Analysis of 4U 0115+53 performed on TESS (left) and at the SKO (right). Top panels: light curves where intra-night variability is clearly detected. Middle panels: periodograms. The dashed lines represent four times the average noise level of the final pre-whitening periodogram. The frequencies on both sides of f₁ on the right panel are aliases at f₁ ± 1 c d⁻¹ and disappear after pre-whitening with f₁. Bottom panels: phase diagrams folded with the 3.3 c d⁻¹ frequency.