Sazuna/UAT_keywords huggingface dataset:
Orbital Modulation of Gamma Rays up to 100 TeV from LS 5039. Gamma-ray binaries are luminous in gamma rays, composed of a compact object orbiting a massive companion star. The interaction between these two objects can drive relativistic outflows, either jets or winds, in which particles can be accelerated to energies reaching hundreds of teraelectronvolts (TeV). However, it is still debated where and under which physical conditions particles are accelerated in these objects and ultimately whether protons can be accelerated up to PeV energies. Among the well-known gamma-ray binaries, LS 5039 is a high-mass X-ray binary with an orbital period of 3.9 days that has been observed up to TeV energies by the High Energy Stereoscopic System. We present new observations of LS 5039 obtained with the High Altitude Water Cherenkov (HAWC) observatory. Our data reveal that the gamma-ray spectrum of LS 5039 extends up to 200 TeV with no apparent spectral cutoff. Furthermore, we confirm, with a confidence level of 4.7σ, that the emission between 2 and 118 TeV is modulated by the orbital motion of the system, and find a 2.2σ hint of variability above 100 TeV. This indicates that these photons are likely produced within or near the binary orbit, where they can undergo absorption by the stellar photons. In a leptonic scenario, the highest energy photons detected by HAWC can be emitted by ∼200 TeV electrons inverse Compton scattering stellar photons, which would require an extremely efficient acceleration mechanism operating within LS 5039. Alternatively, a hadronic scenario could explain the data through proton–proton or proton–gamma collisions of protons accelerated to petaelectronvolt energies.

Keywords: Gamma-ray sources, Gamma-ray observatories, High mass x-ray binary stars, High energy astrophysics
A Wide-field Map of Ultracompact Dwarfs in the Coma Cluster. A data set of 23,351 globular clusters (GCs) and ultracompact dwarfs (UCDs) in the Coma cluster of galaxies was built using Hubble Space Telescope Advanced Camera for Surveys data. Based on the standard magnitude cut of MV ≤ −11, a total of 523 UCD candidates are found within this data set of compact stellar systems (CSS). From a color─magnitude diagram analysis built using this catalog, we find a clear mass─magnitude relation extending marginally into the UCD parameter space. The luminosity function defined by this data set shows an excess of sources at bright magnitudes, suggesting a bimodal formation scenario for UCDs. We estimate the number of UCDs with a different origin than GC to be NUCD ≳ 32 ± 1. We derive the total number of CSS within the core (1 Mpc) of Coma to be NCSS ≍ 69,400 ± 1400. The radial distribution of UCDs in Coma shows that, like GCs, UCDs agglomerate around three giant ellipticals: NGC 4874, NGC 4889, and IC 4051. We find UCDs are more centrally concentrated around these three ellipticals than GCs. IC 4051 has a satellite population of UCDs similar to NGC 4874 and NGC 4889. We estimate only ∼14% of UCDs inhabit the intracluster space (ICUCD) between galaxies in the region, in comparison to ∼24% for GCs (ICGC). We find red (metal-rich) UCDs are more likely located closer to a host galaxy, with blue (metal-poor) UCDs showing a greater dispersion and lower average density in the region.

Keywords: Globular star clusters, Galaxy clusters, Coma Cluster, Galaxy evolution, Ultracompact dwarf galaxies
A Cometary Fluorescence Model for the ν<SUB>3</SUB> Vibrational Band of Cyanogen. Cyanogen (C2N2) has been suspected for a long time to be present in comets and to contribute to the creation of the CN radical. So far no observations with ground-based facilities have managed to detect this species, but the Rosetta mission, thanks to in situ observations with the ROSINA mass spectrometer, detected this species in the coma of 67P/Churyumov─Gerasimenko. To investigate its presence from infrared spectra in other comets, we developed a fluorescence model for the ν3 fundamental band. From new laboratory high-resolution infrared spectra of cyanogen, we analyzed the region of the ν3 band of C2N2, centered around 4.63 μm (2158 cm−1). In addition to line positions and intensities, molecular parameters for the ground and excited vibrational state were obtained. These parameters allowed us to develop a fluorescence model for cyanogen. Line-by-line excitation rates of the ν3 band of cyanogen in cometary comae are presented. An upper limit of the abundance of cyanogen in a spectrum of comet C/2022 E3 (ZTF) is discussed.

