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

TL;DR

This study reports the detection of transient quasi-periodic oscillations in the gamma-ray light curves of two blazars, using Bayesian analysis to identify flux states and analyze periodic behaviors over various timescales.

Contribution

It introduces a method combining Bayesian Blocks and variance analysis to identify transient QPOs in blazar gamma-ray light curves, revealing new periodic behaviors.

Findings

Detected a 225-day QPO in PKS 0244-470 with 4.1σ significance.

Identified 110-day and 60-day QPO-like behaviors in 4C+38.41.

Observed multiple shorter-term QPOs with cycles of 104 days and ~1 week.

Abstract

The continuous monitoring capability of Fermi-LAT has enabled the exploration of Quasi-Periodic Oscillations (QPOs) in the $\gamma$-ray light curve of blazar that has given a new perspective to probe these sources over a wide range of time scales. We report the presence of transient QPOs in the long-term $\gamma$-ray light curve of blazars PKS 0244-470 and 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 the source's 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, AP-4) and two quiescent (QP-1, QP-2) phases. AP-1 phase of PKS 0244-470 shows QPO of $\sim$225 days persisting for 8 cycles ($\sim$ 4.1$\sigma$). In 4C+38.41, AP-1 and AP-2 phases show QPO-like behavior of $\sim$110 days and $\sim$ 60 days, respectively, persisting for 5 cycles. In AP-3, we identified three sub-phases, and all show a $\sim$ week scale possible recurrent rise with five complete cycles, while in QP-1, we could identify 2 sub-phases (Q1, and Q2). Q1 phase shows a period of $\sim$ 104 days with six complete cycles. Q2 phase also shows QPO but with only $\sim$3.7 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.