Sazuna/UAT_keywords huggingface dataset:
Modeling the Energy Release in Solar Eruptive Events. Magnetic reconnection in a flare current sheet is widely believed to be the main energy release process powering solar flares and coronal mass ejections (CMEs). Modeling this process and determining the channels for the energy release, mass motions, and heating has long been a major goal in space science. We present results from a two-fluid magnetohydrodynamic simulation of an eruptive flare/CME using a newly developed version of the Space Weather Modeling Framework that incorporates two major advances in numerical capability. First, we use the STatistical InjecTion of Condensed Helicity formalism for the energy buildup, so that we start with a potential-field minimum-energy state and slowly form a sheared filament channel over a polarity inversion line as is observed on the Sun. Second, we use a new formulation of the plasma energetics that is explicitly energy conserving while calculating separate electron and ion temperatures and separate parallel and perpendicular pressures, as desired. For this first simulation with our new model, we opted for the nonadiabatic heating to go solely into the protons and for an isotropic pressure. We discuss the resulting energetics of the reconnection and, in particular, the plasma heating in the reconnecting current sheets, mass acceleration, and shock formation. We also discuss the implications of our results for flare/CME observations and for understanding solar eruptions in general.

Keywords: Magnetohydrodynamics, Solar active regions, Solar physics, Solar coronal mass ejections, Solar corona
Improving Radio Source Count Estimation Using Kernel Density Estimation. Radio source counts provide a fundamental census of cosmic radio emission, yet their estimation is usually based on coarse histograms that suffer from bin-choice bias, boundary effects, and survey incompleteness. We apply and rigorously evaluate kernel density estimation (KDE) as a nonparametric alternative to the conventional binned method for estimating differential radio source counts. Using simulated flux-limited samples derived from an input luminosity function model, we compare the performance of standard KDE, adaptive KDE, and traditional binning methods. Our results show that KDE-based approaches yield more accurate and stable estimates, particularly in the high-flux regime where data are sparse and conventional methods struggle. We also apply the adaptive KDE method to real observational data from the LOFAR Two-Metre Sky Survey Deep Fields. Our analysis robustly confirms the pronounced "drop and bump" feature at sub-mJy flux densities, but also reveals that a secondary, modest bump seen in the binned data at ∼10 mJy is likely a binning artifact. We also demonstrate the flexibility of KDE in addressing observational incompleteness through weighted estimation, which applies weights continuously at the level of individual sources rather than averaging them in discrete bins. These strengths make KDE a powerful tool for source-count analyses in current and future radio surveys and, more broadly, in analogous studies at other wavelengths. All computations in this study are implemented with AstroKDE, a Python package we have developed for astronomical applications.

Keywords: Extragalactic radio sources, Nonparametric inference, Radio source counts, Astronomy data analysis
Solar-like Oscillations in Accreting Pre-main-sequence Stars: Insights and Prospects. We present theoretical predictions for solar-like oscillators in the pre-main-sequence (pre-MS) phase of stellar evolution. Our pre-MS models start from a stellar seed of 0.01 solar masses that gains mass through accretion, offering an alternative description to the classical approach segmented into the Hayashi and Henyey tracks. Evolutionary models are calculated using the MESA stellar evolution code with a custom accretion routine, and pulsation properties are investigated using the GYRE oscillation code. We present evolutionary tracks and internal structures for accreting pre-MS solar-like stars in a mass range from 0.7 to 1.6 solar masses, adopting 35 mass accretion histories previously extracted from two-dimensional magneto-hydrodynamical simulations. Atmospheric parameters of our models constrain characteristic frequencies of pre-MS solar-like oscillators to be generally greater than 500 μHz. We highlight the imprint of accretion on the buoyancy and Lamb profiles, and illustrate the effects on the small- and large-frequency separations. We additionally quantify individual frequency differences across the 35 accretion histories at the zero-age MS, showcasing differences no larger than 20 μHz for an exemplary model. Finally, we discuss the potential of detecting solar-like oscillations in pre-MS stars with the upcoming ESA PLATO mission.

