2004MNRAS.350..587O -
Mon. Not. R. Astron. Soc., 350, 587-595 (2004/May-2)
High-speed Keck II and RXTE spectroscopy of Cygnus X-2 - I. Three X-ray components revealed by correlated variability.
O'BRIEN K., HORNE K., GOMER R.H., OKE J.B. and VAN DER KLIS M.
Abstract (from CDS):
We have performed simultaneous X-ray and optical spectroscopic observations of the low-mass X-ray binary Cygnus X-2. We have used a new data system attached to the Low Resolution Imaging Spectrograph (LRIS) instrument on Keck II to obtain spectra with a mean time resolution of 72.075 ms, simultaneous with pointed X-ray observations using the Proportional Counter Array (PCA) onboard RXTE. In this paper, we have analysed the variability in both wavebands on time-scales of 16 s. During our observations Cygnus X-2 covered all three branches of the Z-curve, allowing us to study how the changes in X-ray spectral state affect the optical emission. As the optical flux rises, the X-ray intensity first rises on the horizontal branch (0 < Sz < 1) but then falls on the normal branch (1 < Sz < 2) and flaring branch (2 < Sz < 3), where Sz is a rank number characterizing the position on the Z-curve. This linear increase in the optical flux with Sz indicates the optical flux is a good predictor of the accretion rate (possibly normalized by its own long-term average) inferred from the Z-state Sz. We have used this correlation to decompose the total X-ray count rate into three distinct spectral components.
Abstract Copyright:
2004 RAS
Journal keyword(s):
binaries: close - stars: individual: Cyg X-2 - X-rays: binaries
Simbad objects:
3
Full paper
View the references in ADS
To bookmark this query, right click on this link: simbad:2004MNRAS.350..587O and select 'bookmark this link' or equivalent in the popup menu