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P. Lundqvist, J. Sollerman (Stockholm Obs.), T.R. Gull, D. Lindler, C.S.J. Pun, G. Sonneborn (GSFC), R.A. Chevalier (U. Virginia), R.A. Fesen (Dartmouth College), C. Fransson (Stockholm Obs.)
We present observations of the Crab pulsar taken with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The new observations cover the region 1140-1720 Å, which is further into the ultraviolet than has previously been obtained. Using the time-tag mode of the spectrograph we obtain the pulse profile in this spectral regime. The profile is similar to the profile previously obtained by us in the near-UV (Gull et al. 1998), although the primary peak appears somewhat narrower. Together with the near-UV data, and new optical data from the Nordic Optical Telescope, our spectrum of the Crab pulsar covers the entire region from 1140 - 9200 Å. Preliminary analysis shows that a flat spectrum can be obtained by a standard extinction curve. With E(B-V)=0.51, R=3.1 the dereddened spectrum of the Crab pulsar can be fitted by a power law with spectral index \alpha\nu = 0.10. The main uncertainty in determining the spectral index of the pulsar is the extinction correction. In the optical we do not see the absorption feature claimed by Nasuti et al. (1996). In the extended emission covered by our 26 \arcsec \times 0\farcs5 slit in the far-UV, we detect emission from C~IV~\lambda1550 and He~II~\lambda1640 from the Crab nebula. Several interstellar absorption lines are detected along the line of sight to the nebula. Also, absorption from the nebula itself is seen in C IV. The strength and velocity structure of this line can constrain the mass of the proposed fast outer shell around the Crab nebula.
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