Search Results (269)

In this work, the light curve of the Seyfert galaxy Mrk 6 constructed from photometric observations in the B, V, and $R_{\mathrm{c}}$ filters over the period from 5 April 2016 to 1 February 2026 is presented and analyzed. Over the entire monitoring interval (2016–2026), the variability amplitude of the light curve reaches $\mathrm{\Delta }B=1.9$ mag, $\mathrm{\Delta }V=1.5$ mag, and $\mathrm{\Delta }{R}_{\mathrm{c}}=1.4$ mag. During 2024–2026, the galaxy exhibits synchronous photometric variability in the B, V, and $R_{\mathrm{c}}$ filters with an amplitude of ∼0.3 mag. The study also uses spectroscopic observations obtained on 15 and 22 November 2025 and 16 February 2026 at the Shamakhy Astrophysical Observatory (Azerbaijan), as well as on 9 January 2026 at the Fesenkov Astrophysical Institute (Kazakhstan). The fluxes in the H$\beta$ emission line were calibrated using the [O III] $\lambda 5007$ Å line, ensuring consistent relative calibration of the spectral data. A comparison of the optical spectra reveals a pronounced transformation of the H$\beta$ line profile between November 2025 and January 2026. The broad component, clearly present in November 2025, becomes strongly suppressed and nearly disappears in January 2026, while the narrow emission lines remain stable. This behavior is consistent with a changing-look transition, indicating a temporary weakening of the broad-line region emission. The radius of the broad-line region $R_{\mathrm{BLR}}$ was taken to be equal to the average time delays (lags), amounting to ≈20 light days for the H$\beta$ emission and ≈28 light days for the H$\alpha$. Full article

Human diseases are complex and arise from the coordinated action of multiple genes and their protein products. Genes’ behaviors extend beyond genetic variants, mutations, and differential expressions. Their coordinated activity across biological scales (molecules, cells, tissues, organs) produces emergent behaviors that shape health and disease. These emergent behaviors span time and space and are often hard to measure directly from observation when using standard experimental measurements. Yet these “hidden” or latent gene characteristics can be powerful drivers of disease. We propose a Mini-Galaxy Model (MGM), a systems-level AI-driven network framework that models cells as “mini-galaxies” composed of multilayered biological information, with each layer encoding a different dimension of genes’ behavior. Here, we delineate a strategy on how to construct and compare MGMs across health and disease and map their etiological relatedness. We also operationalize the MGM as a discovery platform for translational medicine, offering modules to allow target prioritization and editing. By reframing human diseases as the result of emergent behavior of multilayered multimode biological networks and their perturbations, the MGM yields actionable rules to streamline biomarker discovery, guide target selection and enable rational design of combinatorial interventions, and accelerate drug repurposing. Full article

Wearable device-based Human Activity Recognition (HAR) is widely used in health management, rehabilitation, and personal safety. While contemporary HAR research effectively classifies a wide range of discrete activities, there remains a significant gap in organizing these heterogeneous motions into a structured intensity framework suitable for continuous risk assessment. Furthermore, many high-performing models rely on computationally intensive architectures that hinder real-time deployment on resource-constrained wearables. We propose an on-device method for estimating five-level activity intensity in real time using only accelerometer signals from a commercial smartwatch. To bridge the gap between simple identification and intensity modeling, 13 dynamic and emergency-like wrist motions were integrated with 11 daily activities from the PAMAP2 dataset, yielding 21 activities mapped onto an ordinal five-level intensity scale. A finetuned Multi-Layer Perceptron (MLP) classifier trained on this integrated dataset achieved 0.939 accuracy and a quadratic weighted kappa (QWK) of 0.971. The model was deployed on a Galaxy Watch 7, achieving $<1$ ms inference latency and a size $<0.1$ MB, confirming real-time feasibility. This approach demonstrates that organizing diverse activities into a lightweight, intensity-aware framework provides a robust foundation for safety-aware monitoring systems under real-world, on-device constraints. Full article

