Color-color diagrams as tools for assessment of the variable absorption in high mass X-ray binaries

Abstract

High mass X-ray binaries hold the promise of giving us understanding of the structure of the winds of their supermassive companion stars by using the emission from the compact object as a backlight to evaluate the variable absorption in the structured stellar wind. The wind along the line of sight can change on timescales as short as minutes and below. However, such short timescales are not available to direct measurement of absorption through X-ray spectroscopy with the current generation of X-ray telescopes. In this paper, we demonstrate the usability of color-color diagrams for assessing the variable absorption in wind accreting high mass X-ray binary systems. We employ partial covering models to describe the spectral shape of high mass X-ray binaries and assess the implication of different absorbers and their variability on the shape of color-color tracks. We show that taking into account the ionization of the absorber, and in particular accounting for the variation of ionization with absorption depth, is crucial to describe the observed behavior well.

8 pages, 8 figures, submitted to A&A, comments welcome

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Cited by in corpus (6)

• Revisiting the archetypical wind accretor Vela X-1 in depth -- A case study of a well-known X-ray binary and the limits of our knowledge
• Long term variability of Cygnus X-1. VIII. A spectral-timing look at low energies with NICER
• Observing the onset of the accretion wake in Vela X-1
• The X-ray spectral-timing contribution of the stellar wind in the hard state of Cyg X-1
• Stellar wind variability in Cygnus X-1 from high-resolution excess variance spectroscopy with Chandra
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415