The Swift X-ray Telescope (XRT) is a CCD based X-ray telescope designed for localization, spectroscopy and long term
light curve monitoring of Gamma-Ray Bursts and their X-ray afterglows. Since the launch of Swift in November 2004,
the XRT has undergone significant evolution in the way it is operated. Shortly after launch there was a failure of the
CCD thermo-electric cooling system, which led to the XRT team being required to devise a method of keeping the CCD
temperature below −50C utilizing only passive cooling by minimizing the exposure of the XRT radiator to the Earth. We
present in this paper an update on how the modeling of this passive cooling method has improved in first ~1000 days
since the method was devised, and the success rate of this method in day-to-day planning. We also discuss the changes
to the operational modes and onboard software of the XRT. These changes include improved rapid data product
generation in order to improve speed of rapid Gamma-Ray Burst response and localization to the community; changes to
the way XRT observation modes are chosen in order to better fine tune data acquisition to a particular science goal;
reduction of "mode switching" caused by the contamination of the CCD by Earth light or high temperature effects.
CCD detectors in the focal plane cameras of grazing incidence X-ray telescopes on the XMM-Newton and SWIFT
satellites have encountered damage which has been attributed to impacts by external particles. The apparent mechanism
is one whereby interplanetary micrometeoroid particles or space debris have been ingested by the grazing incidence
mirrors and scattered down the telescope tube on to the CCD detectors in the focal plane.
At the time of writing, there have been 5 such events detected in total by the three XMM telescopes during five years of
operations and one event detected by the SWIFT X-ray Telescope (XRT) during one year in orbit. Significantly, no
events of this type have been reported for Chandra.
Modelling and analysis of scattering of small particles from grazing incidence mirrors allows us to explain the different
impact rates seen by these three satellites. Furthermore, using the ESA MASTER2005 micrometeoroid and space debris
impacts flux model, impact rates have been derived from consideration of Swift's orbit, pointing history and the dust and
debris particle environment. This modelling can be used to determine whether risk mitigation strategies are required for
the continuing operation of SWIFT and other operating observatories, and also provides a basis for predicting particle
impact rates for grazing incidence telescopes on future missions such as XEUS, Constellation-X and others.
The Swift X-ray Telescope (XRT) focal plane camera is a front-illuminated MOS CCD, providing a spectral response kernel of 144 eV FWHM at 6.5 keV. We describe the CCD calibration program based on celestial and on-board calibration sources, relevant in-flight experiences, and developments in the CCD response model. We illustrate how the revised response model describes the calibration sources well. Loss of temperature control motivated a laboratory program to re-optimize the CCD substrate voltage, we describe the small changes in the CCD response that would result from use of a substrate voltage of 6V.
The X-ray telescope (XRT) on board Swift, launched on 2004 Nov 20, is performing astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray burst afterglows in the energy band 0.2-10 keV. In this paper, we describe the results of the in-flight calibration relative to the XRT timing resolution and absolute timing capabilities. The timing calibration has been performed comparing the main pulse phases of the Crab profile obtained from several XRT observations in Low Rate Photodiode and Windowed Timing mode with those from contemporaneous RXTE observations. The XRT absolute timing is well reproduced with an accuracy of 200 μs for the Low Rate Photodiode and 300 μs for the Windowed Timing mode.
The XRT is a sensitive, autonomous X-ray imaging spectrometer onboard the Swift Gamma-Ray Burst Observatory. The unique observing capabilities of the XRT allow it to autonomously refine the Swift BAT positions (~1-4' uncertainty) to better than 2.5 arcsec in XRT detector coordinates, within 5 seconds of target acquisition by the Swift Observatory for typical bursts, and to measure the flux, spectrum, and light curve of GRBs and afterglows over a wide dynamic range covering more than seven orders of magnitude in flux (62 Crab to < 1 mCrab). The results of the rapid positioning capability of the XRT are presented here for both known sources and newly discovered GRBs, demonstrating the ability to automatically utilise one of two integration times according to the burst brightness, and to correct the position for alignment offsets caused by the fast pointing performance and variable thermal environment of the satellite as measured by the Telescope Alignment Monitor. The onboard results are compared to the positions obtained by groundbased follow-up. After obtaining the position, the XRT switches between four CCD readout modes, automatically optimising the scientific return from the source depending on the flux of the GRB. Typical data products are presented here.
