India’s Astrosat Takes Its First Images Of The Crab Nebula

India’s first space observatory satellite has yielded its first results: images of the Crab Nebula, a supernova remnant in the constellation of Taurus.

AsianScientist (Oct. 20, 2015) – Astrosat, India’s first multi-wavelength space observatory, successfully took its first images of the Crab Nebula, the remnant of a supernova first detected by Chinese astronomers in the year 1054.

Launched on September 30, 2015, Astrosat carries five payloads, including the charged particle monitor (CPM) and the cadmium zinc telluride imager (CZTI), which were the first to go fully operational. The CZTI is a hard X-ray detector that was made made fully operational on October 5, 2015.

On October 6, 2015, Astrosat was oriented towards the Crab Nebula, the brightest hard X-ray source in the sky. Unfortunately, ground support software that had been tested using benign ground data failed to detect the Crab Nebula at first pass.

For the second attempt on October 9, 2015, Astrosat observations were made in parallel by both the Mission Operation Center at Peenya, Bengaluru and Payload Operation Center at the Inter-University Center for Astronomy and Astrophysics (IUCAA), Pune.

It was discovered that the difficulty in detecting the Crab Nebula occurred as the satellite happened to pass through the South Atlantic Anomaly (SAA) region when Crab was in the field of view. The SAA avoidance zone was deliberately kept wide to protect the instruments, and detectors were switched off in this interval during the initial days of Astrosat operation.

When all the data were systematically analysed and data points were selected based on the availability of the Crab Nebula in the detector field of view, the Crab Nebula could be seen emerging from the Earth’s shadow. The image generated by deconvolving the coded mask shadows accumulated during this interval clearly shows Crab as a bright object near the centre.

Apart from the Crab Nebula, Astrosat also observed the black hole source Cygnus X-1 for two days. The CZTI will provide spectroscopic data in the 70 keV-300 keV region, which, taken together with data from the NAZA NuStar observations, will provide unprecedented wide band spectroscopic data on Cygnus X-1. This data could help scientists understand the accretion disk geometry in a black hole sources like Cygnus X-1.

In the next few weeks, other X-ray instruments of Astrosat would be made operational. Astrosat would be looking at some of the black hole sources and candidates like GRS 1915+105, Cygnus X-1, Cygnus X-3 during the month of November. Simultaneous observations are also planned using an infra-red telescope at Mt Abu, radio observations at the giant meterwave radio telescope (GMRT), Khodad and using the Himalayan Chandra Telescope.

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Source: Indian Space Research Organization.
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