ALTO is a wide field-of-view air shower detector array for very-high-energy ( VHE ) gamma-ray astronomy , proposed to be installed in the Southern Hemisphere at an altitude of \sim 5.1 Â km above sea level .
The array will use water Cherenkov detectors , as in the HAWC observatory , but combined with scintillator detectors , to detect air showers induced by VHE gamma rays in the atmosphere .
It is being designed to attain a lower energy threshold , better energy and angular resolution , and improved sensitivity .
The array will consist of \sim 1250 small-sized ( 3.6 Â m diameter ) detector units distributed over a circular area of \sim 160 Â m in diameter .
Each detector unit will consist of a water Cherenkov detector and a liquid scintillation detector underneath which will preferentially identify muons , facilitating the background ( cosmic ray ) rejection , thereby improving the sensitivity .
The background rejection will be further enhanced by the close-packed arrangement and the small size of the detectors which will allow a fine sampling of air-shower footprints at the ground .
In this contribution , we present the Monte-Carlo simulation of the experiment performed using CORSIKA and GEANT4 simulation packages .
The expected performance of the array in terms of reconstruction accuracies of the shower core and arrival direction , as well as preliminary estimate of the trigger energy threshold after preliminary selection cuts for a point-like gamma-ray source are presented .