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C. Chang, W. Cui (Purdue University)
Cygnus X-1 has been observed in different spectral states with the Chandra High Energy Transmission Grating Spectrometer(HETGS). Numerous absorption lines have been observed in the HETGS spectrum. The lines are associated with highly ionized material, including H-like, He-like and Li-like resonance lines from S, Si, Mg, Ne and Fe; and several lower ionization lines of Fe XIX, XX, XXII, XXIII, and XXIV. Here, we report the detection of dramatic variability in the absorption lines. Cyg X-1 was fainter during the first half of a 30ks observation. Interestingly, however, the lines are much stronger during the first half of the observation. For example, the flux of Ne X is 5± 1\times 10-3 (photons/cm2 /s/Å) in the first half of the observation. The line is not detected in the second half. The 3\sigma upper limit of the line flux is 0.06\times 10-3 (photons/cm2 /s/Å), implying that it varied by at least a factor of ~ 100 during the observation. The abosrption lines are generally attributed to the absorption by stellar wind in the binary system. Therefore, they may provide useful diagnostics about the physical conditions of the wind. The observed variation of the lines may be due to changes in the conditions of wind from companion star, such as density and ionization state. We will discuss these possibilities.
This work was supported in part by SAO/NASA Grant DD1-2011X and NASA Grant NNG05GF91G.
Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.