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The ATHENA X-ray telescope will be the largest X-ray optics ever built. The ground calibration of this mirror assembly raises significant difficulties due to its unprecedented size, mass and focal length. The VERT-X project aims at developing an innovative calibration system which will be able to accomplish to this extremely challenging task.The design is based on an X-ray parallel beam produced by an X-ray source positioned in the focus of a highly performing X-ray collimator; the beam will be accurately moved by a raster-scan mechanism covering all the ATHENA optics at different off-axis angles. The main driving factor in the VERT-X design is the ATHENA calibration requirement on the accuracy in the HEW measure which is 0.1”, all over the field of view. The VERT-X project, started in January 2019, is financed by ESA and conducted by a consortium that includes INAF together with EIE, Media Lario, BCV Progetti and GPAP.

A new type of x-ray facility, the Beam Expander Testing x-ray facility (BEaTriX), has been designed and is now under construction at INAF– Osservatorio Astronomico di Brera (Merate, Italy) to perform the acceptance tests of the silicon pore optics modules of the ATHENA X-ray telescope. Crystals of high perfection and large dimensions are needed in order to obtain a wide beam (20 × 6 cm2) with an X-ray divergence

The BEaTriX (Beam Expander Testing X-ray) facility, being completed at INAF-Brera Astronomical Observatory, will represent an important step in the acceptance roadmap of Silicon Pore Optics mirror modules, and so ensure the final angular resolution of the ATHENA X-ray telescope. Aiming at establishing the final angular resolution that can be reached and the respective fabrication/positioning tolerances, we have been dealing with a set of comprehensive optical simulations. Simulations based on wave optics were carried out to predict the collimation performances of the paraboloidal mirror, including the effect of surface errors obtained from metrology. Full-ray-tracing routines were subsequently employed to simulate the full beamline. Finally, wavefront propagation simulation allowed us assessing the sensitivity and the response of a wavefront sensor that will be utilized for the qualification of the collimated beam. We report the simulation results and the methodologies we adopted.

The construction of BEaTriX, the Beam Expander Testing X-ray facility, is underway at INAF-OAB (Osservatorio Astronomico di Brera). This laboratory-based X-ray source was designed to generate a broad (170 mm x 60 mm), uniform, and collimated X-ray beam, with a residual divergence of 1.5 arcsec HEW at either 1.49 keV and 4.51 keV. The main scientific driver for BEaTriX is represented by the opportunity to routinely calibrate the modular elements of the ATHENA (ESA) X-ray telescope, based on the silicon pore optics (SPO) technology. Nevertheless, the application domain of BEaTriX is potentially much wider (e.g., X-ray tomography). BEaTriX comprises a microfocus source of X-rays, followed by an optical chain including a collimating mirror, crystal monochromators, and an asymmetric beam expander. The final beam collimation and homogeneity relies on the optical quality of the optical components (X-ray source dimension, mirror polishing, crystal lattice regularity) and on their mutual alignment. In order to determine the most critical parameters, focus the development efforts, and establish specifications, a set of optical simulations has been built. Our paper describes the simulation tool we developed to this specific aim, and discusses the results achieved in terms of manufacturing and alignment tolerances.

ATHENA Silicon Pore Optics (SPO) Mirror Modules (MM) have to be tested and accepted prior to integration in the full ATHENA Mirror Assembly (MA). X-ray tests of the MMs are currently performed at the PTB laboratory of the BESSY synchrotron facility in pencil beam configuration, but they require a PSF reconstruction. Full illumination X-ray tests could be performed using a broad, low-divergent X-ray beam like the one in use at PANTER (MPE, Neuried, Germany), but the large volume to be evacuated makes it impossible to perform the functional tests at the MMs production rate (3 MM/day). To overcome these limitations, we started in 2012 to design a facility aimed at generating a broad (170 x 60 mm2), uniform and low-divergent (1.5 arcsec HEW) X-ray beam within a small lab (∼ 9 x 18 m2), to characterize the ATHENA MM. BEaTriX (the Beam Expander Testing X-ray facility) makes use of an X-ray microfocus source, a paraboloidal mirror, a crystal monochromation system, and an asymmetrically-cut diffracting crystal for the beam expansion. These optical components, in addition to a modular low-vacuum level (10-3 mbar), enable to match the ATHENA SPO acceptance requirements. The realization of this facility at INAF-OAB in Merate (Italy) is now on going. Once completed, BEaTriX can be used to test the Silicon Pore Optics modules of the ATHENA X-ray observatory, as well as other optics, like the ones of the Arcus mission. In this paper we report the advancement status of the facility.

A new type of X-ray facility, the Beam Expander Testing X-ray facility (BEaTriX), has been designed and is now under construction at INAF–Osservatorio Astronomico di Brera (Merate, Italy) to perform the acceptance tests of the silicon pore optics modules of the ATHENA X-ray telescope. Crystals of high perfection and large dimensions are needed in order to obtain a wide beam (20 × 6 cm) with an X-ray divergence of E/E < 10−5. To generate X-ray diffracted beams at an X-ray energy of 1.49 keV, ammonium dihydrogen phosphate (ADP) crystals have been considered among other possible choices, because of their reported crystal quality and because they can be grown at sufficiently large size at a reasonable price. In the present paper, the results of the characterization of crystalline quality and lattice planarity of a 20 × 20 × 2 mm ADP sample are reported.

A simple method is reported for the preparation of self-assembling sulfonated graphene oxide membranes (SGO-X) to be studied as a potential proton conductor for proton exchange membrane fuel cells (PEMFCs). The effect of three different sulfuric acid-to-GO molar ratios is investigated, the main aim being the identification of an optimal sulfonation interval ensuring a successful trade-off among composition, structural stability and functional properties. ATR-FTIR and EDX spectroscopies, SEM, thermogravimetry and static contact angle measurements allow to analyze the efficacy of the functionalization of graphene oxide (GO) with sulfonic acid groups (–SO3H) and the uniformity of the component's structure. A preliminary examination of the proton conductivity is performed on the most promising samples (SGO-1, SGO-20) by means of electrochemical impedance spectroscopy (EIS), together with the evaluation of water uptake, ion exchange capacity and degree of sulfonation. This introductory work demonstrates that the proposed SGO-X membranes exhibit notable water-retaining and proton-exchanging properties at elevated temperatures and reduced humidity, compared to pristine GO and Nafion® 212 benchmark specimens. Therefore, these innovative self-standing materials are proved to be worthy of additional studies for the optimization of their features, foreseeing the assessment of their behavior as a possible electrolyte in a PEM fuel cell.

