20 Years of Indian Gamma Ray Astronomy Using Imaging Cherenkov Telescopes and Road Ahead

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.

Gamma Ray Pulsars and Opportunities for the MACE Telescope

“…In the energy range above 20-150 GeV, the point source sensitivity (∼10 −11 ph cm −2 s −1 ) of MACE is expected to be better than that of MAGIC-I [73,74]. However, beyond 150 GeV, MACE sensitivity (∼10 −10 ph cm −2 s −1 ) is slightly lower than MAGIC-I.…”

“…During this period, it has successfully detected high-energy gamma ray photons from a number of candidate sources, including the recent giant flaring episode of the radio galaxy NGC 1275 in December 2022 and January 2023 [71,72]. The MACE telescope is designed to cover the high-energy gamma ray band above 20 GeV with a point source sensitivity better than the existing stand-alone imaging atmospheric Cherenkov telescopes (IACTs) in the world [73,74]. At present, the telescope is capable of detecting high-energy gamma ray photons from the Crab Nebula with a sensitivity of 5σ in a few minutes (internal communication) in the energy range above 50 GeV.…”

Prospects of detecting gamma-ray signal of dark matter interaction with the MACE telescope

“…Located at an altitude of ∼ 4.3 km above sea level, MACE is the highest existing IACT in the world. The geographical location of the MACE telescope appropriately fills the longitudinal gap among the leading current and future IACTs around the globe [7,8]. Equipped with a 21 m diameter large light…”