Quiescent luminosity long-term evolution. Shown is the L_bol evolution of the quiescent emission over the past ∼12 yr. The dotted-solid line is a possible model discussed in Miniutti et al. (2023). The grey data points refer to observations that are too short to ensure the detection of QPEs (squares for Swift and circles for XMM-Newton data). Coloured and black data points represent instead long enough observations respectively with and without QPEs. The purple star denotes the XMM6 observation with irregular QPEs. A Chandra observation (exhibiting three QPEs) performed between the XMM4 and XMM5 observations was omitted as the corresponding quiescent luminosity is highly uncertain (see Table D.1).