Research inspects a distant gamma-ray-emitting blazar

Research inspects a distant gamma-ray-emitting blazar

Fractional variability of 1ES 0647+250. Credit: Santos et al., 2022.

An international team of astronomers has carried out a long-term, multi-wavelength study of a distant gamma-ray-emitting blazar known as 1ES 0647+250. The research results, published November 23 on arXiv .org, provide important information on the long-term variability of this source.

Blazars, classified as members of a larger group of active galaxies that host active galactic nuclei (AGN), are the most numerous extragalactics gamma ray sources. Their characteristic features are relativistic jets pointed almost exactly at Earth. Based on their optical emission properties, astronomers divide blazars into two classes: flat spectrum radio quasars (FSRQ) which exhibit prominent and broad optical emission lines, and BL Lacertae (BL Lacs) objects, which do not.

At an estimated redshift of at least 0.29, 1ES 0647+250 is a BL Lac object reported to be a very high energy (VHE) gamma-ray emitter (above 100 GeV) with a flux about 3% flux units from the Crab Nebula. The source is bright and variable in all electromagnetic bands and has been observed many times in the optical, radio and X-ray bands.

Previous observations of 1ES 0647+250 detected significant variability in the optical band, but found no evidence of intra-night or short burst variability. However, the timescales of variability of 1ES 0647+250 in the optical band are still uncertain, mainly due to long deviations in the historical light curve.

Therefore, in order to shed light on the variability of 1ES 0647+250, a group of astronomers led by Jorge Otero Santos from the University of La Laguna, Spain, analyzed data at multiple long-wavelength term from various spacecraft and ground-based telescopes.

“In this paper, we perform the first long-term multi-wavelength (MWL) study of 1ES 0647+250,” the researchers wrote.

The study found that 1ES 0647 + 250 has significant long-term benefits variability, particularly in X-rays and HEV gamma rays, with increasing flux in radio, optical, and gamma wavelengths. It was noted that such behavior is observed in other blazars, where the increase in flux on annual time scales is consistent with that expected from variations in accretion disk conditions.

The data indicates a long-term correlation without delay between optical and gamma emission. The radio emission is correlated with the optical and gamma bands with time offsets of 393 and 398 days, respectively. According to the researchers, this delay suggests that the radio emission is emitted from a region distinct from the blazar jet, at a distance of about 11.73 Light years.

The X-ray spectra of 1ES 0647+250 show harsher behavior when brighter during the low state as well as for the flare that occurred in 2019. Additionally, comparing the source’s simultaneous GeV and TeV spectra during flaring activity, allowed astronomers to estimate its redshift, which turned out to be 0.45.

The authors of the paper also analyzed the spectral energy distribution (SED) and found that it could be reasonably well described with the one- and two-component lepton scenarios.

More information:
MAGIC Collaboration, Long-term multi-wavelength study of 1ES 0647+250, arXiv (2022). DOI: 10.48550/arxiv.2211.13268

Journal information:

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