Sazuna/UAT_keywords huggingface dataset:
Effect of Initial Current Sheet and Stratification on Reconnection and Coronal Heating. Understanding the mechanisms behind fast magnetic reconnection and subsequent plasma heating is essential to explain the temperatures of a few million kelvin observed in the solar corona. This study investigates the influence of initial current sheet width and stratification on the reconnection process and coronal temperature within a large-scale magnetohydrodynamics framework. Additionally, it further addresses the contribution of small- to large-scale dynamics through the Hall term. Using numerical simulations, we demonstrate that even modest reductions in the initial current sheet width significantly speed up the reconnection process, yielding faster rates of temperature rise and achieving high peak values without requiring external fluctuations. Moreover, introducing a dependence on scale height in the initial coronal magnetic field and density profiles enhances reconnection rates and temperature increases. We also observe earlier evolution of fast reconnection with narrower current sheets and shorter scale heights, resulting in a more frequent formation of magnetic islands and X-points that evolve dynamically over time. Under these initial settings, the Hall term's curl is amplified by three orders of magnitude, reaching 1% of the characteristic scale required to influence large-scale dynamics and offering insight into the multiscale interactions essential for coronal heating processes. This study underscores the significance of minor adjustments in initial conditions for enhancing magnetic reconnection, coronal heating, and amplifying the Hall term's influence on large-scale dynamics.

Keywords: Magnetohydrodynamics, Solar coronal heating, Solar magnetic reconnection
Probing Large-scale Structures with the Two-point Function and the Power Spectrum: Insights into Cosmic Clustering Evolution. Understanding the large-scale structure of the Universe requires analyses of cosmic clustering and its evolution over time. In this work, we investigate the clustering properties of Sloan Digital Sky Survey blue galaxies, which are excellent tracers of dark matter, along two distinct epochs of the Universe, utilizing estimators like the two-point angular correlation function (2PACF), the angular power spectra, among others. Considering a model-independent approach, we perform analyses in two disjoint redshift shells, 0 ≤ z &lt; 0.06 and 0.06 ≤ z &lt; 0.12, to investigate the distribution of large cosmic structures. Using Bayesian inference methods, we constrain the parameter that quantifies the galaxy clustering in the 2PACF, enabling us to perform comparisons among different regions on the sky and between different epochs in the Universe regarding the gravitational action on matter structures. Our analyses complement previous efforts to map large-scale structures in the Local Universe. In addition, this study reveals differences regarding the clustering of large cosmic structures, comparing two epochs of the Universe, and analyses done with diverse estimators. Results reveal, clearly, distinct evolutionary signatures between the two redshift shells. Moreover, we had the opportunity to test the concordance cosmological model under extreme conditions in the highly nonlinear Local Universe, computing the amplitude of the angular power spectrum at very small scales. Ultimately, all our analyses serve as a set of consistency tests of the concordance cosmological model, the ΛCDM.

Keywords: Observational cosmology, Cosmic web, Large-scale structure of the universe
A New Precise Measurement of the Cosmic Microwave Background Radiation Temperature at z = 0.89 toward PKS1830─211. In this study, we analyzed millimeter-wave data toward the quasar PKS1830─211 observed with the Atacama Large Millimeter/submillimeter Array to obtain absorption spectra of HCN J = 2─1, J = 3─2, J = 4─3, and J = 5─4 lines at the cosmological redshift of z = 0.89. We confirmed multiple absorption components in each spectrum, and the two lower-J lines are highly saturated at the velocity centers of the two most prominent components. The effect of uncertainty in the continuum covering factor was carefully assessed using a Monte Carlo approach. We also accounted for systematic uncertainties in the HCN J = 4─3 and J = 5─4 absorption due to time variability during an intense flaring event of the quasar. Assuming local thermodynamic equilibrium and neglecting molecular collisions, we derived the excitation temperature profiles and their uncertainties in the optically thin regime. We determined the cosmic microwave background radiation temperature at z = 0.89 to be 5.13 ± 0.06 K by taking a weighted average of calculated excitation temperatures; this is highly consistent with that expected from the standard model of the Universe.

