Abstract

The low frequency Quasi Periodic Oscillation has been known in black hole binaries and neutron stars for over 20 years but there is still no consensus in the literature as to its physical origin. I show how this can be naturally interpreted in the context of the truncated disc/hot inner flow models designed to explain the spectral evolution. Lense-Thirring (vertical) precession of the hot inner flow can explain the QPO frequencies and their observed correlation with spectral softness. It also explains the why the QPO spectrum is hard as the modulation is of the Comptonised emission from the hot flow rather than the thin disc. I then show how this model can be tested in atoll sources and extended to produce the broad band continuum noise from MRI fluctuations in the hot flow. This gives the first complete model for the power spectral components seen in black hole binaries and neutron stars.