LAUSR

A systematic search for cyclical sources of gamma-ray emission on the period range from days to years in the Fermi-LAT sky is performed. Looking for cyclical emission, the sky is binned into equal-area pixels and the generalised Lomb-Scargle periodogram is computed for each of these pixels. The search on the period range between 2.5 and 30 days in the Galactic plane confirms periodicities of three binaries, LSI +61 303, LS 5039, and 1FGL J1018.6-5856. The all-sky search on the period range between 30 days and 2.5 years confirms periodicities of three blazars, PG 1553+113, PKS 2155-304, and BL Lacertae. Evidence for periodic behaviours of four blazars, 4C +01.28, S5 0716+71, PKS 0805-07, and PKS 2052-47, are presented. Three of these blazars, 4C +01.28, PKS 0805-07, and PKS 2052-47, are located at high redshifts. These three sources are potential candidates to binary systems of supermassive black holes provided that major galaxy mergers are more frequent and that galaxies are more gas-rich at high redshifts.