Keywords: Interstellar medium, Cosmic microwave background radiation, Observational cosmology, Quasar absorption line spectroscopy
HeXCor: A Hybrid Magnetic Flux-rope Model of Coronal Mass Ejections Combining In Situ Measurements with Remote Sensing Observations. This paper presents Heliospheric conneXions for Coronal mass ejections (HeXCor), a new coronal mass ejection (CME) flux rope (FR) reconstruction model that combines the geometry of the graduated cylindrical shell (GCS) model, defined from remote sensing imagery, with a modified cylindrical magnetic field solution inferred from in situ data. The usage of synergistic remote sensing and in situ data allows HeXCor to reconstruct an advanced magnetic FR model of CMEs with both global 3D geometry and internal magnetic field defined. The model is validated with four case studies of Earth-affecting CMEs from 2010 to 2014 observed in the corona by Solar and Heliospheric Observatory and Solar TErrestrial RElations Observatory's spacecraft with large separation angles. It is shown that the in situ fitting capability is comparable to traditional cylindrical fittings while uniquely providing global structural context. The model also uniquely defines both the poloidal and toroidal impact parameters to fully describe the characteristics of CME impacts. Two of the events (2012 July 12 and 2011 March 25 CMEs) are found to follow the basic assumptions of radial and self-similar expansion from the Sun to Earth, while the other two (2010 May 23 and 2013 April 11 CMEs) likely experience deflection in the propagation direction and change in axial orientation. These results demonstrate how HeXCor provides a realistic and informative CME model that is comprised of accurate 3D global geometry with internal magnetic fields.

Keywords: Solar storm, Ejecta, Interplanetary magnetic fields, Solar coronal mass ejections
Chandra Large Project Observations of the Supernova Remnant N132D: Measuring the Expansion of the Forward Shock. We present results from the Chandra X-ray Observatory Large Project (878 ks in 28 observations) of the Large Magellanic Cloud supernova remnant N132D. We measure the expansion of the forward shock in the bright southern rim to be  0.″10±0.″02  over the ∼14.5 yr baseline, which corresponds to a velocity of 1620 ± 400 km s−1 after accounting for several instrumental effects. We measure an expansion of  0.″23±0.″02  and a shock velocity of 3840 ± 260 km s−1 for two features in an apparent blowout region in the northeast. The emission-measure-weighted average temperature inferred from X-ray spectral fits to regions in the southern rim is 0.95 ± 0.17 keV, consistent with the electron temperature implied by the shock velocity after accounting for Coulomb equilibration and adiabatic expansion. In contrast, the emission-measure-weighted average temperature for the northeast region is 0.77 ± 0.04 keV, which is significantly lower than the value inferred from the shock velocity. We fit 1D evolutionary models for the shock in the southern rim and northeast region, using the measured radius and propagation velocity into constant density and power-law profile circumstellar media. We find good agreement with the age of ∼2500 yr derived from optical expansion measurements for explosion energies of 1.5─3.0 × 1051 erg, ejecta masses of 2─6 M⊙, and ambient medium densities of ∼0.33─0.66 amu cm−3 in the south and ∼0.01─0.02 amu cm−3 in the northeast assuming a constant density medium. These results are consistent with previous studies that suggested the progenitor of N132D was an energetic supernova that exploded into a preexisting cavity.

Keywords: Supernova remnants, Plasma astrophysics, Interstellar medium
Tidal Disruption of Super Star Clusters as the Origin of Bluish Light at the Inner Region of the Perseus Cluster Central Galaxy. Relatively blue light extends beyond a spiral disk from a radius of ∼5 kpc out to ∼14 kpc from the center of NGC 1275. Analyses of its spectrum and broadband colors reveal a population of young stars having subsolar metallicities superposed on a dominant population of old stars having supersolar metallicities. The young stars have a characteristic age of ∼160 Myr and may span ages of a few hundred Myr, similar to that of stars comprising the central spiral disk, and a total mass of about one-third that of this disk for a combined stellar mass (at birth) of ∼4 × 109 M⊙. A multitude of arc-like features embedded in the extended blue light have brightnesses comparable to the somewhat older (∼500 Myr) super star clusters (SSCs) projected against the central spiral disk. The SSCs have a relatively shallow mass function, suggesting that the tidal disruption of an initially larger population that we estimate could have had an initial total mass (far) exceeding ∼1 × 109 M⊙ gave rise to the extended blue light—the arc-like features corresponding to stellar streams tracing disrupted star clusters—and perhaps also the central spiral disk. We speculate that, beginning about 500 Myr ago, an enhanced episode of active galactic nucleus activity in NGC 1275, leaving still visible X-ray bubbles, induced a vigorous cooling of the intracluster medium to fuel the formation of numerous star clusters: many were tidally disrupted to leave bluish light at the inner region of this galaxy, with the survivors being the SSCs projected against the central spiral disk.

