P.hd in X-ray and Gamma ray AstronomyTata Institute of Fundamental Research
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P.hd in X-ray and Gamma ray Astronomy
The Department of Astronomy and Astrophysics at Mumbai, which began in the late sixties as a section for High Altitude Studies, started with experiments in observing heavy cosmic primaries, cosmic electron spectra and hard X-rays from various sources and the cosmic X-ray background. It was mostly based on balloon borne payloads for which a facility was set up in Hyderabad to make and launch stratospheric balloons. This led to balloon based observations in X-ray and infrared astronomy. Soft X-ray astronomy payloads were also launched in sounding rockets from TERLS, Thumba and Sriharikota to study the X-ray sources, hot interstellar medium and soft X-ray cosmic background. These programs were later extended to satellite based instruments in X-ray and gamma ray wavelengths, and the group was renamed as Space Physics section and around the same time the theoretical astrophysics section was added. The department acquired its present name around 1997.
The department members carry out observations over a wide range of wave lengths in the electro-magnetic spectrum, from radio, infrared and optical wavelengths to ultra-violet, X-ray and gamma rays. The work in the department covers a wide range of astronomical objects, from the Sun and other stars to compact stellar objects like the neutron stars and black-holes as well as the interstellar medium, stellar clusters, galaxies, clusters of galaxies and the universe as a whole. The work ranges from observations, data analysis and modelling to building of new detectors and telescopes.
The theorists study a variety of topics in astrophysics, like accretion disks around black-holes and neutron stars, gravitational collapse in general relativity, gravitational lensing, cosmology, quantum gravity, neutron stars, pulsars, supernovae as well as more typical stars like the Sun. The work on helioseismology has provided accurate knowledge of structure and dynamics of the Sun and its temporal variations over the solar cycle. This should be a valuable input to the work on star formation and initial mass function. Thus, new data from instruments like ALMA, could be used to map the star formation history of galaxies at high redshifts. This will be put in the context of constraints on star-formation history currently being obtained from deep X-ray surveys with CHANDRA, with the aid of theoretical understanding of the X-ray evolution of galaxies developed here. Theoretical studies of compact binaries is a major effort, with current interest in the formation and evolution of X-ray binaries in globular clusters. Along with the observational work on supernova and supernova remnants these activities could possibly shed light on massive star formation in early universe, formation of black-holes and re-ionisation of the intergalactic medium. The gravitational lensing work has led to the prediction of the Einstein ring and optically faint hot galaxy clusters at high redshift. Naturally, a firm understanding of the end point of stellar evolution for massive stars will have far reaching implications to some fundamental questions in general relativity, like, the cosmic censorship conjecture. Equally it has relevance to the mechanism of energetic phenomena like gamma ray bursts. This work also provides a framework to develop theory for the challenging problem in quantum gravity, where observational signatures will be valuable. The cosmologists are working on understanding dark energy and structure formation, which are among the important problems in cosmology.
Infrared and X-ray astronomy are core areas in the department for observational studies. The infrared astronomy group has distinguished itself with its expertise in diffraction limited angular resolution and built the world's largest aperture far Infrared telescope for mapping in photometric bands and spectroscopic line. Apart from far infrared observations from balloon based telescope the members have also done ground based observations in near infrared and optical wavelengths and are now developing instruments for space based observations. These observations have been used to study star formation in our galaxy and other spiral galaxies, as well as structure and energetics of galactic star forming regions through high angular resolution far infrared spectroscopic and photometric mapping. The combined strengths of high angular resolution, use of longer wavebands beyond the limit of even stressed photoconductors (~ 200 micron, using bolometers), and robust image de-convolution schemes have created a niche and ensured quality science. This has been demonstrated in numerous studies of galactic star forming regions, leading to a better understanding of physical conditions and processes in their interstellar medium.
The X-ray astronomers have conducted timing and spectral studies of black holes and neutron star binaries, cataclysmic variables, nuclei of active galaxies and quasars and X-ray spectroscopy of stellar coronae and energetic phenomena on the Sun, as well as study of hot interstellar medium and supernova remnants. The study of neutron stars provides a unique opportunity to study superdense (5-10 times the nuclear density) cold matter. X-ray astronomy has made rapid strides using X-ray telescopes in soft X-rays (< 10 keV), while the astrophysics of hard X-rays from cosmic objects has not seen similar advance. This is mainly because of high background and the low flux in high energies from cosmic sources. Instruments are being developed to meet these challenges. Hard X-ray imaging by multi-layer coating and development of new generation hard X-ray detectors are a few of the areas where substantial research is being carried out. Some novel concepts in hard X-ray imaging and spectroscopy like Fresnel Zone Plate imaging, near-room temperature solid state detector technology, CMOS detector for hard X-rays etc., are incorporated in the RT-2 experiment onboard the Coronas-Photon satellite (an Indo-Russian collaborative experiment for solar flare studies in hard X-rays and gamma-rays), scheduled to be launched in December 2008.
Members of the department are actively involved in designing and building instruments for the first Indian multi-wavelength astronomy satellite, ASTROSAT, which will probe, among other things, the physics of black holes, which are among the most exotic predictions of Einstein's general theory of relativity. The instruments being developed in the department include the Large Area Xenon Proportional Counter (LAXPC) for timing and spectral studies in X-rays, as well as a Soft X-ray Telescope (SXT) for imaging studies and a new generation of X-ray detector in the Cadmium-Zinc-Telluride coded mask Imager (CZTI). While some members are involved in the development of Ultra-violet Imaging Telescope (UVIT) on ASTROSAT in collaboration with other institutes in India and abroad. One of the principle aim of ASTROSAT is to perform simultaneous multi-wavelength monitoring of intensity variations in a broad range of cosmic sources.
The department also runs the National Balloon Facility at Hyderabad, which has become a major centre for scientific ballooning. Regular balloon flights are conducted to make observations in Infrared and X-ray wavelengths, which are not accessible from ground. The balloon facility has also exported balloons to various agencies worldwide.
X-ray and Gamma ray Astronomy:
* X-ray Spectroscopy of Stellar Coronae
* Galactic Black Hole Candidates
* Cataclysmic variables
* Nuclei of Active Galaxies and Quasars
* Study of Hot Interstellar Medium and Supernova Remnants
* Binary X-ray Pulsars
* Rotation Powered Pulsars and Magnetars
* Neutron Stars in Accreting Binary Systems