Astrosat
Encyclopedia
Astrosat is India
's first dedicated astronomy
satellite
and is scheduled to launch on board the PSLV in 2012. After the success of the satellite-borne Indian X-ray Astronomy Experiment (IXAE), which was launched in 1996, the Indian Space Research Organization (ISRO) has approved further development for a full fledged astronomy satellite - Astrosat.
A large number of leading astronomy research institutions in India and abroad are jointly building various instruments for the satellite. Important areas requiring broad band coverage include studies of astrophysical
objects ranging from the nearby solar system
objects to distant stars, to objects at cosmological
distances; timing studies of variables ranging from pulsations of the hot white dwarf
s to active galactic nuclei
(AGN) with time scales ranging from milliseconds to few hours to days.
Astrosat is currently proposed as a multi-wavelength
astronomy mission on an IRS-class satellite into a near-Earth, equatorial orbit by the PSLV. The 5 instruments on-board cover the visible
(320-530 nm), near UV
(180-300 nm), far UV
(130-180 nm), soft X-ray (0.3-8 keV and 2-10 keV) and hard X-ray (3-80 keV and 10-150 keV) regions of the electromagnetic spectrum
.
Astrosat will be a proposal-driven general purpose observatory, with main scientific focus on:
Astrosat will carry out multi-wavelength observations covering spectral bands from radio, optical, IR, UV, X-ray and Gamma ray regions both for study of specific sources of interest and in survey mode. While radio, optical, IR observations would be coordinated through ground-based telescopes, the high energy regions, i.e., UV, X-rays and Gamma rays would be covered by the dedicated satellite borne instrumentation of Astrosat.
The mission would also study near simultaneous muti-wavelength data from different variable sources. In a binary system
for example regions near the compact object emit predominantly in X-ray
s, the accretion disc
emitting most of its light in the UV/ optical waveband, and the mass donating star being brightest in the optical band.
The observatory will also carry out (a) low to moderate resolution spectroscopy
over wide energy band with the primary emphasis on studies of X-ray emitting objects, (b) Timing studies of periodic and aperiodic phenomenon in X-ray binaries, (c) Studies of pulsations in X-ray pulsar
s, (d) QPO
s, flickering. Flaring and other variations in X-ray binaries, (e) short and long term intensity variations in AGN
s, (f) time lag studies in low/hard X-rays and UV/optical radiation, (g) detection and study of x-ray transients. In particular, the mission will train its instruments at active galactic nuclei at the core of the Milky Way that is believed to have a super massive black hole.
(IDSN) was operational in July, 2009 to track Astrosat.
(TIFR) have completed the developmental phase of complex science payloads and have begun integrating them before delivery of the 1,650 kg satellite Astrosat. A payload from RRI (Raman Research Institute) is under development, awaiting delivery. The challenges in the design of payloads and Attitude Control System have been overcome and in a recent review committee meeting, it was decided that the delivery of the payload to ISRO satellite Centre will begin from the middle of 2009 and continue till early 2010 to enable the launch of ASTROSAT in 2010 using ISRO workhorse PSLV. As of August 2011, the launch has been rescheduled to 2012.
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
's first dedicated astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
and is scheduled to launch on board the PSLV in 2012. After the success of the satellite-borne Indian X-ray Astronomy Experiment (IXAE), which was launched in 1996, the Indian Space Research Organization (ISRO) has approved further development for a full fledged astronomy satellite - Astrosat.
A large number of leading astronomy research institutions in India and abroad are jointly building various instruments for the satellite. Important areas requiring broad band coverage include studies of astrophysical
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
objects ranging from the nearby solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
objects to distant stars, to objects at cosmological
Cosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
distances; timing studies of variables ranging from pulsations of the hot white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
s to active galactic nuclei
Galactic Center
The Galactic Center is the rotational center of the Milky Way galaxy. It is located at a distance of 8.33±0.35 kpc from the Earth in the direction of the constellations Sagittarius, Ophiuchus, and Scorpius where the Milky Way appears brightest...
(AGN) with time scales ranging from milliseconds to few hours to days.
Astrosat is currently proposed as a multi-wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
astronomy mission on an IRS-class satellite into a near-Earth, equatorial orbit by the PSLV. The 5 instruments on-board cover the visible
Visible spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of...
(320-530 nm), near UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(180-300 nm), far UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(130-180 nm), soft X-ray (0.3-8 keV and 2-10 keV) and hard X-ray (3-80 keV and 10-150 keV) regions of the electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
.
