Sazuna/UAT_keywords huggingface dataset:
Searching for Ultra-light Dark Matter in Spatial Correlations of White Dwarf Structure. If dark matter is ultra-light and has certain Standard Model interactions, it can change the mass─radius relation of white dwarf (WD) stars. The coherence length of ultra-light dark matter (ULDM) imparts spatial correlations in deviations from the canonical mass─radius relation, and thus, WDs can be used to reconstruct the coherence length, or equivalently the particle mass, of the dark matter field. We simulate the observability of such spatial correlations accounting for realistic complications like variable hydrogen envelope thickness, dust, binaries, measurement noise, and distance uncertainties in DA WDs. Using a machine learning approach on simulated data, we measure the dark matter field coherence length and find that large deviations from the mass─radius relation (∼10% change in radius) are needed to produce an observable signal given realistic noise sources. We apply our spatial correlation measurement routine to the Sloan Digital Sky Survey catalog of 10,207 DA WDs. We detect a positive spatial correlation among WDs at separations corresponding to a coherence length of 300 ± 50 pc, with an average Z-score of 85 for WDs separated by less than this coherence length. We conclude that this signal is due to observational bias. The signal can be explained by an offset between measurements and theory for nearby cool WDs, and the presence of few, low-temperature WDs with noisy measurements at farther distances. With future improvements in WD models and measurement techniques, particularly for cool WDs, this method can provide interesting constraints on ULDM models.

Keywords: White dwarf stars, Dark matter, DA stars
Evidence for Substructure on the Inner Broad Line Region of the Lensed Quasar SDSS J1004+4112 from the Recurrence of Microlensing in the C IV Emission Line. We use microlensing to probe the inner broad line region (BLR) of the lensed quasar SDSS J1004+4112, finding evidence of substructure. We study the recurrent microlensing events observed in the blue wing of the C IV emission line in image A of this lensed quasar from a series of 20 spectra taken over 15 yr. We obtain a microlensing light curve and confirm the presence of three high magnification events (∆m &gt; ─0.7 mag). A caustic crossing is a natural explanation for each one of the events. The fast rising and fading of the events imply that the width of the region scanned by the caustic in each event, ≲0.1 μas (≲0.93 ± 0.36 light days), is much smaller than the BLR size. However, the large range of velocities involved implies significant overlapping with the inner BLR velocity field. An elongated thin substructure in the BLR fulfills both requirements at once. A sequence of caustics crossing a single elongated substructure may be a possible explanation of the observed recurrence. However, this hypothesis requires some ad hoc assumptions about the microlens population. Alternatively, a single caustic encountering several narrow-stripped or bow-shaped substructures in the approaching part of the BLR could explain the variability. We discuss the possible identification of these elongated substructures with ripples or spiral structure on the inner BLR. Simulations of caustic crossings of a rippled disk statistically support this interpretation. The study of the C IV emission-line variability in SDSS J1004+4112 illustrates the incomparable scanning power of microlensing in both velocity and space.

Keywords: Gravitational lensing
Isotopic Compositions and Elemental Abundances of Chromium in Presolar Silicon Carbide Grains from Asymptotic Giant Branch Stars. Isotopes of chromium (Cr) and other iron-group elements are predominantly made in the inner shells of supernovae and are later reprocessed via the slow neutron capture process (s-process) in asymptotic giant branch (AGB) stars. Nucleosynthetic models of low-mass, solar metallicity AGB stars yield significant overproduction of 54Cr (δ54Cr values ∼ +160‰) with limited variations in other Cr isotopes, relative to solar system values. Here we report Cr, C, and N isotopic compositions of 16 individual presolar silicon carbide (SiC) grains of the KJG series (1.5─3 μm) from the Murchison (CM2.0) meteorite. 12C/13C and 14N/15N ratios of the 14 mainstream SiC grains range from 29 to 108 and 259 to 7800, respectively. These C, N isotopic compositions are consistent with their formation in red giant and AGB stars. Two types of AB grains could have originated in a J-type C-star (AB2) and a type-II supernova (AB). The majority of mainstream grains display close-to-solar Cr isotopic compositions, indicating the Cr was not significantly processed within their parent AGB stars. A mainstream SiC grain with relatively high 54Cr enrichment of δ54Cr ∼ 700‰ likely originated from a very low metallicity parent star based on the stellar nucleosynthesis model (FRUITY). We consider the plausible origin of this grain from Galactic halo stars, migration from the outer Galactic disk, and other scenarios. Elemental Cr concentrations of the grains vary from ∼1 to 9 ppm, with 75% of the grains displaying an average concentration of ∼2 ppm. Cr concentration does not vary significantly with grain size, suggesting that the Cr in the SiC grains condensed during grain formation and was not implanted at a later stage.

