FUSE Observations of a Full Orbit of Scorpius X-1

TL;DR

This study presents UV spectral observations of Scorpius X-1 over its full orbit, revealing emission sources near the donor star and accretion disk, and modeling the spectral lines to understand the system's structure.

Contribution

First full-orbit UV spectral analysis of Scorpius X-1, combining models of turbulence, Keplerian disk lines, and narrow emission components to interpret the emission regions.

Findings

Emission lines originate near the donor star and accretion disk.

Spectral line models fit the observed data with consistent disk parameters.

Doppler shifts indicate the association of narrow lines with the donor star.

Abstract

We obtained UV spectra of X-ray binary Scorpius X-1 in the 900-1200 A range with the Far Ultraviolet Spectroscopic Explorer over the full 0.79 day binary orbit. The strongest emission lines are the doublet of O VI at 1032,1038 A and the C III complex at 1175 A. The spectrum is affected by a multitude of narrow interstellar absorption lines, both atomic and molecular. Examination of line variability and Doppler tomograms suggests emission from both the neighborhood of the donor star and the accretion disk. Models of turbulence and Doppler broadened Keplerian disk lines Doppler shifted with the orbit of the neutron star added to narrow Gaussian emission lines with undetermined Doppler shift fit the data with consistent values of disk radius, inclination, and radial line brightness profile. The Doppler shift of the narrow component with the orbit suggests an association with the donor star. We test our line models with previously analyzed near UV spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph and archival spectra obtained with the HST Cosmic Origins Spectrograph.