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Title:
Revealing the Focused Companion Wind in Cygnus X-1 with Chandra
Authors:
Miller, J. M.; Wojdowski, P.; Schulz, N. S.; Marshall, H. L.; Fabian, A. C.; Remillard, R. A.; Wijnands, R.; Lewin, W. H. G.
Affiliation:
AA(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; .; National Science Foundation Astronomy and Astrophysics Postdoctoral Fellow.), AB(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.), AC(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.), AD(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.), AE(University of Cambridge Institute of Astronomy, Cambridge CB3 OHA, UK.), AF(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.), AG(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.), AH(Center for Space Research and Department of Physics, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139.)
Publication:
The Astrophysical Journal, Volume 620, Issue 1, pp. 398-404. (ApJ Homepage)
Publication Date:
02/2005
Origin:
UCP
ApJ Keywords:
Accretion, Accretion Disks, Black Hole Physics, Stars: Individual: Constellation Name: Cygnus X-1, X-Rays: Binaries, X-Rays: Individual: Constellation Name: Cygnus X-1
DOI:
10.1086/426701
Bibliographic Code:
2005ApJ...620..398M

Abstract

We have analyzed a Chandra HETGS spectrum of the Galactic black hole Cygnus X-1, obtained at a source flux that is approximately twice that commonly observed in its persistent low-intensity, spectrally hard state. We find a myriad of absorption lines in the spectrum, including H- and He-like resonance lines from Ne, Na, Mg, and Si. We calculate a flux-weighted mean redshift of ~=100 km s-1 and a flux-weighted mean velocity width of ~=800 km s-1 (FWHM) for lines from these elements. We also detect a number of transitions from Fe XVIII-XXIV and Ni XIX-XX in absorption; however, the identification of these lines is less certain and a greater range of shifts and breadth is measured. Our observation occurred at a binary phase of φ~=0.76 the lines observed are consistent with absorption in an ionized region of the supergiant O9.7 Iab companion wind. The spectrum is extremely complicated: a rather large range of temperatures is implied, and it is unlikely that a narrow range of ionization parameters can account for the lines observed. Prior Chandra HETGS spectra of Cygnus X-1 were obtained in a similar transition state (at φ~=0.93) and in the low/hard state (at φ~=0.84). Considered together, these spectra provide evidence for a companion wind that is focused as it flows onto the black hole primary in this system.
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