A candidate ∼270-d γ-ray periodic modulation in the FSRQ 4FGL J0038.2−2459

Abstract Long-term variability and possible quasi-periodic oscillations (QPOs) in blazars provide a potential probe of the physical processes governing relativistic jets and their central engines. We investigated the γ-ray variability of 4FGL J0038.2−2459 using Fermi−LAT observations from 2008 August 5 to 2025 November 20. We applied the Lomb–Scargle periodogram, phase dispersion minimization, and weighted wavelet Z-transform to the 3-day binned light curve. The analyses identify a possible modulation with a characteristic period of 269.8 ± 5.8 days. The feature is associated with the MJD 57700–59800 active interval, which spans approximately eight cycles. Calibration of the LSP matched-profile statistic against 105 first-order autoregressive [AR(1)] red-noise simulations gives the possible oscillation a local significance of 3.43 σ within the selected active interval. We further explored a supermassive black hole binary (SMBHB)-driven jet-precession scenario as one possible interpretation. Under the adopted model assumptions, the observed modulation corresponds to an intrinsic jet-precession period of ∼9.9 yr and implies a binary orbital period of ∼96 days.