Keywords: Cooling flows, Stellar populations, Optical astronomy, Brightest cluster galaxies, Perseus Cluster
Stellar Library of Differential Emission Measures and Extreme Ultraviolet Spectra: Dwarf Stars Observed by the Extreme Ultraviolet Explorer. Extreme ultraviolet (EUV; 100─912 Å) photons influence the formation and evolution of planets by ionizing hydrogen and other species, but the EUV radiation of most exoplanet host stars is poorly constrained. This work applies the differential emission measure (DEM) technique to infer the EUV spectra of eight stars previously observed with high signal-to-noise ratios by the Extreme Ultraviolet Explorer (EUVE; 1992─2002) spanning spectral types from M to F: AD Leo (MV),  E  Eri (KV), κ1 Ceti (GV), Procyon (FIV─V), α Cen A + B (GV + KV), and ξ Boo A + B (GV + KV). The model spectra are accurate to within a factor of 3 for the majority of individual EUVE flux density data points and accurate to within 30% of the integrated 100─300 Å fluxes. We provide the atomic data used for each star's calculations, X-ray/EUV/far-ultraviolet (noncontemporaneous) observational inputs, the DEM models, and the model-predicted EUV spectra (extending beyond the 90─510 Å range of the EUVE spectra) and compare the results to archival EUVE data. We also find that the relative contributions of the transition region and corona to a star's EUV emission vary significantly among the few stars analyzed here. The flare-driven variability of the corona is greater than the transition region, so the EUV spectrum of each star will have stochastic flare excess contributions at different wavelengths depending on the star's temperature structure, flare behavior, and activity cycle. We conclude with a discussion of the implications of this variability for analyses that use EUV estimates to study planetary atmospheric evolution.

Keywords: X-ray astronomy, Stellar chromospheres, Extreme ultraviolet astronomy, Ultraviolet astronomy, Stellar coronae
Simulation of Binary─Single Interactions in Active Galactic Nucleus Disks. II. Merger Probability of Binary Black Holes during Chaotic Triple Process. Stellar-mass binary black hole (BBH) mergers resulting from binary─single interactions (BSIs) in active galactic nucleus (AGN) disks are a potential source of gravitational wave (GW) events with measurable eccentricities. Previous hydrodynamical simulations have shown that ambient gas can significantly influence the dynamics of BSIs. However, due to limitations such as the use of purely Newtonian dynamics and small sample sizes, a direct estimation of the BBH merger probability during BSI has remained elusive. In this work, we directly quantify the merger probability, based on a suite of 1800 two-dimensional hydrodynamical simulations coupled with post-Newtonian N-body calculations. Our results demonstrate that dense gas can enhance the merger probability by both shrinking the spatial scale of the triple system and increasing the number of binary─single encounters. These two effects together boost the merger probability by a factor of ∼5, from 4% to as high as 20%. Among the two effects, our analysis suggests that the increase in encounter frequency plays a slightly more significant role in driving the enhancement. Moreover, this enhancement becomes more significant at larger radial distances from the central SMBH, since the total gas mass enclosed within the Hill sphere of the triple system increases with radius. Finally, the BSI process in AGN disks can naturally produce double GW merger events within a timescale of about 1 yr, which may serve as potential observational signatures of BSI occurring in AGN disk environments.

