Tests and applications of Cherenkov imaging in TeV astronomy

Abstract

The technique of searching for astrophysical sources of TeV (10^^ eV) 7-rays using ground-based air Cherenkov telescopes is about 30 years old. The detection relies upon the extensive air shower created by the primary 7-ray. Alternating pair production and bremsstrahlung create thousands of electrons and positrons which deposit their energy in the atmosphere. The charged particle component is greatly diminished by the time the shower reaches mountain altitudes. What survives is the Cherenkov radiation from fast particles in the cascade. The resulting pool of blue and ultraviolet light is a few hundred meters in diameter and approximately one meter in thickness. An optical reflector and focal plane phototube gated for several nanoseconds can successfully record the flash of light as it rises above the night sky which acts as the only natural source of noise.Aside from opening a new astronomical window on the universe, the search for sources of TeV 7-rays has bearing on the problem of the origin of cosmic rays. The cosmic ray energy spectrum extends up to 10^" eV. The source directions of these energetic particles are completely hidden by bending in the galactic magnetic field.The energetic photons created in the same environment do not have that problem.By looking for sources of very high energy 7-rays the source of cosmic rays may be found.