A recent study utilizing NASA“s Fermi gamma-ray space telescope has led to the discovery of a quasi-periodic oscillation (QPO) in the gamma-ray emissions of a distant blazar designated 4FGL J0309.9-6058. This significant finding was published on October 24 in a paper available on the arXiv preprint server.
Blazars are compact quasars that are linked to supermassive black holes located at the centers of active, large elliptical galaxies. They are part of a broader category of active galaxies that contain active galactic nuclei (AGN) and are the most abundant sources of gamma rays beyond our galaxy. A defining characteristic of blazars is their relativistic jets, which are oriented nearly directly towards Earth.
The research team, led by Jingyu Wu from Shanghai Normal University, focused on 4FGL J0309.9-6058, also known as PKS 0308-611, which is classified as a flat-spectrum radio quasar (FSRQ) with a redshift of approximately 1.48. Previous studies indicated heightened gamma-ray activity from this blazar, prompting the astronomers to conduct further observations to gain deeper insights into its properties.
During their observational campaign, which spanned from Modified Julian Date (MJD) 57983 to 60503, the team noted potential periodic variability. They employed several analytical methods, including the Lomb-Scargle Periodogram, REDFIT, and the weighted wavelet Z-transform, to confirm the presence of a QPO signal.
The analysis revealed a QPO with an approximate period of 550 days in the gamma-ray band, specifically within the range of 0.1 to 300 GeV. The local significance of this QPO was determined to be 3.72σ, while the global significance reached 2.72σ. Additionally, a time lag of 228 days was observed between the optical and gamma-ray emissions, suggesting that these emissions originate from distinct regions within 4FGL J0309.9-6058.
To explain the origin of the observed QPO, the authors considered several hypotheses, including the possibility of a binary supermassive black hole system and the precession of the jet. They concluded that the jet precession model is the most viable explanation. The researchers noted, “The precessing jet generates QPO signals in both the optical and gamma-ray bands, and the observed time lag between these bands reveals the distance between the optical and gamma-ray emission regions.”
This research enhances the understanding of blazar emissions and their underlying mechanisms, providing valuable insights into the nature of these extraordinary cosmic phenomena.
