General description

The INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL ) is a 15 keV-10 MeV gamma-ray observatory mission with concurrent source monitoring in the X-rays (3-35 keV) and in the optical range (V band, 500-600 nm). It is the second medium size satellite of the ESA long term scientific plan Horizon 2000. INTEGRAL is an observatory type facility with most of the observing time open for the astronomical community. The mission is conceived as an observatory led by ESA with contributions from the Russian Space Agency (PROTON launcher) and NASA (Deep Space Network ground station). The overall view of the INTEGRAL is given in Figure 2.

Figure: The INTEGRAL spacecraft with the payload module on the top of the service module. The coded masks for IBIS and JEM-X are located 3.2 m above the detection planes. IBIS and JEM- X detectors are inside the payload module structure. The overall dimensions of the spacecraft (excluding solar arrays which span 16 m) are 4m 6m (w h). The Sun is illuminating the payload module on the IBIS side, leaving SPI in the shadow.

The scientific goals of INTEGRAL are attained by high resolution spectroscopy with fine imaging and accurate positioning of celestial sources of gamma-ray emission. High resolution spectroscopy over the entire energy range permits spectral features to be uniquely identified and line profiles to be determined for physical studies of the source region. The fine imaging capability of INTEGRAL within a large field of view allows an accurate localization and hence identification of the gamma-ray emitting objects with their counterparts at other wavelengths, enables extended regions to be distinguished from point sources and provides considerable serendipitous science which is very important for an observatory-class mission. In summary the INTEGRAL scientific topics address:

• compact objects: white dwarfs, neutron stars, black hole candidates, high energy transients and Gamma Ray Bursts (GRBs);
• extragalactic astronomy: AGNs, Seyferts, blazars, galaxies and clusters, cosmic diffuse background;
• stellar nucleosynthesis: hydrostatic nucleosynthesis (AGB and WR stars), explosive nucleosynthesis (supernovae and novae);
• Galactic structure: mapping of continuum and line emission, ISM, cosmic-ray distribution;
• Galactic Centre: cloud complex regions, mapping of continuum and line emission, ISM, cosmic-ray distribution;
• particle processes and acceleration: trans-relativistic pair plasmas, beams, jets;
• identification of high energy sources: unidentified gamma ray objects as a class;
• unexpected discoveries.