Keywords: Comets, Molecular data, Molecular spectroscopy, Near infrared astronomy
On the Relation between the Inclination Angle of the Accretion Disk and the Broad-line Region in Active Galactic Nuclei. Models of active galactic nuclei (AGN) often invoke a close physical association between the broad-line region (BLR) and the accretion disk. We evaluate this theoretical expectation by investigating the relationship between the inclination angle of the BLR (θBLR) and the inclination angle of the inner accretion disk (θdisk). For a sample of eight AGN that have published values of θBLR estimated from dynamical modeling of the BLR based on velocity-resolved reverberation mapping experiments, we analyze high-quality, joint XMM-Newton and NuSTAR X-ray observations to derive new, robust measurements of θdisk through broadband (0.3─78 keV) reflection spectroscopy. Mock spectra demonstrate that the results are generally not strongly affected by warm absorbers or the model used to fit the soft-band data. We find a strong, positive correlation between θBLR and θdisk (Pearson correlation coefficient 0.856, p-value 0.007), although Monte Carlo simulations indicate that the level of significance is only marginal (&lt;3σ). Nevertheless, the nearly linear relation between θBLR and θdisk suggests a possible physical alignment between the accretion disk and the BLR. Future studies with a larger and more homogeneous sample are needed to confirm the correlation and refine our understanding of the structure and dynamics of the central regions of active galaxies.

Keywords: Accretion, Supermassive black holes, Reverberation mapping, Active galaxies, Seyfert galaxies, X-ray active galactic nuclei
Local Analogs of Potential Ionizers of the Intergalactic Medium: Compact Star-forming Galaxies with Intense C IV λ1550 Emission. We performed spectroscopic analyses of five local compact star-forming galaxies (CSFGs) with extremely high [O III]/[O II] (O32) ratios (&gt;20). These targets remarkably share similar properties with high-redshift C IV emitters at z &gt; 6: high Hβ equivalent widths (EWs &gt; 200Å), extreme O32 ratios, low metallicities (12+log(O/H) ≲ 7.8), low C/O abundances (log(C/O) &lt; −0.7), and high ionization conditions (logU &gt; −2). The ultraviolet (UV) spectra were acquired using the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph. We have identified a wealth of rest-frame UV emission lines (C IV, He II, O III], C III]) in the HST spectra. Notably, all our targets show intense C IV emission lines with rest-frame EWs &gt; 10 Å, indicative of hard ionizing radiation. The rest-frame UV emission line diagnostics disfavor an active galactic nucelus and could be consistent with significant shock contributions to the source of ionizing radiation. Four of our targets show high C IV/C III] ratios (≥1.4), suggestive of strong Lyman-continuum leakage (LyC escape fraction, fesc,LyC &gt; 10%) from these sources. This is consistent with their Lyα-inferred LyC escape fractions (fesc,LyC = 9%─31%). We derive relative C/O abundances from our sources, showing log(C/O) values from −1.28 to −0.77, comparable to those of reionization-era galaxies at z ≳ 6. The properties of the CSFGs, particularly their intense C IV emission and high O32 ratios, which suggest significant LyC escape fractions, are similar to those of the reionization-era C IV emitters. These similarities reinforce the hypothesis that these CSFGs are the closest analogs of significant contributors to the reionization of the intergalactic medium.

Keywords: Abundance ratios, Dwarf galaxies, Compact dwarf galaxies, Emission line galaxies, Ultraviolet astronomy, Interstellar medium, Reionization, Galaxy spectroscopy
The Dust Extinction Curve: Beyond R(V). The dust extinction curve is typically parameterized by a single variable, R(V), in optical and near-infrared wavelengths. R(V) controls the slope of the extinction-versus-wavelength curve, and is thought to reflect the grain-size distribution and composition of dust. Low-resolution, flux-calibrated BP/RP spectra from Gaia have allowed the determination of the extinction curve along sightlines to 130 million stars in the Milky Way and Magellanic Clouds. We show that these extinction curves contain more than a single degree of freedom—that is, that they are not simply described by R(V). We identify a number of components that are orthogonal to R(V) variation, and we show that these components vary across the sky in coherent patterns that resemble interstellar medium (ISM) structure. These components encode variation in the 770 nm extinction feature, intermediate-scale and very broad structure, and a newly identified feature at 850 nm, and they likely trace both dust composition and local conditions in the ISM. Correlations of the 770 and 850 nm features with R(V) suggest that their carriers become more abundant as the carrier of the 2175 Å feature is destroyed. Our 24 million extinction-curve decompositions and feature equivalent-width measurements are publicly available at doi:10.5281/zenodo.14005028.

