Observers detect intraday variability of blazar 1ES 1426+42.8

Astronomers report the detection of optical intraday variability of a blazar known as 1ES 1426+42.8. The new findings, presented in a paper published in the September issue of Monthly Notices of the Royal Astronomical Society, could shed more light on the properties and nature of this blazar.

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 the Earth.

Based on their optical emission properties, astronomers divide blazars 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.

1ES 1426+42.8 is a BL Lac at a redshift of 0.129, discovered in 1984. It is an extreme TeV source with low power and a high synchrotron peak—above 100 keV. Given that previous observations of 1ES 1426+42.8 focused on its high-energy bands, the optical properties of this blazar remain poorly investigated.

That is why a team of astronomers led by Xin Chang of the Yunnan University in China decided to explore 1ES 1426+42.8 in the optical bands using the 1.02 m optical telescope of Yunnan Observations. They observed the blazar for 16 nights between 2021 and 2023.

The observations conducted by Chang’s team detected intraday variability (IDV) of 1ES 1426+42.8 on seven days. The identified IDVs are intermittent, and no correlation was found between brightness level and the presence or absence of these IDVs.

The astronomers explained that the observed IDV of 1ES 1426+42.8 can be interpreted as a result of a convolution of individual synchrotron pulses occurring in the blazar’s turbulent jet. In the case of 1ES 1426+42.8, the analysis conducted by the authors of the paper yields 80 pulses. The size distributions of the radiation turbulent cells, calculated from the fitting results, appear to range from 2.58 to 54.52 AU.

In general, the obtained results for 1ES 1426+42.8 suggest that turbulence exists in most regions of the jet. The distribution of cell sizes was found to be continuous.

The study also detected a possible short-lived quasi-periodic oscillation (QPO) in the light curve of 1ES 1426+42.8. The QPO was identified on April 26, 2022, and had a period of approximately 58.55 minutes. The so-called QPOs are believed to 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.

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