During the three years long assessment phase of the LOFT mission, candidate to the M3 launch opportunity of the ESA Cosmic Vision programme, we estimated and measured the radiation damage of the silicon drift detectors (SDDs) of the satellite instrumentation. In particular, we irradiated the detectors with protons (of 0.8 and 11 MeV energy) to study the increment of leakage current and the variation of the charge collection efficiency produced by the displacement damage, and we “bombarded” the detectors with hypervelocity dust grains to measure the effect of the debris impacts. In this paper we describe the measurements and discuss the results in the context of the LOFT mission.
Protons with energies between tens of keV and some MeV can degrade the performance of X-ray detectors and contribute to the instrument background. In-orbit measurements showed that the flux of soft protons funneled through Wolter-type mirrors is considerably larger than expected from simulations. Up to now, just very few results from laboratory experiments have been reported and the data is not sufficient to pinpoint the best analytical description of the physical process or to validate simulation codes. In order to improve this situation, a small angle scattering experiment to measure the proton reflection properties of X-ray mirrors has been set up at the accelerator facility of the University of Tübingen. The experimental setup and initial preliminary results obtained with samples of eROSITA mirror shells are presented.
Future space-based X-ray observatories will not only have increased sensitivity and energy resolution but will
provide astronomers with high time resolution in the order of microseconds. The detection of millions of single
photons per second with their precise energy and their time of arrival will produce unprecedented data rates that
cannot be downlinked to Earth in their full extend due to telemetry limitations. We present the study of a very
fast, lossless, on-board data compression implemented in an FPGA-based LEON3 microprocessor. We conclude
with performance estimates done with a prototype board developed for the High Time Resolution Spectrometer
(HTRS) on board the International X-ray Observatory (IXO). We also discuss a possible application of the Data
Processing Unit (DPU) for the future X-ray mission Large Observatory for X-ray Timing (LOFT).
We have assembled a stacked setup consisting of a soft and hard X-ray detector with cooling capability and
control-, readout-, and data processing electronics at the Institut für Astronomie und Astrophysik Tübingen
(IAAT). The detector system is a 64 ×64 DePFET-Matrix in front of a CdTe-Caliste module. The detectors were
developed at the Max-Planck Institute Semiconductor Laboratory (HLL) in Neuperlach and the Commissariat
a l'Energie Atomique (CEA) in Saclay, respectively. In this combined structure the DePFET detector works as
Low Energy Detector (LED) while the Caliste module (HED) only detects the high energy photons that have
passed through the LED. In this work we present the current status of the setup. Furthermore, an intended
application of the detector system as a polarimeter is described.
We report on our activities, currently in progress, aimed at performing accelerator experiments with soft protons and
hyper-velocity dust particles. They include tests of different types of X-ray detectors and related components (such as
filters) and measurements of scattering of soft protons and hyper-velocity dust particles off X-ray mirror shells. These
activities have been identified as a goal in the context of a number of ongoing space projects in order to assess the risk
posed by environmental radiation and dust and qualify the adopted instrumentation with respect to possible damage or
performance degradation. In this paper we focus on tests for the Silicon Drift Detectors (SDDs) used aboard the LOFT
space mission. We use the Van de Graaff accelerators at the University of Tübingen and at the Max Planck Institute for
Nuclear Physics (MPIK) in Heidelberg, for soft proton and hyper-velocity dust tests respectively. We present the
experimental set-up adopted to perform the tests, status of the activities and some very preliminary results achieved at
present time.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian
Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in 2013. eROSITA will perform an all-sky
survey lasting four years, followed by a phase of three years for pointed observations. eROSITA consists of seven
identical Mirror Modules, each equipped with 54 Wolter-I shells with an outer diameter of 360 mm. This would provide
an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular
resolution of 28 arcsec averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD
provides a field of view of 1°in diameter. In this paper we report on the instrument development and its status only.
KEYWORDS: Sensors, X-rays, Analog electronics, Electronics, Monte Carlo methods, Aluminum, Silicon, Staring arrays, Field programmable gate arrays, Quantum efficiency
The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments of the International
X-ray Observatory (IXO). The HTRS is the only instrument matching the top level mission requirement of
handling a one Crab X-ray source with an efficiency greater than 10%. It will provide IXO with the capability
of observing the brightest X-ray sources of the sky, with sub-millisecond time resolution, low deadtime, low
pile-up (less than 2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6 keV). The HTRS
is a non-imaging instrument, based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a
circular envelope and a X-ray sensitive volume of 4.5 cm2 x 450 μm. As part of the assessment study carried
out by ESA on IXO, the HTRS is currently undergoing a phase A study, led by CNES and CESR. In this
paper, we present the current mechanical, thermal and electrical design of the HTRS, and describe the expected
performance assessed through Monte Carlo simulations.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The instrument development is in phase C/D since fall 2009. The design driving science is the detection 100.000 Clusters of Galaxies up to redshift z ~1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular resolution of 28 - 30 arcsec, averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD provides a field of view of 1° in diameter.
The Wide Field Imager (WFI) of the International X-ray Observatory (IXO) is an X-ray imaging spectrometer based on a
large monolithic DePFET (Depleted P-channel Field Effect Transistor) Active Pixel Sensor. Filling an area of
10 x 10 cm2 with a format of 1024 x 1024 pixels it will cover a field of view of 18 arcmin. The pixel size of
100 x 100 μm2 corresponds to a fivefold oversampling of the telescope's expected 5 arcsec point spread function. The
WFI's basic DePFET structure combines the functionalities of sensor and integrated amplifier with nearly Fano-limited
energy resolution and high efficiency from 100 eV to 15 keV. The development of dedicated control and amplifier
ASICs allows for high frame rates up to 1 kHz and flexible readout modes. Results obtained with representative
prototypes with a format of 256 x 256 pixels are presented.
We report on simulation results for the eROSITA instrument background obtained with Monte-Carlo simulations
using the Geant4 toolkit. Besides a brief introduction to the simulation environment created at our institute,
the input particle spectrum and flux as well as the post-simulation event treatment and analysis are explained.
Latest results for the background level and spectral shape induced by interactions of cosmic-ray protons with
the camera housing are given. In addition, we show results from different studies concerning variation of the
background level as a function of the CCD thickness and the composition of the graded shield.
