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Athena is an X-ray observatory-class mission concept, developed from April to December 2011 as a result of the reformulation exercise for L-class mission proposals in the framework of ESAs Cosmic Vision 2015-2025. Athenas science case is that of the Universe of extremes, from Black Holes to Large-scale structure. The specific science goals are structured around three main pillars: Black Holes and accretion physics, Cosmic feedback and Large-scale structure of the Universe. Underpinning these pillars, the study of hot astrophysical plasmas offered by Athena broadens its scope to virtually all corners of Astronomy. The Athena concept consists of two co-aligned X-ray telescopes, with focal length 12 m, angular resolution of 10 or better, and totalling an effective area of 1 m2 at 1 keV (0.5 m2 at 6 keV). At the focus of one of the telescopes there is a Wide Field Imager (WFI) providing a field of view of 24times 24, 150 eV spectral resolution at 6 keV, and high count rate capability. At the focus of the other telescope there is the X-ray Microcalorimeter Spectrometer (XMS), a cryogenic instrument offering a spectral resolution of 3 eV over a field of view of 2.3 times 2.3. Although Athena has not been selected as ESAs Cosmic Vision 2015-2025 L1 mission, its science goals and concept conform the basis of what should become ESAs X-ray astronomy flagship.
101 - X. Barcons , D. Barret , M. Bautz 2011
The International X-Ray Observatory (IXO) will address fundamental questions in astrophysics, including When did the first SMBH form? How does large scale structure evolve? What happens close to a black hole? What is the connection between these proc esses? What is the equation of state of matter at supra-nuclear density? This report presents an overview of the assessment study phase of the IXO candidate ESA L-class Cosmic Vision mission. We provide a description of the IXO science objectives, the mission implementation and the payload. The performance will offer more than an order of magnitude improvement in capability compared with Chandra and XMM-Newton. This observatory-class facility comprises a telescope with highly nested grazing incidence optics with a performance requirement of 2.5 sq.m. of effective area at 1.25 keV with a 5 PSF. There is an instrument complement that provides capabilities in imaging, spatially resolved spectroscopy, timing, polarimetry and high resolution dispersive spectroscopy. Since earlier submissions to the Astro2010 Decadal Survey, substantial technological progress has been made, particularly in the mirror development. Risk reduction measures and important programmatic choices have also been identified. An independent internal Technical and Programmatic Review has also been carried out by ESA, concluding with positive recommendations. Subject to successful conclusion of agreements between the partner space agencies, IXO is fully ready to proceed to further definition, moving towards an eventual launch in 2021-2022.
93 - X. Barcons 2007
At low redshift (z<2), almost half of the baryons in the Universe are not found in bound structures like galaxies and clusters and therefore most likely reside in a Warm-Hot Intergalactic Medium (WHIM), as predicted by simulations. Attempts to detect WHIM filaments at cosmological distances in absorption towards bright background sources have yielded controversial results that I review here. I argue that a secure detection of absorption features by the WHIM is at the limit of the XMM-Newton capabilities, but feasible. A proper characterisation of the whole WHIM belongs to the realm of future X-ray missions.
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. We report on the optical identification of the XMS samples, complete to 85-95%. At the intermediate 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 (~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.
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