An optimized method for the reconstruction of the direction of air showers for scintillator arrays

An optimized method is presented for the reconstruction of air shower directions for scintillator arrays. The method takes into account that both the expectation value and the spread of the measured arrival times not only depend on the distance of a counter from the shower axis, but also on the number of particles registered in that counter. It also takes into account that the distributions of the measured arrival times are not Gaussian. For showers recorded with the HEGRA scintillator array above the threshold energy of Ethres = 20 TeV the mean angular resolution obtained with this method is 〈σ63%θ〉 = 1.0°, and above the threshold Ethres = 50 TeV it is 〈σ63%θ〉 = 0.6°. Comparing the new procedure with the HEGRA standard procedure the angular resolution has improved on average by a factor of 1.33. The mis-pointing has been determined with an accuracy of 0.15°. The method is developed using experimental data.