The High Time Resolution Spectrometer (HTRS) is one of six scientific payload instruments of the International X-ray
Observatory (IXO). HTRS is dedicated to the physics of matter at extreme density and gravity and will observe the
X-rays generated in the inner accretion flows around the most compact massive objects, i.e. black holes and neutron
stars. The study of their timing signature and in addition the simultaneous spectroscopy of the gravitationally shifted and
broadened iron line allows for probing general relativity in the strong field regime and understanding the inner structure
of neutron stars. As the sources to be observed by HTRS are the brightest in the X-ray sky and the studies require good
photon statistics the instrument design is driven by the capability to operate at extremely high count rates.
The HTRS instrument is based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a circular
envelope and a sensitive volume of 4.5 cm2 × 450 μm. The SDD principle uses fast signal charge collection on an
integrated amplifier by a focusing internal electrical field. It combines a large sensitive area and a small capacitance, thus
facilitating good energy resolution and high count rate capability. The HTRS is specified to provide energy spectra with
a resolution of 150 eV (FWHM at 6 keV) at high time resolution of 10 μsec and with high count rate capability up to a
goal of 2·106 counts per second, corresponding to a 12 Crab equivalent source. As the HTRS is a non-imaging instrument
and will target only point sources it is placed on axis but out of focus so that the spot is spread over the array of 31 SDD
cells. The SDD array is logically organized in four independent 'quadrants', a dedicated 8-channel quadrant readout chip
is in development.
Like the International X-ray Observatory (IXO) mission, the Simbol-X mission is a projected X-ray space telescope
with spectral and imaging capabilities covering the energy range from 500 eV up to 80 keV. To detect photons
within this wide range of energies, a silicon based "Depleted P-channel Field Effect Transistor" (DePFET)-
matrix is used as the Low Energy Detector (LED) on top of an array of CdTe-Caliste modules, which act as the
High Energy Detector (HED).
A Science Verification Model (SVM) consisting of one LED quadrant in front of one Caliste module will be set
up at our institute (IAAT) and operated under laboratory conditions that approximate the expected environment
in space. As a first step we use the SVM to test and optimize the performance of the LED operation and data
acquisition chain, consisting of an ADC, an event-preprocessor, a sequencer, and an interface controller. All
these components have been developed at our institute with the objective to handle the high readout rate of
approximately 8000 frames per second. The second step is to study the behaviour and the interactions of LED
and HED operating as a combined detector system.
We report on the development status of the SVM and its associated electronics and present first results of
the currently achieved spectral performance.
Simbol-X is a French-Italian-German hard energy X-ray mission with a projected launch in 2014. Being sensitive in the
energy range from 500 eV to 80 keV it will cover the sensitivity gap beyond the energy interval of today's telescopes
XMM-Newton and Chandra. Simbol-X will use an imaging telescope of nested Wolter-I mirrors. To provide a focal
length of 20 m it will be the first mission of two independent mirror and detector spacecrafts in autonomous formation
flight.
The detector spacecraft's payload is composed of an imaging silicon low energy detector in front of a pixelated
cadmium-telluride hard energy detector. Both have a sensitive area of 8 × 8 cm2 to cover a 12 arcmin field of view and a pixel size of 625 × 625 μm2 adapted to the telescope's resolution of 20 arcsec. The additional LED specifications are:
high energy resolution, high quantum efficiency, fast readout and optional window mode, monolithic device with 100 %
fill factor and suspension mounting, and operation at warm temperature.
To match these requirements the low energy detector is composed of 'active macro pixels', combining the large, scalable
area of a Silicon Drift Detector and the low-noise, on-demand readout of an integrated DEPFET amplifier. Flight
representative prototypes have been processed at the MPI semiconductor laboratory, and the prototype's measured
performance demonstrates the technology readiness.
Reaching a low-level and well understood internal instrumental background is crucial for the scientific performance
of an X-ray detector and, therefore, a main objective of the instrument designers. Monte-Carlo simulations
of the physics processes and interactions taking place in a space-based X-ray detector as a result of its orbital
environment can be applied to explain the measured background of existing missions. They are thus an excellent
tool to predict and optimize the background of future observatories. Weak points of a design and the main sources
of the background can be identified and methods to reduce them can be implemented and studied within the
simulations. Using the Geant4 Monte-Carlo toolkit, we have created a simulation environment for space-based
detectors and we present results of such background simulations for XMM-Newton's EPIC pn-CCD camera. The
environment is also currently used to estimate and optimize the background of the future instruments Simbol-X
and eRosita.
The Simbol-X1 Low Energy Detector (LED), a 128 × 128 pixel DEPFET array, will be read out very fast (8000
frames/second). This requires a very fast onboard data preprocessing of the raw data. We present an FPGA
based Event Preprocessor (EPP) which can fulfill this requirements. The design is developed in the hardware
description language VHDL and can be later ported on an ASIC technology. The EPP performs a pixel related
offset correction and can apply different energy thresholds to each pixel of the frame. It also provides a line
related common-mode correction to reduce noise that is unavoidably caused by the analog readout chip of the
DEPFET. An integrated pattern detector can block all invalid pixel patterns. The EPP has an internal pipeline
structure and can perform all operation in realtime (< 2 μs per line of 64 pixel) with a base clock frequency of
100 MHz. It is utilizing a fast median-value detection algorithm for common-mode correction and a new pattern
scanning algorithm to select only valid events. Both new algorithms were developed during the last year at our
institute.
P. Predehl, R. Andritschke, W. Bornemann, H. Bräuninger, U. Briel, H. Brunner, W. Burkert, K. Dennerl, J. Eder, M. Freyberg, P. Friedrich, M. Fürmetz, R. Hartmann, G. Hartner, G. Hasinger, S. Herrmann, P. Holl, H. Huber, E. Kendziorra, W. Kink, N. Meidinger, S. Müller, M. Pavlinsky, E. Pfeffermann, C. Rohé, A. Santangelo, J. Schmitt, A. Schwope, M. Steinmetz, L. Strüder, R. Sunyaev, L. Tiedemann, M. Vongehr, J. Wilms, M. Erhard, S. Gutruf, D. Jugler, D. Kampf, R. Graue, O. Citterio, G. Valsecci, D. Vernani, M. Zimmerman
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) will be one of three main instruments on the
Russian new Spectrum-RG mission which is planned to be launched in 2011. The other two instruments are the wide
field X-ray monitor Lobster (Leicester University, UK) and ART-XC (IKI, Russia), an X-ray telescope working at
higher energies up to 30 keV. A fourth instrument, a micro-calorimeter built by a Dutch-Japanese-US collaboration is
also in discussion. eROSITA is aiming primarily for the detection of 50-100 thousands Clusters of Galaxies up to
redshifts z > 1 in order to study the large scale structure in the Universe and to test cosmological models including the
Dark Energy. For the detection of clusters, a large effective area is needed at low energies (< 2 keV). Therefore,
eROSITA consists of seven Wolter-I telescope modules. Each mirror module contains 54 Wolter-I shells with an outer
diameter of 360 mm. In the focus of each mirror module, a framestore pn-CCD with a size of 3cm × 3cm provides a field
of view of 1° in diameter. The mission scenario comprises a wide survey of the complete extragalactic area and a deep
survey in the neighborhood of the galactic poles. Both are accomplished by an all-sky survey with an appropriate
orientation of the rotation axis of the satellite in order to achieve the deepest exposures in the neighborhood of the
galactic poles. A critical issue is the cooling of the cameras which need a working temperature of -80°C. This will be
achieved passively by a system of two radiators connected to the cameras by variable conductance heat pipes.
