Multi-wavelength time series of J1109 presented in this work. Top: NTT/ULTRACAM (2019 April 12-13). Middle: NTT/ULTRACAM (2019 April 14). Bottom: XMM-Newton/EPIC (pn+MOSs) and NTT/ULTRACAM (2022 March 3). The grey dashed line represents the XMM-Newton/EPIC background level, whereas the orange shaded areas mark the four longest episodes of low mode, which were used to compute the low-mode ingress and egress timescales in X-rays (see text for details). Different vertical scales have been used for the optical time series in the different panels.