The far ultraviolet spectral region (roughly 900 - 1200 Å) is densely packed with strong atomic, ionic and molecular transitions of astrophysical importance. Many of these transitions provide unique access to the associated species. This spectral region is also technically challenging: optical reflectivities are limited, contamination control requirements are severe and detectors must be windowless. The Far Ultraviolet Spectroscopic Explorer (FUSE) covers the spectral region 905 -1187 Å with a resolution ~ 15 km s-1. The mission, launched in June 1999 and now in its fifth year of science operations, has reaped a rich scientific harvest from this spectral region. This paper will examine the lessons learned from the FUSE mission with the perspective of looking ahead to possible future missions. In order to build on the scientific advances of the FUSE mission, such a mission would require both increased sensitivity and higher spectral resolution. We conclude that achieving these requirements will necessitate, among other advances, new approaches to far ultraviolet mirror coating technology. We also examine the possibility of accessing the far ultraviolet using an ultraviolet observatory designed for longer wavelength ultraviolet radiation.
We describe the Galaxy Evolution Explorer (GALEX) satellite that was launched in April 2003 specifically to accomplish far ultraviolet (FUV) and near ultraviolet (NUV) imaging and spectroscopic sky-surveys. GALEX is currently providing new and significant information on how galaxies form and evolve over a period that encompasses 80% of the history of the Universe. This is being accomplished by the precise measurement of the UV brightness of galaxies which is a direct measurement of their rate of star formation. We briefly describe the design of the GALEX mission followed by an overview of the instrumentation that comprises the science payload. We then focus on a description of the development of the UV sealed tube micro-channel plate detectors and provide data that describe their on-orbit performance. Finally, we provide a short overview of some of the science highlights obtained with GALEX.
The Chandra X-ray Observatory is the X-ray component of NASA's Great Observatory Program, which, in addition to Chandra, comprises the Hubble Space telescope and the Spitzer Infrared Telescope Facility. The Chandra X-ray Observatory provides scientific data to the international astronomical community in response to proposals for its use. Data becomes public at most one year after the observation. The Observatory is the result of the efforts of many organizations in the United States and Europe. NASA's Marshall Space Flight Center (MSFC) manages the Project and provides Project Science; NGST (formerly TRW) with the help of many outstanding subcontractors served as prime contractor responsible for providing the spacecraft, the telescope, and assembling and testing the observatory; and the Smithsonian Astrophysical Observatory (SAO) provides technical support and is responsible for ground operations including the Chandra X-ray Center (CXC).
INTEGRAL is an ESA space mission to study the sky at hard X-ray and soft gamma-ray energies. Its two main instruments SPI and IBIS cover the energy range 15 keV to 10 MeV, and are mainly devoted to high resolution spectroscopy (ΔE ~ 2,5 keV at 1 MeV) and fine source imaging (DJ ~ 12 arcmin), respectively. The 4 tons heavy payload was brought into an excentric orbit of 153.000 km apogee and 9.000 km perigee on October 17, 2002 by a Russian Proton rocket. After a successful performance and verification phase, the observational program started in late December 2002 by executing open-time proposals and guaranteed core-time observations. The observations concentrated mainly towards the galactic plane, and especially the inner Galaxy. Highlights from the first 18 months of the mission are results on nucleosynthesis and solar flare gamma-ray lines, on a survey of hard X-ray binary sources and their identification, on the origin of the "diffuse" galactic ridge emission, and on gamma-ray bursts. Whereas line measurements generally require deep exposures of several million seconds (1 month and more), results on compact objects can be obtained much easier - in most cases they require exposures of only one or a few days.
The AGILE gamma-ray mission is in its Phase C-D. The Engineering model of the Payload has been built and tested, and the construction of the flight model has started. We present here the status of the SuperAGILE experiment, the 15-40 keV imaging monitor, based on Silicon microstrip technology and equipped with one dimensional coded masks. We show the design of the experiment and the results of testing campaigns carried out on the engineering model of the experiment.
In various objects, it has been evident that non-thermal processes are
playing important roles in high energy objects. They become
outstanding above 10 keV and its total energy could be comparable to
that of thermal components. In order to examine such non-thermal
processes, we propose a hard X-ray imaging mission NeXT (New X-ray
Telescope mission) together with the soft gamma ray detector and the
high resolution spectrometer. Hard X-ray telescopes consist of
multilayer coated high through put mirrors. The focal plane detectors
are hybrid type imaging detectors to cover both soft and hard
X-rays. Total performance in sensitivity for a point source reaches
100 times better than any currently scheduled missions in 10 - 60(80)
keV range and 10 times better in soft gamma rays. It is planned to
launch it in the time frame of 2011.
Monitor of All-sky X-ray Image (MAXI) is an X-ray all-sky monitor,
which will be delivered to the International Space Station (ISS) in 2008, to scan almost the whole sky once every 96 minutes for a mission life of two years. The detection sensitivity will be 7~mCrab (5σ level) in one scan, and 1~mCrab for one-week accumulation. At previous SPIE meetings, we presented the development status
of the MAXI payload, in particular its X-ray detectors. In this paper, we present the whole picture of the MAXI system, including the downlink path and the MAXI ground system. We also examine the MAXI system components other than X-ray detectors from the point of view of the overall performance of the mission. The engineering model test of the MAXI X-ray slit collimator shows that we can achieve the position determination accuracy of <0.1 degrees, required for the ease of follow-up observations. Assessing the downlink paths, we currently estimates that the MAXI ground system receive more than 50% of the observational data in "real time" (with time delay of a few to ten seconds), and the rest of data with delay of 20 minutes to a few hours from detection, depending on the timing of downlink. The data will be processed in easily-utilised formats, and made open to public users through the Internet.
