Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 2609.34568

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

Stefano Ciprini·Federica Giacchino
View original source ↗Read source document ↗Export metadata ↓

Abstract

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.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Stefano Ciprini, Federica Giacchino. 2026-09-28. Unexpected Gamma-ray Outburst from the CSS Radio Galaxy 3C 216. https://arxiv.org/abs/2609.34568

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Nuclear Physics of Binary Neutron Star Mergers

Binary neutron star mergers provide a unique laboratory for studying matter under conditions that cannot be reproduced in terrestrial experiments. They probe dense matter at supranuclear density, finite temperature, rapid rotation, strong gravity, and extreme neutron excess, while producing observable signals in gravitational waves, electromagnetic radiation, and, in principle, neutrinos. This review focuses on the nuclear physics of binary neutron star mergers. We discuss the dense-matter equation of state (EoS), the inspiral and merger dynamics, the structure and lifetime of the post-merger remnant, transport and dissipative processes, weak interactions and neutrino transport, and the production of heavy elements through $r$-process nucleosynthesis. Particular emphasis is placed on the connection between microscopic physics and multimessenger observables, including tidal deformability, post-merger gravitational-wave spectra, kilonova light curves, short gamma-ray bursts, and afterglows. We also review how observations of events such as GW170817, together with neutron star mass and radius measurements, laboratory nuclear experiments, and theoretical many-body calculations, constrain the EoS and the composition of dense matter. The goal is to summarize the current understanding of how nuclear physics controls the dynamics and observable signatures of binary neutron star mergers, and to identify the open questions that future multimessenger observations and improved nuclear theory will address.

astro-ph.HE↗
arXiv2026

Hunting for Compact Object Binaries from eRASS1 Optical Counterparts through ZTF Time-domain Photometry and Multi-wavelength Surveys

Capitalizing on the eRASS1 optical counterpart catalog, we conduct a systematic census of compact object binary (COB) candidates, with a primary focus on X-ray binaries (XRBs), by integrating ZTF time-domain photometry with multi-wavelength observations. This framework establishes two complementary pipelines, yielding two distinct source samples. The first sample consists of 151 periodically variable sources, from which a highly refined subset of 43 high-priority COB candidates is identified. The second sample comprises 1958 distance-constrained sources selected based on elevated X-ray luminosities or high $\log(F_{\mathrm{X}}/F_{\mathrm{opt}})$. Crucially, cross-matching both samples with radio catalogs reveals seven radio-emitting sources, highlighting four promising XRB candidates. Our results underscore that coupling eROSITA with wide-field time-domain photometric and multi-wavelength surveys offers a highly efficient strategy for uncovering the hidden population of COBs.

astro-ph.HE↗
arXiv2026

Fermi-eROSITA cross-correlations suggest annihilation lines of a $\sim70$ GeV WIMP

Galaxy clusters, with their deep potential wells, provide some of the strongest constraints on the velocity-dependent ($p$-wave) annihilation of weakly interacting massive particle (WIMP) dark matter. Even weaker signals can be extracted from sufficiently many aggregated clusters, by cross-correlating $γ$-rays with large-scale structure tracers. Cross-correlating 16.3 years of Fermi-LAT data with the eROSITA map of the western Galactic hemisphere, a blind composite matched-filter scan of the X-ray-correlated spectrum for the $χχ\toγγ$, $γZ$, and $γh$ annihilation-line triad of a single WIMP $χ$ finds $\overline{m}_χc^2\simeq71.9$ and $67.5$ GeV triads, each with a local $Z$-score $\sim3$ corresponding to a (trial-corrected) global $\sim2σ$. The $\sim72$ GeV candidate coincides with the mass implied by interpreting the recently reported $\sim43.2$ GeV $γ$-ray line in three nearby clusters as its $γZ$ channel. At this externally fixed mass, the triad reaches $\sim3σ$ alone, and combines with the cluster line to $3.9$-$5.1σ$ (depending on the significance of the latter). The inferred intrinsic channel cross sections are a few $10^{-19}$ cm$^3$ s$^{-1}$ for WIMPs tracing the X-ray-emitting gas. Future tests of this interpretation are outlined.

astro-ph.HE↗