Mission
- Simultaneous multi-wavelength monitoring of intensity variations in a broad range of cosmic sources
- Monitoring the X-ray sky for new transients
- Sky surveys in the hard X-ray and UV bands
- Broadband spectroscopic studies of X-ray binaries, AGNActive galactic nucleusAn active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
, SNRSupernova remnantA supernova remnant is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.There are two...
s, clusters of galaxies and stellar coronae - Studies of periodic and non-periodic variability of X-ray sources
Astrosat will carry out multi-wavelength observations covering spectral bands from radio, optical, IR, UV, X-ray and Gamma ray regions both for study of specific sources of interest and in survey mode. While radio, optical, IR observations would be coordinated through ground-based telescopes, the high energy regions, i.e., UV, X-rays and Gamma rays would be covered by the dedicated satellite borne instrumentation of Astrosat.
The mission would also study near simultaneous muti-wavelength data from different variable sources. In a binary system
Binary system
Binary system may refer to:* Binary numeral system, the base-2 internal "machine language" of computers* Binary opposition, a bipolar distinction in philosophy, structuralism and critical theory...
for example regions near the compact object emit predominantly in X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, the accretion disc
Accretion disc
An accretion disc is a structure formed by diffuse material in orbital motion around a central body. The central body is typically a star. Gravity causes material in the disc to spiral inward towards the central body. Gravitational forces compress the material causing the emission of...
emitting most of its light in the UV/ optical waveband, and the mass donating star being brightest in the optical band.
The observatory will also carry out (a) low to moderate resolution spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
over wide energy band with the primary emphasis on studies of X-ray emitting objects, (b) Timing studies of periodic and aperiodic phenomenon in X-ray binaries, (c) Studies of pulsations in X-ray pulsar
X-ray pulsar
X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity...
s, (d) QPO
Quasi-periodic oscillations
In X-ray astronomy, quasi-periodic oscillation is the manner in which the X-ray light from an astronomical object flickers about certain frequencies...
s, flickering. Flaring and other variations in X-ray binaries, (e) short and long term intensity variations in AGN
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
s, (f) time lag studies in low/hard X-rays and UV/optical radiation, (g) detection and study of x-ray transients. In particular, the mission will train its instruments at active galactic nuclei at the core of the Milky Way that is believed to have a super massive black hole.
Payloads
The scientific payload has a total mass of 750 kg and contains six instruments.- The UltraViolet Imaging Telescope (UVIT) - The UltraViolet Imaging Telescope will perform imaging simultaneously in three channels: 130-180 nm, 180-300 nm, and 320-530 nm. The field of view is a circle of ~ 28 arcmin diameter and the angular resolution is 1.8" for the ultraviolet channels and 2.5" for the visible channel. In each of the three channels a spectral band can be selected through a set of filters mounted on a wheel; in addition, for the two ultraviolet channels a grating can be selected in the wheel to do slitless spectroscopy with a resolution of ~ 100.
- Soft X-ray imaging Telescope (SXT)- The soft X-ray telescope on Astrosat will employ focussing optics and a deep depletion CCD camera at the focal plane to perform X-ray imaging in 0.3-8.0 keV band. The optics will consist of 41 concentric shells of gold-coated conical foil mirrors in an approximate Wolter-I configuration. The focal plane CCD camera will be very similar to that flown on SWIFT XRT. The CCD will be operated at a temperature of about -80oC by thermoelectric cooling.
- The LAXPC Instrument - For X-ray timing and low-resolution spectral studies over a broad energy band (3-80 keV) Astrosat will use a cluster of 3 co-aligned identical Large Area X-ray Proportional Counters (LAXPCs), each with a multi-wire-multi-layer configuration and a Field of View of 1o X 1o. These detectors are designed to achieve (I) wide energy band of 3-80 keV, (II) high detection efficiency over the entire energy band, (III) narrow field of view to minimize source confusion, (IV) moderate energy resolution, (V) small internal background and (VI) long lifetime in space.
- Cadmium Zinc Telluride Imager (CZTI) - Astrosat will carry a hard X-ray imager in the form of CZTI. It will consist of a Pixellated Cadmium-Zinc-Telluride detector array of ~1000 cm2 geometric area. These detectors have very good detection efficiency, close to 100% up to 100 keV, and have a superior energy resolution (~2% at 60 keV) compared to scintillation and proportional counters. Their small pixel size also facilitates medium resolution imaging in hard x-rays. The CZTI will be fitted with a two dimensional coded mask, for imaging purposes. The sky brightness distribution will be obtained by applying a deconvolution procedure to the shadow pattern of the coded mask recorded by the detector.
- Scanning Sky Monitor (SSM) - The Scanning Sky Monitor will consist of three position sensitive proportional counters, each with a one-dimensional coded mask, very similar in design to the All Sky Monitor on NASA's RXTE satellite. The gas-filled proportional counter will have resistive wires as anodes. The ratio of the output charge on either ends of the wire will provide the position of the x-ray interaction, providing an imaging plane at the detector. The coded mask, consisting of a series of slits, will cast a shadow on the detector, from which the sky brightness distribution will be derived.
