GLS periodograms of the GBI 8 GHz data. The horizontal lines indicate FAP levels of 10% (dotted), 1% (dashed), and 0.1% (solid). (a) Periodogram of the full light curve shown in Fig. 1. A peak at P_long is present along with a feature at P₁. (b) Zoom onto the region around the orbital period. A distinct two-peaked profile is present. The vertical dashed lines marks the position of the possible third period, P₃. The result of fitting the periodogram with Gaussian functions is shown as the red solid curve. We report the uncertainties of the resulting periods using the 1σ standard deviations of these Gaussians. (c) Periodogram of interval I (green area in Fig. 1). The peak at P_long is absent. (d) The zoom onto the orbital region reveals the presence of only one peak, at P_average. (e) Periodogram of interval II (yellow area in Fig. 1). (f) Zoom onto the orbital region. There is a two-peaked profile, with the periods being largely compatible with the literature values of P₁ and P₂.