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Astronomers investigate multiwavelength emission from the blazar PKS 0537-286

Armenian astronomers investigate multiwavelength emission from the blazar PKS 0537-286
Multiwavelength light curve of PKS 0537-286. Credit: Sahakyan et al, 2023

Using three space telescopes, Armenian astronomers have observed a flaring high-redshift blazar known as PKS 0537-286. Results of the observational campaign, presented February 15 on the pre-print server arXiv, deliver important insights into the properties and origin of the multiwavelength emission from this source.

Blazars, classified as members of a larger group of active galaxies that host (AGN), are the most numerous extragalactic 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: (FSRQs) that feature prominent and broad optical emission lines, and BL Lacertae objects (BL Lacs), which do not.

At a redshift of 3.1 and with an estimated luminosity at a level of one quattuordecillion erg/s (in the 0.1–2.0 keV range), PKS 0537-286 is one of the brightest high-redshift blazars, classified as an FSRQ. The source exhibits gamma-ray flares, which makes it the most distant gamma-ray flaring blazar so far detected.

A team of astronomers led by Narek Sahakyan of the International Center for Relativistic Astrophysics Network (ICRANet) conducted optical/ultraviolet, X-ray and gamma-ray observations of PKS 0537-286 in order to shed more light on the emission from this blazar. For this purpose they used NASA's Fermi, NuSTAR and Swift space telescopes.

"We present a multi-frequency spectral and temporal study of high redshift blazar PKS 0537-286 by analyzing data from Fermi-LAT, NuSTAR Swift XRT and UVOT," the researchers wrote in their paper.

The team analyzed the data collected during a timespan of 14 years (between 2008 and 2022). It was found that the gamma-ray emission from PKS 0537-286 appeared to be relatively constant until 2017, when multiple powerful gamma-ray flares were identified. Afterward, the blazar was in an enhanced gamma-ray emission state when the gamma-ray luminosity reached 61.4 quindecillion erg/s. During the whole observational campaign, the gamma-ray luminosity of the source exceeded one quindecillion erg/s for nearly 62 days in total.

Furthermore, the study found that the gamma-ray photon index of PKS 0537-286 also showcases variability over the observed period. The mean value of the gamma-ray photon index during non-flaring periods was measured to be approximately 2.83, which substantially hardens during the flares. It appears to be a moderate anti-correlation between the gamma-ray photon index and blazar's luminosity.

According to the observations, PKS 0537-286 is very luminous also in the X-ray band with a 0.3–10 keV luminosity between 0.1 and 1.0 quindecillion erg/s. The X-ray emission of this is characterized by a hard spectrum of below 1.38.

The astronomers concluded that the flares of PKS 0537-286 are most likely due to the hardening of the emitting electron spectral index and shifting of the cut-off energy to higher values.

"The modeling in the quiescent to flaring states showed that the flare was caused by the electron distribution changes, i.e., the electron power-law index hardened to ? = 2.2 ± 0.1 and the cut-off energy was ?cut = (2.5 ± 0.2) × 103," the authors of the paper explained.

More information: N. Sahakyan et al, Origin of multiwavelength emission from flaring high redshift blazar PKS 0537-286, arXiv (2023). DOI: 10.48550/arxiv.2302.07682

Journal information: arXiv

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Citation: Astronomers investigate multiwavelength emission from the blazar PKS 0537-286 (2023, February 27) retrieved 18 May 2024 from https://phys.org/news/2023-02-astronomers-multiwavelength-emission-blazar-pks.html
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