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Athena is the European Space Agency's next flagship x-ray telescope, scheduled for launch in the 2030s. Its 2.5-m diameter mirror will be segmented and comprise more than 600 individual Silicon Pore Optics (SPO) grazing-incidence-angle imagers, called mirror modules. Arranged in concentric annuli and following a Wolter-Schwartzschild design, the mirror modules are made of several tens of primary-secondary mirror pairs, each mirror made of mono-crystalline silicon, coated to increase the collective area of the system, and shaped to bring the incoming photons to a common focus 12 m away. Aiming to deliver a half-energy width of 5", and an effective area of about 1.4 m2 at 1 keV, the Athena mirror requires several hundred m2 of super-polished surfaces with a roughness of about 0.3 nm and a thickness of just 110 μm. SPO, using the highest-grade double-side polished 300 mm wafers commercially available, were invented for this purpose and have been consistently developed over the last several years to enable next-generation x-ray telescopes like Athena. SPO makes it possible to manufacture cost-effective, high-resolution, large-area x-ray optics by using all the advantages that mono-crystalline silicon and the mass production processes of the semiconductor industry provide. Ahead of important programmatic milestones for Athena, we present the status of the technology, and illustrate not only recent x-ray results but also the progress made on the environmental testing, manufacturing and assembly aspects of the technology.

The next generation x-ray observatory ATHENA (advanced telescope for high energy astrophysics) requires an optics with unprecedented performance. It is the combination of low mass, large effective area and good angular resolution that is the challenge of the x-ray optics of such a mission. ATHENA is the second large class mission in the science programme of ESA, and is currently in a reformulation process, following a design-to-cost approach to meet the cost limit of an ESA L-class mission. The silicon pore optics (SPO) is the mission enabler being specifically developed for ATHENA, in a joint effort by industry, research institutions and ESA. All aspects of the optics are being addressed, from the mirror plates and their coatings, over the mirror modules and their assembly into the ATHENA telescope, to the facilities required to build and test the flight optics, demonstrating performance, robustness, and programmatic compliance. The SPO technology is currently being matured to the level required for the adoption of the ATHENA mission, i.e., the start of the mission implementation phase. The monocrystalline silicon material and pore structure of the SPO provide these optics with excellent thermal and mechanical properties. Benefiting from technology spin-in from the semiconductor industry, the equipment, processes, and materials used to produce the SPO are highly sophisticated and optimised.

The mirror modules composing Athena’s X-ray optics are made with the Silicon Pore Optics (SPO) technology. SPO is produced as stacks of 38 mirror plates, which are paired to form X-ray Optics Units (XOUs) following a modified Wolter I geometry. In the current design, a mirror module is composed of two confocal XOUs glued in between a pair of brackets that freeze the configuration and provide interfaces to the mirror structure. Mirror modules are assembled at the XPBF2 beamline of PTB at the synchrotron radiation facility BESSY II, using dedicated jigs. In this paper we present the latest developments regarding the assembly of confocal mirror modules for Athena with an emphasis on alignment tolerances and gluing accuracy.

Silicon Pore Optics (SPO) have been chosen as the X-ray optics technology for the European Space Agency's Athena mission. Although in principle SPO can be used to realize classical Wolter-I or Wolter-Schwarzschild systems, technological and manufacturing considerations introduce constraints that lead to a system where some of the parameters of the optics are altered with respect to the classical description. In this paper we describe some of the constraints and how they affect the way one goes about designing optics based on SPO. Further we present ray-tracing results that show how these constraints do not impact the performance goals of a large mission like Athena.

The European Space Agency (ESA) is developing the Athena (Advanced Telescope for High ENergy Astrophysics) X-ray telescope, an L-class mission in their current Cosmic Vision cycle for long-term planning of space science missions. Silicon Pore Optics (SPO) are a new type of X-ray optics enabling future X-ray observatories such as Athena and are being developed at cosine with ESA as well as academic and industrial partners. These high-performance, modular, lightweight yet stiff, high-resolution X-ray optics shall allow missions to reach unprecedented combination of large effective area, good angular resolution and low mass. As the development of the Athena mission progresses, it is necessary to validate the SPO technology under launch conditions. To this end, ruggedisation and environmental testing studies are being conducted to ensure mechanical stability and optical performance of the optics before, during and after launch. In this paper, we report on the results of our completed environmental testing campaigns on mirror modules of middle radius (about 700 mm) of curvature. In these campaigns, each mirror module is first integrated then submitted to sine and random vibration tests, as well as shock tests, all in accordance with the upcoming Ariane launch vehicle and the mission requirements. Additionally, the mirror modules are characterized with X-ray before and after each test to verify the optical performance remains unchanged.

We have designed and modeled a novel optical system composed of a Laue lens coupled to an x-ray tube that produces a focused beam in an energy range near 100 keV (λ = 12.4 picometer). One application of this system is radiation therapy where it could enable treatment units that are considerably simpler and lower in cost than present technologies relying on linear accelerators. The Laue lens is made of Silicon Laue components which exploit the silicon pore optics technology. The lens concentrates photons to a small region thus allowing high dose rates at the focal area with very much lower dose rates at the skin and superficial regions. Monte Carlo simulations with Geant4 indicate a dose deposition rate of 0.2 Gy min−1 in a cylindrical volume of 0.7 mm diameter and 10 mm length, and a dose ratio of 72 at the surface (skin) compared to the focus placed 10 cm within a water phantom. Work is ongoing to newer generation crystal technologies to increase dose rate.

