Simultaneous Hubble Space Telescope/Rossi X-Ray Timing Explorer Observations of Scorpius X-1

Abstract

Scorpius X-1 is the brightest extrasolar 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 the 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 collected by the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope and by the X-Ray Timing Explorer. 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 (resolving power ~= 25,000) with the echelle gratings. The variability behavior does not provide direct support for 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.