Spectroscopy of the stellar wind in the Cygnus X-1 system

TL;DR

This paper uses high-resolution X-ray spectroscopy to study the focused stellar wind in Cygnus X-1 at different orbital phases, revealing insights into the wind's structure and its role in accretion onto the black hole.

Contribution

It provides detailed spectroscopic analysis of the asymmetric stellar wind in Cygnus X-1 across multiple orbital phases, enhancing understanding of wind accretion physics.

Findings

Wind is strongly focused towards the black hole.

Wind structure varies with orbital phase.

Insights into wind dynamics and accretion processes.

Abstract

The X-ray luminosity of black holes is produced through the accretion of material from their companion stars. Depending on the mass of the donor star, accretion of the material falling onto the black hole through the inner Lagrange point of the system or accretion by the strong stellar wind can occur. Cygnus X-1 is a high mass X-ray binary system, where the black hole is powered by accretion of the stellar wind of its supergiant companion star HDE226868. As the companion is close to filling its Roche lobe, the wind is not symmetric, but strongly focused towards the black hole. Chandra-HETGS observations allow for an investigation of this focused stellar wind, which is essential to understand the physics of the accretion flow. We compare observations at the distinct orbital phases of 0.0, 0.2, 0.5 and 0.75. These correspond to different lines of sights towards the source, allowing us to probe the structure and the dynamics of the wind.