Keywords: Accretion, Pre-main sequence stars, Star formation, Circumstellar disks, Solar oscillations, Asteroseismology
Explainable Machine Learning Classification of Chandra X-Ray Sources: SHAP Analysis of Multiwavelength Features. Extensive astronomical surveys, like those conducted with the Chandra X-ray Observatory, detect hundreds of thousands of unidentified cosmic sources. Machine learning (ML) methods offer an efficient, probabilistic approach to classifying them, which can be useful for making discoveries and conducting deeper studies. In earlier work, we applied the LightGBM (ML model) to classify 277,069 Chandra point sources into eight categories: active galactic nuclei (AGNs), X-ray emitting stars, young stellar objects (YSO), high-mass X-ray binaries, low-mass X-ray binaries, ultraluminous X-ray sources, cataclysmic variables, and pulsars. In this work, we present the classification table of 54,770 robustly classified sources (over 3σ confidence), including 14,066 sources at &gt;4σ significance. To ensure classification reliability and gain a deeper insight, we investigate the multiwavelength feature relationships learned by the LightGBM model, focusing on AGNs, stars, and YSOs. We employ explainable artificial intelligence (XAI) techniques, specifically, Shapley Additive Explanations, to quantify the contribution of individual features and their interactions to the predicted classification probabilities. Among other things, we find infrared-optical and X-ray decision boundaries for separating AGN/stars, and infrared-X-ray boundaries for YSOs. These results are crucial for estimating object classes even with limited multiwavelength data. This study represents one of the earliest applications of XAI to large-scale astronomical data sets, demonstrating ML models' potential for uncovering physically meaningful patterns in data in addition to classification. Finally, our publicly available, extensive, and interactive catalog will be helpful to explore the contributions of features and their combinations in greater detail in the future.

Keywords: Classification, Astrostatistics techniques, X-ray point sources, Young stellar objects, Computational methods, X-ray active galactic nuclei, X-ray stars
Probing the Physical and Chemical Characteristics of an Extremely Early Class 0 Protostar in G204.4-11.3A2-NE. We have observed the low-mass molecular cloud core G204.4-11.3A2-NE (G204NE) in the direction of Orion B giant molecular cloud with the Atacama Large Millimeter/submillimeter Array in Band 6. The 1.3 mm continuum images and visibilities unveil a compact central structure with a radius of ∼12 au, while showing no signature of binarity down to 18 au. The bolometric temperature and luminosity of this source are derived to be ∼33 K and ∼1.15 L⊙, respectively. Chemical stratification is observed in dense gas tracers, with C18O emission peaking at the continuum position surrounded by the spatially extended emission of N2D+ and DCO+. This implies that the core is in a very early evolutionary stage in which CO depletion occurs in most regions except for a small area heated by the central source. The envelope kinematics indicate a rotating and infalling structure with a central protostar mass of 0.08─0.1 M⊙. The protostar drives a collimated outflow traced by CO, SiO, SO, and H2CO, with misaligned blueshifted and redshifted lobes exhibiting a pair of bow-like patterns. High-velocity jets, extending up to 720 au, are detected in CO, SiO, and SO lines. The jet launching region is likely within twice of the dust sublimation zone. The absence of a binary signature suggests the outflows and jets are driven by a single protostar, although a close binary cannot be ruled out. The observed deflection of the outflows and jet is likely due to turbulent accretion in a moderately magnetized core.

Keywords: Early stellar evolution, Stellar jets, Astrochemistry, Circumstellar matter, Stellar winds, Young stellar objects, Star formation, Low mass stars, Protostars
Extreme Geoeffectiveness by the Turbulent Sheath of the ICME of the 2024 October Space Weather Event. The impact of severe space weather events driven by interplanetary coronal mass ejections (ICMEs) on the space environment of planets remains an active area of research. The intense space weather event of 2024 October 10─11 was driven by an isolated ICME characterized by well-defined sheath and magnetic cloud structures, which offered a unique opportunity to investigate their sequential impacts on the terrestrial space environment. In situ plasma and magnetic field measurements from NASA's ACE, Wind, and ISRO's Aditya-L1 spacecraft are utilized to identify the structure of this ICME. Concurrently, data from GOES-16 and -18, along with observations from the Magnetospheric Multiscale mission, are employed to analyze the magnetosphere's distinct response to the various components of the ICME. Intense magnetic field compression, driven by enhanced solar wind pressure in the ICME sheath, exposed geostationary satellites positioned in the morning and noon local time sectors to interplanetary space as the magnetopause boundary moved Earthward, reaching below 5 RE. Most of the intensification of the ring current took place within the transit of the ICME sheath, indicative of the superior role of the sheath plasma. During the passage of the turbulent ICME-sheath, a severe intensification of field-aligned currents (FACs), equatorward expansion, and multiple bands of FACs were noted within the Earth's magnetosphere─ionosphere system, unlike in the magnetic cloud phase. These observations underscore the critical role of the ICME sheath in driving extreme space weather effects at Earth. Further, we contrast this storm's drivers and its geoeffectiveness with those of the 2024 May 10 superstorm—the most extreme geomagnetic event at Earth in two decades.