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission studies and technology preparation are continuing to progress. The optics for this future space observatory is based on the Silicon Pore Optics (SPO), and is being evolved in a joint effort by industry, research institutions and ESA. The SPO technology uses the superb properties of monocrystalline Silicon, and spins in technologies developed for the semiconductor industry, benefiting from excellent materials, processes and equipment. In a holistic approach the technical and programmatic challenges of the ATHENA optics are being addressed simultaneously. A comprehensive Technology Development Plan (TDP) was defined and is being implemented to develop this novel X-ray optics technology. The performance, environmental compatibility and serial automated production and testing are being addressed in parallel, aiming at the demonstration of the required technology readiness for the Athena Mission Adopt ion Review (MAR) expected in 2022.

The Silicon Pore Optics (SPO) technology has been established as a new type of X-ray optics and will enable future X-ray observatories such as Athena and Arcus. SPO is being developed at cosine Research B.V. together with the European Space Agency (ESA) and academic as well as industrial partners. For Athena, about 150,000 mirror plates are required. With the technology spin-in from the semiconductor industry, mass production processes can be employed to manufacture rectangular SPO mirror plates in high quality, large quantity and at low cost. Over the last years, several aspects of the SPO mirror plates have been reviewed and undergone further developments in terms of effective area, intrinsic behavior of the mirror plates and mass production capability. The paper will provide an overview of most recent SPO plate designs, mirror plate production status and plan forward including reflective coating process as well as mass production developments.

Athena will be the largest space-based x-ray telescope to be flown by the European Space Agency: its large 2.6 m diameter lens will use a revolutionary new modular technology, Silicon Pore Optics (SPO). The lens will consist of several hundreds of smaller x-ray lenslets, called mirror modules, which each consist of about 70 mirror pairs. Those mirror modules are arranged in circles in a large optics structure and will focus x-ray photons with an energy of 0.5 to 10 keV at a distance of 12 m onto the detectors of Athena. The point-spread function (PSF) of the optic shall achieve a half-energy width (HEW) of 5” at an energy of 1 keV, with an effective area of about 1.4 m2, corresponding to several hundred m2 of super-polished mirrors with a roughness of about 0.3 nm and a thickness of only 150 μm. SPO using the highest grade double-side polished 300 mm wafers commercially available, have been invented to enable such telescopes. SPO allows the cost-effective production of high-resolution, large area, x-ray optics, by using all the advantages that mono-crystalline silicon and the mass production processes of the semi-conductor industry provide. SPO has also shown to be a versatile technology that can be further developed for gamma-ray optics, medical applications and for material research. This paper will present the status of the technology and of the mass production capabilities, show latest performance results and discuss the next steps in the development.

Athena, the largest space-based x-ray telescope to be flown by the European Space Agency, uses a new modular technology to assemble its 2.5 m diameter lens. The lens will consist of several hundreds of smaller x-ray lenslets, called mirror modules, which each consist of up to 76 stacked mirror pairs. Those mirror modules are arranged in circles in a large optics structure and will focus x-ray photons with an energy of 0.5 to 10 keV at a distance of 12 m onto the detectors of Athena. The point-spread function (PSF) of the optic shall achieve a half-energy width (HEW) of 5"at an energy of 1 keV, with an effective area of about 1.4 m2, corresponding to several hundred m2 of super-polished mirrors with a roughness of about 0.3 nm and a thickness of down to 110 μm. This paper will present the status of the technology and of the mass production capabilities, show latest performance results and discuss the next steps in the development.

The X-ray parallel beam facility XPBF 2.0 in the laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY II provides a parallel beam of very low divergence, and adjustable beam sizes between about 100 μm and at least 5 mm. Further, XPBF 2.0 is equipped with a vacuum chamber with a hexapod system for accurate positioning of all silicon pore optic (SPO) sizes to be investigated, and a vertically movable CCD-based camera system to register the direct and the reflected beam at a sample to CCD distance of 12 m corresponding to the envisaged focal length of ATHENA (Advanced Telescope for High ENergy Astrophysics). Since its installation in 2016, the beamline has been constantly upgraded to improve performance and implementing the changing requirements. To accurately and constantly measure the 12 m distance, between the center of the sample (i.e. mirror module) and the CCD detector, a laser-tracker has been installed. Additionally, the cleanroom, housing the vacuum chamber, was upgraded with a cooling unit keeping the temperature at 20°C. The original phosphor screen in front of the CCD has been replaced with a new phosphor screen with different grain size and material. The next upgrade of the XPBF 2.0 is the installation of a new monochromator mirror to operate the beamline at 1.0 keV instead of 1.6 keV. This paper will present the upgrades of the X-ray parallel beam facility XPBF 2.0 and discuss next steps for characterizing SPOs with synchrotron radiation.

Laue lenses use Bragg diffraction to concentrate soft γ -rays onto a detector. This decoupling of the collecting area from the detector volume can generate a significant increase in sensitivity for applications in astrophysics and nuclear medicine. A demonstrator lens was constructed at the UC Berkeley’s Space Sciences Laboratory in 2014 by gluing 48 Fe and Al diffracting crystals to an aluminium substrate. The goal was to demonstrate a fast and accurate assembly technique that is compatible with the large number of crystals required to fabricate a Laue lens telescope for astronomical observations. We present here the lens design, the assembly technique we used, and the results of measurements of the angular misalignments before and after curing of the glue and during environmental testing (thermal, vacuum, and vibration). We conclude that our alignment technique is fast enough to assemble a full lens made of several thousand crystals. The achieved alignment accuracy had an average of 32.7 ′ ′ and a standard deviation of 44.1 ′ ′ . The accuracy could be improved by using an alternative glue or by having better control over the asymmetry angle resulting from the crystal cut.

