Transient structure in the high-energy X-ray light curve of NP 0532

ON 1974 June 21 we observed the Crab Nebula with a balloon-borne X-ray telescope (20–150 keV) with a sensitive area of ∼700 cm 2 . The observations took place between UT 54112 S and 78520 S. At times during this period a transitory third peak was observed in the light curve of NP0532, which we have reported earlier 10 . The peak comprised 2.0±0.5% of the total emission from the Crab, and was detectable for ∼5 min on two occasions (∼40 min apart). We also report pulsed fractions in the primary and secondary peaks, and in the interpulse region.