Sazuna/UAT_keywords huggingface dataset:
The Small Sizes and High Implied Densities of "Little Red Dots" with Balmer Breaks Could Explain Their Broad Emission Lines without an Active Galactic Nucleus. Early JWST studies found an apparent population of massive, compact galaxies at redshifts z ≳ 7. Recently three of these galaxies were shown to have prominent Balmer breaks, demonstrating that their light at λrest ∼ 3500 Å is dominated by a stellar population that is relatively old (∼200 Myr). All three also have broad Hβ emission with σ &gt; 1000 km s‑1, a common feature of such "little red dots." From Sérsic profile fits to the Near Infrared Camera images in F200W we find that the stellar light of galaxies is extremely compact: the galaxies have half-light radii of re ∼ 100 pc, in the regime of ultracompact dwarfs in the nearby Universe. Their masses are uncertain, as they depend on the contribution of possible light from an active galactic nucleus (AGN) to the flux at λrest &gt; 5000 Å. If the AGN contribution is low beyond the Balmer break region, the masses are M* ∼ 1010–1011 M☉, and the central densities are higher than those of any other known galaxy population by 1 order of magnitude. Interestingly, the implied velocity dispersions of ∼1500 km s‑1 are in very good agreement with the measured Hβ line widths. We suggest that some of the broad lines in "little red dots" are not due to AGNs, but simply reflect the kinematics of the galaxies, and speculate that the galaxies are observed in a short-lived phase where the central densities are much higher than at later times. We stress, however, that the canonical interpretation of AGNs causing the broad Hβ lines also remains viable.

Keywords: Compact galaxies, Active galaxies, Galactic and extragalactic astronomy, Galaxy spectroscopy, High-redshift galaxies, Galaxies
Partial Alignment of Astrometric Position Excursions of International Celestial Reference Frame Quasars with Radio Jet Structures. Published analyses of very long baseline interferometry data for the sources included in the third International Celestial Reference Frame catalog have revealed object-specific, excess astrometric variability and quasi-coherent trajectories as functions of time. A fraction of these sources show markedly elongated distributions of positions on the sky measured with diurnal observations. Here we apply a novel statistical and data-processing method to the diurnal position measurements stretching over 40 yr to quantify the degree of elongation and its position angle, for each source with more than 200 data points. We find that 49% of the examined sources have distribution elongations in excess of 1.3. Robust uncertainties of the directions of maximal astrometric dispersion are computed by the bootstrapping method, and the results are compared with a larger catalog of radio jet directions by A. V. Plavin et al. (2022). Nearly one-half of the sources with smaller position angle uncertainties are found to have astrometric position excursions from their mean positions aligned with the radio jet structures within ±30°.

Keywords: Radio jets, Very long baseline interferometry, Radio astrometry, Radio loud quasars, Astrometry, Position angle
Information-theory-based System-level Babcock–Leighton Flux Transport Model–Data Comparisons. System-level Babcock–Leighton flux transport model–data comparisons are performed using information theory. The model is run with a maximum meridional flow speed of 16.5 m s‑1 with the flow speed systematically varied by 20% (BLFT20) and 50% (BLFT50). Overall, the comparisons show that the models qualitatively capture much of the information flow among the toroidal field (sunspot number), polar field, and meridional flow. BLFT20 generally compares better than BLFT50, suggesting that meridional flow variation of 20% may be more realistic than 50%. However, the information flow from the meridional flow to the polar field is captured better in BLFT50. There is more information flow from the sunspot number to the polar field than the other way around in BLFT20 and observations. The information flow from the polar field to the sunspot number peaks at lag times (τ) of ∼2 yr and 7–9 yr in observations and BLFT20. The results can shed light on the nature of the Sun's magnetic memory, the diffusive/dissipative processes, and advection in the turbulent flux transport at the Sun.