The Swift X-ray Telescope (XRT) is a CCD based X-ray telescope designed for localization, spectroscopy and long term light curve monitoring of Gamma-Ray Bursts and their X-ray afterglows. Shortly after launch there was a failure of the thermo-electric cooler on the XRT CCD. Due to this the Swift XRT Team had the unexpected challenge of ensuring that the CCD temperature stayed below -50C utilizing only passive cooling through a radiator mounted on the side of the Swift. Here we show that the temperature of the XRT CCD is correlated with the average elevation of the Earth above the XRT radiator, which is in turn related to the targets that Swift observes in an orbit. In order to maximize passive cooling of the XRT CCD, the XRT team devised several novel methods for ensuring that the XRT radiator's exposure to the Earth was minimized to ensure efficient cooling. These methods include: picking targets on the sky for Swift to point at which are known to put the spacecraft into a good orientation for maximizing XRT cooling; biasing the spacecraft roll angle to point the XRT radiator away from the Earth as much as possible; utilizing time in the SAA, in which all of the instruments on-board Swift are non-operational, to point at "cold targets"; and restricting observing time on "warm" targets to only the periods at which the spacecraft is in a favorable orientation for cooling. By doing this at the observation planning stage we have been able to minimize the heating of the CCD and maintain the XRT as a fully operational scientific instrument, without compromising the science goals of the Swift mission.
The Swift X-ray Telescope (XRT) is designed to make astrometric,
spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows in the 0.2-10 keV energy band. Here we report the initial results of the analysis of Swift XRT effective area as measured both on-axis and off-axis during the in-flight calibration phase using the laboratory results and ray-tracing simulations as a starting point. Our analysis includes the study of the effective area at a range of energies, for different event grade selection and operating modes using two astronomical sources characterized by different intrinsic spectra.
The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from
Gamma-ray bursts and their afterglows, in the energy band 0.2-10 keV.
Swift was successfully launched on 2004 November 20. Here we report the results of the analysis of Swift XRT Point Spread Function (PSF) as measured in the first four months of the mission during the instrument calibration phase.
The analysis includes the study of the PSF of different point-like sources both on-axis and off-axis with different spectral properties. We compare the in-flight data with the expectations from the on-ground calibration. On the basis of the calibration data we built an analytical model to reproduce the PSF as a function of the energy and the source position within the detector which can be applied in the PSF correction calculation for any extraction region geometry.
The Swift Gamma Ray Burst Explorer, chosen in October 1999 as NASA's next MIDEX mission, is now scheduled for launch in October 2004. SWIFT carries three complementary instruments. The Burst Alert Telescope (BAT) identifies gamma-ray bursts (GRBs) and determines their location on the sky to within a few arc-minutes. Rapid slew by the fast-acting SWIFT spacecraft points the two narrow field instruments, an X-ray Telescope (XRT) and an Ultraviolet/Optical Telescope (UVOT), to within the BAT error circle within 70 seconds of a BAT detection. The XRT can determine burst locations to within 5 arc-seconds and measure X-ray spectra and photon flux, whilst the UVOT has a sensitivity down to 24th magnitude and sub arc-second positional accuracy in the optical/uv band. The three instruments combine to make a powerful multi-wavelength observatory with the capability for rapid determination of GRB positions to arc-second accuracy within a minute or so of their discovery, and the ability to measure light-curves and red-shifts of the bursts and after-glows. The paper summarises the mission's readiness for October's launch and operations.
The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report first results of the analysis of Swift XRT effective area at five different energies as measured during the end-to-end calibration campaign at the Panter X-ray beam line facility. The analysis comprises the study of the effective area both on-axis and off-axis for different event grade selection. We compare the laboratory results with the expectations and show that the measured effective area meets the mission scientific requirements.
