Chapter 8: Particle Detection Arrays for Very-High-Energy Gamma-Ray Astrophysics

Remarkable improvements in the sensitivity and image resolution of γ-ray sky surveys provided by the current generation of ground-based particle detection arrays (PDAs) has led to groundbreaking and sometimes paradigm-shifting observations. In addition to the detection of an unprecedented number of PeVatron candidates, and multi-TeV γ-ray emission associated with particle acceleration in the jets of a microquasar, a new source class, γ-ray halos, has been discovered. These halos are produced by electrons and positrons from pulsars, accelerating in their vicinity, and then interacting with the ambient interstellar radiation field outside the classical pulsar wind nebulae. Following the discovery of γ-ray halos by the High-Altitude Water Cherenkov (HAWC) Observatory, the Fermi Large Area Telescope (LAT) confirmed their existence at the GeV scale. Shortly after, the High Energy Stereoscopic System (H.E.S.S.) telescope confirmed extended emission around the Geminga pulsar at the TeV scale using an adapted analysis. The high-duty-cycle, wide field-of-view, and unrivaled sensitivity of PDAs to ultra-high-energy γ-rays enables them to provide real-time alerts and archival data and makes them uniquely suited for multi-messenger astronomy and fundamental physics research. This chapter covers the current status and future plans for PDAs in the field of ground-based γ-ray astronomy. It includes descriptions of currently operating wide-field-of-view instruments, a discussion of their scientific achievements, and an outlook on an exciting future facility in the Southern Hemisphere pursued by the Southern Wide-Field Gamma-Ray Observatory (SWGO) project.