Keywords: Isotopic abundances
Particle Acceleration and Pitch-angle Evolution in Relativistic Turbulence. Synchrotron radiation detected from relativistic astrophysical objects such as pulsar-wind nebulae and jets from active galactic nuclei depends on the magnetic fields and the distribution functions of energetic electrons in these systems. Relativistic magnetically dominated turbulence has been recognized as an efficient mechanism for structure formation and nonthermal particle acceleration in these environments. Recent numerical simulations of relativistic turbulence have provided insights into the energy distribution functions of accelerated electrons. Much less is currently understood about their pitch angle distributions, which are crucial for accurately interpreting the spectra of synchrotron radiation. We perform a detailed case study of the pitch angle distributions formed during the process of turbulent acceleration for B0/δB0 = 10 and  σ∼0∼40 , where B0 is the uniform component of the magnetic field, δB0 is the fluctuating component, and  σ∼0  is the plasma magnetization based on the magnetic fluctuations. We find that even minimal numerical noise can cause substantial pitch angle scattering, but we demonstrate techniques for overcoming the numerical challenges associated with the evolution of very small pitch angles. Our numerical results are consistent with the phenomenological considerations found in C. Vega et al. (2024a, 2025).

Keywords: High energy astrophysics, Galaxies
The Fate of Transonic Shocks around Black Holes and Their Future Astrophysical Implications. Theoretical models have long predicted the existence of shocks in multitransonic accretion flows onto a black hole, yet their fate under general relativistic simulations has not been fully tested. In this study, we present results from high-resolution two-dimensional general relativistic hydrodynamic and general relativistic magnetohydrodynamic simulations of low angular momentum accretion flows onto Kerr black holes, focusing on the formation of shocks in transonic accretion flow. We demonstrate that for specific combinations of energy and angular momentum, global shock solutions naturally emerge between multiple sonic points. These shocks are sustained in both corotating and counterrotating cases, and their locations depend on specific energy, angular momentum, and the spin of the black hole, which is in good agreement with analytical solutions. In magnetized flows, weak magnetic fields preserve the shock structure, whereas strong fields suppress it, enhancing turbulence and driving powerful, magnetically dominated jets/outflows. The strength and structure of the outflow also depend on a black hole spin and magnetization, with higher black hole spin parameters leading to faster jets. Shock solutions are found only in super-Alfvénic regions, where kinetic forces dominate. Our findings provide important insights into the physics of hot corona formation and jet launching in low angular momentum accretion systems such as Sgr A* (weak jet/outflow) and X-ray binaries.

Keywords: Accretion, Black hole physics, X-ray binary stars, High energy astrophysics
The Role of Binary Configuration in Shaping Nova Evolution via Wind Accretion in Symbiotic Systems. We investigate the impact of the Bondi─Hoyle─Lyttleton (BHL) accretion mechanism on the evolution of nova eruptions in symbiotic systems by systematically varying three key input parameters: the initial donor (asymptotic giant branch, AGB) mass, the initial white dwarf (WD) mass, and the initial binary separation (a). We explore models with AGB masses in the range 1.5─3.5 M⊙, WD masses in the range 0.7─1.25 M⊙, and separations in the range 1000─8000 R⊙. We find all our models to show a significant, long-term orbital increase. This trend is primarily driven by the fact that ∼99% of the AGB's mass is lost from the system, either directly via wind—that is never accreted onto the WD—or accreted onto the WD and then ejected during nova eruptions. This results in the effect of the mass loss (or transfer) on the orbit dominating over the effect of the angular momentum loss sinks that could shrink the orbit, leading to a consistent orbit widening. Consequently, all of our WD masses gradually decrease. A more massive WD achieves a higher mass transfer efficiency and accretion rate, meaning a slightly better mass retention efficiency per nova. However, since a higher accretion rate causes more frequent eruptions, the total WD mass loss over the AGB lifetime is more substantial. We conclude that symbiotic systems transferring mass via the BHL mechanism are unlikely to be Type Ia supernova progenitors.

