[en] IBIS (Imager on Board the Integral Satellite) is dedicated to fine imaging in the gamma-ray energy range. The imaging performances are achieved using a coded mask aperture system in conjunction with a position sensitive detector made of two layers. This multilayer structure of position sensitive detectors allows the application of Compton kinematics for background rejection. In order to determine the efficacy of this method, a reduced scale prototype of the instrument has been developed. The detection apparatus is composed by two scintillation matrices of 5x5 elements in the same configuration of IBIS. The upper layer pixel size is 13 x 13 x 3 mm whereas the lower layer pixel size is 13 x 13 x 30 mm. An hybrid technology electronics has been setup for signals shaping and discrimination, moreover a custom software package has been developed for system calibration and data analysis. The equipment has been tested at different energies by employing radioactive sources. The results are presented and compared, when possible, with Montecarlo simulations

[en] The large application of transparent and conducting layers justifies the research of an easy deposition technique, like vacuum thermal evaporation. In the present work Indium Tin Oxide evaporation technique (16% In₂O₃, 84% SnO₂) has been optimized. Then electro-optical properties of these films that have been oxided by two different annealing techniques have been studied

[en] During the 2.5 years of Galactic Bulge Monitoring with the WFC on board the Beppo-SAX satellite new X-Ray Burst sources have been discovered. Some of these sources have also been promptly observed on a wide energy band by using the Narrow Field Instruments of the Satellite and a high energy component up to 200 keV has been detected. Moreover bursts behavior has been discovered with the WFC for 4 more sources previously observed with other high energy instruments enlarging the sample of studied objects. These results support the existence of such a class of previously suggested hard X-ray emitters that are very promising for the future IBIS/INTEGRAL CORE Program observations (Galactic Plane Survey and the Galactic Center Deep Exposure). Simulation results on the IBIS view on this class of object will be presented

[en] The aim of this work is to investigate the opto-electronic properties of amorphous hydrogenated silicon (a-Si:H). The deposition temperature was used as a driving force to modify the morphology and bonded hydrogen distribution. The influence of the hydrogen microstructure on the carrier m-t products was examined. The m-t products, for both carriers, were evaluated from the diffusion length measurement, by using the Steady State Photocarrier Grating (SSPG) technique, and from the photoconductivity in the steady state condition (SSPC). The m-t products were correlated with the defect density and Fermi level position. The effects of the defect density on the Fermi level position were examined within the framework of a defect pool model in order to justify the consistency of the results

[en] The early performance verification phase of the INTEGRAL satellite foresees basically several different observations as part of commissioning of the on-board instruments. The Cygnus region, two empty fields and the Crab have been selected as targets. These observations are necessary in order to obtain imaging performances for point sources and for crowded fields, spectral cross-calibration between the on-board instruments, a background variation study, absolute flux and timing calibration. We report simulation results for the IBIS coded mask telescope of planned calibrations concerning Crab and Cygnus X-1, performed in both staring and dithering observing modes. A Monte Carlo code including a full geometrical and physical model of the instrument has been used

[en] IBIS, the imager on board the INTEGRAL satellite, is a coded mask telescope for X and gamma-ray astronomy with imaging and spectroscopy capabilities from 15 keV to 10 MeV. In order to cover this energy range, IBIS uses two position sensitive detectors: the low energy detector layer ISGRI and the high energy detector layer PICsIT. The sensitivity of a coded mask instrument depends on the detectors efficiencies, imaging efficiency, and on the diffuse photons and particles background count-rate. In the IBIS energy range, also the opacity at low energies of the open mask elements and the transparency of the closed elements at high energies give a significant effect on the sensitivities curves. In this work we present a Monte Carlo evaluation of the IBIS detectors efficiencies. The mask transparency data from the Flight Model (FM) are also presented

[en] The performance of a prototype CdTe linear multipixel detector in the arrangement with the collecting field orthogonal to the incoming radiation (PTF configuration) is reported. This detector was conceived to be employed as the basic element to realise both two-dimensional and linear position sensitive spectrometers with a large number of pixels for hard X- and soft γ-rays. The prototype has been produced from a single CdTe crystal of 10 x 10 x 2 mm³ using strip technology and is geometrically equivalent to a linear array of five microdetectors of 2 x 2 x 10 mm³ with the electrodes deposited on the 2 x 10 mm² sides. The active area of each pixel is about 2 x 2 mm². After the electrical characterisation of the detector, several tests have been performed by radiating the detector with standard sources. Scanning the detector with a ⁵⁷Co source over the pixels has shown the uniformity of spatial response and has allowed the measurement of the spatial resolution of the array. In order to evaluate the spectroscopic capability further tests using sources with energy between 10 and similar 400 keV, moved along the anode-cathode direction, have been performed. The first results have demonstrated that the multipixel CdTe crystal acts as a linear position sensitive spectrometer made of 5 PTF microcrystal at least up to a few hundreds keV. (orig.)

