We present a two-staged approach to wide-field wavefront sensing and demonstrate its ability to estimate and enhance image quality for the upcoming Rubin Observatory. The first stage makes local wavefront estimates with a convolutional neural network; the second stage uses linear regression to solve for the global optical state. The Rubin Observatory will have a 3.5 degree field of view, highly degenerate optical system, and curvature wavefront sensing system, making it the perfect test case. We trained our model on 600,000 simulated Rubin Observatory intra and extra-focal star images (donuts). It learns to estimate the optics contribution to the wavefront and separate it from a myriad of other contributions. This computationally efficient approach can process 1,000 times the number of donuts as proposed alternatives. This significant increase in bandwidth leads to a richer and more accurate characterization of the evolution of the telescope optics.
The Integration and Verification Testing and characterization of the expected performance of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 Gpixel focal plane mosaic of 189 CCDs. In this paper, we describe the verification testing program developed in parallel with the integration of the Camera, and the results from our performance characterization of the Camera. Our testing program includes electro-optical characterization and CCD height measurements of the focal plane, at several steps during integration, as well as a complete functional and characterization program for the finished focal plane. It also includes a suite of functional tests of the major Camera mechanisms: shutter, filter exchange system and thermal control. Finally, we expect to test the fully assembled Camera prior to its scheduled completion and delivery to the LSST observatory in early calendar 2021.
The Large Synoptic Survey Telescope (LSST) Project is a public-private partnership now half way through the 8- year construction period. LSST construction was initiated in 2014 by the US National Science Foundation to build the observing system within a $473M budget and in time to start the survey in October 2022. The US Department of Energy also participates by funding the camera fabrication with a budget of $168M. LSST will construct the system to conduct a wide fast deep survey of the entire visible sky and to process and serve the data to the US, Chilean, and international contributors without any proprietary period. The designs have matured around the 3-mirror wide field optical system; an 8.4 meter primary, 3.4 meter secondary, and 5 meter tertiary mirror that feed three refractive elements and a 64 cm 3.2 gigapixel focal plane camera. The data management system will reduce, transport, alert, archive roughly 15 terabytes of data produced nightly, and will serve raw and catalog data on daily and annual timescales throughout the 10-year survey. Additional access portals and tools will extend the scientific reach to education and public outreach efforts for students and non-professionals. LSST has completed key elements of the system with hardware being sent to the observing site on Cerro Pachón, Chile, factory integration efforts underway, and the focal plane assembly process started. Software development continues as an open-source project and completed demonstrations of key algorithm performance on existing data sets. LSST continues to plan an on-time and on-budget completion.
The Large Synoptic Survey Telescope (LSST) is a large aperture, wide-field, ground-based telescope designed to provide a time domain survey of the entire southern hemisphere in six optical bands. Over the ten-year duration of the survey, LSST will obtain ~800-1,000 images of every part of the southern sky, yielding a catalog of stars, galaxies, and moving small bodies in the solar system with nearly 40 billion objects. A diverse array of scientific investigations can be performed with a common database addressing topics ranging from the detection of potentially hazardous asteroids to the structure and evolution of the Universe as a whole. LSST incorporates an 8-m class primary mirror with a 3.2 billion pixel camera. I will discuss the design of this facility and our technical progress with construction and fabrication of the key components.
Near-future astronomical survey experiments, such as LSST, possess system requirements of unprecedented
fidelity that span photometry, astrometry and shape transfer. Some of these requirements flow directly to the
array of science imaging sensors at the focal plane. Availability of high quality characterization data acquired
in the course of our sensor development program has given us an opportunity to develop and test a framework
for simulation and modeling that is based on a limited set of physical and geometric effects. In this paper we
describe those models, provide quantitative comparisons between data and modeled response, and extrapolate
the response model to predict imaging array response to astronomical exposure. The emergent picture departs
from the notion of a fixed, rectilinear grid that maps photo-conversions to the potential well of the channel.
In place of that, we have a situation where structures from device fabrication, local silicon bulk resistivity
variations and photo-converted carrier patterns still accumulating at the channel, together influence and distort
positions within the photosensitive volume that map to pixel boundaries. Strategies for efficient extraction of
modeling parameters from routinely acquired characterization data are described. Methods for high fidelity
illumination/image distribution parameter retrieval, in the presence of such distortions, are also discussed.
The design of the Large Synoptic Survey Telescope (LSST) requires a camera system of unprecedented size and complexity. Achieving the science goals of the LSST project, through design, fabrication, integration, and operation, requires a thorough understanding of the camera performance. Essential to this effort is the camera modeling which defines the effects of a large number of potential mechanical, optical, electronic or sensor variations which can only be captured with sophisticated instrument modeling that incorporates all of the crucial parameters. This paper presents the ongoing development of LSST camera instrument modeling and details the parametric issues and attendant analysis involved with this modeling.