The SWIFT X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report the results of the analysis of SWIFT XRT Point Spread Function (PSF) as measured during the end-to-end calibration campaign at the Panter X-Ray beam line facility. The analysis comprises the study of the PSF both on-axis and off-axis. We compare the laboratory results with the expectations from the ray-tracing software and from the mirror module tested as a single unit. We show that the measured HEW meets the mission scientific requirements. On the basis of the calibration data we build an analytical model which is able to reproduce the PSF as a function of the energy and the position within the detector.
The Swift Gamma-Ray Explorer is designed to make prompt multiwavelength observations of Gamma-Ray Bursts (GRBs) and GRB Afterglows. The X-ray Telescope (XRT) provides key capabilities that permit Swift to determine GRB positions with a few arcseconds accuracy within 100 seconds of the burst onset. The XRT utilizes a superb mirror set built for JET-X and a state-of-the-art XMM/EPIC MOS CCD detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with effective area of 135 cm2 at 1.5 keV, field of view of 23.6 x 23.6 arcminutes, and angular resolution of 18 arcseconds (HEW). The detection sensitivity is 2x10-14 erg/cm2/s in 104 seconds. The instrument is designed to provide automated source detection and position reporting within 5 seconds of target acquisition. It can also measure redshifts of GRBs for bursts with Fe line emission or other spectral features. The XRT will operate in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and will follow each burst for days as it fades from view.
The Swift X-ray Telescope is a powerful instrument for measuring the X-ray spectral properties of GRB afterglows. The spectroscopic capabilities are obtained through the energy resolving properties of the X-ray CCD imager in the focal plane of the X-ray Telescope. A range of CCD operating modes allow GRB afterglows to be followed over 5 orders of brightness as the afterglow decays. The spectroscopic response in each mode has been determined as part of the XRT calibration program and is being incorporated into the XRT instrument response matrices. These responses are being used to simulate GRB spectra as part of the pre-launch mission planning for Swift.
The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic, and photometric observations of X-ray emission from Gamma-ray Bursts and their afterglows in the energy band 0.2-10 keV. In order to provide rapid-response, automated observations of these randomly occurring objects without ground intervention, the XRT must be able to observe objects covering some seven orders of magnitude in flux, extracting the maximum possible science from each one. This requires a variety of readout modes designed to optimise the information collected in response to shifting scientific priorities as the flux from the burst diminishes.
The XRT will support four major readout modes: imaging, two timing modes and photon-counting, with several sub-modes. We describe in detail the readout modes of the XRT. We describe the flux ranges over which each mode will operate, the automated mode switching that will occur and the methods used for collection of bias information for this instrument. We also discuss the data products produced from each mode.
The Swift Gamma-Ray Burst Explorer will be launched late in 2003 to make prompt multiwavelength observations of Gamma-Ray Bursts and Afterglows. The X-ray Telescope (XRT) provides key capabilities that permit Swift to determine GRB positions with several arcsecond accuracy within 100 seconds of the burst onset. The XRT is designed to observe GRB afterglows covering over seven orders of magnitude in flux in the 0.2-10 keV band, with completely autonomous operation. GRB positions are determined within seconds of target acquisition, and accurate positions are sent to the ground for distribution over the GCN. The XRT can also measure redshifts of GRBs for bursts with Fe line emission or other spectral features.
The Swift X-ray Telescope (XRT)[1] is designed to make astrometric, spectroscopic, and photometric observations of X-ray emission from Gamma-ray Bursts and their afterglows in the energy band 0.2-10 keV. The XRT has a variety of readout modes which it automatically selects in order to observe objects covering 7 orders of magnitude in flux and to extract the maximum possible science from each one, in response to the flux from the burst diminishing. The primary goal of the XRT is to locate the position of the Gamma-Ray Burst to 1 arcsec and to transmit this position to the UVOT and the ground within 100 seconds of the initial observation of the burst. We describe in detail the use of imaging mode and a centroid algorithm to determine the position of the Gamma-Ray Burst with sub-pixel accuracy.