Keywords: Space weather, Solar coronal mass ejections
Cross-correlation of Luminous Red Galaxies with ML-selected Active Galactic Nuclei in HSC-SSP. II. AGN Classification and Clustering with DESI Spectroscopy. An unresolved question in studies of active galactic nuclei (AGNs) is whether their distinct classes probe different evolutionary stages of black hole─host galaxy interaction. We present the projected two-point cross-correlation function between a sample of Dark Energy Spectroscopic Instrument (DESI)-matched AGNs selected from Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) optical + Wide-field Infrared Survey Explorer (WISE) mid-IR photometry, and DESI-designated luminous red galaxies (LRGs), for z ∈ 0.5─1.0. The total overlap area is 43.4 deg2, including ∼27,000 spectroscopic LRGs. We visually classified 1991 matched HSC×DESI objects in our redshift range, spectroscopically confirming that 1517 (76%) of them are AGNs. Of these 1517 objects, 73% are broad-line AGNs, and 27% are obscured AGNs. We infer that the parent HSC+WISE AGN catalog has a number density of at least ∼240 deg−2, confirming it is one of the most complete optical/infrared AGN catalogs to date. We investigate the AGN clustering as a function of the spectroscopic classification. The inferred average mass of the halos &lt;Mh&gt; that host unobscured broad-line AGNs (Mh ≍ 1013.4 h−1M⊙) is ∼5.5 × larger than the halos that host obscured AGNs (Mh ≍ 1012.6 h−1M⊙), at 2.8σ significance, in the same sense as our prior work based on photometric redshifts. This suggests that we may relax our concerns about systematic shifts in the inferred redshift distribution producing this halo mass difference. While we do not yet find statistically significant spectroscopic evidence that unobscured AGNs reside in more-massive halos than their obscured counterparts, further analyses are necessary to distinguish if more complex evolutionary histories are needed to model these AGN populations.

Keywords: Active galactic nuclei, Clustering, Large-scale structure of the universe
A Luminous and Hot Infrared through X-Ray Transient at a 5 kpc Offset from a Dwarf Galaxy. We are searching for hot, constant-color, offset optical flares in the Zwicky Transient Facility data stream that are &gt;10″ from any galaxy in public imaging data from the PanSTARRS survey. Here, we present the first discovery from this search: AT 2024puz, a luminous multiwavelength transient offset by 5 kpc from a ∼108 M⊙ galaxy at z = 0.356 with a low─moderate star formation rate (0.01 ± 0.003 M⊙ yr−1). It produced luminous 1044.79±0.04 erg s−1 optical/UV emission that evolved on a ∼20 day timescale, as well as 1044.12±0.03 erg s−1 X-ray emission with a photon-index  Γ=1.73−0.09+0.10 . No associated radio or millimeter emission was detected. We show that the early time optical emission is likely powered by reprocessing of high-energy, accretion-powered radiation, with a possible contribution from a shock in a dense circumtransient medium. If the shock is dominant at early times, the circumtransient medium has a mass ∼0.1─1 M⊙, a radius 1015 cm, and a density profile shallower than ∼r−1. A near-infrared excess appears at late-times and is suggestive of reprocessing within a wind or other circumtransient medium. The X-rays are most consistent with a central engine. We suggest that AT 2024puz may be associated with an accretion event onto a 50─105 M⊙ black hole, where the lower masses are preferred based on the large projected offset from the host galaxy. AT2024puz exhibits properties similar to both luminous, fast, blue optical transients and tidal disruption events, but is intermediate between them in its energetics and evolution timescale. This highlights the need for broader exploration of the landscape of hot optical transients to trace their origins.

