Constraints on NEI in the hot plasma component. The top panel shows the joint 1 σ-contours of the density n_e and ionization timescale τ_NEI inferred for the hot plasma component in each region. The dashed gray lines correspond to constant shock age t_s, and are logarithmically spaced between 10⁵ and 10⁸ yr. In the bottom panel, the constraints are converted into probability distributions of t_s. The thick black line indicates the combined distribution of all regions. In both panels, the line colors indicate the electron temperature kT_NEI fit for the respective region.