Abstract. The JEM-X monitor provides X-ray spectra and imaging with arcminute angular resolution in the 3 to 35 keV band. The good angular resolution and the low energy response of JEM-X plays an important role in the identification of gamma ray sources and in the analysis and scientific interpretation of the combined X-ray and gamma ray data. JEM-X is a coded aperture instrument consisting of two identical, coaligned telescopes. Each of the detectors has a sensitive area of 500 cm 2 , and views the sky through its own coded aperture mask. The two coded masks are inverted with respect to each other and provides an angular resolution of 3 across an effective field of view of about 10• diameter.
We report on the first results obtained from our development project of focusing gamma-rays (>60 keV) by using Laue lenses. The first lens prototype model has been assembled and tested. We describe the technique adopted and the lens focusing capabilities at about 100 keV
We report on the feasibility study of a Laue lens for hard X-rays (> 60 keV) based on mosaic crystals, for astrophysical applications. In particular we discuss the scientific motivations, its functioning principle, the procedure followed to select the suitable crystal materials, the criteria adopted to establish crystal dimensions and their distribution on the lens in order to obtain the best lens focusing capabilities, and the criteria for optimizing the lens effective area in a given passband. We also discuss the effects of misalignments of the crystal tiles due to unavoidable mechanical errors in assembling the lens. A software was developed to face all these topics and to evaluate the expected lens performance. SCIENTIFIC MOTIVATIONSThe role of hard X-ray astronomy (> 10 keV) is now widely recognized. The numerous results obtained with the most recent satellite missions (BeppoSAX , Rossi-XTE ) on many classes of X-ray celestial sources have demonstrated the importance of the broad band (0.1 ÷ 300 keV) spectroscopy in order to derive an unbiased picture of the celestial source physics, like to establish the source geometry, the physical phenomena occurring in the emission region, the radiation production mechanisms, an unbiased separation of the contribution of thermal emission phenomena from the phenomena due to the presence of high energy plasmas (thermal or not thermal) and/or magnetic fields and/or source rotation.In spite of the excellent performance of the high energy instrument PDS (Phoswich Detection System) aboard BeppoSAX , 1 the most sensitive instrument ever flown in the 15-200 keV energy band, even in the case of the strongest Galactic (e.g., Cyg X-1 in soft state, Her X-1) and extragalactic (e.g., 3C373, MKN 3) X-ray sources, the statistical quality of the measured spectra becomes poor in the highest part of the instrument passband (> 80 keV). Thus the development of focusing optics in this band and, more generally, in the entire passband covered by the BSAX/PDS and possibly beyond it, is of key importance to overcome the limitations of the direct viewing telescopes (with or without masks) and to allow the study of the high energy spectra of the celestial sources with the same detail which is achieved at lower energies (< 10 keV), where focusing optics are available.In fact, X-ray mirrors, based on the external reflections with very high focal lengths (≥ 50 m), or 'supermirrors' based on Bragg diffraction from multilayers of bi-strates made of high and low Z materials (e.g., Joensen et al. 2 ), can overcome the sensitivity problem up to about 70 keV. For higher energy photons, an efficient focusing is a much more challenging task.Goal of our project is the development of a focusing telescope which efficiently focus hard X-/gamma-rays in a broad continuous band, from 70 keV to ≥ 300 keV, by exploiting the Bragg diffraction from mosaic crystals in Laue configuration.
Abstract-Results of reflectivity measurements of mosaic crystal samples of Cu (111) are reported. These tests were performed in the context of a feasibility study of a hard X-ray focusing telescope for space astronomy with energy passband from 60 to 600 keV. The technique envisaged is that of using mosaic crystals in transmission configuration that diffract X-rays for Bragg diffraction (Laue lens). The Laue lens assumed has a spherical shape with focal length f . It is made of flat mosaic crystal tiles suitably positioned in the lens. The samples were grown and worked for this project at the Institute Laue-Langevin (ILL) in Grenoble (France), while the reflectivity tests were performed at the X-ray facility of the Physics Department of the University of Ferrara.
Abstract. The purpose of the paper is to evaluate our capability to model upwelling radiances at high resolution over broad spectral ranges in clear and cloudy conditions. Spectroradiometric measurements are taken from aircraft flying at low altitude over a clear scene and over a low-level stratus cloud. It is the ideal case to capture the change in signal due to the presence of a cloud without the interfering effect of the atmosphere above, unavoidable in higher-altitude measurements. The knowledge of the variability of the radiometric signal over the measurement periods and the availability of in situ measurement from the same aircraft of the meteorological parameters (temperature and humidity profile) and cloud parameters (depth and microphysical parameters of the cloud layer) allow a nearly complete control of the experiment. The results for the clear case show deviations between simulation and measurement generally smaller than 0.5%, while in the cloudy case, differences over most of the spectral range are less than the variability seen during the recording of the measured spectra. The cloud result is not significantly changed when tested with realistic changes in the measured cloud properties. Over cloud an absorbing medium alone is insufficient, and full scattering is required to achieve good agreement. This shows that care is required when assimilating infrared radiances from above such clouds, which can often extend over large areas. The adopted simulation methodology generates spectral radiances in very good agreement with the measurements both in clear air and above the stratus cloud layers.
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