Quasi-periodicities of PKS 2155-304

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We have searched for periodicities in our VRIJHK photometry of PKS 2155-304, which covers the years 2005-2012. A peak of the Fourier spectrum with high significance is found at T 315 days, confirming the recent findings by Zhang2014. The examination of the gamma-ray light curves from the Fermi archives yields a significant signal at 2T, which, while nominally significant, involves data spanning only 6T. Assuming a black hole mass of 10⁹M the Keplerian distance corresponding to the quasi-period T is 10¹⁶ cm, about 50 Schwarzschild radii.