This work focuses on the investigation of the capability of reduced graphene oxide (rGO) filters to remove metals from various wastewater. The process to produce rGO membranes is reported and discussed, as well as their ability to capture ions in complex solutions, such as tap or industrial wastewater. Multi-ion solutions, containing Cu2+, Fe3+, Ni2+, and Mn2+ to simulate mine wastewater, or Ca2+ and Mg2+ to mimic drinkable water, were used as models. In mono-ionic solutions, the best capture efficiency values were proved for Ca2+, Fe3+, and Ni2+ ions, while a matrix effect was found for multi-ion solutions. However, interesting capture efficiencies were measured in the range of 30&ndash, 90%, depending on the specific ion, for both single and multi-ion solutions. An attempt is proposed to correlate ions capture efficiency with ions characteristics, such as ionic radius or charge. Combining a satisfactory capture efficiency with low costs and ease of treatment unit operations, the approach here proposed is considered promising to replace other more complex and expensive filtration techniques.

Lynx is an X-ray mission concept with superb imaging capabilities (< 1arcsec Half Energy Width, HEW) and large throughput (2 m2 effective area @1keV). Several approaches are being considered to meet the challenging technological task of the mirror fabrication. Thin and light substrates are necessary to meet mass constraints. Monolithic fused silica shells are a possible solution if their thickness can be maintained to below 4 mm for mirror shells up to 3 m diameter. In this paper we present the opto-mechanical design of the mirror assembly, the technological processes, and the results achieved so far on a prototypal shells under development. In particular, emphasis is placed on the figuring process that is based on direct polishing and on ion beam figuring and on a temporary stiffening structure designed to support the shell during the figuring and polishing operations and to manage the handling of the shell through all phases up to integration into the telescope supporting structure.

PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required b right stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.

The New Hard X-ray Mission (NHXM) project will be operated by 2017 and is currently undergoing a Phase B study, under the coordination of the Italian Space Agency (ASI). The project is being proposed by an international team in the context of the ESA Call CV M3 as a Small Mission program, with a large Italian participation. It is based on 4 hard X-ray optics modules, each formed by 60 evenly spaced multilayer coated Wolter I mirror shells. An extensible bench is used to reach the 10 m focal length. The Wolter I monolithic substrates with multilayer coating are produced in NiCo by electroforming replication. Three of the mirror modules will host in the focal plane a hybrid a detector system (a soft X-ray Si DEPFET array plus a high energy CdTe detector). The detector of the fourth telescope will be a photoelectric polarimeter with imaging capabilities, operating from 2 up to 35 keV. The total on axis effective area of the three telescopes at 1 keV and 30 kev is of 1500 cm2 and 350 cm2 respectively, with an angular resolution of 20 arcsec HEW at 30 keV. In this paper we report on the design and development of the multilayer coated X-ray mirrors based on NiCo shells.

The high-quality surface characteristics, both in terms of figure error and of micro-roughness, required on the mirrors of a high angular resolution x-ray telescope are challenging, but in principle well suited with a deterministic and non-contact process like the ion beam figuring. This process has been recently proven to be compatible even with very thin (thickness around 0.4mm) sheet of glasses (like D263 and Eagle). In the last decade, these types of glass have been investigated as substrates for hot slumping, with residual figure errors of hundreds of nanometres. In this view, the mirrors segments fabrication could be envisaged as a simple two phases process: a first replica step based on hot slumping (direct/indirect) followed by an ion beam figuring which can be considered as a post-fabrication correction method. The first ion beam figuring trials, realized on flat samples, showed that the micro-roughness is not damaged but a deeper analysis is necessary to characterize and eventually control/compensate the glass shape variations. In this paper, we present the advancements in the process definition, both on flat and slumped glass samples.

The implementation of an X-ray mission with high imaging capabilities, similar to those achieved with Chandra (< 1 arc second Half Energy Width, HEW), but with a much larger throughput (2.5 m2 effective area @1 keV), represents a compelling request by the scientific community. To this end the Lynx/XRS mission is being studied in USA, with the participation of international partners. In order to figure out the challenging technological task of the mirror fabrication, different approaches are considered, based on monolithic and segmented shells. Starting from the experience done on the glass prototypal shell realized in the past years, the direct polishing of thin (2 mm thick) fused silica monolithic shells is being investigated as a possible solution. A temporary stiffening structure is designed to support the shell during the figuring and polishing operations and to manage the handling up to its integration in the telescope structure. After the grinding and the polishing phases, in order to achieve the required surface accuracy, a final ion beam figuring correction is foreseen. In this paper, we present the technological process and the results achieved so far on a prototypal shell under development.

Lynx is a large area and high angular resolution X-ray mission being studied by NASA to be presented to the next Decadal Survey for the implementation in the next decade. It aims to realize an X-ray telescope with the effective area similar to Athena (2 m2 at 1 keV) but with the same angular resolution of Chandra and a much larger Field Of View (up 20 arcmin x 20 arcmin). The science of X-ray Surveyor requires a large-throughput mirror assembly with sub-arcsec angular resolution. These future X-ray mirrors have a set of requirements which, collectively, represents very substantial advances over any currently in operation or planned for missions other than X-ray Surveyor. Of particular importance is achieving low mass per unit collecting area, while maintaining Chandra like angular resolution. Among the possible solutions under study, the direct polishing of both thin monolithic pseudo-cylindrical shells and segments made of fused silica are being considered as viable solutions for the implementation of the mirrors. Fused silica has very good thermomechanical parameters (including a very low CTE), making the material particularly well suited for for the production of the Lynx mirrors. It should be noted that the use of close shells is also very attractive, since the operations for the integration of the shells will be greatly simplified and the area lost due to the vignetting from the interfacing structures minimized even if the management of such big (diameter of 3 m) and thin shells have to be demonstrated. In this paper we will discuss a possible basic layout for a full shell mirror and a hybrid concept (segmented plus monolithic shells made of fused silica) as a second solution, for the Lynx/XRS telescope, discussing preliminary results in terms of optical and mechanical performance.

A technique to obtain lightweight and high-resolution focusing mirror segments for large aperture X-ray telescopes is the hot slumping of thin glass foils. In this approach, already successfully experimented to manufacture the optics of the NuSTAR X-ray telescope, thin glasses are formed at high temperature onto a precisely figured mould. The formed glass foils are subsequently stacked onto a stiff backplane with a common axis and focus to form an XOU (X-ray Optical Unit), to be later integrated in the telescope optic structure. In this process, the low thickness of the glass foils guarantees a low specific mass and a very low obstruction of the effective area. However, thin glasses are subject to deformations that may arise at any stage of the production process, thereby degrading the angular resolution. To solve this problem, several groups are working on the possibility to correct the mirror profile post-manufacturing, using piezoelectric elements exerting a tangential strain on the non-optical side of the glass mirrors. In this paper we show the results of the approach we have adopted, based on the application of piezoceramic patches on the backside of thin glass foils, previously formed by hot slumping. The voltage signals are supplied to the piezoelectric elements by a system of electrodes deposited on the same side of the mirror via a photolithographic process. Finally, the matrix of voltages to be used to correct the mirror shape can be determined in X-rays illumination by detection of the intra-focal image and consequent reconstruction of the longitudinal profile. We describe the production of some active mirrors with different arrangements of piezoelectric elements and the X-ray tests performed at the XACT X-ray facility to determine the optimal actuator geometry.

