Simultaneous HST/XTE Observations of Sco X-1
  Sco X-1 is the brightest extra-solar point source of X-rays, and may serve as a prototype for low mass X-ray binaries as a class. It has been suggested that the UV and optical emission arise as a result of reprocessing of X-rays, and that a likely site for such reprocessing is an accretion disk around the X-ray source. If UV and optical emission are enhanced by reprocessing of X-rays, the X-ray variability may be manifest in UV emission: we test this by using high temporal resolution UV data obtained simultaneously with high temporal resolution X-ray data obtained simultaneously with the GHRS on the Hubble Space Telescope, and with the X-ray Timing Explorer (XTE). We analyze the variability behavior of the UV spectrum and of the X-rays, and we also measure the properties of the emission line profiles as viewed at high resolution with the echelle gratings. The variability behavior does not provide direct support of the reprocessing scenario, although the correlated variability between UV and X-rays does not conflict with this hypothesis. Furthermore, the emission line profiles do not fit with simple models for disk emission lines. 
T. Kallman, B. Boroson, S. Vrtilek