Evidence of Periodic Variability in Gamma-ray Emitting Blazars with Fermi-LAT

It is well known that blazars can show variability on a wide range of time scales. This behavior can include periodicity in their $\gamma$-ray emission, whose clear detection remains an ongoing challenge, partly due to the inherent stochasticity of the processes involved and also the lack of adequately-well sampled light curves. We report on a systematic search for periodicity in a sample of 24 blazars, using twelve well-established methods applied to Fermi-LAT data. The sample comprises the most promising candidates selected from a previous study, extending the light curves from nine to twelve years and broadening the energy range analyzed from $>$1 GeV to $>$0.1 GeV. These improvements allow us to build a sample of blazars that display a period detected with global significance $\gtrsim3\,\sigma$. Specifically, these sources are PKS 0454$-$234, S5 0716+714, OJ 014, PG 1553+113, and PKS 2155$-$304. Periodic $\gamma$-ray emission may be an indication of modulation of the jet power, particle composition, or geometry but most likely originates in the accretion disk, possibly indicating the presence of a supermassive black hole binary system.
Comment: 26 pages, 8 figures, 7 tables