Monitor of All-sky X-ray Image (MAXI) is an astrophysical payload for the Japanese Experiment Module (Kibo) on the International Space Station (ISS). MAXI is designed for monitoring all sky in the X-ray band. MAXI consists of two X-ray detector systems: the Gas Slit Camera (GSC) and the Solid-state Slit Camera (SSC). The SSC consists of two CCD cameras: each contains 16 CCD chips. The CCD chip has 1024 x 1024 pixels and covers 25mm square. The thickness of depletion layer is 70 μm. These CCD chips are cooled down below -60° using a combination of the radiator and the peltier cooler. We have developed the engineering model (EM) of the MAXI/SSC. Combining with the EM electronics, we achieved the low readout noise (~5 e- rms) and a good energy resolution (150 eV at MnKα). We report the current status of the developments of the MAXI/SSC.

The next generation of X-ray astronomy instruments will require position sensitive detectors in the form of charge coupled devices (CCDs) for X-ray spectroscopy and imaging that will have the ability to probe the X-ray universe with a greater efficiency. This will require the development of CCDs with structures that will improve on the quantum efficiency of the current state of the art over a broader spectral range in addition to reducing spectral features, which may affect spectral resolution and signal to background levels. These devices will also have to be designed to withstand the harsh radiation environments associated with orbits that extend beyond the Earth’s magnetosphere. The next generation X-ray telescopes will incorporate larger X-ray optics that will allow deeper observations of the X-ray universe and sensors will have to compensate for this by an increased readout speed. This study will aim to describe some of the results obtained from test CCD structures that may fit many of the requirements described above.

The Rossi X-ray Timing Explorer (RXTE) has demonstrated the power of observations in the time domain in the study of X-ray binaries. The dynamical variation of the X-ray emission from accreting neutron stars and stellar mass black holes is a powerful probe of their strong gravitational fields. At the same time, oscillations at the neutron star spin frequency during X-ray bursts have been used to set important constraints on the mass and radius of neutron stars. The X-ray Evolving Universe Spectroscopy mission (XEUS), the potential follow-on mission to XMM-Newton, will have a mirror aperture more than ten times larger than the effective area of the RXTE proportional counter array (RXTE/PCA). Combined with a small dedicated fast X-ray timing detector in the focal plane (XTRA: XEUS Timing for Relativistic Astrophysics), this collecting area will provide a leap in timing sensitivity of more than one order of magnitude over the RXTE/PCA for bright sources, and will open a brand new window on faint X-ray sources, owing to the negligible detector background. Furthermore, the use of advanced Silicon drift chambers will improve the energy resolution by a factor of ~ 6 over the RXTE/PCA. The spectroscopic diagnostics of the strong field region, such as the gravitational redshift and the relativistic broadening of the Iron line, will become exploitable simultaneous with the fast timing. XTRA will provide unique opportunities, enabling for example the testing of general relativity in the strong gravity field regime and investigating with unprecedented accuracy the equation of state of matter at supranuclear density. XTRA when observing bright X-ray sources will record typically several hundred thousand counts per second and careful design will be necessary to ensure that the full potential of these data can be exploited. We describe the proposed implementation of XTRA in the XEUS focal plane using Silicon drift detectors and present the current performance of these devices.

The ESA mission XMM-Newton was launched in 1999. Two of the three X-ray telescopes include reflection grating spectrometers (RGS). These spectrometers consist of a set of reflection gratings and an array of 9 back-illuminated CCDs, optimized for the soft energy response (0.35 - 2 keV). These CCDs can be passively cooled between -80 and -120°C. After a short description of the instrument we compare the performance of these CCD detectors with the pre-flight expectations and discuss the effect of some design choices on the in-flight performance. We concentrate on the effects of radiation damage due to cosmic rays and coronal mass ejections of the Sun, including flickering pixels and the effects of cooling the detector to -110°C. We also address the stability of the detector response including the assessment of possible contamination of these cooled detectors.

We make a plan of a hard X-ray polarimetry experiment with a small satellite. Bright point-like sources in 20-80keV are prime targets, for which we will not use focusing optics. Comparing various types of polarimeters, we adopt a scattering type in which anisotropy in scattering directions of photons is employed. After optimization of the design is considered with simplified models of scattering polarimeters, we propose to use segmented scatter targets made of plastic scintillators, with which scattering location is identified by detecting recoiled electrons. Simulations show that recoiled electrons are detectable when incident X-ray energies are above 40keV, for which higher polarimetry sensitivity is obtained. We confirmed the performance of such a polarimeter in experiments at a Synchrotron facility and performed a balloon flight in which a proto type unit of the polarimeter was onboard. We finally discuss feasibility of a small satellite experiment in which many of the polarimeter units will be employed. Twenty five units of the polarimeter enable us to detect hard X-ray polarization of 5-10% for a hundred mCrab sources. Improvement in the sensitivity to detect recoiled electrons will significantly improve the polarimetry sensitivity. We also consider a low energy extension of our system down to below 10keV in order to cover wide energy range.

