Sazuna/UAT_keywords huggingface dataset:
Effects of Nonresonant Instability and Magnetic Reconnection on Ion Heating and Acceleration in Quasi-parallel Shock Waves. To understand the ion injection for diffusive shock acceleration in space and astrophysical shock waves, such as in planetary bow shocks and supernova remnant shocks, ion heating and acceleration in high-Alfvén-Mach-number (MA) quasi-parallel shock waves are studied by means of full particle-in-cell (PIC) simulations and theory. We perform 2D and 3D PIC simulations in the regime of MA ≥ 10, where shock-driven turbulence contains a number of current sheets and magnetic reconnection sites. The nonresonant ion─ion beam mode grows in the shock transition region, which creates current sheets, and some of them drive magnetic reconnection. The ion temperature in magnetic islands produced by ion-coupled reconnection becomes significantly higher than those in the surrounding regions. This temperature enhancement is due to two physical reasons: the reduction of the number density of the incident ions in the nonresonant wave, and the energization and heating in the magnetic islands. Ions that enter magnetic islands are energized by the Hall electric field pointing toward the island center. Ions are also energized by the motional electric field produced in the outer regions of the islands and the current sheets. The energy increase rate of ions by these energization mechanisms is much larger than that of the conventional shock drift acceleration. These energetic ions are unmagnetized, and they escape from the shock transition region toward the upstream region; therefore, ions in shocks with reconnecting current sheets can be injected into diffusive shock acceleration more efficiently than those in laminar shock waves.

Keywords: Solar magnetic reconnection, Planetary bow shocks, Supernova remnants, Interplanetary particle acceleration, Shocks
A Reidentification of Six Candidate Gravitationally Lensed Gamma-Ray Bursts. The gravitational lensing effect of gamma-ray bursts (GRBs) holds significant and diverse applications in the field of astronomy. Nevertheless, the identification of millilensing events in GRBs presents substantial challenges. We re-evaluate the gravitational lensing candidacy of six previously proposed GRBs (GRB 081122A, GRB 081126A, GRB 090717A, GRB 110517B, GRB 200716C, and GRB 210812A) using a comprehensive set of temporal and spectral diagnostics. These include χ2 light-curve similarity tests, photon-count-based hardness ratio (HRcount) comparisons, T90 duration measurements, spectral lag, Norris pulse-shape fitting, and both time-resolved and time-integrated spectral analyses. We propose an evaluation framework in which any single test that reveals a statistically significant inconsistency between the two pulses is sufficient to reject the lensing hypothesis for that burst. Although certain diagnostics, such as T90 and parametric model fits, have known limitations, they are applied and interpreted in conjunction with the more robust, model-independent χ2 and HRcount tests. For all six GRBs, at least one diagnostic shows a significant discrepancy, leading us to conclude that none are consistent with a gravitational lensing interpretation.

Keywords: Gamma-ray bursts
Decoding the Single-peaked H I Spectra of Low Redshift Poststarburst Galaxies. Recent observations with the Five-hundred-meter Aperture Spherical Telescope have revealed abundant reservoirs of neutral hydrogen (H I) in low-redshift poststarburst galaxies (PSBs), raising the question of why star formation ceases rapidly in these systems. In this study, we present a detailed analysis of the shape of the integrated H I spectra of 67 PSBs. We find that PSBs exhibit significantly higher H I spectral concentration values (K) compared to a matched sample from xGASS, and are more comparable to those of starburst galaxies. By extending our analysis to spatially resolved H I data from THINGS and ATLAS3D, we show that both centrally concentrated H I distributions and dynamically unsettled H I can effectively increase K, while nonaxisymmetric structures only contribute to the scatter of the K distribution. Distinguishing between central concentration and dynamically unsettled gas as the origin of high K can be achieved by measuring the spectral asymmetry (AF), making the K─AF plane a powerful diagnostic tool for identifying galaxies with unsettled H I using integrated spectra alone. Based on their location in the K─AF plane, we find that most PSBs are not dominated by unsettled H I, but rather exhibit elevated central gas concentration. Both modes of gas redistribution in PSBs may eventually contribute to their quenching.

