Examples of variable Fe K line profile on long and short timescales, as observed with the same instrument. Left panel: Fe K band spectra of PID 203 observed with XMM-Newton in a) 2001−2002 (X1 and X2); and b) 2008−2010 (X3-X6) periods separated by 6 yr. As shown in Fig. 8, the line of a) is unresolved (σ< 0.12 keV) while moderate but significant broadening (σ = 0.18 ± 0.04 keV) is observed in b). Right panel: Chandra data of PID 319 during the first c) and second d) halves of the C4 interval with a 1 Ms exposure each. The C4 interval spans over five months (see Table 3), within which the line shape appears to change over a few months: the line centroid shifted from 6.56 ± 0.05 keV to 6.21 ± 0.17 keV and the line profile broadened from σ< 0.14 keV to keV, while both continuum and line fluxes remain nearly identical with f₂₋₇ = 5.1 × 10^-14/ 5.0 × 10^-14 erg s^-1 cm^-2, and I_Fe = (3.2 ± 1.0) × 10^-7/ (3.7 ± 1.5) × 10^-7 ph cm^-2 s^-1, respectively.