Coded aperture imaging in high energy astronomy represents an important technical advance in instrumentation over the full energy range from X-to y-rays and is playing a unique role in those spectral ranges where other techniques become ineffective or impracticable due to limitations connected to the physics of interactions of photons with matter. The theory underlying this method of indirect imaging is of strong relevance both in design optimization of new instruments and in the data analysis process. The coded aperture imaging method is herein reviewed with emphasis on topics of mainly practical interest along with a description of already developed and forthcoming implementations.
Abstract. PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy detector of the IBIS telescope on-board the INTEGRAL satellite. PICsIT operates in the gamma-ray energy range between 175 keV and 10 MeV, with a typical energy resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a ∼100 square degree field of view, with the possibility to locate intense point sources in the MeV region at the few arcmin level. PICsIT is based upon a modular array of 4096 independent CsI(Tl) pixels, ∼0.70 cm 2 in cross-section and 3 cm thick. In this work, the PICsIT on-board data handling and science operative modes are described. This work presents the in-flight performances in terms of background count spectra, sensitivity limit, and imaging capabilities.
Abstract.BeppoSAX observations of the nearby archetypical starburst galaxies NGC253 and M82 are presented. Spectral analysis shows that the 2-10 keV spectra of both galaxies, extracted from the central 4 ′ regions, are best fitted by a thermal emission model with kT ∼ 6-9 keV and metal abundances ∼ 0.1-0.3 solar. The spatial analysis yields clear evidence that this emission is extended in NGC 253, and possibly also in M82. These results clearly rule out a LLAGN as the main origin of the X-ray emission in NGC 253. For M82, the presence of an Fe-K line at ∼ 6.7 keV, and the convex profile of its 2-10 keV continuum, indicate a significant thermal component. Contributions from point sources (e.g. X-ray binaries, supernova remnants, and/or a LLAGN) and Compton emission are also likely. Altogether, BeppoSAX results provide compelling evidence for the existence of a hot interstellar plasma in both galaxies, possibly in the form of superwind outflows from the disks of these galaxies. Order-of-magnitude estimates and some implications, such as the expelled mass and the energetics of the outflowing gas of this superwind scenario, are discussed. These new results also suggest some similarity between the X-ray emission from these galaxies and that from the Galactic Ridge.
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