The Xeus mission is designed to explore the X-ray emission from objects in the Universe at high redshifts. 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 TES and STJ designs, and a Wide Field Imager with novel Silicon Active - Pixel sensing elements. Finally 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.

A new type of Active Pixel Sensor is proposed which will be capable to meet the requirements of the wide field imager of ESA's future X-ray mission XEUS: the simultaneous energy and position resolved detection of X-rays at high count rate on a large format sensor. The Active Pixel Sensor is based on the integrated detector-amplifier structure DEpleted P-channel Field Effect Transistor (DEPFET). The device operates on a fully depleted bulk and provides internal signal amplification at the position of the charge generation. A very low value of the overall output capacitance leads to extremely low read noise. In the matrix arrangement of an Active Pixel Sensor the single DEPFET pixels can be randomly accessed for readout, and various flexible readout modes are possible. In contrast to CCDs the DEPFET-based Active Pixel Sensor avoids the transfer of signal charges over long distances within the detector bulk, and related problems of transfer loss or out-of-time-events cannot occur. An interesting feature is the non-destructive nature of the DEPFET readout which can be used for the reduction of the low-frequency noise contribution by repetitive readings of the signal information. The device principle of the DEPFET based pixel sensor is explained. First results of single DEPFET measurements are presented.

Fast X-ray timing observations are a method to probe strong gravity fields around compact massive objects. The European X-ray Evolving Universe Spectroscopy (XEUS) mission with its large collecting area telescope will be able to deliver the required extremely good photon statistics for these studies. The fast timing detector in the focal plane must be able to operate at up to 10⁷ incoming photons from the brightest X-ray objects in the sky with an energy resolution of 200 eV FWHM at 5.9 keV at a dead time not exceeding 1% and a time resolution of 10 μsec. Silicon Drift Detectors (SDDs) with their extremely small value of the readout capacitance have proved that they can handle high count rates with simultaneous good energy resolution. For the XEUS fast timing detector it is proposed to operate a multi-channel SDD at an out of focus position to distribute the flux of photons over a number of detector cells.

The fully depleted PN-CCD detector is meanwhile field-tested in several experiments on ground and in space. Its application as focal plane detector aboard ESA's XMM-Newton observatory can be considered as the most impressive one. The further development of this detector type including its readout chip in the MPI semiconductor laboratory is presented here. The new device, called frame store PN-CCD, shows substantial improvement of performance, in particular concerning the energy resolution and the probability of out of time event occurrence. Moreover, the detector offers features which are of great importance for its application in space. This is, besides the radiation hardness of the CCD, the variety of feasible pixel sizes and the high frame rates in combination with the small power consumption of the detector. Because of the thin radiation entrance window and the full depletion of the chip, the detector provides a high quantum efficiency for soft X-rays as well as for optical light and the near infrared. The frame store PN-CCD detector will be applied for the proposed X-ray astronomy missions DUO and ROSITA.

Charge sharing and charge loss measurements for a many-pixel, Cadmium-Zinc-Telluride (CdZnTe) detector are discussed. These properties that are set by the material characteristics and the detector geometry help to define the limiting energy resolution and spatial resolution of the detector in question. The detector consists of a 1-mm-thick piece of CdZnTe sputtered with a 16x16 array of pixels with a 300 micron pixel pitch (inter-pixel gap is 50 microns). This crystal is bonded to a custom-built readout chip (ASIC) providing all front-end electronics to each of the 256 independent pixels. These types of detectors act as precursors to that which will be used at the focal plane of the High Energy Replicated Optics (HERO) telescope currently being developed at Marshall Space Flight Center. With a telescope focal length of 6 meters, the detector needs to have a spatial resolution of around 200 microns in order to take full advantage of the HERO angular resolution. We discuss to what degree charge sharing degrades energy resolution through charge loss and improves spatial resolution through position interpolation.

Measuring the depth of interaction in thick Cadmium-Zinc-Telluride (CZT) detectors allows improved imaging and spectroscopy for hard X-ray imaging above 100 keV. The Energetic X-ray Imaging Survey Telescope (EXIST) will employ relatively thick (5 - 10 mm) CZT detectors, which are required to perform the broad energy-band sky survey. Interaction depth information is needed to correct events to the detector "focal plane" for correct imaging and can be used to improve the energy resolution of the detector at high energies by allowing event-based corrections for incomplete charge collection. Background rejection is also improved by allowing low energy events from the rear and sides of the detector to be rejected. We present experimental results of intereaction depth sensing in a 5 mm thick pixellated Au-contact IMARAD CZT detector. The depth sensing was done by making simultaneous measurements of cathode and anode signals, where the interaction depth at a given energy is proportional to the ratio of cathode/anode signals. We demonstrate how a simple empirical formula describing the event distributions in the cathode/anode signal space can dramatically improve the energy resolution. We also estimate the energy and depth resolution of the detector as a function of the energy and the interaction depth. We also show a depth-sensing prototype system currently under development for EXIST in which cathode signals from 8, 16 or 32 crystals can be read-out by a small multi-channel ASIC board that is vertically edge-mounted on the cathode electrode along every second CZT crystal boundary. This allows CZT crystals to be tiled contiguously with minimum impact on throughput of incoming photons. The robust packaging is crucial in EXIST, which will employ very large area imaging CZT detector arrays.