We report on a new photon-counting detector possessing unprecedented spatial resolution, moderate spectral resolution and high background-rejection capability for 0.1 - 100 keV X-rays. It consists of an X-ray charge-coupled device (CCD) and scintillator. The scintillator is directly deposited on the back surface of the X-ray CCD. Low-energy X-rays below 10 keV can be directly detected in the CCD. The majority of hard X-rays above 10 keV pass through the CCD but can be detected in the scintillator, generating visible lights there. Since CCDs have a moderate detection efficiency for visible lights, they can again be absorbed by the CCD. We coupled the needlelike CsI(Tl) on the front surface of the back-illuminated (BI) CCD. High detection efficiency for visible lights of the BI CCD enables to collect the lights emitted from CsI(Tl) efficiently, leading to the moderate spectral resolution of 25% at 59.5 keV. We also investigated the imaging capability of our device and found it to be (10±3)μm at 17.4 keV.

DUO and ROSITA are two future X-ray astronomy missions observing in the energy band from about 0.3 keV to 10 keV. While the NASA satellite DUO will scan selected areas of the X-ray sky with high sensitivity, the German ROSITA mission shall perform an all-sky survey. Both missions apply an array of seven Wolter telescopes with separated field of views and seven dedicated PN-CCD focal plane detectors. The focal plane detectors are a further development of the flight-proven PN-CCD applied for the XMM-Newton observatory. The advanced device, called 'frame store PN-CCD', is designed and fabricated in the semiconductor laboratory of the Max-Planck-Institute for extraterrestrial physics. An introduction into the detector concept and design are presented as well as the promising results which have been achieved with the prototype devices. This includes an overview about the performance of the PN-CCD and in detail the recent measurements with the detector. An example is the low energy response of the optimized photon entrance window with integrated optical light filter. As the CAMEX analog signal processor chip is a main component of the detector module, we describe its development status. Furthermore, we report about the application of the mesh experiment to the PN-CCD which allows for a study of the electric potential characteristics in the detector bulk, in particular in the charge transfer depth. The information is of great importance for an accurate knowledge about the drift of the generated signal electrons into the potential wells of the pixels.

Using 0.25μm standard CMOS we have developed 2-D semiconductor matrix detectors with sophisticated functionality integrated inside each pixel of a hybrid sensor module. One of these sensor modules is a matrix of 256x256 square 55μm pixels intended for X-ray imaging. This device is called 'Medipix2' and features a fast amplifier and two-level discrimination for signals between 1000 and 100000 equivalent electrons, with overall signal noise ~150 e- rms. Signal polarity and comparator thresholds are programmable. A maximum count rate of nearly 1 MHz per pixel can be achieved, which corresponds to an average flux of 3x10exp10 photons per cm2. The selected signals can be accumulated in each pixel in a 13-bit register. The serial readout takes 5-10 ms. A parallel readout of ~300 μs could also be used. Housekeeping functions such as local dark current compensation, test pulse generation, silencing of noisy pixels and threshold tuning in each pixel contribute to the homogeneous response over a large sensor area. The sensor material can be adapted to the energy of the X-rays. Best results have been obtained with high-resistivity silicon detectors, but also CdTe and GaAs detectors have been used. The lowest detectable X-ray energy was about 4 keV. Background measurements have been made, as well as measurements of the uniformity of imaging by photon counting. Very low photon count rates are feasible and noise-free at room temperature. The readout matrix can be used also with visible photons if an energy or charge intensifier structure is interposed such as a gaseous amplification layer or a microchannel plate or acceleration field in vacuum.

The concept of an Active Pixel Sensor (APS) based on the integrated detector/amplifier structure DEPFET (DEpleted P-channel Field Effect Transistor) has been developed to cope with the challenging requirements of the XEUS Wide Field Imager. The DEPFET-APS combines high energy resolution, fast readout, and random accessible pixels allowing the application of flexible readout modes. First prototypes of DEPFET-based Active Pixel Sensors with a 64 x 64 pixel format and 75 μm x 75 μm pixel area have been produced at the MPI semiconductor laboratory. The APS is read out row by row, i.e. the pixel signals of one row are processed in parallel by a 64 channel CMOS amplifier/multiplexer chip of the CAMEX type. The addressing of one row of pixels for readout and reset is done by two control chips of the SWITCHER type fabricated in a high-voltage CMOS technology. The processing time for one row is of the order of a few micro-seconds. APS operation, the control and data acquisition system are described, and first experimental results are presented.