We have used long observations of galaxy clusters obtained with the Rossi X-ray Timing Explorer to search for the 3.55 keV line from sterile neutrino decay. If a lepton-number asymmetry exists in one or more types of active neutrinos in the early Universe, sterile neutrinos can be produced via the Shi–Fuller mechanism. The data consist of 11 clusters observed for a total of 3.1 megaseconds using the Proportional Counter Array. A 2.5$\sigma$ excess of emission over a thermal model is found over the energy span of the 3.55 keV line in the combined spectra of the eight clusters that individually have an excess. These residuals are added to increase the signal to noise ratio of the excess, which is then modeled with a Gaussian to simulate the instrumental spectral response. We find a significant correlation (r = 0.76) for a line centered at 3.6 keV with a model flux of 3.07 × 10⁻⁵ ph cm⁻² s⁻¹. Mixing angle for detected clusters ranges from 2.0 to 21.6 × 10⁻¹⁰. The decay rate inferred from the line flux is strongly correlated (r = 0.87) with cluster temperature, which is due to hotter, more massive clusters having a larger amount of dark matter. Approximately half of the total flux comes from the Coma cluster. The mixing angle for Coma is calculated to be 6.2 × 10⁻¹⁰. We fit the Coma cluster spectrum with two different three-component models. The first includes a Gaussian fixed at 3.55 keV to model soft emission. The flux of the Gaussian is 5.6 × 10⁻¹² ph cm⁻² s⁻¹ or 1.3% of the total flux. The second three-component model uses a second thermal component to model soft emission. This model gives a temperature of 0–17 keV for the second thermal component and a lower temperature for the hot component. This indicates that the second thermal component is modeling high-energy residuals rather than low ones, where the Gaussian is. Though our line fluxes exceed most reported detections and upper limits, they do not overproduce the dark matter. We conclude that some fraction of the marginally detected excess could be attributed to the decay line since low-temperature thermal emission and systematics fail to model it completely. Full article

We present a comprehensive study of host galaxies of radio sources within the 1.35$R_{200}$ of the Coma cluster by combining deep $144\mathrm{MHz}$ observations from the LOFAR Two-Metre Sky Survey (LoTSS-DR2) with optical spectroscopy and photometry from DESI and SDSS. We identify 79 spectroscopically confirmed cluster members with reliable radio emission and classify them into compact, extended, and tailed subsamples according to their radio morphologies. By combining their radio and optical properties, we find compact radio sources are predominantly associated with massive, quiescent galaxies driven by $\mathrm{AGN}$ activity, while tailed sources are largely hosted by star-forming galaxies, tracing ongoing ram pressure stripping ($\mathrm{RPS}$). Using phase-space analysis and a projected infall time proxy ($d_R$), we find that extended sources are preferentially located in the cluster outskirts ($d_R>1$), while tailed sources are concentrated in the intermediate infall region ($0.4<d_R<1.0$), highlighting the influence of the dense intracluster medium. Full article

In this work we test the possibility of accounting for the positron anomaly with annihilating dark matter particles without contradicting the gamma-ray constraints due to their unconventional space distribution. To achieve that, we consider two-component dark matter, whose major constituent is inert and forms the halo of the Galaxy, while the second, minor, component consists of annihilating particles that could form some different structure. This work is the next logical step after our previous “dark disk model” where an active DM component was considered to form a disk, allowing good suppression of accompanying gamma-radiation. Nowadays that model is not enough to avoid the contradiction, so we are testing a new, more complex one with a spiral spatial distribution like the one of baryons. We have previously tested two simplified toy models of ring-like density profiles and one simple spiral density profile that have shown good improvement compared to the disk case. In this work, we take things further and consider a more physically grounded density profile constructed on the base of a modern model of the baryon density of our Galaxy. Contrary to our expectations, this advanced model shows much worse agreement with the data than previous toy models. Full article

We present a study of the linear polarization properties of radio sources within the 10 deg². Wide Chandra Deep Field South (W-CDFS) in S-band (2–4 GHz). Our W-CDFS image has an angular resolution of 15 arcsec and a 1$\sigma$ RMS in Stokes I of ≈50 $\mathsf{\mu }$Jy/beam. We detect 1920 distinct source components in Stokes I and 175 in linear polarization. We examine the polarized source counts, Faraday Rotation measures, and fractional polarization of the sources in the survey. We show that sources with a total intensity above ≈10 mJy have a mean fractional polarization value of ≈3% from modeling the polarized counts. We also calculate an estimate for the limit on the fractional polarization level of sources with a total intensity below 1 mJy (mostly star-forming galaxies) of ≲3% using stacking. The mean Faraday Rotation we measure is consistent with that due to the Milky Way. We also show that fractional polarization is correlated with in-band spectral index, consistent with a lower mean fractional polarization for the flat-spectrum population. In addition to characterizing the S-band polarization properties of sources in the W-CDFS, this study will be used to validate the shallower, but higher angular resolution S-band polarimetric information that the VLA Sky Survey will provide for the whole sky above Declination −40 degrees over the next few years. Full article

