3.2 INTEGRAL

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is an ESA mission due for launch in 2001 that is dedicated to fine spectroscopy (E/dE = 500) and imaging (12 arcmin FWHM) in the 15 keV to 10 MeV energy range. The two main instruments on board are a spectrometer with high-spectral-resolution germanium detectors and an imager that employs high-spatial-resolution arrays of cadmium telluride and cesium iodide detectors. Optical and X-ray monitors complete the scientific payload. The spectrometer has a field-of-view of 16 degrees (fully coded), an angular resolution of 2 degrees FWHM and a sensitivity to narrow spectral lines of ~4x10^-6 ph cm^-2 s^-1 in a 10⁶ s observation. The imager has a field-of-view of 9 degrees fully coded, an area of ~3000 cm² and a continuum sensitivity of 4x10^-7 ph cm^-2 s^-1 keV^-1 (~1 mCrab) at 100 keV. The key scientific objectives of the INTEGRAL include (1) the study of explosive nucleosynthesis in SN I out to ~15 Mpc through the detection and measurement of ⁵⁶Co lines; (2) a survey of galactic supernovae from the past 300 years through detection and mapping of ⁴⁴Ti line emission; (3) a determination of the sites of nucleosynthesis in the galaxy over the past million years through the mapping of the ²⁶Al line emission; (4) a broad-band (5 keV - 10 MeV) study of AGNs and the spectral characteristics of different classes such as Sy 1, Sy 2, and blazars; (5) a study of the galactic center region and galactic plane to determine the positions, spectra and nature of the compact objects; (6) a sensitive, multi year survey of the galactic plane for study of galactic transient sources such as X-ray novae and Be transient pulsars. The INTEGRAL is being developed primarily by ESA and the European member countries, but will include Russia (USA launch proton rocket) and the United States (tracking instrumentation). A science data center is located at the Geneva Observatory in Switzerland. The observing program will be divided between a core program (~30% of the time) that will be largely devoted to galactic plane scans and a general program that will have observations chosen from an open competition of proposals submitted by the members of the community at large.

3.3 COMPLEMENTARY X-RAY MISSIONS

Two recently launched X-ray missions have instruments observing in the hard X-ray band which provide complementary observations to those of CGRO in addressing the key science objectives identified in sections 1 and 2. The Rossi X-ray Timing Explorer (RXTE) was launched by NASA in December 1995, as a mission to study the temporal and spectral variability of X-ray emission from a broad range of astronomical objects. A complement of three scientific instruments observing in the 2 - 250 keV energy band is addressing important questions concerning the structure and dynamics of compact X-ray sources such as accreting neutron stars, white dwarfs and black holes in our galaxy as well as the massive black holes thought to be present in the nuclei of distant active galaxies. Important features of RXTE are its capabilities for creating high resolution time series for temporal investigations, the incorporation of the All-Sky Monitor that views approximately 70% of the sky per orbit for the detection of new transient sources, and its ability to re-orient quickly (within 7 - 24 hours) for detailed study of new transients. RXTE has expected orbital lifetime of 4-5 years. The primary objective of the Italian-Dutch X-ray mission BeppoSAX is the broad band spectral characterization of galactic and extragalactic X-ray sources. Launched in April 1996, it carries a complement of four co-aligned narrow field-of-view instruments observing in the 0.1 - 300 keV energy band and two wide-field cameras for the detection of new transient sources in the 2 - 30 keV range. The SAX detectors have relatively large area, good energy resolution and approximately 1 arcmin imaging at low energies. The wide-field cameras provide milliCrab sensitivity for transient detection and monitoring. The BeppoSAX mission has a minimum lifetime of 2 years with a possible extension to 4 years of operation.