The NeXT (New X-ray Telescope) satellite to be launched around 2010, has a large effective area in the 0.1-80 keV band with the use of the multilayer super mirror. As the focal plane detector for NeXT, we have been developing the Wideband hybrid X-ray Imager (WXI) consisting of X-ray CCDs and a hard X-ray imager placed under X-ray CCDs. The X-ray CCD of WXI is required to (1) keep the high quantum efficiency up to the high energy band and (2) pass hard X-rays unabsorbed in the depletion (sensitive) layer. In order to meet these requirements, we have been developing the back supportless CCD which has the thick depletion layer, thinned Si wafer and back supportless structure. As the first step, we make the test model with thinned Si wafer in order to (1) learn the handling and thinning process and (2) confirm no change of the performance after the thinning process. The test model has the pixel number and size of 512 x 512 and 24 x 24 μm, respectively. We select the thickness of the wafer is about 200 μm considering the thinning process. We verify the depletion layer and the wafer of the test model are about 65 and 190 μm in thickness, respectively. The energy resolution is about 144 eV at 5.9 keV which is substantially comparable to the un-thinned CCD, hence we confirm our thinning process has no effect on the perfomance. In order to reduce the dead layer ompletely and increase the quantum efficiency at the high energy band, we are also developing the full depleted X-ray CCD with the high resistivity N-type Si wafer.

We have developed X-ray CCD sensors for the Astro-E2 X-ray Imaging Spectrometer. Here we describe the performance benefits obtained from two innovations implemented in the CCD detectors developed for this instrument. First, we discuss the improved radiation tolerance afforded by a novel charge-injection structure. Second, we demonstrate for the first time the potential of a previously-developed chemisorption charging backside treatment process to produce back-illuminated X-ray sensors with excellent soft X-ray spectral resolution as well as improved quantum efficiency. We describe the changes in X-ray event detection algorithms required to obtain this improved performance, and briefly compare the performance of XIS sensors to that of back-illuminated detectors currently operating on-orbit.

We are developing a superconducting transition-edge sensor (TES) microcalorimeter array for the Diffuse Intergalactic Oxygen Surveyor (DIOS) mission. DIOS is a relatively small Japanese X-ray mission which will study large-scale distribution of the warm-hot intergalactic medium (WHIM) using O_VII and O_VIII emission lines. The satellite weighs about 400 kg equipped with a four-reflection X-ray telescope (FXT) and a TES microcalorimeter array (XSA). The design goal of the observing system is an effective area larger than 100 cm² at the oxygen line energy, a field of view about 50 arcmin square, and an energy resolution about 2 eV in the energy range of 0.3-1 keV. The TES microcalorimeter array provides the large field of view and good energy resolution at the same time. We plan to install an array comprising 16 x 16 pixels with an overall size of 1 cm square, which is cooled with a cryogen-free cooler. Pixels are readout by multiplexing signals using a multi-input SQUID amplifier, with each input connected to a TES microcalorimeter which is AC biased with a different frequency. We report the design and present status of the XSA system development.

Superconducting Transition-Edge Sensors (TESs) are generating a great deal of interest in the areas of x-ray astrophysics and space science, particularly to develop them as large-array, imaging x-ray spectrometers. We are developing a novel concept that is based on position-sensitive macro-pixels placing TESs on the backside of a silicon or germanium absorber. Each x-ray absorbed will be position (X/δX and Y/δY ~ 100) and energy (E/δE ~ 1000) resolved via four distributed TES readouts. In the future, combining such macropixels with advances in multiplexing could lead to 30 by 30 arrays of close-packed macro-pixels equivalent to imaging instruments of 10 megapixels or more. We report on our progress to date and discuss its application to a plausible solar satellite mission and plans for future development.

We have investigated the thermal, electrical, and structural properties of Bi and BiCu films that are being developed as X-ray absorbers for transition-edge sensor (TES) microcalorimeter arrays for imaging X-ray spectroscopy. Bi could be an ideal material for an X-ray absorber due to its high X-ray stopping power and low specific heat capacity, but it has a low thermal conductivity, which can result in position dependence of the pulses in the absorber. In order to improve the thermal conductivity, we added Cu layers in between the Bi layers. We measured electrical and thermal conductivities of the films around 0.1 K, the operating temperature of the TES calorimeter, to examine the films and to determine the optimal thickness of the Cu layer. From the electrical conductivity measurements, we found that the Cu is more resistive on the Bi than on a Si substrate. Together with a SEM picture of the Bi surface, we concluded that the rough surface of the Bi film makes the Cu layer resistive when the Cu layer is not thick enough to fill in the roughness. From the thermal conductivity measurements, we determined the thermal diffusion constant to be 2 x 10³ μm²μs^-1 in a film that consists of 2.25 μm of Bi and 0.1 μm of Cu. We measured the position dependence in the film and found that its thermal diffusion constant is too low to get good energy resolution, because of the resistive Cu layer and/or possibly a very high heat capacity of our Bi films. We show plans to improve the thermal diffusion constant in our BiCu absorber.

