Collection area

The collection area of the array reflects a combination of the area over which the array can detect gamma-ray showers and the efficiency for retaining those events after analysis. The effective area of VERITAS as a function of photon energy is shown in Figure 16 for the estimated trigger threshold of 4.2p.e. at which VERITAS will operate. For comparison, the effective area of the Whipple telescope near 1TeV is approximately 4$\times$10⁴m² ([Hillas 1996]). The effective collection area at low energies is reduced because these showers emit fewer Cherenkov photons and so must arrive with optimum geometry to trigger the telescope and allow for event reconstruction. For the highest energies, the collection area levels out because the limited FoV of the telescope truncates these images which develop low in the atmosphere.

  

Figure 16: The collection area of VERITAS as a function of photon energy.