In anticipation of the European Space Agency (ESA) X-ray Evolving Universe Spectroscopy (XEUS) mission, designed
as a follow-on to the ESA X-ray Multi Mirror (XMM-Newton) mission, the instrument background for the XMM-Newton
mission, the Japanese Space Agency Suzaku mission and the NASA Swift mission has been studied. The
instrument background has been modelled using the Geant4 toolkit to establish the constituent components for the
differing orbits and detector designs across the energy range from 1 keV to 12 keV. The results, consistent with the
spectra obtained in-orbit, are then discussed. With knowledge of the dominant components of the instrument
background, methods targeted at reduction in future missions are considered, with experimental results designed to
determine their effects.
Future generations of X-ray astronomy instruments will require position sensitive detectors in the form of charge-coupled devices (CCDs) for X-ray spectroscopy and imaging with the ability to probe the X-ray universe with greater efficiency. This will require the development of CCDs with structures that will improve their quantum efficiency over the current state of the art. The quantum efficiency improvements would have to span a broad energy range (0.2 keV to >15 keV). These devices will also have to be designed to withstand the harsh radiation environments associated with orbits that extend beyond the Earth's magnetosphere. This study outlines the most recent work carried out at the University of Leicester focused on improving the quantum efficiency of an X-ray sensitive CCD through direct manipulation of the device depletion region. It is also shown that increased spectral resolution is achieved using this method due to a decrease in the number of multi-pixel events. A Monte Carlo and analytical models of the CCD have been developed and used to determine the depletion depths achieved through variation of the device substrate voltage, Vss. The models are also used to investigate multi-pixel event distributions and quantum efficiency as a function of depletion depth.
The European Space Agency (ESA) X-ray Evolving Universe Spectroscopy (XEUS) mission is designed as a follow-on
to the ESA X-ray Multi Mirror (XMM-Newton) mission and may contain charge-coupled device (CCD) based
instrumentation. Low instrument background is essential for the mission to maximise sensitivity. Results from
XMM-Newton and the Japanese Space Agency Suzaku mission show that both the detector design and the orbit
(LEO vs. HEO) have major impacts on the instrument background. This gives implications for the optimal instrument
configuration for XEUS and other future missions. Here we use a Monte Carlo simulation technique, utilising the Geant4
toolkit, to model the instrument background for CCDs in-orbit. The model will be initially verified by simulating the
background from the XMM-Newton and Suzaku missions and comparing this to real data obtained
in-orbit. The simulated data will then be analysed to gain a better understanding of the cause of the background.
Suggestions for minimizing the instrument background in future missions based on the results found here are included.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory and is being proposed in response to the
Cosmic Vision 2015-2025 long term plan for ESA's Science Programme. A new mission configuration was developed
in the last year, accommodating the boundary conditions of a European-led mission with a formation-flying mirror and
detector spacecraft in L2 with a focal length of 35m and an effective area of >5 m<sup>2</sup> at 1 keV. Here the new capabilities
are compared with the key scientific questions presented to the Cosmic Vision exercise: the evolution of large scale
structure and nucleosynthesis, the co-evolution of supermassive black holes and their host galaxies, and the study of
matter under extreme conditions.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory and is being proposed in response to the Cosmic Vision 2015-2025 long term plan for ESA's Science Programme. Novel light-weight optics with an effective area of 5 m<sup>2</sup> at 1 keV and 2 m<sup>2</sup> at 7 keV and 2-5" HEW spatial resolution together with advanced detectors will provide much improved imaging, spectroscopic and timing performances and open new vistas in X-ray astronomy in the post 2015 timeframe. XEUS will allow the study of the birth, growth and spin of the super-massive black holes in early AGN, allow the cosmic feedback between galaxies and their environment to be investigated through the study of inflows and outflows and relativistic acceleration and allow the growth of large scale structures and metal synthesis to be probed using the hot X-ray emitting gas in clusters of galaxies and the warm/hot filamentary structures observable with X-ray absorption spectroscopy. High time resolution studies will allow the Equation of State of supra-nuclear material in neutron stars to be constrained. These science goals set very demanding requirements on the mission design which is based on two formation flying spacecraft launched to the second Earth-Sun Lagrangian point by an Ariane V ECA. One spacecraft will contain the novel high performance optics while the other, separated by the 35 m focal length, will contain narrow and wide field imaging spectrometers and other specialized instruments.