Dark Energy dominates the mass-energy content of the universe (about 73%) but we do not understand it. Most of the remainder of the Universe consists of Dark Matter (23%), made of an unknown particle. The problem of the origin of Dark Energy has become the biggest problem in astrophysics and one of the biggest problems in all of science. The major extant X-ray observatories, the Chandra X-ray Observatory and XMM-Newton, do not have the ability to perform large-area surveys of the sky. But Dark Energy is smoothly distributed throughout the universe and the whole universe is needed to study it. There are two basic methods to explore the properties of Dark Energy, viz. geometrical tests (supernovae) and studies of the way in which Dark Energy has influenced the large scale structure of the universe and its evolution. DUO will use the latter method, employing the copious X-ray emission from clusters of galaxies. Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales is dominated by the Dark Energy. In order to take the next step in understanding Dark Energy, viz. the measurement of the 'equation of state' parameter 'w', an X-ray telescope following the design of ABRIXAS will be accommodated into a Small Explorer mission in lowearth orbit. The telescope will perform a scan of 6,000 sq. degs. in the area of sky covered by the Sloan Digital Sky Survey (North), together with a deeper, smaller survey in the Southern hemisphere. DUO will detect 10.000 clusters of galaxies, measure the number density of clusters as a function of cosmic time, and the power spectrum of density fluctuations out to a redshift exceeding one. When combined with the spectrum of density fluctuations in the Cosmic Microwave Background from a redshift of 1100, this will provide a powerful lever arm for the crucial measurement of cosmological parameters.
The mission ROSITA (ROentgen Survey with an Imaging Telescope Array) will perform the first imaging all-sky survey in the medium energy X-ray range up to 10 keV with an unprecedented spectral and angular resolution. Thus, ROSITA leads to an improved understanding of obscured black holes in Active Galactic Nuclei. In addition, ROSITA represents an important pathfinder for beyond 2015 space telescopes like XEUS and Constellation X. Targeting for a flight in 2008/2009 on one side ROSITA is considered as technology test bed for later X-ray cornerstone missions, on the other side the measurement data will form a good basis for later detailed surveys with the corresponding high resolution pointing systems.
The Lobster-ISS instrument is an X-ray all sky monitor proposed as an attached payload on the zenith platform exposed payload facility of the European Space Agency (ESA) Columbus module of the International Space Station (ISS). The basic instrument consists of six microchannel plate X-ray telescopes, collectively providing wide-angle (22.5 x 162 sq.degree) astronomical X-ray imaging in the 0.1 - 3.5 keV energy band. In this paper we describe computer modeling software underway at the University of Melbourne to provide an accurate simulation of the operation of the Lobster-ISS in its low Earth orbit environment. We exhibit some preliminary exposure maps and examples of the X-ray images that the instrument should produce given our simulation of its operation.
In March and April 2003, the Chandra X-ray Observatory carried out a
series of 126 short observations (5 ksec each) covering a continuous
area of the Bootes constellation to construct a large area shallow
X-ray survey. These observations were carried out as collaboration of
Guest Observer (C. Jones PI) and Guaranteed Time Observer (S. Murray
PI) programs. We present here, in Paper I, an initial analysis of the
survey data and the source detection process, showing the sky
coverage, exposure map, and some of the collective properties of the
resulting catalog of sources. The Bo\"otes area was selected to
overlap a well studied region where optical, and radio data, to
sufficient depth, have already been obtained making the identification
of candidate counterparts straight forward. In 5 ksec, we reach a
limiting flux of ≈10-3ct s-1 (corresponding to ≈10-14 erg cm-2s-10.5-7.0 keV). We examine the spatial distribution of the sources in this ~9.3 square degree survey region using several techniques to search for evidence of cosmic variance in the X-ray source density on scales as small as the ACIS-I field of view
(~16x16 arc minutes). With follow up optical spectroscopy using the MMT/Hectospec, we can obtain spectroscopic redshifts for about 1/3 - 1./2 of the X-ray sources, which can be used to look for evidence of large scale structures traced by AGN associated with the cosmic web.
The sensitivity of the Advanced CCD Imaging Spectrometer (ACIS)
instrument on the Chandra X-ray Observatory (CXO) to low-energy X-rays
(0.3 - 2.0 keV) has been declining throughout the mission. The most
likely cause of this degradation is the growth of a contamination
layer on the cold (-60 C) filter which attenuates visible and near-visible light incident on the CCDs. The contamination layer is still increasing 4 years after launch, but at a significantly lower rate than initially. We have determined that the contaminant is composed mostly of C with small amounts of O and F. We have conducted ground experiments to determine the thermal desorption properties of candidate materials for the contaminant. We have conducted experiments to determine the robustness of the thin filter to the thermal cycling necessary to remove the contaminant. We have modeled the migration of the contaminant during this bake-out process to ensure that the end result will be a reduction in the thickness of the contamination layer. We have considered various profiles for the bake-out consisting of different temperatures for the ACIS focal plane and detector housing and different dwell times at these temperatures. The largest uncertainty which affects our conclusions is the volatility of the unknown contaminants. We conclude that bakeout scenarios in which the focal plane temperature and the detector housing temperature are raised to +20~C are the most likely to produce a positive outcome.