We present our latest results from our development of Position-Sensitive Transition-Edge Sensors (PoSTs). Our devices work as one-dimensional imaging spectrometers. They consist of a long absorber (segmented or solid) with a transition-edge sensor (TES) on each end. When X-rays hit the absorber, the comparison of the signals sensed in the two TESs determine the position of the TES, while the addition of the signals gives the energy of the X-ray. We obtained impedance curves for three different devices and obtained reasonable fits with our theoretical PoST model.

A micro-calorimeter array with superconducting transition-edge sensors read out by a SQUID-based frequency-domain multiplexer is under development for the X-ray imaging spectrometer on board ESA’s X-ray Evolving Universe Spectroscopy (XEUS) mission. The XEUS requirements are 2 and 5 eV FWHM energy resolution for 2 and 7 keV X-rays, respectively. An array of 32 x 32 pixels with 250 micron square pixels is envisaged. SRON and MESA⁺ have developed 5 x 5 imaging micro-calorimeter prototype arrays along a bulk micromachining and a surface micromachining route. The present state of array design and development with emphasis on pixel-to-pixel performance measurements of thermal and I-V characteristics, sensor noise and energy resolution are presented. SRON and VTT are developing frequency-domain multiplexing with SQUID current amplifiers to read out the 32 x 32 array. The concept for the frequency division multiplexing read-out will be presented and its performance characteristics discussed. Recent results of sensor operation under AC-bias (500 kHz) are presented.

Soon after launch, the Advanced CCD Imaging Spectrometer (ACIS), one of the focal plane instruments on the Chandra X-ray Observatory, suffered radiation damage from exposure to soft protons during passages through the Earth's radiation belts. The primary effect of the damage was to increase the charge transfer inefficiency (CTI) of the eight front illuminated CCDs by more than two orders of magnitude. The ACIS instrument team is continuing to study the properties of the damage with an emphasis on developing techniques to mitigate CTI and spectral resolution degradation. We will discuss the characteristics of the damage, the detector and the particle background and how they conspire to degrade the instrument performance. We have developed a model for ACIS CTI which can be used to correct each event and regain some of the lost performance. The correction uses a map of the electron trap distribution, a parameterization of the energy dependent charge loss and the fraction of the lost charge re-emitted into the trailing pixel to correct the pixels in the event island. This model has been implemented in the standard Chandra data processing pipeline. Some of the correction algorithm was inspired by the earlier work on ACIS CTI correction by Townsley and collaborators. The details of the CTI model and how each parameter improves performance will be discussed, as well as the limitations and the possibilities for future improvement.

The inclusion of a charge injection structure on a charge coupled device (CCD) allows for the mitigation of charge transfer loss which can be caused by radiation induced charge trapping defects. Any traps present in the pixels of the CCD are filled by the injected charge as it is swept through the device and consequently, the charge transfer efficiency is improved in subsequently acquired images. To date, a number of different types of CCD have been manufactured featuring a variety of charge injection techniques. The e2v Technologies CCD22, used in the EPIC MOS focal plane instruments of XMM-Newton, is one such device and is the subject of this paper. A detailed understanding of charge injection operation and the use of charge injection to mitigate charge transfer losses resulting from radiation damage to CCDs will benefit a number of space projects planned for the future, including the ESA GAIA and X-ray Evolving Universe Spectrometry (XEUS) missions. The charge injection structure and mode of operation of the CCD22 are presented, followed by a detailed analysis of the uniformity and repeatability of the charge injection amplitude across the columns of the device. The effects of proton irradiation on the charge injection characteristics are also presented, in particular the effect of radiation induced bright pixels on the injected charge level.

A Semiconductor Multiple-Compton Telescope (SMCT) is expected to proceed a high-sensitivity soft gamma-ray observation in the energy range of 0.1-20 MeV. Double-sided silicon strip detector (DSSD) is one of key technologies for constructing SMCT, as well as the high-stopping semiconductor CdTe, because of its high energy resolution and high scattering efficiency. We have developed a low-noise system of DSSD and frontend LSI for SMCT, by optimizing geometrical structures of DSSD. We have thus obtained an energy resolution of 1.3 keV (FWHM) for 60 keV and 122 keV at -10°C in the multi-channel reading. Gamma-ray responses such as image flatness and charge splittings were found to be not problematic. We also demonstrated that our system achieved the good angular resolution close to the Doppler-broadening limit in the Compton imaging by two DSSDs.