Keywords: Solar cycle, Cross-validation , Astrostatistics techniques, Solar dynamo, Time series analysis
Fermi-LAT Detection of the Low-luminosity Radio Galaxy NGC 4278 during the LHAASO Campaign. We present a study of the high-energy properties of the compact symmetric object NGC 4278, recently associated with a TeV source by the Large High Altitude Air Shower Observatory (LHAASO) collaboration. We conducted a dedicated analysis of a Fermi Large Area Telescope (LAT) region around NGC 4278, limited to the LHAASO campaign conducted from 2021 March to 2022 October. A statistically significant emission (∼4.3σ) was revealed, spatially consistent with the radio position of NGC 4278 and the LHAASO source. The Fermi-LAT source is detected above 8 GeV, exhibiting a hard spectrum (photon index Γ = 1.3 ± 0.3) and a γ-ray luminosity of L&gt;100 MeV ≃ 4 × 1041 erg s–1. A serendipitous Swift X-Ray Telescope (XRT) observation of NGC 4278 during the TeV campaign reveals the source in a high state, with a flux  , compatible with the highest luminosity level observed in previous Chandra pointings. The high-energy spectral energy distribution of the source and the intense flux variation observed in the X-ray band support a jet origin for the observed radiation. We suggest that the significant enhancement of the high-energy flux observed during the LHAASO campaign is due to a transient, highly energetic perturbation in the jet. The detection of NGC 4278 at both high and very high energies opens new frontiers in studying particle acceleration processes. It reveals that even compact, low-power radio galaxies can exceed the sensitivity thresholds of GeV and TeV instruments, becoming promising targets for the upcoming Cherenkov Telescope Array Observatory.

Keywords: Relativistic jets, Low-luminosity active galactic nuclei, X-ray active galactic nuclei, Gamma-rays
XMM-Newton High-resolution Spectroscopy of EXO 0748─676 after Its Reemergence from a Long Quiescence. EXO 0748─676 is a well-studied, high-inclination, dipping and eclipsing neutron star low-mass X-ray binary that has recently emerged from 16 yr of quiescence into a new outburst. We present results from 55.5 ks of XMM-Newton observation, focusing on high-resolution spectroscopy with the same instrument (the Reflection Grating Spectrometer) that produced significant insights during the previous outburst. The XMM-Newton European Photon Imaging Camera light curve reveals a type I X-ray burst that leads to a corresponding optical burst by 3 s. To understand the effects of the burst on the ionization structure, the data are divided into burstless and pre- and postburst spectra, with additional analysis for dip and nondip phases. The primary spectral feature in all phases is a broad O VII recombination line, accompanied by velocity-broadened O VIII, N VII, and Ne IX lines. Notably, the Ne IX line shows different ionization states for the preburst (11.65 Å) and postburst (13.56 Å) phases, while the dips also substantially affect the spectral lines. The current outburst mirrors many traits from the earlier one, such as a similar spectral state, plasma components with similar ionization structure, and spectral features from the same elements, implying a stable long-term accretion behavior across outbursts.

Keywords: Neutron stars, High resolution spectroscopy, X-ray astronomy, Low-mass x-ray binary stars, X-ray bursts
Ultra-High-Energy Cosmic Rays Accelerated by Magnetically Dominated Turbulence. Ultra-high-energy cosmic rays (UHECRs), particles characterized by energies exceeding 1018 eV, are generally believed to be accelerated electromagnetically in high-energy astrophysical sources. One promising mechanism of UHECR acceleration is magnetized turbulence. We demonstrate from first principles, using fully kinetic particle-in-cell simulations, that magnetically dominated turbulence accelerates particles on a short timescale, producing a power-law energy distribution with a rigidity-dependent, sharply defined cutoff well approximated by the form  . Particle escape from the turbulent accelerating region is energy dependent, with tesc ∝ E‑δ and δ ∼ 1/3. The resulting particle flux from the accelerator follows  , with s ∼ 2.1. We fit the Pierre Auger Observatory's spectrum and composition measurements, taking into account particle interactions between acceleration and detection, and show that the turbulence-associated energy cutoff is well supported by the data, with the best-fitting spectral index being  . Our first-principles results indicate that particle acceleration by magnetically dominated turbulence may constitute the physical mechanism responsible for UHECR acceleration.

Keywords: High energy astrophysics, Plasma physics, Plasma astrophysics, Particle astrophysics, Cosmic rays
Observed Fluctuation Enhancement and Departure from WKB Theory in Sub-Alfvénic Solar Wind. Using Parker Solar Probe data from orbits 8 through 17, we examine fluctuation amplitudes throughout the critical region where the solar wind flow speed approaches and then exceeds the Alfvén wave speed, taking account of various exigencies of the plasma data. In contrast to WKB theory for noninteracting Alfvén waves streaming away from the Sun, the magnetic and kinetic fluctuation energies per unit volume are not monotonically decreasing. Instead, there is clear violation of conservation of standard WKB wave action, which is consistent with previous indications of strong in situ fluctuation energy input in the solar wind near the Alfvén critical region. This points to strong violations of WKB theory due to nonlinearity (turbulence) and major energy input near the critical region, which we interpret as likely due to driving by large-scale coronal shear flows.

