Search

The High Energy X-ray Probe (HEX-P) is a NASA probe-class mission concept that will combine high spatial resolution X-ray imaging (<10 arcsec FWHM) and broad spectral coverage (0.1−150 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. Optimized nanometer-thin Ni-based multilayer coatings enable high performance of focusing X-ray telescopes to energies up to 150 keV and beyond, though current fabricated Ni-based coatings contain high interfacial roughness which will affect the predicted performance of the telescope. As part of the thin film coating development for the High Energy X-ray Probe, we report on the current development of reducing the coating roughness in periodic NiV/Si multilayer coatings. The multilayers are fabricated using the direct current magnetron sputtering coating facility at DTU Space, using different types of sputtering collimators and different reactive sputtering gas concentrations, optimized for the production of low interfacial roughness. The multilayers are characterized using X-ray reflectometry and X-ray photoelectron spectroscopy. More information on HEX-P, including the full team list, is available at hexp.org.

Just like in any other X-ray telescope, stray light is expected to be a potential issue for the ATHENA X-ray telescope, with a significant impact on the scientific goals. The most prominent cause of stray light in Wolter-I type optics is represented by rays that did not undergo double reflection and were reflected only singly, on either the parabolic or the hyperbolic segment. A minor contribution may, additionally, arise from the diffuse reflections on the backside of the pore membrane and ribs. Aiming at determining whether the resulting background is tolerable or not, the effective area for stray light has to be calculated. While ray-tracing is a standard and well-assessed tool to perform this task, it usually takes a considerable amount of computation time to trace a number of rays sufficient to reach an appropriate statistical significance, because only a minority of stray rays emerge unobstructed from the mirror assembly. In contrast, approaching the stray light from the analytical viewpoint takes several upsides: it is faster than ray-tracing, does not suffer from any statistical uncertainties, and allows one to better understand the role of the parameters at play. The only approximation involved is the double cone geometry, which however is largely applicable to ATHENA as far as the sole effective area is concerned. In this paper, we show how the analytical approach can be successfully adopted to model the stray light effective area in the ATHENA mirror assembly, as a function of the X-ray energy and of the source off-axis angle.

ESA’s Athena mission will use silicon pore optics, in which the optics assembly consists of pairs of mirror plates stacked into mirror modules. This paper presents a study of the angular resolution of Athena, using several candidate variants of mirror curvature and wedging. Results were achieved by ray-tracing these variants of Athena’s optics with the ray-tracing software SPORT. The study shows that all polynomial variants yield a PSF below 1” on-axis, at all energies between 0.1 and 12 keV. The secondary-only polynomial variants perform best, for both on- and off-axis point sources. Of these variants, the wedging 0/2 variant is shown to generally yield superior angular resolution at higher energies, the -1/1 variant at lower energies. A ray-tracing analysis using the Crab Nebula as an observation target was also performed. A 2D Fourier analysis was applied to the resulting focal plane responses to determine their angular resolution. This analysis indicates the angular resolution of all polynomial variants to be below 1”, at all but the highest energies. It also shows, though to a lesser extent, that the secondary-only polynomial variants perform best in most circumstances. Nevertheless, this second analysis requires further investigation for a more conclusive outcome.

AstroX is an add-on toolbox to the open source X-ray simulation software package McXtrace, which introduces Astronomical telescope optics and features to the package. Thus, enabling users to draw from the experience and developments of two communities. It may also shed further light into calibration results when measuring optics in ground based test-setups, at synchrotrons and specialized facilities. AstroX now includes a range of optical elements for Wolter class optics, extended source models, lobster eye optics, and gratings etc. Furthermore the open modular nature of McXtrace makes it fairly simple to connect to other software packages. We present a range of simulations of various aspects of telescopes: •A simulation work flow capable of quantifying stray light from Compton scattering at mirror substrates. •A study on the effect of dust contamination inside small-pore silicon pore optics. •A mechanism to include gratings for spectrometry in a telescope simulation.

As part of the manufacturing process of mirror modules for the Athena X-ray telescope, Silicon Pore Optics plates are assembled into mirror module stacks. The plates that form each stack are held together by direct bonding, relying on van der Waals forces and covalent bonds for adhesion. One way to increase the strength of the covalent bonds is through annealing of the mirror stacks. It is of critical importance to the mission to ensure compatibility between the reflective coating and any post-coating processing of the plates. We present our findings of the impact of annealing on the X-ray re ectance of coated mirrors relevant for the Athena mission. These are Ir single layers, as well as Ir/B4C, Ir/SiC, and Ir/C bilayers. We investigate the effect on the performance of the coatings after annealing at atmospheric pressure and at a low vacuum using X-ray reflectometry. B4C is found to suffer degradation from annealing under atmospheric conditions but not when annealed in vacuum. All other materials investigated are robust to atmospheric annealing.