We report progress in the study of thick CZT strip detectors for 3-d imaging and spectroscopy and discuss two approaches to device design. We present the spectroscopic, imaging, detection efficiency and response uniformity performance of prototype devices. Unlike double-sided strip detectors, these devices feature both row and column contacts implemented on the anode surface. This electron-only approach circumvents problems associated with poor hole transport in CZT that normally limit the thickness and energy range of double-sided strip detectors. These devices can achieve similar performance to pixel detectors. The work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma radiation measurements. The low channel count strip detector approach can significantly reduce the complexity and power requirements of the readout electronics. This is particularly important in space-based coded aperture or Compton telescope instruments requiring large area, large volume detector arrays. Such arrays will be required for NASA's Black Hole Finder Probe (BHFP) and Advanced Compton Telescope (ACT).

We have developed a large CdTe pixel detector with dimensions of 23.7 x 13.0 mm² and a pixel size of 448 x 448 μm². The detector is based on recent technologies of an uniform CdTe single crystal, a two-dimensional ASIC, and stud bump-bonding to connect pixel electrodes on the CdTe surface to the ASIC. Good spectra are obtained from 1051 pixels out of total 1056 pixels. When we operate the detector at -50°C, the energy resolution is 0.67 keV and 0.99 keV at 14 keV and 60 keV, respectively. Week-long stability of the detector is confirmed at operating temperatures of both -50°C and -20°C. The detector also shows high uniformity: the peak positions for all pixels agree to within 0.82%, and the average of the energy resolution is 1.04 keV at a temperature of -50°C. When we normalized the peak area by the total counts detected by each pixel, a variation of 2.1% is obtained.

We are developing a Compton telescope based on high resolution Si and CdTe imaging devices in order to obtain a high sensitivity astrophysical observation in sub-MeV gamma-ray region. In this paper, recent results from the prototype Si/CdTe semiconductor Compton telescope are reported. The Compton telescope consists of a double-sided Si strip detector (DSSD) and CdTe pixel detectors, combined with low noise analog LSI, VA32TA. With this detector, we obtained Compton reconstructed images and spectra from line gamma-rays ranging from 81 keV up to 356 keV. The energy resolution is 3.8 keV and 7.9 keV at 122 keV and 356 keV, respectively, and the angular resolution is 9.9° and 5.7° at 122 keV and 356 keV, respectively.

We present results from our compound semiconductor laboratory program and describe the development of a large area GaAs imaging array for planetary remote sensing applications. The device is fabricated from ~150 micron thick epitaxial material, patterned into a 64 x 64 pixel array, back-thinned and contacted. It will be flip-chip bump bonded onto a custom designed, fully spectroscopic, low noise (< 20 e- rms) active pixel sensor ASIC. At present, the ASIC is still under development and so in order to validate and qualify the various technological steps, we have produced a GaAs imager based on the MEDIPIX-1 format using a MEDIPIX-1 readout chip. In X-ray tests, the device was found to work well with a bump yield of 99.9%. After flat field corrections, the spatial uniformity of the array was commensurate with Poisson noise.

We report on the performance of the most recent avalanche photodiodes produced by Hamamatsu Photonics, as low-energy X-rays and γ-rays detectors. APDs share good features of both photo diodes and PMTs, as they are very compact, produce an internal gain of 10-100, and have a high quantum efficiency close to 100% in the visible right. Until very recently, however, APDs were limited to very small surfaces, and were mainly used as a digital device for light communication. We have developed large area (up to 10x10 mm²) APDs which can be used in the physics experiments. The best energy resolution of 6.4% (FWHM) was obtained in direct detection of 5.9 keV X-rays. The FWHM results of 9.4% and 4.9% were obtained for 59.5 keV and 662 keV γ-rays respectively, as measured with the CsI(Tl) crystal. The minimum detectable energy for the scintillation light was as low as 1 keV at lightly cooled environment (-20°C). Note that our results are the best records ever achieved with APDs. Various applications of APDs are presented for future space research and nuclear medicine. In particular 2-dimensional APD arrays will be a promising device for a wide-band X-ray and γ-ray imaging detector.