KEYWORDS: Cameras, Optical filters, Large Synoptic Survey Telescope, Sensors, Charge-coupled devices, Electronics, Telescopes, Control systems, Camera shutters, Imaging systems
The Large Synoptic Survey Telescope (LSST) is a large aperture, wide-field facility designed to provide deep images of
half the sky every few nights. There is only a single instrument on the telescope, a 9.6 square degree visible-band
camera, which is mounted close to the secondary mirror, and points down toward the tertiary. The requirements of the
LSST camera present substantial technical design challenges. To cover the entire 0.35 to 1 μm visible band, the camera
incorporates an array of 189 over-depleted bulk silicon CCDs with 10 μm pixels. The CCDs are assembled into 3 x 3
"rafts", which are then mounted to a silicon carbide grid to achieve a total focal plane flatness of 15 μm p-v. The CCDs
have 16 amplifiers per chip, enabling the entire 3.2 Gigapixel image to be read out in 2 seconds. Unlike previous
astronomical cameras, a vast majority of the focal plane electronics are housed in the cryostat, which uses a mixed
refrigerant Joule-Thompson system to maintain a -100ºC sensor temperature. The shutter mechanism uses a 3 blade
stack design and a hall-effect sensor to achieve high resolution and uniformity. There are 5 filters stored in a carousel
around the cryostat and the auto changer requires a dual guide system to control its position due to severe space
constraints. This paper presents an overview of the current state of the camera design and development plan.
The Large Synoptic Survey Telescope (LSST) uses a novel, three-mirror, modified Paul-Baker design,
with an 8.4-meter primary mirror, a 3.4-m secondary, and a 5.0-m tertiary feeding a refractive camera design with 3
lenses (0.69-1.55m) and a set of broadband filters/corrector lenses. Performance is excellent over a 9.6 square
degree field and ultraviolet to near infrared wavelengths.
We describe the image quality error budget analysis methodology which includes effects from optical and
optomechanical considerations such as index inhomogeneity, fabrication and null-testing error, temperature
gradients, gravity, pressure, stress, birefringence, and vibration.
Extracting science from the LSST data stream requires a detailed knowledge of the properties of the LSST catalogs and
images (from their detection limits to the accuracy of the calibration to how well galaxy shapes can be characterized).
These properties will depend on many of the LSST components including the design of the telescope, the conditions
under which the data are taken and the overall survey strategy. To understand how these components impact the nature
of the LSST data the simulations group is developing a framework for high fidelity simulations that scale to the volume
of data expected from the LSST. This framework comprises galaxy, stellar and solar system catalogs designed to match
the depths and properties of the LSST (to r=28), transient and moving sources, and image simulations that ray-trace the
photons from above the atmosphere through the optics and to the camera. We describe here the state of the current
simulation framework and its computational challenges.
KEYWORDS: Telescopes, Radon, Information operations, Sensors, Space telescopes, Astronomy, Astronomical imaging, Current controlled current source, Denoising, Stars
We report on long exposure results obtained with a Teledyne HyViSI H2RG detector operating in guide mode. The sensor simultaneously obtained nearly seeing-limited data while also guiding the Kitt Peak 2.1 m telescope. Results from unguided and guided operation are presented and used to place lower limits on flux/fluence values for accurate centroid measurements. We also report on significant noise reduction obtained in recent laboratory measurements that should further improve guiding capability with higher magnitude stars.
The LSST camera is a wide-field optical (0.35-1μm) imager designed to provide a 3.5 degree FOV with 0.2
arcsecond/pixel sampling. The detector format will be a circular mosaic providing approximately 3.2 Gigapixels per
image. The camera includes a filter mechanism and shuttering capability. It is positioned in the middle of the telescope
where cross-sectional area is constrained by optical vignetting and where heat dissipation must be controlled to limit
thermal gradients in the optical beam. The fast f/1.2 beam will require tight tolerances on the focal plane mechanical
assembly. The focal plane array operates at a temperature of approximately -100°C to achieve desired detector performance. The
focal plane array is contained within a cryostat which incorporates detector front-end electronics and thermal control.
The cryostat lens serves as an entrance window and vacuum seal for the cryostat. Similarly, the camera body lens serves
as an entrance window and gas seal for the camera housing, which is filled with a suitable gas to provide the operating
environment for the shutter and filter change mechanisms. The filter carousel accommodates 5 filters, each 75 cm in diameter, for rapid exchange without external intervention.
We present the first astronomical results from a 4K2 Hybrid Visible Silicon PIN array detector (HyViSI) read out
with the Teledyne Scientific and Imaging SIDECAR ASIC. These results include observations of astronomical
standards and photometric measurements using the 2.1m KPNO telescope. We also report results from a test
program in the Rochester Imaging Detector Laboratory (RIDL), including: read noise, dark current, linearity,
gain, well depth, quantum efficiency, and substrate voltage effects. Lastly, we highlight results from operation of
the detector in window read out mode and discuss its potential role for focusing, image correction, and use as a
telescope guide camera.
