First light from Large Area X-ray Proportional Counter (LAXPC) instrument on board ASTROSAT
9 December 2015
Astrosat, India's first dedicated science space mission was launched on 28 September 2015. The Large Area X-ray Proportional Counter (LAXPC), designed and developed at TIFR, Mumbai, is one of the major payloads on ASTROSAT. The LAXPC instrument became fully operational on 19 October 2015 for the first time in space. LAXPC will provide the largest effective area among all satellite missions flown so far, worldwide, and will remain so for the next 10 years, for X-ray studies in the 3-80 keV energy range.
“First light from LAXPC has allowed us to observe Black hole X-ray binaries, Microquasars, X-ray pulsars, Active Galactic Nuclei (AGN)s and Supernova remnants, providing us with very high quality data,” says Prof. JS Yadav, lead scientist of the LAXPC team.
The LAXPC instrument is functioning perfectly and has achieved all detector parameters/goals as proposed initially. TIFR Director, Prof. Sandip Trivedi says “All the TIFR payloads on board Astrosat are working just as we would have liked them to. This is very good news for us”.
NASA’s RXTE/PCA has been the most successful X-ray mission in the recent past. However, now, the LAXPC instrument is more efficient than the RXTE/PCA, above 20 keV, showing better spectral and timing characteristics. As Prof. Yadav says, “We have measured a supernova remnant using the LAXPC and the data we have obtained is of a quality higher than that obtained by RXTE/PCA”.
The LAXPC detectors have the largest collecting area among any X-ray instrument ever built in the world, and have been designed and developed at TIFR, Mumbai. A cluster of three co-aligned identical detectors provides a large area of collection of about 8000 cm2. The large detection volume (15 cm depth) filled with xenon gas at ~ 2 atmospheres, results in a detection efficiency greater than 50%, above 30 keV.
It is a large payload with a total of eight flight packages (414 kg out of 730 kg of all five science payloads). Designing and fabricating this payload was highly challenging and took a decade to come to fruition, passing through the leadership of several accomplished scientists at TIFR. Prof. P. C. Agrawal initiated the design and development of the LAXPC payload in 2002. Prof. R. K. Manchanda took over in 2011. When he retired in November, 2012, Prof. J. S. Yadav took over the development of the LAXPC payload. In addition to the central LAXPC team, Prof. H. M. Antia played a leading role in developing the GEANT4 simulation for the LAXPC detectors in record time. ISRO has also been instrumental in making this project a success, as “they have provided extensive support during the fabrication and testing of the LAXPC payload”, says Prof. Yadav.
The LAXPC instrument is best suited to explore extreme conditions such as strong gravity regions, extremely powerful accelerators in the universe and regions of the highest densities & magnetic fields. The primary objectives are to study binary star systems containing neutron stars and black holes, accretion flow, accretion disk- radio jet connection, estimation of the magnetic fields of neutron stars, and to study Active Galactic Nuclei (AGNs) and blazer systems beyond our galaxy.
“Black holes are extremely mysterious objects of which we know very little, which is why it is important to observe many such black hole events to really understand what is going on and to be confident about our interpretation of data. We now have the capability to see many more blackholes than we did in the past”, says Prof Trivedi at a recently held press conference at TIFR, Mumbai.
TIFR now has the unique capability of performing ground based observations through the Giant Metrewave Radio Telescope (GMRT) and space based observations through Astrosat, of the same sources. “Additionally, we can now combine LAXPC’s observations with those of the other instruments on board, thereby getting coverage across many channels and a wider window into the universe”, says Prof Trivedi.
Astrosat is a big step for the Indian astronomy community and the LAXPC instrument is expected to play a leading role in many exciting discoveries. Out of a planned mission span of 5 years which is likely to be extended to 10 years, the first 6 months are dedicated to calibration and fine tuning of the instruments including performance verification. ASTROSAT will be open to national and international astronomers in about a year’s time, when the 6 month guaranteed time phase (for instrument teams) is completed.
From 1 Dec 2015 all instruments on board Astrosat have been switched on and will be running 24 hours a day.
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Written with inputs from JS Yadav