Design of a soft gamma-ray focusing telescope for the study of nuclear lines

Abstract

We have studied the design of astronomical multilayer telescopes optimized for performance from 5 to 200 keV. This region of the spectrum contains important nuclear lines that are observable in supernovae and their remnants. The study of these lines can help to differentiate currently competing theories of supernova explosion. Our telescope design will enable us to measure the spectral lines of isotopes such as Ni-56 in Type Ia supernovae and Ti-44 in core-collapse remnants, as well as to observe active galactic nuclei at gamma-ray energies. We considered the performances of multilayers of various material pairs, including W/Si, Pt/C and Ni93V7/Si, as employed in conical-approximation Wolter I optics. We experimented with dividing the energy band of interest into several sections, and optimizing different groups of mirror shells within a single telescope for each smaller energy band. Different material pairs are also used for different energy bands, in order to obtain a higher overall performance. We also consider the significance of the energy bandwidth on the effectiveness of Joensen's parametrization of the multilayer thickness profile, and on the mirror performance within the band.

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