total sky area of 132.3 deg 2 to compile the largest complete samples of X-ray selected objects to date both in the 0.5− 1k eV, 1− 2k eV, 2−4.5 keV, 4.5−10 keV bands employed in standard XMM-Newton data processing and in the 0.5−2 keV and 2−10 keV energy bands more usually considered in source count studies. Our survey includes in excess of 30 000 sources and spans fluxes from ∼10 −15 to 10 −12 erg cm −2 s −1 below 2 keV and from ∼10 −14 to 10 −12 erg cm −2 s −1 above 2 keV where the bulk of the cosmic X-ray background energy density is produced. Results. The very large sample size we obtained means our results are not limited by cosmic variance or low counting statistics. A break in the source count distributions was detected in all energy bands except the 4.5−10 keV band. We find that an analytical model comprising 2 power-law components cannot adequately describe the curvature seen in the source count distributions. The shape of the logN(>S ) − logS is strongly dependent on the energy band with a general steepening apparent as we move to higher energies. This is due to the fact that non-AGN populations, comprised mainly of stars and clusters of galaxies, contribute up to 30% of the source population at energies <2 keV and at fluxes ≥10 −13 erg cm −2 s −1 , and these populations of objects have significantly flatter source count distributions than AGN. We find a substantial increase in the relative fraction of hard X-ray sources at higher energies, from ≥55% below 2 keV to ≥77% above 2 keV. However, the majority of sources detected above 4.5 keV still have significant flux below 2 keV. Comparison with predictions from the synthesis models suggest that the models might be overpredicting the number of faint absorbed AGN, which would call for fine adjustment of some model parameters such as the obscured to unobscured AGN ratio and/or the distribution of column densities at intermediate obscuration.

A deep ROSAT survey – IV. The evolution of X-ray selected QSOs

We report on a new estimate of the QSO X-ray luminosity function and its evolution with redshift based on a sample of 107 QSOs detected at faint X-ray fluxes,

X-ray absorption evolution in Gamma-Ray Bursts: intergalactic medium or evolutionary signature of their host galaxies?

S{\rm(0.5-2\,keV)}>4\times10^{-15}\,

ASCA observations of deep ROSAT fields — I. The nature of the X-ray source populations

\ergcms , with the {\it ROSAT} X-ray satellite. For