The Most Distant γ-Ray Flare to Date: A Multiwavelength Campaign on the z = 4.715 Blazar GB6 B1428+4217

Gokus A, Errando M, Agudo I, Böttcher M, Eppel F, Pedrosa JE, Heßdörfer J, Jorstad S, Kadler M, Kraus A, Kreter M, McBride F, Morcuende D, Otero-Santos J, Wilms J (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Astrophysical Journal American Astronomical Society

Book Volume: 990

Article Number: 206

Journal Issue: 2

DOI: 10.3847/1538-4357/adf4d2

Abstract

In 2023 November, the Fermi Large Area Telescope detected a γ-ray flare from the high-redshift blazar GB6 B1428+4217 (z = 4.715). We initiated a multiwavelength follow-up campaign involving Swift, NuSTAR, the Sierra Nevada and Perkins Observatories, and the Effelsberg 100 m radio telescope. This source, also known as 5BZQ J1430+4204, has shown an anomalous soft X-ray spectrum in previous observations, including possible ionized absorption features or signatures of bulk Comptonization of thermal electrons, which are also detected during the flaring episode. Simultaneous optical data revealed a polarization fraction of ∼8% in the R band, confirming that synchrotron emission dominated over thermal emission from the accretion disk. The hard X-ray flux was enhanced during the flare. Modeling of the broadband spectral energy distribution suggests that the high-energy component is dominated by Compton scattering by external seed photons from the accretion disk. The origin of the flare is consistent with the injection of a hard-spectrum electron population in the emission region. With a γ-ray luminosity among the top 5% of flaring events, GB6 B1428+4217 exemplifies a prototypical MeV blazar. Its Compton-dominated spectral energy distribution and extreme luminosity are in line with expectations from the blazar sequence. High-redshift flares like this are critical for understanding jet physics in the early Universe and may improve detection prospects with future missions such as the Compton Spectrometer and Imager.

Authors with CRIS profile

Jörn Wilms Professur für Astronomie und Astrophysik

Involved external institutions

Max-Planck-Institut für Radioastronomie / Max Planck Institute for Radio Astronomy DE Germany (DE) Noordwes-Universiteit / North-West University ZA South Africa (ZA) Bowdoin College US United States (USA) (US) Institute of Astrophysics of Andalusia / Instituto de Astrofísica de Andalucía (IAA-CSIC) ES Spain (ES) Washington University in St. Louis US United States (USA) (US) Julius-Maximilians-Universität Würzburg DE Germany (DE) Boston University US United States (USA) (US)

How to cite

APA:

Gokus, A., Errando, M., Agudo, I., Böttcher, M., Eppel, F., Pedrosa, J.E.,... Wilms, J. (2025). The Most Distant γ-Ray Flare to Date: A Multiwavelength Campaign on the z = 4.715 Blazar GB6 B1428+4217. Astrophysical Journal, 990(2). https://doi.org/10.3847/1538-4357/adf4d2

MLA:

Gokus, Andrea, et al. "The Most Distant γ-Ray Flare to Date: A Multiwavelength Campaign on the z = 4.715 Blazar GB6 B1428+4217." Astrophysical Journal 990.2 (2025).

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