The European Space Agency (ESA) is developing the Athena (Advanced Telescope for High ENergy Astrophysics) X-ray telescope, an L-class mission in their current Cosmic Vision cycle for long-term planning of space science missions. Silicon Pore Optics (SPO) are a new type of X-ray optics enabling future X-ray observatories such as Athena and are being developed at cosine with ESA as well as academic and industrial partners. These high-performance, modular, lightweight yet stiff, high-resolution X-ray optics shall allow missions to reach an unprecedentedly large effective area of several square meters, operating in the 0.2 to 12 keV band with an angular resolution better than 5 arc seconds. As the development of Athena mission progresses, it is necessary to validate the SPO technology under launch conditions. To this end, ruggedisation and environmental testing studies are being conducted to ensure mechanical stability and optical performance of the optics before, during and after launch. At cosine, a facility with shock, vibration, tensile strength, long time storage and thermal testing equipment has been set up to test SPO mirror module components for compliance with the upcoming Ariane launch vehicle and the mission requirements. In this paper, we report on the progress of our ongoing investigations regarding tests on mechanical and thermal stability of mirror module components such as single SPO stacks complete mirror modules of inner (R = 250 mm), middle (R = 737 mm) and outer (R = 1500 mm) radii.

Silicon Pore Optics (SPO) uses commercially available monocrystalline double-sided super-polished silicon wafers as a basis to produce mirrors that form lightweight and stiff high-resolution x-ray optics. The technology has been invented by cosine and the European Space Agency (ESA) and developed together with scientific and industrial partners to mass production levels. SPO is an enabling element for large space-based x-ray telescopes such as Athena and ARCUS, operating in the 0.2 to 12 keV band, with angular resolution requirements up to 5 arc seconds. SPO has also shown to be a versatile technology that can be further developed for gamma-ray optics, medical applications and for material research. This paper will summarise the status of the technology and of the mass production capabilities, show latest performance results and discuss the next steps in the development.

Silicon Pore Optic (SPO) is the X-ray mirror technology selected for the Athena X-ray observatory. The optic is modular; in the current design, it is made of about 700 co-aligned mirror modules. SPO is produced as stacks of 35 mirror plates, which are then paired to form X-ray Optics Units (XOUs) following a modified Wolter I geometry. A mirror module is composed of two confocal XOUs bonded in between a pair of brackets allowing interfacing to the mirror structure. Mirror modules are assembled using the XPBF 2.0 beamline of PTB at the synchrotron radiation facility BESSY II, using pencil beam and dedicated jigs. In this paper we present the challenges and solutions related to making confocal mirror modules.

Silicon Pore Optics (SPO) is an enabling technology for future large-area space-based X-ray observatories, such as ESA's Athena mission and NASA's Arcus candidate mission. SPO consist of stacks of thin silicon mirrors, which together provide a large effective area with a relatively low mass. Stacks are produced by custom robots that bend the mirrors into the design shape and stack them. We discuss the latest developments in improving the stacking process. The main challenge is to minimize shape deviations in order to optimize the imaging resolution of the optic. During the stacking process, the shape of each plate is measured directly after it is added to a stack. This metrology allows us to quickly quantify the effect of different stacking recipes, which streamlines the development. We discuss recent improvements in reducing excess meridional curvature. Furthermore, we prepare for mass-production by optimizing the robotics for performance and reproducibility.

Silicon Pore Optics is the X-ray mirror technology selected for the European Space Agency's Athena X-ray observatory. We describe the X-ray testing and characterization cycle that the optics are subjected to at the PTB's X-ray Pencil/Paraller Beam Facility (XPBF) 1 and 2 beamlines at the synchrotron radiation facility BESSY II. Individual stacks are measured with a pencil beam to determine their optical quality and the orientation of the optical axis. Using metrics based on X-ray and manufacturing metrology, stacks are then paired in primary-secondary Wolter-I-like systems, that are in turn characterized to determine their optical performance. Finally, four stacks, two primaries and two secondaries, are assembled into a mirror module, that is also characterized, with pencil and wide X-ray beams. At each step models, metrology, and software are combined to arrive at the relevant parameters. We describe the methods used, and illustrate how the performance of imaging pairs can be described in terms of stack-level parameters.

The PANTER X-ray test facility of the Max Planck Institute for Extraterrestrial Physics (MPE) has over 40 years of heritage in testing and calibrating x-ray optics. Having contributed to missions such as XMM-Newton, Chandra, and eROSITA, the facility measures the performance of x-ray optic technologies that will enable future x-ray telescopes to be realised. Over the last year, PANTER has been testing the latest developments in silicon pore optics for ESA’s ATHENA mission, as well as full-shell eROSITA-like optics for the CAS/ESA/MPE Einstein Probe mission. For ATHENA, complete mirror modules for the outer radius of the telescope have been tested. The latest developments in the optics for the mid-radius of the telescope, including the first confocal mirror module, have been measured for performance. The paper will provide an overview of the most recent testing carried out at PANTER, and the alignment and measurement techniques used.

