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Correlated X-ray and Optical Behavior in Sco X-1 and Cyg X-2

Presentation #231.01 in the session “Binary Stellar Systems II”.

Published onJun 18, 2021
Correlated X-ray and Optical Behavior in Sco X-1 and Cyg X-2

Neutron star low mass x-ray binaries can be divided into three main groups: atoll sources, Cyg-like Z sources, and Sco-like Z sources, based on their shapes on an x-ray color-color diagram. In these systems, a large share of optical emission arises from the reprocessing of x-rays on the outer accretion disk or companion star. As such, this should lead to peaks at positive lags on the order of light travel time within the binary. We searched for these types of correlations in Cyg X-2 and Sco X-1. The optical lightcurves were taken with the Argos instrument on the Otto Struve Telescope at McDonald observatory, and the x-ray lightcurves were obtained with the Rossi X-ray Timing Explorer, for both systems. In the Cyg X-2 data, several instances of near-zero lag cross correlation features were found, but none of them were positive peaks at appropriate lags. The Sco X-1 data contained an instance of reprocessing with contributions from both the companion star and the accretion disk. We also found several relatively small, sharp peaks at lags on the order of seconds that could be due to reprocessed x-rays as well.


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