Cadmium zinc telluride (CZT) pixel detectors show very good spectral and spatial resolution and are suitable for use in compact hard X-ray sensors operated without cryogenics. One of the more interesting astrophysical application is their use as focal plane detectors for multilayer hard X-ray telescopes operating in the 15 - 70 keV energy band. Here we report on results obtained using a 16 x 16 CZT pixel detector (10 x 10 x 1 mm³ single crystal) with 500 μm pixels operated at room temperature using standard commercial electronics. The results clearly show that the use of small pixels is effective in reducing one of the major drawbacks of CZT planar detectors i.e. the considerable amount of charge loss, due to hole trapping, which gives rise to a reduced energy resolution and a low energy tail in the pulse-height spectra.

We made one-dimensional detector arrays applying the newly developed Schottky CdTe technique. Two prototypes are manufactured; one consists of eight pixels of 2 x 2 x 0.5 mm³ each (2 mm module) and the other eight pixels of 25 x 2 x 0.5 mm³ each (25 mm module). The single element read-out test of the 2 mm module showed an energy resolution of ~1.7 keV at 59.5 keV, at 0°C for the bias voltage of 400 V. The 25 mm modules showed an energy resolution of ~4.5 keV at 59.5 keV at 0°C for the bias voltage of 300 V. Signals from the four sets of the CdTe modules (32 pixels in total) are read out by the VA/TA chips made by IDE company. The energy resolution of the 2 mm module is ~3.0 keV on average at 59.5 keV at room temperature for the bias voltage of 350 V. The 25 mm modules have an energy resolution of ~6.1 keV on average at 122.1 keV at room temperature for the bias voltage of 300 V. In view of these results, the manufactured arrays are promising as spectroscopic detectors for hard X-rays and γ-rays. A few modifications are needed in the VA/TA chips to be applied for the CdTe X-ray detector. Applications of CdTe detector arrays to a slit or coded-mask camera, and an imaging polarimeter are stated.

Since December 1999, ESA's large X-ray space observatory XMM-Newton operates in a highly eccentric 48-h orbit which allows for long uninterrupted exposure times. The three payload instruments EPIC, RGS, and OM yield scientific data of high quality and sensitivity. We report here on the current timing capabilities of all three instruments by showing results from analyses on relative and absolute timing. In this context we discuss the process of correlating local onboard event arrival times to terrestrial time frames and present some detailed results from time correlation analyses. This involves investigations on the performance of the onboard quartz oscillator that have been performed. In addition we describe problematic timing data anomalies in the EPIC-pn data and their treatment by the SAS. We show recent examples of timing analyses.

The X-ray Observatory XMM-Newton is in orbit since the 10^th December 1999. In the first half year an extensive program to commission, calibrate and verify the performance of the payload has been carried out. Since then many routine calibrations, using the onboard calibration source as well as many different celestial objects, have been performed. In this paper we will report on the status of the calibration of the EPIC-pn camera in general and focus on major points like the CTI evolution, the effective area, the response function and the instrumental background.

The X-ray Observatory XMM-Newton is in orbit since December 1999. We will report on the current status of the in-flight spectral calibration of the EPIC-pn camera. Using the internal calibration source and line spectra of supernova remnants the calibration of the energy scale has been monitored over the first years of operations. Continuum spectra of celestial objects like Active Galactic Nuclei or isolated neutron stars were used for cross-calibrating the instruments. We report on recent improvements in the spectral calibration as well as still existing problems.

We report on the current status of the background calibration of the EPIC pn-CCD camera on board XMM-Newton. The intrinsic background is comprised of internal electronic noise, and continuous and fluorescent X-ray emission induced by high-energy particles. Soft protons passing through the X-ray telescope (and finally also true cosmic X-rays) contribute to the registered events. The camera background has been monitored by using data in closed filter positions for three years; we review the spectral, spatial, and temporal distribution, for all commissioned instrument modes. This paper also discusses briefly the effects on scientific data analysis and conclusions for further observations and detectors.

The EPIC-pn CCD Camera on board the ESA X-ray observatory XMM-Newton is a very sensitive and versatile instrument with many observing modes. One of the modes, the timing mode, was designed so that a time resolution of 0.029 milliseconds can be achieved. This mode is important for observing bright variable sources with a very high time resolution. Up to now it has only been possible to use the spectra down to 300-400 eV in this mode. Below this energy the data appears to be affected by soft flares which are caused by stack overflows generated by high energy particles. We present a method that can be used to mitigate the effect these flares have on the data and discuss the improvement that this brings to the timing mode spectra. This new method will at last make it possible to get spectra down to the lowest energies detectable in this mode. This is particularly interesting for timing studies of isolated neutron stars and other variable objects, such as magnetic CVs, with very soft spectra.

We are developing a 2-detector high resolution Compton telescope utilizing 3D imaging germanium detectors (GeDs) to be flown as a balloon payload in Spring 2004. This instrument is a prototype for the larger Nuclear Compton Telescope (NCT), which utilizes 12-GeDs. NCT is a balloon-borne soft γ-ray (0.2-15 MeV) telescope designed to study, through spectroscopy, imaging, and timing, astrophysical sources of nuclear line emission and γ-ray polarization. The NCT program is designed to develop and test the technologies and analysis techniques crucial for the Advanced Compton Telescope, while studying γ-ray radiation with very high spectral resolution, moderate angular resolution, and high sensitivity. NCT has a novel, ultra-compact design optimized for studying nuclear line emission in the critical 0.5-2 MeV range, and polarization in the 0.2-0.5 MeV range. The prototype flight will critically test the novel instrument technologies, analysis techniques, and background rejection procedures we have developed for high resolution Compton telescopes. In this paper we present the design and preliminary results of laboratory performance tests of the NCT flight electronics.