An important challenge for the X-ray astronomy of the new millennium is represented by the implementation of an X-ray telescope able to maintain the exquisite angular resolution of Chandra (with a sub-arcsec HEW, on-axis) but, at the same time, being characterized by a much larger throughput and grasp. A mission with similar characteristics is represented by the X-ray Surveyor Mission. The project has been recently proposed in USA and is being currently studied by NASA. It will host an X-ray telescope with an effective area of more than 2 square meters at 1 keV (i.e. 30 times greater than Chandra) and a 15-arcminutes field-of-view, with 1-arcsecond or better half-power diameter (versus the 4 arcmin diameter of Chandra). While the scientific reasons for implementing a similar mission are clear, being related to compelling problems like e.g. the formation and subsequent growth of black hole seeds at very high redshift or the identification of the first galaxy groups and proto-clusters, the realization of a grazing-angle optics system able to fulfil these specs remain highly challenging. Different technologies are being envisaged, like e.g. the use of adjustable segmented mirrors (with use of piezoelectric or magneto-restrictive film actuators on the back surface) or the direct polishing of a variety of thin substrates or the use of innovative correction methods like e.g. differential deposition, ionfiguring or the correction of the profile via controlled stress films. In this paper we present a possible approach based on the direct polishing (with final ion figuring correction of the profile) of thin SiO2 segmented substrates (typically 2 mm thick), discussing different aspects of the technology under implementation and presenting some preliminary results.

The hot slumping glass technology for X-ray mirror is under development and in the last years the results have been improved. Nustar is the first X-ray telescope based on slumped glass foils and it benefit is the low cost compared to the direct polishing of glass. With the slumping technique it is possible to maintain the glass mass to low values with respect to the direct polishing, but in general the angular resolution is worst. A further technique based on glass is the cold shaping of foils. The improved capabilities of manufacturing thin glass foils, pushed by the industrial application for screens, open new possibilities for X-ray mirror. The increase in strength of thin tempered glasses, the reduction of thickness errors and the good roughness of flat foils are potentially great advantages. In this paper a design of a mediumsize X-ray mirror module is analysed. It is based on integration of glass foils, stacked directly on a supporting structure that is part of the X-ray telescope using stiffening ribs as spacer between foils. The alignment of each stack is performed directly into the integration machine avoiding the necessity of the alignment of different stacked modules. A typical module (glass optic and metallic structure) provides an effective area of 10 cm2/kg at 1 keV (with a mass of about 50- 100 kg and a focal length of 10 m).

SOXS (Son Of X-Shooter) will be a unique spectroscopic facility for the ESO-NTT 3.5-m telescope in La Silla (Chile), able to cover the optical/NIR band (350-1750 nm). The design foresees a high-efficiency spectrograph with a resolution-slit product of ~4,500, capable of simultaneously observing the complete spectral range 350 - 1750 nm with a good sensitivity, with light imaging capabilities in the visible band. This paper outlines the status of the project., Comment: 10 pages, submitted to SPIE Astronomical Telescopes & Instrumentation 2016, paper 9908-152

Thermal effects in PLATO are analyzed in terms of uniform temperature variations, longitudinal and lateral temperature gradients. We characterize these effects by evaluating the PSF centroid shifts and the Enclosed Energy variations across the whole FoV. These patterns can then be used to gauge the thermal behavior of each individual telescope in order to improve the local photometric calibration across the PLATO field of view.

PLATO stands for PLAnetary Transits and Oscillation of stars and is a Medium sized mission selected as M3 by the European Space Agency as part of the Cosmic Vision program. The strategy behind is to scrutinize a large fraction of the sky collecting lightcurves of a large number of stars and detecting transits of exo-planets whose apparent orbit allow for the transit to be visible from the Earth. Furthermore, as the transit is basically able to provide the ratio of the size of the transiting planet to the host star, the latter is being characterized by asteroseismology, allowing to provide accurate masses, radii and hence density of a large sample of extra solar bodies. In order to be able to then follow up from the ground via spectroscopy radial velocity measurements these candidates the search must be confined to rather bright stars. To comply with the statistical rate of the occurrence of such transits around these kind of stars one needs a telescope with a moderate aperture of the order of one meter but with a Field of View that is of the order of 50 degrees in diameter. This is achieved by splitting the optical aperture into a few dozens identical telescopes with partially overlapping Field of View to build up a mixed ensemble of differently covered area of the sky to comply with various classes of magnitude stars. The single telescopes are refractive optical systems with an internally located pupil defined by a CaF2 lens, and comprising an aspheric front lens and a strong field flattener optical element close to the detectors mosaic. In order to continuously monitor for a few years with the aim to detect planetary transits similar to an hypothetical twin of the Earth, with the same revolution period, the spacecraft is going to be operated while orbiting around the L2 Lagrangian point of the Earth-Sun system so that the Earth disk is no longer a constraints potentially interfering with such a wide field continuous uninterrupted survey.

The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the selected medium class (M class) missions in the framework of the ESA Cosmic Vision 2015-2025 program. The mean scientific goal of PLATO is the discovery and study of extrasolar planetary systems by means of planetary transits detection. The opto mechanical subsystem of the payload is made of 32 normal telescope optical units (N-TOUs) and 2 fast telescope optical units (FTOUs). The optical configuration of each TOU is an all refractive design based on six properly optimized lenses. In the current baseline, in front of each TOU a Suprasil window is foreseen. The main purposes of the entrance window are to shield the following lenses from possible damaging high energy radiation and to mitigate the thermal gradient that the first optical element will experience during the launch from ground to space environment. In contrast, the presence of the window increases the overall mass by a non-negligible quantity. We describe here the radiation and thermal analysis and their impact on the quality and risks assessment, summarizing the trade-off process with pro and cons on having or dropping the entrance window in the optical train.

