Sazuna/UAT_keywords huggingface dataset:
The Stripped-star Ultraviolet Magellanic Cloud Survey (SUMS): The Ultraviolet Photometric Catalog and Stripped-star Candidate Selection. Most massive stars (∼8─25M⊙) interact with a binary companion during their lifetimes. These interactions can remove the hydrogen-rich envelope, producing intermediate-mass (∼2─8M⊙) and helium-rich stars. These "stripped stars" are predicted to emit predominantly in the ultraviolet (UV) and can therefore be identified via a UV excess—provided they are not outshone by their companion. However, despite their importance to binary evolution, supernovae, and ionizing feedback, few stripped stars have been confirmed. This is likely due to the scarcity of wide-field, high angular-resolution, UV surveys of stellar populations with reliable distances and extinction estimates. To address this, we present the Stripped-Star Ultraviolet Magellanic Clouds Survey catalog. We use the Tractor forward modeling software to perform point-spread function photometry on 2420 Swift UVOT images of the LMC and SMC. The resulting catalog contains 734,862 sources in three UV filters to a depth of ∼20 Vega mag. We perform validation tests on the photometry pipeline and highlight the catalog's broad applicability. We then identify sources with excess UV light compared to main-sequence stars and apply a series of quality cuts. From this, we identify 522 candidate stripped stars in the LMC and 298 in the SMC. We assess the potential contamination from other UV excess systems and argue the dominant uncertainty to be dust: early main-sequence stars can mimic the colors of stripped-star binaries when extinction is overcorrected. This survey lays the groundwork for the first systematic census of stripped stars and opens new windows into binary evolution and massive star populations.

Keywords: Binary stars, Massive stars, Interacting binary stars, Gravitational wave sources, Ultraviolet photometry, Common envelope binary stars
Stellar Populations in the Extreme Outer Halo of the Spiral Galaxy M96. We use deep Hubble Space Telescope imaging to study stellar populations in the outer halo of the spiral galaxy M96, located in the dynamically active Leo I galaxy group. Our imaging targets two fields at a projected distance of 50 kpc from the galaxy's center, with a 50% photometric completeness limit of F814W = 28.0—nearly 2 magnitudes below the tip of the red giant branch (RGB). In both fields, we clearly detect red giant stars in M96's halo, with a space density that corresponds to an equivalent broadband surface brightness of μV ≍ 31.7 mag arcsec−2. We find little evidence for any differences in the spatial density or color of the RGB stars in the two fields. Using isochrone matching, we derive a median metallicity for the red giants of [M/H] = −1.36, with an interquartile spread of ± 0.75 dex. Adopting a power-law radial density profile, we also derive a total halo mass of  Mh=7.8−4.9+17.4×109 M⊙, implying a stellar halo mass fraction of  M*,halo/M*,tot≍15−9+33 %—on the high end for spiral galaxies, but with significant uncertainty. Finally, we find that M96 appears offset from the stellar halo mass─metallicity relationship for spirals, with a halo that is distinctly metal-poor for its halo mass. While a variety of systematic effects could have conspired to drive M96 off this relationship, if confirmed our results may argue for a markedly different accretion history for M96 compared to other spirals in the nearby Universe.

Keywords: Galaxy stellar halos, Stellar populations, Spiral galaxies
Fast X-Ray Transients in NuSTAR Data. Fast X-ray transients (FXTs) are flashes of X-rays that last for a few hundreds of seconds to a few hours. An enigmatic population of these transients that did not have a clear origin has been known for several decades, mostly found serendipitously in soft X-ray imaging observations. Recent progress in this field by the Einstein Probe has found that many FXTs are associated with gamma-ray bursts and the collapse of massive stars. Motivated by this, we searched the NuSTAR archive in the harder 3─79 keV band for ∼1000 s duration transients. From 204 Ms of exposure, we present five candidate FXTs, four of which are spectrally hard, with power-law indices −3 &lt; Γ &lt; 0, setting them apart from FXTs discovered in the soft band. Three have potential associations with galaxies at z = 0.1─2, implying 3─79 keV luminosities of 1043─1048 erg s−1 and volumetric event rates of 125─2900 Gpc−3 yr−1. The properties of these NuSTAR FXTs most resemble low-luminosity gamma-ray bursts and would be much more common than their higher-luminosity counterparts in this redshift range.

