X-ray Space Telescopes Research Articles

Ultra light-weight and high-resolution X-ray mirrors using DRIE and X-ray LIGA techniques for space X-ray telescopes

We are developing novel ultra light-weight and high-resolution X-ray micro pore optics for space X-ray telescopes. In our method, curvilinear micro pore structures are firstly fabricated by silicon deep reactive ion etching (DRIE) or X-ray LIGA processes. Secondly, side walls of the micro structures are smoothed by magnetic field assisted finishing and/or hydrogen annealing techniques for high reflectivity mirrors. Thirdly, to focus parallel X-ray lights from astronomical objects, these structures are elastically or plastically bent into a spherical shape. Fourthly, the bent structures are stacked to form a multi-stage X-ray telescope. In this paper, we report on fabrication and X-ray reflection tests of silicon and nickel X-ray mirrors using the DRIE and LIGA processes, respectively. For the first time, X-ray reflections were confirmed on both of the mirrors. Estimated rms roughnesses were 5 nm and 3 nm for the silicon and nickel mirrors, respectively.

Design for robustness using the [formula omitted]-synthesis applied to launcher attitude and vibration control

The M-V launch vehicle of Japan Aerospace Exploration Agency (JAXA) has successfully injected Japan's fifth X-ray space telescope “SUZAKU” into its low earth orbit in this past July. The attitude and vibration control algorithm of the M-V rocket used to be highlighted by its H ∞ robust stability since its first flight conducted in 1997. Beyond this, its robustness character has been further enhanced using the μ -synthesis approach to get better robust characteristics not only in stability but in tracking performance under uncertainty of the system dynamics. The performance has been validated by the latest back-to-back successful flights of the vehicle: in May 2003 to directly inject Japan's first asteroid sample return spaceship “HAYABUSA” into the planned inter-planetary trajectory and in this past July to launch the telescope. The μ -synthesis has been applied for the first time ever for Japan's launcher control beyond the reliable H ∞ design. The plant dynamics has an extremely high-order and unstable characteristics, thus the standard μ -synthesis format cannot be directly applied. The paper gives a unique methodology to apply the theory to such a real high-order complicated system.

A sealed Gas Pixel Detector for X-ray astronomy

We report on the results of a new, sealed Gas Pixel Detector. The very compact design and the absence of the gas flow system make this detector substantially ready for use as focal plane detector for future X-ray space telescopes. The instrument brings high sensitivity to X-ray polarimetry, which is the last unexplored field of X-ray astronomy. It derives the polarization information from the track of the photoelectrons that are imaged by a high-gain (>1000), fine pitch GEM that matches the pitch of a pixel ASIC which is the collecting anode of the GPD (105k, 50 μm wide, hexagonal cells). The device is able to simultaneously perform good imaging (50–60 μm), moderate spectroscopy (∼15% at 6 keV) as well as fast, high-rate timing in the 1–10 keV range. Moreover, being truly 2D, it is non-dispersive and does not require any rotation. The great improvement of sensitivity, at least two orders of magnitude with respect to traditional polarimeters (based on Bragg crystals or Thomson scattering), will allow the direct exploration of the most dramatic objects of the X-ray sky. At the focus of the large mirror area of the XEUS telescope it will be decisive in reaching many of the scientific goals of the mission. With integration times of the order of 1 day, polarimetry of Active Galactic Nuclei at the percent level will be possible, making for a real breakthrough in high-energy astrophysics.

Imaging few keV photoelectrons tracks with Gas Pixel Detectors

We report on the results of a new, sealed, Gas Pixel Detector. The very compact design and the absence of the gas flow system, make this detector substantially ready for use as focal plane detector for future X-ray space telescopes and other applications in soft X-ray science. The instrument brings high sensitivity to X-ray polarimetry, which is the last unexplored field of X-ray astronomy. It derives the polarization information from the track of the photoelectrons that are imaged by a high gain (>1000), fine pitch GEM that matches the pitch of a pixel ASIC which is the collecting anode of the GPD (105k, 50 μm wide, hexagonal cells). The device is able to simultaneously perform good imaging (50÷60 μm), moderate spectroscopy (∼18% at 6 keV) as well as fast, high rate timing in the 1-10keV range. Moreover, being truly 2D, it is non dispersive and does not require any rotation. The great improvement of sensitivity, at least two orders of magnitude with respect to traditional polarimeters (based on Bragg crystals or Thomson scattering), will allow the direct exploration of the most dramatic objects of the X-ray sky. At the focus of the large mirror area of the XEUS telescope it will be decisive in reaching many of the scientific goals of the mission. With integration times of the order of one day, polarimetry of Active Galactic Nuclei at the per cent level will be possible, making for a real breakthrough in high energy astrophysics

