Optical/X-ray correlations during the V404 Cygni June 2015 outburst

J. Alfonso-Garzon*, C. Sanchez-Fernandez, P. A. Charles, J. M. Mas-Hesse, P. Gandhi, M. Kimura, A. Domingo, J. Rodriguez, J. Chenevez

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Context. We present a multiwavelength analysis of the simultaneous optical and X-ray light curves of the microquasar V404 Cyg during the June 2015 outburst.Aims. We have performed a comprehensive analysis of all the INTEGRAL/IBIS, JEM-X, and OMC observations during the brightest epoch of the outburst, along with complementary NuSTAR, AAVSO, and VSNET data, to examine the timing relationship between the simultaneous optical and X-ray light curves, in order to understand the emission mechanisms and physical locations.Methods. We have identified all optical flares that have simultaneous X-ray observations, and performed a cross-correlation analysis to estimate the time delays between the optical and soft and hard X-ray emission. We also compared the evolution of the optical and X-ray emission with the hardness ratios.Results. We have identified several types of behaviour during the outburst. On many occasions, the optical flares occur simultaneously with X-ray flares, but at other times, positive and negative time delays between the optical and X-ray emission are measured.Conclusions. We conclude that the observed optical variability is driven by different physical mechanisms, including reprocessing of X-rays in the accretion disc and/or the companion star, interaction of the jet ejections with surrounding material or with previously ejected blobs, and synchrotron emission from the jet.
Original languageEnglish
Article numberA110
JournalAstronomy and Astrophysics
Number of pages16
Publication statusPublished - 2018


  • X-rays: binaries
  • Stars: black holes
  • Accretion
  • Accretion disks


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