In this work, preliminary results about the use of a graphene oxide-based membrane as a possible alternative electrolyte for proton exchange membrane fuel cells (PEMFCs) are reported. Currently, one of the key components of a PEMFC is the ionomer electrolyte, typically the perfluorosulfonic acid membrane known as Nafion, due to its high proton conductivity in standard operating conditions (temperature range: 60-80 °C and relative humidity of 60-100 %), good mechanical properties and its effectiveness as gases separator. However, Nafion limits fuel cell maximum operating temperature, reduces its conductivity upon dehydration and suffers shrinkage and swelling if water content changes significantly [1]. An interesting alternative aiming to enhance FCs efficiency and to overcome drawbacks related to Nafion employment could be represented by graphene oxide (GO). GO is obtained by chemical functionalization and exfoliation of graphite and is attracting attention of the scientific community due to its easy dispersion in water, electronically insulating properties and gas barrier properties. Moreover, GO self-standing membranes have been found impermeable to many gases, whilst allowing permeation of water and minimizing fuel crossover [2]. Some works have reported the use of GO in composite membranes with known proton conductors such as Nafion, S-PEEK (sulfonated poly ether ether ketone), PBI (polybenzimidazole) and PVA (polyvinyl alcohol) [3]. Our research group has developed and characterized a pure GO membrane as a self-standing electrolytic membrane. In a typical experiment, a GO aqueous solution was prepared, then it was vacuum filtered and the cake was dried at 40 °C for 6 hours. A uniform self-assembled membrane was obtained and morphologically characterized by SEM, TGA, XRD and FT-IR analysis. A homogeneous surface and the presence of functional groups, i.e. hydroxyl, epoxy oxygen and carboxyl groups, which should be able in ensuring proper proton conductivity [4], have been achieved. A thickness of around 2 μm was measured. Since thickness is strongly related to initial GO solution concentration, other experiments are going to be done in order to increase it. After proper activation in a sulfuric acid solution, proton conductivity of the prepared membranes was determined by using impedance spectroscopy in the frequency range 1 MHz-1 Hz with an AC amplitude of 500 mV. Preliminary measurements were performed at 25 °C and variable relative humidities (RHs), ranging from anhydrous conditions to 100 %. RH was controlled by using sealed-off glass cell specifically designed to be immersed in a thermostatic bath with saturated aqueous solutions of different salts. A value of 8 mS/cm was found at 25 °C and anhydrous conditions. This is a very promising result since at the same operating conditions Nafion 212 has shown a conductivity of almost one magnitude lower. Conductivity increased upon increasing RH but such effect was less sharp than the one observed for Nafion and needs further tests and detailed investigation. Measurements at different temperatures, as well as in-situ electrical tests, are in progress and will be shown during the conference. References [1] Q. Li, R. He, J. O. Jensen, N. J. Bjerrum, “Approaches and Recent Development of Polymer Electrolyte Membranes for Fuel Cells Operating above 100 °C”, Chem. Mater, 15, 2003, 4896-4915 [2] R.R. Nair, H.A. Wu, P.N. Jayaram, I.V. Grigorieva, A.K. Geim, “Unimpeded Permeation of Water Through Helium-Leak-Tight Graphene-Based Membranes”, Science 335, 2012, 442-444 [3] T. Bayer, S.R. Bishop, M. Nishihara, K. Sasaki, S.M. Lyth, “Characterization of a graphene oxide membrane fuel cell”, J. Power Sources, 272, 2014, 239-247 [4] X. Changyan, S. Xiaomei, J. An, S. Lina, Z. Chen, C. Yunqi “Fabrication and Characteristics of Reduced Graphene Oxide Produced with Different Green Reductants”, Plos One, 10, 12, 2015, 1-15

Focusing mirrors for X-ray telescopes in grazing incidence, introduced in the 70s, are characterized in terms of their performance by their imaging quality and effective area, which in turn determines their sensitivity. Even though the on-axis effective area is assumed in general to characterize the collecting power of an X-ray optic, the telescope capability of imaging extended X-ray sources is also determined by the variation in its effective area with the off-axis angle. [...] The complex task of designing optics for future X-ray telescopes entails detailed computations of both imaging quality and effective area on- and off-axis. Because of their apparent complexity, both aspects have been, so far, treated by using ray-tracing routines aimed at simulating the interaction of X-ray photons with the reflecting surfaces of a given focusing system. Although this approach has been widely exploited and proven to be effective, it would also be attractive to regard the same problem from an analytical viewpoint, to assess an optical design of an X-ray optical module with a simpler calculation than a ray-tracing routine. [...] We have developed useful analytical formulae for the off-axis effective area of a double-reflection mirror in the double cone approximation, requiring only an integration and the standard routines to calculate the X-ray coating reflectivity for a given incidence angle. [...] Algebraic expressions are provided for the mirror geometric area, as a function of the off-axis angle. Finally, the results of the analytical computations presented here are validated by comparison with the corresponding predictions of a ray-tracing code., 12 pages, 11 figures, accepted for publication in "Astronomy & Astrophysics", section "Instruments, observational techniques, and data processing". Updated version after grammatical revision and typos correction

Optics for future X-ray telescopes will be characterized by very large aperture and focal length, and will be made of lightweight materials like glass or silicon in order to keep the total mass within acceptable limits. Optical modules based on thin slumped glass foils are being developed at various institutes, aiming at improving the angular resolution to a few arcsec HEW. Thin mirrors are prone to deform, so they require a careful integration to avoid deformations and even correct forming errors. On the other hand, this offers the opportunity to actively correct the residual deformation: a viable possibility to improve the mirror figure is the application of piezoelectric actuators onto the non-optical side of the mirrors, and several groups are already at work on this approach. The concept we are developing consists of actively integrating thin glass foils with piezoelectric patches, fed by voltages driven by the feedback provided by X-rays. The actuators are commercial components, while the tension signals are carried by a printed circuit obtained by photolithography, and the driving electronic is a multi-channel low power consumption voltage supply developed in-house. Finally, the shape detection and the consequent voltage signal to be provided to the piezoelectric array are determined in X-rays, in intra-focal setup at the XACT facility at INAF/OAPA. In this work, we describe the manufacturing steps to obtain a first active mirror prototype and the very first test performed in X-rays., Comment: Preprint version. The fully published paper is found at https://doi.org/10.1117/12.2189990

The Athena mission was selected for the second large-class mission, due for launch in 2028, in ESA's Cosmic Vision program. The current solution for the optics is based on the Silicon Pore Optics (SPO) technology with the goal of 2m2 effective area at 1keV (aperture about 3m diameter) with a focal length of 12m. The SPO advantages are the compactness along the axial direction and the high conductivity of the Silicon. Recent development in the fabrication of mirror shells based on the Slumped Glass Optics (SGO) makes this technology an attractive solution for the mirror modules for Athena or similar telescopes. The SGO advantages are a potential high collecting area with a limited vignetting due to the lower shadowing and the aptitude to curve the glass plates up to small radius of curvature. This study shows an alternative mirror design based on SGO technology, tailored for Athena needs. The main challenges are the optimization of the manufacturing technology with respect to the required accuracy and the thermal control of the large surface in conjunction with the low conductivity of the glass. A concept has been elaborated which considers the specific benefits of the SGO technology and provides an efficient thermal control. The output of the study is a preliminary design substantiated by analyses and technological studies. The study proposes interfaces and predicts performances and budgets. It describes also how such a mirror system could be implemented as a modular assembly for X-ray telescope with a large collecting area.

