The Most Distant <i>γ</i>-Ray Flare to Date: A Multiwavelength Campaign on the <i>z</i> = 4.715 Blazar GB6 B1428+4217
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
- Markus Boettcher (ORCID: https://orcid.org/0000-0002-8434-5692)
- J. Wilms (ORCID: https://orcid.org/0000-0003-2065-5410)
- Florian Eppel (ORCID: https://orcid.org/0000-0001-7112-9942)
- Daniel Morcuende (ORCID: https://orcid.org/0000-0001-9400-0922)
- A. Kraus (ORCID: https://orcid.org/0000-0002-4184-9372)
- Jorge Otero-Santos (ORCID: https://orcid.org/0000-0002-4241-5875)
- I. Agudo (ORCID: https://orcid.org/0000-0002-3777-6182)
- M. Kreter (ORCID: https://orcid.org/0000-0002-3092-3506)
- Andrea Gokus (ORCID: https://orcid.org/0000-0002-5726-5216)
- M. Kadler (ORCID: https://orcid.org/0000-0001-5606-6154)
- Jonas Hessdoerfer (ORCID: https://orcid.org/0009-0009-7841-1065)
- Felicia McBride (ORCID: https://orcid.org/0000-0001-6191-1244)
- M. Errando (ORCID: https://orcid.org/0000-0002-1853-863X)
- Juan Escudero (ORCID: https://orcid.org/0000-0002-4131-655X)
Institutions
- Boston University (US)
- Bowdoin College (US)
- St Petersburg University (RU)
- Friedrich-Alexander-Universität Erlangen-Nürnberg (DE)
- Washington University in St. Louis (US)
- University of Würzburg (DE)
- North-West University (ZA)
- Istituto Nazionale di Fisica Nucleare, Sezione di Padova (IT)
- Center for Astrophysics Harvard & Smithsonian (US)
- Max Planck Institute for Radio Astronomy (DE)
- Instituto de Astrofísica de Andalucía (ES)
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2025-09-09
- DOI
- https://doi.org/10.3847/1538-4357/adf4d2
- Citations
- 1
- Primary Topic
- Astrophysics and Cosmic Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 1.87
Funders
- National Science Foundation
- National Aeronautics and Space Administration
- Ministerio de Ciencia, Innovación y Universidades
- European Commission
- Nuclear Safety and Security Commission
- Junta de Andalucía
- McDonnell Center for Systems Neuroscience
- Consejo Superior de Investigaciones Científicas
- Agencia Estatal de Investigación