Mark Sims, D. Pullan, George Fraser, S. Whitehead, J. Sykes, J. Holt, Gillian Butcher, Nick Nelms, J. Dowson, D. Ross, C. Bicknell, M. Crocker, B. Favill, Alan Wells, L. Richter, H. Kochan, Hans Hamacher, L. Ratke, Andrew Griffiths, A. Coates, N. Phillips, A. Senior, John Zarnecki, M. Towner, M. Leese, M. Patel, C. Wilson, Nicolas Thomas, S. Hviid, Jean-Luc Josset, G. Klingelhoefer, B. Bernhardt, P. van Duijn, G. Sims, K. Yung
The performance of the PAW instrumentation on the 60kg Beagle 2 lander for ESA’s 2003 Mars Express mission will be described. Beagle 2 will search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize acquisition and preparation tools to obtain samples from below the surface, and both under and inside rocks. In situ analysis will include examination of samples with an optical microscope, Mossbauer and fluorescent X-ray spectrometers. Extracted samples will be returned to the lander for analysis, in particular a search for organics and a measurement of their isotopic composition. The PAW experiment performance data will be described along with the status of the project.
The essential optical components of the Swift X-ray Telescope (XRT) are already developed items. They are: the flight spare x-ray mirror from the JET-X/Spectrum-X program and a MOS CCD (CCD22) of the type currently operating in orbit as part of the EPIC focal plane camera on the XMM- Newton. The JET-X mirrors were first calibrated at the Max Plank Institute for Extraterrestrial Physics' (MPE) Panter facility, Garching, Germany in 1996. Half energy widths (HEW) of 16 arc seconds at 1.5 keV were confirmed for the two flight mirrors and the flight spare. The calibration of the flight spare was repeated at Panter in July 2000 in order to establish whether any changes had occurred during the four years that the mirror had been in storage at the OAB, Milan, Italy. This results reported in this paper, confirm that the resolution of the JET-X mirrors has remained stable over this storage period. In an extension of this test program, the flight spare EPIC camera was installed at the focus of the JET-X mirror to simulate the optical system of the Swift X-ray telescope. On-axis and off-axis point spread functions (PSFs) were measured and calibration data sets were used to obtain centroid positions of X-ray point sources. The results confirmed Swift's ability to determine the centroid positions of sources at 100mCrab brightness to better than 1 arc second and provided a calibration of the centroiding process as a function of source flux and off axis angle. The presence of background events in the image frame introduced errors in the centroiding process, making the choice of centroiding algorithm important. Algorithm performance and the trade-off between processing speed and centroiding accuracy were investigated.
Mark Sims, C. Pillinger, I. Wright, G. Morgan, I. Praine, George Fraser, D. Pullan, S. Whitehead, J. Dowson, Alan Wells, L. Richter, H. Kochan, Hans Hamacher, A. Griffiths, A. Coates, S. Peskett, A. Brack, J. Clemmet, R. Slade, N. Phillips, C. Berry, A. Senior, John Zarnecki, Mark Towner, M. Leese, Aaron Zent, Nicolas Thomas, Jean-Luc Josset, G. Klingelhoefer, P. van Duijn, G. Sims
The instrumentation on the 60 kg Beagle 2 lander for ESA's 2003 Mars Express mission will be described. Beagle 2 will be search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize acquisitions and preparation tools to obtain samples from below the surface, and both under and inside rocks. In situ analysis will include examination of samples with an optical microscope, Mossbauer and fluorescent X-ray spectrometers. Extracted samples will be returned to the lander for analysis, in particular a search for organics and a measurement of their isotopic composition. The experiment configuration and design will be described along with the status of the project.
The Swift Gamma Ray Burst Explorer will be launched in 2003 to observe hundreds of gamma-ray bursts per year and study their X-ray and optical afterglows, using a multiwavelength complement of three instruments: a wide-field Burst Alert Telescope (BAT), an X-Ray Telescope (XRT), and a UV/Optical Telescope (UVOT). The XRT is designed to study X-ray counterparts of the gamma-ray bursts and their afterglows, beginning 20 - 70 s from the time of the burst, and continuing for days or weeks. The XRT utilizes a superb mirror set built for JET-X and a state-of-the-art XMM/EPIC CCD detector to provide a sensitive broad-band (0.2 - 10 keV) X-ray imager with effective area of 110 cm2 at 1.5 keV, field of view of 23.6 X 23.6 arcminutes, and angular resolution of 15 arcseconds (HEW). The sensitivity is 2 X 10-14 erg/cm2s in 104 seconds. The telescope electronics are designed to provide automated source detection and position reporting, with a position good to 2.5 arcseconds transmitted to the ground within 100 seconds of the burst detection. The XRT will operate in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return for each frame as the source fades. The XRT will measure spectra and lightcurves of the GRB afterglow beginning within about a minute after the burst and will follow each burst until it fades from view, typically monitoring 2 - 3 'old' bursts at a time while waiting for a new burst to be detected.
