Natural limit to the γ/hadron separation for a stand alone air Cherenkov telescope

The γ/hadron separation in the imaging air Cherenkov telescope technique is based on differences between images of a hadronic shower and a γ induced electromagnetic cascade. One may expect for a large telescope that a detection of hadronic events which contains Cherenkov light from one γ subcascade only is possible. In fact, simulations shows that for the MAGIC telescope their fraction in total protonic background is in order of 3.5% to 1% depending on the trigger threshold. It was found out that such images have small sizes (mainly below 400 ph.e.) what corresponds to the sizes of the low energy primary γ’s (below 100 GeV). It is shown that parameters describing a shape of images from one subcascade have similar distributions like a primary γ events, so those parameters are not efficient in all methods of γ selection. Similar studies based on MC simulations are presented also for the images from 2 γ subcascade which are products of the same π decay.