Keywords: Interplanetary turbulence, Solar wind, Alfven waves, Solar corona, Interplanetary magnetic fields, Solar coronal waves
Acceleration of Ultra-high-energy Cosmic Rays in the Kiloparsec-scale Jets of Nearby Radio Galaxies. Radio galaxies have long been considered as potential sources of ultra-high-energy cosmic rays (UHECRs). Recent analyses of the UHECR spectrum, composition, and arrival directions indicate that the nearest radio galaxy, Centaurus A, could be linked to the reported dipole anisotropy, though the mechanism underlying the acceleration remains elusive. In this Letter, we explore UHECR acceleration in the kiloparsec-scale jets of radio galaxies, exemplified by Centaurus A. Using high-resolution relativistic magnetohydrodynamic and test-particle simulations without subgrid physics, we investigate the acceleration of the highest-energy particles in the turbulent sheath of a fast-moving jet. Our findings demonstrate that acceleration close to the maximum theoretical expectation is possible. When extrapolated to nearby radio galaxies, our results suggest that the kiloparsec-scale jets of Centaurus A could account for the dipole anisotropy in UHECRs, while more potent Fanaroff–Riley type II radio galaxies may account for the observed UHECR spectrum with a rigidity cutoff at a few Exavolts.

Keywords: High energy astrophysics, Relativistic jets, Radio galaxies, Ultra-high-energy cosmic radiation, Magnetohydrodynamical simulations
Detection of the Orbital Modulation of Fe Kα Fluorescence Emission in Centaurus X-3 Using the High-resolution Spectrometer Resolve on board XRISM. The Fe Kα fluorescence line emission in X-ray spectra is a powerful diagnostic tool for various astrophysical objects to reveal the distribution of cold matter around photoionizing sources. The advent of the X-ray microcalorimeter on board the XRISM satellite will bring new constraints on the emission line. We present one of the first such results for the high-mass X-ray binary Centaurus X-3, which is composed of an O-type star and a neutron star (NS). We conducted a 155 ks observation covering an entire binary orbit. A weak Fe Kα line was detected in all orbital phases at an equivalent width (EW) of 10–20 eV. We found for the first time that its radial velocity (RV) is sinusoidally modulated by the orbital phase. The RV amplitude is 248 ± 13 km s‑1, which is significantly smaller than the value (391 km s‑1) expected if the emission is from the NS surface, but is consistent if the emission takes place at the O star surface. We discuss several possibilities of the line production site, including the NS surface, O star surface, O star wind, and accretion stream from the O star to the NS. We ran radiative transfer calculation for some of them assuming spherically symmetric density and velocity profiles and an isotropic distribution of X-ray emission from the NS. None of them explains the observed EW and velocity dispersion dependence on the orbital phase, suggesting that more elaborated modeling is needed. In other words, the present observational results have the capability to constrain deviations from these assumptions.

Keywords: Neutron stars, X-ray binary stars, Radiative transfer, High energy astrophysics
ALMA Observations of the Gamma-Ray Binary System PSR B1259-63/LS 2883 during the 2024 Periastron Passage. We present observations of the gamma-ray binary PSR B1259-63/LS 2883 with the Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (97 GHz), Band 6 (233 GHz), and Band 7 (343 GHz). PSR B1259-63/LS 2883 consists of a pulsar in a highly eccentric orbit around a massive companion star, with the pulsar passing through the circumstellar disk near periastron. Our new data were obtained over several epochs, ranging from ‑61 to +29 days from the periastron passage in 2024. We report an increase in flux in all bands near the periastron. The significant change in Band 3 flux suggests synchrotron emission from the interaction between the pulsar wind and the stellar wind or disk. The Band 6 flux shows an increase around periastron and a transition from thermal emission from the circumstellar disk to synchrotron emission. The Band 7 observation +24 days after periastron shows a brightening, suggesting that the pulsar's passage through the disk does not result in its immediate destruction. We discuss the implications of these results for the interaction between the pulsar wind and the circumstellar disk, such as the possible disk expansion after periastron.

