Hunt for the mHz variability in the TESS and XMM-Newton observations of nova-like cataclysmic variables

We analysed the flickering of selected nova-like cataclysmic variables observed by the TESS satellite and XMM-Newton. We searched for break frequencies ($f_{\mathrm{b}}$) in the corresponding power density spectra (PDS), and for any long-term evolution. We found a new optical $f_{\mathrm{b}}$ in three nova-like systems and confirmed that the value of this frequency is clustered around 1 mHz. V504 Cen and V751 Cyg show possible X-ray counterparts of $f_{\mathrm{b}}$ that had previously only been seen in MV Lyr. This points towards the very central disc for source localisation. We investigated a previously proposed correlation between white dwarf mass and $f_{\mathrm{b}}$, but thanks to the new measurements we do not conclude 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 disappearance of $f_{\mathrm{b}}$. TT Ari and SGRt 062340.2-265715 exhibit smooth changes in the long-term optical light curve, and the corresponding TESS observations show variable $f_{\mathrm{b}}$ during these changes. $f_{\mathrm{b}}$ is higher for lower brightness, which was seen only in MV Lyr so far.