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The International X-ray Observatory (IXO) has a top level requirement that the observing efficiency be 85%. This is a challenging requirement, given that the observing efficiencies for CXO and XMM-Newton are between 60% and 70%. However, the L2 orbit for IXO means that it will not be subject to the earth block/radiation zone effects that are seen for CXO and XMM-Newton. Outside of these effects the efficiencies for CXO and XMM-Newton do approach 85%, so this requirement appears achievable for IXO. In this paper we itemize the effects which impact the observing efficiency, in order to guide the design of the observatory. Meeting the 85% requirement should be possible but will require careful attention to detail.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The International X-ray Observatory (IXO) is a merger of the former ESA XEUS and NASA Constellation-X missions, with additional collaboration from JAXA, proposed for launch ~2020. IXO will address the leading astrophysical questions in the 'hot universe' through its breakthrough capabilities in X-ray spectroscopy. The mission covers the 0.1 to 40 keV energy range, complementing the capabilities of the next generation observatories, such as ALMA, LSST, JWST and 30 meter ground-based telescopes. An X-ray Grating Spectrometer is baselined to provide science in the energy range 0.3-1.0 keV at a spectral resolution of E/DeltaE > 3,000 with an effective area greater than 1,000 cm². This will require an array of soft X-ray enhanced CCDs operating at a modest frame rate to measure the diffracted light in both position and energy. Here we describe the baseline camera for the Off-plane XGS instrument using mature CCD technology.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The next large x-ray astrophysics mission launched will likely include soft x-ray spectroscopy as a primary capability. A requirement to fulfill the science goals of such a mission is a large-area x-ray telescope focusing sufficient x-ray flux to perform high-resolution spectroscopy with reasonable observing times. The IXO soft x-ray telescope effort in the US is focused on a tightly nested, thin glass, segmented mirror design. Fabrication of the glass segments with the required surface accuracy is a fundamental challenge; equally challenging will be the alignment of the ~7000 secondary mirror segments with their corresponding primary mirrors, and co-alignment of the mirror pairs. We have developed a system to perform this alignment using a combination of a coordinate measuring machine (CMM) and a double-pass Hartmann test alignment system. We discuss the technique, its ability to correct low-order mirror errors, and results of a recent pair alignment including progress toward the required alignment accuracy of < 2 arcseconds, and discuss the influence of the alignment process on mirror figure. We then look forward toward its scalability to the task of building the IXO telescope.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

Different optical designs are under consideration for the International X-ray Observatory (IXO). In this paper we show results of simulations of the segmented shell Wolter-I design, of the Silicon Pore Optics (SPO) conical Wolter-I approximation and of the Silicon based Kirkpatrick-Baez design. We focus particularly on the issue of stray light. When a source is off axis, such that it is not imaged on the detector, some of its light may still be directed by the optics onto the detector plane. Sources close to the pointing direction can thereby introduce an extra background radiation level in the detectors. This phenomenon is investigated by numerical ray tracing of the three designs, yielding detector images of the stray light, and an indication of which part of the mirror that light originates. Results show the similarities and differences of the designs with respect to stray light, and give a quantitative indication of the level of background radiation in different cases. Furthermore, for the Silicon Pore Optics design, two different ways of partially blocking the stray light have been modelled, indicating that a reduction of the stray light can be achieved. In general, the results that have been found indicate that for the simulated set-ups the stray light levels are compliant with the design specifications of the International X-ray Observatory.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The International X-ray Observatory (IXO) project is the result of a merger between the NASA Con-X and ESA/JAXA XEUS mission concepts. A facility-class mission, IXO will address the leading astrophysical questions in the "hot universe" through its breakthrough optics with 20 times more collecting area at 1 keV than any previous X-ray observatory, its 3 m² collecting area with 5 arcsec angular resolution will be achieved using a 20m focal length deployable optical bench. To reduce risk, two independent optics technologies are currently under development in the U.S. and in Europe. Focal plane instruments will deliver a 100-fold increase in effective area for high-resolution spectroscopy, deep spectral imaging over a wide field of view, unprecedented polarimetric sensitivity, microsecond spectroscopic timing, and high count rate capability. IXO covers the 0.1-40 keV energy range, complementing the capabilities of the next generation observatories, such as ALMA, LSST, JWST, and 30-m ground-based telescopes. These capabilities will enable studies of a broad range of scientific questions such as what happens close to a black hole, how supermassive black holes grow, how large scale structure forms, and what are the connections between these processes? This paper presents an overview of the IXO mission science drivers, its optics and instrumental capabilities, the status of its technology development programs, and the mission implementation approach.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

