We report on recent progress in the development of Laue lenses for applications in hard X/soft gamma-ray astronomy. Here, we focus on the realization of a sector of such a lens made of 11 bent germanium crystals and describe the technological challenges involved in their positioning and alignment with adhesive-based bonding techniques. The accurate alignment and the uniformity of the curvature of the crystals are critical for achieving optimal X-ray focusing capabilities. We assessed how the errors of misalignment with respect to the main orientation angles of the crystals affect the point spread function (PSF) of the image diffracted by a single sector. We corroborated these results with simulations carried out with our physical model of the lens, based on a Monte Carlo ray-tracing technique, adopting the geometrical configuration of the Laue sector, the observed assembly accuracy, and the measured curvatures of the crystals. An extrapolation of the performances achieved on a single sector to an entire Laue lens based on this model shows that a PSF with a half-power-diameter of 4.8 arcmin can be achieved with current technology. This has the potential to lead to a significant improvement in the sensitivity of spectroscopic and polarimetric observations in the 50 to 600 keV band.
The hard X-/soft gamma-ray band is still not well explored in astrophysics in spite of several unanswered science questions that can only be settled in this energy band, such as the origin of the 511 keV positron annihilation line from the Galactic Center region. The main reason is that this band has been explored so far with non-focusing instruments, that can achieve a limited sensitivity and angular resolution. Our goal is the development of a focusing telescope based on a Laue lens made of bent crystals of Silicon and Germanium, that diffract photons in the 50-700 keV band, with unprecedented angular resolution and sensitivity to continuum spectrum and to lines. Here some result will be reported concerning the elastic bending of the crystals by pressing them on substrates with one of the two main surfaces worked in order to get the same curvature of the lens. This is achieved thanks to accurately anodic bonding them to these substrates, avoiding/without the use of glue, in such a way to satisfy the required angular orientation of the crystals in the lens.
A new detection system for X-/Gamma-ray broad energy passband detectors for astronomy has been developed. This system is based on Silicon Drift Detectors (SDDs) coupled with scintillator bars; the SDDs act as a direct detector of soft (<30 keV) X-ray photons, while hard X-/Gamma-rays are stopped by the scintillator bars and the scintillation light is collected by the SDDs. With this configuration, it is possible to build compact, position sensitive detectors with unprecedented energy passband (2 keV – 10/20 MeV). The X and Gamma-ray Imaging Spectrometer (XGIS) on board the THESEUS mission, selected for Phase 0 study for M7, exploits this innovative detection system. The Wide Field Monitor - Imager and Spectrometer (WFM-IS) of the ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics) mission concept consists of 12 independent detection units, also based on this new technology. For the WFM-IS, a coded mask provides imaging capabilities up to 150 keV, while above this limit the instrument will act as a full sky spectrometer. However, it is possible to extend imaging capabilities above this limit by alternatively exploiting the Compton kinematics reconstruction or by using the information from the relative fluxes measured by the different cameras. In this work, we present the instrument design and results from MEGAlib simulations aimed at evaluating the effective area and the imaging performances of the WFM-IS above 150 keV.
We describe the science case, design and expected performances of the X/Gamma-ray Imaging Spectrometer (XGIS), a GRB and transients monitor developed and studied for the THESEUS mission project, capable of covering an exceptionally wide energy band (2 keV – 10 MeV), with imaging capabilities and location accuracy <15 arcmin up to 150 keV over a Field of View of 2sr, a few hundreds eV energy resolution in the X-ray band (<30 keV) and few micro seconds time resolution over the whole energy band. Thanks to a design based on a modular approach, the XGIS can be easily re-scaled and adapted for fitting the available resources and specific scientific objectives of future high-energy astrophysics missions, and especially those aimed at fully exploiting GRBs and high-energy transients for multi-messenger astrophysics and fundamental physics.
Hard-x/soft gamma-rays are probes of the most powerful phenomena in the universe. Unlike soft x-ray astrophysics, this band has benefited less from the technological advancement due to the difficulty to absorb this radiation and to the lack of focusing instrumentation. For these reasons the quest for innovative soft gamma-ray instrumentation is pressing and their effective recognition and realization are urgent. In this context, and in the framework of the AHEAD project, funded by the European Commission, the ASTENA experiment was proposed as an innovative mission concept to face some of the most debated questions in hard x-/gamma-ray astronomy. This effort will be done through the use of instruments based on groundbreaking technologies, capable of providing unprecedented broad energy passband in a wide field of view, high sensitivity observations and, at the same time, sub-arcminute localization of gamma-ray sources and polarimetric measurement. In this paper we describe the instruments on board ASTENA, the technologies involved, the performances achievable with their exploitation and their level of readiness.
Hard x-/soft gamma-ray astronomy (>100 keV) is a crucial field for the study of important astrophysical phenomena such as the 511 keV positron annihilation line in the galactic center region and its origin, gamma-ray bursts, soft gamma-ray repeaters, nuclear lines from SN explosions and more. However, several key questions in this field require sensitivity and angular resolution that are hardly achievable with present technology. A new generation of instruments suitable to focus hard x-/soft gamma-rays is necessary to overcome the technological limitations of current direct-viewing telescopes. One solution is using Laue lenses based on Bragg’s diffraction in a transmission configuration. To date, this technology is in an advanced stage of development and further efforts are being made in order to significantly increase its technology readiness level (TRL). To this end, massive production of suitable crystals is required, as well as an improvement of the capability of their alignment. Such a technological improvement could be exploited in stratospheric balloon experiments and, ultimately, in space missions with a telescope of about 20 m focal length, capable of focusing over a broad energy pass-band. We present the latest technological developments of the TRILL (technological readiness increase for Laue lenses) project, supported by ASI, devoted to the advancement of the technological readiness of Laue lenses. We show the method we developed for preparing suitable bent germanium and silicon crystals and the latest advancements in crystals alignment technology.
Focusing optics for hard x-/soft gamma-rays (above 100 keV) are in a development phase. One promising method is represented by the Laue lens technology that has already been validated through on-ground prototypes and balloon tests. Laue lens optics will be an outstanding tool for observing weak sources in a notably short integration time thanks to the excellent sensitivity they can provide. Such performances has been further increased with the employ of cylindrical bent crystals that are capable to dramatically narrow the Laue lens Point Spread Function (PSF). One aspect that is under investigation is the image aberrations for off-axis sources. This fact limits the Field of View (FoV) of a Laue lens to few arcmin. The employ of bent crystals in double diffraction configuration would reduce the mentioned aberration, increasing the FoV of the resulting Laue lens. Double diffraction crystals would represent an extension to hundreds of keV of the Lobster Eye (LE) principles that is well tested for focusing < 10 keV photons. We investigate pros and cons of the double diffraction configuration with respect to the single diffraction through Monte Carlo simulations and we compare their performances in terms of efficiency, PSF, pass-band and effective area. We also present preliminary tests performed at the LARIX facility to evaluate the technical feasibility of crystals with the aforementioned characteristics.
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