Silicon Pore Optics are a novel technology for focusing high-energy photons, where pairs of mirror plates stacked into mirror modules. This paper presents a study of the angular resolution of SPO mirror assemblies, using a selection of sagittal mirror curvatures. Results were achieved by ray-tracing the different configurations of the mirror with the ray tracing software SPORT, or Silicon Pore Optics Ray Tracer, using an observation of the Crab Nebula originally obtained by Chandra. It is found that a true Wolter geometry most closely reproduces the original image, while geometries with a conic approximation on either their primary or secondary mirrors create the most diffuse image. A geometry with conic approximations on both primary and secondary mirrors falls in between the two extremes.

The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is the European Space Agency - selected L2 class mission, with launch scheduled in early 2030s. The observatory hosts a large X-ray telescope designed to have 5 arcseconds resolution with an effective area larger than 1.4 m2 at 1 keV. To meet these performance requirements ESA developed the Silicon Pore Optics technology: ribbed Si plates are shaped on a proper mould to copy the defined optical design and then stacked into modules. This technological solution, taking advantage of both replica process and modular implementation, is effective to populate ATHENA’s large aperture (diameter of ~2.5 m). As a result the optical pupil of an SPO will be very different than the classical nested shell one since it would be composed by a high number of small channels (about 106 channels of ~ 1 mm2 in ATHENA current design) and hence requires specific tool to be studied. To this end ESA financed the SIMPOSIuM project aimed to develop an open source, user-friendly SPOs simulation tool. The project is now at a good level of maturity and it offers 2 Graphical User Interfaces implementing a variety of simulation features. The SPORT GUI manages a full ray-tracing code and an analytical effective area calculator. The SWORDS GUI runs a SPOs diffraction effects simulator. In this paper we present the SImPOSIuM package and its collocation in ATHENA optics development framework.

The mirror coatings for the Athena X-ray telescope assumes Ir/SiC bilayer thin films as a baseline design. Adding the soft overcoat to the Ir X-ray mirror coatings for the Athena optics is used to improve the low energy performance necessary to achieve the telescope effective area requirements. The Athena mirror is based on silicon pore optics technology, for which the manufacturing process involves a sequence of wet chemical and thermal post-coating treatments of the mirror plates. Establishing compatibility of the thin film material candidates following exposure to these processes is critical for the Athena mission since the specific coating quality will influence the performance of the X-ray telescope. We present an investigation of Ir and Ir/SiC thin films exposed to post-coating treatments based on coatings produced at DTU Space. The current status of the chemical procedures is presented with representative coatings from the Athena-dedicated coating facility.

We present a number of example studies of telescope optics using the latest version of the AstroX add on toolbox for McXtrace. Among which are first, a benchmark study of effective area and vignetting for the Chandra X-ray Observatory which we find to match well with literature. Second, a convenient way of building a telescope model (in this case NuSTAR) with many similar optical elements scripted using python module. This lends itself well to be included in online notebooks and/or for teaching. Third, we show a new AstroX module for lobster eye optics, and fourth, a study of the proposed solar axion telescope BabyIAXO.

We present an experimental examination of iridium and boron carbide thin-film coatings for the purpose of fabricating x-ray optics. We use a combination of x-ray reflectometry and x-ray photoelectron spectroscopy to model the structure, composition, density, thickness, and micro-roughness of the thin films. We demonstrate in our analyses how the two characterization techniques are complementary, and from this we derive that an overlayer originating from atmospheric contamination with a thickness between 1.0–1.6 nm is present on the surface. The magnetron sputtered iridium films are measured to have a density of 22.4g/cm3. The boron carbide film exhibits a change in chemical composition in the top ∼2nm of the film surface when exposed to the ambient atmosphere. The chemical reaction occurring on the surface is due to an incorporation of oxygen and hydrogen present in the ambient atmosphere. Lastly, we present a correlation between the absorption edges and the emission lines exhibited by the thin films in an energy range from 50–800 eV and the impact on the reflectivity performance due to contamination in thin films.

As part of the thin film development for the Athena X-ray telescope and X-ray optics in general, we investigated the residual stress in iridium and chromium thin films deposited using direct current magnetron sputtering. Residual stresses in thin films can affect the performance and adhesion properties of the fabricated thin film coated X-ray optics. We characterized the thin films using X-ray reflectometry to determine the thin film thicknesses and stylus profilometry to determine the residual film stresses. To counterbalance the compressive stress identified in the iridium thin films, we introduced a chromium thin film layer for which the residual stress is tensile beneath the iridium film. However, chromium thin films are known to exhibit a grainy growth resulting in a high surface roughness which was also observed in this work. In this paper, we evaluated the effect on the iridium surface roughness when introducing a chromium underlayer and discussed the effect on the X-ray optics performance.

The demand for X-ray optics increases and so do their performance requirements. Iridium (Ir) thin film coatings have proven to be very robust and exhibit excellent reflective properties within the X-ray regime. However, the residual stress in Ir thin films is high and studies show that thin film Ir coatings with a thickness of 10–30 nm exhibit residual compressive stress1 as illustrated in Figure 1.