- Charged Particle Monitor (CPM) - A charged particle monitor (CPM) will be included as a part of Astrosat payloads to control the operation of the LAXPC, SXT and SSM. Even though the orbital inclination of the satellite will be 8 deg or less, in about 2/3 of the orbits, the satellite will spend a considerable time (15 – 20 minutes) in the South Atlantic Anomaly (SAA) region which has high fluxes of low energy protons and electrons. The high voltage will be lowered or put off using data from CPM when the satellite enters the SAA region to prevent damage to the detectors as well as to minimize ageing effect in the Proportional Counters.
Ground support
The Ground Command and Control Centre for Astrosat will be located at ISTRAC, Bangalore, India. Commanding and data download will be possible during every visible pass over Bangalore. Ten out of 14 orbits per day will be visible to the ground station. The satellite is capable of gathering 420 gigabits of data every day that can be down loaded in 10 to 11 orbits visible at Tracking and Data receiving center of ISRO in Bangalore. A third 11-meter antenna at the Indian Deep Space NetworkIndian Deep Space Network
The Indian Deep Space Network is a network of large antennas and communication facilities that supports the interplanetary spacecraft missions of India. It is located at Byalalu, a village about 100 km from Bangalore, India. It was officially inaugurated on 17 October 2008 by ISRO chairman...
(IDSN) was operational in July, 2009 to track Astrosat.
Current status
Scientists from Tata Institute of Fundamental ResearchTata Institute of Fundamental Research
The Tata Institute of Fundamental Research is a research institution in India dedicated to basic research in mathematics and the sciences. It is a Deemed University and works under the umbrella of the Department of Atomic Energy of the Government of India. It is located at Navy Nagar, Colaba, Mumbai...
(TIFR) have completed the developmental phase of complex science payloads and have begun integrating them before delivery of the 1,650 kg satellite Astrosat. A payload from RRI (Raman Research Institute) is under development, awaiting delivery. The challenges in the design of payloads and Attitude Control System have been overcome and in a recent review committee meeting, it was decided that the delivery of the payload to ISRO satellite Centre will begin from the middle of 2009 and continue till early 2010 to enable the launch of ASTROSAT in 2010 using ISRO workhorse PSLV. As of August 2011, the launch has been rescheduled to 2012.
Participants
The Astrosat project is a collaborative effort of a growing list of research institutions. The current participants are:- Indian Space Research Organization
- Tata Institute of Fundamental ResearchTata Institute of Fundamental ResearchThe Tata Institute of Fundamental Research is a research institution in India dedicated to basic research in mathematics and the sciences. It is a Deemed University and works under the umbrella of the Department of Atomic Energy of the Government of India. It is located at Navy Nagar, Colaba, Mumbai...
, Mumbai - Indian Institute of AstrophysicsIndian Institute of AstrophysicsThe Indian Institute of Astrophysics , with its headquarters in Bangalore , India, is a premier national institute of India for the study of and research into topics pertaining to astronomy, astrophysics and related subjects....
, Bangalore - Raman Research InstituteRaman Research InstituteRaman Research Institute is a research institute in Bangalore, India. It was started by Nobel laureate Sir C. V. Raman.The main areas of research are:*Astronomy and Astrophysics*Liquid Crystals*Theoretical Physics*Optics...
, Bangalore - Inter-University Centre for Astronomy and AstrophysicsInter-University Centre for Astronomy and AstrophysicsThe Inter-University Centre for Astronomy and Astrophysics is an autonomous institution set up by the University Grants Commission to promote nucleation and growth of active groups in astronomy and astrophysics in Indian universities...
, Pune - Bhabha Atomic Research CentreBhabha Atomic Research CentreThe Bhabha Atomic Research Centre is India's primary nuclear research facility based in Mumbai. It has a number of nuclear reactors, all of which are used for India's nuclear power and research programme.- History :...
, Mumbai - S.N. Bose National Centre for Basic SciencesS.N. Bose National Centre for Basic SciencesS.N. Bose National Centre for Basic Sciences is an autonomous research institute under Department of Science and Technology of Government of India, located in Salt Lake, Kolkata. Named after scientist Satyendra Nath Bose, this institution was established in 1986.Students of this institute can...
, Kolkata - Canadian Space Agency
- University of LeicesterUniversity of LeicesterThe University of Leicester is a research-led university based in Leicester, England. The main campus is a mile south of the city centre, adjacent to Victoria Park and Wyggeston and Queen Elizabeth I College....