We define the angular resolution as the width of a two-dimensional Gaussian fit to the distribution of reconstructed directions for individual photons from a point source. The angular resolution of VERITAS as a function of energy threshold is shown in Figure 15. VERITAS will have better angular resolution than any existing detector (in space or on the ground) operating above a few MeV. The main reason for the excellent angular resolution of VERITAS is its stereoscopic imaging capability. For a single telescope, the photon arrival direction is well-defined only in the direction perpendicular to the axis of the image, though the direction parallel to the direction of the image axis can be roughly estimated ([Buckley et al. 1998]). Multiple sampling of the shower from the VERITAS telescopes overcomes this difficulty and, for larger showers, can average out fluctuations. The angular resolution alone leads to better background rejection than existing single telescopes and it also will allow the emission regions of extended sources to be mapped to arcminute accuracy.
