Ulugh Beg Astronomical Institute

Mountain reservoirs in steep terrain face geomorphic, hydrological, and development pressures, yet vulnerability maps can be hard to interpret in terms of drivers. An ecological vulnerability index (EVI) is developed for the Charvak Reservoir basin (Uzbekistan) from three subindices: topographic–geological risk index (TGRI; slope, lithological resistance, soil organic carbon, and distance to active faults), hydrological–ecological risk index (HERI; shoreline proximity and normalized difference water index (NDWI) trend risk, excluding the trend term in a nearshore band to reduce shoreline artifacts), and climatic–anthropogenic risk index (CARI; trends in the normalized difference vegetation index [NDVI], normalized difference built-up index [NDBI], and land surface temperature [LST], plus proximity to infrastructure). May–August Landsat Collection 2 composites (2000–2023) yield trends; indicators are scaled to 0–1 and aggregated using analytic hierarchy process (AHP) weights. Hotspots cluster on reservoir-facing slopes and access valleys; the subindices separate topographic controls from shoreline and corridor pressures. Changes in 2018–2023 show limited class transitions, whereas a 2030 scenario (extrapolated NDVI/NDBI plus shoreline and infrastructure stressors) increases high–very high vulnerability by ~39 km2 (~3.2 percentage points), mainly in shoreline belts and development corridors. The framework supports zoning and planning in reservoir basins.

Abstract Relativistic reflection is a common feature in the X-ray observations of accreting compact objects. We present reflux , a new X-ray reflection model for spectral analysis of super-Eddington sources. We develop two relativistic reflection frameworks for super-Eddington accretion: a slim-disk model that self-consistently accounts for disk thickening and self-shadowing and an optically thick wind model that treats reflection off a funnel-shaped outflow. The slim-disk model offers a geometry where the inner disk thickness is proportional to radius, becoming thicker as the mass accretion rate increases. The wind model measures the opening angle of the funnel, the wind speed, and wind acceleration radius. The slim-disk profile reduces the brightness of the blue horn in the Fe K emission line for a fixed emissivity and significantly changes the intensity profile for a lamppost geometry. The wind model shows a blueshifted iron line due to high-velocity outflows. Both models assume a spherically symmetric spacetime. We apply the wind model to the XMM-Newton spectrum of the tidal disruption event Swift J1644+57, where the Fe K profile is expected to be shaped by scattering in an outflowing funnel. We constrain the opening angle of the funnel and find a high velocity of the wind.

This study introduces an innovative geospatial approach for monitoring seasonal geodynamic activity and seismic hazard in the Charvak Reservoir region of northeastern Uzbekistan an area characterized by inherited fault systems, frequent shallow earthquakes, and cyclic hydrological loading. Unlike previous studies that assess deformation using long-term seismicity or single-period imagery, this work integrates multi-temporal satellite remote sensing (Landsat-8), automated GIS-based lineament analysis, directional statistics, historical seismicity (1955–2024), and monthly water volume records. Lineament extraction was performed for three hydrological phases in 2024 March (low water), July (peak water), and September (drawdown) to capture the structural response to seasonal stress fluctuations. Results reveal a marked increase in lineament density during and after the peak water phase, particularly near active fault zones. Orientation patterns remained stable (NE–SW, E–W), aligning with regional tectonics, while density shifts indicated dynamic stress redistribution. Spatial overlay with seismic epicenters confirmed a strong correspondence between high-density lineament zones and localized deformation. Based on these multi-source indicators, five geodynamically active subzones were delineated, with the highest hazard concentration in the North Pskem and Kumbel-Kokand sectors. The key contribution of this study lies in applying a seasonal, lineament-based deformation monitoring framework previously untested in the Charvak region which enhances the understanding of reservoir-induced stress responses and provides a transferable model for georisk management in tectonically complex hydrosystems.

