M. T. Ceballos

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 - VII. The third XMM-Newton serendipitous source catalogue

© ESO, 2016.Context. Thanks to the large collecting area (3 × ∼1500 cm2 at 1.5 keV) and wide field of view (30′ across in full field mode) of the X-ray cameras on board the European Space Agency X-ray observatory XMM-Newton, each individual pointing can result in the detection of up to several hundred X-ray sources, most of which are newly discovered objects. Since XMM-Newton has now been in orbit for more than 15 yr, hundreds of thousands of sources have been detected. Aims. Recently, many improvements in the XMM-Newton data reduction algorithms have been made. These include enhanced source characterisation and reduced spurious source detections, refined astrometric precision of sources, greater net sensitivity for source detection, and the extraction of spectra and time series for fainter sources, both with better signal-to-noise. Thanks to these enhancements, the quality of the catalogue products has been much improved over earlier catalogues. Furthermore, almost 50% more observations are in the public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science Centre to produce a much larger and better quality X-ray source catalogue. Methods. The XMM-Newton Survey Science Centre has developed a pipeline to reduce the XMM-Newton data automatically. Using the latest version of this pipeline, along with better calibration, a new version of the catalogue has been produced, using XMM-Newton X-ray observations made public on or before 2013 December 31. Manual screening of all of the X-ray detections ensures the highest data quality. This catalogue is known as 3XMM. Results. In the latest release of the 3XMM catalogue, 3XMM-DR5, there are 565 962 X-ray detections comprising 396 910 unique X-ray sources. Spectra and lightcurves are provided for the 133 000 brightest sources. For all detections, the positions on the sky, a measure of the quality of the detection, and an evaluation of the X-ray variability is provided, along with the fluxes and count rates in 7 X-ray energy bands, the total 0.2-12 keV band counts, and four hardness ratios. With the aim of identifying the detections, a cross correlation with 228 catalogues of sources detected in all wavebands is also provided for each X-ray detection. Conclusions. 3XMM-DR5 is the largest X-ray source catalogue ever produced. Thanks to the large array of data products associated with each detection and each source, it is an excellent resource for finding new and extreme objects.

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.

The XMM-Newton serendipitous survey VI. The X-ray luminosity function

We present the X-ray luminosity function of AGN in three energy bands (Soft: 0.5-2 keV, Hard: 2-10 keV and Ultrahard: 4.5-7.5 keV). We have used the XMS survey along with other highly complete flux-limited deeper and shallower surveys for a total of 1009, 435 and 119 sources in the Soft, Hard and Ultrahard bands, respectively. We have modeled the intrinsic absorption of the Hard and Ultrahard sources (NH function) and computed the intrinsic X-ray luminosity function in all bands using a Maximum Likelihood fit technique to an analytical model. We find that the X-ray luminosity function (XLF) is best described by a Luminosity-Dependent Density Evolution (LDDE) model. Our results show a good overall agreement with previous results in the Hard band, although with slightly weaker evolution. Our model in the Soft band present slight discrepancies with other works in this band, the shape of our present day XLF being significantly flatter. We find faster evolution in the AGN detected in the Ultrahard band than those in the Hard band. The fraction of absorbed AGN in the Hard and Ultrahard bands is dependent on the X-ray luminosity. We find evidence of evolution of this fraction with redshift in the Hard band but not in the Ultrahard band, possibly due to the low statistics. Our best-fit XLF shows that the high-luminosity AGN are fully formed earlier than the less luminous AGN. The latter sources account for the vast majority of the accretion rate and mass density of the Universe, according to an anti-hierarchical black hole growth scenario.

