The scientific objectives of the ASTROSAT mission of ISRO

In this golden age of Space Astronomy high quality data are coming from several spaceborne observatories like Rossi Timing Explorer (RXTE), the Chandra X-ray Observatory, the XMM-Newton, Galex, FUSE and more recently the SUZAKU mission. These missions with capability of high angular resolution, high spectral resolution and large photon throughput are leading to unprecedented advancements in sensitivity for imaging, spectral and timing studies in X-ray and UV bands. These missions have mostly narrow energy band capability in either X-ray or UV regions. There is an urgent need to have a mission with broad spectral band observation capability in X-ray and UV. ASTROSAT is designed to fill this niche area using a variety of experiments covering the 0.3–100 keV band using a combination of an X-ray focusing telescope for soft X-ray imaging, solid state CdZnTe detectors with a coded mask for hard X-ray imaging and spectroscopy and large area proportional counters for high resolution timing studies. Twin UV telescopes operating separately in the near UV (NUV) and far UV (FUV) along with an optical channel provide the highest angular resolution UV imaging over a range of narrow and wide-band filters. The mission also carries an X-ray sky monitor to detect new X-ray transients and monitor known X-ray sources throughout the mission. This complement of scientific instruments, designed and developed by teams in India, Canada and UK, is scheduled for launch in the year 2009. As the first dedicated multiwavelength astronomy mission from India, ASTROSAT is expected to focus on high-resolution UV imaging for morphological studies of galactic and extragalactic objects, broad-band studies of X-ray sources and other multiwavelength targets ranging from nearby stars to the very distant active galactic nuclei. This paper addresses the scientific objectives, description of the instruments to achieve the objectives and the expected science that can emerge from the ASTROSAT mission.