We report on a concept for curved diffractive X-ray optics (CDXO). CDXO would enable potential new optical designs for X-ray instruments, such as a two element spectrometer, in which the secondary element of an X- ray mirror pair is patterned with an X-ray grating. A two-element spectrometer design eliminates the grating assembly, resulting in decreased instrument mass and reduced power requirements. In addition, a two-element spectrometer may realize cost/schedule savings by eliminating a separate grating alignment effort, and yield increased effective area over three element designs. We present a raytrace concept study of a two-element spectrometer compact enough to fit within a sounding rocket payload. We also review the progress made in electron-beam lithography (EBL) techniques that would enable curved diffractive X-ray optics to be patterned, and outline a procedure by which the accuracy of the EBL patterning process can be measured interferometrically.

Currently for the European Space Agency (ESA) ATHENA [1,2] mission Silicon Pore Optic (SPO) [3-8] Mirror Modules (MM) with a focal length of f = 12 m, are being developed and tested. The SPO MMs are also the baseline optic for the NASA medium explorer high-resolution spectroscopy mission Arcus [9-10] with f = 12 m that is currently undergoing a phase A study. SPOs are currently being tested at both the PTB laboratory of the BESSY synchrotron facility in Berlin using an X-ray pencil beam and the PANTER X-ray test facility in Neuried of the Max-Planck-Institut fur extraterrestrische Physik, Garching using a long vacuum beamline (distance source to optic ~120 m). The different types of measurements performed at PANTER to characterise the ATHENA and Arcus optics will be discussed. This will be done on the level of an X-ray optical unit (XOU) composed of both a primary and secondary High Performance Optic (HPO) stack, a mirror module (MM) composed of two XOUs, small (

In this paper, we present the technological basis for the production of structured silicon X-ray mirrors using direct wafer bonding. We dice 12” silicon wafers into rectangular plates, which are then structured to have a thin membrane and several ribs. As a next step we wedge the plates on both sides. Using in-house developed stacking robots, we then elastically deform the plates into conical shapes and bond the plates into a stack, which finally consists of several tens of such plates in a stiff self-supporting structure. Throughout the production of the structured plates and their assembly into stacks, we focus on maintaining pristinely clean surfaces as this is a prerequisite for direct wafer bonding. Several metrology tools have been developed, operating in-line, to ensure precise plate to plate alignment, high cleanliness and an accurate figure. The process is adaptable to work with plates of various dimensions, with metal coatings and with different bend radii.

Silicon direct bonding is a manufacturing process that is used in the fabrication of electronic, optical and mechanical microsystems. The chemical bonds are providing an intimate surface contact and strong structural stiffness that is for this reason also suitable for large assemblies. Together with the knowledge of the surface properties and of X-ray optics, we are making mirror imaging systems. The manufacturing process resorts to the highest-grade 12 inch silicon wafers with double Super Polished and near perfect plan parallel surfaces. With readily available semiconductor manufacturing and lithographic tools the wafers are processed into mirror plates with micrometer accuracy channel structures, yet maintaining the nanometer accurate figure of the silicon wafer. Multiple channeled X-ray mirrors shall subsequently be curved and stacked to form an optical component. We want to use such optical components for a ~3m diameter segmented optical system that would be part of the Athena observatory, European Space Agency's (ESA) next L-class mission, scheduled to launch in 2032. Athena will observe the hot and energetic Universe and answer two big scientific questions: How does ordinary matter assemble into the large-scale structures we see today? and how do black holes grow and shape the Universe? The scientific objectives of Athena require the largest X-ray optic ever flown. Silicon Pore Optics (SPO) is the selected technology that produces the building blocks for Athena's modular mirror. The segmented Athena optic will be made of about 700 X-ray mirror modules all co-aligned to a common focus, with radii of curvature varying from 0.25 m to 1.25 m. Furthermore, SPO has also shown to be a versatile technology that can be further developed for gamma-ray optics, medical applications and for material research. While considerable progress has been made on the performance of the optic, we are also upscaling towards an automated production line including mirror manufacturing, coating, cleaning, stacking and stack integration into mirror modules. The complete production line features many metrology steps to ensure quality and high yield. From the start, the development process has looked not just at the production of a single sample of high quality but at all the processes eventually required for the production of a complete system, and this in an effort to ensure that issues (mechanical, thermal, environment, supply chain etc) are identified early and addressed in a manner compatible with the core goal of producing high quality optics. In this paper we will discuss the challenges and present solutions that we have addressed. Cleanliness assessment, and bond strength enhancement are for instance two current topics of active development.

The Silicon Pore Optics (SPO) technology has been established as a new type of X-ray optics enabling future X-ray observatories such as ATHENA. SPO is being developed at cosine together with the European Space Agency (ESA) and academic as well as industrial partners. The SPO modules are lightweight, yet stiff, high-resolution X-ray optics, allowing missions to reach a large effective area of several square meters. These properties of the optics are mainly linked to the mirror plates consisting of mono-crystalline silicon. Silicon is rigid, has a relatively low density, a very good thermal conductivity and excellent surface finish, both in terms of figure and surface roughness. For Athena, a large number of mirror plates is required, around 100,000 for the nominal configuration. With the technology spin-in from the semiconductor industry, mass production processes can be employed to manufacture rectangular shapes SPO mirror plates in high quality, large quantity and at low cost. Within the last years, several aspects of the SPO mirror plate have been reviewed and undergone further developments in terms of effective area, intrinsic behavior of the mirror plates and mass production capability. In view of flight model production, a second source of mirror plates has been added in addition to the first plate supplier. The paper will provide an overview of most recent plate design, metrology and production developments.

