THE CRAB PULSAR IN THE VISIBLE AND ULTRAVIOLET WITH 20 MICROSECOND EFFECTIVE TIME RESOLUTION

The Crab pulsar (PSR 0531 + 21) was observed with the High Speed Photometer on the Hubble Space Telescope in the visible in 1991 October and in the UV in 1992 January. The time resolution of the instrument was 10.74 mus; the effective time resolution of the light curves folded modulo the pulsar period was 21.5 mus. Contemporaneous UVBR observations were obtained from McDonald Observatory in January. The visible and UV light curves observed from HST are similar, but the main pulse is slightly narrower in the UV. The separation in phase between the main pulse and the interpulse is also 0.7% smaller in the UV than in the visible. The main pulse arrival time is the same in the UV as in the visible and radio to within the accuracy of the establishment of the spacecraft clock, +/- 1.05 ms (+/- 0.031 in pulsar phase). The peak of the main pulse is resolved in time. Corrected for reddening, the intensity spectral index of the Crab pulsar from 1680 to 7400 angstrom is alpha = 0.11 +/- 0.13. The pulsed flux has an intensity less than 0.9% of the peak flux (2 sigma upper limit) just before the onset of the main pulse. The variations in intensity of individual main and secondary pulses are uncorrelated, even within the same rotational period. These results are consistent with the predictions of the standard model of pulsar emission.