KEYWORDS: Space operations, Sensors, Mirrors, Spatial resolution, Physics, Space telescopes, Telescopes, Collimators, Particles, High energy astrophysics
Simbol-X is a hard X-ray mission, operating in the ~ 0.5-80 keV range, proposed as a collaboration between the French
and Italian space agencies with participation of German laboratories for a launch in 2013. Relying on two spacecraft in a
formation flying configuration, Simbol-X uses for the first time a 20-30 m focal length X-ray mirror to focus X-rays
with energy above 10 keV, resulting in over two orders of magnitude improvement in angular resolution and sensitivity
in the hard X-ray range with respect to non-focusing techniques. The Simbol-X revolutionary instrumental capabilities
will allow us to elucidate outstanding questions in high energy astrophysics such as those related to black-holes accretion
physics and census, and to particle acceleration mechanisms, which are the prime science objectives of the mission.
After having undergone a thorough assessment study performed by CNES in the context of a selection of a formation
flight scientific mission, Simbol-X has been selected for a phase A study to be jointly conducted by CNES and ASI. The
mission science objectives, the current status of the instrumentation and mission design are presented in this paper.
The DEPMOSFET (Depleted p-channel MOSFET) is an Active Pixel Sensor (APS) for the XEUS Wide Field
Imager (WFI), which is developed and produced by the MPI semiconductor laboratory in Munich (HLL). The
current prototype detector consists of a hybrid where a 64 x 64 pixel matrix with 75 μm x 75 μm pixel size each
is mounted together with CMOS SWITCHER II ICs for row-selection and a CAMEX 64 ASIC for readout.
First measurements for this device have shown the high energy resolution and quantum efficiency as well as the
potential for fast readout. For fast timing studies on XEUS an instrument is needed which is able to deal with
count rates up to 106 photons s-1 with 10 μs time resolution. At the Institut fuer Astronomie und Astrophysik,
we have built a setup to investigate the timing performance of the current prototype detector and to study
the capability of the DEPMOSFET detector to handle high count rates. In this paper we present the Data
Acquisition System and the future plans for this setup.
The Simbol-X mission, currently undergoing a joint CNES-ASI phase A, is essentially a classical X-ray telescope having an exceptional large focal length obtained by formation flying technics. One satellite houses the Wolter I optics to focus, for the first time in space, X-rays above ~10 keV, onto the focal plane in the second satellite. This leads to improved angular resolution and sensitivity which are two orders of magnitude better than those obtained so far with non-focusing techniques. Tailored to the 12 arcmin field of view and ~15 arcsec angular resolution of the optics, the ~8x8 cm2 detection area of the spectro-imager has ~ 500x500 μm2 pixels, and covers the full energy range of Simbol-X, from ~0.5 to ~80 keV, with a good energy resolution at both low and high energy. Its design leads to a very low residual background in order to reach the required sensitivity. The focal plane ensemble is made of two superposed spectro-imaging detectors: a DEPFET-SDD active pixel sensor on top of an array of pixelated Cd(Zn)Te crystals, surrounded by an appropriate combination of active and passive shielding. Besides the overall concept and structure of the focal plane including the anti-coincidence and shielding, this paper also emphasizes the promising results obtained with the active pixel sensors and the Cd(Zn)Te crystals combined with their custom IDeF-X ASICs.
Simbol-X is a next generation X-ray telescope with spectro-imaging capabilities over the 0.5 to 80 keV energy
range. The combination of a formation flying mirror and detector spacecraft allows to extend the focal length
to 20 m, resulting in a so far unrivaled angular resolution and sensitivity in the hard X-ray range. The focal
plane detector system for Simbol-X is planned to consist of an array of so-called Macro Pixel Detectors (MPD)
on top of a 2 mm thick CdZnTe pixellated detector array. Photons of energy less than about 17 keV will be
primarily absorbed in the MPDs, whereas higher energy photons will be detected in the CdZnTe array below. A
computer model of such stacked detectors and its interaction with the radiation environment encountered by the
spacecraft in orbit is currently being developed by our group using the Monte Carlo toolkit GEANT4. We present
results of the simulation and an outlook for possible optimizations of future detector geometry and shielding.
KEYWORDS: Sensors, Field effect transistors, Mirrors, Monte Carlo methods, Photons, Point spread functions, Spectroscopy, Imaging systems, Detector arrays, Imaging spectroscopy
With its large collecting area XEUS will be ideally suited to probe strong gravity fields around collapsed objects and to constrain the equation of state of dense matter in neutron stars. For these studies, detectors are needed which can measure 106 events/sec with high time resolution (10 μsec) and good energy resolution (ΔE = 200 - 300 eV FWHM) combined with an energy and flux independent dead time. The current baseline for a dedicated fast timing detector on XEUS is an array of 19 silicon drift detectors (SDD) operated as single photon detectors. Optionally we have studied an array of 40 x 20 SDD/DEPFET macro pixel detectors read out at a constant frame rate of 105/sec. Alternatively to these two dedicated detectors, a high time resolution mode of the Wide Field Imager (1024 x 1024 DEPFET array with 78μm x 78μm pixels) is considered here. We have simulated the expected timing performance of these detector options based on results from laboratory measurements. We have performed Monte Carlo simulations using the latest available XEUS mirror response files for Crab like sources and intensities ranging from 102 up to 4x106 events/sec. Our results are discussed in the light of the scientific requirements for fast timing as expressed in the ESA Cosmic Vision 2015-2025 plan.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) will be one out of three main instruments on
the Russian new Spectrum-RG mission which will be launched in the timeframe 2010-2011 into an equatorial Low Earth
Orbit. The other two instruments are the wide field X-ray monitor Lobster (Leicester University, UK) and ART (IKI,
Russia), an X-ray concentrator based on a Kumakhov optics. eROSITA consists of seven Wolter-I telescope modules
similar to the German mission ABRIXAS which failed in 1999 and ROSITA, a telescope which was planned to be
installed on the International Space Station ISS. Unlike these, the eROSITA telescope modules will be extended by
adding another 27 mirror shells to the already existing ABRIXAS design. This will increase the effective area by a factor
of ~5 at low energies. The additional shells do not contribute to the area at higher energies ( > 5 keV) due to the relative
large grazing angles. Here we stay with the old ABRIXAS/ROSITA effective area. However, the primary scientific goal
has changed since ABRIXAS: we are now aiming primarily for the detection of 50-100 thousands Clusters of Galaxies
up to redshifts z > 1 in order to study the large scale structure in the Universe and test cosmological models including the
Dark Energy, which was not yet known at ABRIXAS times. For the detection of clusters, a large effective area is needed
at low (< 2 kev) energies. The mission scenario comprises a wide survey of the complete extragalactic area and a deep
survey in the neighborhood of the Galactic Poles. Both are accomplished by an all-sky survey with a tilt of the rotation
axis in order to shift the deepest exposures away from the ecliptic poles towards the galactic poles.