The INTEGRAL X-ray monitor, JEM-X, (together with the two gamma ray instruments, SPI and IBIS) provides simultaneous imaging with arcminute angular resolution in the 3-35 keV band. The good angular resolution and low energy response of JEM-X plays an important role in the detection and identification of gamma ray sources as well as in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture X-ray telescope consisting of two identical detectors. Each detector has a sensitive area of 500 cm², and views the sky through its own coded aperture mask. The coded masks are located 3.4 m above the detector windows. The detector field of view is constrained by X-ray collimators (6.6° FOV, FWHM).

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a balloon-borne hard-x-ray telescope is under development at the Marshall Space Flight Center. These detectors have an active area of ~ 20 cm², and are filled with a high pressure (10⁶ Pa) xenon-helium mixture. Imaging is via crossed-grid position-sensitive phototubes sensitive in the UV region. The performance of the GSPC is well matched to that of the telescope's x-ray optics which have response to 75 keV and a focal spot size of ~ 500 μm. The detector’s energy resolution, 4% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Full details of the instrument and its performance will be provided.

The High Energy Focusing Telescope (HEFT) is a balloon-borne, hard x-ray/gamma ray (20-70 keV) astronomical experiment. HEFT's 10 arcminute field of view and 1 arcminute angular resolution place challenging demands on its attitude control system (ACS). A microprocessor-based ACS has been developed to manage target acquisition and sidereal tracking. The ACS consists of a variety of sensors and actuators, with provisions for 2-way ground communication, all controlled by an on-board computer. Ground based pointing performance measurements indicate 1σ jitter of 7" and gyro drift rates of <1" s^-1. Jitter is expected to worsen in the flight environment, but star tracker data are expected to reduce drift rates significantly, enabling a predicted 1σ absolute attitude determination of ≥4.7". HEFT is scheduled for flight in Spring 2004.

Swift is a multi-wavelength observatory designed for the autonomous detection and immediate follow-up of gamma-ray bursts and their afterglows. Following launch in early 2004, Swift's Burst Alert Telescope (BAT) will detect 100s of GRBs per year, and autonomously maneuver sensitive UV/optical and X-ray telescopes onto the burst within 10 to 75 seconds. GRB and X-ray positions and UV/optical finding chart will be rapidly distributed thorugh the GCN to promote ground-based observations. Afterglows will be monitored by Swift for days to weeks. All data will be converted into standard FITS formats and rapidly made available to the community from data centers in the US, Italy, and the UK.

The Burst Alert telescope (BAT) is one of 3 instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT instrument is the instrument that first detects the GRB and localizes the burst direction to an accuracy of 1-4 arcmin within 20 sec after the start of the event. These locations cause the spacecraft to autonomously slew to point the two narrow-FOV instruments at the burst location within 20-70 sec to make follow-up x-ray and optical observations. BAT is a wide-FOV coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4x4x2mm), and the coded-aperture mask is composed of ~52,000 pieces of lead (5x5x1mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15-150 keV energy range with ~6 keV resolution, a sensitivity of 0.2 ph/cm²-sec, and a 1.4 sr (half-coded) FOV. We expect to detect >100 GRBs/yr for a 2-year mission. The BAT also performs an all-sky hard x-ray survey with a sensitivity of ~2 mCrab (systematic limit) and as a hard x-ray transient monitor.

In addition to providing the initial gamma-ray burst trigger and location, the Swift Burst Alert Telescope (BAT) will also perform an all-sky hard x-ray survey based on serendipitous pointings resulting from the study of gamma-ray bursts. BAT was designed with a very wide field-of-view (FOV) so that it can observe roughly 1/7 of the sky at any time. Since gamma-ray bursts are uniformly distributed over the sky, the final BAT survey coverage is expected to be nearly uniform. BAT's large effective area and long sky exposures will produce a 15 - 150 keV survey with up to 30 times better sensitivity than any previous hard x-ray survey (e.g. HEAO A4). Since the sensitivity of deep exposures in this energy range is systematics limited, the ultimate survey sensitivity depends on the relative sizes of the statistical and systematic errors in the data. Many careful calibration experiments were performed at NASA/Goddard Space Flight Center to better understand the BAT instrument's response to 15-150 keV gamma-rays incident from any direction within the FOV. Using radioactive sources of gamma-rays with known locations and energies, the Swift team can identify potential systematic errors in the telescope's performance and estimate the actual Swift hard x-ray survey sensitivity in flight. These calibration results will be discussed and a preliminary parameterization of the BAT instrument response will be presented. While the details of the individual BAT CZT detector response will be presented elsewhere in these proceedings, this talk will focus on the translation of the calibration experimental data into overall hard x-ray survey sensitivity.

