India building her first X-ray telescope

The highly sanitised X-ray optics laboratory located in a corner of the Tata Institute of Fundamental Research building is teeming with activity these days.

Technicians donning protective overalls are working furiously to give the finishing touches to a project which is the first of its kind in India. Led by Dr Kulinder Pal Singh, Chairperson of the Department of Astronomy and Astrophysics, the team is building a soft X-ray telescope which will become the first Indian X-ray telescope to be put in space.

The soft X-ray telescope — that can make observations beyond the reach of an optical telescope—is one of the five payloads that will be on board Astrosat, India’s first satellite dedicated to the study of astronomy, to be launched by ISRO in 2008.

India will thus join the select group of countries who have launched telescopes in space.

What is even more significant is the fact that the 70 kg telescope is being built from scratch at TIFR.

Building an X-ray telescope is much more difficult than an optical one. According to   Singh, “Unlike optical telescopes, the incident rays in an X-ray telescope can’t be focused if they are perpendicular to the reflector.”

“As a result special type of reflectors—a combination of hyperboloid and paraboloid (roughly speaking these translate into conical surfaces)—become necessary. X-rays can be reflected by grazing the two surfaces following which they are converged at the focal point,” he adds.

The making of the reflector itself is an extremely intricate and tedious process. The reflector needs to be coated with materials of high atomic number so that the X-rays can be reflected by it and do not pass through. Therefore, the reflector in the X-ray telescope is made of an aluminium alloy and coated with gold.

Moreover, utmost care needs to be taken while making the reflector. “The quality of images produced by telescope depends directly upon the smoothness of the reflector’s surface,” says Singh.

While the TIFR technicians have also built the complex electronics for the imager in the telescope, the University of Leicester is providing the imager chip, cooling system and the design of the vacuum container and proton shield of the camera. The Trivandrum based Vikram Sarabhai Space Centre (VSSC) is making the structure that will hold the telescope along with the imager.

Singh feels that the soft X-ray camera would be an important milestone for the Indian astronomy community. “With Astrosat, Indian scientists can use the telescope for observational astronomy which would pave the way for the growth of research in this field.”

This telescope will be useful in studying a number of deep space objects like black holes, supernovae and quasars.