Links Between Optical and X-ray Light in Cygnus X-2

Abstract

We observed the low mass X-ray binary Cyg X-2 for a total of 18 nights over two observing runs in July and September of 2006, using the Otto Struve Telescope at McDonald Observatory and the Rossi X-ray Timing Explorer. Using discrete cross correlations, we found peaks occurring at near-zero lags in the flaring branch of the colour-colour diagram, which could signify reprocessing, in addition to an anti-correlation within the normal branch. When comparing optical flux to the system's placement on the Z track, two distinct behaviors were seen: (1) a state with no correlation, and (2) a multi-valued (horizontal and normal branches)/correlated (flaring branch) state. The correlation was the result of direct steps and more gradual falls to and from the flaring branch respectively. Finally, we modeled timed spectra with 64 second bins with an extended accretion disc corona model. We found that correlations occurred between the optical and the various fitted parameters, particularly the blackbody normalization (and blackbody radius by extension) in higher intensity regions. Despite this, the Z track location was found to be a far better predictor of physical parameters than the optical flux, with clean correlations seen in every branch of the Z track. Where optical correlations are found, the location on the Z track was a better predictor of optical flux than any individual physical parameter.

19 pages, MNRAS in press

References in corpus (23)

• Hard X-ray Emission From Low Mass X-ray Binaries
• The Optical Light Curves of Cygnus X-2 (V1341 Cyg) and the Mass of its Neutron Star
• Spectral States of XTE J1701-462: Link between Z and Atoll Sources
• RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
• Measurements of accretion disc corona size in LMXB: consequences for Comptonization and LMXB models
• Echoes in X-ray Binaries
• An explanation of the Z-track sources
• Radius Constraints from Reflection Modeling of Cygnus X-2 with NuSTAR and NICER
• Common Patterns in the Evolution between the Luminous Neutron Star Low-Mass X-ray Binary Subclasses
• Heating in an Extended Accretion Disk Corona along the Z-Pattern in Cyg X-2
• On the nature of the Cygnus X-2 like Z-track sources
• NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus~X--2
• Correlations between X-ray Spectral and Timing Characteristics in Cyg X-2
• Simultaneous ASCA and HST/GHRS observations of Cygnus X-2/V1341 Cygni
• High-speed Keck II and RXTE spectroscopy of Cygnus X-2: (I) Three X-ray components revealed by correlated variability
• Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI
• Sco X-1 revisited with Kepler, MAXI and HERMES: outflows, time-lags and echoes unveiled
• Long term radio monitoring of the neutron star X-ray binary Swift J1858.6-0814
• Thermonuclear X-ray bursts detected in Cyg X-2 using AstroSat/LAXPC
• The hard X-ray emission along the "Z" track in GX 17+2
• Dipping -versus Flaring in Z-track sources: resolving the controversy
• Echo Tomography of Black Hole Accretion Flows
• Links Between Optical and X-ray Light in Scorpius X-1