With a number of upcoming spaceborne and ground-based observatories equipped with X-ray telescopes that rely on high throughput at low energies, it is crucial to characterize these optics at the relevant energies to obtain a detailed understanding of their behavior and performance. DTU Space has commissioned a state-of-the-art Low-Energy X-ray Reflectometer (LEXR) with the purpose of studying thin-film performance of especially low-Z X-ray coatings.

A state-of-the-art Low-Energy X-ray Reflectometer (LEXR) is in operation at DTU Space with the main purpose of characterizing coatings for the Advanced Telescope for High-ENergy Astrophysics (ATHENA), a selected Lclass ESA mission. In particular, soft materials are difficult to characterize at higher energies so the 1.487 keV beamline compliments our existing 8.048 keV reflectometer, allowing for a more complete understanding of thinfilm X-ray characteristics. Documenting and qualifying the as-deposited coatings for X-ray telescope optics is of crucial importance, both to ensure that the effective area requirements are met, but also to quantify any temporal evolution in coating characteristics as well as the impact of manufacturing process parameters on mirror performance. It is notably relevant in the case of ATHENA, as there is a desire to enhance the low-energy performance by using a low-Z material overcoating on top of the Ir coating. We report on the commissioning and qualify the performance of the as-built 1.487 keV reflectometer as well as discuss measurement repeatability and system limitations

We present a ray tracing simulation of the Soft X-ray Imager (SXI) optics for the THESEUS observatory using the open-source McXtrace software package. THESEUS is a candidate mission within the Cosmic Vision programme of the European Space Agency and is designed to monitor high-energy transient events in the entire sky, therefore relying on fast slewing of the spacecraft. This capability will however impose large temperature variations and gradients across the optics which can cause thermoelastic deformation of the Soft X-ray Imager microchannel optics. The purpose of this study is to evaluate the impact on the point spread function (PSF) due to in-orbit temperature variation. Based on thermal analysis of the Soft X-ray Imager, perturbations to the ideal microchannel geometry are derived and provided as input to the ray tracer.

The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is an ESA-selected L2 class mission. In the proposed configuration, the optical assembly has a diameter of 2.2 m with an effective area of 1.4 m2 at 1 keV, 0.25 m2 at 6 keV, and requires an angular resolution of 5 arcsec. To meet the requirements of effective area and angular resolution, the technology of Silicon Pore Optics (SPO) was selected for the optics implementation. The ATHENA's optic assembly requires hundreds of SPOs mirror modules (MMs), obtained by stacking wedged and ribbed silicon wafer plates onto silicon mandrels to form the Wolter-I configuration. Different factors can contribute to limit the imaging performances of SPOs, such as i) diffraction through the pore apertures, ii) plate deformations due to fabrication errors and surface roughness, iii) alignment errors among plates in an MM, and iv) co-focality errors within the MMs assembly. In order to determine the fabrication and assembling tolerances, the impact of these contributions needs to be assessed prior to manufacturing. A set of simulation tools responding to this need was developed in the framework of the ESA-financed projects SIMPOSIuM and ASPHEA. In this paper, we present the performance simulation obtained for the recently proposed ATHENA configuration in terms of effective area, and we provide a simulation of the diffractive effects in a pair of SPO MMs. Finally, we present an updated sizing of magnetic diverter (a Halbach array) and the magnetic fields levels that can be reached in order to deviate the most energetic protons out of the detector field.

The ATHENA X-ray observatory is a large-class ESA approved mission, with launch scheduled in 2028. The technology of silicon pore optics (SPO) was selected as baseline to assemble ATHENA’s optic with hundreds of mirror modules, obtained by stacking wedged and ribbed silicon wafer plates onto silicon mandrels to form the Wolter-I configuration. In the current configuration, the optical assembly has a 3 m diameter and a 2 m2 effective area at 1 keV, with a required angular resolution of 5 arcsec. The angular resolution that can be achieved is chiefly the combination of 1) the focal spot size determined by the pore diffraction, 2) the focus degradation caused by surface and profile errors, 3) the aberrations introduced by the misalignments between primary and secondary segments, 4) imperfections in the co-focality of the mirror modules in the optical assembly. A detailed simulation of these aspects is required in order to assess the fabrication and alignment tolerances; moreover, the achievable effective area and angular resolution depend on the mirror module design. Therefore, guaranteeing these optical performances requires: a fast design tool to find the most performing solution in terms of mirror module geometry and population, and an accurate point spread function simulation from local metrology and positioning information. In this paper, we present the results of simulations in the framework of ESA-financed projects (SIMPOSiuM, ASPHEA, SPIRIT), in preparation of the ATHENA X-ray telescope, analyzing the mentioned points: 1) we deal with a detailed description of diffractive effects in an SPO mirror module, 2) we show ray-tracing results including surface and profile defects of the reflective surfaces, 3) we assess the effective area and angular resolution degradation caused by alignment errors between SPO mirror module’s segments, and 4) we simulate the effects of co-focality errors in X-rays and in the UV optical bench used to study the mirror module alignme