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Possibility of Month-scale Quasi-periodic Oscillations in the Gamma-ray Light Curve of OP 313

Sandeep Kumar Mondal, Shubham Kishore, Alok C. Gupta, Gwenael Giacinti

TL;DR

This study investigates a potential month-scale quasi-periodic oscillation (QPO) in the gamma-ray light curve of OP 313 using ~16.8 years of Fermi-LAT data. The authors apply Bayesian blocks to identify four major flares and focus on Flare-D, where a periodic signal near $0.012 d^{-1}$ (∼$83$ days) is suggested. Using Weighted Wavelet Z-transform (WWZ), Generalised Lomb-Scargle (GLSP), and REDFIT analyses, they find a tentative QPO with limited cycle sampling and marginal significance, though harmonics and PSD curvature support the possibility. Among several physical scenarios, a curved-jet model provides the most plausible explanation for the modulation, outperforming straight-jet or hotspot/ISCO interpretations. The results motivate continued monitoring to robustly confirm the QPO and refine jet-geometry constraints.

Abstract

In this work, we report evidence suggesting the potential future detection of a month-scale quasi-periodic oscillation (QPO) in the gamma-ray light curve of OP 313. We analysed almost 16.8 years of Fermi-LAT gamma-ray data and applied the Bayesian block method to the monthly-binned light curve. We identified four high-flux states and investigated the possibility of a QPO in the fourth high-flux state (MJD 59482-60832). Using the Weighted Wavelet Z-transform (WWZ) and Lomb-Scargle Periodogram (LSP) methods, we find tentative evidence for a month-scale QPO; however, its detection significance is limited by the small number of observed cycles. With a sufficiently long data set, the QPO may be detected with higher significance in the future. We further explored possible physical origins of this potential QPO and examined several models. We found that a curved-jet model can explain the observed behaviour.

Possibility of Month-scale Quasi-periodic Oscillations in the Gamma-ray Light Curve of OP 313

TL;DR

This study investigates a potential month-scale quasi-periodic oscillation (QPO) in the gamma-ray light curve of OP 313 using ~16.8 years of Fermi-LAT data. The authors apply Bayesian blocks to identify four major flares and focus on Flare-D, where a periodic signal near (∼ days) is suggested. Using Weighted Wavelet Z-transform (WWZ), Generalised Lomb-Scargle (GLSP), and REDFIT analyses, they find a tentative QPO with limited cycle sampling and marginal significance, though harmonics and PSD curvature support the possibility. Among several physical scenarios, a curved-jet model provides the most plausible explanation for the modulation, outperforming straight-jet or hotspot/ISCO interpretations. The results motivate continued monitoring to robustly confirm the QPO and refine jet-geometry constraints.

Abstract

In this work, we report evidence suggesting the potential future detection of a month-scale quasi-periodic oscillation (QPO) in the gamma-ray light curve of OP 313. We analysed almost 16.8 years of Fermi-LAT gamma-ray data and applied the Bayesian block method to the monthly-binned light curve. We identified four high-flux states and investigated the possibility of a QPO in the fourth high-flux state (MJD 59482-60832). Using the Weighted Wavelet Z-transform (WWZ) and Lomb-Scargle Periodogram (LSP) methods, we find tentative evidence for a month-scale QPO; however, its detection significance is limited by the small number of observed cycles. With a sufficiently long data set, the QPO may be detected with higher significance in the future. We further explored possible physical origins of this potential QPO and examined several models. We found that a curved-jet model can explain the observed behaviour.
Paper Structure (8 sections, 8 equations, 5 figures, 2 tables)

This paper contains 8 sections, 8 equations, 5 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Fermi-LAT Data Acquisition
  3. Fermi-LAT Lightcurve
  4. Analysis and Results
  5. Weighted Wavelet Z (WWZ) analysis
  6. Generalised Lomb Scargle Periodogram (GLSP)
  7. REDFIT analysis
  8. Discussion

Figures (5)

  • Figure 1: In the upper plot, four activity states are identified using the Bayesian Block method on a 30-day binned 16.8 years long ( 4th August 2008- 6th June 2025) Fermi-LAT gamma-ray lightcurve of OP313. In the lower plot, the corresponding TS values of the data points have been shown.
  • Figure 2: Fermi-LAT gamma-ray lightcurve of Flare-D of OP 313 in 10-Day, 7-Day, 5-Day, and 1-Day binning.
  • Figure 3: WWZ map for the light curve portion 'D' (highlighted in Fig. \ref{['fig:BB_LC_30D']}) of OP 313
  • Figure 4: GLSP of the light curve segment MJD 59600 -- MJD 60500
  • Figure 5: REDFIT analysis of the light curve segment MJD 59600 -- MJD 60500