The realization of X-ray telescopes with imaging capabilities in the hard (> 10 keV) X-ray band requires the adoption of optics with shallow (< 0.25 deg) grazing angles to enhance the reflectivity of reflective coatings. On the other hand, to obtain large collecting area, large mirror diameters (< 350 mm) are necessary. This implies that mirrors with focal lengths ≥10 m shall be produced and tested. Full-illumination tests of such mirrors are usually performed with onground X-ray facilities, aimed at measuring their effective area and the angular resolution; however, they in general suffer from effects of the finite distance of the X-ray source, e.g. a loss of effective area for double reflection. These effects increase with the focal length of the mirror under test; hence a "partial" full-illumination measurement might not be fully representative of the in-flight performances. Indeed, a pencil beam test can be adopted to overcome this shortcoming, because a sector at a time is exposed to the X-ray flux, and the compensation of the beam divergence is achieved by tilting the optic. In this work we present the result of a hard X-ray test campaign performed at the BL20B2 beamline of the SPring-8 synchrotron radiation facility, aimed at characterizing the Point Spread Function (PSF) of a multilayer-coated Wolter-I mirror shell manufactured by Nickel electroforming. The mirror shell is a demonstrator for the NHXM hard X-ray imaging telescope (0.3 - 80 keV), with a predicted HEW (Half Energy Width) close to 20 arcsec. We show some reconstructed PSFs at monochromatic X-ray energies of 15 to 63 keV, and compare them with the PSFs computed from post-campaign metrology data, self-consistently treating profile and roughness data by means of a method based on the Fresnel diffraction theory. The modeling matches the measured PSFs accurately.

Optics for future X-ray telescopes will be characterized by very large aperture and focal length, and will be made of lightweight materials like glass or plastic in order to keep the total mass within acceptable limits. Optics based on thin slumped glass foils are currently in use in the NuSTAR telescope and are being developed at various institutes like INAF/OAB, aiming at improving the angular resolution to a few arcsec HEW. Another possibility would be the use of thin plastic foils, being developed at SAO and the Palermo University. Even if relevant progresses in the achieved angular resolution were recently made, a viable possibility to further improve the mirror figure would be the application of piezoelectric actuators onto the non-optical side of the mirrors. In fact, thin mirrors are prone to deform, so they require a careful integration to avoid deformations and even correct forming errors. This however offers the possibility to actively correct the residual deformation. Even if other groups are already at work on this idea, we are pursuing the concept of active integration of thin glass or plastic foils with piezoelectric patches, fed by voltages driven by the feedback provided by X-rays, in intra-focal setup at the XACT facility at INAF/OAPA. In this work, we show the preliminary simulations and the first steps taken in this project.

This work is developed in the framework of AXYOM project, which proposes to study the application of a system of piezoelectric actuators to grazing-incidence X-ray telescope optic prototypes: thin glass or plastic foils, in order to increase their angular resolution. An integrated optomechanical model has been set up to evaluate the performances of X-ray optics under deformation induced by Piezo Actuators. Parametric evaluation has been done looking at different number and position of actuators to optimize the outcome. Different evaluations have also been done over the actuator types, considering Flexible Piezoceramic, Multi Fiber Composites piezo actuators, and PVDF.

Thin glass foils are considered good candidates to build a segmented X -ray telescope with effective area as large as 2 m 2 and angular resolution better than 5 arcsec . In order to produce thin glass mirror segments, we developed a direct hot slumping technique assisted by pressure, in which the shape of a mould is replicated onto the optical surface of the glass. In this paper we present the result obtained with AF32 ( by Schott) and EAGLE XG (by Corning) glass types. The selected mould material is Zerodur K20, as it does not require any anti -sticking layer and has a good matching , in terms of Coefficient of Thermal Expansion, with both glass types. Our group already pro duced a few prototypes, reaching angular resolution near 20 arcsec . In this work , relevant steps forward aimed at attaining a 5 arcsec angular r esolution are described, along with the tuning of f ew key parameters in the slumping process. The results obtain ed on a newly procured cylindrical Zerodur K20 mould are presented. Keywords: hot slumping, thin glass mirrors, Zerodur K20, X-ray astronomy, astronomical telescopes

X-rays are particularly suited to probe the physics of extreme objects. However, despite the enormous improvements of X-ray Astronomy in imaging, spectroscopy and timing, polarimetry remains largely unexplored. We propose the photoelectric polarimeter Gas Pixel Detector (GPD) as an instrument candidate to fill the gap of more than thirty years of lack of measurements. The GPD, in the focus of a telescope, will increase the sensitivity of orders of magnitude. Moreover, since it can measure the energy, the position, the arrival time and the polarization angle of every single photon, allows to perform polarimetry of subsets of data singled out from the spectrum, the light curve or the image of source. The GPD has an intrinsic very fine imaging capability and in this work we report on the calibration campaign carried out in 2012 at the PANTER X-ray test facility of the Max-Planck-Institut f\"ur extraterrestrische Physik of Garching (Germany) in which, for the first time, we coupled it to a JET-X optics module with a focal length of 3.5 m and an angular resolution of 18 arcsec at 4.5 keV. This configuration was proposed in 2012 aboard the X-ray Imaging Polarimetry Explorer (XIPE) in response to the ESA call for a small mission. We derived the imaging and polarimetric performance for extended sources like Pulsar Wind Nebulae and Supernova Remnants as case studies for the XIPE configuration, discussing also possible improvements by coupling the detector with advanced optics, having finer angular resolution and larger effective area, to study with more details extended objects., Comment: Accepted for publication in The Astrophysical Journal Supplement

The Hot Slumping Technology is under development by several research groups in the world for the realization of grazing-incidence segmented mirrors for X-ray astronomy, based on thin glass plates shaped over a mould at temperatures above the transformation point. The performed thermal cycle and related operations might have effects on the strength characteristics of the glass, with consequences on the structural design of the elemental optical modules and consecutively on the entire X-ray optic for large astronomical missions like IXO and ATHENA. The mechanical strength of glass plates after they underwent the slumping process was tested through destructive double-ring tests in the context of a study performed by the Astronomical Observatory of Brera with the collaboration of Stazione Sperimentale del Vetro and BCV Progetti. The entire study has been realized on more than 200 D263 Schott borosilicate glass specimens of dimension 100 mm x 100 mm and thickness 0.4 mm, either flat or bent at a Radius of Curvature of 1000 mm through the particular pressure assisted hot slumping process developed by INAF-OAB. The collected experimental data have been compared to non-linear FEM analyses and treated with Weibull statistic to assess the current IXO glass X-ray telescope design, in terms of survival probability, when subject to static and acoustic loads characteristic of the launch phase. The paper describes the activities performed and presents the obtained results., Comment: Accepted for publication in Optical Enginnering (Jun 26, 2014)

