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.

Context. Transitional millisecond pulsars (tMSPs) in tight binary systems represent an important evolutionary link between low-mass X-ray binaries and radio millisecond pulsars. To date, only three confirmed tMSPs and a few candidates have been discovered. Most of them are γ-ray sources. For this reason, searching for multi-wavelength counterparts to unassociated Fermiγ-ray sources can help us find new tMSPs. Aims. We investigate whether the unassociated γ-ray source 4FGL J1824.2+1231 belongs to the tMSP family. Methods. To find the counterpart to 4FGL J1824.2+1231, we used data from the SRG/eROSITA and Swift X-ray catalogues and from different optical catalogues. We also performed time-series photometric optical observations of the source with the 2.1 m telescope of the Observatorio Astronómico Nacional San Pedro Mártir, the 1.5 m telescope of the Maidanak Astronomical Observatory, and the 1.5 m Russian-Turkish telescope. In addition, we carried out optical spectroscopic observations with the Russian-Turkish telescope and used archival spectroscopic data obtained with the Gemini-North telescope. Results. Within the position error ellipse of 4FGL J1824.2+1231, we find only one X-ray source that coincides with an optical object. We consider it a likely multi-wavelength counterpart to 4FGL J1824.2+1231. The source shows strong optical variability and significant proper motion. The latter strongly implies that it is a Galactic source. Double-peaked H and He emission lines are detected in its spectrum with a flat continuum, as often observed in accretion disks of compact binary systems. The X-ray spectrum is well fitted by a power law with a photon index of ∼1.7. The derived intrinsic X-ray-to-γ-ray flux ratio is about 0.2. Conclusions. Assuming the X-ray/optical source is the true counterpart to 4FGL J1824.2+1231, all its properties suggest that it is a tMSP in the sub-luminous disk state.

Context. Long gamma-ray bursts (GRBs) are characterized by a brief gamma-ray flash followed by a longer-lasting multiwavelength afterglow. The basic mechanism is largely understood, and the early afterglow evolution often shows complex features that provide crucial insights into the transition between prompt and afterglow phases. Aims. We present a detailed analysis of GRB 210312B, detected by INTEGRAL, which exhibits both a precursor and a complex optical afterglow evolution. Through careful modeling using Markov chain Monte Carlo methods, we disentangled the contributions of an early optical flare and forward shock emission. Methods. Our analysis reveals a gamma-ray precursor 17 s before the main pulse with a significantly softer spectrum (hardness ratio 0.37±0.12 versus 1.9±0.4). The optical afterglow shows an early peak at 76.0_‑5.1^+4.4 s characterized by a steep rise (α_flare,1 = ‑4.1_‑2.3^+1.6) and decay (α_flare,2 = 4.0_‑1.5^+2.1), followed by forward shock emission with a broad hydrodynamic peak at around 150 s. In the subsequent plateau phase, the afterglow initially has a complex structure before settling into a final power law decay consistent with an electron distribution index p = 2.36_‑0.15^+0.18. The negligible host extinction (A_V,host = ‑0.073_‑0.078^+0.100) suggests we are observing the intrinsic afterglow spectrum. The host system consists of two luminous (M_B∼‑21.7) components separated by 11.5 kpc at z = 1.069, which are possibly an interacting galaxy pair. Results. GRB 210312B provides a rare opportunity to study the prompt-to-afterglow transition in detail. The consistency of the forward shock component with standard afterglow theory supports our physical interpretation despite the lack of X-ray coverage.

We report a case of a changing-look (CL) active galactic nucleus (AGN) at a redshift of z=0.337, identified as J075947.73+112507.3 (hereafter J0759), which exhibits recurring changing-look (RCL) phenomena accompanied by extreme asymmetry in the broad emission-line profiles. J0759 was discovered through the CL-AGN project conducted with the Dark Energy Spectroscopic Instrument. The most recent CL event was confirmed with new spectroscopic observations obtained using the Big Telescope Alt-azimuthal. Variability trends observed in the optical and mid-infrared light curves reveal multiple flares, indicating four to six potential CL events over time. We decomposed the asymmetric broad Hα emission line into two components, which persist in both high and low states. The RCL events in J0759 are inconsistent with the obscuration model and are more likely driven by variations in the accretion rate. However, the physical mechanism underlying such rapid accretion-rate changes remains unclear.

Long uninterrupted observations of the X-ray binary system Her X-1 were performed with the Mikhail Pavlinsky ART-XC telescope of the Spectrum-Röntgen-Gamma (SRG) X-ray Observatory in the 4–25 keV energy range with total exposure of about two days around the main turn-on of the X-ray source. We present the results of the timing and spectral analysis of these observations. The opening of the X-ray source is determined to occur at the orbital phase ϕ_b ≈ 0.25. The analysis of the X-ray light curve reveals the first direct observational evidence of the nutation of a tilted precessing accretion disk with a period of ≃0.87 days. The appearance of X-ray pulsations near the orbital phase ϕ_b ≃ 0.77 prior to the main turn-on at the maximum of the nutation variability has also been detected. During the X-ray eclipse, a non-zero X-ray flux is measured, which is presumably associated with the scattering of X-ray emission in a hot corona around the optical star illuminated by the X-rays from the central neutron star. An increase in the X-ray flux after the main turn-on can be described by the passage of radiation from the central source through a scattering corona above the precessing accretion disk.