Singular Spectrum Analysis of Fermi-LAT Blazar Light Curves: A Systematic Search for Periodicity and Trends in the Time Domain

TL;DR

This study applies Singular Spectrum Analysis to Fermi-LAT blazar light curves to systematically identify potential quasi-periodic gamma-ray emissions, revealing 46 candidates and doubling known periodic sources, thus advancing understanding of blazar variability.

Contribution

First application of SSA to Fermi-LAT blazar data, systematically isolating periodic signals and identifying new gamma-ray periodic candidates.

Findings

Identified 46 blazars with potential quasi-periodic gamma-ray emission.

Detected 33 sources with high significance (≥4σ local, ≥2.2σ global).

Doubled the number of known periodic gamma-ray blazar candidates.

Abstract

A majority of blazars exhibit variable emission across the entire electromagnetic spectrum, observed over various time scales. In particular, discernible periodic patterns are detected in the $\gamma$-ray light curves of a few blazars, such as PG 1553+113, S5 1044+71, and PKS 0426-380. The presence of trends, flares, and noise complicates periodicity detection, requiring careful analysis to determine whether these patterns arise from emission mechanisms or occur by chance. We employ Singular Spectrum Analysis (SSA) for the first time on data from the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope to systematically search for periodicity using 28-day binned light curves. We aim to isolate any potential periodic nature of the emission from trends and noise, reducing uncertainties in revealing periodicity. Additionally, we characterize long-term trends and develop a forecasting algorithm based on SSA to predict future emission behavior. We apply SSA to analyze 494 sources detected by Fermi-LAT, focusing on isolating oscillatory components from trends and noise in their $\gamma$-ray light curves. We compute the Lomb-Scargle Periodogram for oscillatory components extracted by SSA to determine the most significant periods, assessing their local and global significance. Our analysis identifies 46 blazars as potential candidates for quasi-periodic $\gamma$-ray emissions, each with a local significance $\geq 2\sigma$. Notably, 33 exhibit a local significance of $\geq 4\sigma$ (corresponding to a global significance of $\geq 2.2\sigma$). Our findings introduce 25 new $\gamma$-ray candidates, doubling the number of potentially periodic sources. This study provides a foundation for future investigations by identifying promising candidates and their significance in blazar variability.