The Joint European X-ray Telescope (JET-X) was the core instrument of the Russian Spectrum-X-gamma space observatory. It consisted of two identical soft X-ray (0.3 - 10 keV) telescopes with focusing optical modules having a measured angular resolution of nearly 15 arcsec. Soon after the payload completion, the mission was cancelled and the two optical flight modules (FM) were brought to the Brera Astronomical Observatory where they had been manufactured. After 16 years of storage, we have utilized the JET-X FM2 to test at the PANTER X-ray facility a prototype of a novel X-ray polarimetric telescope, using a Gas Pixel Detector (GPD) with polarimetric capabilities in the focal plane of the FM2. The GPD was developed by a collaboration between INFN-Pisa and INAF-IAPS. In the first phase of the test campaign, we have re-tested the FM2 at PANTER to have an up-to-date characterization in terms of angular resolution and effective area, while in the second part of the test the GPD has been placed in the focal plane of the FM2. In this paper we report the results of the tests of the sole FM2, using an unpolarized X-ray source, comparing the results with the calibration done in 1996., Author's accepted manuscript posted to arXiv.org as permitted by Springer's Self-Archiving Policy. The final publication is available at http://rd.springer.com/article/10.1007%2Fs10686-013-9365-y

The implementation of a X-ray mission with high imaging capabilities, similar to those achieved with Chandra (< 1 arcsec Half Energy Width, HEW), but with a much larger throughput is a very attractive perspective, even if challenging. For such a mission the scientific opportunities, in particular for the study of the early Universe, would remain at the state of the art for the next decades. At the beginning of the new millennium the XEUS mission has been proposed, with an effective area of several m2 and an angular resolution better than 2 arcsec HEW. Unfortunately, after the initial study, this mission was not implemented, mainly due to the costs and the low level of technology readiness. Currently the most advanced proposal for such a kind of mission is the SMART-X project, led by CfA and involving several other US Institutes. This project is based on adjustable segments of thin foil mirrors with piezo-electric actuators, aiming to achieve an effective area < 2 m2 at 1 keV and an angular resolution better than 1 arcsec HEW. Another attractive technology to realize an X-ray telescope with similar characteristics is being developed at NASA/Goddard. In this case the mirrors are based on Si substrates that are super-polished and figured starting from a bulky Si ingot, from which they are properly cut. Here we propose an alternative method based on precise direct grinding, figuring and polishing of thin (a few mm) glass shells with innovative deterministic polishing methods. This is followed by a final correction via ion figuring to obtain the desired accuracy in order to achieve the 1 arc sec HEW requirement. For this purpose, a temporary stiffening structure is used to support the shell from the polishing operations up to its integration in the telescope supporting structure. We will present the technological process under development, the results achieved so far and some mission scenarios based on this kind of optics, aiming to achieve an effective area more than 10 times larger than Chandra and an angular resolution of 1 arcsec HEW on axis and of a few arcsec off-axis across a large field of view (1 deg in diameter).

Long-term maintenance of hepatocyte viability and differentiated function expression is crucial for bioartificial liver support. The maintenance of hepatocyte function in a bioreactor is still a problem. A major advance was the recognition that hepatocytes in attachment cultures can maintain their differentiation longer. To restore hepatocyte polarity and prolong their function, we developed a new bioreactor with a cross-flow geometry configuration and an original hepatocyte extracellular autologous biomatrix (Porcine Bio-Matrix) support. To test this new bioreactor, we compared it with a standard bioartificial liver cartridge in a suitable surgical model of acute liver failure in pigs. In our model, we performed a total hepatectomy, followed by partial liver transplantation after an 18 hour anhepatic phase. The results showed that the bioreactor containing the biomatrix was able to bridge the animal to transplantation and to sustain the transplanted liver until all function recovered (80% of animals survived, p = 0.0027). No animal survived more than 24 hours after liver transplantation in the group treated with the traditional bioartificial liver, whereas hepatocyte viability on the Porcine Bio-Matrix was 65% after 12 hours of treatment. The results suggest that our biomatrix is a suitable cell support and guarantees long-term maintenance of metabolic activity of hepatocytes. Further studies are needed, but the results obtained with this new three-dimensional bioreactor are promising, and its potential is attractive.

This paper want to show an innovative amateur oriented telescope with an unconventional alt-alt conguration. The goal is to make a telescope with good optical quality reducing production costs by adopting a gimbal based mounting to develop an alt-alt conguration suitable for a telescope. Reduce costs while preserving the optical quality is a necessary condition to allow small groups of amateur astronomers, schools and cultural clubs, with reduced economic resources, to acquire an astronomical instrument that encourages learning and advancing astrophysical knowledge. This unconventional mechanism for the realization of a telescope alt-alt provides signicant advantages. The traditional rotary motors coupled with expensive precision bearings are replaced with two simple linear actuators coupled to a properly preloaded gimbal joint and the cell becomes the primary structure of the telescope. A second advantage would be secured by mechanical simplicity evident in the easy portability of the instrument. The frame alt-alt has some limitations on the horizon pointing but does not show the zenith blind spot of the alt-az mount. A dedicated alt-alt pointing and tracking model is under development to be compatible with commercial telescope softwares and with the proposed new mounting.

The mirrors of the International X-ray Observatory (IXO) were based on a large number of high quality segments, aiming at achieving a global spatial resolution better than 5” HEW while giving a large collecting area (around 3m 2 @ 1 keV). A study concerning the hot slumping of thin glass foils was started in Europe, funded by ESA and led by the Brera Astronomical Observatory (INAF-OAB), for the development of a replication technology based on glass material. The study is currently continuing even after the IXO program has been descoped and renamed ATHENA, in the perspective of using the technology under development for other future missions or applications. INAF-OAB efforts have been focused on the "Direct" slumping approach with convex moulds, meaning that during the thermal cycle the optical surface of the glass is in direct contact with the mould surface. The single mirror segments are made of thin glass plates (0.4 mm thick), with a reflecting area of 200 mm × 200 mm. The adopted integration process foresees the use of glass reinforcing ribs for bonding together the plates in such a way to form a rigid and stiff stack of segmented mirror shells; the stack is supported by a thick backplane. During the bonding process, the plates are constrained in close contact with the surface of a precisely figured integration master by the application of vacuum pump suction. In this way, the springback deformations and the low frequency errors still present in the plates' profile after slumping can be corrected. The status of the technology development is presented in this paper, together with the description and metrology of the prototypes already realized or under construction at the Observatory laboratories.

