5@5 - a 5 GeV energy threshold array of imaging atmospheric Cherenkov telescopes at 5 km altitude

We discuss the concept and the performance of a powerful future ground-base d astronomical instrument, 5@5 - a 5 GeV energy threshold stereoscopic arra y of several large imaging atmospheric Cherenkov telescopes (IACTs) install ed at a very high mountain elevation of about 5 km a.s.l. - for the study o f the gamma -ray sky at energies from approximately 5 to 100 GeV, where the capabilities of both the current space-based and ground-based gamma -ray p rojects are quite limited. With its potential to detect the "standard" EGRE T gamma -ray sources with spectra extending beyond several GeV in exposure times from 1 to 10(3) s, such a detector may serve as an ideal "gamma-ray t iming explorer" for the study of transient non-thermal phenomena like gamma -radiation from AGN jets, synchrotron flares of microquasars, the high ene rgy (GeV) counterparts of gamma ray bursts, etc. 5@5 also would allow detai led gamma -ray spectroscopy of persistent nonthermal sources like pulsars, supernova remnants, plerions, radiogalaxies, and others, with unprecedented for gamma -ray astronomy photon statistics. The existing technological ach ievements in the design and construction of multi(1000)-pixel, high resolut ion imagers, as well as of large, 20 m diameter class multi-mirror dishes w ith rather modest optical requirements, would allow the construction of suc h a detector in the foreseeable future, although in the longer terms from t he point of view of ongoing projects of 100 GeV threshold IACT arrays like HESS which is in the build-up phase. An ideal site for such an instrument c ould be a high-altitude, 5 km a.s.l. or more, flat area with a linear scale of about 100 m in a very arid mountain region in the Atacama desert of Nor thern Chile. (C) 2001 Elsevier Science B.V. All rights reserved.