Rapid Optical Variations Correlated with X-rays in the 2015 Second Outburst of V404 Cygni (GS 2023$+$338)

Abstract

We present optical multi-colour photometry of V404 Cyg during the outburst from December, 2015 to January, 2016 together with the simultaneous X-ray data. This outburst occurred less than 6 months after the previous outburst in June-July, 2015. These two outbursts in 2015 were of a slow rise and rapid decay-type and showed large-amplitude ($\sim$2 mag) and short-term ($\sim$10 min-3 hours) optical variations even at low luminosity (0.01-0.1$L_{\mathrm{Edd}}$). We found correlated optical and X-ray variations in two $\sim$1 hour time intervals and performed Bayesian time delay estimations between them. In the previous version, the observation times of X-ray light curves were measured at the satellite and their system of times was Terrestrial Time (TT), while those of optical light curves were measured at the Earth and their system of times was Coordinated Universal Time (UTC). In this version, we have corrected the observation times and obtained a Bayesian estimate of an optical delay against the X-ray emission, which is $\sim$30 s, during those two intervals. In addition, the relationship between the optical and X-ray luminosity was $L_{\mathrm{opt}}\propto L_{\mathrm{X}}^{0.25-0.29}$ at that time. These features can be naturally explained by disc reprocessing.

14 pages, 8 figures, Accepted for publication in MNRAS (includes supplementary information), plus an erratum

References in corpus (13)

• X-ray Properties of Black-Hole Binaries
• Modelling the behaviour of accretion flows in X-ray binaries
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
• Rapid optical and X-ray timing observations of GX 339-4: flux correlations at the onset of a low/hard state
• Repetitive Patterns in Rapid Optical Variations in the Nearby Black-hole Binary V404 Cygni
• SWIFT J1753.5-0127: a surprising optical/X-ray cross-correlation function
• Flares, wind and nebulae: the 2015 December mini-outburst of V404 Cygni
• High-energy gamma-ray observations of the accreting black hole V404 Cygni during its June 2015 outburst
• Time-resolved optical/near-IR polarimetry of V404 Cyg during its 2015 outburst
• Detection of Very Low-Frequency Quasi-Periodic Oscillations in the 2015 Outburst of V404 Cygni
• MASTER optical polarization variability detection in the Microquasar V404 Cyg/GS2023+33
• A challenging view of the 2015 summer V404 Cyg outburst at high energy with INTEGRAL/SPI: The finale