Keywords: Symbiotic binary stars, Stellar winds, Asymptotic giant branch, Novae
Historical Reconstruction of Solar Surface Magnetism from Cycles 1─24 Using the Synthetic Active Region Generator and the Advective Flux Transport Model. The historical reconstruction of the Sun's surface magnetic field remains a persistent challenge, limiting our ability to investigate the long-term global properties of the Sun, including the evolution of the large-scale magnetic field, solar cycle prediction, reconstruction of total solar irradiance, and secular solar variability. In this study, we employ the Advective Flux Transport (AFT) model in conjunction with our newly developed Synthetic Active Region Generator (SARG) to construct a catalog of synthetic active regions (ARs) spanning solar cycles 1─24 (1755─2020). We use the SIDC/SILSO sunspot number version 2.0 as the sole input governing the properties of the synthetic ARs in this catalog. This SARG catalog is then incorporated into the AFT model, which simulates the emergence of new ARs on the Sun, which are then transported under the influence of surface flows to produce maps of the full-Sun radial photospheric magnetic field over the entire 265 yr period. We modulate the AR tilt for each cycle in order to ensure that the polar fields are consistent with the solar cycle amplitudes. We find that the polar fields derived from these simulations exhibit excellent correlation (r &gt; 0.8) with observational proxies, including polar faculae counts and Ca II K polar network indices. Daily synchronic maps from these simulations for the entire 265 yr period are made publicly available to support a wide range of applications beyond those presented in this work.

Keywords: Solar cycle, Sunspots, Bipolar sunspot groups, Solar physics, Solar active regions
EIGER. VII. The Evolving Relationship between Galaxies and the Intergalactic Medium in the Final Stages of Reionization. We present a comprehensive analysis of the relationship between galaxies and the intergalactic medium (IGM) during the late stages of cosmic reionization, based on the complete JWST EIGER dataset. Using deep NIRCam 3.5 μm slitless spectroscopy, we construct a sample of 948 [O III]λ5008-emitting galaxies with −21.4 ≲ MUV ≲ −17.2 spanning 5.33 &lt; z &lt; 6.97 along six quasar sight lines. We correlate these galaxies with Lyα and Lyβ transmission measured from high-resolution quasar spectra across multiple redshift intervals. We find clear redshift evolution in the correlation between galaxy density and transmission: it is suppressed in overdense regions at z &lt; 5.50, while enhanced at 5.70 &lt; z &lt; 6.15. The intermediate range exhibits a transitional behavior. Cross-correlation measurements further reveal excess absorption within ∼8 cMpc of galaxies at low redshifts, and enhanced transmission at intermediate scales (∼5─20 cMpc) at z &gt; 5.70. Statistical tests using mock catalogs with realistic galaxy clustering but no correlation with the transmission field confirm that the observed correlations are unlikely to arise by chance. The evolving signals can be explained by stronger absorption in overdense regions, combined with the competing influences of local radiation fields and the rising background radiation. While local radiation dominates ionization of the surrounding IGM at earlier times, the background becomes increasingly important, eventually surpassing the impact of nearby galaxies. These results support an inside-out progression of reionization, with ionized regions originating around clustered, star-forming galaxies and gradually extending into underdense regions.

Keywords: Galaxy formation, Galaxy evolution, Intergalactic medium, Reionization, High-redshift galaxies
MINDS. Anatomy of a Water-rich, Inclined, Brown Dwarf Disk: Lack of Abundant Hydrocarbons. 2MASS J04381486+2611399 (or J0438) is one of the few young brown dwarfs (BDs) with a highly inclined (i ∼ 70°) disk. Here we report results from JWST Mid-Infrared Instrument (MIRI) Medium Resolution Spectroscopy, Hubble Space Telescope (HST) Advanced Camera for Surveys, and Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations. Despite its late spectral type (M7.25), the spectrum of J0438 resembles those of inner disks around earlier-type stars (K1─M5, T Tauri stars), with a volatile reservoir lacking hydrocarbons (except for acetylene, C2H2) and dominated by water. Other identified species are H2, CO2, HCN, [Ar+], and [Ne+]. The dominance of water over hydrocarbons is driven by multiple factors such as disk dynamics, young disk age, low accretion rate, and possible inner disk clearing. J0438 appears highly dynamic, showing a seesaw-like variability and extended emission in H2 S(1), S(3), S(5), [Ne+], and CO (J = 3─2). Interestingly, the CO emission reaches up to 400 au from the BD, suggesting ongoing infalling/outflowing activity impacting the disk chemistry. These observations underscore the combined power of MIRI, HST, and ALMA in characterizing the chemical diversity and dynamics of BD disks.