Keywords: X-ray transient sources, Gamma-ray bursts, Transient sources, X-ray bursts
A Multiwavelength ALMA View of Gas and Dust in Binary Protoplanetary System AS 205: Evidence of Dust Asymmetric Distribution. We present Atacama Large Millimeter/submillimeter Array observations of multiwavelength dust emissions at 3.1 and 1.3 mm, along with molecular line emissions of CO(2─1), CO(3─2), 13CO(3─2), and C18O(3─2) at spatial resolutions of 7─45 au toward the protoplanetary system AS 205. The dust emissions exhibit two distinct components of AS 205 N and AS 205 S, separated by 1 .″ 3. While gas kinematics within the dust disk regions are dominated by Keplerian rotation, the more extended gas emission displays complex morphology and kinematics strongly affected by the binary gravitational interaction in the outer regions. The stellar masses of AS 205 N and AS 205 S are estimated at 0.78 ± 0.19 and 1.93 ± 0.86 M⊙, respectively. Azimuthal variation is observed in the spectral index distribution of both disks. In AS 205 N, the spectral index minimum in the southwest is coincident with the peaks of CO(2─1), CO(3─2), and 13CO(3─2) integrated intensity and the relative position of its southern counterpart. On the other hand, the spectral index distribution in AS 205 S exhibits two prominent maxima, with the one in the northeast aligning with the peak of 13CO(3─2), and the peak in the south coinciding with local maxima in CO(2─1) and CO(3─2) azimuthal profiles. These results suggest a correlation between dust grain size and/or optical depth with the gas distributions. Dust trapping along the spiral arms possibly contributes to the spectral index minima in AS 205 N; however, the observed asymmetry across both disks suggests the involvement of additional mechanisms.

Keywords: Millimeter astronomy, Circumstellar dust, Protoplanetary disks, Circumstellar gas
Universal Stochastic Process in Blazar Gamma-Ray Variability Revealed by Bayesian Kernel Comparison. Although Gaussian processes have been widely applied in modeling the high-energy light curves of blazars, a systematic comparison of the performances of different kernel functions within Gaussian processes has remained lacking. Based on a Bayesian inference framework, we systematically compare the performances of three Gaussian process kernel functions in modeling blazars' long-term gamma-ray light curves. The results indicate that, among the tested kernel functions, the Matérn 1/2 kernel performs best for both types of blazars—BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs)—suggesting that a universal stochastic process likely governs the high-energy variability of the blazar population. Statistically, this kernel is equivalent to the "shot-noise" model, supporting the scenario that the gamma-ray variability in blazars originates from the random superposition of numerous independent flares. A statistical analysis of hyperparameters reveals that the variability amplitude of FSRQs is significantly higher than that of BL Lacs, which may be related to their radiation being more strongly modulated by external photon fields. The intrinsic correlation timescales of both sources are similar and show no dependence on black hole mass or intrinsic luminosity. This indicates that the timescale is primarily determined by local physical conditions within the jet, rather than by the global properties of the central engine.

Keywords: Blazars, Gamma-rays, Gaussian Processes regression
Effect of Flow-aligned External Magnetic Fields on Mushroom Instability. Mushroom instability (MI) is a shear instability considered to be related to generating and amplifying magnetic fields in relativistic jets. While astrophysical jets are usually magnetized, how MI acts in magnetized jets remains poorly understood. In this paper, we investigate the effect of a flow-aligned external magnetic field on MI with both theoretical analyses and particle-in-cell (PIC) simulations. In the limit of a cold and collisionless plasma, we derive a generalized dispersion relation for linear growth rates of the magnetized MIs. Numerical solutions of the dispersion relation reveal that the external magnetic field always suppresses MI, though MIs are more robust against the field than electron-scale Kelvin─Helmholtz instabilities. Replacing protons in the shear flow with positrons enhances the instability growth in weakly magnetized regimes but suppresses it in strongly magnetized cases. Analyses are also extended to instabilities with an arbitrary wavevector in the shear interface plane, where a coupling effect is observed for subrelativistic scenarios. The 2D PIC simulations of single-mode MIs reach a good agreement with our analytical predictions, and we observe formation of a quasi-steady saturation structure of electrons in magnetized runs. In simulations with finite temperatures, we observe the competition and cooperation between MIs and a diffusion-induced direct current magnetic field.

