Consistent improvements in the design and fabrication of thin-foil, epoxy-replicated x-ray mirrors for astronomical telescopes have yielded increasingly higher quality and more precise astrophysical data. The Neutron Star Interior Composition Explorer (NICER) x-ray timing mission optics continues this tradition and introduces design elements that promise even more accurate measurements and precise astrophysical parameters. The singly reflecting concentrators have a curved axial profile to improve photon concentration and a sturdy full shell structure for enhanced module stability. These design elements introduced the challenge of reliably forming mirror substrates at an acceptable production rate. By developing a technique using heat shrink tape to compress and conform thin aluminum mirror substrates to shaping mandrels, production rate improved with successful fabrication. The technique’s efficiency was analyzed by measuring hundreds of substrate profiles postforming, performance testing completely assembled concentrators composed of every size substrate, and comparing the results to simulated fabrication scenarios. On average, the profiles were copied within 4.6±3.7%. These measurements and the overall success of NICER’s optics, via ground calibration, have shown that the heat-shrink tape method is reliable, repeatable, and could be used in future missions to increase production rate and improve performance.
We performed a series of measurements using X-rays to assess the current performance of the Neutron star Interior Composition ExploreR (NICER) X-ray concentrators during the mission's concept study stage. NICER will use 56 grazing-incidence X-ray concentrators in the optical system with each module focusing the incoming photons to co-aligned silicon drift detectors with 2 mm apertures. Successful X-ray timing and navigation studies require optimal signal to noise, thus by optimizing high throughput concentrators with a large collecting area we can minimize the PSF and reduce the detector aperture size, reducing background. The performance measurements were conducted in a 600 meter X-ray beamline which collimated photons from a soft X-ray source to an X-ray CCD which was used as the detector. Several engineering test units were used to perform these studies by measuring the effective area, on and off-axis resolution, and to assess the effects of a vibration test on the module's optical performance. We have shown that the concentrators have made significant progress towards exceeding NICER's final goals.
The scientific objective of the X-ray Advanced Concepts Testbed (XACT) is to measure the X-ray polarization
properties of the Crab Nebula, the Crab pulsar, and the accreting binary Her X-1. Polarimetry is a powerful tool for
astrophysical investigation that has yet to be exploited in the X-ray band, where it promises unique insights into neutron
stars, black holes, and other extreme-physics environments. With powerful new enabling technologies, XACT will
demonstrate X-ray polarimetry as a practical and flight-ready astronomical technique. Additional technologies that
XACT will bring to flight readiness will also provide new X-ray optics and calibration capabilities for NASA missions
that pursue space-based X-ray spectroscopy, timing, and photometry.
NICER will use full shell aluminum foil X-ray mirrors, similar to those that are currently being developed for the
optics to be used for the XACT sounding rocket mission. Similar X-ray optics have been produced at Goddard
Space Flight Center since the late 1970's. The mirror geometry used in the past and on some present missions
consists of concentric quadrant shell mirrors with a conical approximation to the Wolter 1 geometry. For XACT,
we are developing the next generation of these optics. Two innovations introduced in the mirrors are complete
shells with a curve is in the reflectors' profile to produce a sharper focus than a conical approximation. X-ray
imagers, such as those of Suzaku, ASCA, GEMS, and Astro-H require two reflections. Since XACT and NICER
are using the optics as X-ray concentrators rather than full imaging optics, only one set of reflections is necessary.
The largest shell in the NICER concentrator is 10cm diameter. Small diameter optics benefit from the rigidity
of the full shell design. Also, the simplified support hardware reduced mass, which increases the effective area
per unit mass. With 56 optics on NICER, each consisting of 24 full shell mirrors, an effective production process
is needed for efficient manufacture of these mirrors. This production process is based on heritage techniques but
modified for these new mirrors. This paper presents the production process of the innovative full shell optics
and also results of optical and X-ray tests of the integrated optics.
A suspension-mounting scheme is developed for the IXO (International X-ray Observatory) mirror segments in which
the figure of the mirror segment is preserved in each stage of mounting. The mirror, first fixed on a thermally compatible
strongback, is subsequently transported, aligned and transferred onto its mirror housing. In this paper, we shall outline
the requirement, approaches, and recent progress of the suspension mount processes.
