Co-evolution of the observed QPO frequency ν_QPO and the Kepler rotation frequency ν_K(r_J) for the 4 different outbursts, showing both hard-to-soft and soft-to-hard transitions (see red annotations). On the left Y-axis, the Kepler frequency at the transition radius, ν_K(r_J), and the 5% and 10% confidence intervals. On the right Y-axis, the observed QPO frequency, ν_QPO. Different markers are used to disentangle the different works: Motta et al. (2011) in upper-triangles, Nandi et al. (2012) in lower-triangles, Gao et al. (2014) in crosses, Zhang et al. (2017) in plus signs, and new detections in circle markers (see text). We also use different colors for the different types of QPOs (see legend).