Mission studies and technology preparation for the ATHENA (Advanced Telescope for High ENergy Astrophysics) [1- 5] mission are continuing to progress. The X-ray optics of this future space observatory are based on the Silicon Pore Optics (SPO) technology [6-58], and is being evolved in a joint effort by industry, research institutions and ESA. The SPO technology benefits from substantial investments made by the semiconductor industry, and spins-in materials, processes and equipment into the development of novel X-ray optics. A comprehensive Technology Development Plan (TDP) is being implemented, funded by ESA and involving a large number of experts in key areas ranging from micro machining of Silicon, over sophisticated automation and robotic systems, to hybrid manufacturing. The performance, environmental compatibility and serial automated production and testing are being addressed in parallel, aiming at the demonstration of the required technology readiness for the ATHENA Mission Adoption Review (MAR) expected by the end of 2021. A formal Technology Readiness Assessment is in place and is being currently exercised in preparation of the ATHENA Mission Formulation review (MFR). The programmatics for the flight model implementation is being defined in detail, and preparations are starting for the design and implementation of the necessary facilities. An overview of the ATHENA optics technology preparation, the technology readiness assessment and the related activities is provided.

The Laue lens is an emerging technology that uses crystal diffraction to concentrate gamma-rays. The Darwin model describes diffraction in mosaic crystals at high energies (>50 keV) and is the basis for assessing the throughput of a Laue lens. While the Darwin model has been used successfully to describe binary alloys, it has shown inconsistencies when applied to diffraction with pure-metal crystals. This paper presents a systematic study of diffraction in pure-metal silver mosaic crystals and the performance of the Darwin model when applied to the data. Two cut silver crystals were tested at the Institute Laue–Langevin facility at three gamma-ray energies and at three different crystallographic orientations. The rocking curves were fitted using the Darwin model. A single Gaussian for the distribution of crystallite orientations leads to poor quality fits. A crystallite distribution that is the sum of two Gaussians gives improved fits. However, for each crystal, the Darwin model gives mosaicities and crystallite sizes that are not consistent with one another as a function either of energy or of crystallographic orientation, despite these being physical properties of the materials. Without an adequate model to describe diffraction in pure-metal crystals, either a Laue lens design must severely limit its catalogue of usable materials or each crystal in the design must be tested at the exact energy at which it is to be used. A more general theory to describe hard X-ray diffraction using pure-metal mosaic crystals, possibly involving a distribution of crystallite sizes, is therefore required.

The development of the X-ray optics for ATHENA (Advanced Telescope for High ENergy Astrophysics)[1-4], the selected second large class mission in the ESA Science Programme, is progressing further, in parallel with the payload preparation and the system level studies. The optics technology is based on the Silicon Pore Optics (SPO) [5-48], which utilises the excellent material properties of Silicon and benefits from the extensive investments made in the semiconductor industry. With its pore geometry the SPO is intrinsically very robust and permits the use of very thin mirrors while achieving good angular resolution. In consequence, the specific mass of the resultant ATHENA optics is very low compared to other technologies, and suitable to cope with the imposed environmental requirements. Further technology developments preparing the ATHENA optics are ongoing, addressing additive manufacturing of the telescope structure, the integration and alignment of the mirror assembly, numerical simulators, coating optimisations, metrology, test facilities, studies of proton reflections and meteorite impacts, etc. A detailed Technology Development Plan was elaborated and is regularly being updated, reflecting the progress and the mission evolution. The required series production and integration of the many hundred mirror modules constituting the ATHENA telescope optics is an important consideration and a leading element in the technology development. The developments are guided by ESA, implemented in industry and supported by research institutions. The many ongoing SPO technology development activities aim at demonstrating the readiness of the optics technology at the review deciding the adoption of ATHENA onto the ESA Science flight programme, currently expected for 2021. Technology readiness levels of 5/6 have to be demonstrated for all critical elements, but also the compliance to cost and schedule constraints for the mission.

The development of a Laue lens to focus soft gamma rays appears today as the only solution to improve significantly telescopes’ sensitivity and angular resolution in the 100 keV – 1 MeV domain. A Laue lens makes use of diffraction in the volume of a large number of crystal tiles carefully orientated to concentrate incident radiations from a large collecting area in a small focal spot. Various type of crystal have been measured and show excellent results, with angular spread of diffracting planes in the range 15-45 arcsec, and reflectivities up to 31 % at 600 keV. Precision of orientation of crystals is demanding because of the long focal length involved by small angles of diffraction. A prototype currently being built by a French collaboration including the CESR, the CNES and Thales Alenia Space aims to achieve 10 arcsec of tolerance.

The European Space Agency (ESA) is studying the ATHENA (Advanced Telescope for High ENergy Astrophysics) X-ray telescope, the second L-class mission in their Cosmic Vision 2015 – 2025 program with a launch spot in 2028. The baseline technology for the X-ray lens is the newly developed high-performance, light-weight and modular Silicon Pore Optics (SPO). As part of the technology preparation, ruggedisation and environmental testing studies are being conducted to ensure mechanical stability and optical performance of the optics during and after launch, respectively. At cosine, a facility with shock, vibration, tensile strength, long time storage and thermal testing equipment has been set up in order to test SPO mirror module (MM) materials for compliance with an Ariane launch vehicle and the mission requirements. In this paper, we report on the progress of our ongoing investigations regarding tests on mechanical and thermal stability of MM components like single SPO stacks with and without multilayer coatings and complete MMs of inner (R = 250 mm), middle (R = 737 mm) and outer (R = 1500 mm) radii.