The Swift Gamma-Ray Explorer is designed to make prompt multiwavelength observations of Gamma-Ray Bursts (GRBs) and GRB Afterglows. The X-ray Telescope (XRT) provides key capabilities that permit Swift to determine GRB positions with a few arcseconds accuracy within 100 seconds of the burst onset. The XRT utilizes a superb mirror set built for JET-X and a state-of-the-art XMM/EPIC MOS CCD detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with effective area of 135 cm² at 1.5 keV, field of view of 23.6 x 23.6 arcminutes, and angular resolution of 18 arcseconds (HEW). The detection sensitivity is 2x10^-14 erg/cm²/s in 10⁴ seconds. The instrument is designed to provide automated source detection and position reporting within 5 seconds of target acquisition. It can also measure redshifts of GRBs for bursts with Fe line emission or other spectral features. The XRT will operate in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow each burst for days as it fades from view.

The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic, and photometric observations of X-ray emission from Gamma-ray Bursts and their afterglows in the energy band 0.2-10 keV. In order to provide rapid-response, automated observations of these randomly occurring objects without ground intervention, the XRT must be able to observe objects covering some seven orders of magnitude in flux, extracting the maximum possible science from each one. This requires a variety of readout modes designed to optimise the information collected in response to shifting scientific priorities as the flux from the burst diminishes. The XRT will support four major readout modes: imaging, two timing modes and photon-counting, with several sub-modes. We describe in detail the readout modes of the XRT. We describe the flux ranges over which each mode will operate, the automated mode switching that will occur and the methods used for collection of bias information for this instrument. We also discuss the data products produced from each mode.

The SWIFT X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report the results of the analysis of SWIFT XRT Point Spread Function (PSF) as measured during the end-to-end calibration campaign at the Panter X-Ray beam line facility. The analysis comprises the study of the PSF both on-axis and off-axis. We compare the laboratory results with the expectations from the ray-tracing software and from the mirror module tested as a single unit. We show that the measured HEW meets the mission scientific requirements. On the basis of the calibration data we build an analytical model which is able to reproduce the PSF as a function of the energy and the position within the detector.

The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report first results of the analysis of Swift XRT effective area at five different energies as measured during the end-to-end calibration campaign at the Panter X-ray beam line facility. The analysis comprises the study of the effective area both on-axis and off-axis for different event grade selection. We compare the laboratory results with the expectations and show that the measured effective area meets the mission scientific requirements.

The Swift X-ray Telescope is a powerful instrument for measuring the X-ray spectral properties of GRB afterglows. The spectroscopic capabilities are obtained through the energy resolving properties of the X-ray CCD imager in the focal plane of the X-ray Telescope. A range of CCD operating modes allow GRB afterglows to be followed over 5 orders of brightness as the afterglow decays. The spectroscopic response in each mode has been determined as part of the XRT calibration program and is being incorporated into the XRT instrument response matrices. These responses are being used to simulate GRB spectra as part of the pre-launch mission planning for Swift.

The UV/optical telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (~1 minute) UV and optical photons from the afterglow of gamma-ray bursts as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey-Chretien design with micro-channel plate intensified charged-coupled device detectors that provide sub-arcsecond imaging. Unlike most UV/optical telescopes the UVOT can operate in a photon-counting mode as well as an imaging mode. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.

The Swift/UVOT is a 30-cm aperture imaging telescope that is sensitive to photons in the wavelength range 170nm-600nm and is designed to provide near-ultraviolet and optical measurements of γ-ray bursts and other targets that the Swift observatory observes. The performance of the telescope and its photon counting detectors has been assessed in a series of calibration measurements made under vacuum conditions in a test facility at the Goddard Space Flight Center. We describe some of the results of this campaign, including measurements of the instrument throughput, image quality and distortion, and linearity of response. We also describe the spectroscopic capability of the instrument, which is enabled by the use of two grisms operating in the UV and optical bands respectively. The results from the ground calibration activities will form the basis for establishing the full calibration matrix of the instrument once on orbit.

The Swift mission requires that the Swift UV optical telescope (UVOT) have the autonomous functionality to protect itself against the potentially damaging effects of observing bright sources. This capability had to be added to an existing heritage camera design, which was used for the Optical Monitor telescope (OM) on ESA's XMM-Newton spacecraft. The solution used a two part mechanism employing data from a catalogue of known bright sources, and a real-time system for monitoring the raw pixel data from the camera and automatically reducing the detector gain when a signal above a programmed threshold is seen. This discussion will describe the resulting Field Programmable Gate Array (FPGA) based implementation that sits alongside the heritage camera and processing electronics and can be programmed and monitored by the UVOT instrument controller.

The SWIFT/UVOT has a requirement for on-board autonomous control of exposures, health and safety. It is anticipated that the optimal form of control may not emerge until after launch and may change during the course of the mission. A flexible and readily re-configurable system is therefore required. Two schemes have been adopted. As well as the more usual approach of tables of experimental configurations, action tables mapping command sequences to key events have been implemented. The command sequences, consisting of a series of command words located in EEPROM, are executed using a stack-based software 'virtual CPU.' Each command word, analogous to hardware CPU assembler instructions, results in the execution of well-checked Ada code fragments. As well as implementing the UVOT commands, the code includes functionality such as delaying a specified time, awaiting action completion, 'subroutine' calls and simple flow control. These permit the construction of complex control sequences. A C-like language is used to describe the required sequences. A translator converts them to the required command word sequence that is then validated on a simulator. Reloading the command sequence or the tables referring to it alters the autonomous behavior of the instrument.

