Non-imaging Gamma Ray Telescopes

Abstract

Despite continual improvement of the Atmospheric Cherenkov Technique, the number of astrophysical gamma ray sources that have been well studied from the ground remains small (less than a half-dozen), due mainly to the nature of the cosmic accelerators themselves. For most Active Galactic Nuclei of the blazar class, the energy range in which imagers are sensitive lies beyond the inverse Compton peak, where the flux falls rapidly with increasing energy. A few galactic sources are very bright in EGRET but the spectra roll over (e.g. Geminga), while many have no break in the EGRET data but are intrinsically weak. The Crab nebula is an exception, along with a some others. Increasing the data sample thus requires a lower energy threshold, increased flux sensitivity, or a combination of the two. Long term progress will come with the imager arrays (HESS & VERITAS, beginning in 2002), the very large imagers (MAGIC & MACE) and with GLAST (2006). This paper reviews work-in-progress aimed at reaching the 50 GeV range using solar plants.