The mirrors of the International X-ray Observatory (IXO) were based on of a large number of high quality segments, aiming at achieving a global spatial resolution better than 5 arcsec (HEW). A study concerning the slumping of thin glass foils for the IXO mirrors is under development in Europe, funded by ESA and led by the Brera Observatory and is continuing even after that the programhas been descoped, in the perspective of using the technology under development for other future missions. After a preliminary trade-off study, we have focused our the effort on the "Direct" slumping approach, based on the use of convex moulds. In this case during the thermal cycle the optical surface of the glass is in direct contact with the mould surface. The thin plates are made of thin glass sheets (0.4 mm thick), with a reflecting area of 200 mm × 200 mm. The adopted integration process foresees the use of reinforcing ribs for bonding together the plates and forming in that way a rigid and stiff stack of segmented mirror shells; the stack is supported by a thick backplane. During the bonding process the plates are constrained to stay in close contact with the surface of the master (i.e. the same mould used for the hot slumping process) by the application of vacuum pump suction. In this way the spring-back deformations and low frequency errors still present on the foil profile after slumping can be corrected. In this paper we will give an overview and a status report of the project.

The large dimensions of the future X-ray telescopes, with diameters ranging from 3.5 m and up to several meters, will require the adoption of segmented optics and hence the development of new technologies for their manufacturing. These technologies are based on lightweight materials and structures to comply with the mass constrains imposed by the launcher. The Astronomical Observatory of Brera (INAF-OAB) is involved in the development of a glass shaping technology for the production of grazing incidence segmented optics to be employed onboard the next generation of Xray Observatories. This technique, named "Hot slumping technology with pressure", is based on the viscosity change of the glass with the temperature: by applying a suitable thermal cycle the viscosity of the glass is decreased enough to allow its slumping on a mould so to replicate its shape without significantly degrade its surface finishing. Following this replication approach, it is possible to obtain, with the same mould, a number of equal mirror segments that will be integrated and aligned in the telescope aperture so to create a mirror shell in configuration Wolter I. The entire study has been financed by ESA in the context of the International X-ray Observatory (IXO) mission with the aim of developing a back-up technology for the IXO mirror manufacturing. The study started in 2009 and it is scheduled to finish in 2012 with the production of representative module prototypes, named POC and XOU_BB. After a brief review of past results, this paper reports the latest advancement in the slumping of Schott glass D263 foils on Fused Silica and Zerodur moulds and its status as for summer 2011.

Effective area requirements for the large X-ray mirror of the International X-ray Observatory (IXO) are about 3 m2 at 1keV, 0.65 m2 at 6 keV and 150 cm2 at 30 keV. Because of its large dimension, the telescope cannot be realized as a monolithic structure but rather it requires the integration and assembly in the telescope optical bench of a number of basic module units, called X-ray Optical Unit (XOU). We are currently studying a method for the production of these basic units that is based on the slumping technology for the production of thin glass segmented mirrors. It foresees the implementation of a stacking integration concept based on the use of reinforcing ribs connecting the glass segments in order to create very stiff structures. This paper reports on the last design of the single optical module and describe the results of FEM analyses that show how it is possible to use an innovative approach to the integration of the slumped glass foils.

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 arcmin $\times$ 15 arcmin and with an energy resolution of 20 % at 6 keV. The Minimum Detectable Polarization is 12 % for a source having a flux of 1 mCrab and 10^5 s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher.The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75 % open to the community while 25 % + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument., 42 pages, 28 figures

PLATO is the acronym of PLAnetary Transits and Oscillations of stars, and it is a mission proposed for the ESA Cosmic Vision program in the Medium size program, with the target to detect and characterize exoplanets by the means of their transit on a bright star. The instrumental overall layout proposed by the Plato Payload Consortium consists in a multitelescope concept instrument, composed by several tens of telescope units, for which we are developing an all refractive optical solution. These devices are characterized by a very large Field of View (more than 20 degrees on one side) with an optical quality that fits most of the energy into a single CCD pixel. Such a goal can be achieved in a variety of solutions, some including aspheric elements as well. A complete prototype of one telescope unit is foreseen to be built initially (during phase B1) to show the alignment feasibility and, only in a second moment (Phase B2), to perform full environmental and functional test. The aim of this article is to describe the alignment, integration and verification strategy of the opto-mechanics of the prototype. Both the approaches of testing the telescope at the target working temperature or to test it at ambient temperature around a displaced zero point, taking into account the effects of thermal deformations, are considered and briefly sketched in this work.

The New Hard X-ray Mission (NHXM) project will be operated by 2016 and is currently undergoing the Phase B study. It is based on 4 hard X-ray optics modules, each formed by 60 evenly spaced multilayer coated Wolter I mirror shells. An extensible bench is used to reach the 10 m focal length. The Wolter I monolithic substrates with multilayer coating are produced in NiCo by electroforming replication. Three of the mirror modules will host in the focal plane a hybrid a detector system (a soft X-ray Si DEPFET array plus a high energy CdTe detector). The detector of the fourth telescope will be a photoelectric polarimeter with imaging capabilities, operating from 2 up to 35 keV. The total on axis effective area of the three telescopes at 1 keV and 30 kev is of 1500 cm 2 and 350 cm 2 respectively, with an angular resolution of 20 arcsec HEW at 30 keV. In this paper we report on the design and development of the multilayer optics of the mission, based on thin replicated Ni mirror shells.

The Energetic X-ray Imaging Survey Telescope (EXIST) will continuously survey the full sky in scanning mode for 2- years followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded mask Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band. SXI is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. Here we will present the optical and mechanical design of the SXI mirror module, that includes also a pre-collimator and a magnetic diverter to ensure a low background on the detector. In particular we will describe the mirror module characteristics in term of effective area, imaging capability, thermal requirement and mechanical properties. The current optical design foresees 26 shells providing an effective area comparable to one XMM-Newton mirror module up to 3 keV. The realization of these shells is based on the well-proven Nickel replication-process technology.

The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the three medium class (M class) missions selected in 2010 for definition study in the framework of the ESA Cosmic Vision 2015-2025 program. The main scientific goals of PLATO are the i) discovery and study of extra-solar planetary systems, (including those hosting Earth-like planets in their habitable zone) by means of planetary transits detection from space and radial velocity follow-up from ground, and ii) the characterization of the hosting stars through seismic analysis, in order to determine with high accuracy planetary masses and ages. According to the study made by the PLATO Payload Consortium (PPLC) during the PLATO assessment phase, the scientific payload consists of 34 all refractive telescopes having small aperture (120 mm) and wide field of view (greater than 1000 degree2) observing over 0.5-1 micron wavelength band. The telescopes are mounted on a common optical bench and are divided in four families with an overlapping line-of-sight in order to maximize the science return. In this paper, we will describe the detailed design of the Telescope Optical Units (TOUs) focusing on the selected optical configuration and the expected performances.

