Sazuna/UAT_keywords huggingface dataset:
Gemini Near Infrared Spectrograph─Distant Quasar Survey: The Chandra View. We present Chandra observations of 63 sources from the Gemini Near Infrared Spectrograph−Distant Quasar Survey, of which 54 were targeted by snapshot observations in Cycle 24. A total of 55 sources are clearly detected in at least one X-ray band, and we set stringent upper limits on the X-ray fluxes of the remaining eight sources. In combination with rest-frame ultraviolet─optical spectroscopic data for these sources, we assess whether X-rays can provide a robust accretion rate indicator for quasars, particularly at the highest accessible redshifts. We utilize a recently modified Hβ-based Eddington luminosity ratio estimator, as well as the C IV λ1549 emission-line parameter space, to investigate trends and correlations with the optical─X-ray spectral slope (αox) and the effective hard X-ray power-law photon index (Γ). We find that αox does not improve current accretion rate estimates based on Hβ or C IV. Instead, within the limitations of our sample, we confirm previous findings that the C IV parameter space may be a better indicator of the accretion rate up to z ∼ 3.5. We also find that the average Γ values for a small subset of our sources, as well as the average Γ value in different groupings of our sources, are consistent with their respective relatively high Eddington luminosity ratios. Deeper X-ray observations of our X-ray-detected sources are needed for measuring Γ accurately and testing whether this parameter can serve as a robust, unbiased accretion rate diagnostic.

Keywords: Supermassive black holes, Quasars, X-ray point sources, X-ray active galactic nuclei, Active galactic nuclei
The Warm─Hot Disk─Halo Interface below the Perseus Spiral Arm. The Milky Way's disk─halo interface mediates energy and mass exchange between the interstellar thin disk and the halo. In the first detailed study of the Perseus arm's disk─halo interface, we combine Hubble Space Telescope/Space Telescope Imaging Spectrograph and Cosmic Origins Spectrograph absorption spectra toward six stars and 23 active galactic nuclei (AGNs) projected behind a narrow section (95° &lt; l &lt; 145°, −46° &lt; b &lt; 0°). This provides a unique data set that bridges the disk and its extended vertical structure in these directions. We measure S II, Si IV, and C IV absorption, along with H I 21 cm emission, at heights −70 pc to −3.3 kpc from the midplane. The arm's southern vertical structure shows distinct height-dependent behaviors: H I and S II column densities sharply decline with height up to 1.5 kpc, then continue declining at a much shallower rate at greater heights. In contrast, high ion (Si IV and C IV) column densities remain relatively constant throughout the entire height range. In the disk─halo interface, where warm neutral medium dominates, S II and the high ions show similar kinematics, and we find a remarkably uniform C IV/Si IV ratio (&lt;NC IV/NSi IV&gt; = 2.5 ± 0.5) within −0.9 to −3.25 kpc. Both the kinematic correspondence and high-ion ratio are consistent with the high ions probing turbulent mixing layers at the interfaces between warm/cool and hot gas phases. The AGN sight lines reveal minimal circumgalactic medium contribution in the low-velocity gas at ∣vLSR∣ &lt; 100 km s−1. The extraplanar absorbing gas may trace material ejected from previous Galactic fountain activity. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: Stellar feedback, Galaxy structure, Spiral arms, Interstellar absorption, Milky Way Galaxy fountains, Milky Way evolution
Probing the Energy-dependent Temporal Nature of MAXI J1803-298 with AstroSat and NICER. We perform a spectral and temporal analysis of MAXI J1803-298, using AstroSat/Large Area X-ray Proportional Counters and Neutron Star Interior Composition Explorer observations taken in 2021 May, during the initial phase of the outburst. We find that the source traverses through the hard, intermediate, and soft spectral states during the outburst. The spectrum in all states can be described using soft emissions from the thermal disk and hard emissions from the coronal regions. The variation in the inner-disk temperature and normalization of the disk indicate the motion of the truncated disk across these different spectral states. We confirm the presence of broad features, type C, and type B quasiperiodic oscillations in the power spectra of the different spectral states. We investigate the fractional rms and lags of all the variability features and discover that the lags swing between positive and negative during the outburst evolution. While modeling the features with a simple model that considers variations in accretion parameters, such as the accretion rate, heating rate, and inner-disk radius, along with the delays between them, we find a dynamic reversal in the origin of the variability between the corona and the disk. Furthermore, our results are consistent with previous works and a radio study conducted on this source during its outburst.

