Astrophysics and Space Science最新文献

The imminent influx of astronomical data from upcoming ground-based all-sky surveys underscores the necessity for rapid and efficient deconvolution algorithms to mitigate atmospheric seeing effects. This paper presents three novel models that synergistically combine U-Net with an efficient transformer called Linformer and its variants. This proposed models are named as AstroLinformer (AL), AstroConvLinformer (ACL), and AstroInfoLinformer (AIL). This hybrid approach leverages the strengths of U-Net and a transformer. We get the U-Net’s proven excellence at hierarchical feature extraction and spatial reconstruction for images, perfectly complemented by the transformer’s ability to efficiently model the global context and long-range relationships that a standard U-Net struggles to capture. Our comprehensive analysis, benchmarked against several existing deep learning methods, demonstrates that the proposed models achieve better performance. Most significantly, they show a marked superiority in recovering key physical parameters of galaxies, exhibiting the lowest RMS errors in the estimation of ellipticity, Sérsic index, half-light radius, and intensity of half-light radius. The cross-data generalization tests confirm the models’ robustness to mismatched PSF and noise conditions, a critical feature for real-world applications. Although all three models performed exceptionally well, the AL model displayed notable robustness under both low and high noise conditions. This work provides a powerful and computationally efficient solution for enhancing the quality of ground-based survey data, directly benefiting high-precision science cases such as weak gravitational lensing and detailed galaxy evolution studies.

It is shown that a simple quasi–equilibrium analysis of a multi-component plasma can be harnessed to explain catastrophic energy transformations in astrophysical objects. We limit ourselves to the particular class of binary systems for which the typical plasma consists of one classical ion component, and two relativistic electron components – the bulk degenerate electron gas with a small contamination of hot electrons. We derive, analytically, the conditions conducive to such a catastrophic change. The pathway to such sudden changes is created by the slow changes in the initial parameters so that the governing equilibrium state can no longer be sustained and the system must find a new equilibrium that could have vastly different energy mix– of thermal, flow–kinetic and magnetic energies. In one such scenario, macro–scale flow kinetic, and magnetic energies abound in the final state. For the given multi–component plasma, we show that the flow (strongly Super–Alfvénic) kinetic energy is mostly carried by the small hot electron component. Under specific conditions, it is possible to generate strong macro–scale magnetic (velocity) field when all of the flow (magnetic) field energy is converted to the magnetic (velocity) field energy at the catastrophe. The analysis is applied to explain various observed characteristics of white dwarf (WD) systems, in particular, of the magnetic and dense/degenerate type.

We have proposed wave modes physics to explain the power spectrum scaling in the magnetic presence of magnetic islands of the magnetopause. In the present manuscript, a model to study the role of waves in turbulence generation by taking the powerful whistler wave and weak KAW has been presented. The corresponding power spectrum, current sheet structures, and energy dissipation at magnetopause presence of magnetic islands are also analysed and discussed its relevance with observational data. This study is carried out numerically using the pseudospectral method here, space integration for spatial integrations and finite difference method for temporal integration have been used. To understand the physics behind the field localization, we developed a semianalytical model and got the development of electron and ion scale localization. Our study enhances the understanding of the role of wave-wave interaction physics in the presence of magnetic islands and the role of multi-scale physics in turbulence generation in space plasmas.

The Megamaser Cosmology Project inferred a value for the Hubble constant given by (H_{0}=73.9 pm 3.0 ) km/sec/Mpc. This value was obtained using Bayesian inference by marginalizing over six nuisance parameters, corresponding to the velocities of the megamaser galaxy systems. We obtain an independent estimate of the Hubble constant with the same data using frequentist inference. For this purpose, we use profile likelihood to dispense with the aforementioned nuisance parameters. The frequentist estimate of the Hubble constant is given by (H_{0}=73.5^{+3.0}_{-2.9}) km/sec/Mpc and agrees with the Bayesian estimate to within (0.2sigma ), and both approaches also produce consistent confidence/credible intervals. Therefore, this analysis provides a proof-of-principle application of profile likelihood in dealing with nuisance parameters in cosmology, which is complementary to Bayesian analysis.

The present work focused on the low latitude ionospheric perturbation during the 21 June 2020 annular solar eclipse. The study is performed by using Global Navigation Satellite System (GNSS) derived total electron content (TEC) data from GNSS sites located across the annularity path. The annularity path was divided into four major regions: Africa, Arab, India and Taiwan, corresponding to morning, afternoon and evening local time. The GNSS sites are lying nearly the same eclipse magnitude/obscuration chosen for TEC analysis with two PRNs 06 & 19. The most remarkable finding is the presence of pre-eclipse enhancement in the TEC over the Indian region. The average change in TEC varies as ∼3.0-0.5 TECu (Total Electron Content Unit) during the morning (at Africa & Arab sites), ∼2.8 TECu during the afternoon (at Indian sites), and ∼3.5 TECu during the evening (at Taiwan sites). TEC derived from the COSMIC-2 satellite and global ionospheric maps (GIM) showed a maximum decrease in the evening and morning, while it was a minimum during the afternoon. The O/N₂ ratio from the GUVI payload onboard the TIMED satellite shows a significant increase of ∼12% on the eclipse day over the Indian region. Such thermosphere composition changes are suggested to be induced due to eclipse associated temperature change over the Tibetan plateau, which brought N₂ down and increased O/N₂ ratio, particularly over the Indian region. The enhanced O/N₂ ratio, in turn, enhances ionospheric electron density, thus explaining the pre-eclipse effect and minimum electron density change over the Indian region.

