Top panel: light curves of Cyg OB2 #5 and evolution of HR for XMM-Newton (left, pn in green, MOS1 in black, and MOS2 in red) and Swift data (right). Bottom panel: light curves folded with the two orbital periods of Cyg OB2 #5. XMM-Newton-pn data were divided by 10 and are shown as red stars, while Swift data are shown as black dots. On the left, quadratic ephemeris from Eq. (2) were used to derive the phase, while the ephemeris of the long orbit from Sect. 4.3 were used for the right panel.