The LSST camera is a wide-field optical (0.35-1um) imager designed to provide a 3.5 degree FOV with better than 0.2 arcsecond sampling. The detector format will be a circular mosaic providing approximately 3.2 Gigapixels per image. The camera includes a filter mechanism and, shuttering capability. It is positioned in the middle of the telescope where cross-sectional area is constrained by optical vignetting and heat dissipation must be controlled to limit thermal gradients in the optical beam. The fast, f/1.2 beam will require tight tolerances on the focal plane mechanical assembly.
The focal plane array operates at a temperature of approximately -100°C to achieve desired detector performance. The focal plane array is contained within an evacuated cryostat, which incorporates detector front-end electronics and thermal control. The cryostat lens serves as an entrance window and vacuum seal for the cryostat. Similarly, the camera body lens serves as an entrance window and gas seal for the camera housing, which is filled with a suitable gas to provide the operating environment for the shutter and filter change mechanisms. The filter carousel can accommodate 5 filters, each 75 cm in diameter, for rapid exchange without external intervention.
The most recent observations of the cosmic microwave background (e.g., WMAP) show that baryons contribute about 4% to the total density of the Universe. However at redshift less than or equal to 1, about half of these baryons have not yet been observed. Cosmological simulations predict that these "missing" baryons should be distributed in filaments, have temperatures of 105 to 107 K and overdensities of a few to hundred times the average baryon density, forming the so-called Warm-Hot Intergalactic Medium (WHIM). There is increasing evidence from Chandra and XMM-Newton that the WHIM may indeed exist. However it is clear that to map the morphology of the WHIM and to measure its physical conditions, a completely different class of instruments is required. Measuring the WHIM in emission in the soft X-ray band is a promising option. To detect the relatively weak, extended emission of the WHIM, the instrument should have a large grasp (collecting area times field of view), and an energy resolving power of about 500 at 1 keV is required to separate the emission of these large scale filaments from foreground emission.
We discuss a design that includes X-ray mirrors in combination with a large 2D cryogenic detector, which will allow us to map a significant fraction of this gas. Such detector and its read-out based on Frequency Domain Multiplexing, are currently under development at SRON. It seems feasible to build an array of 24 x 24 pixels of TES microcalorimeters with good energy resolution (few eV). This detector will be combined with a mirror design which is based on 2 and 4 reflections and gives a large area (> 500 cm2) over a relatively large field of view. A preliminary study of the mission concept indicates that this can be implemented in a relatively small satellite (total weight 650 kg). While the main goal of this satellite will be to map and study the physical properties of the missing baryons, the instrument's large area and large field of view will also result in major progress in related fields.
Michael Sholl, Michael Lampton, Greg Aldering, W. Althouse, R. Amanullah, James Annis, Pierre Astier, Charles Baltay, E. Barrelet, Stephane Basa, Christopher Bebek, Lars Bergstrom, Gary Bernstein, Manfred Bester, Bruce Bigelow, Roger Blandford, Ralph Bohlin, Alain Bonissent, Charles Bower, Mark Brown, Myron Campbell, William Carithers, Eugene Commins, W. Craig, C. Day, F. DeJongh, Susana Deustua, T. Diehl, S. Dodelson, Anne Ealet, Richard Ellis, W. Emmet, D. Fouchez, Josh Frieman, Andrew Fruchter, D. Gerdes, L. Gladney, Gerson Goldhaber, Ariel Goobar, Donald Groom, Henry Heetderks, M. Hoff, Stephen Holland, M. Huffer, L. Hui, Dragan Huterer, B. Jain, Patrick Jelinsky, Armin Karcher, Steven Kahn, Steven Kent, Alex Kim, William Kolbe, B. Krieger, G. Kushner, N. Kuznetsova, Robin Lafever, J. Lamoureux, Olivier Le Fevre, Michael Levi, P. Limon, Huan Lin, Eric Linder, Stewart Loken, W. Lorenzon, Roger Malina, J. Marriner, P. Marshall, R. Massey, Alain Mazure, Timothy McKay, Shawn McKee, Ramon Miquel, Nicholas Morgan, E. Mörtsell, Nick Mostek, Stuart Mufson, J. Musser, Peter Nugent, Hakeem Oluseyi, Reynald Pain, Nick Palaio, David Pankow, John Peoples, Saul Perlmutter, Eric Prieto, David Rabinowitz, Alexandre Refregier, Jason Rhodes, Natalie Roe, D. Rusin, V. Scarpine, Michael Schubnell, Gérard Smadja, Roger Smith, George Smoot, Jeffrey Snyder, Anthony Spadafora, A. Stebbins, Christopher Stoughton, Andrew Szymkowiak, Gregory Tarlé, Keith Taylor, A. Tilquin, Andrew Tomasch, Douglas Tucker, D. Vincent, Henrik von der Lippe, Jean-Pierre Walder, Guobin Wang, W. Wester
Mission requirements, the baseline design, and optical systems budgets for the SuperNova/Acceleration Probe (SNAP) telescope are presented. SNAP is a proposed space-based experiment designed to study dark energy and alternate explanations of the acceleration of the universe’s expansion by performing a series of complementary systematics-controlled astrophysical measurements. The goals of the mission are a Type Ia supernova Hubble diagram and a wide-field weak gravitational lensing survey. A 2m widefield three-mirror telescope feeds a focal plane consisting of 36 CCDs and 36 HgCdTe detectors and a high-efficiency, low resolution integral field spectrograph. Details of the maturing optical system, with emphasis on structural stability during terrestrial testing as well as expected environments during operations at L2 are discussed. The overall stray light mitigation system, including illuminated surfaces and visible objects are also presented.
