Search

Nanometer scale structures such as multilayers, gratings and natural crystals are playing an increasing role in spectroscopic applications for X-ray astrophysics. A few examples are briefly described as an introduction to current and planned applications pursued at the Danish Space Research Institute in collaboration with the FOM Institute for Plasma Physics, Nieuwegein, the Max-Planck-Institut fur Extratemestrische Physik, Aussenstelle Berlin, the Space Research Institute, Russian Academy of Sciences, the Smithsonian Astrophysical Observatory, Ovonics Synthetic Materials Company and Lawrence Livermore National Laboratory

We study the effects of the Point Spread Function (PSF) on the performance of the Objective Crystal Spectrometer (OCS) of the SODART telescope. The advantage of OCS/SODART over XMM and AXAF instruments in studying of the diffuse sources is illustrated by modelling of the OCS/SODART observation of Tycho and Cas A Supernova Remnants (SNR).

The Objective Crystal Spectrometer (OXS) is part of the SODART X-ray telescope onboard the future SPECTRUM-RONTGEN-GAMMA (SRG) mission. The SODART-OXS energy resolution is compared with those of the gratings of the XMM-NEWTON and CHANDRA telescopes. It is shown that for the high-energy region (2 - 10 keV) SODART-OXS has a substantially better energy resolution (up to 1 order of magnitude). However, the Bragg reflection principle of OXS leads to small photon numbers to be registrated in the detectors. Therefore, a careful choice of observation time and other parameters is necessary. We describe software including a complete ray-tracing procedure which simulates a whole SODART-OXS observation cycle to support the potential observer in his experiment planning. Presently, the software is limited to point sources.

The SODART x-ray telescope includes an objective crystal spectrometer (OXS) providing an energy resolving power around 1000 by Bragg reflection upon crystals. A program to calculate the SODART-OXS response function is described. It includes the simulation of the arrangement of the LiF, Si, and RAP crystals on the Bragg panel, the angle-dependent projection of the infalling x rays onto the mirrors, and the partial shadowing of the panel by the entrance door. The response function depends also on the parameters of the crystals (reflectivity and rocking curve width), using calculated and measured values in their energy dependence. The effective area of the mirror shells and the detector efficiencies are included, too. The energy dependences of the individual factors are shown and used to define an optimal crystal layout taking simulated and measured x-ray source lines (within the XANADU package) to find the most important Bragg-angle regions. It turns out that the optimal Si-RAP crystal distribution on the panel is asymmetric, thus favoring high-energy Si and low-energy RAP line regions. The response functions are displayed and used for the calculation of count rates for line and continuum registration.

The flight version of the Objective Crystal Spectrometer (OXS) on the SPECTRUM-X- GAMMA satellite is presented. The spectrometer is a panel that is placed in front of one of the SODART telescopes. It is composed of an array of the three Bragg crystals, LiF(220), Si(111) and RAP(001) for high resolution spectroscopy in the energy bands that encompass the H- and He-like emission line features from the cosmically important elements Fe, S, Ar and O. An energy resolution (E/(Delta) E) of 1250 will be obtained for He-like Fe emission, > 3000 for He-like S and Ar, > 700 for He-like O. In addition, the Si crystals will be coated with a multilayer that will allow spectroscopy with an energy resolution of approximately 80 in the energy band immediately below the C-K absorption edge of 0.284 keV. All the flight crystals are available and detailed calibrations have been obtained for each crystal. They confirm our specifications for the overall performance of the OXS. An estimate of the effective area in the 4 energy windows that are available to OXS yields > 100 cm2 from 5 to 7.4 keV, > 200 cm2 from 2.3 to 4.6 keV, approximately 10 cm+2) from 0.55 to 0.81 keV and approximately 100 cm2 from 0.175 to 0.28 keV.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Objective Crystal Spectrometer (OXS) on the SPECTRUM-X-GAMMA satellite will carry these types of natural crystals LiF(220), Ge(111) and RAP(001). They will be used to study, among others, the H- and the He-like emission from the cosmically important elements Fe, S, Ar and O. More than 300 LiF-crystals of dimension approximately 23 X 63 mm2 are required to cover one side of a large (approximately 1000 X 600 mm2) panel which is to be mounted in front of one of the high throughput X-ray telescopes. A qualification study, performed at the Danish Space Research Institute (DSRI), examined a large sample of LiF(220) crystals at Cu-K(alpha) 2 (8.0278 keV). Data from 124 flight crystals yields an average FWHM of rocking curves of 2.3 arcmin with a standard deviation of 0.4 arcmin. For more than 80% of the crystals, angular deviation of the (220) planes from the actual crystal surface is less than 1.5 arcmin. These data will be used to select the best crystals for the flight panel and will determine precisely the orientation of the crystals mounted on the OXS. Eight crystals were glued onto a small test panel of the OXS and for only one crystal was there measured a significant deviation of the crystal properties, including alignment relative to the others.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The SODART X-ray telescope includes an Objective Crystal Spectrometer (OCS) providing an energy resolving power around 1000 by Bragg reflection upon crystals. The SODART-OCS response function is used within the XSPEC package for the calculation of count rates for x-ray line and continuum registration from different classes of cosmic x-ray sources.

OCS, the Bragg spectrometer for the SODART X-ray telescope onboard the SPECTRUM–RONTGEN–GAMMA (SRG) satellite has been completed. Preliminary results of his performance are presented.

The influence of antinucleons from hadronically decaying gravitinos of mass 300 GeV G TeV on cosmological nucleo-synthesis processes is analyzed by including annihilation reactions into the balance equations of light element abundances. Requiring to stay inside the atrophysically allowed regions yields under conservative assumptions an upper boundary on the gravitino abundance corresponding in supersymmetric inflationary cosmology to a minimum reheating temperature of the universe of 10 9−11 GeV depending on m G , which improves earlier limits by five to three orders of magnitude in this mass range. Other bounds on the gravitino abundance like photofission processes are shortly rediscussed for the hadronic decay mode, and 3 He, d overproduction is shown to set the limit for 20 GeV G GeV at temperatures of 10 8−10 GeV. Such low temperatures values are hardly to reconcile within minimal N =1 supergravity models.