Sazuna/UAT_keywords huggingface dataset:
Fundamental Understanding of Magnetic Reconnection via Spiral CT Scan. V. Ion Demagnetization, Electron Demagnetization, and Hall Effect. For the first time, we reveal the distribution of ion demagnetization, electron demagnetization, and Hall effect around a reconnection X-line by using the spiral CT scan technique, which is a novel technique analogous to that in the hospital. This X-line was detected by the Magnetospheric Multiscale mission and has been widely believed to host a non-guide-field reconnection. With the help of such an advanced technique, we find that: (1) the ion demagnetization is prominent everywhere at scale &lt;1di, with a clear enhancement corresponding to the out-of-plane electron jet near the X-point; (2) the Hall electric field is large in both the magnetosheath-side and magnetosphere-side inflow regions, but is small at the current sheet center; (3) the electron demagnetization is strong in the magnetosheath-side inflow region and at the out-of-plane electron jet, but is weak in the magnetosphere-side inflow region and at the separatrix; (4) there is a good correlation between the ion demagnetization and Hall electric field at scale 0.25di &lt; ∆ &lt; 1di, indicating that at such scale the Hall electric field is responsible for the breaking of the ion frozen-in law; (5) there is a good correlation between the electron demagnetization and whistler-wave power around the whole X-line, meaning that whistler waves lead to the electron demagnetization; (7) apparently, there is no correlation between the electron demagnetization and Hall electric field, so that the Hall effect does not contribute to electron demagnetization; and (8) at scale &lt;0.25di, the ion demagnetization should be attributed to other effects, rather than the Hall electric field. The exact mechanism for whistler waves to cause electron demagnetization is the anomalous resistivity. All these results clearly demonstrate that magnetic reconnection is triggered (electron demagnetization) by whistler waves and is developed (ion demagnetization) by Hall effects in space.

Keywords: Space plasmas, Solar magnetic reconnection, Plasma physics
Cosmic Dust as a Prerequisite for the Formation of Complex Organic Molecules in Space?. In cold, dense astrophysical environments dust grains are mixed with molecular ices. Chemistry in those dust/ice mixtures is determined by diffusion and reaction of molecules and radicals. However, investigations of diffusion of astrophysically relevant radicals and molecules across the surface and through the pores of cosmic dust grains and of surface reactions consequent to such diffusion are largely uncharted territory. This paper presents results of a study of a solid-state reaction of two molecular species, CO2 and NH3, separated by a layer of porous silicate grain aggregates, analogues of cosmic dust. The experiments demonstrate that the presence of the dust layer was necessary for a pure thermal CO2 + 2NH3 reaction to proceed, leading to the formation of ammonium carbamate (NH4+NH2COO−), an ionic solid containing a complex organic moiety of prebiotic interest recently detected in a protoplanetary disk. This result speaks for (i) efficient diffusion of molecules on/within cosmic dust, (ii) an underestimated role for surface catalysis in the astrochemistry of cosmic dust, and (iii) potentially efficient dust-promoted chemistry in warm cosmic environments, such as protostellar envelopes and protoplanetary disks.

Keywords: Interstellar molecules, Interstellar dust, Laboratory astrophysics
The Relation between the Optical Variability Timescale, Magnetic Field of Jets, and Black Hole Spin in Active Galactic Nuclei. We investigate the relationship among the jet magnetic field, black hole spin, black hole mass, Eddington ratio, and optical variability timescales in jetted active galactic nuclei (AGNs). By fitting a damped random walk (DRW) model to the g-band light curves, we obtain the characteristic variability timescale (τDRW) for 41 jetted AGNs with precise supermassive black hole (SMBH) mass measurements. Our main results are as follows: (i) Our analysis reveals a significant correlation between the jet magnetic field (B1 pc), black hole spin (j) and the characteristic variability timescale within our sample. These findings suggest that the optical variability of jetted AGNs is influenced by the jet magnetic field and black hole spin. Furthermore, the characteristic variability timescale aligns with the electron escape timescale, as evidenced by the relationship between the characteristic variability timescale and jet magnetic field ( τDRW∝B1pc0.76±0.22 ). (ii) We confirm a significant correlation between the characteristic variability timescale and SMBH mass, expressed as:  logτDRW=0.52(±0.21)logMBH/M⊙−3.12(±1.90) , with an intrinsic scatter of 0.08 dex. The slope of this relationship is consistent with that between the thermal timescale and black hole mass. Our results support the hypothesis that magnetorotational instability fluctuations drive the intrinsic variability observed in the light curves emitted by the AGN's accretion disk.