XMM-Newton was launched into space on a highly eccentric 48 hour orbit on December 10th 1999. XMM-Newton is now in its fifth year of operation and has been an outstanding success, observing the Cosmos with imaging, spectroscopy and timing capabilities in the X-ray and optical wavebands. The EPIC-MOS CCD X-ray detectors comprise two out of three of the focal plane instruments on XMM-Newton. In this paper we discuss key aspects of the current status and performance history of the charge transfer ineffiency (CTI), energy resolution and spectral redistribution function (rmf) of EPIC-MOS in its fifth year of operation.
High resolution X-ray spectroscopy of optically thin sources is discussed. Based on a brief description of the general properties of highly ionized, optically thin sources and their spectra, and a set of specific examples drawn from the recent literature, I outline arguments for the importance of routine spectroscopy of faint sources as a science driver for future missions.
The Constellation-X mission will address the questions: "What happens to matter close to a black hole?" and "What is Dark Energy?" These questions are central to the NASA Beyond Einstein Program, where Constellation-X plays a central role. The mission will address these questions by using high throughput X-ray spectroscopy to observe the effects of strong gravity close to the event horizon of black holes, and to observe the formation and evolution of clusters of galaxies in order to precisely determine Cosmological parameters. To achieve these primary science goals requires a factor of 25-100 increase in sensitivity for high resolution spectroscopy. The mission will also perform routine high-resolution X-ray spectroscopy of faint and extended X-ray source populations. This will provide diagnostic information such as density, elemental abundances, velocity, and ionization state for a wide range of astrophysical problems. This has enormous potential for the discovery of new unexpected phenomena. The Constellation-X mission is a high priority in the National Academy of Sciences McKee-Taylor Astronomy and Astrophysics Survey of new Astrophysics Facilities for the first decade of the 21st century.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory. Novel light-weight optics with an effective area of 10 m2 at 1 keV and 2-5" HEW spatial resolution together with advanced imaging detectors will provide a sensitivity around 200 times better than XMM-Newton as well as much improved high-energy coverage, and spectroscopic performance. This enormous improvement in scientific capability will open up new vistas in X-ray astronomy. It will allow the detection of massive black holes in the earliest AGN and estimates of their mass, spin and red-shift through their Fe-K line properties. XEUS will study the first gravitationally bound, Dark Matter dominated, systems small groups of galaxies and trace their evolution into today's massive clusters. High-resolution spectroscopy of the hot intra-cluster gas will be used to investigate the evolution of metal synthesis to the present epoch. The hot filamentary structure will be studied using absorption line spectroscopy allowing the mass, temperature and density of the intergalactic medium to be characterized. As well as these studies of the deep universe, the enormous low-energy collecting area will provide a unique capability to investigate bright nearby objects with dedicated high-throughput, polarimetric and time resolution detectors.
The Beyond Einstein Program in NASA's Office of Space Science Structure and Evolution of the Universe theme spells out the top level scientific requirements for a Black Hole Imager in its strategic plan. The MAXIM mission will provide better than one tenth of a microarcsecond imaging in the X-ray band in order to satisfy these requirements. We will overview the driving requirements to achieve these goals and ultimately resolve the event horizon of a supermassive black hole. We will present the current status of this effort that includes a study of a baseline design as well as two alternative approaches
The Constellation X-ray Mission is a high-throughput X-ray facility emphasizing observations at high spectral resolution (R ~ 300-3000) while covering a broad energy band (0.25-60 keV). The mission is intended to achieve a factor of 25-100 increase in sensitivity over current high resolution X-ray spectroscopy missions. Constellation-X is the X-ray astronomy equivalent of the Keck and the VLT, complementing the high spatial resolution capabilities of Changra. Constellation-X achieves its high-throughput and reduces mission risk by dividing the collecting area across four separate spacecraft launched two at a time into an L2 orbit. We describe the overall mission concept and also present a brief overview of alternate concepts which are under consideration. We discuss recent progress on the key technologies, including: lightweight, high-throughput X-ray optics, micro-caloriment spectrometer arrays, low-power and low-weight CCD arrays, lightweight gratings, multilayer coatings to enhance the hard X-ray performance of X-ray optics, and hard X-ray detectors.
The status of technology development for the Constellation-X Spectroscopy X-ray Telescope (SXT) mirror is presented. The SXT mirror combines a large (1.6 m) aperture with modest (12 arc sec half power diameter) angular resolution and low mass (750 kg). The overall collecting area, larger than 9,600 square cm at 0.25 keV, requires high throughput, and thus nesting of a substantial number of thin reflectors. A phased development program is underway to develop reflectors, mounting and alignment approaches, and metrology techniques for components and the mirror has a whole. The latest results in all these areas are summarized, along with an overview of results of optical testing of reflector performance.
