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 Photo meter 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 mo dulo the pulsar period was 21.5 mus. Contemporaneous UVBR observations were obtained from McDonald Observatory in January. The visible and U V light curves observed from HST are similar, but the main pulse is sl ightly narrower in the UV. The separation in phase between the main pu lse and the interpulse is also 0.7% smaller in the UV than in the visi ble. The main pulse arrival time is the same in the UV as in the visib le and radio to within the accuracy of the establishment of the spacec raft clock, +/- 1.05 ms (+/- 0.031 in pulsar phase). The peak of the m ain 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 th e peak flux (2 sigma upper limit) just before the onset of the main pu lse. The variations in intensity of individual main and secondary puls es are uncorrelated, even within the same rotational period. These res ults are consistent with the predictions of the standard model of puls ar emission.