Keywords: Interstellar dust, Polycyclic aromatic hydrocarbons, Interstellar dust extinction, Principal component analysis, Interstellar medium
Effect of Magnetic Field on the Accretion Phase of Population III Star Formation. We examine the impact of the magnetic field on Population III star formation by varying its strength. We perform simulations with magnetic field strengths ranging from 10‑20 G to 10‑4 G, in addition to a model without a magnetic field. The simulations are run for &gt;1000–1400 yr after the first protostar forms. In weak-field models, the surrounding disk fragments, forming multiple protostars, and the magnetic field is amplified by the orbital motion and rotation of these protostars. In the model without a magnetic field, frequent fragmentation occurs, and the most massive protostar reaches ∼200 M⊙. However, in models with a magnetic field, once the magnetic field is amplified, the protostars merge to form a single massive protostar, and no further fragmentation occurs except in the model with the strongest magnetic field. Even after the formation of the single protostar, the magnetic field continues to amplify, leading to the formation of a thick disk supported by magnetic pressure and a global spiral pattern. In models with moderate or strong magnetic fields, a rotating disk can form, but fragmentation does not occur, and a strong magnetic field drives an outflow. However, the range of parameters for both disk formation and outflow driving is very narrow, making their appearance under realistic conditions unlikely. Given the weak magnetic field in the early Universe, Population III stars are expected to form as single stars, surrounded by a thick disk with a spiral pattern. Thus, the magnetic field, regardless of its strength, plays a crucial role in Population III star formation.

Keywords: Population III stars, Primordial magnetic fields, Stellar jets, Star formation, Protostars, Magnetohydrodynamical simulations
On the Origin of Jupiter's Fuzzy Core: Constraints from N-body, Impact, and Evolution Simulations. It has been suggested that Jupiter's fuzzy core could be a result of a giant impact. Here, we investigate the expected impact conditions from N-body simulations. We then use state-of-the-art smoothed particle hydrodynamics simulations to investigate the results of impacts with different conditions including various impactor masses and composition, different formation stages in Jupiter's growth, and different resolutions. We next simulate the long-term thermal evolution of Jupiter postimpact. We find that 3D N-body simulations predict rather oblique impacts, and that head-on collisions are rare. Moreover, our results show that, even under a head-on collision, Jupiter's fuzzy core cannot be formed. We next simulated Jupiter's thermal evolution and showed that, unless postimpact temperatures are extremely low, a giant impact would not lead to an extended dilute core as inferred by interior models. We conclude that Jupiter's fuzzy core is not caused by an impact and is likely to be an outcome of its formation process.

Keywords: Solar system gas giant planets, Jupiter, Atmospheric composition, Planetary interior, Planet formation
The Milky Way Radial Metallicity Gradient as an Equilibrium Phenomenon: Why Old Stars Are Metal Rich. Metallicities of both gas and stars decline toward large radii in spiral galaxies, a trend known as the radial metallicity gradient. We quantify the evolution of the metallicity gradient in the Milky Way as traced by APOGEE red giants with age estimates from machine learning algorithms. Stars up to ages of ∼9 Gyr follow a similar relation between metallicity and Galactocentric radius. This constancy challenges current models of Galactic chemical evolution, which typically predict lower metallicities for older stellar populations. Our results favor an equilibrium scenario, in which the gas-phase gradient reaches a nearly constant normalization early in the disk lifetime. Using a fiducial choice of parameters, we demonstrate that one possible origin of this behavior is an outflow that more readily ejects gas from the interstellar medium (ISM) with increasing Galactocentric radius. A direct effect of the outflow is that baryons do not remain in the ISM for long, which causes the ratio of star formation to accretion,  Σ̇⋆/Σ̇in , to quickly become constant. This ratio is closely related to the local equilibrium metallicity, since its numerator and denominator set the rates of metal production by stars and hydrogen gained through accretion, respectively. Building in a merger event results in a perturbation that evolves back toward the equilibrium state on ∼Gyr timescales. Under the equilibrium scenario, the radial metallicity gradient is not a consequence of the inside-out growth of the disk but instead reflects a trend of declining  Σ̇⋆/Σ̇in  with increasing Galactocentric radius.

