The SIGMA/Granat telescope: Calibration and data reduction

The SIGMA Telescope was a French experiment, designed to provide high-resol ution images in the hard X-ray and soft gamma -ray band (35-1300 keV). It f eatured a coded mask, a NaI(Tl) position-sensitive detector based on the An ger camera principle, and active and passive shielding devices. It was laun ched on 1989 December 1 on board the Soviet Granat satellite and successful ly continued its in-orbit activities until 1997 October. During its lifetim e, the SIGMA orbital conditions evolved. Its highly eccentric orbit, with p erigee and apogee of 2000 and 200,000 km at the beginning of the mission, c ontinuously evolved to reach 60,000 and 180,000 km. Moreover, Granat experi enced both solar maximum and solar minimum environments. The orbital evolut ion 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 an alysis. We discuss how the effects induced by the charged particle environm ent (mainly protons) affected the telescope performance and how we take the se changes into account in the data reduction process.