Keywords: Post-starburst galaxies, Galaxy evolution, Galaxies, Interstellar atomic gas
Particle-in-cell Simulation of Current-driven Solar Type III Radiation and Whistler Waves in a Core–strahl Plasma: Relevance to PSP and Other Space Observations. The aim of this paper is to demonstrate that electron current oscillations may generate electromagnetic waves as type III radiation and whistler waves without the involvement of the classical plasma emission via the coalescence of waves. Particle-in-cell (PIC) simulation results of a core–strahl plasma without initial current compensation are presented, which describe the conversion of current-driven Langmuir oscillations/waves into type III radiation, whereby simultaneously whistler waves are excited. In contrast to the classical approach of V. L. Ginzburg &amp; V. V. Zhelezniakov, after which beam-excited Langmuir waves in a two-step process are converted into electromagnetic radiation, any instability is suppressed by selecting a low strahl velocity. Rather, electric field oscillations at the electron plasma frequency are triggered by the initially noncompensated current of the strahl. The arising electromagnetic fields exhibit amplitude oscillations, which are caused by the superposition of the two wave modes of mixed polarization at the point of mode coupling. This basic mechanism of wave generation and transformation has already been described in earlier papers using simple fluid models. It is also the topic of the companion paper. Besides the fundamental electromagnetic radiation, the second harmonic of nearly the same intensity has been obtained, which is an indication of its generation by nonlinear currents. Measurements of Langmuir waves, type III radiation, and whistler waves on board various satellites in the solar wind, in particular Parker Solar Probe observations, are analyzed in the light of our results. Interpretations of earlier PIC simulations are critically reviewed.

Keywords: Solar radio emission
Particle Acceleration and Transport in the Large-scale Current Sheet under an Erupting Magnetic Flux Rope. We investigate the acceleration and transport of electrons in the highly fine-structured current sheet that develops during magnetic flux rope (MFR) eruptions. Our work combines ultraresolved magnetohydrodynamic (MHD) simulations of MFR eruption, with test-particle studies performed using the guiding center approximation. Our grid-adaptive, fully 3D, high-resolution MHD simulations model MFR eruptions that form complex current-sheet topologies, serving as background electromagnetic fields for particle acceleration. Within the current sheet, tearing-mode instabilities give rise to mini flux ropes. Electrons become temporarily trapped within these elongated structures, undergoing acceleration and transport processes that significantly differ from those observed in 2D or 2.5D simulations. Our findings reveal that these fine-scale structures act as efficient particle accelerators, surpassing the acceleration efficiency of single X-line reconnection events, and are capable of energizing electrons to energies exceeding 100 keV. High-energy electrons accelerated in different mini flux ropes follow distinct trajectories, due to spatially varying magnetic field connectivity, ultimately precipitating onto opposite sides of flare ribbons. Remarkably, double electron sources at the flare ribbons originate from different small-flux-rope acceleration regions, rather than from the same reconnecting field line, as previously suggested. Distinct small flux ropes possess opposite magnetic helicity, to accelerate electrons to source regions with different magnetic polarities, establishing a novel conjugate double-source configuration. Furthermore, electrons escaping from the lower regions exhibit a broken-power-law energy spectrum. This spectral break arises from electrons accelerated in disparate mini flux ropes, each exhibiting magnetic reconnection rates and acceleration efficiencies, which reflect the varying local reconnection conditions.