The Ultraviolet and Optical Telescope (UVOT) is one of the three astronomical instruments onboard the SWIFT spacecraft. The optical calibration of this instrument, which was done prior to integration to the SWIFT spacecraft optical bench, is key to determine if UVOT will meet its science objectives. In this paper, we describe the optical ground support equipment (GSE) used for the calibration of UVOT. These tests, which were carried out in the Diffraction Grating Evaluation Facility (DGEF), at NASA Goddard Space Flight Center, required building an optical stimulus. We report the radiometric measurements of all the optical components used in putting together this stimulus. This includes a vacuum collimator with a Cassegrain design, a Pt/Cr-Ne light source, a complete set of neutral density filters spanning 6 orders of magnitude in transmission levels, a set of narrow-band filters matching the center of each of the six bands of UVOT, a set of pinholes of various sizes, flat fielding diffusers, and a set of parabolic mirrors.

We present a concept for an imaging gamma-ray polarimeter operating from ~50 MeV to ~1 GeV. Such an instrument would be valuable for the study of high-energy pulsars, active galactic nuclei, supernova remnants, and gamma-ray bursts. The concept makes use of pixelized gas micro-well detectors, under development at Goddard Space Flight Center, to record the electron-positron tracks from pair-production events in a large gas volume. Pixelized micro-well detectors have the potential to form large-volume 3-D track imagers with ~100 μm (rms) position resolution at moderate cost. The combination of high spatial resolution and a continuous low-density gas medium permits many thousands of measurements per radiation length, allowing the particle tracks to be imaged accurately before multiple scattering masks their original directions. The polarization of the incoming radiation may then be determined from the azimuthal distribution of the electron-positron pairs. We have performed Geant4 simulations of these processes to estimate the polarization sensitivity of a simple telescope geometry at 100 MeV.

We have developed a modular design for a hard X-ray and soft gamma-ray polrimeter that we call GRAPE (Gamma RAy Polarimeter Experiment). Optimized for the energy range of 50-300 keV, the GRAPE design is a Compton polarimeter based on the use of an array of plastic scintillator scattering elements in conjunction with a centrally positioned high-Z calorimeter detector. Here we shall review the results from a laboratory model of the baseline GRAPE design. The baseline design uses a 5-inch diameter position sensitive PMT (PSPMT) for readout of the plastic scintillator array and a small array of CsI detectors for measurement of the scattered photon. An improved design, based on the use of large area multi-anode PMTs (MAPMTs), is also discussed along with plans for laboratory testing of a prototype. An array of GRAPE modules could be used as the basis for a dedicated science mission, either on a long duration balloon or on an orbital mission. With a large effective FoV, a non-imaging GRAPE mission would be ideal for studying polarization in transient sources (gamma ray bursts and solar flares). It may also prove useful for studying periodically varying sources, such as pulsars. An imaging system would improve the sensitivity of the polarization measurements for transient and periodic sources and may also permit the measurement of polarization in steady-state sources.

Photoelectric X-ray polarimeters based on pixel micropattern gas detectors (MPGDs) offer order-of-magnitude improvement in sensitivity over more traditional techniques based on X-ray scattering. This new technique places some of the most interesting astronomical observations within reach of even a small, dedicated mission. The most sensitive instrument would be a photoelectric polarimeter at the focus of a very large mirror, such as the planned XEUS. Our efforts are focused on a smaller pathfinder mission, which would achieve its greatest sensitivity with large-area, low-background, collimated polarimeters. We have recently demonstrated a MPGD polarimeter using amorphous silicon thin-film transistor (TFT) readout suitable for the focal plane of an X-ray telescope. All the technologies used in the demonstration polarimeter are scalable to the areas required for a high-sensitivity collimated polarimeter.

The current status is reported of the development of Monitor of All-sky X-ray Image and the measurement of its observational response. MAXI is a scanning X-ray camera to be attached to the Japanese Experiment Module of the International Space Station in 2008. MAXI is mainly composed of two kinds of instruments, GSC which is sensitive to the 2 - 30 keV photons, and SSC to the 0.5 - 10 keV ones. As an X-ray all-sky monitor, MAXI has an unprecedented sensitivity of 7 mCrab in one orbit scan, and 1 mCrab in one week. Using the engineering mode of the proportional counter and of the collimator for GSC, the observational response of GSC is extensively measured. The acceptable performances are obtained as a whole for both the collimator and the counter. The engineering models of the other part of MAXI are also constructed and the measurement of their performance is ongoing.

MAXI, Monitor of All-sky X-ray Image, is an X-ray observatory on the Japanese Experimental Module (JEM) Exposed Facility (EF) on the international space station. MAXI is a slit scanning camera which consists of two kinds of X-ray detectors: one is a one-dimensional position-sensitive proportional counter with a total area of ~5000 cm², the Gas Slit Camera (GSC), and the other is an X-ray charge-coupled device (CCD) array with a total area ~200 cm², the Solid-state Slit Camera (SSC). The GSC subtends a field of view with an angular dimension of 1degree X 180degree while the SSC subtends a field of view with an angular dimension of 1degree times a little less than 180degree. In the course of one station orbit, MAXI can scan almost the entire sky with a precision of 1degree and with an X-ray energy range of 0.5-30keV. So far, we have fabricate 25 CCDs for flight candidates and production of devices are still continued. We need to select 32 and 16 CCDs to install a flight camera and a spare camera, respectively. We therefore developed the efficient screening method using ⁵⁵Fe sources. The key parameters of the CCDs for the screening are readout noise, dark current, charge transfer efficiency, and detection efficiency. The performance criteria used to rank devices are discussed.