X-ray timing with musec time resolution can be used to probe strong
gravity fields around collapsed objects and to constrain the equation
of state of dense matter in neutron stars. With its large collecting
area, XEUS will be ideally suited for very high signal to noise
studies of such objects. An instrument dedicated to X-ray timing of
bright Galactic sources has thus been foreseen as part of the XEUS
instrumentation. In this contribution we present numerical simulations
for silicon based detectors (silicon drift detectors and pixel based
sensors) for a variety of astrophysical sources such as neutron star
power spectra (including kHz quasi-periodic oscillations) and black
hole lightcurves to illustrate the expected scientific capabilities of
the fast timing mode instrument.
Monitor e Imageador de RAios-X (MIRAX) is a Brazilian high energy astronomy mission dedicated to monitoring the central 1000 sq. deg. of the Galactic plane to observe unpredictable transient phenomena from compact objects in the 2-200 keV range through nearly continuous imaging with good spatial/temporal/energy resolution. The strength of MIRAX lies in the departure of its observing strategy from traditional pointed programs and scanning monitors. MIRAX will achieve two major advantages over previous and existing missions. First, it will detect, localize, and study transient phenomena, which last on all timescales from milliseconds to years, and are very likely to be missed by traditional observing strategies. Second, MIRAX will study longer lived phenomena in exquisite detail. The mission elements and science will be presented.
KEYWORDS: Cameras, Mirrors, Charge-coupled devices, Telescopes, X-rays, Sensors, CCD cameras, Galaxy groups and clusters, Electronics, Digital signal processing
What is the nature of the Dark Energy that is driving the universe apart? Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales which is dominated by the Dark Energy. DUO will measure 10.000 clusters of galaxies, the power spectrum of density fluctuations of clusters and their number density as a function of cosmic time. Although designed long before the existence of Dark Energy was claimed, the ABRIXAS type X-ray telescope turns out to be ideally suited for this task: DUO is, in essence, a re-flight of the ABRIXAS X-ray telescope which some modifications of the focal plane instrumentation. First of all, we will use new CCDs which are improved versions of the pn-CCDs successfully flown on XMM-Newton. A modular concept having seven individual cameras in the foci of the seven mirror systems allows us to design the orientation of the seven telescopes with respect to each other matching the scientific needs of the DUO mission. Details of the concept including mechanical, electrical and thermal aspects are given.
High quantum efficiency over a broad spectral range is one of the main properties of the EPIC pn camera on-board XMM-Newton. The quantum efficiency rises from ~75% at 0.2 keV to ~100% at 1 keV, stays close to 100% until 8 keV, and is still ~90% at 10 keV. The EPIC pn camera is attached to an X-ray telescope which has the highest collecting area currently available, in particular at low energies (more than 1400 cm2 between 0.1 and 2.0 keV). Thus, this instrument is very sensitive to the low-energy X-ray emission. However, X-ray data at energies below ~0.2 keV are considerably affected by detector effects, which become more and more important towards the lowest transmitted energies. In addition to that, pixels which have received incorrect offsets during the calculation of the offset map at the beginning of each observation, show up as bright patches in low-energy images. Here we describe a method which is not only capable of suppressing the contaminations found at low energies, but which also improves the data quality throughout the whole EPIC pn spectral range. This method is then applied to data from the Vela supernova remnant.
Dark Energy dominates the mass-energy content of the universe (about 73%) but we do not understand it. Most of the remainder of the Universe consists of Dark Matter (23%), made of an unknown particle. The problem of the origin of Dark Energy has become the biggest problem in astrophysics and one of the biggest problems in all of science. The major extant X-ray observatories, the Chandra X-ray Observatory and XMM-Newton, do not have the ability to perform large-area surveys of the sky. But Dark Energy is smoothly distributed throughout the universe and the whole universe is needed to study it. There are two basic methods to explore the properties of Dark Energy, viz. geometrical tests (supernovae) and studies of the way in which Dark Energy has influenced the large scale structure of the universe and its evolution. DUO will use the latter method, employing the copious X-ray emission from clusters of galaxies. Clusters of galaxies offer an ideal probe of cosmology because they are the best tracers of Dark Matter and their distribution on very large scales is dominated by the Dark Energy. In order to take the next step in understanding Dark Energy, viz. the measurement of the 'equation of state' parameter 'w', an X-ray telescope following the design of ABRIXAS will be accommodated into a Small Explorer mission in lowearth orbit. The telescope will perform a scan of 6,000 sq. degs. in the area of sky covered by the Sloan Digital Sky Survey (North), together with a deeper, smaller survey in the Southern hemisphere. DUO will detect 10.000 clusters of galaxies, measure the number density of clusters as a function of cosmic time, and the power spectrum of density fluctuations out to a redshift exceeding one. When combined with the spectrum of density fluctuations in the Cosmic Microwave Background from a redshift of 1100, this will provide a powerful lever arm for the crucial measurement of cosmological parameters.