Keywords: X-ray astronomy, Stellar accretion disks, Black holes, Stellar accretion, Low-mass x-ray binary stars
The Impact of External Radiation on the Inner Disk Chemistry of Planet Formation. The vast majority of young stars hosting planet-forming disks exist within clustered environments, like the Orion Nebula, implying that seemingly "extreme" UV environments (104 G0 and above) are not so atypical in the context of planet formation. Using thermochemical modeling, we explore how the temperature and chemistry within a protoplanetary disk around a T Tauri star are impacted by the surrounding UV environment. The disk becomes hotter due to heating by photodissociation of molecules, photoelectric heating, H2, and atomic processes, and as a result, the area in which molecules exist in the ice phase shrinks, being pushed both downward and inward. Beyond 1 au, the chemistry changes most significantly in a UV-rich background; the atmosphere becomes more H2O, OH, and atomic-rich. Hydrocarbons, however, reside primarily well within 1 au of the disk; thus, their abundance and distribution are not impacted by the UV field up to 106 G0. The products of photodissociation and photochemistry are formed deeper into the disk with increasing UV background field strength beyond 1 au, impacting the chemistry near the midplane. Effectively, a "reset" chemistry takes place, with an enhancement of atoms, simple molecules, and molecules in the gas phase. Planets that form in highly irradiated regions will be exposed to a different chemical reservoir in the gas and ice phases than that in an isolated disk, and the impact from the UV background should only be detectable in highly irradiated disks (∼106 G0).

Keywords: Star forming regions, Protoplanetary disks, Astrochemistry
The HCO<SUP>+</SUP>/N<SUB>2</SUB>H<SUP>+</SUP> Flux Ratio as a Novel Tracer of Accretion Burst Activity in Protostars. Massive young stellar objects (MYSOs) accrete mass primarily through episodic accretion events, yet detecting these events remains challenging, relying chiefly on infrared and maser variability. We investigated environmental changes during accretion burst and post-burst stages in the MYSO G36.115+0.552 using multiepoch 3 mm molecular lines observed with the Purple Mountain Observatory 13.7 m telescope during 2022–2023. Significant variability was detected in the HCO+ (1–0)/N2H+ (1–0) flux ratio. Radiative transfer analysis indicates this ratio variability likely results from temperature fluctuations driven by an accretion burst, as chemical processes operate on timescales exceeding our observational window. Correlation with a 6.7 GHz methanol maser light curve suggests the HCO+/N2H+ ratio serves as a novel tracer of accretion bursts in MYSOs. This method complements infrared and maser techniques, providing a valuable tool for assessing the impact of accretion bursts on MYSO evolution.

Keywords: Interstellar line emission, Molecular spectroscopy, Star formation, Molecular clouds
Cosmic-Ray Constraints on the Flux of Ultrahigh-energy Neutrino Event KM3-230213A. The detection of a ≃220 PeV muon neutrino event by the KM3NeT telescope offers an unprecedented opportunity to probe the Universe at extreme energies. A photopion interaction origin of the neutrino requires a parent cosmic-ray energy of ≳4 EeV per nucleon. We analyze the origin of this event under three scenarios, i.e., a transient point source, diffuse astrophysical emission, and a line-of-sight interaction of an ultrahigh-energy cosmic ray (UHECR; E ≳ 0.1 EeV). Our analysis includes the flux from both a KM3NeT-only fit and a joint fit, incorporating data from KM3NeT, IceCube, and the Pierre Auger Observatory. If the neutrino event originates from transients, it requires a new population of transients that is energetic, γ-ray-dark, and more abundant than the known ones. In the framework of diffuse astrophysical emission, we compare the required local UHECR energy injection rate at ≳4 EeV with the rate derived from the flux measurements by Auger, across various models of source redshift evolution. This disfavors the KM3NeT-only fit, considering the source evolution up to high values of redshift, while the joint fit remains viable for sources contributing up to a maximum redshift  zmax≳1  for the limiting case of photopion interaction efficiency, fpγ = 0.1. For a cosmogenic origin from point sources, the luminosity obtained at redshifts z ≲ 1 from the joint fit is compatible with the Eddington luminosity of ∼109 M⊙ black holes in active galactic nuclei, assuming a proton composition and optimistic values of extragalactic magnetic field strength.

