Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips

Abstract

High-mass X-ray binary systems are powered by the stellar wind of their donor stars. The X-ray state of Cygnus X-1 is correlated with the properties of the wind which defines the environment of mass accretion. Chandra-HETGS observations close to orbital phase 0 allow for an analysis of the photoionzed stellar wind at high resolution, but because of the strong variability due to soft X-ray absorption dips, simultaneous multi-satellite observations are required to track and understand the continuum, too. Besides an earlier joint Chandra and RXTE observation, we present first results from a recent campaign which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008 April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE, INTEGRAL, Swift, and AGILE in X- and γ-rays, as well as with VLA in the radio. After superior conjunction of the black hole, we detect soft X-ray absorption dips likely due to clumps in the focused wind covering ≥ 95% of the X-ray source, with column densities likely to be of several 10²³ cm⁻², which also affect photon energies above 20 keV via Compton scattering.