Objective: We examine whether a finite-range scalar–tensor modification of gravity can be simultaneously compatible with cosmological background data, galaxy rotation curves, and local/astrophysical consistency tests, while satisfying the luminal gravitational-wave propagation constraint ($c_T=1$) implied by GW170817 at low redshifts. Methods: We formulate the model at the level of an explicit covariant action and derive the corresponding field equations; for cosmological inferences, we adopt an effective background closure in which the late-time dark-energy density is modulated by a smooth activation function characterized by a length scale $\lambda$ and amplitude $ϵ$. We constrain this background model using Pantheon+, DESI Gaussian Baryon Acoustic Oscillations (BAOs), and a Planck acoustic-scale prior, including an explicit $\Lambda$CDM comparison. We then propagate the inferred characteristic length by fixing $\lambda$ in the weak-field Yukawa kernel used to model 175 SPARC galaxy rotation curves with standard baryonic components and a controlled spherical approximation for the scalar response. Results: The joint background fit yields ${\Omega }_m=0.293\pm 0.007$, $\lambda =7.{69}_{-1.71}^{+1.85}$$\mathrm{Mpc}$, and $H_0=72.33\pm 0.50$$\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$. With $\lambda$ fixed, the baryons + scalar model describes the SPARC sample with a median reduced chi-square of ${\chi }_{\nu }^2=1.07$; for a 14-galaxy subset, this model is moderately preferred over the standard baryons + NFW halo description in the finite-sample information criteria, with a mean $\Delta$AICc outcome in favor of the baryons + scalar model (≈2.8). A Vainshtein-type screening completion with $\Lambda =1.3\times {10}^{-8}$ eV satisfies Cassini, Lunar Laser Ranging, and binary pulsar bounds while keeping the kpc scales effectively unscreened. For linear growth observables, we adopt a conservative General Relativity-like baseline (${\mu }_0=0$) and show that current $f{\sigma }_8$ data are consistent with ${\mu }_0\simeq 0$ for our best-fit background; the model predicts $S_8=0.791$, consistent with representative cosmic-shear constraints. Conclusions: Within the present scope (action-level weak-field dynamics for galaxy modeling plus an explicitly stated effective closure for background inference), the results support a mutually compatible characteristic length at the Mpc scale; however, a full perturbation-level implementation of the covariant theory remains an issue for future work, and the role of cold dark matter beyond galaxy scales is not ruled out. Full article

The gravitational wave event GW190521 seems to be the only BH merger event possibly correlated with an electromagnetic counterpart, which appeared about 34 days after the GW event. This work aims to confirm that the electromagnetic bump towards the Active Galactic Nucleus (AGN) J1249+3449 can be explained within the framework of the gravitational microlensing phenomenon. In particular, considering the data of the Zwicky Transient Facility (ZTF), what emerges from a detailed analysis of the observed light curve using three fitting models (Point Source Point Lens, Finite Source Point Lens, Uniform Source Binary Lens) is that the optical bump can be explained as a microlensing event caused by a lens with mass $\sim$0.1 $M_{\odot }$, lying in the host galaxy of the AGN in question. Full article

The study of high-redshift active galactic nuclei (AGN) and their small-scale environment is necessary to investigate the different processes that control and influence the evolution of massive galaxies. In this paper we present a case study of cid_1253 ($z=2.15$) and its companion galaxy using archive CO(3–2) and 340 GHz continuum observations with the Atacama Large Millimeter/submillimeter Array, supplemented by multi-wavelength photometry. Previous studies treated the system as a whole, without separating its components in order to match large-beam infrared observations. Our goal is to study cid_1253 and its companion separately by re-analysing the available archive data of the system. Based on our analysis, the companion galaxy is not only more gas-rich ($M_{{\mathrm{H}}_2}\sim {10}^{11}{\mathrm{M}}_{\odot }$) but also has a higher dust mass, indicative of obscured star formation. Moreover, as cid_1253 is not detected at 340 GHz, it is possible that a large fraction of the unresolved, Herschel-detected infrared emission is associated with the companion, rather than cid_1253. The presented case study highlights the need to be more cautious with blended sources before drawing our conclusions and the necessity of high-resolution observations. Full article

We present the results of long-term photometric and spectroscopic monitoring of the Seyfert galaxy NGC 4151 based on new observational data complemented by archival material spanning several decades. NGC 4151 is one of the most extensively studied active galactic nuclei, exhibiting pronounced variability in both optical continuum and emission-line fluxes, which makes it a key object for investigating physical processes in the central engine and the broad-line region. Our study covers the optical and near-infrared wavelength ranges, including the Ic band and the standard BVRc photometric filters. Using multi-band optical photometry and optical spectroscopy, we construct light curves of the continuum and emission lines and perform a comparative analysis of their temporal behavior during different activity states of the galaxy. The analysis focuses on variability amplitudes, long-term trends, and correlations between photometric and spectral characteristics, allowing us to examine the relationship between continuum variations and the line-emitting regions. Full article

