The first x-rays detected were detected on 1999, August 12. The instrumentation is operating as expected. Together with other space observatories we are entering a new era of discovery in high-energy astrophysics.

The XMM-Newton X-ray Observatory was launched by an ARIANE V from Kourou, French Guiana, on 10 December 1999. First light was received by one of the three X-ray telescopes on 19 January 2000. Since then an extensive program, comprising commissioning, calibration and performance verification of the scientific payload, has been carried out, followed by regular scientific Guaranteed Time Observations which are interleaved with observations drawn from the Guest Observer (AO-1) program. I present the in-orbit performance of the three X-ray telescopes and demonstrate the excellent agreement with the ground calibration measurements. This includes the imaging characteristics both on-axis and off-axis, the effective collecting area and vignetting making use of in-orbit images and spectra. The scientific impact of a few of these observations is highlighted as well.

In this paper we will review the activities devoted to the development of soft (0.1-10 keV) and hard (10-100 keV) X-ray optics for future astronomical missions that were carried out at the Brera Astronomical Observatory (OAB, Italy) during the last year. Concerning the soft X-ray optics, we are studying the approach based on the use of ceramic carriers for making monolithic Wolter I mirror shells of large diameter by epoxy replication. The ceramic materials investigated in our study are SiC and Alumina (Al₂O₃), respectively produced by Chemical Vapor Deposition and plasma spray. We fabricated a number of mirror shell prototypes ($PHI equals 60 cm) using carriers based on both materials. X-ray imaging tests performed at the PANTER X-ray facility (Germany) with a full illumination of the optics demonstrated that the mirror shells based on SiC show much better performances than in the case of Alumina. These results can be explained in terms of the thermal-mechanical parameters of the two materials, being in the case of SiC much more performing than for Alumina. Concerning the development of hard X-ray multilayer optics, we are exploring the approach based on Ni electroforming replication. In the last period of activity we in particular concentrated our work on the surface superpolishing methods for the mandrel to be used in the replication process, to be much improved with respect the case Au coated single layer mirrors for soft X-rays. Concerning the specific aspect of the mandrel superpolishing, the results that we obtained can be considered very good and it is possible to claim that we achieved the goal prefixed at the beginning of the development program. The last part of the paper is dedicated to theoretical considerations on large-size and low-weight optics based on segmented mirrors like e.g., those under study for the petals of the XEUS project. In particular, the expected imaging performances by segmented optics produced using different kinds of materials will be compared.

We present results from a program to develop an X-ray telescope made from thin plastic shells. Our initial results have been obtained from multi-shell cylindrical lenses that are used in a point-to-point configuration to image the small focal spot of a an X-ray tube on a microchannel plate detector. We describe the steps that led up to the present design and present data from the tests that have been used to identify the properties of the plastic material that make it a suitable X-ray reflector. We discuss two applications of our technology to X-ray missions that are designed to address some of the scientific priorities set forth in NASA's long term plans for high energy astrophysics. One mission will observe in the 1- 10 keV band, the other will extend up to ca. 100keV.

The segmented approach in the design of grazing incidence X-ray optics has been utilized in constructing conical foil mirrors for several missions such as BBXRT, ASCA, as well as the failed mission Astro-E. The advantages include lightweight construction, a large collecting area, and broadband response in the X-ray band. A key weakness, which places these mirrors increasingly at a disadvantage with regard to other high throughput mirrors, e.g., those used for XMM, is a spatial resolution considerably worse than limits imposed by the geometry. Our first major breakthrough in addressing this problem was the introduction of surface replication, a technique which transfers the smooth surface of glass mandrels onto conical aluminum foil segments via a thin epoxy buffer layer. More recently we have made a concerted effort to evaluate the remaining spatial error, still well above that expected from the approximate geometry. We investigated the major error terms that include the curvature error of the reflectors along the axial direction, roundness error along the circumference of reflectors, and positioning error of the reflectors in the supporting structure. This effort leads to an improved overall angular resolution for such quadrant-segmented systems. Positioning error is reduced by reduction in the distortion of the two-stage telescope housings with new reflector alignment and mounting techniques. We report the current status in the improvement of angular resolution in the segmented foil optics and our understanding of remaining errors.

We report on progress in developing low-cost methods for shaping thin-foil glass x-ray optics. Such optics might serve as substrates for reflection gratings or as foil mirrors in high-throughput missions such as Constellation-X. Novel thermal shaping to lithographically defined pin chucks leads to the desired shape with high accuracy, thereby avoiding the need for replication. To demonstrate this method we have produced 200 micron-thick glass sheets with sub-micron flatness and half power diameter below 10 arc seconds. We also present a process for depositing low-stress metallic coatings that provides high x-ray reflectivity without significant foil distortion.

