We draw a bow over developments in X-ray optics in the last two decades, relevant to high-resolution imaging, and sketch a potential path to future space telescopes in that energy range. In terms of aberrations and focal length, (Wolter) mirrors and diffractive-refractive transmission optics complement each other: near diffraction-limited (milli-arcsec or less) capabilities of the latter come at the expense of an inexpedient lens-detector distance of at least 100 km. Nonetheless, the predicted performance of “hybrid” doublets inspired their realization on a small scale: a(po)chromatic assemblies operate at synchrotron and free-electron laser facilities. Such lenses transform the planar wavefront to a sphere – or vice versa, when a zone plate is applied to test an X-ray telescope. Like in micro- or spectroscopy, figure errors of the mirror shape manifest themselves in blurry focal spots. Besides refractive phase plates to compensate for the wavefront deformation, an all-diffractive method modifies the Fresnel grooves where the narrow spectral bandwidth is acceptable. In any case, the reflective surface profile should be determined in-situ and at wavelength. We present a sensitive but robust technique to unveil perturbations of an axisymmetric XUV or X-ray mirror. Developed for a cm-sized ellipsoid, the method compares two CCD measurements of defocused intensity distributions. An algorithm extracts the geometrical phase precisely, limited only by the pixel size. As an advantage vs. other wavefront sensors, besides relaxed requirements on coherence, no radiation is lost at masks or gratings, beneficial for use at faint laboratory sources. For our tabletop setup, the wavefront error of 50 nm (rms) can be corrected by a “reflection zone plate”. We conclude with work in progress, conceptualizing “achromatic wavefront correction” by combining adapted grating- and prism-like components to correct the figure error of X-ray mirrors across an energy bandwidth accessible by a CCD or CMOS camera.

NewAthena is the next-generation X-ray telescope being developed by the European Space Agency (ESA) as an L-class mission, planned for adoption in 2027 and launch around 2038. Covering the 0.2–10 keV range, it will feature the largest X-ray optic ever built: a 2.6 m diameter, 12 m focal length system with more than 1 m² effective area at 1 keV. The optic is enabled by Silicon Pore Optics (SPO), developed by ESA, cosine, and partners, which assemble up to 600 mirror modules into a single lens. This talk presents the status of SPO production and the path to mass manufacturing.

Laue-lenses may improve the signal to noise (S/N-) ratio in the sub-MeV gamma domain by one to two orders of magnitude relative to direct-view instruments like COMPTEL and COSI. But the lenses are only effective for point sources; for extended sources the S/N-ratio drop off rapidly. The drop in the S/N-ratio is not caused by a reduction of the diffraction efficiency of the lens crystals, but by an unavoidable deterioration of the focusing quality for off-axis photons related to Brag’s law and Darwin’s model for mosaic crystals. The use of Laue lenses will significantly improve the detectability of soft gamma emission from suspected sources localized at other wavelengths. The much-improved S/N-ratio will allow for timing and spectral studies inaccessible for direct-view instruments. Guidelines for the construction of future Laue-lens systems will be presented.

The “Deutsches Röntgen-Museum” in Remscheid (Germany) is the institution that uniquely and comprehensively explores and documents the life and work of Wilhelm Conrad Röntgen and the impact of his discovery. It preserves a collection of X-ray images taken by W. C. Röntgen during his research. Among them are three images of Röntgen's own hands and those of his wife, Anna Bertha. Three more images show Röntgen's hunting rifle, which he was able to analyze internally by using the new X-ray technology. These two series of historical pictures from the years 1895 and 1896 provide an outstanding illustration of the scientific revolution that Röntgen's discovery triggered especially in medicine and in materials science. Therefore, his discovery of X-rays ranks among the most groundbreaking scientific achievements of modern times. In April 2025, those very first recorded X-ray photographs were added on the UNESCO Memory of the World Register. The corresponding public ceremony took place on September 10, 2025 in Röntgen´s birth town Remscheid. Representatives of the German UNESCO Commission, of politics, and of the German Röntgen Society were present. UNESCO is thus honoring not only Röntgen's groundbreaking discovery of X-rays, but also the cultural, scientific, and technological implications of his early radiographs. The "Deutsches Röntgen-Museum" presents six famous historical X-ray documents to the public, which are now part of UNESCO´s Memory of the World Register.