Keywords: Supermassive black holes, Galaxy jets, Active galactic nuclei, Time domain astronomy, Time series analysis
RapidGBM: An Efficient Tool for Fermi-GBM Visibility Checking and Data Analysis with a Case Study of EP240617a. We have developed a lightweight tool, RapidGBM, featuring a web-based interface and capabilities of rapid calculation of Fermi Gamma-ray Burst Monitor (GBM) visibilities and performance of basic data analysis. It has two key features: (1) it can immediately check the visibility of Fermi-GBM for new transients, and (2) it can check the light curve and perform spectral analysis after the hourly Time-Tagged Event data are released. The visibility check and the response matrix generation required for spectral analysis can be achieved through the historical pointing file after the orbit calculation, even when the real-time pointing file is not yet available. As a case study, we apply the tool to EP240617a, an X-ray transient triggered by Einstein Probe (EP). We demonstrate the workflow of visibility checking, data processing, and spectral analysis for this event. The results suggest that EP240617a can be classified as an X-ray-rich gamma-ray burst and confirm the feasibility of using historical pointing files for rapid analysis. Further, we discuss possible physical interpretations of such events, including implications for jet launching and progenitor scenarios. Therefore, RapidGBM is expected to assist EP transient advocates, Space-based multiband astronomical Variable Objects Monitor burst advocates, and other members of the community in cross checking high-energy transients. Based on prompt emission parameter relations (e.g., Ep─Eγ,iso), it can also help identify peculiar GRBs (e.g., long-short burst, magnetar giant flare, etc.) and provide useful references (e.g., more accurate T0) for scheduling follow-up observations.

Keywords: Gamma-ray bursts
FOGGIE. X. Characterizing the Small-scale Structure of the Circumgalactic Medium and Its Imprint on Observables. One of the main unknowns in galaxy evolution is how gas flows into and out of galaxies in the circumgalactic medium (CGM). Studies observing the CGM in absorption using multiple or extended background objects suggest a high degree of variation on relatively small (≲1 kpc) spatial scales. Similarly, high-resolution simulations generally exhibit small-scale substructure in the gas around galaxies. We examine the small-scale structure of the z = 1 CGM using simulations from the Figuring Out Gas and Galaxies in Enzo (FOGGIE) project. We select gaseous substructures ("clumps") by their local overdensity and investigate their physical properties, including temperature, metallicity, and kinematics with respect to the galaxy and the nearby surroundings. FOGGIE resolves clumps down to sphericalized radii R ∼ 0.25 kpc at z = 1. The distribution of clumps peaks at ∼105 M⊙ and 104 K, consistent with relatively condensed, cool gas with a slight preference for inflow-like velocities. Many clumps show internal temperature and density variations, and thus internally varying ionization levels for key diagnostic ions such as H I, Mg II, and O VI. The average metallicity in clumps is about a factor 1.5─2× lower in metallicity than nearby gas, suggesting that the metals are not well mixed between structured and diffuse CGMs, which may have implications for observational metallicity estimations of dense CGM clouds. We estimate the survivability of CGM clumps and find that structures larger than 0.5 kpc are generally long-lived. Finally, we qualitatively compare the simulated cloud properties to Milky Way high-velocity clouds.