Anne Ealet, Eric Prieto, Alain Bonissent, Roger Malina, Gérard Smadja, A. Tilquin, Gary Bernstein, Stephane Basa, D. Fouchez, Olivier Le Fevre, Alain Mazure, Greg Aldering, R. Amanullah, Pierre Astier, E. Barrelet, Christopher Bebek, Lars Bergstrom, Manfred Bester, Roger Blandford, Ralph Bohlin, Charles Bower, Mark Brown, Myron Campbell, William Carithers, Eugene Commins, W. Craig, C. Day, F. DeJongh, Susana Deustua, H. Diehl, S. Dodelson, Richard Ellis, M. Emmet, Josh Frieman, Andrew Fruchter, D. Gerdes, L. Gladney, Gerson Goldhaber, Ariel Goobar, Donald Groom, Henry Heetderks, M. Hoff, Stephen Holland, M. Huffer, L. Hui, Dragan Huterer, B. Jain, Patrick Jelinsky, Armin Karcher, Steven Kent, Steven Kahn, Alex Kim, William Kolbe, B. Krieger, G. Kushner, N. Kuznetsova, Robin Lafever, J. Lamoureux, Michael Lampton, Michael Levi, P. Limon, Huan Lin, Eric Linder, Stewart Loken, W. Lorenzon, J. Marriner, P. Marshall, R. Massey, Timothy McKay, Shawn McKee, Ramon Miquel, Nicholas Morgan, E. Mörtsell, Nick Mostek, Stuart Mufson, J. Musser, Peter Nugent, Hakeem Oluseyi, Reynald Pain, Nick Palaio, David Pankow, John Peoples, Saul Perlmutter, David Rabinowitz, Alexandre Refregier, Jason Rhodes, Natalie Roe, D. Rusin, V. Scarpine, Michael Schubnell, Michael Sholl, Roger Smith, George Smoot, Jeffrey Snyder, Anthony Spadafora, A. Stebbins, Christopher Stoughton, Andrew Szymkowiak, Gregory Tarlé, Keith Taylor, Andrew Tomasch, Douglas Tucker, Henrik von der Lippe, D. Vincent, Jean-Pierre Walder, Guobin Wang, W. Wester
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Iz supernovae and to standardize the magnitude of each candidate by determining explosion parameters. The spectrograph is also a key element for the calibration of the science mission. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have high efficiency and low spectral resolution (R~100), constant through the wavelength range (0.35-1.7μm), adapted to the scientific goals of the mission.
A very significant fraction of the baryonic matter in the local universe is predicted to form a Warm Hot Intergalactic Medium (WHIM) of very low density, moderately hot gas, tracing the cosmic web. Its X-ray emission is dominated by metal features, but is weak (< 0.01 photons/cm2/s/sr) and potentially hard to separate from the galactic component. However, a mission capable of directly mapping this component of the large scale structure of the universe, via a small number of well chosen emission lines, is now within reach due to recent improvements in cryogenic X-ray detector energy resolution. To map the WHIM, the energy resolution and grasp are optimized. A number of missions have been proposed to map the missing baryons including MBE (US/SMEX program) and DIOS (Japan). The design of the mirror and detector have still room for improvements which will be discussed. With these improvements it is feasible to map a 10 x 10 degree area of the sky in 2 years out to z = 0.2 with sufficient sensitivity to directly detect WHIM structure, such as filaments connecting clusters of galaxies. This structure is predicted by the current Cold Dark Matter paradigm which thus far appears to provide a good description of the distribution of matter as traced by galaxies.
The ESA mission XMM-Newton was launched in 1999. Two of the three X-ray telescopes include reflection grating spectrometers (RGS). These spectrometers consist of a set of reflection gratings and an array of 9 back-illuminated CCDs, optimized for the soft energy response (0.35 - 2 keV). These CCDs can be passively cooled between -80 and -120°C. After a short description of the instrument we compare the performance of these CCD detectors with the pre-flight expectations and discuss the effect of some design choices on the in-flight performance. We concentrate on the effects of radiation damage due to cosmic rays and coronal mass ejections of the Sun, including flickering pixels and the effects of cooling the detector to -110°C. We also address the stability of the detector response including the assessment of possible contamination of these cooled detectors.