Keywords: Gravitational interaction, Hydrodynamical simulations, Active galactic nuclei, Gravitational waves
Probing the Accreting Millisecond X-Ray Pulsar SAX J1808.4─3658 Using the Evolution of Its Spectral and Aperiodic Timing Properties. Understanding accretion components in neutron star low-mass X-ray binary systems is important to probe fundamental aspects of the accretion mechanism and evolution of the system, constraining its physical properties. Here, we present spectral and aperiodic timing analyses of the Neutron star Interior Composition Explorer and AstroSat data from the accretion-powered millisecond X-ray pulsar SAX J1808.4−3658 during its 2022 outburst. We find that emissions from a softer accretion disk and a harder, centrally located, compact, partially covering, Comptonizing corona explain the continuum spectra from the source throughout the outburst. The disk inner edge temperature, the coronal electron temperature, and photon index are found to be around ∼0.5−0.9 keV, a few keV, and ∼1.1─1.8, respectively, during the entire outburst. We also find an intrinsic atomic hydrogen medium in the system, which substantially and systematically evolved throughout the outburst. We detect two broadband aperiodic features (∼0.004─2 Hz; ∼10─100 Hz), with the former having a significant hard lag of ∼11 ms between 1.5─10.0 and 0.5─1.5 keV photons. We conclude that both the disk photons and the photons upscattered by the corona contributed to each aperiodic feature, with the disk and the corona contributing more to the low and high-frequency ones, respectively.

Keywords: X-ray astronomy, Neutron stars, Accretion, Millisecond pulsars, Low-mass x-ray binary stars
Laplace─Fourier Linear Stability Analysis of Non-relativistic Magnetized Rotational Jets: Mode Identification by Hamiltonian Analysis and the Occurrence of Mode Transitions. In this paper, we conduct a linear stability analysis of magnetized and/or rotating jets propagating in ambient matter that is also magnetized and/or rotating, having in mind the application to the jet penetrating the core/envelope of a massive star. We solve the linearized magnetohydrodynamic (MHD) equations in the nonrelativistic regime by Laplace transform in time and Fourier transform in space. In this formulation, all unstable modes with the same translational and azimuthal wave numbers can be obtained simultaneously by searching for pole singularities in the complex plane. In order to unambiguously determine their driving mechanisms, we evaluate the second-order perturbation of the MHD Hamiltonian for individual eigenfunctions derived at these singular points. We identify in our nonrotating models the Kelvin─Helmholtz instability (KHI) as one of the shear-driven modes and the current-driven instability such as the kink instability (KKI). In rotational models, we also find the magnetorotational instability (MRI) as another shear-driven mode. In some cases, we find that a mode changes its character continuously from KKI to KHI (and vice versa) or from MRI to KHI as the jet velocity is increased.

Keywords: High energy astrophysics, Magnetohydrodynamics, Jets, Core-collapse supernovae
Higher-order Analysis of Three-dimensional Anisotropy in Imbalanced Alfvénic Turbulence. We examine the applicability of homogeneous, negligible cross-helicity magnetohydrodynamic (MHD) turbulence models incorporating "critical balance" (CB) and "scale-dependent dynamic alignment" (SDDA) to Parker Solar Probe observations of a highly Alfvénic, high cross-helicity solar wind stream. At energy-injection scales, both Alfvénic modes satisfy  χλ±≡τA±/τnl±≪1 , where  τA± and  τnl±  denote the linear and nonlinear timescales. The outward cascade remains weak,  χλ+≍0.2 , across all scales, while the inward cascade reaches CB at the onset of the inertial range ( χλ−∼1 ), yet with spectral scalings that depart from the canonical weak-to-strong transition. Within the domain conventionally designated as the inertial range, we identify two statistically distinct subranges. At larger scales (R2; 200─6000, di), the average eddy displays a field-aligned, tube-like morphology. An inverse correlation is observed between alignment angle and gradient intensity, and the conditional structure-function exponents ζn—measured perpendicular to both the local mean field and fluctuation direction—agree with the predictions of B. D. G. Chandran et al. and A. Mallet &amp; A. A. Schekochihin, although the parallel and displacement components show more concave scaling than anticipated. At smaller scales (R1; 10─100, di), spectra steepen, eddies become ribbon-like, and intermittency weakens. Within a narrow interval near the ion characteristic scales, eddies approach isotropy before the trend of increasing anisotropy resumes at smaller scales. Analysis using five-point increments further demonstrates a stronger multifractal character at kinetic scales than is resolved with conventional two-point methods. Finally, we discuss the influence of solar wind expansion, finite cross helicity, "anomalous coherence," and the emergence of a "helicity barrier" in modifying CB/SDDA phenomenology and shaping the statistical properties of solar wind turbulence.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Solar wind, Alfven waves
A New Wavelet Scattering Transform-based Statistic for Cosmological Analysis of Large-scale Structure. Large-scale structure (LSS) analysis in galaxy surveys is a powerful cosmological probe but is limited by tracer bias, which can obscure underlying information and weaken parameter constraints. Existing methods either model bias or restrict analyses to low-density regions, yet their sensitivity to bias remains poorly understood. We propose a novel method based on the wavelet scattering transform (WST) to distinguish LSS across cosmological models while mitigating tracer bias. Central to our approach are the WST m-mode ratios, Rwst, a new statistical measure, and a high-density apodization preprocessing that smoothly rescales extreme values. We use a reduced chi-square to assess the cosmological parameter constraints and find that Rwst, in the scale range j ∈ [3, 7], achieves  χν,cos2≍6  for cosmology while maintaining  χν,bias2∼1 —a regime unattained by other statistics. Rwst thus provides robust cosmological sensitivity with effective bias mitigation for future surveys.

