Variation of 2−10 keV observed-band total source flux (top panel), 2−10 keV observed-band flux of the reflection component alone (middle panel) and reflection fraction R (bottom panel), of Chandra (magenta circles), XMM-Newton (light, dark and medium green pentagons for EPIC pn, EPIC MOS, and EPIC pn+MOS, respectively) and NuSTAR (ivory, brown, orange triangles for FPMA, FPMB, and FPMA+FPMB, respectively) data from year 2000 to 2019. Top axis shows the dates, bottom axis the modified Julian dates. Top panel: values up to 2009 are taken from C09, the first two points are evaluated from re-analyzed data. Errors are given at 68% confidence, as in C09. When they are not visible, errorbars are smaller than the point size. Middle panel: upper limits are computed using the 90% upper limit of the reflection fraction. Bottom panel: upper limits are computed at 90% confidence level. The first Chandra observation (i.e., the shortest one – see main text) is left out due to the low count statistics.