Light curve of PKS J0805−0111. Credit: De La Parra et al., 2024.
An international team of astronomers has reported the detection of a blazar with highly significant sinusoidal radio variability using the Owens Valley Radio Observatory (OVRO). The discovery was detailed in a research paper published August 5 in the arXiv pre-print deposit.
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 (AGNs) and are the most numerous sources of extragalactic gamma-rays. Their characteristic features are relativistic jets pointed almost exactly toward Earth.
Based on their optical emission properties, astronomers divide blazars into two classes: flat-spectrum radio quasars (FSRQs), which exhibit prominent, broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.
PKS J0805−0111 was first identified in 2007 as a FSRQ with a redshift of 1.39. Further observations of this blazar suggested that it might contain a supermassive black hole binary (SMBHB).
A group of astronomers, led by Philipe Vergara De La Parra of the University of Concepción in Chile, used OVRO to study the properties of PKS J0805-0111. They discovered that the blazar exhibits a peculiar behavior.
According to the paper, the 15 GHz light curve of PKS J0805−0111 exhibits a clear sinusoidal variation that dominates the variability for a significant fraction of the observation period. This variation has a period of about 1.42 years, which has been shown to be stable in long-term observational data.
The researchers explained that the observed periodicity can be attributed to the red noise tail of the power spectral density (PSD). They added that the detected sinusoidal radio variation of PKS J0805−0111 adds to the regular variations of the blazar.
Moreover, the astronomers found that the sinusoidal fluctuations disappeared in less than one period and also reappeared in less than one period and with different amplitudes. Therefore, they predict that the sinusoidal variations will reappear in PKS J0805−0111 after an interval of a few years, with the same period and in phase with the sinusoidal variations reported in the study.
Summarizing the results, the authors of the paper pointed out that the properties of the detected sinusoidal variations indicate that this could be a SMBHB blazar. If so, it would be the second SMBHB blazar to exhibit sinusoidal variations in its radio light curve, after PKS 2131-021. However, further observations of PKS J0805-0111 are needed to confirm this hypothesis.
“The discovery of a second SMBHB candidate with these rare features reveals that PKS 2131-021 is not a unique and isolated case,” the scientists concluded.
More information:
PV de la Parra et al, PKS~J0805−0111: A Second Owens Valley Blazar Radio Observatory Showing Very Significant Sinusoidal Radio Variability—The Tip of the Iceberg, arXiv (2024). DOI: 10.48550/arxiv.2408.02645
Journal information:
arXiv
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