We report on a detailed study of a luminous, heavily obscured ($N_{\mathrm{H}}\sim 2\times {10}^{23}$ 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 ($L_{\mathrm{X}}={1.0}_{-0.3}^{+0.8}\times {10}^{45}$ erg s${}^{-1}$, absorption corrected, 2–10 keV) compared to its discovery ($L_{\mathrm{X}}=6_{-3}^{+6}\times {10}^{45}$ erg s${}^{-1}$), which indicates significant intrinsic variability on a rest-frame time-scale of $\sim 1$ 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.

Aims. We investigate the X-ray emission from the Galactic centre (GC) region, focusing on the 6.4 keV fluorescent line of neutral or weakly ionised iron, which is commonly attributed to X-ray reflection from dense molecular clouds. Our goal is to separate the reflection signal from other physical X-ray components. We aim to produce a clean map of the 6.4 keV emission, thus providing a better understanding of the X-ray reflection processes in the GC. Methods. We utilised a deep mosaic of all available XMM-Newton observations, encompassing the central 40 square degrees of the Galaxy. This dataset integrates information from 503 individual observations, resulting in a total clean exposure time of 7.5 Ms. The mosaics of two narrow bands centred at 6.7 keV and 6.4 keV, and a broader continuum band at lower energies (5‑6.1 keV), provided valuable spatial and spectral information on the X-ray emission. These combined with the stellar mass distribution of our Galaxy enabled us to decompose the observed signal into physically meaningful components. Results. Our analysis shows that the cleaned 6.4 keV band map, free from the contribution of bright and unresolved point sources, is predominantly shaped by X-ray reflection from dense molecular clouds. The spatial distribution of this emission, which strongly correlates with the molecular gas distribution in the central molecular zone (CMZ), supports the interpretation that this map provides the best estimate of the X-ray reflection signal averaged over the last two decades. This cleaned reflection map could serve as a tool for future studies aiming to quantify upper limits on the reflection contribution from low-energy cosmic rays in unilluminated regions. Moreover, we estimate that, on average, within the CMZ, approximately 65% of the ridge emission contributes to the observed emission in the 6.4 keV band, a factor that should be incorporated into upcoming investigations of the GC, such as polarisation studies of the reflected X-ray continuum from molecular clouds and statistical assessments of the reflection surface brightness.

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.