The Reflection Grating Spectrometer of the Constellation-X mission has
two strong candidate configurations. The first configuration, the
in-plane grating (IPG), is a set of reflection gratings similar to
those flown on XMM-Newton and has grooves perpendicular to the
direction of incident light. In the second configuration, the
off-plane grating (OPG), the grooves are closer to being parallel to
the incident light, and diffract along a cone. It has advantages of
higher packing density, and higher reflectivity. Confinement of these
gratings to sub-apertures of the optic allow high spectral
resolution. We have developed a raytrace model and analysis technique
for the off-plane grating configuration. Initial estimates indicate
that first order resolving powers in excess of 1000 (defined with
half-energy width) are achievable for sufficiently long wavelengths
(λ ≥ 12Å), provided separate accommodation is made
for gratings in the subaperture region farther from the zeroth order
The Xeus mission is designed to explore the X-ray emission from objects in the Universe at high redshifts, and these science requirements necessitate a very large effective area. We describe a completely revised mission scenario that mitigates previous concerns about the deployable mass and use of the ISS. New mirror technology with lightweight optics enables a direct launch to a L2 operational orbit, and we describe the outline of the Mirror and Detector Spacecraft that are deployed in formation flying to achieve the 50m focal distance separation.
The XEUS (X-ray Evolving Universe Spectroscopy) mission is designed to explore the X-ray emission from objects in the Universe at high red shifts. A package of instruments has been defined in some detail that allows the scientific goals of the mission to be met. It comprises narrow field imaging spectrometers of both Transition Edge Sensor (TES) and Superconducting Tunnel Junction (STJ) designs, and a Wide Field Imager with novel Silicon Active - Pixel sensing elements. We discuss the utilisation of the largest yet conceived mirror collecting area that facilitates secondary science such as high time resolution, polarimetry and extensions to high energies >10keV, and briefly mention some future trade-off studies that must be addressed.
Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe.
CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and background rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors.
In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD).
We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.
The NeXT mission has been proposed to study high-energy non-thermal phenomena in the universe. The high-energy response of the super mirror will enable us to perform the first sensitive imaging observations up to 80 keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixelated CdTe detector, will provide spectra and images in the wide energy range from 0.5 keV to 80 keV. In the soft gamma-ray band upto ~1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several x 10-8 photons/s/keV/cm2 in the hard X-ray region and a few x 10-7 photons/s/keV/cm2 in the soft gamma-ray region.
The new frontier in astrophysics is the study of the very first stars, galaxies and black holes in the early Universe. These objects are beyond the grasp of the current generation of X-ray telescopes such as Chandra, and so the Generation-X Vision Mission has been proposed as an X-ray observatory which will be capable of detecting these earliest objects. Xray imaging and spectroscopy of such distant objects will require an X-ray telescope with large collecting area and high angular resolution. The Generation-X concept has 100 m2 collecting area at 1 keV (1000 times larger than Chandra) and 0.1 arcsecond angular resolution (several times better than Chandra and 50 times better than the resolution goal for Constellation-X). The baseline mission involves four 8 m diameter telescopes operating at Sun-Earth L2. Such large telescopes will require either robotic or human-assisted in-flight assembly. To achieve the required effective area with launchable mass, very lightweight grazing incidence X-ray optics must be developed, having an areal density 100 times lower than in Chandra, with perhaps 0.1 mm thick mirrors requiring on-orbit figure control. The suite of available detectors for Generation-X should include a large-area high resolution imager, a cryogenic imaging spectrometer and a grating spectrometer.
X-ray interferometry has the potential to provide imaging at ultra high angular resolutions of 100 micro arc seconds or better. However, designing a practical interferometer which fits within a reasonable envelope and that has sufficient collecting area to deliver such a performance is a challenge. A simple system which can be built using current X-ray optics capabilities and existing detector technology is described. The complete instrument would be ~20 m long and ~2 m in diameter. Simulations demonstrate that it has the sensitivity to provide high quality X-ray interferometric imaging of a large number of available targets.
The proposed Micro-Arcsecond X-ray Imaging Mission (MAXIM) uses an array of spacecraft containing grazing incidence optics to create and acquire an image on a distant detector spacecraft. Among the technical challenges facing the mission, maintaining an acceptably small wavefront error in the optical system is addressed in this paper. Starting with a performance model for the observatory and both analytically- and raytrace-based optical sensitivities to misalignment and figure error, an error budget is constructed that includes the effects of the individual optical surfaces, the alignment of the optical elements within the 4-mirror periscope sub-assemblies, and the relative alignment of the many periscopes that make up the MAXIM optical imaging system. At this stage of conceptual development, the allocations to different sub-systems that affect wavefront error is based on the philosophy of "spreading the pain" associated with performance requirements of the contributing elements. The performance model and error budget become tools with which to explore different architectures and requirements allocations as the mission concept develops.
