Giant Pulses from PSR B0540-69 in the Large Magellanic Cloud

We report the discovery of the first giant pulses from an extragalactic radiopulsar. Observations of PSR B0540-69 in the Large Magellanic Cloud made withthe Parkes radio telescope at 1.38 GHz show single pulses with energy more than5000 times that of the average pulse energy. This is only the second youngpulsar, after the Crab, to show giant pulse emission. Similar to the Crabpulsar, the giant pulses occur in two distinct phase ranges and havesignificant arrival time jitter within these ranges. The location of the giantpulses appears to lag the peak of the (sinusoidal) X-ray profile by 0.37 and0.64 phase, although absolute timing between the radio and X-ray data is notyet secure. The dispersion measure of the giant pulses is 146.5 pc/cc, inagreement with the detection of the pulsar at 0.64 GHz by Manchester et al.(1993). The giant pulses are scatter broadened at 1.4 GHz with an exponentialscattering time of 0.4 ms and have an emission bandwidth of at least 256 MHz.In 8 hr of integration we have failed to detect any integrated flux densityfrom the pulsar to a level of 13 microJy, assuming a duty cycle of 10%. Thisimplies the spectral index between 0.64 and 1.38 GHz is steeper than -4.4.Comment: Accepted by ApJ Letters. 11 pages, 3 figure