XEUS is the potential successor to ESA's XMM-Newton X-ray observatory. Novel light-weight optics with an effective area of 10 m<sup>2</sup> at 1 keV and 2-5" HEW spatial resolution together with advanced imaging detectors will provide a sensitivity around 200 times better than XMM-Newton as well as much improved high-energy coverage, and spectroscopic performance. This enormous improvement in scientific capability will open up new vistas in X-ray astronomy. It will allow the detection of massive black holes in the earliest AGN and estimates of their mass, spin and red-shift through their Fe-K line properties. XEUS will study the first gravitationally bound, Dark Matter dominated, systems small groups of galaxies and trace their evolution into today's massive clusters. High-resolution spectroscopy of the hot intra-cluster gas will be used to investigate the evolution of metal synthesis to the present epoch. The hot filamentary structure will be studied using absorption line spectroscopy allowing the mass, temperature and density of the intergalactic medium to be characterized. As well as these studies of the deep universe, the enormous low-energy collecting area will provide a unique capability to investigate bright nearby objects with dedicated high-throughput, polarimetric and time resolution detectors.
XMM-Newton was launched into space on a highly eccentric 48 hour orbit on December 10th 1999. XMM-Newton is now in its fifth year of operation and has been an outstanding success, observing the Cosmos with imaging, spectroscopy and timing capabilities in the X-ray and optical wavebands. The EPIC-MOS CCD X-ray detectors comprise two out of three of the focal plane instruments on XMM-Newton. In this paper we discuss key aspects of the current status and performance history of the charge transfer ineffiency (CTI), energy resolution and spectral redistribution function (rmf) of EPIC-MOS in its fifth year of operation.
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.
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.
XEUS is the post-XMM next generation x-ray observatory which is currently under study by ESA. The mission aims to image the x-ray early universe through the study of feint, high red-shift objects. To provide sufficient photons to enable spectroscopy on these distant objects requires a telescope collecting area greatly in excess of those in use today, and an x-ray optic with collecting area ~100x of XMM is ultimately envisaged. With a focal length of 50m, the plate scale of the optic is 6.5x that of XMM, which using existing focal plane technology will reduce the effective field of view to a few arc minutes. Cryogenic instrumentation, with detector sizes of a few mm can only be used for narrow field studies of target objects, and a wide field instrument is under consideration using a DEPFET pixel array to image out to a diameter of 5 arcminutes, requiring an array of dimension 70mm. Since the useful field of view of the XEUS optic will extend to a diameter of 30 arcminutes, the potential of the optic could be very under-utilized. Here we propose an extension to the wide field imager, the E-WFI, comprised of a ring array of CCDs which will increase the coverage of the focal plane, and greatly increase the serendipitous science resulting from the mission. Here we describe the first design concept for the E-WFI, and discuss the technical advancements in MOS CCD technology which will enhance the science of the mission.
The XMM-Newton observatory has the largest collecting area flown so
far for an X-ray imaging system, resulting in a very high sensitivity
over a broad spectral range. In order to exploit fully these
performances, an accurate calibration of the XMM-Newton
instruments is required. This calibration is being continuously
updated, in order to refine the stable calibration parameters as well
as to account for the detector response changes induced by radiation damage. We report here on the current overall status of the EPIC/MOS cameras calibrations, and in particular on the recent work involving Charge Transfer Inefficiency evolution and recovery.
EPIC, on the Newton Observatory, comprises three CCD cameras that provide spectroscopic imaging over the band 0.1-12 keV, with full coverage of the 30' diameter field of view of the three telescopes. The combination of bandwidth, throughput, and spectral resolution, has produced many interesting observations in more than two years of operation. These range from stars, normal, and neutron, SNR & Pulsars, via galaxies, to clusters of galaxies and the most distant quasars. Some of the latest results will be presented. A few days' operation on orbit provides more instrument performance data that can be gathered in the most thorough ground calibration, and many new facets of the instrument performance become evident in orbit. The high throughput of the Newton telescopes provides images and spectra of high statistical precision. This puts an additional burden on the calibration, and there has been much progress by the EPIC team in defining a precise and accurate calibration at the few percent level. The EPIC MOS CCDs perform well in orbit and show considerable radiation hardness against soft protons, due to their peculiar architecture. The degradation of spectral resolution, due to radiation damage, is dominated by hard solar flare protons. At present, this is within the predicted limits and the good spectral performance of EPIC is maintained.
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.
A feasibility study of an imaging 32 by 32 pixel micro- calorimeter array, intended for the XEUS mission is presented. Three different concepts, theoretically leading to a detector that combines an energy resolution of 5 eV for 8 keV x-rays and a count rate of at least 100 counts/pixel, are presented and discussed. The starting point for this study is the current progress in the field of single pixel micro-calorimeters employing voltage biased transition edge sensors. The design concepts originate from different philosophies for the thermal design and geometrical lay-out and will use state of the art micro-machining and lithography. Moreover, both from an electrical and a cooling point of view SQUID read-out will be the challenge and grouping of pixels might be considered.