[en] The microquasar 1E 1740.7-2942 is observed with INTEGRAL since Spring 2003. Here, we report on the source high-energy behavior by using the first three years of data collected with SPI and IBIS telescopes, taking advantage of the instruments complementarity. Light curves analysis showed two main states for 1E 1740.7-2942: the canonical low/hard state of black hole candidates (BHCs) and a ^dimstate, characterized by an ∼20 times fainter emission, detected only below 50 keV and when summing more than 1 Ms of data. For the first time the continuum of the low/hard state has been measured up to ∼600 keV with a spectrum that is well represented by a thermal Comptonization plus an additional component necessary to fit the data above 200 keV. This high-energy component could be related to nonthermal processes as already observed in other BHCs. Alternatively, we show that a model composed of two thermal Comptonizations provides an equally representative description of the data: the temperature of the first population of electrons results as (kT _e)₁∼ 30 keV while the second, (kT _e)₂, is fixed at 100 keV. Finally, searching for 511 keV line showed no feature, either narrow or broad, transient or persistent.

[en] The merger of two neutron stars is predicted to give rise to three major detectable phenomena: a short burst of gamma-rays, a gravitational-wave signal, and a transient optical-near-infrared source powered by the synthesis of large amounts of very heavy elements via rapid neutron capture (the r-process). Such transients, named 'macronovae' or 'kilonovae', are believed to be centres of production of rare elements such as gold and platinum. The most compelling evidence so far for a kilonova was a very faint near-infrared rebrightening in the afterglow of a short γ-ray burst at redshift z = 0.356, although findings indicating bluer events have been reported. Here we report the spectral identification and describe the physical properties of a bright kilonova associated with the gravitational-wave source GW170817 and γ-ray burst GRB 170817A associated with a galaxy at a distance of 40 megaparsecs from Earth. Using a series of spectra from ground-based observatories covering the wavelength range from the ultraviolet to the near-infrared, we find that the kilonova is characterized by rapidly expanding ejecta with spectral features ∼ those predicted by current models. The ejecta is optically thick early on, with a velocity of about 0.2 times light speed, and reaches a radius of about 50 astronomical units in only 1.5 days. As the ejecta expands, broad absorption-like lines appear on the spectral continuum, indicating atomic species produced by nucleosynthesis that occurs in the post-merger fast-moving dynamical ejecta and in two slower (0.05 times light speed) wind regions. Comparison with spectral models suggests that the merger ejected 0.03 to 0.05 solar masses of material, including high-opacity lanthanides. (authors)

[en] The amorphous/crystalline silicon (a-Si/c-Si) heterostructure has recently attracted new interest due to higher open circuit voltage V_oc and low temperature fabrication processes. By reducing the wafer thickness all these characteristics become a necessity, together with the requirement of a back reflecting mirror, to obtain an effective optical confinement. To this aim dielectric mirrors can be adopted in the rear side of the solar cells, together with a local process of laser fired back Al contact. Taking advantage of a-Si/SiN_x passivation properties of c-Si surface a Bragg reflector configuration can be formed on the rear side of the c-Si wafer by Plasma Enhanced Chemical Vapor Deposition (PECVD) alternating several couples of a-Si/SiN_x and choosing their thicknesses to maximize the reflectance inward the c-Si wafer in the NIR spectrum. In this work we have adopted this mirror on the rear side of an n-a-Si/i-a-Si/p-c-Si heterostructure solar cell to obtain a full low temperature process. The cell back contact has been ensured by an Al diffusion into the c-Si wafer promoted by Nd-YAG pulsed laser. The front cell contact has been enhanced by chromium silicide CrSi formation on top of the n-a-Si layer and ITO deposition followed by an Ag grid. A V_oc of 681 mV and 94% of IQE at 1000 nm have been reached.