Keywords: Intermediate-mass black holes, Tidal disruption, Dwarf galaxies, Transient sources, X-ray transient sources, Ultraviolet transient sources, Astrophysical black holes
Analyses of the Ancient Chinese Report on the Total Solar Eclipse in 709 BCE: Implications for the Contemporaneous Earth's Rotation Speed and Solar Cycles. Total solar eclipses have occasionally left their footprints on human history for millennia, serving as spot references for the Earth's rotation speed and the solar cycle variations in the past. The earliest datable accounts with explicit mention date back to 709 BCE (hereafter −708) in ancient Chinese records, although the observational site and date were documented differently in previous studies. This study revisits the source reports and confirms the explicit mentions of the eclipse totality and a later addendum concerning the yellowish structure that has been traditionally associated with the K-corona "above and below" the eclipsed Sun. Archeological evidence allows us to revise the coordinate of Qūfù, the observational site, to N35°36', E116°59', in contrast to the previous studies. This location contradicts the recent ∆T spline curve, revising the ∆T constraint in −708 to 20,264 s ≤ ∆T ≤ 21,204 s and modifying other ∆T constraints from the eighth and sixth centuries BCE. The later addendum regarding the possible coronal structure requires a philological caveat on the source provenance, although it corroborates well with the recent solar cycle reconstruction. During the total solar eclipse, the solar disk was inclined at ≍58° from the local zenith at Qūfù, locating the possible coronal streamer belts at heliographic latitude ≍+32° ± 45° and −32° ± 45°. Our result broadly agrees with the inclination and width of the streamer belt reconstructed from the recent estimate of open solar flux based on radiocarbon data in the first millennium BCE and offers possible independent support for the recent solar cycle reconstruction in the late eighth century BCE.

Keywords: Solar cycle, Total eclipses, Sunspot number, Solar eclipses, Solar wind, Celestial mechanics, Solar corona, Planetary science
A Precessing, Magnetically Dominated, Structured Jet Powering the Hour-scale Quasiperiodic GRB 250702B. GRB 250702B shows ultralong episodic prompt activity (three hard-gamma-ray episodes over ≃3.2 hr with quasi-regular spacing P ≃ 2825 s) preceded by a soft-X-ray flare about one day earlier. We interpret these phenomena with a unified scenario in which a stellar-mass black hole accretes from a massive misaligned debris disk and launches a magnetically dominated, precessing, structured (spine─sheath) jet. The engine "clock" arises from Lense─Thirring precession of the outer annulus of a geometrically thick inner torus at r ≍ 250─300 rg, while the hard spectra reflect magnetic reconnection dissipation in the spine. A slightly off-axis viewing geometry resolves the apparent opening-angle tension without invoking late energy injection. "Missing" pulses in the second/third cycles occur naturally when low-amplitude nutation causes the beaming cone to miss the line of sight. The model yields concrete, falsifiable predictions, providing a self-consistent explanation of GRB 250702B's radiative and outflow anomalies.

Keywords: Accretion, Black hole physics, Gamma-ray bursts, Relativistic jets
Multiple Shells in Supernova 2023ixf Support the Jittering Jets Explosion Mechanism. Examining the photospheric time evolution of the core-collapse supernova (CCSN) SN 2023ixf from the literature, we identify two (possibly three) evolutionary time periods with constant expansion velocities, which we attribute to two (or three) ejecta shells. We find that several CCSN remnants have morphologies with two or more complete or partial shells, compatible with the presence of two (or three) photospheric shells during the photospheric phase of the explosion. Studies have attributed these CCSN remnants to the jittering-jet explosion mechanism (JJEM), which involves two or three energetic pairs of jets participating in the explosion. We, therefore, conclude that the structure of the photospheric shells of SN 2023ixf supports its explosion by the JJEM. This study adds to the accumulating evidence that the JJEM is the primary explosion mechanism of CCSNE.

