SRGAJ230631.0+155633: an extremely X-ray luminous, heavily obscured, radio-loud quasar at z=0.44 discovered by SRG/ART-XC

We report on a detailed study of a luminous, heavily obscured ($N_{\mathrm{H}}\sim 2\times {10}^{23}$ cm${}^{-2}$), radio-loud quasar SRGAJ230631.0+155633, discovered in the 4–12 keV energy band by the Mikhail Pavlinsky 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 AGN according to optical spectroscopy (SDSS, confirmed by DESI). We combine radio-to-X-ray data, including near-simultaneous ART-XC and Swift/XRT observations conducted in June 2023. During these follow-up observations, the source was found in a significantly fainter but still very luminous state ($L_{\mathrm{X}}=1.0_{-0.3}^{+0.8}\times {10}^{45}$ erg s${}^{-1}$, absorption corrected, 2–10 keV) compared to its discovery during the all-sky survey ($L_{\mathrm{X}}=6_{-3}^{+6}\times {10}^{45}$ erg s${}^{-1}$), which indicates significant intrinsic variability on a rest-frame time scale of $\sim 1$ year. The radio data show a complex morphology with a core and two extended radio lobes, indicating a giant FRII radio galaxy. From multi-wavelength 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 $\sim 1.4\times {10}^9{M}_{\odot }$, implying accretion at $\sim 30$% of the Eddington limit. SRGAJ230631.0+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.