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 appealing astrophysical applications is their use as focal plane detectors for multilayer hard X-ray telescopes operating in the (10 - 80) keV energy band. This paper reports experimental results obtained from two 16x16 pixellated CZT detectors (10x10x1 mm³ and 10x10x2 mm³ single crystals) with 450x450 μm² pixel operated at room temperature using standard commercial read-out electronics. We have investigated about energy resolution and material properties of both detectors. Both arrays gave similar results showing an energy resolution less then 5%@59.5 keV and a good material uniformity. The good energy resolution of both detectors demonstrates as the pixellated anode structure reduces (small pixel effect) the incomplete charge collection due to severe hole trapping typically presents in CZT crystals. A calibration curve, obtained using three different energies, shows a linear response of the detectors.

A new concept of photon counting camera for fast and low-light-level imaging applications is introduced. The possible spectrum covered by this camera ranges from visible light to gamma rays, depending on the device used to transform an incoming photon into a burst of visible photons (photo-event spot) localized in an (x,y) image plane. It is actually an evolution of the existing "PAPA" (Precision Analog Photon Address) Camera that was designed for visible photons. This improvement comes from a simplified optics. The new camera transforms, by diffraction, each photo-event spot from an image intensifier or a scintillator into a cross-shaped pattern, which is projected onto a specific Gray code mask. The photo-event position is then extracted from the signal given by an array of avalanche photodiodes (or photomultiplier tubes, alternatively) downstream of the mask. After a detailed explanation of this camera concept that we have called "DIAMICON" (DIffraction Addressed Mask ICONographer), we briefly discuss about technical solutions to build such a camera.

Many experiments in X-ray astronomy require absolutely calibrated detectors. Calibrations can be performed in the Radiometry Laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the electron storage ring BESSY II in Berlin. This synchrotron radiation source can be operated as primary source standard, providing a calculable spectral photon flux for the calibration of energy-dispersive detectors like Si(Li), HPGe or cryogenic STJ detectors. All detectors including non energy-dispersive devices like semiconductor photodiodes can be calibrated with monochromatized synchrotron radiation of high spectral purity against a primary detector standard, mainly a cryogenic electrical substitution radiometer, in the photon energy range from the UV up to about 60 keV with relative uncertainties of 1% or less. By using pencil beams, the homogeneity of the detector responsivity and the response function can be investigated, also for pixel detectors.

The Hard X-ray Detector (HXD-II), one of instruments onboard the Astro-E2 satellite to be launched in February 2005, is in the final stage of its development. The HXD-II probes the universe in the energy range of 10-600 keV with a sensitivity by an order of magnitude better than those of previous missions. The assembly of the HXD-II completed in January 2004, followed by a series of pre-launch qualification tests. As a result, the design goals of the HXD-II have been met. These include; a background level of 5 x 10^-6 counts/s/keV/cm² at 200 keV for GSO and 1 x 10^-5 counts/s/keV/cm² at 30 keV for PIN; energy resolutions of 2.9 keV (PIN diode, at 59.5 keV) and 10% (GSO scintillator, at 662 keV); and low energy thresholds of 10 keV for PIN diodes and 30 keV for GSO scintillators. The measured background predicts a continuum sensitivity of a few x 10^-6 photons/s/keV/cm². Anti-Counter units surrounding the HXD-II provide 50 keV-5 MeV information on gamma-ray bursts and bright X-ray transients.

NeXT is the X-ray satellite proposed for the next Japanese space science mission. While the satellite total mass and the launching vehicle are similar to the prior satellite Astro-E2, the sensitivity is much improved; it requires all the components to be lighter and faster than previous architecture. This paper shows the data processing architecture of the X-ray CCD camera system SXI (Soft X-ray Imager), which is the top half of the WXI (Wide-band X-ray Imager) of the sensitivity in 0.2-80keV. The system is basically a variation of Astro-E2 XIS, but event extraction speed is much faster than it to fulfill the requirements coming from the large effective area and fast exposure period. At the same time, data transfer lines between components are redesigned in order to reduce the number and mass of the wire harnesses that limit the flexibility of the component distribution.

An active anticoincidence detector system for background reduction cannot be integrated in CCD detectors for X-ray astronomy. The background rate within an integration-readout interval would result in an unacceptable dead time of about 50% or more. Events of minimum ionizing particles can be discriminated in CCD detectors due to their high energy deposit and their image pattern. Events of X-rays or charged particles within the accepted energy band originating from cosmic ray interaction with the material surrounding the CCD cannot be distinguished from valid cosmic X-ray events and therefore contribute to the background noise. Graded-Z shielding is an efficient method to shift the energy of the locally produced X-rays to low energies. At low energies low-Z shielding material can be used, which rather produces Auger electrons than fluorescent X-rays. Low energy electrons can be stopped in the passivation layer of the CCD. Due to the low operating temperature of the CCD (~170 K) the shielding material has to have a similar thermal expansion coefficient as silicon. With regard to future X-ray missions the properties of several shielding materials like aluminium oxide, aluminium nitride, silicon nitride and boron carbide were investigated in more detail. The results are presented.

