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Register a new userThe unresolved hard X-ray background: the missing source population implied by the Chandra and XMM-Newton deep fields
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We extend our earlier work on X-ray source stacking in the deep XMM-Newton observation of the Lockman Hole, to the 2 Ms Chandra Deep Field North and the 1 Ms Chandra Deep Field South. The XMM-Newton work showed the resolved fraction of the X-ray background to be ~80-100 per cent at <2 keV but this decreased to only ~50 per cent above ~8 keV. The CDF-N and CDF-S probe deeper, and are able to fill-in some of the missing fraction in the 4-6 keV range, but the resolved fraction in the 6-8 keV band remains only ~60 per cent, confirming the trend seen with XMM-Newton. The missing X-ray background component has a spectral shape that is consistent with a population of highly obscured AGN at redshifts ~0.5-1.5 and with absorption column densities of ~10^23 - 10^24 cm^-2.
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(abridged) The XMM-Newton survey in the Chandra Deep Field South (XMM-CDFS) aims at detecting and studying the spectral properties of a significant number of obscured and Compton-thick AGN. The large effective area of XMMin the 2--10 and 5--10 keV bands, coupled with a 3.45 Ms nominal exposure time, allows us to build clean samples in both bands, and makes the XMM-CDFS the deepest XMM survey currently published in the 5--10 keV band. The large multi-wavelength and spectroscopic coverage of the CDFS area allows for an immediate and abundant scientific return. We present the data reduction of the XMM-CDFS observations, the method for source detection in the 2--10 and 5--10keV bands, and the resulting catalogues. A number of 339 and 137 sources are listed in the above bands with flux limits of 6.6e-16 and 9.5e-16 erg/s/cm^2, respectively. The flux limits at 50% of the maximum sky coverage are 1.8e-15 and 4.0e-15 erg/s/cm^2, respectively. The catalogues have been cross-correlated with the Chandra ones: 315 and 130 identifications have been found with a likelihood-ratio method, respectively. A number of 15 new sources, previously undetected by Chandra, is found; 5 of them lie in the 4 Ms area. Redshifts, either spectroscopic or photometric, are available for ~92% of the sources. The number counts in both bands are presented and compared to other works. The survey coverage has been calculated with the help of two extensive sets of simulations, one set per band. The simulations have been produced with a newly-developed simulator, written with the aim of the most careful reproduction of the background spatial properties. We present a detailed decomposition of the XMM background into its components: cosmic, particle, and residual soft protons.
We present the results obtained from the analysis of three XMM-Newton observations of M83. The aims of the paper are studying the X-ray source populations in M83 and calculating the X-ray luminosity functions of X-ray binaries for different regions of the galaxy. We detected 189 sources in the XMM-Newton field of view in the energy range of 0.2-12 keV. We constrained their nature by means of spectral analysis, hardness ratios, studies of the X-ray variability, and cross-correlations with catalogues in X-ray, optical, infrared, and radio wavelengths. We identified and classified 12 background objects, five foreground stars, two X-ray binaries, one supernova remnant candidate, one super-soft source candidate and one ultra-luminous X-ray source. Among these sources, we classified for the first time three active galactic nuclei (AGN) candidates. We derived X-ray luminosity functions of the X-ray sources in M83 in the 2-10 keV energy range, within and outside the D_25 ellipse, correcting the total X-ray luminosity function for incompleteness and subtracting the AGN contribution. The X-ray luminosity function inside the D_25 ellipse is consistent with that previously observed by Chandra. The Kolmogorov-Smirnov test shows that the X-ray luminosity function of the outer disc and the AGN luminosity distribution are uncorrelated with a probability of about 99.3%. We also found that the X-ray sources detected outside the D_25 ellipse and the uniform spatial distribution of AGNs are spatially uncorrelated with a significance of 99.5%. We interpret these results as an indication that part of the observed X-ray sources are X-ray binaries in the outer disc of M83.
We present the first results of an XMM-Newton EPIC observation of the luminous X-ray source population in the supergiant spiral galaxy M101. We have studied the properties of the fourteen most luminous sources, all of which have intrinsic X-ray luminosities exceeding the Eddington limit for a 1.4 solar mass neutron star, with a subset in the ultraluminous X-ray source (ULX) regime. Eleven sources show evidence of short-term variability, and most vary by a factor of ~2-4 over a baseline of 11-24 yrs, providing strong evidence that these sources are accreting X-ray binary (XRB) systems. The sources show a variety of spectral shapes, with no apparent spectral distinction between those above and below the ULX threshold. Nine are well-fit with either simple absorbed disc blackbody/powerlaw models. However for three of the four sources best-fit with powerlaw models, we cannot exclude the disc blackbody fits and therefore conclude that, coupled with their high luminosities, eight out of nine single-component sources are possibly high state XRBs. The nuclear source has the only unambiguous powerlaw spectrum (photon index~2.3), which may be evidence for a low-luminosity AGN. The remaining five sources require at least two-component spectral fits. We have compared the spectral shapes of nine sources covered by both this observation and an archival 100ks Chandra observation of M101; the majority show behaviour typical of Galactic XRBs i.e. softening with increasing luminosity. We find no definitive spectral signatures to indicate that these sources contain neutron star primaries, and conclude that they are likely to be stellar-mass black hole XRBs, with black hole masses of ~2-23 solar masses if accreting at the Eddington limit (abridged).
We present the X-ray spectra of 86 optically-identified sources in the 13H XMM-Newton/Chandra deep field which have >70 X-ray counts. The sample consists of 50 broad line AGN, 25 narrow emission line galaxies, 6 absorption line galaxies, and 5 Galactic stars. The majority (42/50) of the broad line AGN have X-ray spectra which are consistent with a power law shape. They have a mean photon index of Gamma = 2.0 +- 0.1 and an intrinsic dispersion sigma = 0.4 +- 0.1. Five BLAGN show a deficit of soft X-rays, indicating absorption. Significant absorption is more common in the narrow emission line galaxies (13/25) and absorption line galaxies (2/6) than in the broad line AGN (5/50), but is not universal in any of these classes of object. The majority of the 20 absorbed sources have X-ray spectra consistent with a simple cold photoelectric absorber, but 6/20 require more complex models with either an additional component of soft X-ray emitting plasma, or an ionised absorber. Of the 16 galaxies which do not show evidence for X-ray absorption, only 2 objects are likely to be powered by star formation, and both have 2-10 keV X-ray luminosities of <= 10^40 cgs. The X-ray emission in the other 14 unabsorbed NELGs and galaxies is most likely powered by AGN, which are not detected in the optical because they are outshone by their luminous host galaxies. The Galactic stars show multi-temperature thermal spectra which peak between 0.5 and 1 keV. Star/AGN discrimination is possible for 4 of the 5 stars solely from their X-ray spectra.
We present a work in progress aimed at measuring the spectrum of the Cosmic X-ray Background (CXB) with the EPIC detectors onboard XMM-Newton. Our study includes a detailed characterization of the EPIC non X-ray background, which is crucial in making a robust measurement of the spectrum of CXB. We present preliminary results, based on the analysis of a set of Commissioning and Performance Verification high galactic latitude observations.
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