Keywords: Galactic winds, Galaxy chemical evolution, Chemical abundances, Chemical enrichment, Milky Way disk, Milky Way evolution
Application of Deep Learning to the Classification of Stokes Profiles: From the Quiet Sun to Sunspots. The morphology of circular polarization profiles from solar spectropolarimetric observations encodes information about the magnetic field strength, inclination, and line-of-sight velocity gradients. Previous studies used manual methods or unsupervised machine learning (ML) to classify the shapes of circular polarization profiles. We trained a multilayer perceptron comparing classifications with unsupervised ML. The method was tested on quiet Sun data sets from Daniel K. Inouye Solar Telescope (DKIST), Hinode, and GREGOR, as well as simulations of granulation and a sunspot. We achieve validation metrics typically close to or above 90%. We also present the first statistical analysis of quiet Sun DKIST/ViSP data using inversions and our supervised classifier. We demonstrate that classifications with unsupervised ML alone can introduce systemic errors that could compromise statistical comparisons. DKIST and Hinode classifications in the quiet Sun are similar, despite our modeling indicating spatial resolution differences should alter the shapes of circular polarization signals. Asymmetrical (symmetrical) profiles are less (more) common in GREGOR than DKIST or Hinode data, consistent with narrower response functions in the 1564.85 nm line. Single-lobed profiles are extremely rare in GREGOR data. In the sunspot simulation, the 630.25 nm line produces "double" profiles in the penumbra, likely a manifestation of magneto-optical effects in horizontal fields; these are rarer in the 1564.85 nm line. We find the 1564.85 nm line detects more reverse polarity magnetic fields in the penumbra, in contradiction to observations. We detect mixed-polarity profiles in nearly one fifth of the penumbra. Supervised ML robustly classifies solar spectropolarimetric data, enabling detailed statistical analyses of magnetic fields.

Keywords: Magnetic fields, Solar photosphere, Classification, Neural networks
Expectation for the Hard X-Ray and Gamma-Ray Emission from Pair-instability Supernovae. Pair-instability supernovae (PISNe) are predicted thermonuclear explosions of massive stars with helium core masses exceeding ∼65M⊙, and they synthesize substantial amounts of radioactive 56Ni (M(56Ni) ∼ 60 M⊙ in extreme cases). To investigate their observational signatures, we developed a multi-D Monte Carlo radiation transport code, assuming spherical symmetry in the background medium and the photon sources distribution, and performed simulations of gamma-ray and hard X-ray emissions from the decay chain 56Ni→56Co→56Fe. We find that key gamma-ray lines (847 and 1238 keV) from 56Co decay in the 130 M⊙ helium core model can be detected up to 300–400 Mpc by next-generation MeV gamma-ray telescopes. In contrast, the signals from the 100 M⊙ model remain below the detection limits. Our results provide the template for gamma-ray follow-up observations of PISNe. Considering theoretical predictions and observational constraints, we estimate PISN event rates within 300 Mpc to be approximately 0.01–0.1 events per year, highlighting their rarity but also emphasizing their feasibility as targets for future gamma-ray observations over the decade.