We present the Event Pre Processor (EPP) for the Cadmium-Zinc-Telluride-strip detector of the Hard X-ray Imager (HXI) onboard of the MIRAX satellite. The purpose of the EPP is to provide an onboard data reduction and event filtering by applying a non linear energy gain correction for each detector strip. This data reduction is necessary because of the limited telemetry capacity of the MIRAX satellite. We decided to use hardwired data processing electronics based on a Field Programmable Gate Array (FPGA) chip designed in VHDL. This solution allows us to combine high computation power with low power consumption. We discuss the functionality and status of the EPP design developed in T&diaeru;bingen.

Over the last year a GEANT model of the Astro-E2 XRS instrument (including the surrounding structure of the telescope) has been developed in order to determine the rate and energy spectrum of background events due to cosmic ray protons. Background events, in the x-ray signal energy band, can be caused by the primary protons themselves, secondaries which are created in the material surrounding the XRS, or by decays of nearby activated materials. This paper will present the details of the GEANT model and will discuss the effectiveness of the telescope structure in shielding the XRS instrument and efficiency of the anti-coincidence detector at further reducing the background rate. We will also present an investigation of the rate and spectrum of cosmic ray particles passing through the Si frame, which acts as a mechanical support and thermal sink to the x-ray pixels, in order to determine whether sufficient heating will occur in the Si frame to affect the response of the x-ray pixels.

The low-energy sensitivity of the Advanced CCD Imaging Spectrometer (ACIS) instrument on board the Chandra X-ray Observatory (CXO) has been continuously degrading since launch due to the accumulation of a layer of contamination on the ACIS optical blocking filter (OBF). This contamination layer, the result of out-gassing and off-gassing within the observatory, introduces a new, energy dependent absorption into the ACIS response. The thickness of this layer has been increasing with time and its spatial distribution across the OBF has been continually changing with time. We utilize multiple observations of the SMC Supernova Remnant 1E0102.2-7219 to verify the models for the spectral, temporal, and spatial dependence of the contamination layer. We also use this source to investigate cross-calibration between the front illuminated (FI) and back illuminated (BI) CCDs. 1E0102.2-7219 has a soft, line-dominated spectrum which is very sensitive to the additional absorption of the contamination layer. The extensive calibration observations of 1E0102.2-7219 over the course of the mission at several different locations on the ACIS Imaging (I) and Spectroscopy (S) arrays allows for a verification of the temporal and spatial dependence of the contamination model.

A focal plane array of high-pressure gas scintillation proportional counters (GSPC) for a High Energy X-Ray Observatory (HERO) has been developed at the Marshall Space Flight Center. The array consists of eight GSPCs and is a part of balloon-born payload scheduled to fly in May 2004. These detectors have an active area of ~ 20 cm² each, 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 ~ 0.5 mm. The detector’s energy resolution, 5.0% FWHM at 60 keV, is adequate for resolving the broad spectral lines of astrophysical importance and for accurate continuum measurements. Results of the ground detector array testing are presented.

X-ray microcalorimeters using metallic magnetic sensors show great promise for use in astronomical x-ray spectroscopy. In the last year, magnetic microcalorimeters demonstrated their potential in high resolution spectroscopy when an energy resolution of 3.4 eV (FWHM) was achieved for 6 keV X-rays in single pixels with a 5 micron thick, 160 micron square gold absorber attached to a magnetic sensor. We have recently formed a collaboration to develop arrays of magnetic microcalorimeters suitable for future X-ray astronomy missions. This collaboration includes scientists from the University of Heidelberg, Brown University, NIST, SAO, PTB-Berlin, IPHT Jena and GSFC. We are developing array construction techniques for building arrays of magnetic calorimeters with mushroom absorbers. We are studying different alternatives for the circuit that couples the signal from the detector to the SQUID amplifier. We are developing magnetic calorimeter multiplexing capabilities using time division multiplexing similar to that used for transition edge sensors. On behalf of the collaboration, in this paper I will review the measured performance of magnetic microcalorimeters achieved so far and then focus on the present status of our array technology development.

A frame transfer CCD intended for X-ray detection on-board ASTRO-E2 spacecraft was modified to include an input serial register and a charge injection structure which allows a very uniform injection of charge into the imaging section of the device. A variation of the fill-and-spill method was implemented to inject charge into the CCD. The operation of the structure is described, and results of the measurements are presented. Very small charge packets (a few tens of electrons) can be reproducibly injected with noise as low as 5 electrons rms. The amount of injected charge can be controlled by the external voltage with very high accuracy. We have applied this technique to study various characteristics of the proton irradiated CCD, such as the column-to-column nonuniformity of charge losses and the amplitude dependence of the charge loss. The latter is related to the charge-volume relation in the charge storage site and for the first time we accurately measure this relationship at very low signal levels.

