Quasi-periodic oscillation detected in γ-rays in blazar PKS 0346−27

Abstract

Aims. We present a variability study of the blazar PKS 0346−27 conducted between December 2018 and January 2022 using archival γ-ray observations from Fermi-LAT. Methods. We used Lomb–Scargle periodogram and weighted wavelet transform methods to detect the presence of periodicity or quasi-periodicity and localize this feature in time and frequency space. We estimated the significance of the periodicity feature using a Monte Carlo simulation approach. We also determined the global significance of the periodicity to test the robustness of our claim. To explore the most probable scenario, we modeled the light curve with both a straight-jet and a curved-jet model. Results. We detect a periodicity feature of ∼100 days in the entire period of observation with a statistical significance of 3σ, which amounts to a 99.7% confidence level. The global significance of this feature is found to be 96.96%. Based on the Akaike information criterion, the most probable explanation is that the observed emission is enhanced due to the helical motion of a blob within a curved jet. Conclusions. The origin of this quasi-periodic oscillation is very likely a region of enhanced emission moving helically inside a curved jet. This work presents strong evidence for jet curvature in the source and an independent (albeit a little serendipitous) procedure to estimate the curvature in blazar jets.