The large collecting area of XMM-Newton combined with the good energy resolution of the EPIC-pn CCDs allows the study, with unprecedented detail, of accretion processes onto neutron stars and black holes. The EPIC-pn CCD camera in Timing mode, in which data are read out continuously, is among the fastest X-ray CCD camera available; however, telemetry constraints do not allow full use of these capabilities for many sources because currently randomly distributed data gaps are introduced by the on-board data handling electronics. As an alternative, we have proposed to implement a modification of the Timing mode in which data from soft X-ray events are not transmitted to Earth. Here we discuss the properties of this modified Timing mode, which will first be used in simultaneous XMM-Newton, RXTE, and INTEGRAL observations of the Galactic black hole binary Cygnus X-1 in autumn 2004. We discuss the predicted performance of this new mode based upon laboratory measurements, Monte Carlo simulations, and data from existing Timing mode observations.
KEYWORDS: Sensors, Field programmable gate arrays, Data communications, Data processing, Data conversion, Electrodes, Image processing, Satellites, Control systems, Imaging systems
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.
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.
Marcus Kirsch, Werner Becker, Sara Benlloch-Garcia, Fred Jansen, Eckhard Kendziorra, Markus Kuster, Uwe Lammers, Andy Pollock, Francesco Possanzini, Edmund Serpell, Antonio Talavera
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.
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.
KEYWORDS: Sensors, Mirrors, Field effect transistors, Spatial resolution, Electrons, Space telescopes, Space operations, Telescopes, Hard x-rays, X-ray telescopes
SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is proposed by a consortium of European laboratories for a launch around 2010. Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a 30 m focal length X-ray mirror to achieve an unprecedented angular resolution (30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV) in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions in high energy astrophysics, such as the physics of accretion onto Black Holes, of acceleration in quasar jets and in supernovae remnants, or the nature of the hard X-ray diffuse emission. The scientific objectives and the baseline concepts of the mission and hardware design are presented.
We describe a proposal for an added capability of fast timing to the European x-ray astronomy mission XEUS. The scientific value of fast timing observations for the investigation of compact objects is recognized and has been demonstrated through observations by the Rossi x-ray Timing Explorer. We propose to make use of the huge collecting area of XEUS for timing studies with unparalleled photon statistics and time resolution. We describe the sceintifc motivation, e.g. to probe strong gravity fields around collapsed objects and to constrain the equation of state of dense matter in neutron stars. We discuss options for the implementation of detectors which coudl be small silicon drift detectors out of focus.
We describe the hard x-ray mission MIRAX - jointly proposed by teams from Brazil, the USA, Germany and the Netherlands. The scientific objective is to provide continuous 2-200 keV imaging of the central 1000 square degrees of our Galaxy for 9 months per year over up to 5 years. Durign times when the sun crosses the Galactic Center other areas like the Cygnus-, Vela- and the Magellanic Cloud-regions can be observed. MIRAX will detect, localize, identify and study sources of medium to hard x-ray emission, with special emphasis on short-lived, rare and unpredictable events, including weak x-ray transients and fast x-ray movae. MIRAX will reach in a one day observation a sensitivity of 1mCrab in 2-10 keV and 2.5mCrab in 10-100keV. MIRAX will provide a unique capability to study compact galactic objects - notably accreting neutron stars and black holes. It will:- Probe neutron star and x-ray burst theory wiht 20,000 type I x-ray bursts and 50 'superbursts' - Measure spin frequencies of neutron stars from 10-100 burst oscillations - Observe explosive flares and x-ray light curves during ejections in superluminal jets - Study soft gamma-ray repeaters, fast x-ray novae and new types of phenomena yet to be discovered. We describe the science and the instrumentation.
The main scientific objective of the ROSITA mission is to extend the X-ray all-sky survey of ROSAT to higher energies to gain an unbiased sample of all types of celestial X-ray sources in the medium energy band. During this mission the whole sky will be scanned by seven imaging X-ray telescopes. The telescopes have different viewing directions with an offset angle between 4 and 6 deg. The focal plane instrumentation of the telescopes is based on a novel type of pn-CCD with a frame store, an advanced version of the pn-CC operating quite successfully on XMM-Newton. The pixel size is adapted to the
mirror resolution and the fast readout time guaranties the required angular accuracy despite the scan motion. The X-ray camera carries seven separate CCDs arranged on a circle in the foci of the Wolter type I mirror systems of the seven telescopes. The CCDs are mounted on ceramic frames, which carry dedicated front-end electronics for each CCD. The CCDs are operated at a temperature of-80 deg C. Except for the entrance window, the CCDs are covered by graded shielding for suppression of fluorescent X-ray background, generated by cosmic rays in the surrounding materials. Filters in front of the the CCDs, inhibit optical and UV photons. For in-orbit calibration a radioactive
source producing fluorescent X-rays in the desired energy band is provided. We will give an overview of the mechanical, thermal and electrical concept of the camera system.
The pn-CCD camera on board of XMM-Newton as well as the Wide Field Imager (WFI) currently being designed for the XEUS mission can be read out in special fast timing modes, providing spectroscopy at very high time resolution. The two fast modes, Timing and Burst mode, of the pn-CCD camera on board XMM-Newton provide a time resolution of 30 μs, respectively. However, this fast timing is only possible at the expense of spatial resolution in readout direction. In contrast, the current baseline design of the WFI for XEUS will provide 25 μs timing at full spatial resolution. We describe the basic principles of the fast readout schemes of the pn-CCD and the SFI, discuss the potential of XEUS for high time resolution spectroscopy and present first results of pulse phase resolved spectroscopy of the Crab pulsar with the pn-CCD in Timing mode.
After the launch of Chandra, it was realized that low energy protons (below approximately 300 keV) are funnelled by grazing incident mirrors onto the focal plane detectors. Front illuminated CCD detectors are very sensitive to soft protons causing radiation damage in their electrode structures and transfer channels. The back-illuminated 280 micrometer thick fully depleted pn-CCD of the European Photon Imaging Camera (EPIC) on board the X-ray Multi Mirror mission (XMM) is by far less sensitive to low energy proton radiation. Commanding the camera in a special low gain mode, even allows to directly measure proton spectra and event patterns up to 300 keV per pixel. At the 3 MV Van-de-Graaff accelerator of the Institute for Physics in Tubingen we have irradiated and tested a 3 cm2 flight-like pn-CCD with protons from 1 to 300 keV up to a fluence of 1.4 (DOT) 109 protons/cm2. This is about a factor of 1000 above the expected solar proton fluence for a 10 year XMM-Newton mission under nominal operational conditions. In this paper we given an overview of the proton irradiation experiment, discuss the performance of the detector after proton irradiation and finally present proton spectra directly measured with the pn-CCD on board XMM-Newton during solar flares. In addition, we briefly describe the precautionary measures taken to minimize the proton radiation dose of the EPIC CCD detectors in orbit.
