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Session 50 - Pulsars in the UV and Visible.
Topical, Oral session, Wednesday, June 10

[50.05] UV Spectra of Pulsars: Crab Pulsar from STIS


During the checkout phase of the Hubble Space Telescope(HST) after the Second Servicing Mission, the Crab Pulsar was observed with the Space Telescope Imaging Spectrograph(STIS) to verify timing capability of the ultraviolet Multi Anode Multi Array (MAMA) detectors (HST proposal 7108). We tested only the Near Ultraviolet (NUV) MAMA as a Guest Observer program is scheduled to observed the Crab Pulsar in the Far Ultraviolet (FUV, P. Lundqvist, HST proposal 7761). The spectrum from 1600 to 3200 A was recorded using the G230L grating with 1.6 A per pixel and 0.025 arcseconds per pixel. A total of 4800 seconds integration over two orbits was utilized to record the spectrum in time-tag mode. One additional orbit (1800 seconds) was used with the NUV MAMA in ACCUM mode to permit cross-comparison of the spectrum obtained by two different methods.

Using the data to internally derive the pulse period, which agreed very well with the radio-derived pulse period, we obtained a data cube with the coordinates of slit length, spectral dispersion and pulse profile. Different slices were taken to look for color dependency of the pulse profile across the 1600 - 3200 A spectral region. To the limit of the photon statistics, no color dependence was noticed. Moreover, we compared the spectra of the rising edges, the falling edges and the peaks of the pulse and interpulse. Again no color changes could be detected. The interpulse portion of the profile has significantly lower photon statistics, so little can be stated about its color dependence. No evidence was found for giant pulses as have been reported in radio studies of the Crab Pulsar (Lundgren, et al, 1995, ApJ, 453, 433).

The STIS promises to be an excellent tool for spectroscopic and imaging timing studies of pulsars, and other rapidly varying objects, in the ultraviolet spectral region from 1175 to 3200A with angular resolutions defined by the HST wavelength-dependent point spread function. In the visible (2000 to 10500A) the STIS CCD can be used in both imaging and spectroscopic modes with exposures as short as 0.1 sec.

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