2002/08/26 by J. M. Mïller, J. M. Miller, P. Wojdowski +10 · 1 citation
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Chemistry #Experimental and Theoretical Physics Studies #Flux (metallurgy) #Galaxy #Ion #Ionization #Optics #Physics #Redshift #Spectral line #Stars #Supergiant #astro-ph
paper · pdf · doi:10.1086/426701
published as Astrophys.J. 620 (2005) 398-404 · 10 pages, 7 color figures, uses emulateapj.sty and apjfonts.sty. Submitted to ApJ
arxiv created 2002/08/26 · openalex publication_date 2005/02/09 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
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.