XEUS: The X-ray Evolving Universe Spectroscopy mission represents a potential follow-on mission to the ESA XMM cornerstone currently nearing completion. XEUS represents the next logical step forward in x-ray astrophysics after the current set of mission have been launched and completed their operational lives. The development and ultimate success relies heavily on the capability of the International Space Station (ISS). In this paper we describe the key characteristics of the mission including the requirements placed specifically on the ISS and discuss the significant advances in high energy astrophysics expected from such an observatory.
Measurements made during the selection and evaluation of flight CCD detectors for the XMM EPIC MOS cameras have demonstrated near Fano limited resolution at x-ray energies above approximately 3keV. At lower energies some devices exhibit a fractional charge loss which is believed to be due to recombination at the epitaxy/oxide interface. This has been modeled through a Monte-Carlo simulation by assuming that the pinning implant in the etched electrode structure can cause electrons to flow to the front surface, rather than to the buried channel. In spite of this charge loss, spectral response may be characterized using a double Gaussian with residuals of < 5 percent. Quantum efficiency has been measured using a lithium drifted silicon reference detector and these measurements combined with analytical and Monte Carlo simulation, event size ratios and cosmic ray detection, all give a value for the effective depletion depth of 30 to 35 micrometers .
Measuring the polarization of x-rays emitted from cosmological objects yields explanations of the structure which characterize these sources. Polarization detection efficiencies of up to 18% have been measured for two, small pixel, charge coupled devices (CCDs) using an 80% polarized monochromatic synchrotron beam between energies of 7.5 keV and 35 keV. The device efficiencies at less than 15 keV are of particular interest for astronomical purposes where imaging, spectroscopy and polarization measurements can be carried out simultaneously. Polarization measurements using a CCD rely on the preferential direction of the ejected photoelectron along the E-field of the incident x-ray beam. The resultant charge cloud is sampled by the pixellated array of the CCD. It will be shown that the CCD polarization detection efficiency (modulation factor) is a function of the pixel size and the energy of the incident photons. The effect of depletion depth and impact of a field-free layer in the detector are reviewed. The two devices used were a commercial optical CCD, Kodak KAF1400, with 6.8 by 6.8 micrometer squared pixels and a specialized CCD, designed by EEV Ltd., deeply depleted with 4 by 9 micrometer squared pixels.
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 10<SUP>5</SUP> seconds of 2 multiplied by 10<SUP>-15</SUP> erg/cm<SUP>-2</SUP>. 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 x-ray astronomy group at the University of Leicester is responsible for the development of two out of three of the focal plane cameras for the EPIC instrument on ESA's cornerstone mission XMM. CCDs are being developed in collaboration with EEV Ltd. of Chelmsford, UK, to perform the imaging spectroscopy at the prime focus of two of the XMM telescopes. The detectors require Fano-limited energy resolution and high detection efficiency over the 0.1 to 15 keV band. Devices are being constructed using high resistivity epitaxial silicon of 80 micrometer thickness, producing deep depletion, with an efficiency at the iron line (6.4 keV) of 75%. The low energy (less than 1 keV) x- ray performance is being maximized in the front-illumination devices by using novel 'open electrode' structures resulting in an efficiency of 25% at carbon-K (277 eV). This paper provides an update on the instrument concept and performance which is now entering the flight model build phase. The test results of the new custom CCD detectors are presented.
The X-ray Astronomy group at the University of Leicester is responsible for the development of two out of three of the focal plane cameras for the EPIC instrument on ESA's cornerstone mission XMM. CCDs are being developed in collaboration with EEV Ltd. of Chelmsford, UK, to perform the imaging spectroscopy at the prime focus of the telescope. The detectors require Fano-limited energy resolution and high detection efficiency over the 0.1 - 15 keV band. Devices are being constructed using high resistivity bulk silicon (> 8000 (Omega) cm) producing deep depletion, with an efficiency at the iron line (6.4 keV) of 85%. The low energy (< 1 keV) X-ray performance is being maximized in the front-illumination devices by using novel `open electrode' structures resulting in an efficiency of 23% at carbon- k (277 eV). The test results of devices manufactured are presented for a range of X-ray lines and the data are compared to modelled results based on the device parameters.
The Joint European X-ray Telescope, JET-X, is one of the core instruments in the scientific payload of the USSR''s Spectrum Roentgen-Gamma (RG) high energy astrophysics mission. JET-X consists of two identical co-aligned X-ray imaging telescopes, each with a spatial resolution of 20 arc second. Focal plane imaging is achieved with cooled X-ray sensitive CCD detectors, which provide high spectral resolution and good background rejection efficiency, in addition to the necessary imaging capability. An optical monitor telescope, also co-aligned with the two X-ray telescopes, permits simultaneous observation and identification of optical counterparts of X-ray target sources. The system design of JET-X is reviewed, and performance data obtained from measurements on the instrument prototype are presented.
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.