Mark Sims, C. Pillinger, I. Wright, G. Morgan, George Fraser, D. Pullan, S. Whitehead, J. Dowson, Richard Cole, Alan Wells, L. Richter, H. Kochan, Hans Hamacher, Alan Johnstone, A. Coates, S. Peskett, A. Brack, J. Clemmet, R. Slade, N. Phillips, C. Berry, A. Senior, J. Lingard, J. Underwood, John Zarnecki, Mark Towner, M. Leese, A. Gambier-Parry, Nicolas Thomas, Jean-Luc Josset, G. Klingelhoefer
The 60 kg Beagle 2 lander for ESA's 2003 Mars Express mission will be described. Beagle 2 will search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Such samples will be returned to the lander for detailed analysis. Analysis will include examination of samples and rocks and soils with an optical microscope and X-ray Spectrometer and Mossbauer Spectrometers as well as a search for organics and a measurement of their isotopic composition. The lander systems design as well as the experiment configuration will be described along with the status of the project.
D. Anagnostopoulos, M. Augsburger, Gunther Borchert, D. Chatellard, Michael Daum, J.-P. Egger, Detlev Gotta, P. Hauser, P. Indelicato, E. Jeannet, K. Kirch, Nick Nelms, O. Schult, T. Siems, Leopold Simons, Alan Wells
An experiment is described which aims to determine the pion mass to 1 ppm or better, from which a new determination of the upper limit of the muon neutrino mass is anticipated. The approach utilizes spectroscopy of X-ray emissions from pionic atoms formed in gaseous targets. The spectroscopy is performed with a Bragg crystal spectrometer, with an energy resolution of approximately 300 meV, using an array of X-ray CCDs mounted at the focus to measure the spectral line structure of the 4 keV pionic nitrogen transition. To achieve sub-ppm accuracy, as energy calibration a muonic oxygen transition is used. It is known with a precision of 0.3 ppm and almost coincides in energy with the pionic transition.
Mark Sims, C. Pillinger, I. Wright, Richard Cole, S. Whitehead, Alan Wells, K. Wittmann, L. Richter, H. Kochan, Hans Hamacher, Alan Johnstone, K. Rees, R. Turner, S. Peskett, A. Brack, J. Hobbs, L. Berthoud, R. Durrant, J. Higgins, J. Windsor, Horst Keller, H. Rosenbauer, Nicolas Thomas, J. Lingard, J. Underwood, Gerhard Neukum
The proposed Beagle 2 lander for ESA's 2003 Mars Express mission will be described. The aim of Beagle 2 will be to search for organic material on and below the surface of Mars in addition to a study of the inorganic chemistry and mineralogy of the landing site. The lander will utilize a small rover equipped with a mechanical and grinder to obtained samples from below the surface, under rocks, and inside rocks. Samples will be returned to the lander for analysis. Analysis performed by Beagle 2 will include examination of samples with an optical microscope and APX and Mossbauer Spectrometers as well as a search for organics and a measurement of their isotopic composition. The lander systems design as well as the experiment configuration will be described.
