Optical and X-ray observations of the microquasar V404 Cyg during its June 2015 outburst

We present a multiwavelength analysis of the simultaneous optical and X-ray light curves of the microquasar V404 Cyg during the June 2015 outburst. 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.

We identified all optical ares with simultaneous X-ray observations, and performed cross-correlation analysis to estimate the time delays between the optical and soft and hard X-ray emission. We have also compared the evolution of the optical and X-ray emission with the hardness-ratios. From this analysis, we identified several types of behaviour during the outburst, including simultaneous optical/X-ray ares, optical ares lagging the X-ray ares, and optical emission preceding the X-ray emission.