SRGA J2306+1556: 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 (NH ~ 2 × 10^23 cm^-2), radio-loud quasar SRGA J230631.0+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 compared to its discovery, which indicates significant intrinsic variability on a rest-frame time scale of ~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 ~6 × 10^46 erg s-1 and a black hole mass of ~1.4 × 10^9 M⊙, implying accretion at ~30% 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.