We present new schemes for a next-generation X-ray telescope for the energy range between approximately 1 and 10 keV providing an angular resolution of at least 1 milli-arcsec. Its technology will be based on diffractive transmission optics, e.g. Fresnel zone plates and their derivatives. Beside near-diffraction limited imaging, these devices hold the potential of a large collecting area well beyond 10 square meters at a simple and lightweight construction, compared to conventional mirror telescopes. However, there are drawbacks. Firstly the intrinsically long focal lengths do require separation and precise
formation flight of lens and detector spacecraft. Accordingly, techniques will be discussed for relative stabilization on the one hand and possibilities to reduce focal length and thus lever arm on the other hand. For this purpose, large arrays of small, independent lenses might offer a notable perspective. Secondly, diffractive optics
feature severe focal length dispersion which has to be accepted using narrow-band spectral selection or-better-should be corrected over a practicable wide energy range. In the hard X-ray regime, hybrid lens devices made of beryllium, lithium or plastics like polycarbonate will be an appropriate solution for a fixed energy, while tunable systems with variable correction lenses possess-in principle-the capability for dispersion compensation in the soft X-ray region, too. An overview on the science case of milli-arcsec X-ray imaging will conclude the contribution. We show that significant new insights in astrophysical processes are expected just at and beyond this angular scale and give examples from X-ray binaries over AGN's up to gamma-ray bursts.
The large collecting area of XMM-Newton combined with the good energy resolution of the EPIC-pn CCDs allows the study, with unprecedented detail, of accretion processes onto neutron stars and black holes. The EPIC-pn CCD camera in Timing mode, in which data are read out continuously, is among the fastest X-ray CCD camera available; however, telemetry constraints do not allow full use of these capabilities for many sources because currently randomly distributed data gaps are introduced by the on-board data handling electronics. As an alternative, we have proposed to implement a modification of the Timing mode in which data from soft X-ray events are not transmitted to Earth. Here we discuss the properties of this modified Timing mode, which will first be used in simultaneous XMM-Newton, RXTE, and INTEGRAL observations of the Galactic black hole binary Cygnus X-1 in autumn 2004. We discuss the predicted performance of this new mode based upon laboratory measurements, Monte Carlo simulations, and data from existing Timing mode observations.
Constellation-X is NASA's next major X-ray astronomical observatory. Its salient features are its very large effective X-ray collecting area (about 30,000 cm2 at 1 keV) and high resolution gratings and cryogenic detector systems. The large mirror effective area presents unique and unprecedented challenges in optical fabrication and metrology. In this paper we report on the development of very lightweight X-ray mirrors that address these challenges. We use a two-step mirror fabrication process: (1) slumping thin (0.4mm) flat glass sheets to generate high quality substrates that may have mid-frequency figure errors, and (2) reducing or eliminating the mid-frequency errors using an epoxy replication process. We discuss problems and the potential associated with each of these two steps. Based on our work to date, we expect that this technology to be able to meet the baseline Constellation-X requirements, i.e, 15" HPD (half-power diameter) at the observatory level. In the next few years, we will further advance this technology and expect it to reach the Constellation-X goal: 5" HPD at the observatory level.
The success of the XEUS mission depends critically on the deployment of a 10 square metre class telescope system in a suitable orbit for science observations. The minimisation of the telescope mass and volume becomes of critical importance for such a large facility. We describe developments of novel light weight optics that enable a reduction in mass per unit area of more than an order of magnitude, compared with traditional replication optics technology. With such a large collection area, image confusion limits become a scientific driver as well, demanding arcsecond class resolution. We describe measurements that demonstrate the improvement in resolution that gives very high confidence that these requirements can be met.
What is the nature of the Dark Energy that is driving the universe apart? Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales which is dominated by the Dark Energy. DUO will measure 10.000 clusters of galaxies, the power spectrum of density fluctuations of clusters and their number density as a function of cosmic time. Although designed long before the existence of Dark Energy was claimed, the ABRIXAS type X-ray telescope turns out to be ideally suited for this task: DUO is, in essence, a re-flight of the ABRIXAS X-ray telescope which some modifications of the focal plane instrumentation. First of all, we will use new CCDs which are improved versions of the pn-CCDs successfully flown on XMM-Newton. A modular concept having seven individual cameras in the foci of the seven mirror systems allows us to design the orientation of the seven telescopes with respect to each other matching the scientific needs of the DUO mission. Details of the concept including mechanical, electrical and thermal aspects are given.
Recent development of cryogenic detectors enabled high resolution
diagnostics of emission line and absorption line/edge
structures. These studies are quite important to investigate physics
of interstellar/intergalactic plasma and dynamics of matters around
black holes, for example.
Soft X-ray telescopes for such purpose, sensitive up to 10 keV, are
usually designed using Au, Pt, or Ir for their large electron density
and large critical angle. However in fact, these materials are not
very suitable in a few to 8 keV region, because they have wide and
deep M-shell absorption edge structures in 2--4 keV region.
Considering absorption edges and also thin-film characteristics, C or
Ni can be alternatives. However, these materials alone cannot be a
good mirror, again from absorption edges in the energy region of
interest (0.1-10 keV). We designed composite structure consisting of
C, Ni and Pt with thickness of 30 to 300 A, to get smooth and high
reflectivity all across the energy region. Test fabrication showed
interfacial roughness is as low as expected, indicating match of
materials is also good.
We applied this result to the baseline design of NeXT/Soft X-ray
Telescope, by substituting current material (Au) with C-Ni-Pt
composite, and obtained 20% larger effective area in 2-8 keV region.