MAXI is an X-ray all-sky monitor which will be mounted on the Japanese Experimental Module (JEM) of the International Space Station (ISS) in 2008. The Gas Slit Camera (GSC) consists of 12 one-dimensional position sensitive proportional counters and the sensitivity will be as high as 1 mCrab for a one-week accumulation in the 2-30 keV band. In order to calibrate the detectors and electronic systems thoroughly before the launch, a fast and versatile Ground Support Electronic (GSE) system is necessary. We have developed a new GSE based on VME I/O boards for a Linux workstation. These boards carry reconfigurable FPGAs of 100,000 gates, together with 16 Mbytes of SDRAM. As a demonstration application of using this GSE, we have tested the positional response of a GSC engineering counter. We present a schematic view of the GSE highlighting the functional design, together with a future vision of the ground testing of the GSC flight counters and digital associated processor.

The on-orbit performance of the Chandra X-Ray Observatory over its first four years of operation is reviewed. The Observatory is running smoothly and the scientific return continues to be superb.

The mirrors flown in the Chandra Observatory are, without doubt, some of the most exquisite optics ever flown on a space mission. Their angular resolution is matched by no other X-ray observatory, existing or planned. The promise of that performance, along with a goal of achieving 1% calibration of the optics' characteristics, led to a decision early in the construction and assembly phase of the mission to develop an accurate and detailed model of the optics and their support structure. This model has served in both engineering and scientific capacities; as a cross-check of the design and a predictor of scientific performance; as a driver of the ground calibration effort; and as a diagnostic of the as-built performance. Finally, it serves, directly and indirectly, as the primary vehicle with which Chandra observers interpret the contribution of the optics' characteristics to their data. We present the underlying concepts in the model, as well the mechanical, engineering and metrology inputs. We discuss its use during ground calibration and as a characterization of on-orbit performance. Finally, we present measures of the model's accuracy, where further improvements may be made, and its applicability to other missions.

We discuss the calibration of the wings of the Chandra point spread function. In order to achieve high resolution imaging, the X-ray mirror surfaces must be extremely smooth in order to suppress the effects of scattering from microroughness. In the Chandra program, surfaces with only 1.3-3 Å roughness were achieved over more than 90% of the mirror length. We describe the current state of the calibration of the Chandra PSF wings, incorporating the results of a deep observation of the X-ray source Her X-1. The galactic Hydrogen column density (N_H) to Her X-1 is small, reducing the amplitude of any astrophysical dust scattering halo which would contaminate the mirror scattering wings. The X-ray data clearly show the shadows of the mirror support struts, confirming that the observed halo is predominantly due to mirror scattering. The extreme brightness of the source allows the energy dependence of the PSF wings to be probed with good statistics. The deep observation (heavily piled up in the core) is combined with a zero order gratings observation (unpiled in the core) to construct an energy-dependent profile.

The Chandra X-ray Observatory point spread function (PSF) is a complex function of source position and energy. On-orbit calibration observations with sufficient S/N sample only a small fraction of the possible parameter space, and are complicated by detector systematics. Thus, the standard method of analyzing Chandra data uses the standard Chandra optics model as a reference. The optics model accurately simulates the telescope's PSF, but as it is a raytrace based technique, it can be time-consuming to run and is not always appropriate for a given analysis task. A simple parameterization of the PSF would be useful for many analysis purposes, in many cases obviating the need for users to run lengthy raytraces. We present an approach to a simple PSF parameterization of off-axis point sources, discussing its applicability to analysis of Chandra observations in light of the complicated PSF structure. We also present some results of our PSF parameterization and discuss its accuracy.

The Chandra X-Ray telescope has excellent angular resolution for on-axis sources. While the Wolter type I design optimizes on-axis performance, there is a relatively large region in which 0.5" to 1" imaging is possible. The Chandra PSF was first characterized during ground calibration and, most recently, from actual on-orbit measurements. The ground calibration provided data with the highest signal to noise but, because of gravity-induced distortions of the optics, could not completely characterize their performance. We present the results of on-orbit calibrations of the optics' performance, focusing on the near on-axis field of view. We present for the first time an analysis of the energy dependence of the on-orbit PSF.

We present a study of Chandra's optical distortions by examining the positional accuracy of observed sources on the HRC-I. We investigate the Chandra mirror and detector models' ability to reproduce the detector locations of observed sources by simulating ~160 calibration observations of AR Lac, HR 1099, and LMC X-1. To study the optical distortions of the mirrors more directly, we compare a 63 ksec observation of the Orion Nebular Cluster (ONC) with positions based on the well-determined optical astrometry of the cluster. We simulate observations of 100 reasonably bright sources from the Hillenbrand 1997 catalog of the ONC and compare the simulated positions with their observed positions. Offsets between the optical positions and the observed X-ray positions help determine a map of the optical distortions of the Chandra mirrors.

We present results from in-flight calibration of the High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray Observatory. Basic grating assembly parameters such as orientation and average grating period were measured using emission line sources. These sources were also used to determine the locations of individual CCDs within the flight detector. The line response function (LRF) was modeled in detail using an instrument simulator based on pre-flight measurements of the grating alignments and periods. These LRF predictions agree very well with in-flight observations of sources with narrow emission lines. Using bright continuum sources, we test the consistency of the detector quantum efficiencies by comparing positive orders to negative orders.