Keywords: Magnetohydrodynamics, Solar flares, Solar magnetic reconnection, Solar energetic particles, Magnetohydrodynamical simulations
Magnetic Reconnection as a Potential Driver of X-Ray Variability in Active Galactic Nuclei. We present a systematic analysis on the X-ray variability in 13 bright quasars at z &gt; 4.5, combining recent Swift observations from 2021 to 2023 and archival multiepoch observations. Upper limits of the luminosity measurements were included in the analysis by using the Kaplan─Meier estimator method. It is found that the high-redshift quasars exhibit X-ray variability on both short-term (hours to days) and intermediate-term (weeks to months) timescales, with short-term variability dominating the overall variation. A linear correlation exists between the global mean ( μL2−10keV ) and standard deviation ( σL2−10keV ) of X-ray luminosities, which is independent of the X-ray photon index and optical-to-X-ray spectral slope. The localized stochastic magnetic reconnection mechanism is strongly favored, which can naturally lead to a scale-invariant power-law energy distribution and satisfactorily explain the correlation. The σ─μ correlation parallels the well-documented rms─flux relation of low-redshift active galactic nuclei (AGNs), implying that the magnetic reconnection mechanism could drive short-timescale X-ray variability in both high- and low-redshift AGNs. The highest-redshift quasar in our sample, J142952+544717 (z = 6.18), shows a luminosity distribution extending to 1047 erg s−1 with a not conspicuous median luminosity. On the other hand, J143023+420436 (z = 4.7), which hosts the most relativistic jet among known high-redshift blazars, is dominated in the high-luminosity regime (1047 erg s−1), making it an ideal target for multiwavelength follow-up observations. J090630+693030 is found to have a rest-frame period of 182.46 days, and J143023+420436 has a period of 16.89 days; both could be explained by the global evolution of plasmoid chains, in which magnetic islands formed during reconnection may merge successively.

Keywords: Galaxy magnetic fields, Supermassive black holes, Blazars, Astrostatistics, X-ray quasars, X-ray active galactic nuclei
Petrogenesis of Lunar Farside Highland Lithologies: Implications for Lunar Crust Formation. The lunar soil samples collected by the Chang'e-6 (CE-6) mission provide a unique opportunity to study the composition and formation of the lunar crust on the farside of the Moon. This study examines the petrogenesis of anorthosites and noritic anorthosites from the lunar farside using samples collected by the CE-6 mission. The analysis reveals that the ferroan anorthosite (FAN) clasts display plagioclase An# and mafic mineral Mg# within the range of Apollo FANs, highlighting the compositional similarity between the lunar nearside and farside. The identification of FANs on the farside underscores the global nature of these lithologies, indicating that the early lunar crust formation processes were not confined to the nearside but were widespread across the Moon. The noritic anorthosite clast shows characteristics consistent with KREEP-free/poor Mg-suite rocks. This finding supports the idea that both the nearside and farside experienced similar magmatic processes, challenging the simplistic hemispheric dichotomy models. The study emphasizes significant lithological variations at local scale and the need for further sample-return missions to elucidate the compositional diversity and formation history of the lunar crust.

Keywords: Lunar petrology, Lunar mineralogy
Deep Potential: Recovering the Gravitational Potential and Local Pattern Speed in the Solar Neighborhood with GDR3 Using Normalizing Flows. The gravitational potential of the Milky Way encodes information about the distribution of all matter—including dark matter—throughout the Galaxy. Gaia Data Release 3 has revealed a complex structure that necessitates flexible models of the Galactic gravitational potential. We make use of a sample of 5.6 million upper-main-sequence stars to map the full three-dimensional gravitational potential in a 1 kpc radius from the Sun using a data-driven approach called "Deep Potential." This method makes minimal assumptions about the dynamics of the Galaxy—that the stars are a collisionless system that is statistically stationary in a rotating frame (with pattern speed to be determined). We model the distribution of stars in six-dimensional phase space using a normalizing flow and the gravitational network using a neural network. We recover a local pattern speed of Ωp = 28.2 ± 0.1 km s−1 kpc−1, a local total matter density of ρ = 0.086 ± 0.010 M⊙ pc−3, and local dark matter density of ρDM = 0.007 ± 0.011 M⊙ pc−3. The full three-dimensional model exhibits spatial fluctuations, which may stem from the model architecture and nonstationarity in the Milky Way.

