Quasi-periodic oscillation detected in distant blazar's gamma-ray band
Tomasz Nowakowski
astronomy writer
Sadie Harley
scientific editor
Robert Egan
associate editor
Using NASA's Fermi gamma-ray space telescope, astronomers from Shanghai Normal University in China and elsewhere have investigated a distant blazar known as 4FGL J0309.9-6058. As a result, they identified quasi-periodic oscillation in the gamma-ray band of this object. The finding was detailed in a published Oct. 24 on the arXiv pre-print server .
Blazars are very compact quasars associated with supermassive black holes (SMBHs) at the centers of active, giant elliptical galaxies. They belong to a larger group of active galaxies that host active galactic nuclei (AGN), and are the most numerous extragalactic gamma-ray sources. Their characteristic features are relativistic jets pointed almost exactly toward Earth.
Based on their optical emission properties, blazars can be divided into two classes: flat-spectrum radio quasars (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.
4FGL J0309.9-6058, also known as PKS 0308-611, is an FSRQ at a redshift of approximately 1.48. Previous observation of this blazar has found that it exhibits enhanced gamma-ray activity.
Recently, a team of astronomers led by Shanghai Normal University's Jingyu Wu observed 4FGL J0309.9-6058 with Fermi, hoping to get more insights into its properties. This resulted in the identification of a QPO signal.
"With visual inspection, we found a possible periodic variability during the campaign of MJD 57983鈭�60503. In order to identify the existence of a QPO signal and to quantify the period, we employed the Lomb-Scargle Periodogram (LSP), REDFIT, and weighted wavelet Z-transform (WWZ)," the scientists wrote in the study.
According to the paper, the observations revealed the presence of a QPO with a period of approximately 550 days in the gamma-ray band (0.1鈥�300 GeV) of the blazar. The identified QPO has a maximum local significance of 3.72饾湈 and global significance of 2.72饾湈.
Furthermore, the study detected a time lag of 228 days between the optical and gamma-ray bands. This finding points to the separated emission regions in 4FGL J0309.9-6058 for optical and gamma-ray emissions.
Trying to explain the origin of the observed QPO in 4FGL J0309.9-6058, the authors of the paper consider a few hypotheses, including a binary supermassive black hole and jet precession. However, due to the timescale of the QPO and the detected time lag, they found the jet precession scenario as the most plausible.
"The jet precession model emerges as the most promising explanation. 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," the researchers explain.
Written for you by our author , edited by , and fact-checked and reviewed by 鈥攖his article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a (especially monthly). You'll get an ad-free account as a thank-you.
More information: Jingyu Wu et al, Detection of Quasi-periodic Oscillations in the 纬-Ray Light Curve of 4FGL J0309.9-6058, arXiv (2025).
Journal information: arXiv
漏 2025 Science X Network
