A CdTe gamma-camera for the space observatory INTEGRAL: software charge-loss corrections

The IMAGER gamma-ray telescope on board INTEGRAL features a coded aperture and a two-layer detector. The first of these layers, ISGRI, is a 16 384 pixel CdTe gamma-camera which will operate in the 20 keV–1 MeV energy range. The spectral performances of ISGRI at energies greater than 50 keV are obtained using a software charge-loss correction based on pulse rise-time measurements. At high energy, the study of the Compton interactions between the two IMAGER layers should ensure a good background rejection. This device will provide unprecedented performances in this energy range: a spatial resolution of 4 mm, a spectral resolution better than 7% at 122 keV and a broad band sensitivity at 3σ of about 10−6 cm−2 s−1 keV−1 at 100 keV for a 105 s observation. Galactic X-ray binary sources, supernovae and active galactic nuclei will be prime targets for ISGRI.