The 8.4m Large Synoptic Survey Telescope (LSST) is a wide-field telescope facility that will add a qualitatively new capability in astronomy. For the first time, the LSST will provide time-lapse digital imaging of faint astronomical objects across the entire sky. The LSST has been identified as a national scientific priority by diverse national panels, including multiple National Academy of Sciences committees. This judgment is based upon the LSST's ability to address some of the most pressing open questions in astronomy and fundamental physics, while driving advances in data-intensive science and computing. The LSST will provide unprecedented 3-dimensional maps of the mass distribution in the Universe, in addition to the traditional images of luminous stars and galaxies. These mass maps can be used to better understand the nature of the newly discovered and utterly mysterious Dark Energy that is driving the accelerating expansion of the Universe. The LSST will also provide a comprehensive census of our solar system, including potentially hazardous asteroids as small as 100 meters in size. The LSST facility consists of three major subsystems: 1) the telescope, 2) the camera and 3) the data processing system. The baseline design for the LSST telescope is a 8.4m 3-mirror design with a 3.5 degree field of view resulting in an A-Omega product (etendue) of 302deg2m2. The camera consists of 3-element transmisive corrector producing a 64cm diameter flat focal plane. This focal plane will be populated with roughly 3 billion 10μm pixels. The data processing system will include pipelines to monitor and assess the data quality, detect and classify transient events, and establish a large searchable object database. We report on the status of the designs for these three major LSST subsystems along with the overall project structure and management.
Cosmic soft X-ray spectroscopy exploits principal transitions of astrophysically abundant elements to infer physical properties of objects in the sky. Most of these transitions, however, fall well below 2 keV, or 6 Angstroms. Consquently, grating spectrometers offer the current, best means by which to analyze soft X-rays from such sources, where throughput and resolving power must be maximized together. We describe grating spectrometer design candidates for the future mission Constellation-X, and how the grating array on board (~1000 gratings in a 1600mm diameter, each for 4 instruments) may be implemented. Grating fabrication and grating alignment approaches require special consideration (over the XMM-Newton RGS experience), because of grating replication fidelity and instrument mass constraints.
XMM-Newton was launched in December 1999 and science operations started in March 2000. Following two years of very successful operations, a report on the instrument performance and a selection of exciting new results are presented. Behind two of the three telescopes of XMM-Newton Reflection Grating Spectrometers (RGS) are placed. Each spectrometer consists of an array of reflection gratings and a set of back illuminated CCDs. They cover the wavelength band between 6 and 38 Angstromwith a resolution varying between 100 and 600 (E/DE) and a maximum effective area of 140 cm2 for the two spectrometers combined. The selected wavelength band covers the K-shell transitions of C, N, O, Ne, Mg and Si as well as the L- and M-shell transitions of Fe. After a short introduction to the instrument design, the in-orbit performance is given. This includes the line spread function, the wavelength scale and the effective area including their stability during the more than 2 years of operations. Following this a number of key scientific results are briefly addressed, illustrating the power of the RGS instrument in combination with the other instruments on-board of XMM-Newton as well as the wealth of information which is obtained as the RGS instruments operate continuously.
The proposed Reflection Grating Spectrometer (RGS) on the Constellation-X mission is designed to provide high-resolution x-ray spectroscopy of astrophysical sources. Two types of reflection grating geometries have been proposed for the RGS. In-plane gratings have relatively low-density rulings (~500 lines/mm) with lines perpendicular to the plane of incidence, thus dispersing x-rays into the plane. This geometry is similar to the reflection grating spectrometer flown on the X-ray Multi-Mirror (XMM) mission. Off-plane, or conical, gratings require much higher density rulings (>5000 lines/mm) with lines parallel to the plane of incidence, thus dispersing x-rays perpendicular to the plane. Both types present unique challenges and advantages and are under intensive development. In both cases, however, grating flatness and assembly tolerances are driven by the mission's high spectral resolution goals and the relatively poor resolution of the Wolter foil optics of the Spectroscopy X-ray Telescope (SXT) that is used in conjunction with the RGS. In general, to achieve high spectral resolution, both geometries require lightweight grating substrates with arcsecond flatness and assembly tolerances. This implies sub-micron accuracy and precision which go well beyond that achieved with previous foil optic systems. Here we present a progress report of technology development for the precision shaping, assembly and metrology of the thin, flat grating substrates.