Si and Glass - Novel Technologies for Space

The thermally formed thin glass foils and optically shaped Si wafers are considered to belong to the most promising technologies for future large space X-ray telescopes. We present and discuss the recent progress in these technologies, as well as properties of test mirrors produced and tested.

Unresolved X-ray background: clues on galactic nuclear activity at z > 6

We study, by means of dedicated simulations of massive black hole build-up, the possibility to constraint the existence and nature of the active galactic nucleus (AGN) population at z ≥ 6 with available and planned X-ray and near-infrared space telescopes. We find that X-ray deep field observations can set important constraints to the faint-end of the AGN luminosity function at very high redshift. Planned X-ray telescopes should be able to detect AGN hosting black holes with masses down to ≥10 5 M ⊙ (i.e. X-ray luminosities in excess of 10 42 erg s -1 ), and can constrain the evolution of the population of massive black hole at early times (6 ≤ z ≤ 10). We find that this population of AGN should contribute substantially (∼25 per cent) to the unresolved fraction of the cosmic X-ray background in the 0.5-10 keV range, and that a significant fraction (∼3-4 per cent) of the total background intensity would remain unaccounted even after future X-ray observations. As byproduct, we compute the expected ultraviolet background from AGN at z ≥ 6, and we discuss the possible role of AGN in the reionization of the Universe at these early epochs, showing that AGN alone can provide enough ionizing photons only in the (improbable) case of an almost completely homogeneous intergalactic medium. Finally, we show that super-Eddington accretion, suggested by the observed quasi-stellar objects at z ≃ 6, must be a very rare event, confined to black holes living in the highest density peaks.

Late‐Time X‐Ray, UV, and Optical Monitoring of Supernova 1979C

We present results from observations of supernova (SN) 1979C with the Newton X-Ray Multi-Mirror (XMM-Newton) mission in X-rays and in UV, archival X-ray, and Hubble Space Telescope (HST) data, and follow-up ground-based optical imaging. The XMM-Newton MOS spectrum shows the best-fit two-temperature thermal plasma emission characteristics of both the forward (kT(high) = 4:1(-2.4)(+76) keV) and reverse shock (kT(low) = 0.79(-0.17)(+0.24) keV) with no intrinsic absorption. The long-term X-ray light curve, constructed from all X-ray data available, reveals that SN 1979C is still radiating at a flux level similar to that detected by ROSAT in 1995, showing no sign of a decline over the last 6 years, some 16-23 yr after its outburst. The high inferred X-ray luminosity (L(0.3-2) = 8 x 10(38) ergs s(-1)) is caused by the interaction of the SN shock with dense circumstellar matter, likely deposited by a strong stellar wind from the progenitor with a high mass- loss rate of. M approximate to 1.5 x 10(-4) M(circle dot) yr(-1) (v(w)/10 km s(-1)). The X-ray data support a strongly decelerated shock and show a mass-loss rate history that is consistent with a constant progenitor mass-loss rate and wind velocity over the past greater than or similar to 16,000 yr in the stellar evolution of the progenitor. We find a best-fit circumstellar medium (CSM) density profile of rho(CSM) proportional to r(-s) with index s less than or similar to 1.7 and high CSM densities (greater than or similar to 10(4) cm(-3)) out to large radii from the site of the explosion (r greater than or similar to 4 x 10(17) cm). Using XMM-Newton Optical Monitor data, we further detect a pointlike optical/UV source consistent with the position of SN 1979C, with B-, U-, and UVW1-band luminosities of 5, 7, and 9 x 10(36) ergs s(-1), respectively. The young stellar cluster in the vicinity of the SN, as imaged by the HSTand follow- up ground- based optical imaging, can only provide a fraction of the total observed flux, so that a significant contribution to the output likely arises from the strong interaction of SN 1979C with dense CSM.

