A challenging view of the 2015 summer V404 Cyg outburst at high energy with INTEGRAL/SPI: The finale

Understand

During its strong outburst of 2015 June/July, the X-ray transient V404 Cygni (= GS2023+338) was observed up to a level of 50 Crab in the hard X-ray domain.

• We focus here on a particularly intense episode preceeding a definitive decline of the source activity.
• We benefit from large signal-to-noise ratios to investigate the source spectral variability on a timescale of 5 minutes.
• A Hardness-Intensity study of three broad bands reveals clearly different behaviors at low and high energy (below and above around 100 keV).