We describe a new technical approach for observations of Galactic and extra-Galactic soft X-ray sources with ultra-high angular resolution. The technique is based on the use of recently developed diffraction-limited, normal-incidence mirror substrates and ultra-short-period multilayer coatings, tuned to specific bright emission lines in the range 16 < l < 40 Å, for the construction of a diffraction-limited X-ray telescope. Sub-milliarcsecond resolution could be achieved in a moderately-sized Cassegrain or prime-focus geometry, while resolution of order 0.01 microarcseconds could be achieved using a synthetic aperture X-ray interferometer constructed from an array of such telescopes spread over a 50 km baseline. We describe our technical approach in detail and outline some of the observations that would become possible with the proposed instrumentation.
KEYWORDS: Monte Carlo methods, Data modeling, Photons, X-rays, Spectrometers, Dispersion, Roentgenium, Galaxy groups and clusters, Charge-coupled devices, 3D modeling
We discuss multivariate Monte Carlo methods appropriate for X-ray dispersive spectrometers. Dispersive spectrometers have many advantages for high resolution spectroscopy in the X-ray band. Analysis of data from these instruments is complicated by the fact that the instrument response functions are multi-dimensional and relatively few X-ray photons are detected from astrophysical sources. Monte Carlo methods are the natural solution to these challenges, but techniques for their use are not well developed. We describe a number of methods to produce a highly efficient and flexible multivariate Monte Carlo. These techniques include multi-dimensional response interpolation and multi-dimensional event comparison. We discuss how these methods have been extensively used in the XMM-Newton Reflection Grating Spectrometer in-flight calibration program. We also show several examples of a Monte Carlo applied to observations of clusters of galaxies and elliptical galaxies with the XMM-Newton observatory.
The XRS instrument on Astro-E is a fully self-contained microcalorimeter x-ray instrument capable of acquiring, optimally filtering, and characterizing events for 32 independent pixels. We have recently integrated a full engineering model XRS detector system into a laboratory cryostat for use on the electron beam ion trap (EBIT) at Lawrence Livermore National Laboratory. The detector system contains a microcalorimeter array with 32 instrumented pixels heat sunk to 60 mK using an adiabatic demagnetization refrigerator. The instrument has a composite resolution of 8 eV at 1 keV and 11 eV at 6 keV with a minimum of 98% quantum efficiency and a total collecting area of 13 mm2. This will allow high spectral resolution, broadband observations of plasmas with known ionization states that are produced in the EBIT experiment. Unique to our instrument are exceptionally well characterized 1000 Angstrom thick aluminum on polyimide infrared blocking filters. The detailed transmission function including the edge fine structure of these filters has been measured in our laboratory using a variable spaced grating spectrometer. This will allow the instrument to perform the first broadband absolute flux measurements with the EBIT instrument. The instrument performance as well as the results of preliminary measurements of Fe K and L shell at fixed electron energy, Fe emission with Maxwellian electron distributions, and phase resolved spectroscopy of ionizing plasmas will be discussed.
The activities during the instrument calibrations are summarized and first data are presented. The main instrument features, the line-spread function and the effective area, are discussed and the status of the in-flight calibrations is summarized.
The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers behind two of its three nested sets of Wolter I type mirrors. The instrument allows high-resolution (E/(Delta) E equals 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum effective area of about 150 cm2 at 15 A. The satellite was successfully launched on December 10, 1999, from Guyana Space Center. Following the launch the instrument commissioning was started early in 2000. First results for the Reflection Grating Spectrometers are presented concentrating on instrumental parameters such as resolution, instrument background and CCD performance. The instrument performance is illustrated by first results from HR 1099, a non-eclipsing RS CVn binary.
The optical chain of the spectroscopic x-ray telescopes aboard the Constellation-X spacecraft employs a reflective grating spectrometer to provide high resolution spectra for multiple spectra as a slitless spectrometer in the spectral feature rich, soft x-ray band. As a part of the spectroscopic readout array, we provide a zero-order camera that images the sky in the soft band inaccessible to the microcalorimeters. Technological enhancements required for producing the RGS instruments are described, along with prototype development progress, fabrication and testing results.
The Reflection Grating Spectrometer (RGS) aboard XMM is a large collecting area, dispersive soft x-ray spectrometer providing high resolution and a bandpass of 5-35 angstrom. We have built and characterized the two, nearly identical, flight model reflection grating arrays for the RGS instrument. Precision alignment and assembly of 182 grating elements into each array was performed at Columbia Astrophysics/Nevis Laboratory, and end-to-end X-ray calibration and testing were performed at the MPE-Panter facility. Preliminary results from the calibration are summarized, and reconciliation of those results with baseline optical design, simulations and error budgets are discussed.