Focusing optics are now poised to dramatically improve the sensitivity and angular resolution at energies above 10 keV to levels that were previously unachievable by the past generation of background limited collimated and coded-aperture instruments. Active balloon programs (HEFT), possible Explorer-class satellites (NuSTAR - currently under Phase A study), and major X-ray observatories (Con-X HXT) using focusing optics will play a major role in future observations of a wide range of objects including young supernova remnants, active galactic nuclei, and galaxy clusters. These instruments call for low cost, grazing incidence optics coated with depth-graded multilayer films that can be nested to achieve large collecting areas. Our approach to building such instruments is to mount segmented mirror shells with our novel error-compensating, monolithic assembly and alignment (EMAAL) procedure. This process involves constraining the mirror segments to successive layers of graphite rods that are precisely machined to the required conic-approximation Wolter-I geometry. We present results of our continued development of thermally formed glass substrates that have been used to build three HEFT telescopes and are proposed for NuSTAR. We demonstrate how our experience in manufacturing complete HEFT telescopes, as well as our experience developing higher performance prototype optics, will lead to the successful production of telescopes that meet the NuSTAR design goals.
We report on innovative X-ray mirror technologies with focus on requirements of future X-ray astronomy space projects. Various future projects in X-ray astronomy and astrophysics will require large light-weight but highly accurate segments with multiple thin shells or foils. The large Wolter 1 grazing incidence multiple mirror arrays, the 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 (shaped, bent or flat foils) with high X-ray reflectivity and excellent mechanical stability.
Ultraviolet astronomy is an important tool for the study of the interplanetary medium, comets, planetary upper atmospheres, and the near space environments planets and satellites. In addition to brightness distributions, emission line profiles offer insight into winds, atmospheric escape, energy balance, currents, and plasma properties. Unfortunately, the faintness of many target emissions and the volume limitations of small spacecraft and remote probes limit the opportunities for incorporating a high spectral resolution capability. An emerging technique to address this uses an all-reflective form of the spatial heterodyne spectrometer (SHS) that combines very high (R >105) spectral resolution and large étendue in a package small enough to fly as a component instrument on small spacecraft. The large étendue of SHS instruments makes them ideally suited for observations of extended, low surface brightness, isolated emission line sources, while their intrinsically high spectral resolution enables the study of the dynamical and spectral characteristics described above. We are developing three forms of the reflective SHS to observe single line shapes, multiple lines via bandpass scanning, and precision spectro-polarimetry. We describe the basic SHS approach, the three variations under development and their scientific potential for the exploration of the solar system and other faint extended targets.
We present the optical design of the spectrometer for imaging spectroscopy in the extreme-ultraviolet (EUV) spectral region for the Solar Orbiter mission. The instrument consists of a telescope making an image of the Sun on an entrance slit of a grating spectrometer. Two different optical designs are presented: a) a normal-incidence off-axis paraboloid telescope feeding a normal-incidence spectrometer and b) a grazing-incidence Wolter-type telescope feeding a normal-incidence spectrometer. The spectral region of operation is the 58-63 nm region, with the possibility of extending the range to the 116-126 nm region. The two designs are discussed in terms of optical performance, effective area and thermal load.
We have measured the topography and near-normal incidence EUV efficiency of five flat multilayer-coated polymer-overcoated blazed ion-etched holographic test gratings. Blaze angles were in the range 2.0-4.1°. All gratings had a surface roughness <3 Å rms (20-4000 Å). The best grating had a measured efficiency of 29.9% in the second order at 157.9 Å and a derived groove efficiency of 53.0%. At the shortest wavelength investigated (100.0 Å) another grating produced a measured efficiency in the first order of 12.9% and a derived groove efficiency of 33.6%. In third order another grating produced a measured efficiency at 137.8 Å of 13.4% and a derived groove efficiency of 21.8%. To the best of our knowledge these values exceed previous published results. Some issues remain that may be associated with modification of the groove profile by the multilayer coating.
A very significant fraction of the baryonic matter in the local universe is predicted to form a Warm Hot Intergalactic Medium (WHIM) of very low density, moderately hot gas, tracing the cosmic web. Its X-ray emission is dominated by metal features, but is weak (< 0.01 photons/cm2/s/sr) and potentially hard to separate from the galactic component. However, a mission capable of directly mapping this component of the large scale structure of the universe, via a small number of well chosen emission lines, is now within reach due to recent improvements in cryogenic X-ray detector energy resolution. To map the WHIM, the energy resolution and grasp are optimized. A number of missions have been proposed to map the missing baryons including MBE (US/SMEX program) and DIOS (Japan). The design of the mirror and detector have still room for improvements which will be discussed. With these improvements it is feasible to map a 10 x 10 degree area of the sky in 2 years out to z = 0.2 with sufficient sensitivity to directly detect WHIM structure, such as filaments connecting clusters of galaxies. This structure is predicted by the current Cold Dark Matter paradigm which thus far appears to provide a good description of the distribution of matter as traced by galaxies.