The XMM-Newton serendipitous surveyVI. The X-ray luminosity function

We present the X-ray luminosity function of AGN in three energy bands (Soft: 0.5-2 keV, Hard: 2-10 keV and Ultrahard: 4.5-7.5 keV). We have used the XMS survey along with other highly complete flux-limited deeper and shallower surveys for a total of 1009, 435 and 119 sources in the Soft, Hard and Ultrahard bands, respectively. We have modeled the intrinsic absorption of the Hard and Ultrahard sources (NH function) and computed the intrinsic X-ray luminosity function in all bands using a Maximum Likelihood fit technique to an analytical model. We find that the X-ray luminosity function (XLF) is best described by a Luminosity-Dependent Density Evolution (LDDE) model. Our results show a good overall agreement with previous results in the Hard band, although with slightly weaker evolution. Our model in the Soft band present slight discrepancies with other works in this band, the shape of our present day XLF being significantly flatter. We find faster evolution in the AGN detected in the Ultrahard band than those in the Hard band. The fraction of absorbed AGN in the Hard and Ultrahard bands is dependent on the X-ray luminosity. We find evidence of evolution of this fraction with redshift in the Hard band but not in the Ultrahard band, possibly due to the low statistics. Our best-fit XLF shows that the high-luminosity AGN are fully formed earlier than the less luminous AGN. The latter sources account for the vast majority of the accretion rate and mass density of the Universe, according to an anti-hierarchical black hole growth scenario.

XMM-Newton observations of the Lockman Hole IV: spectra of the brightest AGN ,

This paper presents the results of a detailed X-ray spectral analysis of a sample of 123 X-ray sources detected with XMM-Newton in the Lockman Hole field. This is the deepest observation carried out with XMM-Newton with more that 600 ks of good EPIC-pn data. We have spectra with good signal to noise (>500 source counts) for all objects down to 0.2−12 keV fluxes of ∼5 × 10 −15 erg cm −2 s −1 (flux limit of ∼6 × 10 −16 erg cm −2 s −1 in the 0.5− 2a nd 2−10 keV bands). At the time of the analysis, we had optical spectroscopic identifications for 60% of the sources, 46 being optical type-1 AGN and 28 optical type-2 AGN. Using a single power law model our sources’ average spectral slope hardens at faint 0.5−2 keV fluxes but not at faint 2−10 keV fluxes. We have been able to explain this effect in terms of an increase in X-ray absorption at faint fluxes. We did not find in our data any evidence for the existence of a population of faint intrinsically harder sources. The average spectral slope of our sources is ∼1.9, with an intrinsic dispersion of ∼0.28. We detected X-ray absorption (F-test significance ≥95%) in 37% of the sources, ∼10% in type-1 AGN (rest-frame NH ∼ 1.6 × 10 21 −1.2 × 10 22 cm −2 )a nd∼77% (rest-frame NH ∼ 1.5 × 10 21 −4 × 10 23 cm −2 ) in type-2 AGN. Using X-ray fluxes corrected for absorption, the fraction of absorbed objects and the absorbing column density distribution did not vary with X-ray flux. Our type-1 and type-2 AGN do not appear to have different continuum shapes, but the distribution of intrinsic (rest-frame) absorbing column densities is different among both classes. A significant fraction of our type-2 AGN (5 out of 28) were found to display no substantial absorption (NH < 10 21 cm −2 ). We discuss possible interpretations to this in terms of Compton-thick AGN and intrinsic Broad Line Region properties. An emission line compatible with Fe Kα was detected in 8 sources (1 type-1 AGN, 5 type-2 AGN and 2 unidentified) with rest frame equivalent widths 120−1000 eV. However weak broad components can be easily missed in other sources by the relatively noisy data. The AGN continuum or intrinsic absorption did not depend on X-ray luminosity and/or redshift. Soft excess emission was detected in 18 objects, but only in 9 (including 4 type-1 AGN and 4 type-2 AGN) could we fit this spectral component with a black body model. The measured 0.5− 2k eV luminosities of the fitted black body were not significantly different in type-1 and type-2 AGN, although the temperatures of the black body were slightly higher in type-2 AGN (� kT� = 0.26 ± 0.08) than in type-1 AGN (� kT� = 0.09 ± 0.01). For 9 sources (including 1 type-1 AGN and 3 type-2 AGN) a scattering model provided a better fit of the soft excess emission. We found that the integrated contribution from our sources to the X-ray background in the 2−7 keV band is softer ( Γ= 1.5−1.6) than the background itself, implying that fainter sources need to be more absorbed.

