  We present the results of bicoherence analysis on observations of GRS
1915+105 that exhibit quasi-periodic oscillations (QPOs). The bicoherence is a
higher order statistic that can be used to probe the relation between the
phases of a triplet of Fourier frequencies. Despite showing very similar power
spectra, the observations exhibit different patterns in their bicoherence,
indicating that the QPOs are phase coupled to the noise in different ways. We
show that the bicoherence pattern exhibited correlates with the frequency of
the QPO, the hardness ratio, as well as the radio properties of the source. In
particular, we find that the nature of phase coupling between the QPO and the
high and low frequency broadband components is different between radio quiet,
radio plateau and radio steep conditions. We also investigate the phase lag
behaviour of observations with QPO frequency above 2Hz that show different
bicoherence patterns, and find statistically significant differences between
them, indicating a change in the underlying physical mechanism. Finally, we
present a scenario whereby the cooling of the jet electrons by soft photons
from the accretion disc could explain the observed correlations between the
bicoherence and radio properties.
