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Fig. 4


Chandra-HETGSs spectra of Vela X-1 from ObsID 1928 from low-(blue) and high-(black)hardness periods. The best fitting absorbed power-law model with the same photon index, but varying normalization and absorption between the high- and low-hardness spectra, is shown in red in the modeled range. Shaded areas indicate the four regions used in the local power-law fits in Sect. 3.

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