The combined effective area of the three EPIC cameras of the XMM-Newton Observatory, offers the greatest collecting power ever deployed in an X-ray imaging system. The resulting potential for high sensitivity, broad-band spectroscopic investigations demands an accurate calibration. This work summarizes the initial in-orbit calibration activities that address these requirements. We highlight the first steps towards effective area determination, which includes the maintenance of gain CTI calibration to allow accurate energy determination. We discuss observations concerning the timing and count-rate capabilities of the detectors. Finally we note some performance implications of the optical blocking filters.
On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we started the Calibration and Performance Verification Phase, which will last until the end of May 2000. In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit performance of the camera. We also show some of the early results with the pn-camera, the first light image of a region in the Large Magellanic Cloud, and an observation of the Crab Nebular.
XMM-Newton, the most powerful X-ray telescope ever built was launched from the european space port Kourou on december 10 last year. Three large X-ray Wolter type mirror systems are focusing the incoming X-rays from 100 eV up to 15,000 eV onto the focal instruments: fully depleted backside illuminated pn-CCDs and frontside illuminated MOS-CCDs. The concept of the pn-CCD camera will be briefly described and its performance on ground and in orbit will be shown. Special emphasis will be given to the radiation hardening of the devices, to the instrument background and to the experience of charged particle background in space. A comparison of the performance on ground and after 5 months in space will be shown.
A 6 cm X 6 cm large monolithic charge coupled device has been developed and fabricated as focal plane x-ray detector for the European XMM satellite mission and the German ABRIXAS mission. This spectroscopic silicon detector is denominated pn-CCD because of its use of reverse biased pn- junctions as charge transfer registers, as ultra-thin homogeneous photon entrance window and for the on-chip electronics. Due tot he pn-CCD concept, the whole wafer thickness of 300 micrometers is sensitive to ionizing radiation. The read-out is performed in parallel and needs only 73 ms for the 36 cm2 large detector area. A uniform low noise performance is realized by on-chip integrated JFET electronics. The two best pn-CCDs have been integrated in the flight cameras for XMM and abrixas and extensively tested for the long term operation in space. The presentation comprises the basic concept of the detector, a short description of the flight device and its fabrication, test and operating as well as the key performance parameters. The concluding outlook describes methods of further development of the pn-CCD.
The XMM, the second corner stone mission of the European Space Agency's Horizon 2000, will be launched in December 1999. One of the instruments on board of XMM will be the EPIC pn-CCD. The detector consists of four independent quadrants integrated monolithically on a single silicon wafer. Each quadrant is divided into 3 CCDs with 200 X 64 pixels and 280 micrometers depletion depth. The pn-CCD will be able to perform high resolution timing analysis as well as high throughput imaging and spectroscopy in six different readout modes. In the standard imagin mode the CCDs are read out sequentially every 73.3 ms. In addition, different readout modes allow high resolution timing analysis by reducing the integration time down to 7 microsecond(s) and reading out only one CCD. In this paper we show results of the calibration of the flight spare unit of the EPIC pn camera with respect to time resolution of all observation modes. In the first part we explain the detailed timing of each mode and show how one can calculate the best possible arrival time for photons in each observation mode. In the second part of the paper, we analyzed the influence of the readout noise on the time resolution of the pn-CCD camera, by combining dead time functions with simulated light curves.
The quantum efficiency of the pn-CCD detector on the XMM satellite mission was determined in the spectral range between 150 eV and 15 keV. The unstructured entrance window of the device, which is formed by an ultrathin reverse biased pn-junction, results in an excellent spatial homogeneity with a good spectroscopic performance and high detection efficiency for low energy photons. The large sensitive thickness of the detector guarantees a high quantum efficiency for photons up to 10 keV. We give a review of the calibration techniques applied for quantum efficiency measurements at the Synchrotron Radiation Facility at the Institut d'Astrophysique Spatial in Orsay and the radiometry laboratory of the Physikalisch-Technische Bundesandstalt at the electron storage ring BESSY in Berlin. We summarize the applied data correction such as charge transfer loss and split event recognition and describe the data analysis to conclude in an absolute quantum efficiency of the pn-CCD.
The pn-Charge Coupled Device (pn-CCD) camera was developed as one of the focal plane instruments for the European Photon Imaging Camera on board the x-ray multi mirror mission. An identical camera was foreseen on board ABRIXAS, a German x-ray satellite. The pn-CCD camera is an imaging x- ray detector for single photon counting, operating at a temperature below -80 degrees C. Due to a 0.3 mm depletion depth of the CCDs, the detector has a high quantum efficiency up to 15 keV. The effective area of the instrument is 6 cm X 6 cm with 12 CCDs monolithically integrated on a single silicon wafer. The camera includes a filter wheel with different filters for suppression of optical and UV light. A radioactive source provides an in- orbit calibration. In this paper we give an overview of the mechanical, thermal and electrical design of the instrument and a description of different readout and test modes. More detailed information about the performance and calibration of the instrument can be found in companion papers.
The European X-ray satellite XMM will be launched in December 1999. One of the focal plane instruments of the European Photon Imaging Camera (EPIC) on board XMM is equipped with a monolithic pn-CCD consisting of 12 individual CCDs with 200 X 64 pixels each. In order to exploit the god intrinsic energy resolution of the pn-CCD, the charge transfer efficiency (CTE) must be well known. Impurities in the wafer material act as traps for electrons, thus removing a fraction of the signal charge at each transfer step towards the readout anode. Electronics generated by optical light from the observed source or other optical sources may well saturate those traps, which results in a different CTE for x-ray generated charge packets. Using single CCDs of flight type, we have analyzed in our test facility at the Institut fuer Astronomie und Astrophysik der Universitaet Tuebingen, the influence of optical light on the CTE of the pn-CCD. In this paper we describe the result of our investigation of the CTE at different x-ray energies and varying optical light intensities.
In the near future the European x-ray satellite XMM will be launched into orbit. The satellite is equipped with a PN-CCD camera with a sensitive area of 60 mm X 60 mm, integrated on a single silicon wafer. The same camera is on board of the German x-ray satellite ABRIXAS. The main feature of this camera type is the very good quantum efficiency of more than 90 percent in the energy range from 0.3 to 10 keV and the high time resolution, selectable between 7 microsecond(s) ec and 280 msec. All flight cameras are extensively calibrated, utilizing the long beam test facility Panter in Muenchen, the Synchrotron Radiation Facility beam lines at the Institut d'Astrophysique Spatiale in Orsay, and the PTB beam line at the Bessy Synchrotron in Berlin. We will give an overview of all the calibrations and calibration methods as well as some global results.
