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XEUS is under study by ESA as part of the Horizon 2000+ program to utilize the International Space Station (ISS) for astronomical applications. XEUS will be a long-term X-ray observatory with an initial mirror area of 6 m2 at 1 keV that will be grown to 30 m2 following a visit to the ISS. The 1 keV spatial resolution is expected to be 2–5″ HEW. XEUS will consist of separate detector and mirror spacecraft aligned by active control to provide a focal length of 50 m. A new detector spacecraft, complete with the next generation of instruments, will also be added after visiting the ISS. The limiting sensitivity will then be ∼4×10−18 erg cm−2 s−1 around 250 times better than XMM. The properties of a 350 eV (rest-frame) equivalent width Fe line from a 1044 erg s−1 AGN will be measurable out to z=10, paving the way for detailed spectroscopic X-ray studies of some of the earliest known objects.XEUS is under study by ESA as part of the Horizon 2000+ program to utilize the International Space Station (ISS) for astronomical applications. XEUS will be a long-term X-ray observatory with an initial mirror area of 6 m2 at 1 keV that will be grown to 30 m2 following a visit to the ISS. The 1 keV spatial resolution is expected to be 2–5″ HEW. XEUS will consist of separate detector and mirror spacecraft aligned by active control to provide a focal length of 50 m. A new detector spacecraft, complete with the next generation of instruments, will also be added after visiting the ISS. The limiting sensitivity will then be ∼4×10−18 erg cm−2 s−1 around 250 times better than XMM. The properties of a 350 eV (rest-frame) equivalent width Fe line from a 1044 erg s−1 AGN will be measurable out to z=10, paving the way for detailed spectroscopic X-ray studies of some of the earliest known objects.

A new BeppoSAX broad-band (0.6-150 keV) spectrum of the Seyfert 2 galaxy Mkn 3 is presented. The spectrum provides a direct measurement of a large, neutral column of gas with Nh~10**24 cm**-2 in the source direction. The source, as bright as 3C 273 above 10 keV, has a steep (Gamma~1.8) spectrum without any evidence of a high-energy cutoff up to at least 150 keV. At lower energies, the data are best modeled with the addition of an unabsorbed reflection component. Combining these data with previous Ginga and ASCA observations, the Fe K$_{\alpha}$ and reflection continuum indicate that the reprocessed emission is responding slower than the intrinsic continuum variations suggesting a size of the reprocessor >= 2 pc. Identifying such a reprocessor with a (close to edge-on) obscuring torus, the overall result fits well into unified models since, presumably, one can interpret the strong absorption as due to transmission through the rim of the torus and the unabsorbed (directly viewed) reflection component as due to reprocessing from the torus inner surface., Comment: 12 LateX pages, 10 figures, accepted for publication in Astronomy and Astrophysics

The broad band 0.1-200 keV spectra of a sample of 5 Seyfert 2 galaxies (NGC 7172, Mkn 3, NGC 2110, NGC 4507 and NGC 7674) have been measured within the first year of the $BeppoSAX$ Core program. All sources have been detected up to \~ 100 keV and their spectral characteristics derived with good accuracy. Although the results obtained from the detailed analysis of individual sources indicate some ``source-by-source'' differences, we show in the following that all spectra are consistent, at least qualitatively, with what expected from a ``0th-order'' version of unified models. Indeed, a simple test on these data indicates that these Seyfert 2 galaxies are on average intrinsically very similar to Seyfert 1 galaxies (i.e., steep at E>10 keV) and that the main difference can be ascribed to a different amount of absorbing matter along the line of sight (i.e. different inclinations of our line of sight with respect to a putative molecular torus or different thicknesses of the tori)., 4 Latex pages, 6 figures, uses psfig.sty. Accepted for publication in Advances in Space Research, in Proceedings of 32nd Sci. Ass. of COSPAR, "Broad-Band X-ray Spectroscopy of Cosmic Sources"

BeppoSAX and ASCA observations of the nearby (z = 0.184), high-luminosity, radio-quiet quasar PDS 456 are presented. The X-ray spectrum is characterized by a prominent ionized edge at 8-9 keV (originally discovered by RXTE, Reeves et al. 2000) and by a soft excess below 1.5 keV. The lack of any significant iron K alpha emission line suggests for the edge an origin from line-of-sight material rather than from reflection from a highly ionized accretion disc. The hard X-ray continuum is indeed well modelled by transmission through a highly-ionized medium with a large column density (N-Hwarm similar to 4.5 x 10(24) cm(-2)) plus an additional cold absorber with a lower column density (N-Hcold similar to 2.7 x 10(22) cm(-2)).

The broad-band 0.1–200 keV spectra of a selected sample of Seyfert 2 galaxies have been measured within the BeppoSAX Core Programme. Here we present the first results obtained for 3 objects, NGC 7172, MKN 3 and NGC 7674. The broad band BeppoSAX data illustrate the high spectral complexity often found in Seyfert 2 galaxies predicted by unified models: NGC 7172 is found to be a Compton-thin source in which the primary emission is seen through absorbing material; MKN 3 is a border line object where the emission is partly seen directly and partly reprocessed by the absorbing material; NGC 7674 is an example of a Compton-thick source where the primary emission is hidden and only reprocessed radiation is observed.