We present optical constants derived from synchrotron reflectance measurements of iridium-coated X-ray witness mirrors over 0.05-12 keV, relevant to the Chandra X-ray Observatory effective area calibration. In particular we present for the first time analysis of measurements taken at the Advanced Light Source Beamline 6.3.2 over 50-1000 eV, Chandra's lower-energy range. Refinements to the currently tabulated iridium optical constants (B. L. Henke et al., At. Data Nucl. Data Tables 54, 181-343, 1993 and on the Web at http://www-cxro.lbl.gov/optical_constants/) will become important as the low-energy calibration of Chandra's X-ray detectors and gratings are further improved, and as possible contaminants on the Chandra mirror assembly are considered in the refinement of the in-flight Ir absorption edge depths. The goal of this work has been to provide an improved tabulation of the Ir optical constants over the full range of Chandra using a self-consistent mirror model, including metallic layers, interface roughness, contaminating overlayer, and substrate. The low-energy data present us with a considerable challenge in the modeling of the overlayer composition, as the K-absorption features of C, O, and N are likely to be present in the ~10A overlayer. The haphazard contamination and chemical shifts may significantly affect optical constants attributed to this overlayer, which will distort the iridium optical constants derived. Furthermore, the witness mirror contamination may be considerably different from that deposited on the flight optics. The more complex modeling required to deal with low-energy effects must reduce to the simpler model applied at the higher energies, which has successfully derived optical constants for iridium in the higher energy range, including the iridium M-edges, already used in the Chandra calibration. We present our current results, and the state of our modeling and analysis, and our approach to a self-consistent tabulation.

Chandra X-ray Observatory (CXO) -- the third of NASA's Great Observatories -- has now been successfully operated for four years and has brought us fruitful scientific results with many exciting discoveries. The major achievement comparing to previous X-ray missions lies in the heart of the CXO -- the High Resolution Mirror Assembly. Its unprecedented spatial resolution and well calibrated performing characteristics are the keys for its success. We discuss the effective area of the CXO mirrors, based on the ground calibration measurements made at the X-Ray Calibration Facility in Marshall Space Flight Center before launch. We present the derivations of both on-axis and off-axis effective areas, which are currently used by Chandra observers.

The Advanced CCD Imaging Spectrometer (ACIS) on the Chandra X-ray Observatory is suffering a gradual loss of low energy sensitivity due to a buildup of a contaminant. High resolution spectra of bright astrophysical sources using the Chandra Low Energy Transmission Grating Spectrometer (LETGS) have been analyzed in order to determine the nature of the contaminant by measuring the absorption edges. The dominant element in the contaminant is carbon. Edges due to oxygen and fluorine are also detectable. Excluding H, we find that C, O, and F comprise >80%, 7%, and 7% of the contaminant by number, respectively. Nitrogen is less than 3% of the contaminant. We will assess various candidates for the contaminating material and investigate the growth of the layer with time. For example, the detailed structure of the C-K absorption edge provides information about the bonding structure of the compound, eliminating aromatic hydrocarbons as the contaminating material.

Accurate calibration of the Chandra Low Energy Transmission Grating (LETG) higher-order (|m|>1) diffraction efficiencies is vital for proper analysis of spectra obtained with the LETG's primary detector, the HRC-S, which lacks the energy resolution to distinguish different orders. Pre-flight ground calibration of the LETG was necessarily limited to sampling a relatively small subset of spectral orders and wavelengths, and virtually no higher-order data are available in the critical region between 6 and 10 Å. In this paper, we describe an analysis of diffraction efficiencies based on in-flight data obtained using the LETG's secondary detector, the ACIS-S. Using ACIS, the relative efficiency of each order can be studied out to |mλ| ~ 80 Å, which is nearly one-half of the LETG/HRC-S wavelength coverage. We find that the current models match our results well but can be improved, particularly for the even orders just longward of the Au-M edge at 6 Å.

The dispersion relation for the Chandra Low Energy Transmission Grating Spectrometer (LETGS) is known to better than 1 part in 1000 over the wavelength range 5-150 Å. A recent resolution of a data processing software bug that lead to a systematic error in the computation of photon wavelengths has allowed us to trace further discrepancies in the dispersion relation to the boundaries between different microchannel plate segments of the HRC-S imaging detector. However, data acquired during in-flight calibration with the HRC-S detector have always shown the presence of additional non-linear deviations in the positions of some spectral lines by as much as 0.05 Å, which is of the order of a full width half maximum (FWHM) of a line profile. These latter effects are thought to be caused by spatial non-linearities in the imaging characteristics of the HRC-S detector. Here, we present an improved dispersion relation for the LETG+HRC-S and new methods to help characterize the spatial non-linearities. We also describe an empirical approach that might be used to help improve the position determination of photon events.

