[en] The supernova SN1987A have been observed in the range of hard X-rays (15 / 180 KeV) and high energy γ-rays (50 / 500 MeV) with a payload launched from the balloon facility of Alice Springs (Australia) during April 1987 and 1988. The low energy detector based on a MWPC had a sensitive area of 500 cm/sup 2/. In the second flight a complete plastic shield was added for the first time to the Multiwire Proportional Counter (MWPC). In this way, switching on the active shield, the background counting rate dropped from 4.2 to 2.8 x 10/sup -4/ ct/cm/sup 2/ s keV with no change in the dead time of the counter. This clearly demonstrates the advantage of the use of a multitechnique rejection system for this kind of gaseous detectors