2014ApJ...793L...1S

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 Zhang et al. 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 10⁹ M_☉, the Keplerian distance corresponding to the quasi-period T is ∼10¹⁶ cm, about 50 Schwarzschild radii.