Keywords: Solar neighborhood, Milky Way dynamics, Milky Way rotation
Radiative Nonideal Magnetohydrodynamic Simulations of Inner Protoplanetary Disks: Temperature Structures, Asymmetric Winds, and Episodic Surface Accretion. We perform 2D global magnetohydrodynamic (MHD) simulations including the full nonideal MHD effects (ohmic diffusion, Hall effect, and ambipolar diffusion) and approximate radiation transport to understand the dynamics and thermal structure of the inner protoplanetary disks (PPDs). We have developed a simple radiative transfer model for PPDs that reasonably treats stellar nonthermal (X-ray and ultraviolet (XUV)), stellar thermal (optical/infrared), and reemitted radiation, reproducing the temperature structures from Monte Carlo radiative transfer. Our simulations show fast one-sided surface accretion (∼10% of Keplerian velocity) and asymmetric disk winds when the vertical magnetic field is aligned with the disk angular momentum. The asymmetry is due to the failure of the wind on the side with the accretion layer. On the accreting surface, clumps are repeatedly generated and accrete, driven by radiative feedback. For the antialigned fields, surface accretion becomes more moderate and time variable, while the winds remain largely symmetric. For the thermal structure, accretion heating does not affect the disk temperature in any of our runs. This is because (1) the accretion energy dissipates via Joule heating at two to three gas scale heights, where low optical depth enables efficient radiative cooling, and (2) the winds remove ≳10% of the accretion energy. In contrast, the winds enhance radiative heating by elevating the irradiation front. These results highlight the importance of coupling between gas dynamics and radiation transport in PPDs and provide observable magnetic activities such as fast episodic accretion, wind asymmetry, and molecular survival in XUV-irradiated winds.

Keywords: Magnetohydrodynamics, Radiative magnetohydrodynamics, Protoplanetary disks, Radiative transfer, Stellar accretion disks, Planet formation
Discovery of Giant Bubbles in the Hot Gaseous Halo of the Massive Disk Galaxy NGC 6286. Based on archival Chandra X-ray observation, optical integral-field spectroscopic data, and radio interferometric data, we report the discovery of a pair of giant bubbles (with a projected radius ∼5 kpc) of ionized gas emerging from a highly inclined starburst galaxy NGC 6286, which is undergoing strong tidal interactions with its close neighbor NGC 6285. The bubbles are manifested by extraplanar soft X-ray emission with an X-shaped morphology, which is tightly cospatial with Hα line emission and partially coincident with radio continuum. Low surface brightness diffuse X-ray emission can be traced out to ∼90 kpc from the galactic center, revealing the presence of an extended hot gaseous halo. X-ray spectral analysis of the bubbles yields a gas temperature of  0.70−0.18+0.16  keV, a relatively high value among known galactic-scale bubbles in the local Universe. An average energy injection rate of ∼1043 erg s−1 is required to inflate the bubbles within an estimated dynamical age of ∼6.4 Myr. The multiwavelength properties of the bubbles can be understood with the conventional superwind scenario, in which disk/halo gas is swept up into an expanding, cooling shell by a hot tenuous wind. The current starburst in NGC 6286 is energetically sufficient to launch the superwind, although we cannot rule out the possibility of a more violent active galactic nucleus in the recent past as the driving source. Future high-resolution spectroscopic observations will help to shed light on the origin of the superwind and its role as an important galactic feedback process.