Keywords: Neutron stars, Be stars, High mass x-ray binary stars, Radio pulsars
Detection of Gas Inflow during the Onset of a Starburst in a Low-mass Galaxy at z = 2.45. The baryon cycle is crucial for understanding galaxy formation, as gas inflows and outflows vary throughout a galaxy's lifetime and affect its star formation rate. Despite the necessity of accretion for galaxy growth at high redshifts, direct observations of inflowing gas have proven elusive, especially at z ≳ 2. We present a spectroscopic analysis of a galaxy at redshift z = 2.45, which exhibits signs of inflow in several ultraviolet interstellar absorption lines, with no clear outflow signatures. The absorption lines are redshifted by ∼250 km s‑1 with respect to the systemic redshift, and C IV shows a prominent inverse P-Cygni profile. Simple stellar population models suggest that this galaxy has a low metallicity (∼5% solar), with a very young starburst of age ∼4 Myr dominating the ultraviolet luminosity. The gas inflow velocity and nebular velocity dispersion suggest an approximate halo mass of order ∼1011M⊙, a regime in which simulations predict that bursty star formation is common at this redshift. We conclude that this system is likely in the beginning of a cycle of bursty star formation, where inflow and star formation rates are high, but where supernovae and other feedback processes have not yet launched strong outflows. In this scenario, we expect the inflow-dominated phase to be observable (e.g., with net redshifted interstellar medium absorption) for only a short timescale after a starburst onset. This result represents a promising avenue for probing the full baryon cycle, including inflows, during the formative phases of low-mass galaxies at high redshifts.

Keywords: Galaxy formation, Interstellar absorption, Galaxy evolution, Circumgalactic medium, High-redshift galaxies
Silicon Isotopic Composition of Mainstream Presolar SiC Grains Revisited: The Impact of Nuclear Reaction Rate Uncertainties. Presolar grains are stardust particles that condensed in the ejecta or in the outflows of dying stars and can today be extracted from meteorites. They recorded the nucleosynthetic fingerprint of their parent stars and thus serve as valuable probes of these astrophysical sites. The most common types of presolar silicon carbide grains (called mainstream SiC grains) condensed in the outflows of asymptotic giant branch stars. Their measured silicon isotopic abundances are not significantly influenced by nucleosynthesis within the parent star but rather represent the pristine stellar composition. Silicon isotopes can thus be used as a proxy for galactic chemical evolution (GCE). However, the measured correlation of 29Si/28Si versus 30Si/28Si does not agree with any current chemical evolution model. Here, we use a Monte Carlo model to vary nuclear reaction rates within their theoretical or experimental uncertainties and process them through stellar nucleosynthesis and GCE models to study the variation of silicon isotope abundances based on these nuclear reaction rate uncertainties. We find that these uncertainties can indeed be responsible for the discrepancy between measurements and models and that the slope of the silicon isotope correlation line measured in mainstream SiC grains agrees with chemical evolution models within the nuclear reaction rate uncertainties. Our result highlights the importance of future precision reaction rate measurements for resolving the apparent data–model discrepancy.

Keywords: Isotopic abundances, Galaxy chemical evolution, Reaction rates, Circumstellar grains, Stellar nucleosynthesis
Comprehensive Study of Near-Earth Asteroid 2024 MK: Testing Planetary Encounters as a Source for Surface Refreshing. Near-Earth object 2024 MK was discovered on 2024 June 16, less than 2 weeks before it made a sub-lunar-distance close approach. This close approach provided an ideal opportunity to determine how planetary encounters affect asteroid surfaces in preparation for the numerous missions to (99942) Apophis during its close approach in 2029. We collected spectroscopic data before and after its close approach to determine if planetary encounters induce spectral changes due to surface refreshing. We used NASA's Infrared Telescope Facility's (IRTF) near-infrared spectrometer SpeX prism mode (0.7–2.5 μm) to observe 2024 MK pre and postapproach. We also observed the asteroid before its close approach using Las Cumbres Observatory's FLOYDS visible spectrometer and after its close approach using IRTF's SpeX long-wavelength cross-dispersed short grating mode, resulting in full spectral coverage from 0.32 to 4.2 μm. 2024 MK is an S-type asteroid that is compositionally most analogous to an L-ordinary chondrite. Spectral analysis of the 3 μm region indicates no surficial water or hydroxide within the level of noise. Band parameter analysis of the pre and postapproach data shows the planetary encounter did not induce any significant spectral changes, suggesting that surface refreshing did not occur on a measurable scale. Similar studies of other targets at smaller encounter distances are required to determine if the lack of spectral changes on 2024 MK indicates it was not close enough to Earth to affect its surface or if the spectral similarity pre and postapproach instead indicates planetary encounters do not cause surface refreshing.