Keywords: Hydrodynamical simulations, Galaxy evolution, Circumgalactic medium
Do White Dwarfs Sample Water-rich Planetary Material?. Polluted white dwarfs offer a unique way to directly probe the compositions of exoplanetary bodies. We examine the water content of accreted material using the oxygen abundances of 51 highly polluted white dwarfs. Within this sample, we present new abundances for three H-dominated atmosphere white dwarfs that showed promise for accreting water-rich material. Throughout, we explore the impact of the observed phase and lifetime of accretion disks on the inferred elemental abundances of the parent bodies that pollute each white dwarf. Our results indicate that white dwarfs sample a range of dry to water-rich material, with median uncertainties in water mass fractions of ≍15%. Among the He-dominated white dwarfs, 35/39 water abundances are consistent with corresponding H abundances. While for any individual white dwarf it may be ambiguous as to whether or not water is present in the accreted parent body, when considered as a population, the prevalence of water-rich bodies is statistically robust. The population as a whole has a median water mass fraction of ≍25%, and enforcing chondritic parent body compositions, we find that 31/51 WDs are likely to have nonzero water concentrations. This conclusion is different from a similar previous analysis of white dwarf pollution and we discuss reasons why this might be the case. Pollution in H-dominated white dwarfs continues to be more water-poor than in their He-dominated cousins, although the sample size of H-dominated white dwarfs remains small and the two samples still suffer a disjunction in the range of host star temperatures being probed.

Keywords: Stellar abundances, White dwarf stars, Exoplanet systems
The Cygnus X-1 Puzzle: Implications of X-Ray Polarization Measurements in the Soft and Hard States on the Properties of the Accretion Flow and the Emission Mechanisms. In this paper, we summarize key observational constraints of the accretion flow on the black hole X-ray Binary Cygnus X-1 (Cyg X-1). The discussion highlights the flows of energy close to the black hole and the importance of the distance range from which the radiating zone draws its energy. For the hard state, we examine compact and extended corona models. We find that compact corona models are energetically favored, but extended models cannot be fully excluded. We discuss the high linear polarization of the Cyg X-1 X-rays in the soft and hard states parallel to the direction of the radio jet. We propose the presence of a pair layer enveloping the accretion disk moving at approximately half the speed of light away from the disk for both the soft and the hard state. In the soft state, the pairs cool to the Compton temperature of the disk emission. In the hard state, the pairs acquire thermal and bulk motion allowing them to Comptonize the emission to produce the observed power law emission. In both emission states, the bulk motion away from the disk leads to a net polarization parallel to the radio jet. We emphasize that the geometry of the accretion flow in the hard state is still not well constrained, and that observed spectral (including the relativistically broadened Fe K-α line) and spectro-polarimetric signatures depend strongly on the plasma processes responsible for energy dissipation in the plasma.

Keywords: X-ray astronomy, Accretion, X-ray binary stars, Kerr black holes, Stellar mass black holes, Astrophysical black holes
CHIME/FRB Outriggers: Design Overview. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has emerged as the world's premier facility for studying fast radio bursts (FRBs) through its fast transient search backend CHIME/FRB. The CHIME/FRB Outriggers project will augment this high detection rate of 2─3 FRBs per day with the ability to precisely localize them using very long baseline interferometry (VLBI). Using three strategically located stations in North America and deploying recently developed synoptic VLBI observing techniques, the Outriggers will provide ∼50 mas localization precision for the majority of detected FRBs. This paper presents an overview of the design and implementation of the Outriggers, covering their geographic distribution, structural design, and observational capabilities. We detail the scientific objectives driving the project, including the characterization of FRB populations, host galaxy demographics, and the use of FRBs as cosmological probes. We also discuss the calibration strategies available to mitigate ionospheric and instrumental effects, ensuring high-precision localization. With two stations currently in science operations, and the third in commissioning, the CHIME/FRB Outriggers project is poised to become a cornerstone of the FRB field, offering unprecedented insights into this enigmatic cosmic phenomenon.