For more than a decade, cosine has been developing silicon pore optics (SPO), lightweight modular X-ray optics made of stacks of bent and directly bonded silicon mirror plates. This technology, which has been selected by ESA to realize the optics of ATHENA, can also be used to fabricate soft gamma-ray Laue lenses where Bragg diffraction through the bulk silicon is exploited, rather than grazing incidence reflection. Silicon Laue Components (SiLCs) are made of stacks of curved, polished, wedged silicon plates, allowing the concentration of radiation in both radial and azimuthal directions. This greatly increases the focusing properties of a Laue lens since the size of the focal spot is no longer determined by the size of the individual single crystals, but by the accuracy of the applied curvature. After a successful proof of concept in 2013, establishing the huge potential of this technology, a new project has been launched in Spring 2017 at cosine to further develop and test this technique. Here we present the latest advances of the second generation of SiLCs made from even thinner silicon plates stacked by a robot with dedicated tools in a class-100 clean room environment.

Continuing improvement of Silicon Pore Optics (SPO) calls for regular extension and validation of the tools used to model and predict their X-ray performance. In this paper we present an updated geometrical model for the SPO optics and describe how we make use of the surface metrology collected during each of the SPO manufacturing runs. The new geometrical model affords the user a finer degree of control on the mechanical details of the SPO stacks, while a standard interface has been developed to make use of any type of metrology that can return changes in the local surface normal of the reflecting surfaces. Comparisons between the predicted and actual performance of samples optics will be shown and discussed.

While predictions based on the metrology (local slope errors and detailed geometrical details) play an essential role in controlling the development of the manufacturing processes, X-ray characterization remains the ultimate indication of the actual performance of Silicon Pore Optics (SPO). For this reason SPO stacks and mirror modules are routinely characterized at PTB’s X-ray Pencil Beam Facility at BESSY II. Obtaining standard X-ray results quickly, right after the production of X-ray optics is essential to making sure that X-ray results can inform decisions taken in the lab. We describe the data analysis pipeline in operations at cosine, and how it allows us to go from stack production to full X-ray characterization in 24 hours.

Laue lenses constitute a promising option for concentrating soft gamma rays with a large collection area and reasonable focal lengths. In astronomy they could lead to increased telescope sensitivity by one to two orders of magnitude, in particular for faint nuclear gamma-ray lines, but also for continua like hard X-ray tails from a variety of compact objects. Other fields like Homeland security and nuclear medicine share the same need for more sensitive gamma-ray detection systems and could find applications for gamma-ray focusing optics. There are two primary challenges for developing Laue lenses: the search for high-reflectivity and reproducible crystals, and the development of a method to accurately orient and fix the thousands of crystals constituting a lens. In this paper we focus on the second topic. We used our dedicated X-ray beamline and Laue lens assembly station to build a breadboard lens made of 15 crystals. This allowed us to test our tools and methods, as well as our simulation code and calibration procedure. Although some critical points were identified, the results are very encouraging, with a crystal orientation distribution lower than $10''$, as required to build a Laue lens telescope dedicated to the study of Type Ia supernovae (30-m focal length). This breadboard lens represents an important step towards raising the technology readiness level of Laue lenses., Comment: Accepted for publication in Nuclear Instrument and Methods in Physics Research Section A

The work on the definition and technological preparation of the ATHENA (Advanced Telescope for High ENergy Astrophysics) mission continues to progress. In parallel to the study of the accommodation of the telescope, many aspects of the X-ray optics are being evolved further. The optics technology chosen for ATHENA is the Silicon Pore Optics (SPO), which hinges on technology spin-in from the semiconductor industry, and uses a modular approach to produce large effective area lightweight telescope optics with a good angular resolution. Both system studies and the technology developments are guided by ESA and implemented in industry, with participation of institutional partners. In this paper an overview of the current status of the telescope optics accommodation and technology development activities is provided.

Silicon Pore Optics is a high-energy optics technology, invented to enable the next generation of high-resolution, large area X-ray telescopes such as the ATHENA observatory, a European large (L) class mission with a launch date of 2028. The technology development is carried out by a consortium of industrial and academic partners and focuses on building an optics with a focal length of 12 m that shall achieve an angular resolution better than 5”. So far we have built optics with a focal length of 50 m and 20 m. This paper presents details of the work carried out to build silicon stacks for a 12 m optics and to integrate them into mirror modules. It will also present results of x-ray tests taking place at PTB’s XPBF with synchrotron radiation and the PANTER test facility.

ATHENA (Advanced Telescope for High ENergy Astrophysics) is being studied by the European Space Agency (ESA) as the second large science mission, with a launch slot in 2028. System studies and technology preparation activities are on-going. The optics of the telescope is based on the modular Silicon Pore Optics (SPO), a novel X-ray optics technology significantly benefiting from spin-in from the semiconductor industry. Several technology development activities are being implemented by ESA in collaboration with European industry and institutions. The related programmatic background, technology development approach and the associated implementation planning are presented.

A new X-ray parallel beam facility (XPBF 2.0) has been installed in the laboratory of the Physikalisch-Technische Bundesanstalt at the synchrotron radiation facility BESSY II in Berlin to characterize silicon pore optics (SPOs) for the future X-ray observatory ATHENA. As the existing XPBF which is operated since 2005, the new beamline provides a pencil beam of very low divergence, a vacuum chamber with a hexapod system for accurate positioning of the SPO to be investigated, and a vertically movable CCD-based camera system to register the direct and the reflected beam. In contrast to the existing beamline, a multilayer-coated toroidal mirror is used for beam monochromatization at 1.6 keV and collimation, enabling the use of beam sizes between about 100 μm and at least 5 mm. Thus the quality of individual pores as well as the focusing properties of large groups of pores can be investigated. The new beamline also features increased travel ranges for the hexapod to cope with larger SPOs and a sample to detector distance of 12 m corresponding to the envisaged focal length of ATHENA.

