Hunt for the mHz Variability in TESS and XMM-Newton Observations of Nova-like Cataclysmic Variables

Abstract We analysed the flickering of selected nova-like cataclysmic variables observed by the TESS satellite and XMM-Newton. We searched for break frequencies ( f b ) in the corresponding power density spectra (PDSs), and for any long-term evolution. We find a new optical f b in three nova-like systems, and confirm that the value of this frequency is clustered around 1 mHz. V504 Cen and V751 Cyg show possible X-ray counterparts of f b that had previously only been seen in MV Lyr. This points toward the very central disk for source localization. We investigated a previously proposed correlation between white dwarf mass and f b , but thanks to the new measurements, we do not confirm its existence. V3885 Sgr and V1193 Ori show flaring activity in the long-term light curve during which TESS observations were made. The corresponding PDSs show changes in shape and the disappearance of f b . TT Ari and SGRt 062340.2−265715 exhibit smooth changes in the long-term optical light curve, and the corresponding TESS observations show variable f b during these changes. f b is higher at lower brightness levels, which so far has been observed only in MV Lyr.