Various future projects in X-ray astronomy and astrophysics will require large segments with multiple thin shells or foils. The large Kirkpatrick-Baez modules, as well as the large Lobster-Eye X-ray telescope modules in Schmidt arrangement may serve as examples. All these space projects will require high quality and light segmented shells (bent or flat foils) with high X-ray reflectivity and excellent mechanical stability. Generally, the X-ray reflecting flats and foils are well suited for numerous applications such as grazing incidence X-ray flat mirrors, bent X-ray mirrors, various X-ray focusing elements, X-ray wave-guides, X-ray planar capillaries, lobster-eye type X-ray elements etc. We report here on the development of X-ray reflecting one-and double-sided flats as well as foils considered as segments for future astronomical X-telescopes. Several test modules have been designed and realized. Theoretical aspects and experimental results are discussed especially from the point of view of potential applications.

The Constellation-X mission has seen significant evolution in its concept over the previous two years. These evolutions yield a mission concept that achieves all of the originally proposed science goals, while meeting launch vehicle constraints. The most obvious change to the mission concept has been to reduce the number of satellites in the mission from six to four, while increasing the size of the optics to maintain the effective area. In a parallel evolution, the telescope focal lengths have increased from 8.4 to 10m to maintain approximately the same energy response from the optics. This paper will summarize the current designs and some of the issues associated with the optics for its two telescope systems.

At the European Space Agency (ESA) X-ray optics are being developed for future astrophysics and planetary missions. The cosmology mission XEUS requires very large effective area X-ray optics which high angular resolution. This implies a large aperture for a single telescope system, which will necessarily require assembly in space from basic mirror modules known as petals. The technology for the implementation of the Wolter-I design is based on the heritage of the XMM-Newton optics, but requires substantial further research and development. With 6 m² effective area at 1 keV the XEUS optics is initially composed of 32 petals arranged in a circular aperture of 4.5m diameter, compatible with single Arian 5 launch into the XEUS orbit. Utilising the available infrastructure at the International Space Station (ISS) 96 additional petals, organised into 8 segments, are added to XEUS, increasing the effective area to 30 m². Key aspects of the XEUS optics are therefore low-mass design, industrialisation of the production and ISS compatibility. As a potential optics for a remote sensing X-ray fluorescence spectrometer, extremely low mass Wolter-I optics are being developed. Based on Micro-Channel Plates (MCP), the mirror thickness can be dramatically reduced, making an accommodation on such missions as the Mercury orbiter of BeppiColombo possible. With a resolution of about 1 arcminute and compact construction, such imaging X-ray optics are well matched to modern Si or GaAs based detector arrays and will allow the mapping of the planetary surface in fluorescent X-ray light with unprecedented sensitivity.

We have been working on the design of a wide-field, short focal length, grazing incidence mirror shell set with a desired rms image spot size of 15 arcsec. The baseline design consists of Wolter I type mirror shells with polynomial perturbations applied to the baseline design. The overall optimization technique is to efficiently optimize the polynomial coefficients that directly influence the angular resolution without stepping through the entire multi-dimensional coefficient space. We have previously investigated the use of Response Surface Designs and Artificial Neural Networks as a means for optimizing the polynomial coefficients. The results have been published elsewhere. Here we have investigated Markov chain Monte Carlo (MCMC) algorithms as a method for optimizing the multi-dimensional coefficient space. Although MCMC algorithms are traditionally used to explore probability densities that result from a particular model specification, they can be used to create irreducible algorithms for optimizing arbitrary, bounded functions. In situations where very little is known, a priori, about a function and where the function may have multiple minimums, the irreducible nature of the MCMC algorithm combined with the ability to adapt MCMC algorithms offers a promising framework for optimizing this multi-dimensional complex function.

There is broad interest in a next generation timing mission to succeed the PCA of RXTE which will provide more effective area than its 0.6 square meters and much better energy resolution. Currently prospective missions are, like the PCA, based upon large area detectors. Serious consideration should also be given to a focusing system. The focusing system would be a modular array of relatively small diameter imaging telescopes or concentrators with solid state detectors in their focal planes. For areas exceeding a square meter a focusing system could actually be less complex, more reliable, and for one particular optical design perhaps not much more massive. The total detector area would be only a few percent of the telescope aperture, which makes the acquisition of detectors much less challenging. Today it is possible to obtain commercially a sufficient number of detectors with good energy resolution for all the focal planes of the focusing array. They require only modest cooling and that could be accomplished passively in space. Several optical designs are possible. The disadvantages of an optical system are larger mass, more difficultly obtaining broad bandwidth, smaller field of view, and larger volume to accommodate the focal length distance and a larger diameter. On the other hand, the focusing system is more sensitive to fainter sources, is much more efficient below 2 keV, is less sensitive to background and is likely to be less costly overall than an array of solid state area detectors with equally good energy resolution.