The International X-ray Observatory (IXO) is designed to conduct spectroscopic, imaging, and timing studies
of astrophysical phenomena that take place as near as in the solar system and as far as in the early universe. It
is a collaborative effort of ESA, JAXA, and NASA. It requires a large X-ray mirror assembly with an
unprecedented X-ray collection area and a suite of focal plane detectors that measure every property of each
photon. This paper reports on our effort to develop the necessary technology to enable the construction of the
mirror assembly required by IXO.
For the last decade we have been developing conical approximation of the Wolter I type thin foil/shell grazing incidence x-ray mirrors. Several missions have come out of these developments, e.g., BBXRT, and Astro-D (a U.S. - Japanese collaboration now known as ASCA), and Sodart on board SPECTRUM-X-GAMMA in the near future. The spatial resolution of this type of telescope is an order of magnitude worse than the theoretical limit, which hosts a great potential of improving these high throughput and relatively inexpensive x- ray instruments. In summary, x-ray image can be improved by reducing surface roughness and profile error for specularly reflecting x-rays in a better defined direction. The conventional way, coating reflecting surface of substrates with a thin layer of acrylic lacquer, was not effective in smoothing the surface roughness in spatial wavelength longer than a few microns. The profile of the foils was controlled by forming the substrate under certain mechanical pressure and/or combining heat treatment, but very often, the process is detrimental to the surface quality of roughness in millimeter wavelength. We report a new development of using epoxy replication technique on smooth pyrex mandrels. The results show very encouraging improvements over the conventional method. The half power diameter (HPD) of the x-ray image has dropped from 3.5 arcmins to 1.0 arcmin, and the extended image blur, i.e. the tail part of the encircled energy function (EEF), which was attributed to the roughness at higher spatial frequencies, was drastically reduced by 10 times. In this report we summarize the new technique in progress and the direction for future development.
The x-ray optical properties of X-Ray Telescopes (XRTs) on board Asca were evaluated with an x-ray pencil beam at ISAS 30 m x-ray beam line. The total effective area of four XRTs is obtained to be about 1300 cm2, 800 cm2, and 450 cm2 at each energy of 1.5 keV, 4.5 keV, and 8.0 keV, respectively. These values are about 15% less than those calculated by ray tracing method in an ideal case. The shadow effect of closely packed foils might be the main reason for the degradation of effective area. The Point Spread Function of XRT was also measured by an x-ray CCD. We have also measured the contamination of stray light, which were caused by the one time reflected photons (by primary or secondary mirror) and photons reflected on the back side surface of the mirror shells. The stray light profile and intensity were consistent to the results simulated by the ray tracing.
The Advanced Satellite for Cosmology and Astrophysics, ASCA, is a joint Japanese-United State X-ray astrophysics observatory which was launched on February 20th 1993. The scientific payload comprises four identical grazing incidence X-ray mirrors complemented by two charge-coupled devices and two gas scintillation proportional counters as the focal plane detectors. This paper presents the latest work carried out to improve the quality of ASCA images using the Lucy-Richardson deconvolution method. The ability to resolve two point sources is studied under various conditions of separation, relative intensity, and signal-to- noise. The method is also tested with an extended source. The minimum separation which can be resolved is 30 arcseconds, corresponding approximately to the radius of the core of the PSF. There is also some advantage to be gained in the relative orientation of the sources. Sources of unequal intensity must be separated further in order to be resolved, for example, when one source is half the intensity of the other source the minimum separation is 45 arcseconds. A signal-to-noise ratio of 5(sigma) is the lower limit for resolving two sources of equal strength 30 arcseconds apart. Deconvolution of the simulated image of the supernova remnant CAS-A is successfully carried out and the resulting image has about one arcminute resolution, limited by the PSF core width.
Thin foil X-ray mirrors are to be used as the reflecting elements in the telescopes of the X-ray satellites Spectrum-X-Gamma (SRG) and ASTRO-D. High resolution X-ray scattering measurements from the Au coated and dip-lacquered Al foils are presented. These were obtained from SRG mirrors positioned in a test quadrant of the telescope structure and from ASTRO-D foils held in a simple fixture. The X-ray data is compared with laser data and other surface structure data such as STM, atomic force microscopy (AFM), TEM, and electron micrography. The data obtained at Cu K-alpha(1), (8.05 keV) from all the mirrors produced on Al foils shows a scatter which limits the obtainable half-power width to above 1.5 arcmin. Mirrors based on electroformed Ni foils, however, show local regions with a factor of 4 better performance, and they are being developed for future applications.