Keywords: Near-Earth objects, Asteroids, Near infrared astronomy, Close encounters, Spectroscopy, Asteroid surfaces
Theoretical Studies on the Evolution of Solar Filaments in Response to New Emerging Flux. New emerging flux (NEF) has long been considered a mechanism for solar eruptions, but the detailed process remains an open question. In this work, we explore how NEF drives a coronal magnetic configuration to erupt. This configuration is created by two magnetic sources of strengths M and S embedded in the photosphere, one electric-current-carrying flux rope (FR) floating in the corona, and an electric current induced on the photospheric surface by the FR. The source M is fixed, accounting for the initial background field, and S changes, playing the role of NEF. We introduce the channel function C to forecast the overall evolutionary behavior of the configuration. The location, polarity, and strength of NEF govern the evolutionary behavior of the FR before eruption. In the case of ∣S/M∣ &lt; 1, with reconnection occurring between new and old fields, the configuration in equilibrium evolves to the critical state, invoking the catastrophe. In this case, if the polarities of the new and old fields are opposite, reconnection occurs as NEF is close to the FR, and if the polarities are the same, reconnection happens as NEF appears far from the FR. With different combinations of the relative polarity and the location, the evolutionary behavior of the system gets complex, and the catastrophe may not occur. If ∣S/M∣ &gt; 1 and the two fields have opposite polarity, the catastrophe always takes place, but if the polarities are the same, the catastrophe occurs only as NEF is located far from the FR; otherwise, the evolution ends up either with a failed eruption or without a catastrophe at all.

Keywords: Solar magnetic flux emergence, Solar coronal mass ejections, Solar filament eruptions
A Magnetic Pressure Difference Rule on Moving Bipolar Pores. Solar pores are transient dark spots in the continuum images of the Sun. Their dynamics are closely associated with solar magnetic fields and plasma motion. Their motions have been found to be correlated with their magnetic pressure differences. This work is aimed to investigate possible reasons for this correlation. Our examination of 19 pairs of bipolar pores reveals a magnetic pressure difference rule between the pores of a same pair: their signs of the differences between the magnetic pressures at the front and back sides are always opposite, and their directions of the maximum positive difference between the magnetic pressures at the opposite ends are always both pointing toward the left or right and are always slightly toward the higher latitudes. The rule indicates that the properties of the bipolar pores are influenced by the solar global magnetic fields and rotation.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar magnetic flux emergence, Sunspots, Solar active regions, Solar magnetic fields
An Eccentric Binary with a Misaligned Circumbinary Disk. We present spectroscopic and photometric observations of Bernhard-2, which was previously identified as a candidate system that hosts a misaligned circumbinary disk. Our spectroscopic measurements confirm that Bernhard-2 indeed contains an eccentric (e = 0.69 ± 0.08) binary and thus that the periodic variability in the photometric light curve is best explained by the occultation by the misaligned circumbinary disk. By modeling the spectral energy distributions at different phases, we infer the masses of the two binary components to be ∼1.1 M⊙ and ∼0.9 M⊙, respectively. The system age is determined to be ≲20 Myr by combining the stellar isochrone model with lithium abundance. Our new photometric observations show clear deviations from the model prediction based on the archival data, suggesting ongoing precession of the circumbinary disk. The Hα line of Bernhard-2 also shows an inverse P-Cygni profile at epochs close to the pericenter passage, which could be attributed to the pulsed accretion around the pericenter. Bernhard-2 therefore closely resembles the well-studied KH 15D system. Further detailed observations and studies of such rare systems can provide useful information about disk physics and evolution.

Keywords: Pre-main sequence stars, Spectroscopy, Variable stars, Circumstellar disks