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

Abstract

<p><em>Context.</em> The flat spectrum radio quasar OP 313, is a high-redshift (<em>z</em> = 0.997) blazar that entered an intense <em>γ</em>-ray active phase from November 2023 to March 2024, as observed by the as observed by the Large Area Telescope (LAT) on board the <em>Fermi Gamma-ray Space Telescope</em>.</p><p><em>Aims.</em> We present a multiwavelength analysis covering 15 years of data, from August 2008 to March 2024, to contextualize this period of extreme <em>γ</em>-ray activity within the long-term emission of the source.</p><p><em>Methods.</em> We analyzed a long-term, comprehensive, multiwavelength dataset from different facilities and projects from radio to <em>γ</em> rays. We identified the seven most intense <em>γ</em>-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).</p><p><em>Results.</em> 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 <em>γ</em>-ray flares. By comparing the timing of the VLBA-BU-BLAZAR knots’ ejection with the <em>γ</em>-ray flaring periods, we constrained the setup of the SED modeling. We also found that the first <em>γ</em>-ray flaring period is less Compton-dominated than the others.</p><p><em>Conclusions.</em> 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 <em>γ</em>-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 <em>γ</em>-ray flaring period than the later ones.</p>