Unexpected Gamma-ray Outburst from the CSS Radio Galaxy 3C 216

@misc{ciprini2026unexpected,
  title = {{Unexpected Gamma-ray Outburst from the CSS Radio Galaxy 3C 216}},
  author = {Stefano Ciprini and Federica Giacchino},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.34568},
  eprint = {2609.34568},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.34568},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Unexpected Gamma-ray Outburst from the CSS Radio Galaxy 3C 216
AU  - Stefano Ciprini
AU  - Federica Giacchino
PY  - 2026
DA  - 2026/09/28
PB  - arXiv
DO  - 10.48550/arxiv.2609.34568
UR  - https://arxiv.org/abs/2609.34568
AB  - While compact steep-spectrum (CSS) radio galaxies, genuine young/intermittent-jet or frustrated-jet radio galaxies trapped in gas-rich environments, are rarely detected in GeV gamma-ray energy bands, 3C 216 is an interesting exception. In 2023, the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected an unexpected, rapid, and powerful GeV gamma-ray outburst from this CSS radio galaxy, which was followed up by UV and X-ray observations from the Neil Gehrels Swift Space Observatory. During the outburst its spectral energy distribution is dominated by synchrotron and synchrotron self-Compton radiation, produced in the relativistic jet, suggesting a young quasar classification. Radio-band features, such as superluminal motion and a flat-spectrum core component, confirm that 3C 216 harbors a distinct blazar-like core, bent and viewed under a small angle to the line of sight. This is the unique large and energetic event from the source observed in 17 years of Fermi-LAT continuous all-sky and time-domain monitoring.
ER  -