We have been developing the high throughput hard X-ray telescope, using reflectors coated with the depth graded multilayer known as supermirror, which is considered to be a key technology for future satellite hard X-ray imaging missions. InFOC(mu) $S, the International Focusing Optics Collaboration for (mu) -Crab Sensitivity is the project of the balloon observation of a cosmic hard X-ray source with this type of hard X-ray telescope and CdZnTe pixel detector as a focal plane imager. For the fist InFOC(mu) S balloon experiment, we developed the hard X-ray telescope with outermost diameter of 40cm, focal length of 8m and energy band pass of 20-40 keV, for which Pt/C multilayer was used. From the pre-flight X-ray calibration, we confirmed its energy band and imaging capability of 2 arcmin HPD and 10 arcmin FOV of FWHM, and a effective area of 50 cm² for 20-40 keV X-ray. We report the current status of our balloon borne experiment and performance of our hard X-ray telescope.

Mass production of replicated thin aluminum x-ray reflecting foils for the InFOC(mu) S (International Focusing Optics Collaboration for Micro-Crab Sensitivity) balloon payload is complete, and the full mirror has been assembled. InFOC(mu) S is an 8-meter focal length hard x-ray telescope scheduled for first launch in July 2001 and will be the first instrument to focus and image x-rays at high energies (20-40 keV) using multilayer-based reflectors. The individual reflecting elements are replicated thin aluminum foils, in a conical approximation Wolter-I system similar to those built for ASCA and ASTRO-E. These previous imaging systems achieved half-power-diameters of 3.5 and 1.7-2.1 arcminutes respectively. The InFOC(mu) S mirror is expected to have angular resolution similar to the ASTRO-E mirror. The reflecting foils for InFOC(mu) S, however, utilize a vertically graded Pt/C multilayer to provide broad-band high-energy focusing. We present the results of our pre-flight characterization of the full mirror, including imaging and sensitivity evaluations. If possible, we will include imaging results from the first flight of a multilayer-based high-energy focusing telescope.

Previously we have reported on our work on coating a truncated-cone-shaped engineering (not high quality in terms of smoothness) mandrel and have removed the layers, intact, on the inside of an electroform with a cylindrical, truncated-cone geometry. We have advanced to using a high quality (about 0.5 nm) smooth truncated cone. We report our latest advances in refining our fabrication techniques and the results of X-ray measurements. The X-ray measurements made at the Argonne APS SRI-CAT 2-BM-B beam-line were at 10 and 30 keV. The results showed that we had produced excellent Si/W multilayers on the inside of a 10 cm long by about 10 cm diameter truncated cone shaped mirror. We estimate the reflectivity of the layers at the primary Bragg peak to be well above 10%. We also show that the multilayers were uniform around the mirror.

We report the results obtained during the second phase of a program which consists of comparing the performance of different multilayer material combinations. These coatings will be used to extend the bandpass of current hard X-ray optics toward 100 keV, an order of magnitude higher than present technology. The materials studied here are W/Si, Pt/C, and W/C. A comparison of the performance of depth graded multilayers of these different materials at energies 30-80 keV was undertaken. Specular reflectivity data were acquired at 30-80 keV using the X17B1 beamline of the National Synchrotron Light Source. Reflectivity versus energy plots showed a high enough reflectivity for the bandpass of interest at grazing angles typical for hard x-ray telescope mirror shells. The next phase of our program will continue with similar high-energy pencil beam measurements on multilayer coated telescope prototype shells.

A planar magnetron sputtering facility has been established at the Danish Space Research Institute (DSRI) for the production coating of depth graded multilayers on the thermally slumped glass segments which form the basis for the hard X-ray telescope on the HEFT balloon project. The facility is capable of coating 20-45 mirrors segments in each run. The coatings are optimized W/Si coatings. The paper describes the facility, the results of the calibration and presents data for the X-ray testing of flight mirrors.

HERO is a balloon payload featuring shallow-graze angle replicated optics for hard-x-ray imaging. When completed, the instrument will offer unprecedented sensitivity in the hard-x-ray region, giving thousands of sources to choose from for detailed study on long flights. A recent proof-of-concept flight captured the first hard-x-ray focused images of the Crab Nebula, Cygnus X-1 and GRS 1915+105. Full details of the HERO program are presented, including the design and performance of the optics, the detectors and the gondola. Results from the recent proving flight are discussed together with expected future performance when the full science payload is completed.