By analyzing the data from the Whole Earth Blazar Telescope (WEBT), an international team of astronomers has discovered optical quasi-periodic oscillation (QPO) in a bright quasar known as 3C 454.3. It is so far one of the most persistent QPOs detected in the optical band. The finding was reported in a paper published April 30 on the arXiv pre-print server.
Oscillating blazars
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.
Observations show that some blazars may exhibit periodic-like fluctuations in the optical light curves known as optical QPOs. Given that QPOs were historically discovered and extensively studied in the X-ray band, it is believed that they occur when X-rays are emitted near the inner edge of an accretion disk in which gas swirls onto a compact object like a neutron star or a black hole.
In the case of optical QPOs, they are assumed to come from the outer accretion disk, or they can be “reprocessed” X-ray light.
Bright and well known
At a redshift of 0.86, 3C 454.3 is one of the brightest and best-studied FSRQs. It has strong optical polarization, substantial variability throughout the electromagnetic spectrum, and non-thermal emission. The mass of its SMBH is estimated to be 0.5–2.3 billion solar masses.
Given that previous studies of 3C 454.3 have suggested the presence of QPO in this blazar, a group of astronomers led by Karan Dogra of the Aryabhatta Research Institute of Observational Sciences (ARIES) in India decided to comb through the data from the WEBT archive spanning 19 years of observations.
Their study was complemented by data from the Small and Medium Aperture Research Telescope System (SMARTS) and the Steward Observatory.
QPO found in 3C 454.3 but what produces it?
The research conducted by Dogra’s team resulted in the detection of an optical QPO in 3C 454.3 with a period of 433 days, which is consistently present from 2009 to 2018. Therefore, it makes it one of the most persistent QPOs ever identified in the optical regime.
Trying to explain the origin of the detected QPO in 3C 454.3, the researchers employed models focused on the accretion disk around the SMBH, and those based purely on jet emissions. Although they see models relying on processes within relativistic jets as more plausible to explain the observed QPO signatures in this blazar, they noted that currently available data do not permit definite distinction among the two scenarios.
“However, future long-term monitoring may help establish the physical origin of the apparent QPO and determine whether it reflects a persistent dynamical mechanism or a transient manifestation of stochastic variability,” the scientists conclude.
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Publication details
Karan Dogra et al, Detection of optical quasi-periodic oscillation in the blazar 3C 454.3, arXiv (2026). DOI: 10.48550/arxiv.2604.27503
Journal information:
arXiv
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Bright blazar reveals 433-day optical quasi-periodic oscillation across nine years (2026, May 12)
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