Dramatic Variability of X-ray Absorption Lines in the Black Hole Candidate Cygnus X-1

Abstract

We report results from a 30 ks observation of Cygnus X-1 with the High Energy Transmission Grating Spectrometer (HETGS) on board the {\em Chandra X-ray Observatory}. Numerous absorption lines were detected in the HETGS spectrum. The lines are associated with highly ionized Ne, Na, Mg, Al, Si, S, and Fe, some of which have been seen in earlier HETGS observations. Surprisingly, however, we discovered dramatic variability of the lines over the duration of the present observation. For instance, the flux of the Ne X line at 12.14 Å was about $5\times 10^{-3}$ photons cm${}^{-2}$ s${}^{-1}$ in the early part of the observation but became subsequently undetectable, with a 99% upper limit of $0.06\times 10^{-3}$ photons cm${}^{-2}$ s${}^{-1}$ on the flux of the line. This implies that the line weakened by nearly two orders of magnitude on a timescale of hours. The overall X-ray flux of the source did also vary during the observation but only by 20--30%. For Cyg X-1, the absorption lines are generally attributed to the absorption of X-rays by ionized stellar wind in the binary system. Therefore, they may provide valuable diagnostics on the physical condition of the wind. We discuss the implications of the results.

19 pages, 7 figures, 1 table, accepted by ApJ

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Cited by in corpus (4)

• Chandra X-ray spectroscopy of the focused wind in the Cygnus X-1 system. I. The non-dip spectrum in the low/hard state
• Laboratory Measurements of the K-shell transition energies in L-shell ions of Si and S
• Highly Ionized Fe-K Absorption Line from Cygnus X-1 in the High/Soft State Observed with Suzaku
• XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures