Understanding rapid X-ray variability from black hole binaries using the bispectrum

Quasi-periodic oscillations (QPOs) observed from X-ray binaries are a signature of rapid X-ray variability and a powerful diagnostic tool to study the regions closest to the central compact object. However, the physical origin of these QPOs is still under debate. One way to break degeneracies between the different models that have been proposed is to go beyond the simple power spectrum, and use higher order time series analysis techniques. One such technique is the bispectrum. I will summarize the results obtained from applying such analysis to X-ray binaries and how these can be used to probe the geometry of the region close to black holes.