Abstract. The IBIS telescope is the high angular resolution gamma-ray imager on-board the INTEGRAL Observatory, successfully launched from Baikonur (Kazakhstan) the 17th of October 2002. This medium size ESA project, planned for a 2 year mission with possible extension to 5, is devoted to the observation of the gamma-ray sky in the energy range from 3 keV to 10 MeV (Winkler 2001). The IBIS imaging system is based on two independent solid state detector arrays optimised for low (15−1000 keV) and high (0.175−10.0 MeV) energies surrounded by an active VETO System. This high efficiency shield is essential to minimise the background induced by high energy particles in the highly excentric out of van Allen belt orbit. A Tungsten Coded Aperture Mask, 16 mm thick and ∼1 squared meter in dimension is the imaging device. The IBIS telescope will serve the scientific community at large providing a unique combination of unprecedented high energy wide field imaging capability coupled with broad band spectroscopy and high resolution timing over the energy range from X to gamma rays. To date the IBIS telescope is working nominally in orbit since more than 9 month.

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Abstract. IBIS is the high energy imager on board the INTEGRAL satellite. The gamma-ray instruments on board will take advantage of the long uninterrupted observation made possible by the very eccentric orbit (10 000 km perigee and 152 000 km apogee). A disadvantage for orbits outside the protection of the van Allen belts is the exposure to cosmic and solar particles. Conversely, the background is quite stable throughout the 3 days orbit. In order to maximise the scientific returns and take full use of these almost 3 days continuous observations, IBIS is equipped with a light, very effective Veto System. This ensures a substantial reduction of the background due to the induced photon and hadronic component, in turn enhancing the detector sensitivity. The performance of the IBIS veto as evaluated during telescope commissioning is reviewed. In particular, the efficiency of background rejection and the resulting IBIS dead time are evaluated as well as the impact of different zoning configurations. Measured over the whole energy range, the veto system provides a background suppression effect of ∼50% for ISGRI and ∼40% for PICsIT. The definitive veto settings optimised for the operational working temperature and background conditions are described.

How structures of various scales formed and evolved from the early Universe up to present time is a fundamental question of astrophysical cosmology. EDGE (Piro et al., 2007) will trace the cosmic history of the baryons from the early generations of massive stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing gravitational collapse by dark matter (the so-called warm hot Spectrometer (0.1-2.2 eV) with excellent energy resolution (3 eV at 0.6 keV), a Wide-Field Imager (0.3-6 keV) with high angular resolution (HPD=15") constant over the full 1.4 degree field of view, and a Wide Field Monitor (8-200 keV) with a FOV of ¼ of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part of the Cosmic Vision call. We will outline the science drivers and describe in more detail the payload of this mission.

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