Soft X-ray sources at the centers of the elliptical galaxies NGC 4472 and NGC 4649

Analysis of recent observations of the elliptical galaxies NGC 4472 and NGC 4649 with the Chandra X-ray space telescope has revealed faint soft X-ray sources at their centers. The sources are located at the galactic centers, to within 1″, and are most likely associated with the radiation from the supermassive black holes that are assumed to be at the optical centers of these galaxies. Interest in these and several other similar objects stems from the unusually low luminosity of the supermassive black hole embedded in a dense interstellar medium. The sources have soft energy spectra in the Chandra energy range 0.2–10 keV. The source is detected at a 3σ confidence level only in the range 0.2–0.6 keV with a luminosity of ∼6×1037 erg s−1 in NGC 4649 and in the range 0.2–2.5 keV with a luminosity of ∼ 1.7×1038 erg −1 in NGC 4472.

Class separation and parameter estimation with neural networks for the XEUS wide field imager

The X-ray space telescope XEUS is the proposed follow-up project to ESA's cornerstone mission XMM-Newton which is now in orbit. To face the high data rate from the pixel detector and to improve event processing neural networks are under study to be integrated into the electronics on board (online) and to serve as analysis tool on ground (offline). For two applications results are presented. First as a typical online application, the separation of single photon events from pileup: here the unwanted event topologies are separated from useful ones belonging to a single X-ray photon. Second a typical off-line application, the estimation of the incident position of a photon: here the charge splitting (i.e. signal charges are collected by two or more adjacent pixels) can be used to determine a precise incident position of a photon. The neural network results are compared with standard methods.

Monochromatic X-ray source for calibrating X-ray telescopes

A quasi-monochromatic X-ray source for calibrating X-ray space telescopes was developed, manufactured and tested. The source consists of a powerful X-ray tube of an open type with changeable anode targets and a regulated double-crystal monochromator.

Parametric X-ray radiation for calibration of X-ray space telescopes and generation of several X-ray beams

The setup based on a moderate energy linear accelerator (linac) is proposed to provide users with a tunable, quasi-monochromatic, linearly polarized X-ray beam. The effect of parametric X-ray radiation (PXR) from relativistic electrons in a crystal is used in an X-ray source. The application of the setup for calibration of X-ray space telescopes and other equipment is considered. The setup allows calibration of angular, spectral, polarization parameters of telescopes with smooth tuning of X-ray energy from several keV to hundreds of keV. Estimates of X-ray flux intensities and spectral line widths on the telescope aperture at a distance of several hundred meters are presented. Besides, the PXR-based facility for simultaneous generation of several X-ray beams is proposed.

Microcomb design and fabrication for high accuracy optical assembly

There are two popular optic designs for x-ray space telescopes: the traditional monolithic design, which has demonstrated subarcsecond resolution but at enormous weight and cost per collecting area, and the foil design, which has achieved far greater collecting area per weight and cost, but with resolution limited to the arcminute level, in part due to foil assembly inaccuracy. In this article, we present the design and the fabrication of a novel micromechanical device, the so-called microcomb, which is used to assemble high-accuracy foil x-ray optics. To achieve submicron foil alignment accuracy, two types of microcombs have been fabricated via microelectromechanical systems technology. Reference combs provide highly accurate single-point contacts against which foils are registered, and spring combs provide the mechanical actuation needed to properly position and shape the foils. Briefly, we introduce some basic concepts regarding grazing-incidence x-ray optics. We then present a theoretical model that has given rise to the unique shape of the spring microcomb. Finally, the fabrication process used to produce the microcombs is discussed.

X-ray space technology for focusing small-angle neutron scattering and neutron reflectometry

In Jülich, a small-angle neutron scattering instrument and neutron reflectometer will be built, both of them use a double-focusing mirror, which produces an one-to-one image of the entrance on the detector. This neutron focusing technique, known since 50 years, has become practicable only recently, since very smooth mirror surfaces were produced for X-ray space telescopes. The neutron mirrors are produced by the same technique. The focusing is especially good for high-resolution experiments (with the momentum transfer Q<10 −3 Å −1). Compared to pinhole collimation, the focusing technique in this region has intensity advantages of several orders of magnitude. In this contribution mainly the influence of the shape of the mirror and the influence of gravity on the quality of the image is discussed. We explain, how these effects can be minimized.

Control system for giant X-ray space telescope

Control system for giant X-ray space telescope