The Chandra X-ray Observatory (CXO), NASA's latest "Great Observatory", was launched on July 23, 1999 and reached its final orbit on August 7, 1999. The CXO is in a highly elliptical orbit, with an apogee altitude of 120,000 km and a perigee altitude 20,000 km, and has a period of approximately 63.5 hours (≈ 2.65 days). It transits the Earth's Van Allen belts once per orbit during which no science observations can be performed due to the high radiation environment. The Chandra X-ray Observatory Center currently uses the National Space Science Data Center's "near Earth" AP-8/AE-8 radiation belt model to predict the start and end times of passage through the radiation belts. Our earlier analysis (Virani et al, 2000) demonstrated that our implementation of the AP-8/AE-8 model (a simple dipole model of the Earth's magnetic field) does not always give sufficiently accurate predictions of the start and end times of transit of the Van Allen belts. This led to a change in our operating procedure whereby we "padded" the start and end times of transit as determined by the AE-8 model by 10 ks so that ACIS, the Advanced CCD Imaging Spectrometer and the primary science instrument on-board Chandra, would not be exposed to the "fringes" of the Van Allen belts on ingress and egress for any given transit. This additional 20 ks per orbit during which Chandra is unable to perform science observations integrates to approximately 3 Ms of "lost" science time per year and therefore reduces the science observing efficiency of the Observatory. To address the need for a higher fidelity radiation model appropriate for the Chandra orbit, the Chandra Radiation Model (CRM) was developed. The CRM is an ion model for the outer magnetosphere and is based on data from the EPIC/ICS instrument on-board the Geotail satellite as well as data from the CEPPAD/IPS instrument on-board the Polar satellite. With the production and implementation of the CRM Version 2.3, we present the results of a study designed to investigate the science observing time that may be recovered by using the CRM for science mission planning purposes. In this paper, we present a scheme using the CRM such that for a modest increase in ACIS CTI, approximately 500 ks can be recovered each year for new science observations.

Determination of the photon interaction depth offers numerous advantages for an astronomical hard X-ray telescope. The interaction depth is typically derived from two signals: anode and cathode, or collecting and non-collecting electrodes. We present some preliminary results from our depth sensing detectors using only the anode pixel signals. By examining several anode pixel signals simultaneously, we find that we can estimate the interaction depth, and get sub-pixel 2-D position resolution. We discuss our findings and the requirements for future ASIC development.

Large area, high spatial resolution CdZnTe pixel detectors are being developed for hard X-ray astronomy. We have designed and fabricated custom readout chips and bump-bond these to pixelated CdZnTe crystals using indium bump bonding technology. The resulting detectors have 16 x 16 pixels with 300 micron pitch, enabling low noise operation and permitting detailed imaging. These devices are ideally suited for the focal plane of future high-resolution hard x-ray focusing telescopes now being considered, such as the HXT on Constellation-X. An initial demonstration using the sparse read-out capabilities of these detectors is presented.

The Chandra X-ray Observatory (CXO), launched in July of 1999, contains two focal-plane imaging detectors and two transmission-grating spectrometers. Maintaining an optimal performance level for the observatory is the job of the Chandra X-ray Center (CXC), located in Cambridge, MA. One very important aspect of the observatory's performance is the science observing efficiency. The single largest factor which reduces the observing efficiency of the observatory is the interruption of observations due to passage through the Earth's radiation belts approximately every 2 2/3 days. During radiation belt passages, observations are suspended on average for over 15 hours and the Advanced CCD Imaging Spectrometer (ACIS) is moved out of the focus of the telescope to minimize damage from low-energy (100-200 keV) protons. The CXC has been using the National Space Science Data Center's "near Earth" AE-8/AP-8 radiation belt model to predict the entry and exit from the radiation belts. However, it was discovered early in the mission that the AE-8/AP-8 model predictions were inadequate for science scheduling purposes and a 10ks "pad time" was introduced on ingress and egress of perigee to ensure protection from radiation damage. This pad time, totaling 20 ks per orbit, has recently been the subject of much analysis to determine if it can be reduced to maximize science observing efficiency. A recent analysis evaluating a possible correlation between the Chandra Radiation Model (CRM) and the Electron Proton Helium Instrument (EPHIN) found a greatest lower bound (GLB) in lieu of a correlation for the ingress and egress of each perigee. The GLB is a limit imposed on the CRM such that when the CRM exceeds this limit on ingress, this defines the new safing time and similarly for egress. We have shown that using this method we can regain a significant amount of lost science time at the expense of minimal radiation exposure. The GLB analysis also found that different GLB's produce varied results and hint that there could be a time dependence associated with the GLB, possibly related to the orientation of the Observatory's orbit. Utilizing CRM V2.3, we present the search for a seasonal dependence on the value of the GLB; we find a seasonal effect that appears to depend on the orientation of Chandra's orbit with respect to the Earth's magnetic field.

The high-energy response of XEUS will be of crucial importance for a number of astrophysical topics, e.g.: highly obscured AGNs, non-thermal emissions from SNRs, AGNs and clusters of galaxies, nuclear line emission from SNRs and hard X-ray emission in GRB afterglows. The XEUS telescope will achieve high-energy response (up to 90 keV) employing super mirror technology whereby the inner mirrors will be coated with graded multi layers. The detectors will be implemented as part of the Wide Field Imager which also has DEPFET and CCDs to cover the soft-X-ray survey science. Solutions for the associated focal plane Hard X-ray Imaging Camera have been investigated by the XEUS Instrument Working Group and will be discussed in the present contribution.

In this paper we present preliminary work on a spatial, arrival time and energy resolving x-ray detector for the study of magnetic reconnection in the solar corona. Our detectors are cryogenic phonon-mediated superconducting Transition-Edge Sensors (TESs). X-rays are incident on a silicon substrate; the generated phonons propagate to the opposite side of the substrate and are absorbed in the tungsten TES electron system. Through a novel spatial distribution of four TESs we aim to achieve simultaneous measurement resolutions of ~10 μm, sub μs, and ~4 eV and with count rates of ~1 kHz. This four TES system is described and preliminary data obtained with a prototype two-channel detector is presented.