Comparisons of 2006 and 2021 light curves with the respective hardness-ratio light curves (see respective horizontal axes labels). In the third panel (2006d39.7), the observed hardness ratio light curve is shown with a dotted line while the solid line represents the hardness ratio light curve shifted by −1000 s (see Ness et al. 2007; Schönrich & Ness 2008; Ness 2015). No such lag is seen on days 2006d54 and 2021d55.6, although a small lag might be present. On days 2006d26.1 and 2021d37.1 (top two panels), hardness and brightness are anti-correlated, reflecting the appearance and disappearance of the complex soft emission component, while much less variability is seen during the decline observed on day 2006d66.9 (bottom panel).