We model these features with Gaussians of the form: $$P(\nu_{i}) = A\cdot \rm\,exp\it\left[(\nu_{i} - B)^{2}/C^{2}\right]$$ where $\nu_{i}$ are the Fourier frequencies, A is a normalization factor, B is the centroid frequency ($\nu_{0}$ or $2\nu_{0}$) and C is related to the FWHM through:$\rm\,FWHM=2C\cdot\,\left[ln(2)\right]^{1/2}$. The typical value for the FWHM of the two Gaussians is $\sim1$Hz for all the three outbursts. The Gaussian that we use to fit the 1 Hz modulation usually has a quality factor $Q=\nu_{0}/\rm\,FWHM < 2$. When $Q<1$ the power spectrum does not show a clear peak, but sometimes it does show a break in the noise (see for example the bottom panel in Fig. \[QPO\]). Here we call the 1 Hz modulation “QPO” regardless of its quality factor. When $Q<1$ we did not try to fit the power spectra with gaussians because the centroid frequency is ill defined. When the 1 Hz QPO is fitted by 2 Gaussians $\nu_{0}$ is defined as being the frequency of the Gaussian with the highest peak power in the power spectrum. With this choice $\nu_{0}$ is consistent with being always the fundamental frequency of the 1 Hz modulation (varying between 0.8 and 1.6 Hz), as the harmonic peak at $2\nu_{0}$ is 