The sensitivity of the CANGAROO I analyses of the Crab and Vela plerions to image selection cuts

Observations of the Crab nebula from 1996 to 1998 and the Vela synchrotron nebula during 1997, made with the recoated CANGAROO 3.8 m imaging Cerenkov telescope at Woomera, South Australia, have been analysed using the results from new MOCCA simulations (Dazeley and Patterson, paper 1). Our analyses do not reproduce the previously published levels of emission from the Vela and Crab plerions, and we discuss the possible reasons, including a sensitivity of the results to the cuts used. The 3(7 upper limits derived from these observations are 2.5*10^-12 photons cm ^-2 s ^-1 above -2.7 TeV for Vela and 9.3 * 10^-13 photons cm^-2 s^-1 above -12 TeV for the Crab.