Celestial gamma rays, being energetic photons, provide non-thermal view of the Universe complementing our view at other wavelengths. Using them we could explore the Universe at its extreme. They are invisible to the human eye and are absorbed in the atmosphere. However at higher energies, above a few tens of GeV, they may be detected on ground, though indirectly, through their interactions in the atmosphere. I shall introduce the subject of ground-based gamma-ray astronomy using the atmospheric Cherenkov technique and briefly trace its historical development in India. The current facilities at Hanle (Ladakh) will be highlighted along with other operating ground-based facilities elsewhere for gamma ray astronomy. After discussing some of the sources of gamma rays, I will conclude with the future prospects, especially with the Cherenkov Telescope Array (CTA), an international project for the next generation of observatories in this field covering a broad energy range.
About Speaker :
Dr. B. S. Acharya is a retired professor and chairperson of the Department of High Energy Physics (DHEP), TIFR, Mumbai. He is one of the leading figures in the very high-energy (VHE) gamma-ray astronomy in India and is also involved in various international VHE projects. This colloquium is a part of the activities commemorating "75 years of India's Independence: Azadi ka Amrit Mahotsav" at ARIES.