Simultaneous ASCA and HST/GHRS observations of Cygnus X-2/V1341 Cygni

Abstract

We present results from ultraviolet and X-ray observations of the low mass X-ray binary Cygnus X-2. The simultaneous HST/GHRS and ASCA observations took place during the low state of an 82-day cycle. We compare our observations as well as archival IUE and RXTE data with models that predict ultraviolet and optical continuum emission from an X-ray heated disk and a Roche-lobe-filling star. The model predictions are consistent with observed optical, ultraviolet, and X-ray variations over both orbital and long-term periods. The X-ray spectral state, the luminosities implied by fits to the X-ray data, the ultraviolet continuum and line fluxes, and the mass accretion rates obtained from fits to the ultraviolet continuum are consistent with location of our observations on the normal and horizontal branches of the Z-shaped X-ray color-color diagram. A combination of changes to mass accretion rate and obstruction by a warped disk can be invoked as a possible explanation for the motion of the ``Z'' in the color-color plane. The GHRS/G160M measurements concentrated on NV and HeII. The low-resolution (GHRS/G140L) observations captured SiIV, NIV, and CIV. Although the relative line fluxes are consistent with emission from an X-ray heated accretion disk corona, predictions from models of line emission from simple disks do not fit the observed emission line profiles.The radial velocities (80-130 km s${}^{-1}$) are consistent with emission from the optical star at the orbital phase (0.70-0.74) of our observations.

35 pages, 11 figures. Accepted for Sept. 2003 issue of PASP

References in corpus (7)

• First Results from the All-Sky Monitor on the Rossi X-ray Timing Explorer
• Long-term Properties of Accretion Disks in X-ray Binaries: I. the variable third period in SMC X-1
• X-Ray Spectra of Z Sources
• Warped Disks as a Possible Origin of Torque Reversals in Accretion-Powered Pulsars
• Changes in the long term intensity variations in Cyg X-2 and LMC X-3
• Hopkins Ultraviolet Telescope Observations of Her X-1
• Simultaneous HST/ASCA Observations of LMC X-4: X-ray Ionization Effects on a Stellar Wind

Cited by in corpus (10)

• X-ray Absorption Line Spectroscopy of the Galactic Hot Interstellar Medium
• Optical spectroscopy and Doppler tomography of Cygnus X-2
• Measuring the black hole masses in accreting X-ray binaries by detecting the Doppler orbital motion of their accretion disk wind absorption lines
• Chemical abundances of the secondary star in the Neutron star X-ray binary Cygnus X-2
• XMM-Newton/RGS Detection of the Missing Interstellar OVII Kalpha Absorption Line in the Spectrum of Cyg X-2
• Variable O VI and N V Emission from the X-ray Binary LMC X-3: Heating of the Black Hole Companion
• Swift monitoring of Cygnus X-2: investigating the NUV-X-ray connection
• Simultaneous optical and X-ray high speed photometry of Cyg X-2
• First IBIS results on the high energy emission of Cyg X-2
• Links Between Optical and X-ray Light in Cygnus X-2