Keywords: High energy astrophysics, Neutrino astronomy, Transient sources, Cosmic ray sources, Ultra-high-energy cosmic radiation, Cosmic rays
Measurements of the Perpendicular Correlation Length of Coronal Alfvénic Waves with DKIST. We have measured the perpendicular correlation length L⊥ of Alfvénic waves in the corona using data from the Daniel K. Inouye Solar Telescope (DKIST) Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP) instrument. These data have high spatial resolution and were collected using a raster, enabling us to unambiguously identify the parallel and perpendicular directions with respect to the wave propagation. We find that the measured median L⊥ ≈ 3.5 Mm, which is about half the value found by previous measurements. We ascribe the smaller value measured here to the improved spatial resolution of DKIST. There is a gradual decrease of L⊥ as a function of frequency. We also computed the spatial correlation length of the observed static density structures and found that their typical correlation lengths of ≈8.4 Mm were significantly larger than those of the waves.

Keywords: Quiet sun, Solar coronal heating, Solar coronal waves, Alfven waves, Solar coronal streamers
Polarized Emission of Intrabinary Shocks in Spider Pulsars from Global 3D Kinetic Simulations. In spider pulsar systems, a relativistic intrabinary shock (IBS) forms when the pulsar wind collides with the massive outflow driven off the pulsar's low-mass stellar companion. The shock is a site of nonthermal particle acceleration, likely via shock-driven magnetic reconnection, and produces synchrotron emission. These shocks are among the few systems in which global scales can be reasonably captured with kinetic simulations, enabling first-principles particle acceleration and emission studies. We perform the first global 3D kinetic simulations of spider pulsar IBSs and predict their polarized emission properties. We report emission spectra, light curves, and polarization patterns as a function of the stripe-averaged magnetic field, cooling strength, and viewing inclination. At 90° inclination and for a low stripe-averaged magnetic field, we reproduce the double peaked light curve observed in spider systems. We predict a significant polarization degree ≳15%, which monotonically increases with the stripe-averaged field strength. Our results can be applied to and tested by forthcoming X-ray polarization observations of spider pulsars.

Keywords: Millisecond pulsars, Plasma astrophysics, Pulsars, Non-thermal radiation sources, Shocks, Binary pulsars
Line-of-sight Bias in Dark Matter Inferences from Galaxy Cluster Mergers. In collisions of galaxy clusters, the lack of displacement between dark matter and galaxies suggests that the dark matter scattering depth is small. This yields an upper limit on the dark matter cross section if the dark matter column density is known. We investigate a bias in such constraints: the measured column density (along the line of sight, using gravitational lensing) is lower than that experienced by a dark matter particle, as follows. Dark matter halos are triaxial and generally collide along their major axes, yielding a high scattering column density—but the merger is obvious only to observers whose line of sight is nearly perpendicular to that axis, yielding a low observed column density. We trace lines of sight through merging halos from the BigMDPL n-body simulation, both with and without mock observational effects. We find that a hypothetical skewer through the center of the halo along the merger axis (more precisely, along the current separation vector of the two halos) has nearly twice the column density of a typical line of sight. With weak lensing measurements, which involve some spatial averaging, this ratio is reduced to 1.25, suggesting that existing constraints on the scattering cross section are biased high by about 25%.