Silicon mono-crystals have been bent thanks to a series of parallel superficial indentations on one of the largest faces of the crystals. This technique relies on irreversible compression of the crystal beneath and beside the indentations. This latter causes deformation with no need for external device, resulting in a uniform self-standing curvature within the crystal. Indented Si crystals have been characterized at European Synchrotron Radiation Facility using a monochromatic beam ranging from 150 to 700 keV. Crystals exhibited very high diffraction efficiency over a broad range of energy, peaking 95% at 150 keV. Measured angular spread of the diffracted beam was always very close to the morphological curvature of the sample under investigation, proving that the energy passband of bent crystals can be controlled by simply imparting a selected curvature to the sample. The method of superficial indentations was found to offer high reproducibility and easy control of diffraction properties of the crystals. Moreover the method is cheap and simple, being based on mass production tools. A Laue lens made of crystals bent by superficial indentations can provide high-efficiency concentration of hard x-ray photons, leading significant improvement in many astrophysical applications.

Nuclear astrophysics presents an extraordinary scientific potential for the study of the most powerful sources and the most violent events in the Universe. But in order to take full advantage of this potential, telescopes should be at least an order of magnitude more sensitive than present technologies. Today, Laue lenses have demonstrated their capability of focusing gamma-rays in the 100 keV–1 MeV domain, enabling the possibility of building a new generation of instruments for which sensitive area is decoupled from collecting area. Thus we have now the opportunity of dramatically increase the signal/background ratio and hence improve significantly the sensitivity. With a lens, the best detector is no longer the largest possible within a mission envelope. The point spread function of a Laue lens measures a few centimeters in diameter, but the field of view is limited by the detector size. Requirements for a focal plane instrument are presented in the context of the Gamma-Ray Imager mission (proposed to European Space Agency, ESA in the framework of the first Cosmic Vision AO): a 15–20 cm a side finely pixellated detector capable of Compton events reconstruction seems to be optimal, giving polarization and background rejection capabilities and 30 arcsec of angular resolution within a field of view of 5 arc min.

Crystals are the elementary constituents of Laue lenses, an emerging technology which could allow the realization of a space-borne telescope 10–100 times more sensitive than existing ones, in the 100 keV–1.5 MeV energy range. This paper addresses the development of efficient crystals for the realization of a Laue lens. In the theoretical part, 35 candidate crystals, both pure and two-component crystals, are considered. Their peak reflectivity at 100, 500 keV and 1 MeV is calculated assuming they are mosaic crystals. It is found that, by careful selection of crystals, it is possible to achieve a reflectivity above 30% over the whole energy range, and even up to 40% in the lower part of the energy range. In the experimental part, three different materials (Si1−xGexwith a gradient of composition, mosaic Cu and Au) have been measured at both ESRF and ILL using highly monochromatic beams ranging from 300 to 816 keV. The aim was to check their homogeneity, quality and angular spread (mosaicity). These crystals have shown outstanding performance, such as reflectivity up to 31% at ∼600 keV (Au) or 60% at 300 keV (SiGe) and angular spread as low as 15 arcsec for Cu, fulfilling very well the requirements for a Laue lens application. An unexpected finding is that there are important discrepancies with Darwin's model when a crystal is measured using various energies.

The ATHENA mission, a European large (L) class X-ray observatory to be launched in 2028, will essentially consist of an X-ray lens and two focal plane instruments. The lens, based on a Wolter-I type double reflection grazing incidence angle design, will be very large (similar to 3 m in diameter) to meet the science requirements of large effective area (1-2 m(2) at a few keV) at a focal length of 12 m. To meet the high angular resolution (5 arc seconds) requirement the X-ray lens will also need to be very accurate. Silicon Pore Optics (SPO) technology has been invented to enable building such a lens and thus enabling the ATHENA mission. We will report in this paper on the latest status of the development, including details of X-ray test campaigns.

The Geant4 based ray-tracer used to support the development of Silicon Pore Optics is being extended to take into account more subtle effects that affect the performance of the optics, like thermo-mechanical stresses and detailed surface metrology. Its performance has also been increased to make it possible to simulate rapidly and in detail the optics of Athena so that various possible configurations can be explored and characterized providing important feedback to the development and system teams. In this paper we report on the state of the development.

With focusing of gamma rays in the nuclear-line energy regime starting to establish itself as a feasible and very promising approach for high-sensitivity γ-ray (line) studies of individual sources, optimizing the focal plane instrumentation for γ-ray lens telescopes is a prime concern. Germanium detectors offer the best energy resolution available at ∼2 keV FWHM at 1MeV and thus constitute the detector of choice for a spectroscopy mission in the MeV energy range. Using a Compton detector focal plane has three advantages over monolithic detectors: additional knowledge about (Compton) events enhances background rejection capabilities, the inherently finely pixellated detector naturally allows the selection of events according to the focal spot size and position, and Compton detectors are inherently sensitive to γ-ray polarization. We use the extensive simulation and analysis package assembled for the ACT vision mission study to explore achievable sensitivities for different Ge Compton focal plane configurations as a first step towards determining an optimum configuration.

