Abstract
The field of ground-based γ-ray astronomy has made very significant advances over the last three decades with the extremely successful operations of several atmospheric Cherenkov telescopes worldwide. The advent of the imaging Cherenkov technique for indirect detection of cosmic γ rays has immensely contributed to this field with the discovery of more than 220 γ-ray sources in the Universe. This has greatly improved our understanding of the various astrophysical processes involved in the non-thermal emission at energies above 100 GeV. In this paper, we summarize the important results achieved by the Indian γ-ray astronomers from the GeV-TeV observations using imaging Cherenkov telescopes over the last two decades. We mainly emphasize the results obtained from the observations of active galactic nuclei with the TACTIC (TeV Atmospheric Cherenkov Telescope with Imaging Camera) telescope, which has been operational since 1997 at Mount Abu, India. We also discuss the future plans of the Indian γ-ray astronomy program with special focus on the scientific objectives of the recently installed 21 m diameter MACE (Major Atmospheric Cherenkov Experiment) telescope at Hanle, India.
Highlights
The concept of gamma-ray astronomy (GRA) was first coined by Phillip Morrison in 1958 [1]
We present the scientific achievements of the Indian GRA program using imaging atmospheric Cherenkov telescopes (IACTs) in the last twenty years and future roadmap for the decade
The journey of Indian GRA using IACTs over the last two decades seems to be very satisfying on the whole
Summary
The concept of gamma-ray astronomy (GRA) was first coined by Phillip Morrison in 1958 [1]. This motivated the Crimean group to develop a ground-based experimental technique for recording the extensive air showers initiated by the TeV γ-ray photons by detecting the Cherenkov radiation produced from them in the Earth’s atmosphere [3] Using this experiment, Crab Nebula, radio galaxies, and supernova remnants were observed by the Crimean group. An experimental set-up consisting of six equatorially mounted parabolic search light mirrors, similar to the Pachmarhi facility, was installed at Gulmarg in 1984 [7] This was the first generation of indigenously developed multi-mirror atmospheric Cherenkov telescope commissioned at Gulmarg for dedicated GRA in the TeV energy range.
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