Keywords: Galaxy clusters, Dark matter
Scattering of Continuously Injected Pickup Ions of Oblique Pickup Angles in the Outer Heliosheath. Pitch angle scattering of pickup ions (PUIs) in the outer heliosheath is studied using two-dimensional hybrid simulations, with the PUIs continuously injected at specified injection rates and pickup angles. The simulations reveal the growth of quasiparallel-propagating waves, quasi-antiparallel-propagating waves, and the oblique mirror mode. The excited waves scatter the PUIs and can reverse their parallel velocities with respect to the background magnetic field. The scattering time, defined as the time when the squared standard deviation of the pitch angles of the PUIs approaches thresholds of 0.2 or 0.4, increases as the PUI injection rate decreases, approximately following a power law. The scattering time estimated for a realistic injection rate in the outer heliosheath is about 0.5 yr at a 45° pickup angle. This scattering time is shorter than the average charge exchange time of about 2 yr for the PUIs to be converted into energetic neutral atoms (ENAs). This result conflicts with the spatial retention scenario of the secondary ENA mechanism, which assumes weak (or incomplete) scattering of PUIs in the off-ribbon directions to explain the ENA ribbon discovered by the Interstellar Boundary Explorer.

Keywords: Pickup ions, Interstellar plasma
The DECam MAGIC Survey: Spectroscopic Follow-up of the Most Metal-poor Stars in the Distant Milky Way Halo. In this work, we present high-resolution spectroscopic observations for six metal-poor stars with [Fe/H] &lt; –3 (including one with [Fe/H] &lt; –4), selected using narrowband Ca II HK photometry from the DECam MAGIC Survey. The spectroscopic data confirm the accuracy of the photometric metallicities and allow for the determination of chemical abundances for 16 elements, from carbon to barium. The program stars have chemical abundances consistent with the [Fe/H] &lt; –3 range. A kinematic/dynamical analysis suggests that all program stars belong to the distant Milky Way halo population (heliocentric distances 35 &lt; dhelio/kpc ≲ 55), including three with high-energy orbits that might have been associated with the Magellanic system and one, J0026‑5445, having parameters consistent with being a member of the Sagittarius stream. The remaining two stars show kinematics consistent with the Gaia-Sausage/Enceladus dwarf galaxy merger. J0433‑5548, with [Fe/H] = –4.12, is a carbon-enhanced ultra metal-poor star, with [C/Fe] = +1.73. This star is believed to be a bona fide second-generation star, and its chemical abundance pattern was compared with yields from metal-free supernova models. Results suggest that J0433‑5548 could have been formed from a gas cloud enriched by a single supernova explosion from an ∼11 M⊙ star in the early Universe. The successful identification of such objects demonstrates the reliability of photometric metallicity estimates, which can be used for target selection and statistical studies of faint targets in the Milky Way and its satellite population. These discoveries illustrate the power of measuring chemical abundances of metal-poor Milky Way halo stars to learn more about early galaxy formation and evolution. *Based on observations gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: High resolution spectroscopy, Population III stars, Narrow band photometry, Stellar kinematics, Chemical abundances, Stellar dynamics, Population II stars, CEMP stars, Metallicity, Stellar atmospheres
A Linearly Polarized Merger Shock Down to 550 MHz: A uGMRT Study of the Merging Cluster A746. Radio relics, arc-like polarized sources with highly aligned magnetic fields, are typically found on the outskirts of merging galaxy clusters. The magnetoionic media responsible for the significant coherence observed in radio relics remain poorly understood. Low-frequency measurements of radio relics are essential for constraining depolarization models, which provide crucial insights into the magnetic field distribution. However, these measurements are challenging due to the emission properties and interferometer systematics. We have detected polarization signals from the northwest radio relic in A746 at 650 MHz with the upgraded Giant Meterwave Radio Telescope, marking the first-ever detection of polarization from radio relics below 1 GHz. At this frequency, the average rotation-measure-corrected magnetic fields align well with shock radio emission, typical of radio relics. The fractional polarization at 650 MHz is ∼18% ± 4%. Our results indicate that a single internal depolarization model cannot explain the observed depolarization spectra, suggesting a nonuniform magnetic field distribution or complex contribution of different polarized regions in the radio relic. Our detection of polarization signals at 650 MHz reveals critical insights into radio relic magnetic field structures, offering a low-frequency approach to understanding intracluster medium magnetic fields in merging galaxy clusters.

