Monthly Notices of the Royal Astronomical Society
07/2025
MNRAS
SRGA J2306 + 1556: an extremely X-ray luminous, heavily obscured, radio-loud quasar at z = 0.44 discovered by SRG/ART-XC
Усков, Г.
Сазонов, С.
Лапшов, И.
Mikhailov A.
Филиппова, Е.
We report on a detailed study of a luminous, heavily obscured ($N_{\rm H}\sim 2\times 10^{23}$ cm$^{-2}$), radio-loud quasar SRGA J230631.0 + 155633 discovered in the 4–12 keV energy band by the Mikhail Pavlinsky Astronomical Roentgen Telescope X-ray Concentrator (ART-XC) telescope aboard the SRG observatory during the first two years of its all-sky X-ray survey in 2020–2021. The object is located at $z=0.4389$ and is a type 2 active galactic nucleus according to optical spectroscopy (Sloan Digital Sky Survey, confirmed by Dark Energy Spectroscopic Instrument). We combine radio-to-X-ray data, including near-simultaneous ART-XC and Swift X-ray Telescope (XRT) observations conducted in 2023 June. During these follow-up observations, the source was found in a significantly fainter but still very luminous state ($L_{\rm X}=1.0^{+0.8}_{-0.3}\times 10^{45}$ erg s$^{-1}$, absorption corrected, 2–10 keV) compared to its discovery ($L_{\rm X}=6^{+6}_{-3}\times 10^{45}$ erg s$^{-1}$), which indicates significant intrinsic variability on a rest-frame time-scale of $\sim 1$ yr. The radio data show a complex morphology with a core and two extended radio lobes, indicating a giant FRII radio galaxy. From multiwavelength photometry and the black hole–bulge relation, we infer a bolometric luminosity of $\sim 6\times 10^{46}$ erg s$^{-1}$ and a black hole mass of $\sim 1.4\times 10^{9}\, \mathrm{ M}_\odot$, implying accretion at $\sim 30$ per cent of the Eddington limit. SRGA J230631.0 + 155633 proves to be one of the most luminous obscured quasars out to $z=0.5$. As such, it can serve as a valuable testbed for in-depth exploration of the physics of such objects, which were much more abundant in the younger Universe.