The pn-CCD camera is developed as one of the focal plane instrument for the European Photon Imaging Camera (EPIC) on board the x-ray multi mirror mission (XMM) to be launched in December 1999. On 28 April 1999 an almost identical camera was launched on the German x-ray satellite ABRIXAS. The detector consists of four quadrants of three pn-CCDs each, which are integrated on a single silicon wafer. Each CCD has 200 X 64 pixels with 280 micrometers depletion depth, resulting in good quantum efficiency up to 15 keV. To minimize photon pile-up and/or image smearing by out-of-time events, six standard readout modes with integration times ranging from 7 microsecond(s) ec up to 280 msec can be selected by the observer. Background and noise reduction is achieved by means of on board generated offset maps and hard wired common mode filtering. Tracks of minimum ionizing particles are identified and suppressed by the experiment software on board. In this paper we give an overview of the on board event processing and describe important operation aspects of the pn-CCD camera.
The x-ray multi mirror (XMM) mission, the second cornerstone of the European Space Agency's Horizon 2000 program, will be launched in August 1999 and will perform high throughput imaging and spectroscopy in the energy range form 0.1 to 15 keV. One of the focal plane instruments is the EPIC pn CCD camera with a sensitive area of 60 mm by 60 mm, integrated on a single silicon wafer. The camera is divided into 4 redundant quadrants of three 10 mm by 30 mm CCDs with 64 by 200 pixels each. The thin entrance window in combination with a depletion depth out modes give the flexibility to observe targets of different source strength up to several Grab with some reduction in spectral and spatial performance. We will report on the calibration of the flight unit of the EPIC pm camera, performed at the long beam test facility Panter in Muenchen and at the Synchrotron Radiation Facility beam lines at the Istitute d'Astrophysique Spatiale in Orsay. In this paper we describe the preliminary results of the calibration of the imaging modes.
The pm-CCD camera is one of the three focal plane instruments of the European Photon Imaging Camera (EPIC) on board the x-ray multi mirror (XMM) mission scheduled for launch in August 1999. The detector consists of four quadrants of three pn-CCDs each, which are integrate don one 4 inch silicon wafer. Each CCD has 200 by 64 pixels with 280 micrometers depletion depth. One CCD of a quadrant is readout at a time, while the four quadrants can be processed independently of each other. Observations of point sources brighter than 11 mCrab in imaging mode will be effected by photon pile-up. However, special operating modes can be used to observe bright sources up to 150 mCrab in Timing Mode with 30 microsecond(s) time resolution and very bright sources up to several Crab in Burst Mode with 7 microsecond(s) time resolution. We have tested and calibrate the flight model FM of the EPIC pn-CCD camera at the long beam test facility Panter near Munich and at the synchrotron monochromators of the Institut d'Astrophysique Spatiale in Orsay, France. In this paper describe the calibration of the pn-CCD detector in high time resolution/bright source operating modes and present preliminary results on the performance in these modes.
The concept and performance of the fully depleted pn- junction CCD system, developed for the European XMM- and the German ABRIXAS-satellite missions for soft x-ray imaging and spectroscopy in the 0.1 keV to 15 keV photon range, is presented. The 58 mm X 60 mm large pn-CCD array uses pn- junctions for registers and for the backside instead of MOS registers. This concept naturally allows to fully deplete the detector volume to make it an efficient detector to photons with energies up to 15 keV. For high detection efficiency in the soft x-ray region down to 100 eV, an ultrathin pn-CCD backside deadlayer has been realized. Each pn-CCD-channel is equipped with an on-chip JFET amplifier which, in combination with the CAMEX-amplifier and multiplexing chip, facilitates parallel readout with a pixel read rate of 3 MHz and an electronic noise floor of ENC < e-. With the complete parallel readout, very fast pn-CCD readout modi can be implemented in the system which allow for high resolution photon spectroscopy of even the brightest x-ray sources in the sky.
The pn-charge coupled device (pn-CCD) camera was developed as one of the focal plane instruments for the European photon imaging camera (EPIC) on board the x-ray multi mirror (XMM) mission. The homogeneously sensitive detector consists of four quadrants of three pn-CCDs each, which are integrated on a single silicon wafer. Each CCD has an area of 10 mm by 30 mm divided into 64 by 200 pixels with a depletion depth of 280 micrometers. Altogether the sensitive area is 60 mm by 60 mm. In the standard imaging mode (full frame mode) the CCDs are read out sequentially every 70 ms. In addition, different window modes allow imaging of brighter sources by restricting the detector area and reducing the integration time down to 6 ms. We have tested one quadrant of the EPIC pn-CCD camera at line energies from 0.52 keV to 17.4 keV at the long beam test facility PANTER in focus of the qualification mirror module for XMM as well as in a homogeneous x-ray beam. In this paper we describe the tests in the different imaging modes and report on the performance.
The pn-CCD camera is developed as one of the focal plane instruments for the European photon imaging camera (EPIC) on board the x-ray multi mirror (XMM) mission to be launched in 1999. The detector consists of four quadrants of three pn-CCDs each, which are integrated on one silicon wafer. Each CCD has 200 by 64 pixels (150 micrometer by 150 micrometers) with 280 micrometers depletion depth. One CCD of a quadrant is read out at a time, while the four quadrants can be processed independently of each other. In standard imaging mode the CCDs are read out sequentially every 70 ms. Observations of point sources brighter than 1 mCrab will be effected by photon pile- up. However, special operating modes can be used to observe bright sources up to 150 mCrab in timing mode with 30 microseconds time resolution and very bright sources up to several crab in burst mode with 7 microseconds time resolution. We have tested one quadrant of the EPIC pn-CCD camera at line energies from 0.52 keV to 17.4 keV at the long beam test facility Panter in the focus of the qualification mirror module for XMM. In order to test the time resolution of the system, a mechanical chopper was used to periodically modulate the beam intensity. Pulse periods down to 0.7 ms were generated. This paper describes the performance of the pn-CCD detector in timing and burst readout modes with special emphasis on energy and time resolution.