Keywords: Galaxy clusters, Extragalactic radio sources, Intracluster medium, Polarimetry, Extragalactic magnetic fields
Quasar Spectral Energy Distributions in the Rest-frame Extreme Ultraviolet: Hubble-COS Spectra of Two Ultraluminous Quasars. Using the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope with both far-UV (FUV) and near-UV (NUV) gratings, we measure the ionizing spectra of two bright, intermediate-redshift quasars in their rest-frame extreme ultraviolet (EUV). The availability of both NUV and FUV spectra allows us to define the quasar continuum and correct for strong Lyman-limit systems (LLSs) that fall in the gap between the FUV and optical. Each active galactic nucleus (AGN) has a prominent LLS, but the flux recovery shortward of their Lyman edges allows us to fit and restore the true AGN continuum. In the EUV (450─912 Å), these AGN have flux distributions,  Fν∝ν−αν , with spectral indices αν = 1.11 ± 0.22 (SBS 1010+535, zAGN = 1.5086) and αν = 0.98 ± 0.22 (HS 0747+4259, zAGN = 1.9006), both considerably harder than the mean index, αν = 1.41 ± 0.15, in a COS composite spectrum of 159 UV-bright AGN. These two AGN are outliers in the index distribution, perhaps resulting from their extremely high UV luminosity (0.4-0.9) × 1048 erg s−1), estimated black-hole masses (0.5─1) × 1010 M⊙, and effects on the inner accretion disk and Comptonized winds.

Keywords: Intergalactic medium, Lyman limit systems, Ultraviolet spectroscopy, Quasars
Exploring SEP Transport in Widespread Events with Different Heliospheric Current Sheet Models. Understanding solar energetic particle transport in wide-longitude events remains a significant question in heliophysics. By utilizing the increasing number of available observers at various heliographic distances and longitudes, such as Parker Solar Probe and Solar Orbiter, we are able to further our understanding of these widespread events. This study presents 3D test particle modeling of three widespread events during the Parker era, each detected by at least four observers. The role of the heliospheric current sheet (HCS) in transporting particles to the wide longitudes observed in these events is evaluated. A newly updated and more sophisticated HCS model is used, incorporating three different configurations derived from the Wilcox Solar Observatory, Air Force Data Assimilative Photospheric Flux Transport, and Solar Dynamics Observatory/Helioseismic and Magnetic Imager (HMI) data (via Predictive Science, PSI) for each event. The modeled proton flux profiles at each observer location are compared against energetic proton measurements for each HCS configuration. We find that inclusion of the HCS is essential to reproduce both the wide longitudinal spread of particles and the observed flux profiles in all three events. For events with longitudinal separations exceeding 100°, the most intense fluxes, both observed and modeled, are associated with observers located nearest to the HCS. This is observed for the 2023 March 13 event, where two observers were located closer in longitude and radial distance than other observers to the source region, yet observed no solar energetic particle signatures due to their lack of proximity to the HCS. Among the three configurations, the HMI-PSI-derived HCS consistently yields the best agreement between observed and modeled flux profiles.

Keywords: Heliosphere, Solar energetic particles, Space weather, Solar activity, Solar particle emission
Validation and Calibration of Semianalytical Models for the Event Horizon Telescope Observations of Sagittarius A*. The Event Horizon Telescope (EHT) enables the exploration of black hole accretion flows at event-horizon scales. Fitting ray-traced physical models to EHT observations requires the generation of synthetic images, a task that is computationally demanding. This study leverages ALINet, a generative machine learning model, to efficiently produce radiatively inefficient accretion flow (RIAF) images as a function of the specified physical parameters. ALINet has previously been shown to be able to interpolate black hole images and their associated physical parameters after training on a computationally tractable set of library images. We utilize this model to estimate the uncertainty introduced by a number of anticipated unmodeled physical effects, including interstellar scattering and intrinsic source variability. We then use this to calibrate physical parameter estimates and their associated uncertainties from RIAF model fits to mock EHT data via a library of general relativistic magnetohydrodynamics models.

Keywords: Accretion, Supermassive black holes, Galactic center, High energy astrophysics, Millimeter astronomy, Very long baseline interferometry, Convolutional neural networks, Astronomy data analysis, Computational methods, Astrophysical black holes