Hanle, Ladakh, is one of the proposed sites for the $268-million project

Scientists and engineers from 27 countries, including India, are pitching for a next-generation gamma-ray telescope that could transform the future of high-energy astrophysics.

Called the Cherenkov Telescope Array (CTA), the project involves a large array of telescopes to complement existing observatories, the most potent of which orbit the Earth. By building it on land, scientists feel the CTA could be much more sophisticated than orbiting observatories, which have logistical constraints.

The CTA’s preliminary designs reveal that it boasts of greater angular resolution, and 10 times more sensitivity and energy-coverage, than existing telescopes. The collaboration will finalise the locations by end-2013 for setting up the CTA, which will consist of two networked arrays in the northern and southern hemispheres.

One proposed northern hemisphere location is in Ladakh, Jammu and Kashmir.

Dr. Pratik Majumdar, Saha Institute of Nuclear Physics (SINP), Kolkata, said via email, “A survey was undertaken in the late 1980s. Hanle, in Ladakh, was a good site fulfilling most of our needs: very clear and dark skies throughout the year, with a large number of photometric and spectroscopic nights at par with other similar places in the world, like La Palma in Canary Islands and Arizona desert, U.S.”

However, it serves to note that the Indian government does not permit foreign nationals to visit Hanle.

Each network will consist of four 23-metre telescopes to image weaker gamma-ray signals, and dozens of 12-metre and 2-4-metre telescopes to image the really strong ones. Altogether, they will cover an area of 10 sq. km on ground.

Scientists from SINP are also conducting simulations to better understand the performance of CTA. Led by it, the Indian collaboration comprises Indian Institute of Astrophysics, BARC, and TIFR. They will be responsible for building the calibration system with the Max Planck Institute, and developing structural sub-systems of various telescopes to be fabricated in India.

Dr. B.S. Acharya, TIFR, believes the CTA can add great value to existing telescopes in India, especially the HAGAR gamma-ray telescope array in Hanle. “It is a natural extension of our work on ground-based gamma-ray astronomy in India, since 1969,” he said in an email to this Correspondent.

While existing telescopes, like MAGIC (Canary Islands) and VERITAS (Arizona), and the orbiting Fermi-LAT and Swift, are efficient up to the 100-GeV energy mark, the CTA will be able to reach up to 100,000 GeV with the same efficiency.

Gamma rays originate from sources like dark matter annihilation, dying stars and supermassive black holes, whose physics is little understood. Such sources accelerate protons and electrons to huge energies and these interact with ambient matter, radiation and magnetic fields to generate gamma rays, which then travel through space.

When gamma-rays hit atoms in Earth’s upper atmosphere, a shower of particles is produced that cascades downward. Individual telescopes pick these up, but a network of telescopes, such as CTA, spread over a large area would collect greater amounts, tracking them back better to their sources.

Dr. Subir Sarkar of Rudolf Peierls Centre for Theoretical Physics, Oxford University noted in an email to this Correspondent: “No telescope based at one point on Earth can see the whole sky. The proposed CTA southern observatory will be able to study the centre of the galaxy, while the northern observatory will focus on extragalactic sources.” Dr. Sarkar is a member of the collaboration.

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