We present a study of the background for the array of microcalorimeters onboard of the International X-ray Observatory space mission. We investigated through simulations the rates at the focal plane of soft and hard particles in L2 orbit. Assuming the presence of an anticoincidence instrument, we derived an estimate of the residual background. The preliminary results reported in this paper are based on a number of simplifications of the actual picture. Efforts to improve the model are on-going.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The International X-ray Observatory (IXO) is being studied as a joint mission by the NASA, ESA and JAXA space agencies. The main goals of the mission are large effective area (>3m² at 1 keV) and a good angular resolution (<5 arcsec HEW at 1 keV). This paper reports on an activity ongoing in Europe, supported by ESA and led by the Brera Astronomical Observatory (Italy), aiming at providing an alternative method for the realization of the mirror unit assembly. This is based on the use of thin glass segments and an innovative assembly concept making use of glass reinforcing ribs that connect the facets to each-other. A fundamental challenge is the achievement with a hot slumping technique of the required surface accuracy on the glass segments. A key point of the approach is represented by the alignment of the mirror segments and co-alignment of the mirror pairs assembled together. In this paper we present the mirror assembly conceptual design, starting from the design of the optical unit, the error budgets contributing to the image degradation and the performance analysis to assess error sensitivities. Furthermore the related integration concept and the preliminary results obtained are presented.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

