Diffuse radio emission in galaxy clusters is a tracer of ultra-relativistic particles and μG-level magnetic fields, and is thought to be triggered by cluster merger events. In the distant Universe (i.e. z > 0.6), such sources have been observed only in a handful of systems, and their study is important to understand the evolution of large-scale magnetic fields over the cosmic time. Previous studies of nine Planck clusters up to z ∼ 0.9 suggest a fast amplification of cluster-scale magnetic fields, at least up to half of the current Universe's age, and steep spectrum cluster scale emission, in line with particle re-acceleration due to turbulence. In this paper, we investigate the presence of diffuse radio emission in a larger sample of galaxy clusters reaching even higher redshifts (i.e. z ≳ 1). We selected clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) with richness λ₁₅ > 40 covering the area of the second data release of the LOFAR Two-Meter Sky Survey (LoTSS-DR2) at 144 MHz. These selected clusters are in the redshift range 0.78 ‑ 1.53 (with a median value of 1.05). We detect the possible presence of diffuse radio emission, with the largest linear sizes of 350 ‑ 500 kpc, in five out of the 56 clusters in our sample. If this diffuse radio emission is due to a radio halo, these radio sources lie on or above the scatter of the P_ν ‑ M₅₀₀ radio halo correlations (at 150 MHz and 1.4 GHz) found at z < 0.6, depending on the mass assumed. We also find that these radio sources are at the limit of the detection by LoTSS, and therefore deeper observations are important for future studies.

Aims. TXS 0506+056 was the first active galactic nucleus to be identified as a convincing counterpart of an extremely high-energy neutrino, IceCube-170922A. Prior to this, IceCube data revealed evidence of enhanced neutrino activity in 2014–2015 from the direction of the same source. Renewed neutrino activity from TXS 0506+056 was confirmed by Baikal-GVD on April 18, 2021, and another IceCube detection on September 18, 2022. We revisited this blazar to study its evolution in light of the new high-energy data. Methods. We reanalyzed VLBA data observed at 8 GHz between 2010 and 2019, as well as 15 GHz data observed between 2019 and 2023. We combined these new data with 15 GHz data obtained earlier and performed a detailed study of the temporal evolution of the parsec-scale radio structure to search for a possible correlation with the neutrino events. We complemented our study of the morphology with an investigation of the radio, optical (Abastumani Observatory), and Fermi-LAT light curves. Results. The parsec-scale jet continues to reveal unexpected and puzzling properties that are not comparable with those of any known typical blazar jet. The total of all the jet component positions, obtained from this and earlier work, reveals a very wide-spread distribution in xy-coordinates. This could indicate an interaction of jet components with surrounding clouds, most likely material from the broad line region. However, a more detailed investigation reveals that the arrangement of jet component positions changes drastically with time. While the jet morphology resembles a crossing of two jets around 2010, a sudden ordering into a ring-like structure sets in around 2016 with the start of the major radio flare. In addition to this ring-like accumulation of jet components, we find arc-like gatherings of jet features in the jet before (2011–2016) and during the major radio peak, which occurred from 2016 to 2023. We discuss the possibility that the radio core flaring and the ring-like arrangement of jet components with time is explained by gravitational lensing. Conclusions. If we interpret the observed distribution of the jet components as being related to a potential neutrino generation mechanism, our calculations show that the neutrino production site could be either co-spatial with or within a distance of about 10¹⁸ cm of the core, which corresponds to the broad line region. If instead we take the data at face value and examine them in a more rigorous way, we find that strong gravitational lensing might alter the very long-baseline interferometry morphology of TXS 0506+056. As no intervening galaxy is found in the optical data, we assume the lens is an isolated non-accreting supermassive black hole. At an intermediate distance, a mass of 10⁵ ‑ 10⁶ solar masses would be required. Assuming instead that TXS 0506+056 is a binary or dual system with a second non-emitting black hole acting as the lens, then gravitational lensing by a supermassive black hole of 10¹⁰ solar masses located some kiloparsecs away significantly changes the morphology of the jet of TXS 0506+056 and magnifies the jet and core flux density.

