Gamma-ray astronomy from the ground -- future perspectives

TL;DR

The paper surveys the near-term and longer-term future of ground-based gamma-ray astronomy, arguing that both wide-field ground detectors and precise IACT arrays are needed to achieve full-sky coverage from TeV to PeV energies. It reviews CTAO and SWGO as the dominant facilities in the next decade and outlines emerging concepts—Plenoscope, very small IACTs, and lake-based UHE arrays—that could extend reach to low energies and ultra-high energies. The analysis emphasizes complementary capabilities for transient science and dark matter searches, with southern-hemisphere access identified as a critical factor for key phenomena such as Galactic Center PeV emission and WIMP signals. Collectively, these developments promise substantial gains in sensitivity, angular resolution, duty cycle, and sky coverage, enabling transformative discoveries in high-energy astrophysics.

Abstract

I provide a personal perspective on the future of the field of ground-based gamma-ray astronomy, on the occasion of the 2024 {\it Gamma} conference in Milan. I discuss some of the scientific motivations for new instrumentation and the major new projects that are in development or already under construction, together with emerging concepts for instrumentation in the farther future. I stress the strong complementarity of the ground-level particle detector arrays, with their wide-field capabilities, and the more precise Cherenkov telescope arrays. The key science topics for the next decades require both approaches and both are developing rapidly towards major performance advances and full sky coverage. I will briefly outline the status and roles of the projects CTAO and SWGO which will dominate the next decade. Beyond these projects are several developments which might boost performance at both ends of the ground-based gamma-ray energy range, including the plenoscope approach at low energies and diverse approaches to ultra-high-energy gamma-ray astronomy; from lake-based instruments to arrays of very small Cherenkov telescopes. I will again briefly review these activities and how they may contribute long term.

Figures (5)

• Figure 1: Illustration of the two approaches to ground-based gamma-ray astronomy: the imaging atmospheric Cherenkov technique and the ground-level particle technique. Adapted from armelle_thesis.
• Figure 2: Current and near future projects for ground-based gamma-ray astronomy, together with concepts for future development. The projects are organised by approximate maturity / timescale for realisation and indicative energy ranges. Instruments based on ground-level particle detection (orange bars) are distinguished from those utilising air-Cherenkov telescopes (blue bars). The location of the instruments is indicated by the text colour with Southern hemisphere instruments in black.
• Figure 3: Approximate coverage of the Milky Way by ground-based gamma-ray surveys. Background image from ESA/Gaia/DPAC, Stefan Payne-Wardenaar, CC BY-SA 4.0 IGO.
• Figure 4: Sensitivity comparison of CTAO and SWGO to existing instruments HESS and LHAASO, in terms of differential sensitivity to point-like gamma-ray sources.
• Figure 5: Left: lake simulation tank at MPIK, Heidelberg, with deployed prototype WCDs (reproduced from lake_icrc). Right: PANOSETI telescope in-front of VERITAS telescope T4 (reproduced from panoseti).