  IceTop is an air shower array that is part of the IceCube Observatory
currently under construction at the geographic South Pole. When completed, it
will consist of 80 stations covering an area of 1 km2. Previous analyzes done
with IceTop studied the events that triggered five or more stations, leading to
an effective energy threshold of about 0.5 PeV. The goal of this study is to
push this threshold lower, into the region where it will overlap with direct
measurements of cosmic rays which currently have an upper limit around
300TeV.We select showers that trigger exactly three or exactly four adjacent
surface stations that are not on the periphery of the detector (contained
events). This extends the energy threshold down to 150TeV.