The X and Gamma-ray Imaging Spectrometer (XGIS) is the high-energy monitor proposed for THESEUS (Transient High-Energy Sky and Early Universe Surveyor), a candidate mission within ESA M7 program aimed at exploring the transient high-energy sky for investigating the Early Universe and advancing in multi-messenger astrophysics. XGIS is designed to detect and localize transient X-ray and gamma-ray sources across a broad energy range (2 keV – 10 MeV), enabling high-resolution timing and spectroscopy. The instrument consists of two identical cameras, employing coded mask techniques to image the sky in the range 2–150 keV, while acting as a half-sky monitor in the 150 keV–10 MeV energy range. Its innovative detection system is based on Silicon Drift Detectors (SDDs) optically coupled to CsI(Tl) scintillator bars. This configuration, combined with a low-noise distributed electronics system (ORION-ASICs), enables spectroscopy over an unprecedentedly wide energy band within a single, modular, and compact device. The design of XGIS emphasizes modularity and robustness, with each camera integrating 100 detector modules that require extensive development, testing and qualification. The ongoing development of XGIS includes performance testing of the silicon sensors and the ORION readout chain, alongside optimization of the mechanical assembly. These efforts will lead to the construction of a second demonstrator module for XGIS, supported by ESA funding. In this poster we present the XGIS architecture and performance, and we will summarize the technological advancements since M5 Phase A, highlighting progresses made in the current M7 Phase A in terms of technological readiness.

Insights from previous X-ray missions like Chandra have shown that contamination build-up on cold focal plane detectors is a problem that needs to be mitigated in future orbital missions. These contamination concerns can be addressed with the use of free-standing blocking filters that can be heated to room temperature via the filter support mesh. Using SiC grids, it is possible to manufacture large, high-throughput grids that can be held at room temperature with a lower power consumption than traditional grids. In this presentation, we present large SiC grids with geometries that increase X-ray filter strength, transmittance, and temperature uniformity, with up to 128 mm apertures. This size is suitable for AXIS, newAthena, or a future Lynx style mission. A key part of the research is to understand how the temperature profile of the SiC grids behave when in a radiative cooling environment and determine the power needed to return the grids to room temperature. Here, we describe the planned research to prove this grid technology in flight-like conditions in order to increase technology readiness level.

Electromagnetic radiation is scattered by small dust particles in the interstellar medium. Unlike in the visible range, this occurs at small angles in the X-ray range. This offers the unique opportunity to measure both components of extinction, namely scattering and absorption, in a single observation, because X-ray sources behind sufficiently large dust column densities are surrounded by a diffuse halo whose morphology and spectrum contain information about the grain size distribution and composition of the dust, as well as the geometry of the intervening medium. In this review, I will summarize the fundamental physics of X-ray scattering—including the relevant cross sections, angular dependence, and energy scaling—and discuss how observations over the past decades, from ROSAT to eROSITA have contributed to our understanding of the interstellar medium. I will also highlight how scattering halos from time-variable or transient sources have enabled precise distance measurements to dust clouds and sources alike

Since the recurrence times Tc of outbursts in soft X-ray transients (SXTs) are not periodic and their typical length is months, years, or decades, X-ray monitors are needed to detect them and investigate their evolution. Significant values can be obtained even when the different monitors with various energy bands, available for the individual time segments (years or decades), are used (e.g., ASM/RXTE, MAXI/ISS, BAT/Swift). The observations show that changes of Tc between the neighboring (or nearby) outbursts were often much smaller than the length of Tc in a given object. Jumps of Tc only sometimes replaced them. Evolution of Tc in a given SXT shows a complex curve with episodes of increase and decrease. For example, the analysis of the recurrence time Tc of outbursts in Aql X-1, using the method of O-C residuals, revealed that the character of the O-C curves bears a striking similarity to that of dwarf novae observed in the optical band. It means that variations of Tc are large, but generally not chaotic, and long-term trends in the O-C curves can be resolved. The evolution of Tc shows several large jumps. The switches of Tc can occur within just a single epoch. Observing the variety of the X-ray evolution of many dwarf novae is still limited by the low sensitivity of the current X-ray monitors.

The AXRO history is related to the history of X–ray astronomy in general and to the history of X-ray optics developments in the Czech Republic (and formerly in Czechoslovakia) in particular. The first Czech X-ray mirror was built already in the years 1969/1970, for a solar telescope within the Eastern Europe/Soviet INTERKOSMOS program, There were also essential efforts devoted to the development of novel technologies for satellite projects which were either canceled or interrupted. The two wasted years of development on the technology of high-quality Ni foils for the Danish SODART telescope (Schnopper, 1990), 1986-1988, can serve as an example. The SOviet-DAnish Roentgen Telescope (SODART) was planned for on board the Spectrum Roentgen Gamma (SRG) satellite equipped with three different instruments devoted to X–ray spectroscopy. Each of the two thin foil telescopes had an 8m focal length, a 60 cm diameter, a 1 deg field-of-view (FOV), a half-power width better than 2 arcmin and ca. 1 700 and 1 200 cm2 collecting area at 2 and 8 keV, respectively. In the last three decades developments of innovative technologies for X-ray optics continued with an emphasis on glass foils and silicon wafers mostly in Multi Foil Optics arrangements and Schmidt Lobster Eye and Kirkpatrick Baez geometries. The late achievements are then related to the AHEAD2020 PROJECT recently finished.