Keywords: Starburst galaxies, Galactic winds, Circumgalactic medium, Interacting galaxies, Superbubbles
Lyα Emission from K and M Dwarfs: Intrinsic Profiles, Variability, and Flux in the Habitable Zone. Lyman-alpha (Lyα) is the most prominent ultraviolet (UV) emission line in low-mass stars, playing a crucial role in exoplanet atmospheric photochemistry, heating, and escape. However, interstellar medium (ISM) absorption typically obscures most of the Lyα profile, requiring reconstructions that introduce systematic uncertainties. We present intrinsic Lyα profiles for 12 high-radial-velocity (RV) K and M dwarfs, where Doppler shifting minimizes ISM contamination, allowing direct measurements of ∼50%─95% of the line flux. Our sample spans the K-to-M spectral transition, enabling us to constrain the dependence of self-reversals in Lyα emission profiles on effective temperature (Teff). The depth of self-reversal, driven by non─local thermodynamic equilibrium effects, decreases with decreasing Teff, with M dwarfs exhibiting little to none. Two stars, Ross 1044 and Ross 451, were observed over multiple days, revealing ∼20% Lyα variability confined to the line core—implying that studies relying on reconstructions may underestimate temporal variability. We find strong correlations between Lyα flux, peak-to-trough ratio, and hydrogen departure coefficients with Teff, providing empirical constraints for stellar atmosphere models. A comparison of Lyα flux in the habitable zone shows measured values for high-RV stars less than the reconstructed values for the rest of the sample, likely due to the older ages of the high-RV stars and/or overestimated reconstructed fluxes due to model deficiency (e.g., neglecting self-reversal). Our results establish an empirical foundation for Lyα emission in K and M dwarfs, reducing uncertainties in reconstructions and improving models of stellar UV emission relevant to exoplanetary studies.

Keywords: Stellar chromospheres, Stellar activity, Ultraviolet astronomy, Stellar astronomy, Low mass stars
Radial Profiles of Radio Halos in Massive Galaxy Clusters: Diffuse Giants Over 2 Mpc. We present new, high frequency radio observations of the merging galaxy clusters PLCK G287.0+32.9, A2744, and Bullet. These clusters are known to host ∼Mpc scale sources, known as radio halos, which are formed by the acceleration of cosmic rays by turbulence injected into the intracluster medium during cluster mergers. Our new images reveal previously undetected faint outermost regions of halos, extending to over 2 Mpc. This discovery highlights the presence of radio halos with large extents at high frequencies and suggests that their observable size depends on a combination of the observation sensitivity and uv-coverage, as well as their radio power. We additionally compare the properties of these three clusters with MACS J0717+3745 and A2142, both of which are known to host prominent large radio halos. Remarkably, all five halos, despite their exceptionally large extents, exhibit properties similar to other classical halos: their radial profiles are described by a single-component exponential fit, they show radial spectral index steepening, and have an average radio emissivity of about 10‑42 erg s‑1 cm‑3 Hz‑1. Our results demonstrate that radio halos can extend to the cluster's periphery, without the transition to an observationally distinguishable different halo component in the outermost regions. Our findings also highlight that careful subtraction of unrelated sources embedded in the halo is necessary to measure the radio surface brightness accurately, since incomplete subtraction can introduce an apparent secondary component in the peripheral regions.

Keywords: Radio continuum emission, Galaxy clusters, Intracluster medium, Large-scale structure of the universe
The Role of Farside Magnetic Structures in Modeling the 2024 Solar Eclipse. The corona is a crucial region that connects the solar surface to the solar wind and serves as the primary site of solar activity. The 2024 total solar eclipse (TSE) provides a unique opportunity to investigate the large-scale coronal structure. Combined with TSE observations, we study the impact of the magnetic structure of the farside active region, located in the eastern hemisphere of the Sun that has not yet rotated into the Earth field of view, on a global magnetohydrodynamic simulation. To address the limitation of single-view measurements for the routine synoptic map, we correct the magnetic field in the farside region by incorporating full-disk magnetograms measured several days after the TSE, allowing us to capture the temporal evolution of the photospheric magnetic field in near real time. Simulation results demonstrate that the local magnetic field in the farside active region can significantly influence the global coronal structure, by altering the position of the heliospheric current sheet, and further affect the global distribution of plasma parameters, even in polar regions. A comparison of the simulation results with white-light TSE + Large Angle and Spectrometric Coronagraph C2 observations and in situ measurements by the Parker Solar Probe reveals that the composite synoptic map improves the accuracy of the coronal modeling. This work provides robust support for advancing our understanding of coronal evolution, as well as deepening the link between the photosphere and large-scale coronal structure. Furthermore, it establishes a theoretical foundation for the future development of multiview stereoscopic measurements of the photospheric magnetic field.

Keywords: Magnetohydrodynamics, Solar eclipses, Solar active regions, Solar corona, Magnetogram