"Convergent observations" with the stereoscopic HEGRA CT system

Abstract

Observations of air showers with the stereoscopic HEGRA IACT system are usually carried out in a mode where all telescopes point in the same direction. Alternatively, one could take into account the finite distance to the shower maximum and orient the telescopes such that their optical axes intersect at the average height of the shower maximum. In this paper we show that this ``convergent observation mode'' is advantageous for the observation of extended sources and for surveys, based on a small data set taken with the HEGRA telescopes operated in this mode.