Elena Aprile, Valeri Egorov, Karl-Ludwig Giboni, Steven Kahn, Tomotake Kozu, Uwe Oberlack, S. Centro, Sandro Ventura, Tadayoshi Doke, Jun Kikuchi, Edward Chupp, Philip Dunphy, Dieter Hartmann, Mark Leising, H. Bloemen
XENA is a new Compton telescope concept, designed to image about 50% of the gamma-ray sky with a sensitivity that would significantly surpass CGRO/COMPTEL's multi-year sensitivity with a 2 weeks balloon flight from the Southern Hemisphere. The detector, based on liquid xenon time-projection chambers, is optimized for approximately 0.3 - 10 MeV and combines high efficiency within a 3 sr field-of-view with approximately 1 degree(s) angular resolution and excellent background reduction capability. XENA's primary scientific goal is the discovery and mapping of 60Fe radioactivity from the Galaxy, which is pivotal for understanding nucleosynthesis. XENA will detect 60Fe even if current predictions are 7X overestimated. At 1.8 MeV, XENA's sensitivity (6 10-6 cm-2 s-1) will significantly refine the COMPTEL 26Al mapping along the Southern Milky Way. Also, XENA would be the first instrument capable to decide whether the 3 - 7 MeV excess seen in Orion is indeed due to nuclear lines from 12C and 16O, and it could discover the predicted lower-energy lines. The scanned sky area includes many continuum (gamma) -ray sources as well, such as pulsars and numerous (gamma) -ray AGNs. Secondary scientific objectives include also supernova remnants, gamma-ray bursts, and solar flares.
The x-ray multi-mirror (XMM) mission is the second of four cornerstone projects of the ESA long-term program for space science, Horizon 2000. The payload comprises three co- aligned high-throughput, imaging telescopes with a FOV of 30 arcmin and spatial resolution less than 20 arcsec. Imaging CCD-detectors (EPIC) are placed in the focus of each telescope. Behind two of the three telescopes, about half the x-ray light is utilized by the reflection grating spectrometer (RGS). The x-ray instruments are co-aligned and measure simultaneously with an optical monitor (OM). The RGS instruments achieve high spectral resolution and high efficiency in the combined first and second order of diffraction in the wavelength range between 5 and 35 angstrom. The design incorporates an array of reflection gratings placed in the converging beam at the exit from the x-ray telescope. The grating stack diffracts the x-rays to an array of dedicated charge-coupled device (CCD) detectors offset from the telescope focal plane. The cooling of the CCDs is provided through a passive radiator. The design and performance of the instrument are described below.
The reflection grating spectrometer (RGS) on-board the x-ray multi-mirror (XMM) mission incorporates an array of reflection gratings oriented at grazing incidence in the x- ray optical path immediately behind a grazing incidence telescope. Dispersed light is imaged on a strip of CCD- detectors slightly offset from the telescope focal plane. The grating array picks off roughly half the light emanating from the telescope; the other half passes undeflected through the array where it is imaged by the European photon imaging camera (EPIC) experiment. XMM carries two such identical units, plus a third telescope with an EPIC detector, but no RGS. The basic elements of the RGA include: 202 identical reflection gratings, a set of precision rails with bosses that determine the position and alignment of each grating, a monolithic beryllium integrating structure on which the rails are mounted, and a set of three, kinematic support mounts which fix the array to the telescope. In this paper, we review our progress on the fabrication and testing of the RGA hardware, with particular attention to the components comprising the engineering qualification model, a flight-representative prototype which will be completely assembled in September of this year.
The High Throughput X-ray Spectroscopy (HTXS) mission is dedicated to observations at high spectral resolution. The HXTS mission represented a major advanced, providing as much as a factor of 100 increase in sensitivity over currently planned high resolution X-ray spectroscopy missions. This X- ray equivalent of the Keck Telescope will mark the start of a new era when high quality X-ray spectral will be obtained for all classes of X-ray sources, over a wide range of luminosity and distance. With its increased capabilities, HTXS will address many fundamental astrophysics questions such as the origin and distribution of the elements from carbon to zinc, the formation and evolution of clusters of galaxies, the validity of general relativity in the strong gravity limit, the evolution of supermassive black holes in active galactic nuclei, the details of supernova explosions and their aftermath, and the mechanisms involved in the heating of stellar coronae and driving of stellar winds.
We obtained monochromatic emission line images with a prototype model of the Reflection Grating Spectrometer for XMM, at the MPE Panter long beam test facility in Munich. We concentrate on the interpretation and analysis of the distribution of dispersed light from single gratings. We present the outline of an exact first order scalar diffraction calculation of the effects of scattering on a grating on the angular profile of the dispersed radiation. Using the resulting predicted scattering profile, we extract the core of the measured profiles for individual gratings, and find good agreement between the shape of these cores and the shape predicted for the long-spatial wavelength slope distribution on the gratings, obtained from interferometry. The widths of the cores meet the specifications for the flatness of the grating substrates.
