Long-term spectral and flux variation of the X-ray source. Left panel: blackbody temperature and emission radius as a function of MJD (“variable” model 4; see Tables 4–5). Right panel: long-term evolution of the 0.2 − 2 keV X-ray flux of the target, including upper limits and previous detection by other X-ray missions. The time interval extends back to the ROSAT All-Sky Survey (RASS) and pointed (PSPC) era and include data points from Swift XRT and XMM-Newton slew observations (see the text, for details). In all plots the purple horizontal shaded areas show the 1σ median absolute deviation of the parameters.