Keywords: Relativistic jets, Magnetic fields, Plasma physics, Plasma jets
Ion-neutral Drift Velocity as a Diagnostic of Dust Growth and Magnetic Fields in Star-forming Environments. Recent observations have revealed that the ion-neutral drift velocity in star-forming molecular clouds and dense cores is on the order of ∼100 m s−1. Theoretical studies have shown that, in ambipolar diffusion—the process responsible for the differential motion between ions and neutrals—the dust size distribution has a significant impact on the magnetic resistivities. In this study, we perform simulations to investigate how dust growth through accretion and coagulation affects the ion-neutral drift velocity in molecular clouds and cores. We find that, on core scales, both dust growth and a magnetic field strength of 200 μG are required to reproduce the observed drift velocity. We suggest that measurements of ion-neutral drift velocity, particularly on core scales, may serve as a new diagnostic to constrain the dust size distribution and magnetic field strength in such environments.

Keywords: Dust physics, Magnetic fields, Molecular clouds
On High-frequency Kinetic Alfvén Waves in Space and Solar Plasma. Kinetic Alfvén waves (KAWs) are ubiquitous in space and solar plasmas and are believed to be crucial for energy transfer and particle energization. Existing studies on KAWs primarily focus on the low-frequency approximation, where the wave frequency is much smaller than the proton cyclotron frequency (i.e., ω ≪ ωcp). However, the wave properties of high-frequency KAWs with ω ≳ ωcp remain unclear. In this work, based on the two-fluid theory, we derive a general dispersion relation for KAWs spanning low-frequency to high-frequency regimes, and examine this dispersion relation and the electromagnetic properties of both low-frequency and high-frequency KAWs. Our findings reveal that, compared to low-frequency KAWs, high-frequency KAWs exhibit several distinct features: higher wave frequency (ω ≳ ωcp), propagation angle over a broader oblique angle range, significantly larger ratio of parallel to perpendicular electric field, and the magnetic helicity and magnetic compressibility that are highly sensitive to the plasma beta. The enhanced parallel electric field highlights the pivotal role of high-frequency KAWs in field-aligned particle acceleration. This work extends KAW theory to the high-frequency domain, providing key insights into KAW properties and the particle acceleration process in space and solar plasmas.

Keywords: Space plasmas, Solar wind, Alfven waves
Characterizing the Roman Grism Redshift Efficiency of Type Ia Supernova Host Galaxies for the High-latitude Time-domain Survey. The High-latitude Time-domain Survey (HLTDS) for the Nancy Grace Roman Space Telescope (Roman) will discover thousands of high-redshift Type Ia supernovae (SNe Ia) to set generation-defining cosmological constraints on dark energy. To construct the Roman SN Hubble diagram, a strategy to obtain redshifts must be determined. While the nominal HLTDS will use only the Roman prism, in this work, we consider the utility of the Roman grism observations from overlap with the High-latitude Wide-area Survey for SN Ia cosmology. We determine a galaxy grism redshift recovery rate by simulating dispersed grism images and measuring redshifts with the Grizli software, obtaining an H-band 50% redshift recovery at magnitude 20.61 and 90% recovery at magnitude 19.27. To estimate the total number of spectroscopic redshifts expected for Roman SN cosmology, we also consider a Roman prism SN redshift efficiency and a ground-based telescope redshift efficiency for host galaxies. We apply these redshift efficiencies to SN Ia catalog-level simulations and predict that ∼6800 SNe will have an SN or host spectroscopic redshift. Second, we evaluate the size of potential systematics related to modeling the grism redshift efficiency by considering the impact of additional dependences on stellar mass and host-galaxy color. We estimate the largest potential size of this systematic to be 0.0066 ± 0.002 and −0.0266 ± 0.0079, roughly 42.9% and 49.6% of the statistical uncertainty, for w0 and wa, respectively. Lastly, we consider the effects of assuming different redshift sources on the optimization of the HLTDS survey strategy by measuring relative changes to the dark energy figure of merit.