We formulate the dispersion relation for magnetorotational instability (MRI) in the accretion disk of a Kerr black hole, incorporating general relativistic effects and pressure anisotropy. By linearizing the general relativistic magnetohydrodynamic (GRMHD) equations in Boyer-Lindquist coordinates, we derive the MRI dispersion relation while explicitly accounting for frame-dragging effects, the gravitational potential, and the interaction between the magnetic field and the rotating plasma. Our analysis considers both toroidal and poloidal magnetic field components, allowing us to explore how different field geometries influence the MRI growth rate across three regimes corresponding to varying frame-dragging effects. The results show that the MRI growth rate is strongly influenced by plasma beta, pressure anisotropy, and the black hole spin parameter. Specifically, we find that pressure anisotropy alters the MRI dispersion relation by introducing additional instability criteria, which can either enhance or suppress MRI growth, depending on the alignment of the magnetic field components. These findings have important implications for electron acceleration in black hole accretion disks, as MRI-driven turbulence plays a key role in energy dissipation and particle energization. Our results provide a theoretical foundation for understanding plasma instabilities in relativistic accretion flows and their impact on high-energy astrophysical phenomena.

We aim to investigate an accretion disk (AD) temperature profile of a doubly lensed quasar SBS 1520+530. Temperature profiles of accretion disks are known to be diagnostic of many of the physical properties of AGNs and quasars. Our approach involves application of the photometric reverberation mapping to the light curves of SBS 1520+530 obtained in the Johnson-Cousins (V) and (R) filters. The RM method implies that the time shift between the light curves taken in different spectral ranges determines the light travel time between the AD zones with different physical conditions. In determining the time shifts, we applied a method based on some useful properties of the orthogonal polynomials. The variations in filter (R) lag those in filter (V), with 1.25±0.63 days for the inter-band time shift averaged between the two image components and over the three seasons. The obtained time lag noticeably exceeds the value following for SBS 1520+530 from the classical model of optically thick geometrically thin AD. We considered two possible ways to resolve the discrepancy between the theory and observations. The first assumes an AD temperature profile flatter than the classical one. The second way is to consider an extended optically thick scattering envelope originated due to matter outflow from an AD interior. Both explanations may be consequences of the super-Eddington accretion in SBS 1520+530. Using bolometric luminosity estimates available for SBS 1520+530 from the literature, we obtained a value of (approx 3.4) for the Eddington ratio, which indeed indicates a moderately super-Eddington accretion regime.

We study the mechanisms of energy transfer and coronal formation in the accretion disks of neutron star (NS) remnants from neutron star-neutron star (NS-NS) collisions. Using magnetohydrodynamic (MHD) simulations with relativistic corrections to plasma inertia and quantum electrodynamics (QED) corrections to magnetic energy, we investigate the interplay of magnetic pressure, plasma pressure, and high-frequency Alfvén waves in the energy transit from the relativistic chromosphere to the non-relativistic corona. It shows that kinetic energy becomes important in the corona, preserving its dynamic structure and high temperatures, even though magnetic energy predominates in the chromosphere and is amplified by vacuum-polarization effects, driving energy transfer through Alfvén waves. Efficient energy redistribution is made possible in the transition region through wave-particle interactions and energy loss. These results improve our understanding of the dynamics of accretion disks in NS remnants and their function in the maintenance of high-energy astrophysical phenomena.

One of the most powerful evidence for the Big Bang theory is the prediction of the primordial abundances of the elements by the Big Bang Nucleosynthesis (BBN) theory. The BBN theory in its standard formulation is a parameter-free theory, with the precise knowledge of the baryon-to-photon ratio of the Universe, obtained from studies of the anisotropies of cosmic microwave background radiation. The theoretical abundances of light elements during primordial nucleosynthesis and those determined from observations are in good agreement throughout a range of nine orders of magnitude. However, there is still a significant difference of the ⁷Li abundance, overestimated by a factor of ∼ 2.5 when calculated theoretically. In the present work we will consider the nucleosynthesis process in the framework of the Weyl-type f(Q,T) theory, a modified gravity theory representing an extension of the f(Q) and f(Q,T) type theories, obtained under the assumption that the scalar non-metricity Q of the space-time is expressed in its standard Weyl form. Hence, the nonmetricity of the spacetime is fully determined by a vector field (w^{mu }). The theory can give a good description of the observational data, and of the evolution of the late-time Universe. We show that in some parameter ranges the Lithium abundance can be explained, and these ranges have a relatively weak dependence on the initial value of the Weyl vector.

After my paper “Perihelion precession in non-Newtonian central potentials” on Astrophysics and Space Science was accepted, it was brought to my attention that the simplest case (s=2), for was missing. As this provides a simple illustration of the methodology employed throughout the rest of the paper, it is provided here for completeness.