Keywords: Molecular gas, Brown dwarfs, Molecular spectroscopy, Planetary system formation, Infrared astronomy, James Webb Space Telescope, Protoplanetary disks, Circumstellar disks, Molecular spectroscopic constants
First Mid-infrared Detection and Modeling of a Flare from Sgr A*. II. Mid-infrared Spectral Energy Distribution and Millimeter Polarimetry. S. D. von Fellenberg et al. reported the first mid-infrared detection of a flare from Sgr A*. The JWST/MIRI/Medium Resolution Spectrometer observations were consistent with an orbiting hotspot undergoing electron injection with a spectrum that subsequently breaks from synchrotron cooling. However, mid-infrared extinction measurements appropriate for these data were not yet determined, and, therefore, the temporal evolution of the absolute spectral index remained unknown. This work applies new Sgr A* extinction measurements to the flare observations. The evolution of the spectral index after the peak is fully consistent with that reported in Paper I with a maximum absolute mid-infrared spectral index αMIR = 0.45 ± 0.01stat ± 0.08sys during the second mid-infrared flare peak, matching the known near-infrared spectral index during bright states (αNIR ≍ 0.5). There was a near-instantaneous change in the mid-infrared spectral index of ∆αMIR = 0.33 ± 0.06stat ± 0.11sys at the flare onset. We propose this as a quantitative definition for this infrared flare's beginning, physically interpreted as the underlying electron distribution's transition into a hard power-law distribution. This paper also reports the Submillimeter Array millimeter polarization during the flare, which shows a small, distorted, but overall CW-oriented Stokes Q─U loop during the third mid-infrared peak. Extrapolating the mid-infrared flux power law to the millimeter yields a variable flux consistent with the observed 220 GHz emission. These results, together with the Paper I modeling, plausibly suggest a single hotspot produced both the mid-infrared and millimeter variability during this event. However, additional flares are required to make a general statement about the millimeter and mid-infrared connection.

Keywords: Supermassive black holes, Galactic center, Infrared astronomy, Time domain astronomy, Polarimetry
Two Epochs of VLBI Observations of Eight KISSR Seyfert and LINER Galaxies: Suggestions of Fast and Filamentary Outflows. We present here the results from a second epoch of phase-referenced VLBA observations of eight Seyfert and LINER galaxies from the KISSR sample. These sources were chosen based on the presence of double peaks or asymmetries in their emission lines as observed in SDSS spectra. Parsec-scale radio emission is detected in seven of the eight sources in the second epoch. Jet-like features appear to persist over a ∼4─9 yr timeline in these "radio-quiet" AGN. A few sources like KISSR1494, however, show significantly different structures after a 9 yr interval. KISSR102, which was previously suggested to be a binary black hole candidate based on the presence of two compact cores, shows the tentative signatures of superluminal jet motion (1.05 ± 0.45c). Tentative superluminal motion in a jet knot has been reported in another source, KISSR872 (1.65 ± 0.57c). We present 1.5 GHz images from the VLA A-array of four sources. These images reveal core-lobe or core-halo structures. The alignment of the VLBI jet direction with the kiloparsec-scale spectral index gradient, as well as the mismatch between the star formation rate derived from the radio and Hα line emission, support the suggestion that the kiloparsec-scale emission is AGN-jet-related. The jets in KISSR sources appear to lose collimation over spatial scales between 200 pc and 1 kpc. Overall, the characteristics of the KISSR jets are reminiscent of similar properties observed in VLBI monitoring studies of "radio-loud" AGN jets even as subtle differences related to the compactness and brightness of jet features remain.