A single stage Adiabatic Demagnetization Refrigerator (ADR), has been set-up at the X-ray Astronomy Calibration and Testing (XACT) facility of INAF - Osservatorio Astronomico di Palermo G.S. Vaiana, for the development and testing of cryogenic X-ray detectors for laboratory and astrophysical applications. The ADR allows to cool detectors at temperatures below 40 mK and to maintain them at constant operating temperature for many hours. We describe the design and construction of the ADR and present test results and performances.

The X-ray Imaging Spectrometer (XIS) on the Astro-E2 mission contains X-ray CCDs fabricated at MIT Lincoln Laboratory. We present results from CCD subassembly calibration of these detectors. Absolute detection efficiency and spectral resolution in the 0.3-10 keV band are presented for four front-illuminated and two back-illuminated flight candidate devices. In addition, we characterize the charge injection capabilities of these devices. The quantum efficiency measurements have been used to model the various dead layers in the gate structure and to constrain the depletion depth of the detectors. Noise levels of 2 electrons, RMS, and spectral resolution better than 50 eV (FWHM) at 525 eV have been achieved. The small but measurable charge transfer inefficiency (less than 1e-5 per transfer at 5.9 keV) of these devices has been characterized as a function of X-ray energy.

The Extreme Universe Space Observatory (EUSO) on the International Space Station (ISS) will detect the Ultra High Energy Cosmic Rays (UHECRs with E > 4 x 10¹⁹ eV) and the high energy cosmic neutrino flux looking at the streak of fluorescence light produced when the particles interact with the Earth’s atmosphere. The photo-detector of EUSO experiment will consist of several Multi-Anode PhotoMultipliers (MAPMTs) arranged on the aspheric focal surface. Accurate pre-flight ground calibration and in-flight calibration are essential topics of the EUSO experiment to detect reliably the fluorescence light. In particular, the main target of calibration is to achieve spectroradiometric measurements of the telescope performance and of the absolute response of the detectors. This report will describe a first approach to, and some possible solutions for, the calibration system of the EUSO telescope and focal plane. This proposal will address the requirements to design the EUSO calibration system and the crucial items for further analyses and discussions.

We report the results of a series of experiments designed to assess the relative radiation hardness of a range of compound semiconductor X-ray detectors. The specific compounds tested were GaAs, InP, CdZnTe, HgI₂ and TlBr, along with an elemental Si device. To allow meaningful comparisons, all devices were of a similar size and, with the exception of the InP detector, had sub-keV energy resolution at 5.9 keV. The irradiations were carried out using the University of Helsinki’s Cyclone 10/5 10 MeV proton cyclotron. Each detector was given six consecutive exposures - the integral fluences being; 2.66 x 10⁹ p cm^-2, 7.98 x 10⁹ p cm^-2, 2.65 x 10¹⁰ p cm^-2, 7.97 x 10¹⁰ p cm^-2, 1.59 x 10¹¹ p cm^-2, and 2.65 x 10¹¹ p cm^-2, respectively. In Si, these correspond to absorbed radiation doses of 2, 6, 20, 60, 120 and 200 krads. During the exposures, the detectors were kept unbiased and at room temperature. After each irradiation, the effects of the exposure were assessed, both at room temperature and at a reduced temperature using ⁵⁵Fe, ¹⁰⁹Cd and ²⁴¹Am radioactive sources. It was found that with the exception of the HgI₂ and TlBr detectors all materials showed varying degrees of damage effects.

Operating in the 0.5-70 keV energy range, Simbol-X is a next generation hard X-ray space mission proposed by a collaboration of European laboratories for high energy astrophysics. Simbol-X will consist of two satellites flying in formation. In the first satellite, an X-ray mirror, having a focal length of 30 m, will focus the X-rays on the second satellite containing a silicon low energy detector on top of a Cd(Zn)Te (CZT) high energy detector. The latter consists of a mosaic of ~1 cm² elementary arrays with 256 pixels (0.5x0.5 mm²). As a first step in the development, a prototype CZT detector of 10x10x2 mm³, having one side covered with 0.9x0.9 mm² pixels, is used. A 3-D modeling is performed of the latter. The photon interaction inside the detector is simulated. The spatial distribution of the energy deposition and the amount of charge sharing of the pixels are obtained. The results serve as input parameters for the development and choice of the detector final geometry and electronics.