Keywords: Cosmology, Type Ia supernovae
A Spatially Resolved Turbulent Transport Model of the Spectrum and Extension of the Crab Nebula. The Crab Nebula is an exceptional astrophysical laboratory for studying the acceleration, transportation, and radiation of ultrarelativistic particles, since its nonthermal emission extends across the entire electromagnetic spectrum up to the PeV γ-rays. Utilizing the latest spectral energy distribution (SED) and energy-dependent morphological measurements, we develop a spatially resolved turbulent transport model that enables us to explore the transport and radiative cooling mechanisms of particles within the Crab Nebula. The model self-consistently links turbulent waves and particles via bidirectional coupling: turbulent scattering regulates particle diffusion escape, while self-generated waves via particle-induced streaming instability mediate turbulent amplification. We simultaneously reproduce the SED and extension of the Crab Nebula, finding the energy-dependent morphologies more favorable to the Kolmogorov-type turbulence. The observed radial shrinkage at both X-ray and TeV γ-ray energies can be attributed to the synchrotron burn-off and particle diffusion escape. Our model predicts a radially increasing diffusion coefficient profile, transitioning from an approximately linear energy dependence in the inner nebula to a quasi-linear regime in outer regions.

Keywords: Pulsar wind nebulae, Pulsars
A Serendipitous NuSTAR Detection of a Giant Radio Source Harboring an Obscured Active Galactic Nucleus. Giant radio sources (GRSs) harbor the Universe's largest structures generated by individual galaxies, with projected source sizes exceeding 700 kpc. These enigmatic objects have been mainly studied at radio frequencies, and their physical properties in the high-energy domain are poorly understood. Here we present the results of a multiwavelength study focused on NuSTAR J112829+5831.8 (J1128+5831), the only known GRS serendipitously detected with the Nuclear Spectroscopic Telescope Array. Being located in proximity to the famous interacting galaxy system, Arp 299, J1128+5831 has been serendipitously observed also by the Chandra X-ray Observatory, Hubble Space Telescope, and XMM-Newton satellites. From radio observations with the Low Frequency Array, the NRAO VLA Sky Survey, and the Very Large Array Sky Survey, we have determined that J1128+5831 has an overall steep radio spectrum (α = −0.86; Fν ∝ να) and a low core dominance (CD = −2.4, in log-scale), indicating the source to be viewed at large angles. From the X-ray spectral analysis, we found J1128+5831 to harbor an obscured active galactic nucleus (AGN) with neutral hydrogen column density exceeding 1023 cm−2. Its optical spectrum, taken with the Dark Energy Spectroscopic Instrument, exhibits prominent narrow emission lines but lacks broad components, thus confirming J1128+5831 to be a Type 2 AGN powered by a radiatively efficient accreting system. Overall, the broadband properties of J1128+5831 are consistent with those observed for the general GRS population.

Keywords: X-ray active galactic nuclei, Giant radio galaxies
Studies in Astronomical Time Series Analysis. VIII. The Double Lomb─Scargle Periodogram and Super Resolution. Multiple-frequency periodograms—based on time-series models consisting of two or more independent sinusoids—have long been discussed. What is new here is the presentation of a practical, simple-to-use computational framework implementing this concept. Our algorithms have super resolution that evades the Rayleigh criterion, as well as provision for statistical weighting and tapering. They can be used for essentially any time series (e.g., time-tagged events or point measurements) with arbitrary sampling—even or uneven. Examples of super resolution of synthetic data, sunspot numbers, and the rich pulsations of white dwarf J0135+5722 demonstrate practical applications. Appendices derive generalized periodograms using an arbitrary number of arbitrary basis functions and define several examples of nonsinusoidal bases for these omnigrams. Application beyond the frequency domain is demonstrated with an autoregressive model exhibiting super resolution in the time domain. A GitHub repository contains omnigram code and symbolic algebra scripts for generating it.