Keywords: Large-scale structure of the universe
Crowning the Queen: Membership, Age, Rotation, and Activity for the Open Cluster Coma Berenices. Despite being only 85 pc away, the open cluster Coma Berenices (Coma Ber) has not been extensively studied. This is due in part to its sparseness and low proper motion, which together made Coma Ber's membership challenging to establish. Gaia data for ≍400 previously cataloged candidate cluster stars allowed us to identify ≍300 as members. With [Fe/H] measurements for nine members, we found that Coma Ber has a solar metallicity, and then fit isochrones to its color─magnitude diagram to determine that it is 675 ± 100 Myr old. With photometry obtained by the Transiting Exoplanet Survey Satellite and Zwicky Transient Facility, we measured rotation periods (Prot) for 137 of Coma Ber's low-mass stars, increasing the sample of members with measured Prot by a factor of six, and extending the rotational census for the cluster from its late F stars through to its fully convective M dwarfs. By measuring the equivalent width of the Hα line for ≍250 stars and collecting X-ray detections for ≍100 (≍85% and ≍33% of the cluster's members, respectively), we characterized magnetic activity in Coma Ber and examined the dependence of chromospheric and of coronal activity on rotation in these stars. Despite having a metallicity that is 0.2 dex below that of their coeval cousins in Praesepe and the Hyades, low-mass stars in Coma Ber seem to follow a similar rotation─activity relation. In detail, however, there are differences that may provide further insight into the impact of metallicity on this still poorly understood relation.

Keywords: Stellar chromospheres, Stellar activity, Low mass stars, Open star clusters, Stellar rotation, Stellar coronae
Gas-induced Perturbations on the Gravitational Wave Inspiral of Live Post-Newtonian LISA Massive Black Hole Binaries. We investigate the effect of dynamically coupling gas torques with gravitational wave (GW) emission during the orbital evolution of an equal-mass massive black hole binary (MBHB). We perform hydrodynamical simulations of eccentric MBHBs with total mass M = 106 M⊙ embedded in a prograde locally isothermal circumbinary disk (CBD). We evolve the binary from 55 to 49 Schwarzschild radii separations using up to 2.5 post-Newtonian corrections to the binary dynamics, which allow us to follow the GW-driven inspiral. For the first time, we report the measurement of gas torques onto a live binary a few years before the merger, with and without concurrent GW radiation. We also report the gas-induced orbital dephasing δϕorb ∼ −0.007 rad over 278 orbital cycles that is likely driven mainly by disk-induced precession, and LISA should be able to detect it at redshift z = 1. Our results show how GWs alone can be used to probe the astrophysical properties of CBDs and have important implications for multimessenger strategies aimed at studying the environments of MBHBs.

Keywords: Accretion, Supermassive black holes, Hydrodynamical simulations, Gravitational wave astronomy, Computational methods, Active galactic nuclei, Astrophysical black holes