Keywords: Transit instruments, Radio bursts, Very long baseline interferometers, Radio transient sources
The Epoch of Reionization 21 cm Bispectrum at z = 8.2 from MWA Data. I. Foregrounds and Preliminary Upper Limits. We attempt to measure the z = 8.2 Epoch of Reionization (EoR) 21 cm bispectrum (BS) using Murchison Widefield Array 154.2 MHz data. We find that B(k1⊥, k2⊥, k3⊥, k1∥, k2∥), the 3D cylindrical BS, exhibits a foreground wedge, similar to P(k1⊥, k1∥), the 21 cm cylindrical power spectrum. However, the BS foreground wedge, which depends on (k1⊥, k1∥), (k2⊥, k2∥), and (k3⊥, k3∥), the three sides of a triangle, is more complicated. Considering various foreground avoidance scenarios, we identify the region where all three sides are outside the foreground wedge as the EoR window for the 21 cm BS. However, the EoR window is contaminated by a periodic pattern of spikes that arises from the periodic pattern of missing frequency channels in the data. We evaluate the binned 3D spherical BS for triangles of all possible sizes and shapes, and present results for ∆3, the mean-cube brightness temperature fluctuations. The best 2σ upper limits we obtain for the EoR 21 cm signal are  ∆UL3=(1.81×103)3mK3  at k1 = 0.008 Mpc−1 and  ∆UL3=(2.04×103)3mK3  at k1 = 0.012 Mpc−1 for equilateral and squeezed triangles, respectively. These are foreground dominated and are many orders of magnitude larger than the predicted EoR 21 cm signal (∼103 mK3).

Keywords: Diffuse radiation, Observational cosmology, Astronomy data analysis, H I line emission, Non-Gaussianity, Interferometric correlation, Reionization, Radio interferometry
Radiation-magnetohydrodynamic Simulations of Accretion Flow Formation After a Tidal Disruption Event. We perform 3D radiation-magnetohydrodynamic simulations of the evolution of the fallback debris after a tidal disruption event (TDE). We focus on studying the effects of magnetic fields on the formation and early evolution of the accretion flow. We find that large magnetic fields can increase the debris stream thickness, moderately reducing the efficiency of the radiative acceleration of outflows during the first self-intersecting collisions. As gas accumulates and the collisions happen instead between the infalling stream and the accretion flow, magnetized and nonmagnetized systems evolve similarly at these early times: radiation-driven outflows dominate early after the initial stream─stream collision, and a few days later, the accretion rate exceeds the mass outflow rate. We find that magnetorotational instability does not play a significant role in angular momentum transport and dissipation. Nor do we find evidence of a magnetocentrifugal-driven outflow. Instead, collisions continue to dissipate kinetic energy into radiation that launches outflows and powers TDE luminosities reaching L ∼ 4─6 × 1044 erg s−1. Shock-driven outflows and inflows redistribute angular momentum throughout the extent (∼50rs) of the forming eccentric disk. Even in the presence of magnetic stresses, the accretion flow remains mostly eccentric with e ∼ 0.2─0.3 for r ≲ 8rs and e ∼ 0.4─0.5 for 10 ≲ r (rs) ≲ 50. Lastly, we find a polar angle-dependent density structure compatible with the viewing-angle effect, along with an additional azimuthal angle dependence established by the collisions.

Keywords: Accretion, Black hole physics, Tidal disruption, Radiative magnetohydrodynamics
Learning to Estimate Photospheric Vector Fields from Line-of-sight Magnetograms. Solar photospheric line-of-sight magnetograms are easier to estimate than full vector magnetograms since the line-of-sight component (Blos) can be obtained from total intensity and circular polarization signals, unlike the perpendicular component (B⊥), which depends on harder-to-measure linear polarization. Unfortunately, the line-of-sight component by itself is not physically meaningful, as it is just one component of the underlying vector and one whose relationship to the gravity vector changes pixel-to-pixel. To produce an estimate of the radial component (BR), a common "correction" is often applied that assumes the field is radial, which is nearly always false. This paper investigates recovering full vector field information from Blos by building on the recent SuperSynthIA approach that was originally used with Stokes vectors as input for simultaneous inversion and disambiguation. As input, the method accepts one or more line-of-sight magnetograms and associated metadata; as output, our method estimates full vector field in heliographic components, meaning that the physically relevant vector components are returned without need for further disambiguation steps or component transforms. We demonstrate the ability to produce good estimates of the full vector field on unseen examples from both HMI and GONG, including examples that predate the Solar Dynamics Observatory mission. Our results show that learning is not a replacement for a dedicated vector-field observing facilities, but may serve to unlock information from past data and at the very least, provide more accurate BR maps from Blos than are created using the simple viewing angle assumption.