The optical filters on board the JET-X telescope comprise thin foils of aluminum coated Lexan. During ground calibration of the filters, narrow spectral regions of high UV leakage, with peak levels of up to a few percent, were observed in broad band optical measurements in the 1000 to 10,000 angstrom range. Furthermore, transmission values were typically up to two orders of magnitude higher than calculated for the aluminum thickness. Investigation showed that these effects were attributed to a combination of aluminum oxidation, which reduces the opacity, and the use of a double sided aluminum layer in the filter design which behaves as a Fabry-Perot interference filter. These effects were verified by a multi- layer model of the filter UV response. Recent redesign of the filters for the flight program eliminated the UV leakage by adopting a single aluminum layer configuration, thus eliminating interference effects, and increasing the thickness by 30% to compensate for oxidation levels. The integrated x- ray transmission below 1 keV was found to be only reduced by 3%. In parallel with the production of the new Lexan flight filters, a set of qualification model filters was produced by the Luxel Corporation in the USA. These filters use polyimide as a substrate material which has the advantage that it is optically opaque to wavelengths below 3000 angstroms, unlike Lexan which is transparent. These new filters were found to have superior mechanical strength, being able to survive extended qualification vibration without any visible degradation in performance, and had a higher cosmetic quality and attenuation levels. As a result, these filters have now been included in the JET-X flight program. We report on the optical tests results from both Lexan and polyimide filters along with high resolution x-ray transmission results carried out at the BESSY synchrotron facility in Germany. Results of the mapping of the filter edge structures, global transmission values and uniformity are presented.
Construction of the flight model joint European X-ray telescope (JET-X) for the Russian spectrum-X mission has been completed and performance tests and calibration of the instrument have been carried out. Separate measurements of the responses of the x-ray mirrors, the CCD detectors and the optical filters already indicate that JET-X will achieve spatial resolutions of around 20 arcsec, an on-axis collecting area of 310 cm2 at 1.5 keV and an energy resolution of 130 eV at 6 keV. As a final step in the calibration of the telescope assembly, end-to-end x-ray tests on the complete instrument have been performed in the x-ray beam line facility at MPE Garching. Results from this calibration program are reported and the overall response of the two x-ray telescopes are compared with the previously measured responses of the mirror, the CCD detectors and the optical filters. In-orbit sensitivity responses are derived from these calibration data sets, for the normal operating modes of JET-X.
The x-ray mirror calibration program for the JET-X telescope on spectrum-X has recently been carried out at the 130 m long Panter x-ray beam line of the Max Plank Institute fur Extraterrestriche Physik. The excellent spatial resolution achieved with these mirrors, 15 arcsec half energy width (HEW) at 1.5 keV and 19 arcseconds at 8 keV, has proved to be difficult to measure precisely using previously established calibration methods (involving either slit detectors or the ROSAT PSPC imaging proportional counter). New diagnostic techniques have, therefore, been developed using a CCD imaging camera which utilized newly available x- ray CCD technology. Details of the calibration technique and the performance of the camera are provided and results are compared with those obtained from the slit and PSPC detectors.
The detection efficiency of charge coupled devices (CCDs) in the x-ray band is dependent on the thickness of the active depletion layer in the silicon. This is typically under 35 micrometer and limited by the purity of available epitaxial substrates. For x-ray imaging, this results in a reduced CCD detection efficiency above 8 keV. In this paper, we show that by using a novel illumination geometry, CCDs can detect high energy (up to 100 keV) x rays with reasonable efficiency and good energy resolution. A novel 2-D imaging had x-ray detector based on this geometry is discussed.
We present preliminary results from a comprehensive program to calibrate the CCDs to be used as the focal plane detectors on the Joint European X-ray telescope (JET-X). The goal of the program is to calibrate the response of the flight CCDs (efficiency and energy resolution) down to a limiting precision of 1%. In addition to using conventional characteristic X-ray emission line calibration techniques to quantify the broad-band response, the devices have also been taken to the Synchrotron Radiation Source (SRS) at the Daresbury Laboratory to map the detailed X-ray Absorption Fine Structure (XAFS) around the silicon K-edge. To carry out the latter measurements, the SRS had to be operated with a ring current reduced by 5 orders of magnitude so that individual photons could be recorded by the CCD. The data show considerable near edge structure which is similar in shape to pure Si XAFS obtained by photocurrent measurements, but modified by the presence of the various oxide insulation layers used in MOS construction. Lastly, an analysis oft he pulse height spectra obtained at the SRS, has demonstrated that the Fano factor and the energy to create an electron hole pair vary with energy in agreement with the photoionization theory of Fraser et al. and the semi- empirical analysis of Owens et al.