Monolithic arrays of 12 CCDs, 3 by 1 cm2 each, have been developed and produced for the focal plane instrumentation of the European photon imaging camera (EPIC) on XMM and the German ABRIXAS x-ray satellite mission. The design parameters have been optimized to match the properties of the x-ray imaging optics as well as the x-ray intensity, energy bandwidth and characteristic time constants of the objects to observe. The pixel size is 150 by 150 micrometer2; readout is performed in parallel; low noise, spectroscopic performance is realized by on-chip integrated JFET electronics; highohmic, ultrapure bulk material allows full depletion and enhances the efficiency for higher energy x-ray detection. The fabrication process, the layout topology and the operating conditions guarantee for a ten year operation in space without performance degradation.
The European photon imaging camera (EPIC) is one of the two main instruments onboard the ESA X-Ray Cornerstone Mission XMM. It is devoted to performing imaging and spectroscopy of the x-ray sky in the domain 0.1 10 keV with a peak sensitivity in 105 seconds of 2 multiplied by 10-15 erg/cm-2. The x-ray instrumentation is complemented by a radiation monitor which will measure the particle background. The spectral resolution is approximately 140 eV at 6.4 keV and 60 eV at 1 keV. The instrumentation consists of three separate focal plane cameras at the focus of the three XMM telescopes, containing CCDs passively cooled to typically minus 100 degrees via radiators pointing toward the anti-Sun direction. The two cameras with the field of view partially occulted by the RGS grating boxes will have MOS technology CCDs while the third camera, with full field of view, will be based on p-n technology. The CCDs in the focal plane of the cameras will cover the entire 30 foot by 30 foot field of view of the telescope while the pixel size (40 by 40 (mu) for the MOS camera and 150 multiplied by 150 (mu) for the p-n) will be adequate to sample the approximately 20' PSF of the mirrors. In order to cope with a wide range of sky background and source luminosity in the visible/UV band, a filter wheel with six positions has been implemented in each camera. The six positions correspond to: open position, closed position, one thin filter (1600 angstrom of plastic support and 400 angstrom of Al), one medium filter (1600 angstrom of plastic support and 800 angstrom of Al) and one thick filter (approximately 3000 angstrom of plastic support, approximately 1000 angstrom of Al and 300 Angstrom of Sn). The final position will be a redundant filter of type still to be decided. A set of radioactive sources in each camera will allow the calibration of the CCDs in any of the operating modes and with any filter wheel position. Vacuum doors and valves operated will allow the operation of other camera heads on the ground, in a vacuum chamber and/or in a controlled atmosphere, and will protect the CCDs from contamination until the spacecraft is safely in orbit. The MOS camera will have 7 CCDs, each of 600 by 600 pixels arranged in a hexagonal pattern with one central and six peripheral. The p-n camera head will have 12 CCDs, each with 200 multiplied by 64 pixels, in a rectangular arrangement, 4 quadrants of 3 CCDs each. The radiation monitor is based on two separate detectors to monitor the low (electrons greater than 30 keV) and the high (electrons greater than 200 keV and protons greater than 10 MeV) energy particles impinging on the telescope along its orbit.
The pn-charge coupled device (pn-CCD) detector system was developed as the focal plane instrument of an x-ray telescope for the European photon imaging camera (EPIC) on the x-ray multi mirror (XMM) mission. The second cornerstone mission of the European Space Agency's Horizon 2000 plan performs high throughput imaging and spectroscopy of the x- ray sky in the domain of 0.1 keV - 15 keV. The pn-charge coupled device will also be used for a German x-ray astronomy satellite mission, called ABRIXAS (a broad-band imaging x-ray all-sky survey). While XMM will perform pointed observations. ABRIXAS will carry out an all sky survey with imaging telescopes. Both projects are planned to be launched in 1999. The homogeneous coherent sensitive area of the detector consists of a 6 cm by 6 cm large array of 12 pn-CCDs which are monolithically integrated on a single silicon wafer together with the first stage of amplification. The pn-CCD detector has been optimized for high-resolution x-ray spectroscopy and its performance is close to the theoretical limits given by the Fano noise. High quantum efficiency essential for the investigation of faint objects is accomplished over the whole energy range by a thin photon entrance window and a full sensitive detector thickness. A fast readout achieves excellent time resolution for the observation of pulsed x-ray sources and avoids pile- up for bright objects. The relevant performance parameters reflecting the state of the detector development are presented. The radiation hardness of the pn-CCD was verified for the ten year satellite mission. No significant increases in the thermally generated current, charge transfer losses and transfer noise occurred in the temperature range planned for detector operation. A correction of the signal charge losses, which occur already before irradiation in all types of charge coupled devices during the charge transfer to the anodes, is necessary to achieve the highest energy resolution of the detector. Methods to reduce the signal charge losses which were successfully tested, are described.
PN-CCDs are being developed as focal plane detectors for ESA's X-ray Multi-Mirror satellite mission (XMM), to be launched at the end of this century. As a part of the European Photon Imaging Camera (EPIC) the pn-CCDs will convert the incoming X-ray radiation with high quantum efficiency, low readout noise, excellent background rejection, timing in the microsec regime, radiation tolerance up to several hundreds of krads and a position resolution tailored according to the angular resolution of the telescope. The goal of our laboratorial efforts for this mission is to fabricate a monolithic pn-CCD of an active area of 6 x 6 sq cm having 768 on-chip JFET amplifiers located at the end of each CCD line. It is the aim of this contribution to report on the ongoing work of the pn-CCD system. This article focuses on the position resolution capabilities of fully depleted pn-CCDs, some recent results in the noise analysis and preliminary results on 10 MeV proton damage.
The capabilities of the European Photon Imaging Camera (EPIC), the main instrument of ESA's 'Cornerstone' mission in X-ray astronomy with multiple mirrors (XMM), are discussed. The CCD characteristics, spatial resolution, energy bandpass and faint source sensitivity, spectral resolution and sensitivity, and timing capability are addressed, and the scientific rationale of the EPIC is summarized. The EPIC instrument system concept is briefly described.
Recent results on the on-chip electronics, transfer properties, and radiation entrance window of pn-CCDs are presented. With recently fabricated devices, an improved charge transfer efficiency per pixel of 0.9995 and an energy resolution of the CCD output stage of 5 e(-) rms have been measured. This performance is achieved without a degradation of other characteristics of the devices, such as an X-ray efficiency of 90 percent at 10 keV, more than a factor of 1000 better time resolution in the full frame mode in comparison with all other CCD concepts, and a one-dimensional spatial resolution of 24 microsec in the timing mode. The use of pn-junctions instead of MOS structures makes the devices intrinsically radiation resistant.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.