How do atmospheric Cerenkov telescopes detect very-high-energy gamma rays?

Atmospheric Cerenkov telescopes detect very-high-energy gamma rays by observing the secondary effects of these particles as they interact with Earth's upper atmosphere.12

When a high-energy gamma ray strikes the atmosphere, it initiates a cascade of secondary particles, including fast electrons. Because these electrons travel at speeds greater than the speed of light in the atmosphere, they emit Cherenkov radiation. This light is emitted in a brief, forward-directed cone along the path of the particles.243

Ground-based atmospheric Cerenkov telescopes are designed to capture these faint, short-lived optical flashes. By detecting this specific radiation, scientists can infer the presence and direction of the original high-energy gamma rays. Unlike charged cosmic ray particles, which are deflected by magnetic fields, gamma rays travel in straight lines, allowing these telescopes to pinpoint their origins in energetic cosmic objects such as supernova remnants and active galaxies.412