Despite several efforts to investigate the accretion disk and torus, near-simultaneous broadband studies of the nuclear regions of radio-quiet AGNs remain lacking. NGC 4151, one of the closest and brightest Seyfert galaxies, provides an excellent laboratory for probing the circum-nuclear regions of AGNs. A detailed, near-simultaneous broadband spectral study of NGC 4151 is carried out during one of its historic minimum activity states, using archival data from the Ultraviolet (UV) to the Infrared (IR) regions. We used the radiative transfer code SKIRT to model the source and to constrain the properties of the torus. We found that the observed broadband spectral energy distribution is best explained by a two-torus geometry with a polar conical shell structure. Full article

Perseus A (3C 84), a powerful radio source located at the centre of the giant elliptical galaxy NGC 1275—classified as a Seyfert type II AGN and the dominant member of the X-ray bright Abell 426 cluster–exhibits radio emission variability over a wide range of timescales, from decades to hours. This study investigates intraday variability (IDV) in the 6.5 GHz radio emission of 3C 84 using the RT-32 radio telescope in Zolochiv, Ukraine. A novel low-amplitude azimuthal scanning method enabled quasi-simultaneous measurements of antenna and system temperatures, allowing for separation of intrinsic source variations from propagation effects. During an observation session in August 2021, a burst with a peak intensity of 13.5 Jy above the background was detected, likely corresponding to a Fast Radio Burst (FRB). Additionally, quasi-periodic low-amplitude variations with timescales from 0.3 to 6 h were observed. These fluctuations correlate strongly with local atmospheric changes, such as dew formation on the telescope structure, and, to a lesser extent, with ionospheric acoustic–gravity waves. The findings highlight the importance of accounting for propagation conditions when interpreting short-timescale radio variability in AGNs and suggest the need for multi-station, multi-frequency monitoring campaigns to distinguish between intrinsic and environmental modulation of AGN flux densities. Full article

We review some aspects of accretion disks physics, spacetime photon shell and photon orbits, related to retrograde (counter-rotating) motion in Kerr black hole (BH) spacetimes. In this brief review, we examine the counter-rotating components of the Kerr BH shadow boundary, under the influence of counter-rotating accretion tori, accreting flows and proto-jets (open critical funnels of matter, associated with the tori) orbiting around the central BH. We also analyze the redshifted emission arising from counter-rotating structures. Regions of the shadows and photon shell are constrained in their dependence of the BH spin and observational angle. The effects of the counter-rotating structures on these are proven to be typical of the fast-spinning BHs, and accordingly can be observed only in the restricted classes of the Kerr BH spacetimes. This review is intended as a concise guide to the main properties of counter-rotating fluxes and counter-rotating disks in relation to the photon shell and the BH shadow boundary. Our findings may serve as the basis for different theoretical frameworks describing counter-rotating accretion flows with observable imprints manifesting at the BH shadow boundary. The results can eventually enable the distinction of counter-rotating fluxes through their observable imprints, contributing to constraints on both the BH spin and the structure of counter-rotating accretion disks. In particular, photon trajectories and their impact parameters can manifest in the morphology of the BH shadow. Such features, when accessible through high-resolution imaging and spectral or polarization measurements, could provide a direct avenue for testing different theoretical models on accretion disk dynamics and their BH attractors. Full article

Measuring supermassive black hole (SMBH) masses is fundamental to understanding active galactic nuclei (AGN) and their coevolution with host galaxies. Among existing techniques, H₂O megamaser observations with Very Long Baseline Interferometry (VLBI) provide the most direct and geometric determinations of SMBH masses by tracing molecular gas in sub-parsec Keplerian disks. Over the past two decades, the Megamaser Cosmology Project (MCP) has surveyed thousands of nearby AGNs and obtained high-sensitivity VLBI maps of dozens of maser disks that lead to accurate SMBH masses with uncertainties typically below 10%. In this paper, we present a comprehensive review that summarizes the essential elements required to obtain accurate black hole masses with the H₂O megamaser technique—including the physical conditions for maser excitation, observational requirements, disk modeling, and sources of SMBH mass uncertainty—and we discuss the implications of maser-based measurements for exploring SMBH demographics. In particular, we will show that maser-derived black hole masses, largely free from the systematic biases of stellar or gas-dynamical methods, provide critical anchors at the low-mass end of the SMBH population (M_BH∼10⁷M_⊙), and reveal possible deviations from the canonical M_BH–σ_∗ relation. With forthcoming spectroscopic surveys and advances in millimeter/submillimeter VLBI, the maser technique promises to extend precise dynamical mass measurements to both larger local samples and high-redshift galaxies. Full article