The detection of possible transient Quasi-Periodic Oscillations in the $γ$-ray light curve of PKS 0244-470 and 4C+38.41

Abstract

The continuous monitoring capability of Fermi-LAT has enabled the exploration of Quasi-Periodic Oscillations (QPOs) in the γ-ray light curve of blazar that has given a new perspective to probe these source and jet physics over a wide range of time scales. We report the presence of transient QPOs in the long-term γ-ray light curve of blazars PKS 0244-470 & 4C +38.41. We first identified different flux states using the Bayesian Block algorithm and then explored the possible transient QPOs in the segments of each flux phase where the flux level changes over fairly regular intervals. Combining this with source intrinsic variance, we identified two flux phases for PKS 0244-470: one activity (AP-1) and one quiescent phase (QP-1). For 4C+38.41, we similarly identified four activity (AP-1, AP-2, AP-3, and AP-4) and two quiescent (QP-1 and QP-2) phases. AP-1 phase of PKS 0244-470 shows QPO of ∼ 225 days persisting for 8 cycles (∼ 4.1 σ). In 4C+38.41, AP-1 and AP-2 phases show QPO of ∼ 110 days and ∼ 60 days, respectively, persisting for 5 cycles. In AP-3, we identified three sub-phases, and all show a ∼ week scale recurrent rise with five complete cycles, while in QP-1, we could identify 2 sub-phases (Q1 and Q2). Q1 phase shows a significant period of ∼ 104 days with six complete cycles. Q2 phase also shows significant QPO but with only ∼ 3.7 cycles. All the detections are locally significant with at least four or more cycles. We discuss the possible origin and argue that the current driven kink instability and curved jet model seem the most likely cause for shorter and longer QPOs though the latter requires continuous acceleration or injection of particles to explain these.