Influence of the scattered Cherenkov light on the width of shower images as measured in the EAS fluorescence experiments

We calculate the lateral distribution of Cherenkov light at different levels of shower development. The calculations use the universal characteristics of large showers. We derive that the angular and lateral distributions of Cherenkov photons emitted by a shower path element depend only on the shower age and height in the atmosphere of this element. The width of a shower image in the Cherenkov scattered light also depends, however, on the zenith angle and X-max. We also show that below shower maximum it is considerably wider than the width in the fluorescence light. (C) 2009 Elsevier B.V. All rights reserved.