  We report the discovery of the correlated optical/X-ray low-frequency
quasi-periodic oscillations (QPOs) in black hole binary SWIFT J1753.5-0127. The
phase lag between two light-curves at the QPO frequency is close to zero. This
result puts strong constraints on the nature of the optical emission in this
object and on the origin of the QPOs in general. We demonstrate that the QPO
signal and the broadband variability can be explained in terms of the hot
accretion flow radiating in both optical and X-ray bands. In this model, the
QPO appears due to the Lense-Thirring precession of entire flow, while the
broadband variability in the optical is produced by two components: the hot
flow and the irradiated disc. Using the phase-lag spectra, we put a lower limit
on the orbital inclination i>50 deg, which can be used to constrain the mass of
the compact object.