While the energy density of the Cosmic X-ray Background (CXB) provides
a statistical estimate of the super massive black hole (SMBH) growth
and mass density in the Universe, the lack, so far, of focusing
instrument in the 20-60 keV (where the CXB energy density peaks),
frustrates our effort to obtain a comprehensive picture of the
SMBH evolutionary properties. HEXIT-SAT (High Energy X-ray Imaging
Telescope SATellite) is a mission concept capable of exploring the
hard X-ray sky with focusing/imaging instrumentation, to obtain an
unbiased census of accreting SMBH up to the redshifts where galaxy
formation peaks, and on extremely wide luminosity ranges. This will
represent a leap forward comparable to that achieved in the soft
X-rays by the Einstein Observatory in the late 70'. In addition to
accreting SMBH, and very much like the Einstein Observatory, this
mission would also have the capabilities of investigating almost any
type of the celestial X-ray sources. HEXIT-SAT is based on high
throughput (>400 cm2 @ 30 keV; >1200 cm2 @ 1 keV), high quality
(15 arcsec Half Power Diameter) multi-layer optics, coupled with focal
plane detectors with high efficiency in the full 0.5-70keV
range. Building on the BeppoSAX experience, a low-Earth, equatorial
orbit, will assure a low and stable particle background, and thus an
extremely good sensitivity for faint hard X-ray sources. At the flux
limits of 1/10 microCrab (10-30 keV) and 1/3 microCrab (20-40 keV)
(reachable in one Msec observation) we should detect ~100 and
~40 sources in the 15 arcmin FWHM Field of View respectively,
thus resolving >80% and ~65% of the CXB where its energy
The primary scientific mission of the Black Hole Finder Probe (BHFP), part of the NASA Beyond Einstein program, is to survey the local Universe for black holes over a wide range of mass and accretion rate. One approach to such a survey is a hard X-ray coded-aperture imaging mission operating in the 10-600 keV energy band, a spectral range that is considered to be especially useful in the detection of black hole sources. The development of new inorganic scintillator materials provides improved performance (for example, with regards to energy resolution and timing) that is well suited to the BHFP science requirements. Detection planes formed with these materials coupled with a new generation of readout devices represent a major advancement in the performance capabilities of scintillator-based gamma cameras. Here, we discuss the Coded Aperture Survey Telescope for Energetic Radiation (CASTER), a concept that represents a BHFP based on the use of the latest scintillator technology.
Monitor e Imageador de RAios-X (MIRAX) is a Brazilian high energy astronomy mission dedicated to monitoring the central 1000 sq. deg. of the Galactic plane to observe unpredictable transient phenomena from compact objects in the 2-200 keV range through nearly continuous imaging with good spatial/temporal/energy resolution. The strength of MIRAX lies in the departure of its observing strategy from traditional pointed programs and scanning monitors. MIRAX will achieve two major advantages over previous and existing missions. First, it will detect, localize, and study transient phenomena, which last on all timescales from milliseconds to years, and are very likely to be missed by traditional observing strategies. Second, MIRAX will study longer lived phenomena in exquisite detail. The mission elements and science will be presented.
We propose a university-class micro-satellite "Hu-ring" to localize
and study gamma-ray bursts. The primary mission of "Hu-ring" is to
localize gamma-ray bursts with an 10 arcmin accuracy in real time, and
transmit promptly the coordinates to the ground. Although many of its
mission concepts are modeled after HETE-2, use of avalanche
photodiodes (APDs), innovative photon detector device, make it
possible to further reduce the size and the mass of the satellite. We
designed "Hu-ring" within a size of 50 cm cube and a weight limit of 50 kg, so that it can be launched as a piggy-back payload of the Japanese H-IIA Launch Vehicle. The satellite is spin-stabilized, and has a half-sky field of view centered on the anti-sun direction. A set of scintillation counters equipped with rotation modulation collimators are employed for localization of GRBs. We also measure the soft/medium X-ray spectra of GRBs using APDs as a direct X-ray photon detectors. These two kinds of instruments cover the 0.5--200 keV energy range. The satellite bus is designed mostly with commercially available components in order to reduce the cost and the lead time. Following the HETE-2 model, in order to receive the prompt burst alerts it is designed to rely on a global network of receive-only low-cost ground stations, which may be hosted at research instutions with a small footprint. We performed analyses in many aspects: mechanical and thermal design of the satellite bus, attitude control simulations, power budget, ground contact schedule and downlink capacity, etc. We verified that the mission goal can be achieved with this proposed design philosophy.
The MEGA mission would enable a sensitive all-sky survey of the medium-energy ?-ray sky (0.3-50 MeV). This mission will bridge the huge sensitivity gap between the COMPTEL and OSSE experiments on the Compton Gamma Ray Observatory, the SPI and IBIS instruments on INTEGRAL and the visionary ACT mission. It will, among other things, serve to compile a much larger catalog of sources in this energy range, perform far deeper searches for supernovae, better measure the galactic continuum emission as well as identify the components of the cosmic diffuse emission. The large field of view will allow MEGA to continuously monitor the sky for transient and variable sources. It will accomplish these goals with a stack of Si-strip detector (SSD) planes surrounded by a dense high-Z calorimeter. At lower photon energies (below ~30 MeV), the design is sensitive to Compton interactions, with the SSD system serving as a scattering medium that also detects and measures the Compton recoil energy deposit. If the energy of the recoil electron is sufficiently high (> 2 MeV), the track of the recoil electron can also be defined. At higher photon energies (above ~10 MeV), the design is sensitive to pair production events, with the SSD system measuring the tracks of the electron and positron. We will discuss the various types of event signatures in detail and describe the advantages of this design over previous Compton telescope designs. Effective area, sensitivity and resolving power estimates are also presented along with simulations of expected scientific results and beam calibration results from the prototype instrument.
The Chandra Low Energy Transmission Grating Spectrometer (LETGS) is
comprised of 3 micro-channel plate (MCP) segments and is primarily
used with the High Resolution Camera spectroscopic array (HRC-S).