Keywords: X-ray astronomy, Gamma-ray astronomy, Supernovae
FAST Observation of Polarized Radio Emission of Rotating Radio Transient J2325‑0530. In this study, we present a detailed analysis of single-pulse emission from the rotating radio transient (RRAT) J2325‑0530, observed at 1250 MHz using the Five-hundred-meter Aperture Spherical Radio Telescope. A total of 168 burst pulses were detected within 0.8 hr of observation, yielding a detection rate 3 to 4 times higher than those previously reported. For the first time in this RRAT, we detected sequences of consecutive single-pulse emission lasting two to six spin periods. The single pulses exhibit significant variability in linear polarization, circular polarization, and polarization position angle, while the average profile displays weak polarization and a complex position angle structure. The distributions of fluence and waiting time, together with the significant correlation between fluence and pulse width, indicate that the emission behavior of RRAT J2325‑0530 resembles that of giant pulse phenomena. We also measured the scintillation bandwidth and timescale at 1250 MHz to be 3.45 ± 0.07 MHz and 16.67 ± 0.35 minutes, respectively. In three single pulses, we detected quasiperiodic microstructure in the Stokes I, L, and V parameters, with differing microstructure periods across these components. Nevertheless, the observed microstructure periods follow the known linear relationship with the pulsar rotation period. These results support the view that RRATs share the same underlying emission physics of normal pulsars, while also revealing additional complexity in the origin of microstructure.

Keywords: Radio transient sources, Pulsars, Radio pulsars
Observation of Diffuse Galactic Light Near the Galactic Center with ONC-T on Board Hayabusa2. Diffuse Galactic light (DGL) is starlight scattered by interstellar dust. In visible wavelengths, earlier studies observed DGL toward regions of low optical depth in high Galactic latitude, and show marginal consistency with a theoretical model assuming single scattering by dust grains. However, a model for DGL in regions of high optical depth has not been established. In this study, we analyze wide-field imaging data toward a region of high optical depth near the Galactic center, which was obtained with the Optical Navigation Camera on board the Hayabusa2 spacecraft. The data are reduced by dark-current and stray-light subtraction, flat-field correction, and sensitivity calibration for the DGL measurement. In the image, we select dark low-intensity areas where background starlight is highly absorbed by interstellar dust, and extract the DGL component by masking pixels contaminated by stars. As a result, we find that the DGL intensity decreases toward high optical depth, and this trend is reversed from the previous measurements in optically thin regions. To explain the observed trend, we introduce DGL models inferred from a radiative transfer equation in a plane-parallel dusty slab. By assuming literature values for the albedo and scattering asymmetry factor of interstellar dust, the measured DGL intensity can be fitted by a model in which a dust slab without internal emitters is illuminated by backside stars.

Keywords: Interstellar dust, Galactic center, Diffuse radiation, Interstellar dust extinction, Astrophysical dust processes, Dark interstellar clouds, Radiative transfer, Interstellar scattering
Insight into the Origin of Multiwavelength Emissions of PKS 1510−089 Through Modeling 12 SEDs from 2008 to 2015. PKS 1510−089 is one of the most peculiar sources among the flat spectrum radio quasars, exhibiting a notable big blue bump. This provides a unique opportunity to explore the coupling between the activity of the central engine and the relativistic jet, offering further insight into the origin of the multiwavelength emissions. To this end, we collected multiwavelength data spanning four periods from 2008 to 2015 and performed the spectral energy distribution (SED) modeling using a one-zone homogeneous leptonic model. In the model, a multichromatic accretion disk (AD) is used to fit the optical/UV data sets, while the external radiation fields from the broad-line region (BLR) and dusty torus (DT) are properly considered to produce the high-energy γ-ray emissions. Our best fit to 12 SEDs yields the following results: (i) The innermost stable orbit (RISO) of the AD is not stable but varies between 3 RS and 18 RS during these observations. (ii) The high-energy hump of the SED is well dominated by Compton scattering of the BLR photons, while the X-ray flux may be comprised of multiple radiation components. (iii) The γ-ray emitting regions are generally matter-dominated, with low magnetization, and are located beyond the BLR but within the DT. At such distance, the multiwavelength emissions are likely to originate from shock accelerations. (iv) For the energization of the relativistic jet, our study supports the Blandford−Znajek mechanism, instead of the Blandford−Payne mechanism, as the latter fails to power the jet.

Keywords: Spectropolarimetry, Gamma-ray sources, Blazars, Flat-spectrum radio quasars, Relativistic jets, Non-thermal radiation sources