The SIGMA/Granat Telescope: Calibration and Data Reduction

The SIGMA Telescope was a French experiment, designed to provide high-resolution images in the hard X-ray and soft γ-ray band (35-1300 keV). It featured a coded mask, a NaI(Tl) position-sensitive detector based on the Anger camera principle, and active and passive shielding devices. It was launched on 1989 December 1 on board the Soviet Granat satellite and successfully continued its in-orbit activities until 1997 October. During its lifetime, the SIGMA orbital conditions evolved. Its highly eccentric orbit, with perigee and apogee of 2000 and 200,000 km at the beginning of the mission, continuously evolved to reach 60,000 and 180,000 km. Moreover, Granat experienced both solar maximum and solar minimum environments. The orbital evolution was such that SIGMA was more and more exposed to cosmic-ray fluxes. We present the calibration of the telescope and the standard data reduction analysis. We discuss how the effects induced by the charged particle environment (mainly protons) affected the telescope performance and how we take these changes into account in the data reduction process.