Cosmic Matter 2007

80th Annual Scientific Meeting of the Astronomische Gesellschaft
Würzburg, Germany
2007 September 24–29

Wind absorption in Cygnus X-1

M. Hanke, J. Wilms, M.A. Nowak, K. Pottschmidt, N.S. Schulz, J.C. Lee, J. Xiang, A. Young, A. Juett

ADS Although Cygnus X-1 is the best studied BH X-ray binary, whose persistent brightness is powered by accretion of the focused stellar wind of the supergiant companion, the detailed accretion geometry is not yet understood. We present the spectroscopic analysis of the photoionized wind from a 50 ks observation obtained with the Chandra ACIS-S/HETGS on April 2003 during superior conjunction of the black hole, when the source was in its hard state. Detection of absorption lines from mostly H- and He-like ions allow us to study the ionization state and composition of the stellar wind in detail. We use a model that consistently describes the whole series of lines from each ion at once. Furthermore, the observation contains absorption dips, probably from clumps in the accretion flow, which are analyzed as well.

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