Chandra's First Decade of Discovery

Spectroscopy of the photoionized wind and absorption dips in the Cyg X-1 system

We present results from our simultaneous observations of the high-mass X-ray binary system Cygnus X-1 / HDE 226868 with Chandra-HETGS, XMM-Newton, Suzaku, RXTE, INTEGRAL, and Swift in 2008 April. The observations have been performed shortly after phase 0 of the 5.6 d orbit when our line of sight to the accreting black hole passes through the densest part of the wind of the donor star. The high resolution gratings spectra, in the context of a consistent description for the 0.5--600 keV spectrum, allow us to study the composition and dynamics of the highly photoionized wind. The soft X-ray band is strongly affected by transient absorption dips, caused by dense structures in the clumpy O-star wind. A color-color diagram shows evidence that the additional absorber causing the dips only covers part of the X-ray emitting region. The spectroscopic analysis reveals changes in the ionization state of the wind material between dip and non-dip phases.

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