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 2 and contains 1137 sources with ∼10 −15 10 43 erg s −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 NH ∼ 10 22 −10 24 cm −2 ) in our sample in comparison with the models. We therefore conclude that the synthesis models require some revision in their specific parameters.

The XMM-Newton serendipitous survey: II - First results from the AXIS high galactic latitude medium sensitivity survey

We present the first results on the identifications of a medium sensitivity survey (X-ray flux limit 2 x 10(-14) erg cm(-2) s(-1) in the 0.5-4.5 keV band) at high galactic latitude (\b\ > 20degrees) carried out with the XMM-Newton X-ray observatory within the AXIS observing programme. This study is being conducted as part of the XMM-Newton Survey Science Centre activities towards the identification of the sources in the X-ray serendipitous sky survey. The sample contains 29 X-ray sources in a solid angle of 0.26 deg(2) (source density 113 +/- 21 sources deg(-2)), out of which 27 (93%) have been identified. The majority of the sources are broad-line AGN (19), followed by narrow emission line X-ray emitting galaxies (6, all of which turn out to be AGN), 1 nearby non-emission line galaxy (NGC 4291) and 1 active coronal star. Among the identified sources we find 2 broad-absorption line QSOs (z similar to 1.8 and z similar to 1.9), which constitute similar to10% of the AGN population at this flux level, similar to optically selected samples. Identifications of a further 10 X-ray sources fainter than our survey limit are also presented.

The XMM-Newton serendipitous survey - III. The AXIS X-ray source counts and angular clustering

Context. Recent results have revised upwards the total X-ray background (XRB) intensity below∼10 keV, therefore an accurate determination of the source counts is needed. There are also contradicting results on the clustering of X-ray selected sou rces. Aims. We have studied the X-ray source counts in four energy bands soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV), to evaluate the contribution of s ources at different fluxes to the X-ray background. We have also studied the angular clustering of X-ray sources in those bands. Methods. AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitu de XMM-Newton observations covering 4.8 deg 2 and containing 1433 serendipitous X-ray sources detected with 5-σ significance. This survey has similar depth to the XMM-Newton catalogues and can serve as a pathfinder to explore their poss ibilities. We have combined this survey with shallower and deeper surveys, and fitted the source counts with a Maximu m Likelihood technique. Using only AXIS sources, we have studied the angular correlation using a novel robust technique. Results. Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. We have improved on previous results in the latter band. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux are n ot enough to saturate the XRB intensity. Only galaxies and/or absorbed AGN may be able contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent r evisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within a bout a decade of the break in the source counts (∼ 10 −14 cgs), reaching ∼50% of the total in the soft and hard bands. Angular clustering (widely distributed over the sky and not confined to a few dee p fields) is detected at 99-99.9% significance in the soft and XID bands , with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection o f significantly stronger clustering in the hard-spectrum ha rd sources. Conclusions. Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV.

On the intensity of the extragalactic X-ray background

Measurements of the intensity of the cosmic X-ray background (XRB) carried out over small solid angles are subject to spatial variations due to the discrete nature of the XRB. This cosmic variance can account for the dispersion of XRB intensity values found within the ASCA, BeppoSAX and ROSAT missions separately. However there are differences among the values obtained in the different missions which are not due to spatial fluctuations but, more likely, to systematic cross-calibration errors. Prompted by recent work which shows that ROSAT PSPC has calibration differences with all the other missions, we compute a bayesian estimate for the XRB intensity at 1 keV of 10.0 −0.9 keV cm −2 s sr keV (90 per cent confidence errors) using the ASCA and BeppoSAX data points. However, this value is still significantly larger than the HEAO−1 intensity measured over many thousands of square degrees (8 keV cm s sr keV).