A prototype array consisting of eight diffraction gratings has been fabricated for the XMM Reflection Grating Spectrometer. A component of the full spectrometer is an array of approximately 200 diffraction gratings. The diffraction gratings were produced using lightweight silicon carbide substrates and a replication technique. The prototype array was developed and assembled using the same tolerances as the flight arrays which have typical tolerances of 3 micrometers in translation and sub-arc seconds in rotation. The metrology applied during inspection and assembly included precision linear measurements, full aperture figure measurements, and angular interferometry.
X-ray calibration of the Electro-Optical Breadboard Model (EOBB) of the XMM Reflection Grating Spectrometer has been carried out at the Panter test facility in Germany. The EOBB prototype optics consisted of a four-shell grazing incidence mirror module followed by an array of eight reflection gratings. The dispersed x-rays were detected by an array of three CCDs. Line profile and efficiency measurements were made at several energies, orders, and geometric configurations for individual gratings and for the grating array as a whole. The x-ray measurements verified that the grating mounting method would meet the stringent tolerances necessary for the flight instrument. Post EOBB metrology of the individual gratings and their mountings confirmed the precision of the grating boxes' fabrication. Examination of the individual grating surface's at micron resolution revealed the cause of anomalously wide line profiles to be scattering due to the crazing of the replica's surface.
The Reflection Grating Spectrometer (RGS) onboard the ESA satellite XMM (X-ray Multi Mirror mission) combines a high resolving power (approximately 400 at 0.5 keV) with a large effective area (approximately 200 cm2). The spectral range selected for RGS (5 - 35 angstroms) contains the K shell transitions of N, O, Ne, Mg, Al, Si and S as well as the important L shell transitions of FE. The resolving power allows the study of a wide variety of challenging scientific questions. Detailed temperature diagnostics are feasible as the ionization balance is a unique function of the distribution of the electron temperature. Density diagnostics are provided by studying He-like triplets where the ratio of the forbidden to intercombination lines varies with density. Other fields of interest include the determination of elemental abundances, the study of optical depth effects, velocity diagnostics by measuring Doppler shifts and the estimate of magnetic fields through the observation of Zeeman splitting. The resolving power is obtained by an array of 240 gratings placed behind the mirrors of the telescope, dispersing about half of the X-rays in two spectroscopic orders. The X-rays are recorded by an array of 9 large format CCDs. These CCDs are operated in the frame transfer mode. They are back illuminated as the quantum efficiency of front illuminated devices is poor at low energies because of their poly-silicon gate structure. To suppress dark current the CCDs are passively cooled. In order to obtain the effective area of about 200 cm2, grating arrays and CCD cameras are placed behind two of the three XMM telescopes. A model of RGS was tested last autumn ('93) at the Panter long beam X-ray facility in Munich. The model consisted of a subset of four mirrors, eight representative gratings covering a small section of the inner mirror shells and a CCD camera containing three CCDs. The purpose of these tests was to verify the resolution and sensitivity of the instrument as a function of X-ray energy. Extensive simulations, using a Monte Carlo raytracing code, are used to interpret these tests. Preliminary results of these tests will be discussed and compared to the calculated response.
The X Ray Multimirror Mission will include a spectrometer consisting of two arrays of variable line-spaced reflection gratings for use in the 350 eV to 2.5 keV energy range. Approximately 720 replica gratings will be needed for two flight grating arrays and one spare. Evaluation of potential master gratings to be used in the replication process has begun. Both reflectivity and scattering x-ray measurements for three mechanically ruled prototype master gratings have been reported.
The Reflection Grating Spectrometer Experiment (RGS), which has been selected for flight on the
European Space Agency's X-Ray Multi-Mirror Mission (XMM), includes two arrays of reflection gratings
that are placed in the X-ray optical path behind two separate grazing incidence X-ray telescopes. Each of
the grating arrays picks off roughly half the X-ray light emanating from its telescope and diffracts it to a
dedicated strip of charge-coupled device (CCD) detectors offset from the telescope focal plane. The arrays
contain 224 100 mm X 200 mm gratings, each mounted at a graze angle of 1.58° to the incident beam.
The gratings are produced by epoxy replication of a common master onto very thin substrates. Both the
gratings and the detectors are mounted on a Rowland circle which also includes the telescope focus. In
this paper, we review the current state of both the engineering and the optical designs for the grating
arrays.
This paper discusses the optimization of the performance of imaging scintillation detectors used in the hard X-ray/soft gamma-ray (20-300) keV region of the spectrum. In these devices, absorption of an incident gamma-ray within an alkali halide crystal induces a scintillation light distribution which is centroided by an imaging photomultiplier tube mounted to the crystal. The ultimate imaging resolution is strongly affected by the detailed propagation of the scintillation light within the crystal and at the interface between the crystal and the phototube face plate. A number of refined techniques for preparing the scintillation crystals so as to optimize the imaging resolution have been investigated. The results indicate very good agreement with relatively simple models of the light propagation. It is shown that it is possible to achieve resolution consistent with the most optimistic models.
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.