• AstroSat is the first dedicated Indian astronomy mission aimed at studying celestial sources in X-ray, optical and UV spectral bands simultaneously.
• One of the unique features of AstroSat mission is that it enables the simultaneous multi-wavelength observations of various astronomical objects with a single satellite.
• AstroSat with a lift-off mass of 1515 kg was launched on September 28, 2015 into a 650 km orbit inclined at an angle of 6 deg to the equator by PSLV-C30 from Satish Dhawan Space Centre, Sriharikota.
• The minimum useful life of the AstroSat mission is expected to be 5 years.

Objectives of the Mission

1. To understand high energy processes in binary star systems containing neutron stars and black holes.
2. Estimate magnetic fields of neutron stars.
3. Study star birth regions and high energy processes in star systems lying beyond our galaxy.
4. Detect new briefly bright X-ray sources in the sky.
5. Perform a limited deep field survey of the Universe in the Ultraviolet region

AstroSat spacecraft has the following five payloads:

1. Ultra Violet Imaging Telescope (UVIT), developed by IIA, consist of two identical telescopes of aperture 380 mm. One telescope covers FUV (130–180 nm) band and the other covers NUV (200–300 nm) and visible band (320–550 nm). The hyperbolic mirrors are super polished.
2. Large Area X-ray Proportional Counter (LAXPC), developed by TIFR has three identical gas detectors. LAXPC has a total effective area of 8000 cm2.
3. Cadmium–Zinc–Telluride Imager (CZTI), developed by TIFR works in 20–100 keV. The imaging capability is achieved with coded mask. CZTI also has the capability of making X-ray polarization measurements.
4. Soft X-ray Telescope (SXT), developed by TIFR, uses X-ray reflecting mirrors and an X-ray CCD for imaging and spectral studies in 0.3–8 keV.
5. Scanning Sky Monitor (SSM) developed by ISRO is an all sky monitor for detecting and monitoring transient sources and for follow-up studies of known X-ray sources in 2.5–10 keV region.

• AstroSat carried several firsts to its credit. UVIT has the highest angular resolution of 1.5 arc sec which is 3 times better than the next best UV telescope (GALEX-Galaxy evolution explorer) operational today. LAXPC has the highest collecting area in comparison to any other X-ray detector till today. CZTI possesses a unique capability of measuring X-ray polarization and also acts as an open detector beyond 100 keV
• AstroSat data has produced several discoveries and interesting results, for example discovery of UV photons from redshift of 1.42, solving the puzzle of a cosmic source which is bright both in IR and UV, discovery of X-ray polarization from off pulse region of Crab pulsar to name a few
• AstroSat has produced more than of 275 articles in refereed journals and more than 500 GCN circular, Astronomer’s telegram and conference proceedings as of Sept, 2022.
• AstroSat is operated as an observatory class telescope. The observations time is open to national and international users. The call for proposals is usually issued once in a year during the first quarter of the calendar year.Currently, AstroSat has close to 2000 registered users from 54 countries.

Major Scientific results from ASTROSAT

Some of the major interesting discoveries from AstroSat are mentioned below:

1. “India’s ASTROSAT makes rare discovery”, is an exceptional and a welcome headline in the history of Indian media for the importance given in recent times to Science, particularly space science shared from PTI PUNE, on August 25, 2020. This is the first detection of a FUV photons from Lyman Alpha emitting galaxy AUDFs01 at a distance of 9.3 billion light years (redshift z=1.42). This observation is made possible due to the high sensitivity and low background of the UVIT detectors combined with the long exposure time. The importance is well recognised in the international community which has led to a growing list of scientists from all over the world joining the AstroSat Ultraviolet Deep Field project, as well as initiating a number of new collaborative projects, including the AMUSEDLy (AstroSat-MUSE Detection of Lyman continuum sources) project with the European Southern Observatory.
2. Deep survey of M31 galaxy, popularly known as Andromeda galaxy with UVIT led to the first detection of young main-sequence stars in the bulge of M31 outside the nucleus. This survey has produced UVIT point source catalogue of 75,000+ sources in NUV/FUV.
3. For the first time, CZTI discovered X-ray polarization from the off-pulse region of Crab pulsar. CZTI has also detected polarised prompt emission from gamma ray bursts (GRB) in about 20% of CZTI observed GRBs. The results indicate that in a fraction of cases the magnetic field in the emitting region is strongly ordered while in the rest the field is randomly distributed. These results have spawned multiple theoretical investigations worldwide in the radiative properties of GRBs and the planning of space missions dedicated to the polarimetry of GRBs.
4. AstroSat detection and characterisation of star formation in and around Jellyfish galaxies: These galaxies are members of galaxy clusters. AstroSat UVIT observations find that new stars are being formed in the outflowing gas streams, away from the confines of the galaxies themselves. This is providing major new clues to the gas-gas interaction in galaxy clusters and the formation process of stars. Given the importance of these observations, AstroSat UVIT has been integrated into the multi-nation GASP (Gas stripping phenomena in galaxies) programme.
5. AstroSat UV/X-ray observations of OJ287 shows the importance of simultaneous broad-band observations as the FUV data from UVIT leads to strong constraints on the contribution of synchrotron component in driving the X-ray spectral changes observed in OJ287 over multiple epochs.
6. LAXPC and SXT observations of 4U 1630-17 found that the blackhole in the binary is rotating at a speed close to the maximum possible speed of spin.