Keywords: Computational methods, Convolutional neural networks
Observed Evidence for the Primordial Origin of Galaxy Sizes. We present observational evidence supporting the scenario that the protogalactic angular momenta play an important role in molding the optical sizes of present galaxies. Analyzing the NASA-Sloan Atlas catalog in the redshift range of 0.02 ≤ z &lt; 0.09, we observationally determine the probability density distributions, p(r50) and p(r90), where r50 and r90 denote the galaxy sizes enclosing 50% and 90% of their r-band luminosities, respectively. Both of the distributions are found to be well described by a bimodal Gamma mixture model, which is consistent with the recent numerical results. Classifying the local galaxies by their ratios, r50/r90, we also show that for the case of late-type galaxies with r50/r90 ≥ 0.45, both p(r50) and p(r90) exhibit no bimodal feature, following a unimodal Gamma model. Assuming the existence of a linear causal correlation between {r50, r90} of the late-type galaxies and the primordial spin factor, τ, defined as the degree of misalignments between the initial tidal and protogalaxy inertia tensors, we reconstruct the probability density distributions, p(τ), directly from the observationally determined p(r50) and p(r90) of the late-type galaxies. It is shown that the reconstructed p(τ) is in excellent agreement with the real distribution of τ that was determined at the protogalactic stages by numerical experiments. A critical implication of our result on reconstructing the initial conditions from observable galaxy sizes is discussed.

Keywords: Large-scale structure of the universe
Reynolds Number and Viscosity in the Solar Wind. The Reynolds number is a key dimensionless parameter used to distinguish turbulent flow from laminar flow. We present generalized expressions for both the Reynolds number and viscosity, incorporating the spectral indices of the inertial range, applicable across Kolmogorov, Iroshnikov─Kraichnan (IK), and k−2 scaling regimes. We show that turbulence governed by Kolmogorov scaling yields a larger Reynolds number than that governed by IK scaling, while viscosity behaves oppositely. We apply these generalized formulations to the data from Parker Solar Probe encounters 1 through 17 and Solar Orbiter encounters 1 through 4 to study the radial evolution of Reynolds number and viscosity from ∼15 R⊙ to 1 au. We find that the Reynolds number is highest for the steepest spectral slopes and lowest for the shallowest ones, while viscosity shows the opposite trend, being lowest for the steepest slopes and highest for the shallowest ones throughout the inner heliosphere.

Keywords: Interplanetary turbulence, The Sun, Heliosphere
Neutron Star─Main Sequence Collisions Robustly Form Dynamically Stable Thorne─Żytkow Objects. Thorne─Żytkow objects (TŻOs) are hypothetical hybrid stars with a neutron star at the core of a large, diffuse envelope. TŻOs may be formed when a newly formed neutron star that is kicked by its supernova collides with its main-sequence companion. Using a moving-mesh hydrodynamics solver integrated into the parallel-code Charm N-body GrAvity solver, we demonstrate that these "impact scenario" formation processes robustly form TŻOs for periastron distances less than one stellar radius. These TŻOs are dynamically stable, and they can serve as initial models for further evolutionary studies.

Keywords: Neutron stars, Hydrodynamical simulations, High energy astrophysics, Stellar mergers
Oscillatory Behaviors in General Relativistic Magnetohydrodynamical Simulations of Interacting Toroids. Oscillatory behavior in the total flux emitted from both single and double torus structures was observed in our general relativistic magnetohydrodynamical simulations performed using the High-Accuracy Astrophysical Relativistic MHD code. These features became evident during a ray tracing conducted with the postprocessing tool IPOLE. Fast Fourier transform analysis of the resulting light curves revealed the presence of dominant frequency components. Two dominant frequencies are observed for interacting counterrotating tori, demonstrating a frequency ratio ∼3 : 2 that is generated during the most intensive interaction of the tori. For corotating tori, the situation is more complex. There are indications that increasing magnetic field intensity enlarges the number of observed oscillations.

Keywords: Black hole physics, Black holes, High energy astrophysics