In the last decade a new window for ground-based high energy astrophysics has been opened. It explores the energy band from about 100 GeV to 10 TeV making use of Imaging Atmospheric Cherenkov Telescopes (IACTs). Research in Very High Energy (VHE) gamma-ray astronomy is improving rapidly and thanks to the newest facilities as MAGIC, HESS and VERITAS astronomers and particle physicists are obtaining surprising implications in the theoretical models. New projects have been started as the European Cherenkov Telescope Array (CTA) and the U.S. Advanced Gamma-ray Imaging System (AGIS). The aim is to enhance both the sensitivity and the energy band coverage to perform imaging, photometry and spectroscopy of sources. In this framework, tens of thousands of optical mirror panels have to be manufactured, tested and mounted into the telescopes. Because of this high number of mirrors it is mandatory to develop a technique easily transferable to industrial mass production, but keeping the technical and cost-effectiveness requirements of the next generation of TeV telescopes. In this context the Astronomical Observatory of Brera (INAF-OAB) is investigating a technique for the manufacturing of stiff and lightweight glass mirror panels with modest angular resolution. These panels have a composite sandwich-like structure with two thin glass skins on both sides of a core material; the reflecting skin is optically shaped using an ad-hoc slumping procedure. The technology here presented is particularly attractive for the mass production of cost-effective mirror segments with long radius of curvature like those required in the primary mirrors of the next generation of Cherenkov telescopes. In this paper we present and discuss some relevant results we have obtained from the latest panels realized.

The New Hard X-ray Mission (NHXM) Italian project will be operated by 2016. It is based on 4 hard X-ray optics modules, each formed by 60 evenly spaced multilayer coated Wolter I mirror shells. For the achievement of a long focal length (10 m) an extensible bench is used. The pseudo-cylindrical Wolter I monolithic substrates where the multilayer coating is applied will be produced using the Ni electroforming replica approach. For three of the four mirror modules the focal plane will host a hybrid a detector system, consisting in the combination of a Si-based low energy detector (efficient from 0.5 up to ~ 15 keV) , on top of a high energy CdTe pixellated detector (efficient from 10 keV up to ~ 80 keV); the two cameras will be surrounded by both a passive shield and an anticoincidence shield. The total on axis effective area of the three telescopes at 1 keV and at 30 kev is of 1500 cm2 and 350 cm2 respectively. The angular resolution requirement is better than 20 arcsec HEW at 30 keV, while the Field of View at 50% vignetting is 12 arcmin (diameter). The payload is finally completed with the fourth telescope module, that will have as a focal plane detector a high sensitivity imaging photoelectric polarimetric system, operating from 2 up to 35 keV. In this paper, after an overview of the mission configuration and its scientific goals, we report on the design and development of the multilayer optics of the mission, based on thin replicated Ni mirror shells.

The Energetic X-ray Imaging Survey Telescope (EXIST) is a mission that has been studied for the NASA Physics of the Cosmos Program. EXIST will continuously survey the full sky by scanning for 2-years (with 2-3 interruptions per day for GRB follow-up) followed by a 3-years pointing phase. The mission includes three instruments: a High Energy coded mask Telescope; a 1.1m aperture optical-IR Telescope; and a Soft X-ray Imager (SXI), sensitive in the 0.1-10 keV band. SXI is proposed as a contribution of ASI-Italy, fully developed by Italian institutes. The current optical design foresees 26 shells providing an effective area comparable to one XMM-Newton mirror module up to 3 keV and somewhat lower from 3 to 10 keV. The realization of these shells is based on the well-proven Nichel replication-process technology. Here we will present the optical design of the SXI mirror module and describe its characteristics in term of effective area and imaging capability, summarizing also the characteristics of the full SXI telescope.

In the last decade Very High Energy (VHE) gamma-ray astronomy has improved rapidly opening a new window for ground-based astronomy with surprising implications in the theoretical models. Nowadays, it is possible to make imaging, photometry and spectroscopy of sources with good sensitivity and angular resolution using new facilities as MAGIC, HESS and VERITAS. The latest results of astronomy in the TeV band obtained using such facilities demonstrate the essential role of this window for high energy astrophysics. For this reason new projects (e.g. CTA and AGIS) have been started with the aim to increase the sensitivity and expand the energy band coverage. For such telescopes arrays probably tens of thousands of optical mirror panels must be manufactured with an adequate industrial process, then tested and mounted into the telescopes. Because of the high number of mirrors it is mandatory to perform feasibility studies to test various techniques to meet the technical and cost-effectiveness requirements for the next generation TeV telescopes as CTA and AGIS. In this context at the Astronomical Observatory of Brera (INAF-OAB) we have started the investigation of different techniques for the manufacturing of stiff and lightweight optical glass mirror panels. These panels show a sandwich-like structure with two thin glass skins on both sides, the reflective one being optically shaped using an ad-hoc slumping procedure. The technologies here presented can be addressed both for primary or secondary mirrors for the next generation of Cherenkov telescopes. In this paper we present and discuss the different techniques we are investigating with some preliminary results obtained from test panels realized.

The Astronomical Observatory of Brera (INAF-OAB) is investigating a novel slumping technique for the manufacturing of stiff and lightweight optical segments. We propose a 2-steps technique: initially the procedure foresees to manufacture a mirror segment using the hot slumping technique. This step produces a thin and floppy Borofloat glass shell using the slumping of a glass sheet onto a ceramic mould that has a surface with a high optical quality. After this step, this curved shell is assembled and glued to a stiff substrate made in foamed and pre-shaped material. On the back of the substrate it is also glued a flat sheet of the same glass. This procedure combine the good optical performances achievable on optics produced by means of the hot slumping technique with the lightweight and stiffness of the foamed material and, finally, the good structural properties achievable in sandwich-like structures. This approach could be in principle used for the production of mirrors for a number of applications, from the primary segmented mirror for large telescopes to the mirrors for the future Cherenkov telescopes nowadays under development. This paper describes the process of production of a prototype optical segment and the status of the investigation.

The study of Gamma-ray bursts (GRBs) is a key field to expand our understanding of several astrophysical and cosmological phenomena. SVOM is a Chinese-French Mission which will permit to detect and rapidly locate GRBs, in particular those at high redshift, and to study their multiwavelength emission. The SVOM satellite, to be launched in 2013, will carry wide field instruments operating in the X/gamma-ray band and narrow field optical and soft X-ray telescopes. Here we describe a small soft X-ray telescope (XIAO) proposed as an Italian contribution to the SVOM mission. Thanks to a grazing incidence X-ray telescope with effective area of ~120 cm^2 and a short focal length, coupled to a very compact, low noise, fast read out CCD camera, XIAO can substantially contribute to the overall SVOM capabilities for both GRB and non-GRB science., 12 pages, 7 figures; Presented at ``SPIE Astronomical Telescopes and Instrumentation 2008'' - Marseille, June 23-28, 2008