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

[50.11] Reprocessed UV Pulses from Vela X-1

P. T. Boyd (USRA and LHEA NASA/GSFC), J. F. Dolan (LASP NASA/GSFC), R. J. Hill, J. M. Silvis (HSTX NASA/GSFC), E. L. Robinson (U Texas, Austin), J. W. Percival, R. C. Bless (U. Wisconsin), G. W. van Citters (NSF)

The High Speed Photometer (HSP), a first generation scientific instrument aboard the Hubble Space Telescope, observed a number of X-ray binary systems in the ultraviolet for evidence of x-ray pulses being reprocessed in the atmospheres of the main sequence primaries. One of these systems, Vela X-1, displayed UV pulses at a period quite near the X-ray pulsar period. Analysis of archival IUE data indicates this reprocessed radiation is mainly line radiation, whose phase variation is consistent with the interpretation that a fraction of the companion starŐs surface is reradiating the pulses.The compact companion in this system, presumably a neutron star pulsar, has the highest neutron star mass measured by previous techniques. The maximum NS mass has ramifications on the equation of state of neutron star matter, and so is an important parameter to measure accurately. If we observe pulses from both the primary and the compact companion, this system may be studied as a double-lined spectroscopic binary, yielding an estimate for the mass twice as accurate as previous measurement techniques.

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