Keywords: Seyfert galaxies
Preflight Background Estimates for COSI. The Compton Spectrometer and Imager (COSI) is a Compton telescope designed to survey the 0.2─5 MeV sky, consisting of a compact array of cross-strip germanium detectors. It is planned to be launched in 2027 into an equatorial low-Earth (530 km) orbit with a prime mission duration of 2 yr. The observation of MeV gamma rays is dominated by background. Thus, background simulation and identification are crucial for predicting the sensitivities of instruments. In this work we perform Monte Carlo simulations of the background for the first 3 months in orbit, and we extrapolate the results to 2 yr in orbit in order to determine the buildup of the activation due to long-lived isotopes. The simulations account for the known background components and include time-dependent rate variations due to the geomagnetic cutoff and South Atlantic Anomaly (SAA) passages. In addition, they include detailed modeling of the delayed activation due to short- and long-lived isotopes. We determine the rates of events induced by the background that are reconstructed as Compton events in the simulated COSI data. We find that the extragalactic background photons dominate at low energies (&lt;660 keV), while delayed activation from cosmic-ray primaries (proton/alpha) and albedo photons dominate at higher energies. As part of this work, a comparison at low latitude (∣b∣ ≤ 1°) between recent measurement of the SAA and the AP9/AE9 model has been made, showing an overestimation of the flux by a factor ∼9 by the model. The systematic uncertainties associated with these components are quantified.

Keywords: Gamma-ray astronomy
Radio Counterparts of Ultraluminous X-Ray Sources in Nearby Galaxies. Radio surveys of ultraluminous X-ray sources (ULXs) allow us to find supercritically accreting compact objects (SS 433/W50-like systems) or stripped nuclear black holes in nearby galaxies. We identified 21 such objects by crossmatching a ULX catalog with the Rapid ASKAP Continuum Survey and Very Large Array Sky Survey. They may have a diverse population. (i) Three have a double-lobed radio structure with a compact core found in two of them and could be quasars. (ii) Five associated with an extended radio structure reside in star-forming regions, and their radio emission is likely due to star-forming activities. Two of them show X-ray variability suggesting that they are ULXs embedded in star-forming regions. (iii) Thirteen are associated with an unresolved radio source, with a steep spectrum seen in eight and a flat or inverted spectrum seen in two. Those with a steep spectrum are arguably candidates for SS 433/W50-like objects, with radio emission due to optically thin synchrotron radiation in a surrounding jet/wind powered nebula. Remarkable cases include NGC 925 ULX 1 and NGC 6946 ULX 1, which are associated with an optical nebula. Those with a flat or inverted spectrum could be accreting black holes with a compact jet, while the black hole mass is estimated to be several 106─108 M⊙ based on the fundamental plane. Redshift measurements are needed to firmly determine the association with their apparent host galaxy.

Keywords: Accretion, Ultraluminous x-ray sources, Radio sources, Ultracompact dwarf galaxies
Statistical Study of the Timing of the Appearance of Hα Postflare Loops: Simple Scaling Law Based on Radiative Cooling. Recent Sun-as-a-star studies have shown that postflare loops can manifest as a secondary peak in the Hα light curve, suggesting that stellar postflare loops are detectable. To understand what determines the timing of such a secondary peak in the Hα light curve associated with postflare loops, we must quantitatively identify the key physical processes controlling the appearance of Hα postflare loops. Previous case studies have indicated that the timing of the appearance of Hα postflare loops is likely governed by radiative cooling. However, the statistical characteristics of the timing of Hα postflare loops' appearance remain insufficiently investigated. In this study, we statistically investigated the timing of the appearance of Hα postflare loops to quantify their cooling processes. As a result, we found a negative correlation between the time difference between the soft X-ray peak and the appearance of the Hα postflare loops (∆t) and the soft X-ray peak flux (FX). This relationship is consistent with the theoretical scaling between radiative cooling timescale (τrad) and FX, where  τrad∝FX−1/2 . This statistical result indicates that the timing of the appearance of Hα postflare loops relative to the soft X-ray peak is primarily controlled by radiative cooling. Furthermore, we examined the dependence of the scaling law on flare spatial scales (L). Consequently, we demonstrated that the spatial scale of unresolved stellar flares can be estimated using the following scaling law:  L∝FX1/3∆t2/3 . Our results are useful for interpreting secondary peaks in the Hα data of stellar flares and provide a new method to estimate the spatial scale of unresolved stellar flares.

Keywords: Solar flares, Stellar flares, Optical flares, Flare stars