Development work on JET-X has been completed and the flight model instrument is under construction. The X-ray performance of the mirror system and of the CCD detector have been determined by measurement and simulation in the course of development and optimization of JET-X over the past two years. New data on fine structure in the spectral response of CCD quantum efficiency and mirror reflectivity are presented. These results indicate that low intensity synchrotron radiation is an important new tool in the calibration of X-ray telescopes and is essential for determining the fine structure in the spectral efficiency and spectral resolution of X-ray telescopes that use CCD focal plane detectors.
We describe an experiment to quantify reflected X-ray Absorption Fine Structure (XAFS) in the mirrors to be used on the Joint European X-ray Telescope (JET-X). This instrument is due to be launched on the Russian Spectrum-X platform into deep orbit in December 1995. As part of the calibration program, samples of the Wolter type I, X-ray mirrors were taken to the Synchrotron Radiation Source at the Daresbury Laboratory and exposed to monochromatic X- rays across the energy range of the gold MI - MV edges (2 keV to 3.5 keV). We outline our research program and present preliminary results of both direct and reflected XAFS measurements at a variety of incident angles. We find that, while the position of the MII edge occurs within 3 eV of its tabulated value, the MI, MIII, MIV and MV edges are shifted to higher energies by approximately 10 eV, 13 eV, 40 eV and 40 eV, respectively. We attribute these discrepancies to inaccuracies in the field equations used to generate atomic and nuclear data tables.
The rational behind optical filter design for satellite-borne soft X-ray telescopes is elucidated by a series of sample calculations. By way of example we present the filter designs for two filters to be flown on-board the Joint European X-ray telescope (JET-X).
Large area CCD arrays, 770 X 1024 pixels, with 27 micrometers square pixels and packaged in matching pairs in a ruggedized focal plane assembly have been developed for the JET-X instrument for the Russian Spectrum-RG spacecraft. The devices achieve low noise readout (<EQ 5 electrons rms), low dark current (< 1 electron/pixel/frame-integration time) and high charge transfer efficiency (> 0.99997) enabling the device to combine high quantum efficiency and good energy resolution over the operating range of JET-X. New results from flight prototype JET-X CCD's will be presented which reveal the detail of charge spreading behavior in the device and the consequent effect on quantum efficiency, energy resolution and background rejection. Theoretical modelling and simulation of these processes are used to analyze the experimental results.
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 two co-aligned x-ray imaging telescopes in the JET-X instrument on Spectrum R-G use passively cooled x-ray sensitive CCDs in the focal plane imagers. Development of the CCD for JET-X, the design and performance of the focal plane assembly are reviewed and improvements to both the low energy and high energy quantum efficiency are described. Performance data on spatial and energy resolution, and the rejection efficiency to charged particle background, obtained with prototype CCDs, 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.
The main design features and the early findings of the Rosat XUV wide field camera (WFC) are discussed. The most important data on the WFC telescope and detectors are presented. The WFC operational features, observing efficiency, filter performance, thermal performance star tracker performance, and single-event upsets are discussed. The first WFC images are compared with preflight calibration data.
The ROSAT project is an international collaboration between the Federal Republic of Germany, the United Kingdom, and the United States. The satellite, due to be launched in June 1990, carries a payload of two coaligned imaging telescopes: the German X-Ray Telescope (XRT), which operates in the soft x-ray band (0.1 to 2 keV or 6 to 100 A), and the UK Wide Field Camera (WFC), which operates in the XUV band (0.02 to 0.2 keV or 60 to 600 A). ROSAT will perform two main tasks in its anticipated two to four year lifetime: a six-month all-sky survey in the soft x ray and XUV bands followed by a program of pointed observations for detailed studies of thousands of individual targets. In this paper we review the
design and performance of the WFC. The instrument is a grazing incidence telescope comprising a set of three nested, Wolter-Schwarzschild Type I, gold-coated aluminum mirrors with a microchannel plate detector at their common focus. Thin plastic and metal film filters define the wavelength passbands.
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