SPACE TELESCOPE IMAGING SPECTROGRAPH NEAR-ULTRAVIOLET TIME-TAGGED SPECTRA OF THE CRAB PULSAR

We present the spectrum and the pulse profile of the Crab Pulsar in th e near-ultraviolet (1600-3200 Angstrom) observed with the Space Telesc ope Imaging Spectrograph (STIS) during the Hubble Space Telescope (HST ) second Servicing Mission Orbital Verification (SMOV) period. The two -dimensional near-ultraviolet Multianode Microchannel Array (NUV MAMA) was used in time-tag mode with a 2'' x 2'' aperture and the low-dispe rsion grating, G230L, to obtain a cube with axes of slit position, wav elength, and time. The observation-derived pulse period is consistent with radio measurements, and the pulse profile agrees well with previo us NUV broadband measurements by the High Speed Photometer. The pulsar spectrum includes the 2200 Angstrom dust absorption feature, plus sev eral interstellar absorption lines. Dereddening the spectrum using the Savage-Mathis model with E(B - V) = 0.55 +/- 0.05 leads to a good fit to a power law with slope alpha(v) = -0.3 +/- 0.2. The spectra of the main pulse, the interpulse, and the individual rising and falling edg es are similar to the total spectrum within the limits of photon stati stics. The four pulse profiles produced by breaking the spectrum into 400 Angstrom bins show the pulse profile to be stable across the NUV s pectral range. Histogram analysis reveals no evidence for the superpul ses seen at radio wavelengths. The interstellar absorption-line equiva lent widths of Mg I, Mg II, and Fe II are lower than expected based on the implied H I column density from E(B - V) = 0.5. While several exp lanations are possible, additional studies will be necessary to narrow the options.