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We conduct a systematic search for quasars with periodic variations from thearchival photometric data of the Zwicky Transient Facility by cross-matchingwith the quasar catalogs of the Sloan Digital Sky Survey and V{\'e}ron-Cetty \&V{\'e}ron. We first select out 184 primitive periodic candidates using thegeneralized Lomb-Scargle periodogram and auto-correlation function and thenestimate their statistical significance of periodicity based on two red-noisemodels, i.e., damped random walk (DRW) and single power-law (SPL) models. Assuch, we finally identify 106 (DRW) and 86 (SPL) candidates with the mostsignificant periodic variations out of 143,700 quasars. We further compare DRWand SPL models using Bayes factors, which indicate a relative preference of theSPL model for our primitive sample. We thus adopt the candidates identifiedwith SPL as the final sample and summarize its basic properties. We extend thelight curves of the selected candidates by supplying other archival survey datato verify their periodicity. However, only three candidates (with 6-8 cycles ofperiods) meet the selection criteria. This result clearly implies that, insteadof being strictly periodic, the variability must be quasi-periodic or caused bystochastic red-noise. This exerts a challenge to the existing search approachesand calls for developing new effective methods.

Searching for quasar candidates with periodic variations from the Zwicky Transient Facility: results and implications