In-flight calibration data observed with the LETG+HRC-S show that
there are non-linear deviations in the positions of some lines by as
much as 0.1 Å. These deviations are thought to be caused by spatial non-linearities in the imaging characteristics of the HRC-S detector. Here, we present the methods we used to characterize the non-linearities of the dispersion relation across the central plate of the HRC-S, and empirical corrections which greatly reduce the observed non-linearities by a factor of 2 or more on the central MCP.
High quantum efficiency over a broad spectral range is one of the main properties of the EPIC pn camera on-board XMM-Newton. The quantum efficiency rises from ~75% at 0.2 keV to ~100% at 1 keV, stays close to 100% until 8 keV, and is still ~90% at 10 keV. The EPIC pn camera is attached to an X-ray telescope which has the highest collecting area currently available, in particular at low energies (more than 1400 cm2 between 0.1 and 2.0 keV). Thus, this instrument is very sensitive to the low-energy X-ray emission. However, X-ray data at energies below ~0.2 keV are considerably affected by detector effects, which become more and more important towards the lowest transmitted energies. In addition to that, pixels which have received incorrect offsets during the calculation of the offset map at the beginning of each observation, show up as bright patches in low-energy images. Here we describe a method which is not only capable of suppressing the contaminations found at low energies, but which also improves the data quality throughout the whole EPIC pn spectral range. This method is then applied to data from the Vela supernova remnant.
We present the current status of soft X-ray calibration of X-ray CCD cameras, X-ray Imaging Spectrometer (XIS), onboard Astro-E2. We perform soft X-ray calibration of four front illuminated (FI) CCD cameras and two back illuminated (BI) CCD cameras, among which four cameras will be selected to be installed on the satellite. The calibration aims to measure the quantum efficiency and re-distribution function of the CCDs as a function of incident X-ray energy. A soft X-ray spectrometer is used to measure these items. In addition, we employ a gas proportional counter and an XIS engineering unit as reference detectors for the quantum efficiency measurement. We describe how we calibrate the absolute quantum efficiency of the XIS using these instruments. We show some of the preliminary results of the calibration including quick look results of BI CCD cameras.
We report a ground-based X-ray calibration of the Astro-E2 X-ray
telescope at the PANTER test facility. Astro-E2, to be launched in
February 2005, has five X-Ray Telescopes (XRTs). Four of them focus on
the X-Ray Imaging Spectrometers (XIS) while the other on the X-Ray
Spectrometer (XRS). They are designed with a conical approximation of
Wolter-I type optics, nested with thin foil mirrors to enhance their
throughput. A calibration test of the first Astro-E2 flight XRT for
XIS was carried out at the PANTER facility in August 2003. This
facility has an 130 meter long diverging beam from X-ray generator to
XRT. Owing to the small X-ray spot size of about 2 mm dia., we verified that the focal position of each quadrant unit converged within 10 arcsec. The energy band around Au-M edge structures was
scanned with a graphite crystal. The edge energy (Au M5) is consistent with that listed in Henke et al. 1997. Owing to the large area coverage of the PSPC detector which is a spare of the ROSAT satellite, off-axis images including stray lights at large off-axis angle (up to 6 degree) were obtained with a large field of view. We also compared the results with those measured with the parallel pencil beam at ISAS which is in detail reported in our companion paper by Itoh A. et al..
We present X-ray characteristics of X-ray telescopes (XRTs) onboard the Astro-E2 satellite. It is scheduled to be launched in February 2005. We have been performed X-ray characterization measurements of XRTs at Institute of Space and Astronautical Science (ISAS) since January 2003. We adopted a raster scan method with a narrow X-ray pencil beam. Angular resolution of the Quadrants composed of the Astro-E2 XRT was evaluated to be 1'.6-2'.2 (HPD; Half Power Diameter), irrespective of the X-ray energy, while those of the Astro-E XRT was 2'.0-2'.2. The effective area of a telescope is approximately 450, 330, 250, and 170 [cm2] at energies of 1.49, 4.51, 8.04, and 9.44 keV, respectively. The field of view (FOV) of the XRTs which is defined as Full Width Half Maximum (FWHM) of the vignetting function is ≈18' at 4.51 keV. We summarize these characters of the XRTs.
ESA's large X-ray space observatory XMM-Newton is in its fifth year of operations. We give a general overview of the status of calibration of the five X-ray instruments and the Optical Monitor. A main point of interest in the last year became the cross-calibration between the instruments. A cross-calibration campaign started at the XMM-Newton Science Operation Centre at the European Space Astronomy Centre in collaboration with the Instrument Principle Investigators provides a first systematic comparison of the X-ray instruments EPIC and RGS for various kind of sources making also an initial assessment in cross calibration with other X-ray observatories.
The HRC-S is a microchannel plate detector on board Chandra and is primarily used for spectroscopic observations with the Low Energy Transmission Grating Spectrometer (LETGS) in place. Photons are detected via signals read out from evenly spaced wires underneath the plates and positions are computed by centroiding around the strongest amplifier signals. This process leads to gaps in between the taps where no events are placed. A deterministic correction is then made during ground processing to these event locations to remove the gaps. We have now developed a new, empirical degap corrections from flight data. We describe the procedure we use, present comparisons between the new degap and lab-data based degap, and investigate the temporal stability of the degap corrections.