A long-term multiwavelength study of the flat spectrum radio quasar OP 313

¹ Università di Trento, Via Sommarive 14 I-38123 Trento, Italy
² Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari Via Amendola 173 I-70126 Bari, Italy
³ Istituto Nazionale di Fisica Nucleare, Sezione di Bari I-70126 Bari, Italy
⁴ Department of Physics and Astronomy, University of Turku FI-20014 Turku, Finland
⁵ Department of Astronomy, University of Geneva Chemin Pegasi 51 1290 Versoix, Switzerland
⁶ Istituto di Radioastronomia – INAF Via Piero Gobetti 101 I-40129 Bologna, Italy
⁷ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomia E-18008 Granada, Spain
⁸ Section of Astrophysics, Astronomy & Mechanics – Department of Physics, National and Kapodistrian University of Athens Panepistimiopolis Zografos 15784, Greece
⁹ Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata” I-00133 Roma, Italy
¹⁰ ASI Space Science Data Center Via del Politecnico I-00133 Roma, Italy
¹¹ Sapienza Università di Roma – Dipartimento di Fisica P.le A. Moro 00185 Roma, Italy
¹² Finnish Centre for Astronomy with ESO University of Turku, Finland
¹³ Department of Fundamental Physics, University of Salamanca Plaza de la Merced s/n E-37008 Salamanca, Spain
¹⁴ Center for Astrophysics | Harvard & Smithsonian 60 Garden Street Cambridge MA 02138, USA
¹⁵ Institute for Astrophysical Research, Boston University 725 Commonwealth Ave. Boston MA 02215, USA
¹⁶ Max-Planck-Institut für Radioastronomie Auf dem Hügel 69 D-53121 Bonn, Germany
¹⁷ Aalto University Metsähovi Radio Observatory Metsähovintie 114 02540 Kylmälä, Finland
¹⁸ Aalto University Department of Electronics and Nanoengineering P.O. Box 15490 FI-00076 Aalto, Finland
¹⁹ Institut de Radiostronomie Millimétrique, Avenida Divina Pastora 7 Local 20 E–18012 Granada, Spain

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Received: 26 July 2025
Accepted: 11 January 2026

Abstract

Context. The flat spectrum radio quasar OP 313, is a high-redshift (z = 0.997) blazar that entered an intense γ-ray active phase from November 2023 to March 2024, as observed by the as observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope.

Aims. We present a multiwavelength analysis covering 15 years of data, from August 2008 to March 2024, to contextualize this period of extreme γ-ray activity within the long-term emission of the source.

Methods. We analyzed a long-term, comprehensive, multiwavelength dataset from different facilities and projects from radio to γ rays. We identified the seven most intense γ-ray flaring periods and performed a kinematic analysis of Very Long Baseline Array (VLBA) data to determine whether new jet components emerged before or during these flares. For two of these flaring periods, we performed the modeling of the spectral energy distribution (SED).

Results. The VLBA-BU-BLAZAR and MOJAVE datasets reveal a new jet component appearing in both visibility datasets prior to the onset of one of the strongest γ-ray flares. By comparing the timing of the VLBA-BU-BLAZAR knots’ ejection with the γ-ray flaring periods, we constrained the setup of the SED modeling. We also found that the first γ-ray flaring period is less Compton-dominated than the others.

Conclusions. Our results suggest that the recent activity of OP 313, is triggered by new jet components emerging from the core and interacting with a standing shock. The γ-ray emission likely arises from dusty torus photons upscattered via inverse Compton (IC) by relativistic jet electrons. The SED modeling indicates that this component is less dominant during the first γ-ray flaring period than the later ones.