The first Indian astronomy satellite Astrosat was launched on 28th September, 2015, by the Indian Space Research Organisation (ISRO) from Sriharikota, on a PSLV (Polar Satellite Launch Vehicle) rocket. Astrosat has unprecedented capability to simultaneously observe cosmic objects in visible light, the ultraviolet waveband and the entire X-ray waveband from very low energy to very high energy X-rays. This unique ability to observe the universe in multi-wavelengths, simultaneously, is aimed at performing cutting-edge research in astrophysics.
Researchers from the Tata Institute of Fundamental Research (TIFR) have led this multi institutional effort and have made significant contributions to the design, fabrication and development of three out of five payloads that are on board Astrosat.
The Large Area Xenon Proportional Counters (LAXPC), a Soft X-ray Telescope (SXT), and a Cadmium-Zinc- Telluride Imager (CZTI), all of which will observe the universe in the X-ray wavebands, are the three payloads built in the Department of Astronomy and Astrophysics (DAA) of TIFR Colaba, Mumbai. These instruments demonstrate a major Indian technological advance. In addition, DAA/TIFR has significantly contributed to the twin Ultraviolet Imaging Telescopes (UVIT) on board Astrosat. ‘The instruments developed by TIFR will give us a capability unrivalled in the world for the next 5 to 10 years. We look forward to some great science results’ says Prof. S. Trivedi, Director TIFR.
Cosmic objects (stars, galaxies, quasars etc.) emit in multiple wavebands. Therefore, in order to unravel their mysteries it is essential to observe them in as many wavebands as possible. As X-rays and ultraviolet (UV) energy from cosmic objects cannot penetrate the Earth's atmosphere, suitable instruments must be sent above the atmosphere by satellites. TIFR has been a pioneer in X-ray astronomy research in India. Soon after the discovery of the first extra-solar X-ray source in 1962, TIFR scientists built X-ray instruments for astronomical research, and sent them above the atmosphere by sub-orbital rockets and balloons. Astrosat is a legacy of these activities. As Prof. P.C. Agrawal, one of the lead scientists who gave shape to the concept of this mission, says, ‘Astrosat is a quantum leap from previous modest sized payloads on other Indian satellites. It is an internationally competitive observatory that will enable Indian scientists to work in frontier areas of high energy physics.’
The LAXPC detectors with the largest collecting area among any X-ray instrument ever built in the world, have been fully fabricated at TIFR, by a series of leaders, namely Prof. P.C. Agrawal, Prof. R.K. Manchanda, Prof. J.S. Yadav, and Prof. H.M. Antia. For the next 5 to 10 years LAXPC will be the only instrument in the world that will be able to study X-ray intensity fluctuations of cosmic objects on time scales as small as a milli-second. This will be essential to probe the fundamental physics of exotic objects, like black holes and super-dense neutron stars.
The SXT is the first X-ray focusing telescope built in India. The SXT will conduct imaging and X-ray spectroscopy of hot plasma in cosmic sources and the absorption of x-rays by intervening matter. The SXT team at TIFR, overcame major challenges in building and assembling the mirrors of this X-ray telescope. ‘It is common knowledge that X-rays easily penetrate through materials but it is extremely difficult to focus x-rays with a telescope. Placing the 320 mirrors in the telescope, required great precision’, says Prof. K.P. Singh, lead scientist of the SXT team. The focal plane camera for the SXT containing a cooled charge coupled device (CCD) was built in collaboration with the University of Leicester (UK).
The CZTI, will image celestial objects in the high-energy X-ray band using a coded mask. It has the ability to also perform unique polarization measurements in very high energy X-rays. Built under the leadership of Prof. A.R. Rao of TIFR, the team overcame several challenges to ensure a uniform response from a large number of detectors, as the development of such detectors and electronics for use in high-energy X-ray imaging is a recent technology. Scientific data obtained through Astrosat will be distributed from a few payload operation centres (POC), two of which will be located at TIFR. These two POCs, will control the operations of SXT and LAXPC, making DAA/TIFR a major centre of worldwide X-ray astronomical activities for the next few years.
Astrosat will be available to the Indian astronomy community as an observational opportunity. It will address fundamental scientific problems that cannot be probed in terrestrial laboratories. These will include testing Einstein's general theory of relativity, studying superdense cold matter deep inside a neutron star which is a fundamental problem of particle physics, and understanding flow of matter in astronomical scales, often in extremely strong gravity regions, relativistically accelerated plasma jets, extremely hot ionised plasmas, and absorption by cold matter. Astrosat will observe a variety of objects in the universe, such as black holes, neutron stars, white dwarfs, explosive events like supernovae, stars, galaxies, and clusters of galaxies.
Images can be found on http://www.isro.gov.in/pslv-c30-astrosat-mission/gallery. Kindly credit ISRO if any of the images are used.