Simultaneous X-ray and optical spectroscopy of V404 Cygni supports the multi-phase nature of X-ray binary accretion disc winds

Vol. 664
7. Stellar structure and evolution

Simultaneous X-ray and optical spectroscopy of V404 Cygni supports the multi-phase nature of X-ray binary accretion disc winds

The signatures of these winds were first found in X-ray spectra, as narrow emission or absorption features. In the last few years, similar features have also been discovered in the optical and near-infrared spectra of X-ray binaries. In this paper, Muñoz-Darias and Ponti, for the first time, merge simultaneous X-ray and optical data on the black hole transient V404 Cygni. Wind signatures are found in both energy bands: lines are shifted by the same amount and have a characteristic P-Cygni profile. This behavior occurs at different luminosities too. These observations strongly suggest a solution for the nature of the disk wind: a dynamic, multiphase (hot for the X-ray features and colder for the optical ones) accretion disk wind in which both phases coexist in time and space.