Overview of the Chandra data from HESS J1731−347 in the 0.5–7 keV band throughout the mission’s lifetime (left). The red contours show regions that were found to exhibit significant variability (3σ confidence level) between the 2008 and 2021 observations. The yellow sectors (R1–R5) depict regions that were used to obtain the surface brightness radial profiles used to measure the expansion rate of shell parts. The inset on the right shows a close-up view of a bright knot and two narrow filaments (F1–F2) that exhibit a significant flux variability between the 2008 and 2021 observations, as discussed in the text. All images are adaptively smoothed to contain at least 30 counts per pixel to improve visual appearance and are plotted using a linear scale between 0 and 10⁻⁸ counts cm⁻² s⁻¹.