Multi-wavelength behaviour of the radio galaxy SBS 1343+537: γ-ray flaring activity discovered by Fermi-LAT and coordinated Swift and SRT observations

¹ Istituto Nazionale di Fisica Nucleare Roma Tor Vergata, via della Ricerca Scientifica, 00133, Roma, Italy
² ASI – Space Science Data Center, via del Politecnico, 00133, Roma, Italy
³ Dipartimento di Fisica, Sapienza Università di Roma, P.le A. Moro, 00185, Roma, Italy
⁴ Università di Trento, via Sommarive 14, 38123, Trento, Italy
⁵ Dipartimento di Fisica “M. Merlin”, Università e Politecnico di Bari, via Amendola 173, 70126, Bari, Italy
⁶ Istituto Nazionale di Fisica Nucleare Bari, via Giovanni Amendola 173, 70126, Bari, Italy
⁷ INAF-Osservatorio Astronomico di Cagliari, via della Scienza, 09047, Cuccuru Angius, Selargius, Italy
⁸ Space Science Division, Naval Research Laboratory, Washington, DC, 20375, USA
⁹ Department of Fundamental Physics and IUFFyM, University of Salamanca, Plaza de la Merced S/N, E-37008, Salamanca, Spain
¹⁰ ASI – Sardinia Deep Space Antenna, Casa Cantoniera di Pranu Sanguni, 09040, San Basilio, Italy
¹¹ INAF – Istituto di Radio Astronomia, Via P. Gobetti 101, I-40129, Bologna, Italy
¹² Istituto Nazionale di Fisica Nucleare Trieste, via Valerio, 34127, Trieste, Italy
¹³ Università di Roma Tor Vergata, Dipartimento di Fisica, via della Ricerca Scientifica, 00133, Roma, Italy
¹⁴ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290, Versoix, Switzerland
¹⁵ INAF – Osservatorio Astronomico di Roma, viale del Parco Mellini, 00136, Monte Porzio Catone, Italy

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Received: 9 September 2025
Accepted: 14 February 2026

Abstract

The SBS 1343+537 radio galaxy has a kiloparsec-scale radio jet, and complex kiloparsec-scale morphology. Although its classification is still uncertain, in literature it is indicated as a possible Fanaroff-Riley type I (FR-I) object with extended wings of emission, and core blazar-like properties. It was recently spatially associated with the GeV γ-ray source 4FGL J1346.5+5330, which detected by the Large Area Telescope (LAT), on board the Fermi Gamma-Ray Space Telescope. In June 2024, the Fermi Large Area Telescope (Fermi-LAT) observed enhanced γ-ray activity from SBS 1343+537. The event was followed up by the Neil Gehrels Swift Observatory satellite (Swift) and Sardinia Radio Telescope (SRT) observations. Here, we present multi-frequency data (radio, optical, Ultra Violet (UV), X-ray, and γ-ray) collected during this observing campaign. Our results confirm the detection of a short-lived γ-ray flare, consistent with a power-law spectrum. We report a stable X-ray flux, minor activity in the UV band, and a flux density increase in the radio 20 GHz band, which might indicate a mild spectral index inversion. The broadband spectral energy distribution (SED) modelling confirms a typical blazar-like emission in the core of this source, dominated by one-zone Synchrotron Self-Compton (SSC) and external Compton (EC) leptonic processes.