We report on two NuSTAR observations of GRS 1741.9-2853, a faint neutron star low mass X-ray binary burster located 10' away from the Galactic center. NuSTAR detected the source serendipitously as it was emerging from quiescence: its luminosity was $6\times 10^{34}$ erg~s$^{-1}$ on 2013 July 31, and $5\times 10^{35}$ erg~s$^{-1}$ in a second observation on 2013 August 3. A bright, 800-s long, H-triggered mixed H/He thermonuclear Type I burst with mild photospheric radius expansion (PRE) was present during the second observation. Assuming that the luminosity during the PRE was at the Eddington level, a H mass fraction $X=0.7$ in the atmosphere, and a neutron star mass $M=1.4 M_{\odot}$, we determine a new lower limit on the distance for this source of $6.3 \pm 0.5$ kpc. Combining with previous upper limits, this places GRS 1741.9-2853 at a distance of 7 kpc. Energy independent (achromatic) variability is observed during the cooling of the neutron star, which could result from the disturbance of the inner accretion disk by the burst. The large dynamic range of this burst reveals a long power-law decay tail. We also detect, at a 95.6\% confidence level (1.7 $\sigma$), a narrow absorption line at $5.46\pm0.10$ keV during the PRE phase of the burst, reminiscent of the detection by Waki et al. (1984). We propose that the line, if real, is formed in the wind above the photosphere of the neutron star by a resonant K$\alpha$ transition from H-like Cr gravitationally redshifted by a factor $1+z=1.09$, corresponding to a radius range of 29.0 -- 41.4 km for a mass range of 1.4 -- 2.0 $M_{\odot}$., Comment: Accepted for publication in The Astrophysical Journal

We present a statistical analysis of the X-ray flux distribution of Sgr A* from the Chandra X-ray Observatory's 3 Ms Sgr A* X-ray Visionary Project (XVP) in 2012. Our analysis indicates that the observed X-ray flux distribution can be decomposed into a steady quiescent component, represented by a Poisson process with rate $Q=(5.24\pm0.08)\times10^{-3}$ cts s$^{-1},$ and a variable component, represented by a power law process ($dN/dF\propto F^{-\xi},$ $\xi=1.92_{-0.02}^{+0.03}$). This slope matches our recently-reported distribution of flare luminosities. The variability may also be described by a log-normal process with a median unabsorbed 2-8 keV flux of $1.8^{+0.9}_{-0.6}\times10^{-14}$ erg s$^{-1}$ cm$^{-2}$ and a shape parameter $\sigma=2.4\pm0.2,$ but the power law provides a superior description of the data. In this decomposition of the flux distribution, all of the intrinsic X-ray variability of Sgr A* (spanning at least three orders of magnitude in flux) can be attributed to flaring activity, likely in the inner accretion flow. We confirm that at the faint end, the variable component contributes ~10% of the apparent quiescent flux, as previously indicated by our statistical analysis of X-ray flares in these Chandra observations. Our flux distribution provides a new and important observational constraint on theoretical models of Sgr A*, and we use simple radiation models to explore the extent to which a statistical comparison of the X-ray and infrared can provide insights into the physics of the X-ray emission mechanism., Comment: 13 pages, 7 figures, accepted for publication in ApJ. Comments welcome

The Laue lens is a technology for gamma-ray astrophysics whereby gamma-rays of particular energies can be focused by a suitable arrangement of crystals. The Laue lens assembly station at UC Berkeley was used to build a technological demonstrator addressing the key issues of crystal mounting speed, crystal position and orientation accuracy, and crystal reflectivity. The new prototype is a lens segment containing a total of 48 5 x 5 mm2 crystals - 36 Iron and 12 Aluminium. The segment is composed of 8 partial rings, each of which is aligned to diffract an energy between 95 and 130 keV from a source at 12.5m with a focal length of 1.5 m.

We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with $\Gamma\sim1.3$-$2.3$ up to ~50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe K$\alpha$ fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broad-band X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density ($\sim10^{23}$ cm$^{-2}$), primary X-ray spectra (power-laws with $\Gamma\sim2$) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to $L_X \stackrel{>}{\sim} 10^{38}$ erg s$^{-1}$. Above ~20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses $M_{\rm WD} \sim 0.9 M_{\odot}$. Spectral energy distribution analysis suggests that G359.95-0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745-290, strongly favoring a leptonic origin of the GC TeV emission., Comment: 27 pages. Accepted for publication in the Astrophysical Journal

We use a 43-ks XMM-Newton observation to investigate the nature of sources first distinguished by a follow-up Chandra observation of the field surrounding INTEGRAL source IGR J17448-3232, which includes extended emission and a bright point source previously classified as a blazar. We establish that the extended emission is a heretofore unknown massive galaxy cluster hidden behind the Galactic bulge. The emission-weighted temperature of the cluster within the field of view is 8.8 keV, with parts of the cluster reaching temperatures of up to 12 keV; no cool core is evident. At a redshift of 0.055, the cluster is somewhat under-luminous relative to the X-ray luminosity-temperature relation, which may be attributable to its dynamical state. We present a preliminary analysis of its properties in this paper. We also confirm that the bright point source is a blazar, and we propose that it is either a flat spectrum radio quasar or a low-frequency peaked BL Lac object. We find four other fainter sources in the field, which we study and tentatively identify. Only one, which we propose is a foreground Galactic X-ray binary, is hard enough to contribute to IGR J17448-3232, but it is too faint to be significant. We thus determine that IGR J17448-3232 is in fact the galaxy cluster up to $\approx$45 keV and the blazar beyond., Accepted for publication in the Astrophysical Journal