LOCATING TEV GAMMA-RAY SOURCES WITH SUB-ARCMINUTE PRECISION - THE POINTING CALIBRATION OF THE HEGRA SYSTEM OF IMAGING ATMOSPHERIC CHERENKOVTELESCOPES

Stereoscopic viewing of TeV gamma-ray air showers with systems of Imag ing Atmospheric Cherenkov Telescopes (IACTs) allows us to reconstruct the origin of individual primary particles with an accuracy of 0.1 deg rees or better. The shower impact point can be determined within 15 me ters. To actually achieve this resolution, the pointing of the telesco pes of an IACT system needs to be controlled with high precision. For the HEGRA IACT system, a procedure to calibrate telescope pointing was established, using bright stars distributed over the sky as reference s. On the basis of these measurements, one determines parameters of a correction function which is valid for che complete hemisphere. After correction a pointing accuracy of 0.01 degrees is achieved. (C) 1997 E lsevier Science B.V.