Keywords: Supernova remnants, Type II supernovae, Stellar jets, Core-collapse supernovae
OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration. We present the OASIS survey program discovery of a substellar companion orbiting the young A1V star HIP 71618, detected using precision astrometry from Gaia and Hipparcos and high-contrast imaging with SCExAO/CHARIS and Keck/NIRC2. Atmospheric modeling favors a spectral type of M5─M8 and a temperature of ∼2700 ± 100 K. Dynamical modeling constrains HIP 71618 B's mass to be  60−21+27 MJup or  65−29+54 MJup, depending on the adopted companion mass prior. It has a nearly-edge-on 11 au orbit with high eccentricity. HIP 71618 B will be located within the Roman Coronagraph's dark-hole region during the instrument's technological demonstration phase. A high-signal-to-noise-ratio detection of HIP 71618 B at 575 nm would demonstrate a 5σ contrast of 10−7 or better. The system is also located within or very close to the Roman Coronagraph's Continuous Viewing Zone—near multiple candidate reference stars for dark-hole digging—and its primary is bright (V ≍ 5). The suitability of HIP 71618 as a potential Roman Coronagraph target for demonstrating the instrument's core requirement (TTR5) should motivate the timely deep vetting of candidate reference stars. *Based in part on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: High contrast techniques, Brown dwarfs, Astrometric exoplanet detection, Adaptive optics, Direct imaging
Quasar Radiative Feedback May Suppress Galaxy Growth on Intergalactic Scales at z = 6.3. We present observational evidence that intense ionizing radiation from a luminous quasar suppresses nebular emission in nearby galaxies on intergalactic scales at z = 6.3. Using JWST/NIRCam grism spectroscopy from the Slitless Areal Pure-Parallel High-Redshift Emission survey and Emission-line galaxies and Intergalactic Gas in the Epoch of Reionization programs, we identify a moderate but statistically significant decline in [O III] λ5008 luminosity relative to the UV continuum (L5008/L1500) among galaxies within ∼7 comoving Mpc (cMpc) of the quasar J0100+2802, the most UV-luminous quasar known at this epoch (M1450 = −29.26). While L1500 remains roughly constant with transverse distance, L5008 increases significantly, suggesting suppression of very recent star formation toward the quasar. The effect persists after controlling for completeness, local density, and UV luminosity, and correlates with the projected photoionization-rate profile Γqso. A weaker but directionally consistent suppression in L5008/L1500 is also observed along the line of sight. The transverse suppression radius (∼7 cMpc) implies a recent radiative episode with a cumulative duration ∼3.1 Myr, shorter than required for thermal photoheating to dominate and thus more naturally explained by rapid H2 photodissociation and related radiative processes. Environmental effects alone appear insufficient to explain the signal. Our results provide direct, geometry-based constraints on large-scale quasar radiative feedback and recent quasar lifetimes.

Keywords: Intergalactic medium, High-redshift galaxies, Quasars
Machine Learning Confirms GW231123 is a "Lite" Intermediate Mass Black Hole Merger. The LIGO─Virgo─KAGRA Collaboration recently reported GW231123, a black hole merger with total mass of around 190─265 M⊙. This event adds to the growing evidence of "lite" intermediate mass black hole (IMBH) discoveries of postmerger black holes ≳100 M⊙. GW231123 posed several data analysis challenges owing to waveform-model systematics and the presence of noise artifacts called glitches. We present the first comprehensive machine learning analysis to further validate this event, strengthen its astrophysical inference, and characterize instrumental noise in its vicinity. Our approach uses a combination of tools tailored for specific analyses: GW-WHISPER, an adaptation of OpenAI's audio transformer; ARCHGEM, a Gaussian mixture model─based soft clustering and density approximation software; and AWARE, a convolutional autoencoder. We identify the data segment containing the merger with &gt;70% confidence in both detectors and verify its astrophysical origin. We then characterize the scattered light glitch around the event, providing the first physically interpretable parameters for the glitch. We also reconstruct the real waveforms from the data with slightly better agreement to model-agnostic reconstructions than to quasi-circular models, hinting at possible astrophysics beyond current waveform families (such as noncircular orbits or environmental imprints). Finally, by demonstrating high-fidelity waveform reconstructions for simulated mergers with total masses between 100 and 1000 M⊙, we show that our method can confidently probe the IMBH regime. Our integrated framework offers a powerful complementary tool to traditional pipelines for rapid, robust analysis of massive, glitch-contaminated events.

Keywords: Gravitational waves, Gravitational wave sources