Periodograms of 8.3 GHz (filled squares) and 2.2 GHz (circles) data. a) Output of Lomb-Scargle method. The Lomb-Scargle analysis gives on the y-axis the significance of the frequency. Two frequencies are found at ν₁ = 0.03775 d^-1 (P₁ = 26.49 d) and at ν₂ = 0.03715 d^-1 (P₂ = 26.92 d). b) Output of Lomb-Scargle method for data ≥4σ. c) Output of PDM. The most likely period yields the minimum dispersion and appears as a minimum in the PDM curve, i.e., specular to the maximum in the Lomb-Scargle plot. d) Output of PDM for data ≥4σ.