A suspension-mounting scheme is developed for the IXO (International X-ray Observatory) mirror segments in which the figure of the mirror segment is preserved in each stage of mounting. The mirror, first fixed on a thermally compatible strongback, is subsequently transported, aligned and transferred onto its mirror housing. In this paper, we shall outline the requirement, approaches, and recent progress of the suspension mount processes.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The requirements for the IXO (International X-ray Observatory) telescope are very challenging in respect of angular resolution and effective area. Within a clear aperture with 1.7 m > R > 0.25 m that is dictated by the spacecraft envelope, the optics technology must be developed to satisfy simultaneously requirements for effective area of 2.5 m² at 1.25 keV, 0.65 m² at 6 keV and 150 cm² at 30 keV. The reflectivity of the bare mirror substrate materials does not allow these requirements to be met. As such the IXO baseline design contains a coating layout that varies as a function of mirror radius and in accordance with the variation in grazing incidence angle. The higher energy photon response is enhanced through the use of depth-graded multilayer coatings on the inner radii mirror modules. In this paper we report on the first reflectivity measurements of wedged ribbed silicon pore optics mirror plates coated with a depth graded W/Si multilayer. The measurements demonstrate that the deposition and performance of the multilayer coatings is compatible with the SPO production process.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments of the International X-ray Observatory (IXO). The HTRS is the only instrument matching the top level mission requirement of handling a one Crab X-ray source with an efficiency greater than 10%. It will provide IXO with the capability of observing the brightest X-ray sources of the sky, with sub-millisecond time resolution, low deadtime, low pile-up (less than 2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6 keV). The HTRS is a non-imaging instrument, based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a circular envelope and a X-ray sensitive volume of 4.5 cm² x 450 microns. As part of the assessment study carried out by ESA on IXO, the HTRS is currently undergoing a phase A study, led by CNES and CESR. In this paper, we present the current mechanical, thermal and electrical design of the HTRS, and describe the expected performance assessed through Monte Carlo simulations.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The technique which combines high resolution spectroscopy with imaging capability is a powerful tool to extract fundamental information in X-ray Astrophysics and Cosmology. TES (Transition Edge Sensors)-based microcalorimeters match at best the requirements for doing fine spectroscopy and imaging of both bright (high count rate) and faint (poor signal-to-noise ratio) sources. For this reason they are considered among the most promising detectors for the next high energy space missions and are being developed for use on the focal plane of the IXO (International X-ray Observatory) mission. In order to achieve the required signal-to-noise ratio for faint or diffuse sources it is necessary to reduce the particle-induced background by almost two orders of magnitude. This reduction can only be achieved by adopting an active anticoincidence technique. In this paper, we will present a novel anticoincidence detector based on a TES sensor developed for the IXO mission. The pulse duration and the large area of the IXO TESarray (XMS X-ray Microcalorimeter Spectrometer) require a proper design of the anticoincidence detector. It has to cover the full XMS area, yet delivering a fast response. We have therefore chosen to develop it in a four-pixel design. Experimental results from the large-area pixel prototypes will be discussed, also including design considerations.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The Hard X-ray Imager (HXI) is one of the instruments onboard International X-ray Observatory (IXO), to be launched into orbit in 2020s. It covers the energy band of 10-40 keV, providing imaging-spectroscopy with a field of view of 8 x 8 arcmin². The HXI is attached beneath the Wide Field Imager (WFI) covering 0.1-15 keV. Combined with the super-mirror coating on the mirror assembly, this configuration provides observation of X-ray source in wide energy band (0.1-40.0 keV) simultaneously, which is especially important for varying sources. The HXI sensor part consists of the semiconductor imaging spectrometer, using Si in the medium energy detector and CdTe in the high energy detector as its material, and an active shield covering its back to reduce background in orbit. The HXI technology is based on those of the Japanese-lead new generation X-ray observatory ASTRO-H, and partly from those developed for Simbol-X. Therefore, the technological development is in good progress. In the IXO mission, HXI will provide a major assets to identify the nature of the object by penetrating into thick absorbing materials and determined the inherent spectral shape in the energy band well above the structure around Fe-K lines and edges.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The Wide Field Imager (WFI) of the International X-ray Observatory (IXO) is an X-ray imaging spectrometer based on a large monolithic DePFET (Depleted P-channel Field Effect Transistor) Active Pixel Sensor. Filling an area of 10 x 10 cm² with a format of 1024 x 1024 pixels it will cover a field of view of 18 arcmin. The pixel size of 100 x 100 microns² corresponds to a fivefold oversampling of the telescope's expected 5 arcsec point spread function. The WFI's basic DePFET structure combines the functionalities of sensor and integrated amplifier with nearly Fano-limited energy resolution and high efficiency from 100 eV to 15 keV. The development of dedicated control and amplifier ASICs allows for high frame rates up to 1 kHz and flexible readout modes. Results obtained with representative prototypes with a format of 256 x 256 pixels are presented.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding. In the central array (40 x 40 pixels) an energy resolution of < 2.5 eV is required, whereas the energy resolution of the outer array is more relaxed (~ 10 eV) but the detection elements have to be a factor 16 larger in order to keep the number of read-out channels acceptable for a cryogenic instrument. Due to the large collection area of the IXO optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. In this paper we will summarize the instrument status and performance. We will describe the results of design studies for the focal plane assembly and the cooling systems. Also the system and its required spacecraft resources will be given.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

