A Thorough Look at the Photoionized Wind and Absorption Dips in the Cygnus X-1 / HDE 226868 X-ray Binary System

TL;DR

This study analyzes multi-instrument observations of Cygnus X-1 to understand the structure and ionization state of the stellar wind, revealing a complex wind with neutral cores and ionized outer regions.

Contribution

It provides the first simultaneous detection of a scattering trough in hard X-rays alongside absorption dips, indicating a complex, multi-phase wind structure in Cygnus X-1.

Findings

Detection of simultaneous absorption dips and scattering troughs.

Identification of neutral cores within larger ionized wind blobs.

Most of the wind outside clumps is highly photoionized.

Abstract

We present results from simultaneous observations of the high-mass X-ray binary system Cygnus X-1 / HDE 226868 with Suzaku, Chandra-HETGS, XMM-Newton, RXTE, INTEGRAL, and Swift in 2008 April. Performed shortly after orbital phase 0, when our line of sight to the black hole passes through the densest part of the O-star's wind, these obervations show common transient absorption dips in the soft X-ray band. For the first time, however, we detect a simultaneous scattering trough in the hard X-ray light curves. The more neutral clump is thus only the core of a larger ionized blob, which contains a significant fraction of the total wind mass. The diluted wind outside of these clumps is almost completely photoionized.