Abstract We present multiband observations and analysis of EP240801a, a low-energy, extremely soft gamma-ray burst (GRB) discovered on 2024 August 1 by the Einstein Probe (EP) satellite with a weak contemporaneous signal also detected by the Fermi Gamma-ray Burst Monitor (GBM). Optical spectroscopy of the afterglow, obtained by Gran Telescopio Canarias and Keck, identified the redshift of z = 1.6734. EP240801a exhibits a burst duration of 148 s in X-rays and 22.3 s in gamma rays, with X-rays leading by 80.61 s. Spectral lag analysis indicates that the gamma-ray signal arrived 8.3 s earlier than the X-rays. Joint spectral fitting of EP Wide-field X-ray Telescope and Fermi/GBM data yields an isotropic energy E γ , iso = ( 5.5 7 − 0.50 + 0.54 ) × 1 0 51 erg , a peak energy E peak = 14.9 0 − 4.71 + 7.08 keV , and a fluence ratio S(25–50 keV)/S ( 50 – 100 keV ) = 1.6 7 − 0.46 + 0.74 , classifying EP240801a as an X-ray flash (XRF). The host-galaxy continuum spectrum, inferred using Prospector, was used to correct its contribution for the observed outburst optical data. Unusual early R-band behavior and EP Follow-up X-ray Telescope observations suggest multiple components in the afterglow. Three models are considered: a two-component jet model, a forward-reverse shock model, and a forward shock model with energy injection. All three provide reasonable explanations. The two-component jet model and the energy injection model imply a relatively small initial energy and velocity of the jet in the line of sight, while the forward-reverse shock model remains typical. Under the two-component jet model, EP240801a may resemble GRB 221009A (BOAT) if the bright narrow beam is viewed on-axis. Therefore, EP240801a can be interpreted as an off-beam (narrow) jet or an intrinsically weak GRB jet. Our findings provide crucial clues for uncovering the origin of XRFs.

Investigation of dynamical and physical properties of the main-belt and near-Earth asteroids is a priority research area, which has reached a new level in recent years. This progress has been facilitated by space missions to asteroids as well as modern all-sky surveys aimed to discover new objects which also provide highly accurate astrometric and photometric data. However, the role of ground-based programs remains valuable. The long-term monitoring program is crucial for retrieving asteroid physical properties and its evolution. The primary aim of our Project is obtaining new observational data of asteroids by carrying out their spectrophotometric (Shevchenko et al. 2022) and polarimetric (Belskaya, Krugly 2024) observations which allow us to determine absolute magnitudes, rotation periods, surfaces properties, albedo, sizes and shapes of these objects. Our observations are based on cooperation with colleagues from different observatories in several countries (Bulgaria, Georgia, Kazakhstan, Slovakia, Uzbekistan, Chili, USA) with using the 0.6 - 2 m telescopes which are equipped with modern CCD cameras. Our priority targets include newly discovered and potentially hazardous near-Earth asteroids, binary asteroids, especially those observed by Gaia, objects studied through radar observations, and targets of ongoing and future space missions (Hayabusa2#, Hera etc). During January-April 2025, new photometric observations of over 40 NEAs (4 newly discovered, 17 PHAs, for 18 the rotation periods were determined for the first time) and 8 known main-belt binary asteroids were carried out, as well as polarimetric observations of 2 NEAs were obtained at high phase angles. Preliminary results of our new and long-term observations will be presented. AcknowledgmentsThe Kharkiv team is thankful to Ukrainian soldiers who defend our lives and freedom against russian aggression. YK thanks the French PAUSE program for its support of scientists at risk. ReferencesShevchenko, V. G., I. N. Belskaya, I. G. Slyusarev, O. I. Mikhalchenko, Yu. N. Krugly et al. 2022. Kharkiv database of asteroid absolute magnitudes: Comparative analysis with other datasets. 2022A&A...666A.190S Belskaya I., Y. Krugly. 2024. Study of near-Earth asteroids by polarimetric technique. Report on “EU-ESA Workshop on Size Determination of Potentially Hazardous Near-Earth Objects”, 11–13 Nov 2024, Darmstadt, Germany.

Abstract This study explores the dynamics of charged Hayward black holes, focusing on the effects of electric charge and the length factor on accretion disk characteristics. Our results show that increasing both parameters reduces the size of the event horizon and innermost stable circular orbits (ISCO) radius, with the electric charge exerting a more pronounced influence. Additionally, the length factor and electric charge can effectively replicate the spin of a Kerr black hole. Both parameters also affect the electromagnetic radiation emitted from the accretion disk, increasing the flux, temperature, and radiative efficiency. The peak radiation occurs in the soft x-ray band, with higher values of electric charge and length factor enhancing disk luminosity and shifting the peak to higher frequencies. These findings can offer valuable insights into the accretion processes around black holes and their observable signatures, particularly in x-ray astronomy.

Three light curves of the V1059 Cep eclipsing binary obtained in 2012, 2013 and 2021 were analyzed. We found the rapid apsidal motion in this system at the ratedw/dt= 7.2°per year. Assuming the equality of observed and theoretical apsidal motion rates we estimated physical characteristics of the components based on the data on their temperatures from the literature. According to our calculations the components are two very similar stars of the B7 V–B7.5 V spectral type with masses≈(3.4 ± 0.3)M⊙and age 180 ± 30 million years.