In this work, we studied X-ray source SRGe J021932.4‑040154 (SRGe J021932), which we associated with a single X-ray active star of spectral class G2V-G4V and the rotational period Prot<9.3 days. Additional analysis of TESS light-curves allowed for the rotational period estimation of 3.2±0.5 days. SRGe J021932 was observed with the SRG/eROSITA during eUDS survey in 2019 in a much dimmer state compared to the XMM-Newton catalogue 4XMM-DR12. Detailed analysis revealed that the archival XMM-Newton observations captured the source during a flaring event in 2017. The XMM-Newton light curve demonstrates a strong flare described with the Gaussian rise and exponential decay, typical for stellar flares, characterized by timescales of ∼400 s and ∼1300 s, respectively. The spectral analysis of the quiescent state reveals ∼10 MK plasma at luminosity of (1.4±0.4)×1029ergs‑1 (0.3‑4.5 keV). The spectrum of the flare is characterized by temperature of ∼40 MK and luminosity (5.5±0.6)×1030ergs‑1. The total energy emitted during the flare ∼1.7×1034 erg exceeds the canonical threshold of 10³³ erg, allowing us to classify the observed event as a superflare on a rapidly-rotating solar-type star. Additionally, we present the upper limit on the surface starspot area based on the brightness variations and consider the hypothesis of the object being a binary system with G-type and M-type stars, suggested by two independent estimations of radial velocity variations from APOGEE-2 and Gaia.

We present results of a study of the Galactic hard X-ray and soft γ-ray background emission performed with the IBIS telescope aboard the INTEGRAL observatory using data obtained over more than 20 years of operations. The study of the Galactic background at energies between 10 keV and a few MeV is problematic due to the contribution of point sources, high instrumental background and large-scale extent of the emission, which leads to the need of utilizing complex model-dependent methods. Using the unique properties of the IBIS coded-mask telescope, we developed a model-independent approach to study diffuse continuum emission near the Galactic plane in the 25‑60, 60‑80, and 80‑200 keV bands. The comparison of the 25‑60 keV longitude profile with the near infrared intensity shows excellent agreement, confirming the stellar origin of the Galactic Ridge X-ray Emission (GRXE). The Galactic X-ray background is significantly detected from the direction of the Galactic bulge up to 200 keV. We built broad-band spectra of the Galactic background in three large regions, the Galactic bulge and two spiral arms at l≈±20∘. The spectral analysis reveals two distinct components with a minimum at about 80 keV. The low-energy (≲60 keV) component, associated with the GRXE, is consistent with a one-dimensional accretion flow model of intermediate polars with an average white dwarf mass of about 0.7 M⊙. The high-energy part of the spectrum, dominating above ∼60 keV and attributed to the γ-ray background, is consistent with a power-law model with photon index Γ=1.55. The total 30‑80 keV flux budget of 1.5×10‑9 erg s^‑1 cm^‑2 observed within the effective IBIS field of view (≈286 deg²) in the Galactic bulge region, consists of 2/3 of GRXE and 1/3 of γ-ray background. Finally, we provide the Python code of the IBIS/ISGRI background model, which can be used to measure the X-ray intensity of the Galactic background in different parts of the Milky Way.

We search for reflection-dominated Compton-thick active galactic nuclei (CT AGN) candidates in the Lockman Hole (LH) region using the data of SRG/eROSITA LH survey. We selected sources with anomalously hard photon indices in the 0.3-8.0 keV band, untypical for Type I AGN. In particular, we required that the upper end of the 90 per cent error interval did not exceed a fiducial boundary of $\Gamma =1.3$. We found 291 sources which constitute a rare sub-population among extragalactic X-ray sources detected by eROSITA in the LH field, $\approx 5~{{\ \rm per\ cent}}$. These sources constitute the eROSITA sample of CT AGN candidates in the LH field. We further divide the sources into three categories depending on the availability of reliable redshift and statistically significant detection of intrinsic absorption. We present two catalogues: the bright sample (37 sources) and the faint one (254). We estimate the fraction and sky density of reflection-dominated CT AGN candidates. We show examples of individual spectra and use stacking analysis to search for possible redshift evolution of their properties with redshift. We analyse combined eROSITA spectra of bright sources of different categories with a physically motivated spectral model UXCLUMPY and find them fully consistent with the fits to the $\sim 1$ Ms XMM-Newton data for one of our reflection-dominated CT candidates, Type 2 galaxy SRGe J105348.6+573032. The catalogues of CT AGN candidates could be a good starting point for planning future studies and follow-ups at all wavelengths.