Keywords: Lomb-Scargle periodogram
Long-term Timing Evolution of Four Anomalous X-Ray Pulsars. Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are believed to be manifestations of magnetars. Typically, AXPs exhibit higher X-ray luminosities, whereas SGRs are generally fainter and display significantly high signal-to-noise ratios only during their outburst phases. In this work, we report the long-term timing evolution of four AXPs: 1E 2259+586, 4U 0142+61, 1RXS J170849.0─400910, and 1E 1841-045, which were regularly monitored with Neutron Star Interior Composition Explorer from 2017 to 2024. Over this period, we identify a total of 10 timing events. In addition to one glitch and one antiglitch in 1E 2259+586 reported in the literature, we detect another eight new timing events: five glitches, two antiglitches, and one unusual state transition event. Notably, both antiglitches were observed in 4U 0142+61, making it the most frequent source of such events, and there is a hint of regular evolution in its pulse profile. In the case of 1RXS J170849.0─400910, it continues to exhibit pronounced high-frequency timing anomalies and undergoes a state transition event. Finally, we study the evolution of the pulse profiles and find that the profiles of 1E 2259+586 and 4U 0142+61 both evolve. This is consistent with the earlier finding that pulse profile evolution is a generic feature of magnetars.

Keywords: Neutron stars, Pulsar timing method, Pulsars
Detecting Neutrino Emission from Supernova Remnants: A Theoretically Motivated Target Catalog. Galactic supernova remnants (SNRs) are thought to accelerate cosmic rays (CRs) to several PeV energies, but this has yet to be confirmed as general behavior. Although several sources show ∼100 TeV γ-rays, their hadronic origin is uncertain; a matching neutrino signal would provide definitive evidence. Using insight from the theory of diffusive shock acceleration, we evaluate the spectra and environments of the sample of Galactic SNRs to identify those most likely to be hadronic, categorizing them into a tiered catalog, depending on their likelihood to produce neutrinos detectable in the TeV─PeV range. We then calculate the estimated stacked sensitivity of IceCube for each tier using IceCube's 10-year public data. Our results suggest that this strategy of stacking SNRs and carefully excluding leptonic sources by using theoretical arguments may allow for a detection of this source class that would otherwise be impossible. A follow-up analysis of these catalogs using TeV─PeV sensitive neutrino data from IceCube (or similar telescopes like KM3NeT/ARCA) offers the most decisive, near-future test for the hadronic nature of these SNRs and the maximum energies of their CR spectra.

Keywords: High energy astrophysics, Neutrino astronomy, Supernova remnants, Galactic cosmic rays, Gamma-rays
Investigating the Efficacy of Topologically Derived Time Series for Flare Forecasting. II. XGBoost Model. Solar flares are a primary driver of space weather, and forecasting their occurrence remains a significant challenge. This paper presents a novel flare prediction model based on topologically derived photospheric magnetic parameters. We employ the ARTop framework to compute the time-dependent input rates of magnetic winding and helicity across &gt;105 active region observations, decomposing them into current-carrying and potential components to reduce sensitivity to optical flow methods. An XGBoost machine learning model is trained on these time series, alongside engineered features including rolling statistics, kurtosis, and flare history, to predict the probability of ≥M1.0 class flares within the next 24 hr. The model demonstrates strong performance on a validation set, with a true skill statistic (TSS) of 0.804 for once-daily operational region forecasts. When applied to a fully independent dataset, the model achieves a TSS of 0.524. A SHAP analysis confirms the model's physical interpretability, identifying flare history and accumulated current-carrying winding and helicity as the most important features. The main challenges identified are false positives arising from active regions with frequent C-class flaring and systematic errors via projection effects when active regions are near the limb. Excluding limb-affected data yields no improvement in the holdout set TSS (0.521 versus 0.524), due to the overall decreased number of flares. However, our per-region analysis indicates that mitigating these projection effects is crucial for future operational deployment. This work establishes magnetic topology, particularly its current-carrying components, as a highly effective and physically meaningful set of predictors for solar flare forecasting.

Keywords: Solar active region magnetic fields, Solar flares, Astronomy databases, Classification, Neural networks, Space weather