Revisiting Quasi-Periodic modulation in $\gamma$-ray Blazar PKS 2155-304   with Fermi Pass 8 data
  We examine the gamma-ray quasi-periodic variability of PKS 2155-304 with the latest publicly available \emph{Fermi}-LAT Pass 8 data which covers the years from 2008 August to 2016 October. We produce the light curves in two ways, i.e., the exposure-weighted aperture photometry and the maximum likelihood optimization. The light curves are then analyzed by using Lomb-Scargle Periodogram (LSP) and Weighted Wavelet Z-transform (WWZ); and the results reveal a significant quasi-periodicity with a period of $1.74\pm0.13$ years and a significance of $\sim$ 4.9 $\sigma$. The constraint of multifrequencies quasi-periodic variabilities on blazar emission model is discussed. 
Pengfei Zhang, Dahai Yan, Nenghui Liao, Jiancheng Wang
astro-ph.HE