We describe the experimental apparatus in use to test an off-plane reflection grating for the soft x-ray (0.3-1.0 keV) bandpass. The grating is a prototype for the X-ray Grating Spectrometer on the International X-ray Observatory (IXO). It has holographically-ruled radial grooves to match the converging beam of a 6.5 m focal length telescope. Laboratory tests are ongoing, with ray tracing indicating that a resolution (DeltaE/E) >3,000 is achievable across the 0.3-1.0 keV bandpass- the requirement to achieve IXO science goals.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The optics for the International X-Ray Observatory (IXO) require alignment and integration of about fourteen thousand thin mirror segments to achieve the mission goal of 3.0 square meters of effective area at 1.25 keV with an angular resolution of five arc-seconds. These mirror segments are 0.4 mm thick, and 200 to 400 mm in size, which makes it hard not to impart distortion at the sub-arc-second level. This paper outlines the precise alignment, verification testing, and permanent bonding techniques developed at NASA's Goddard Space Flight Center (GSFC). These techniques are used to overcome the challenge of aligning thin mirror segments and bonding them with arc-second alignment and minimal figure distortion. Recent advances in technology development in the area of permanent bonding have produced significant results. This paper will highlight the recent advances in alignment, testing, and permanent bonding techniques as well as the results they have produced.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

High-resolution spectroscopy at energies below 1 keV covers the lines of C, N, O, Ne and Fe ions, and is central to studies of the Interstellar Medium, the Warm Hot Intergalactic Medium, warm absorption and outflows in Active Galactic Nuclei, coronal emission from stars, etc. The large collecting area, long focal length, and 5 arcsecond half power diameter telescope point-spread function of the International X-ray Observatory will present unprecedented opportunity for a grating spectrometer to address these areas at the forefront of astronomy and astrophysics. We present the current status of a transmission grating spectrometer based on recently developed high-efficiency critical-angle transmission (CAT) gratings that combine the traditional advantages of blazed reflection and transmission gratings. The optical design places light-weight grating arrays close to the telescope mirrors, which maximizes dispersion distance and thus spectral resolution and minimizes demands on mirror performance. It merges features from the Chandra High Energy Transmission Grating Spectrometer and the XMM-Newton Reflection Grating Spectrometer, and provides resolving power R = E/DeltaE = 3000 - 5000 (full width half max) and effective area >1000 cm² in the soft x-ray band. We discuss recent results on ray-tracing and optimization of the optical design, instrument configuration studies, and grating fabrication.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The Soft X-Ray Telescope (SXT) modules are the fundamental focusing assemblies on NASA's next major X-ray telescope mission, the International X-Ray Observatory (IXO). The preliminary design and analysis of these assemblies has been completed, addressing the major engineering challenges and leading to an understanding of the factors effecting module performance. Each of the 60 modules in the Flight Mirror Assembly (FMA) supports 200-300 densely packed 0.4 mm thick glass mirror segments in order to meet the unprecedented effective area required to achieve the scientific objectives of the mission. Detailed Finite Element Analysis (FEA), materials testing, and environmental testing have been completed to ensure the modules can be successfully launched. Resulting stress margins are positive based on detailed FEA, a large factor of safety, and a design strength determined by robust characterization of the glass properties. FEA correlates well with the results of the successful modal, vibration, and acoustic environmental tests. Deformation of the module due to on-orbit thermal conditions is also a major design driver. A preliminary thermal control system has been designed and the sensitivity of module optical performance to various thermal loads has been determined using optomechanical analysis methods developed for this unique assembly. This design and analysis furthers the goal of building a module that demonstrates the ability to meet IXO requirements, which is the current focus of the IXO FMA technology development team.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.

The International X-ray Observatory (IXO) is a collaborative effort between NASA, ESA, and JAXA. The IXO science goals are heavily based on obtaining high quality X-ray spectra. In order to achieve this goal the science payload will incorporate an array of gratings for high resolution, high throughput spectroscopy at the lowest X-ray energies, 0.3 - 1.0 keV. The spectrometer will address a number of important astrophysical goals such as studying the dynamics of clusters of galaxies, determining how elements are created in the explosions of massive stars, and revealing most of the "normal" matter in the universe which is currently thought to be hidden in hot filaments of gas stretching between galaxies. We present here a mature design concept for an Off-Plane X-ray Grating Spectrometer (OP-XGS). This XGS concept has seen recent significant advancements in optical and mechanical design. We present here an analysis of how the baseline OP-XGS design fulfills the IXO science requirements for the XGS and the optical and mechanical details of this design.

This paper was presented at the SPIE conference on Astronomical Instrumentation 2010 conference.