Sazuna/UAT_keywords huggingface dataset:
Delayed Launch of Ultrafast Outflows in the Tidal Disruption Event AT2020afhd. We report the detection and characterization of ultrafast outflows (UFOs) in the X-ray spectra of the tidal disruption event (TDE) AT2020afhd, based on observations from NICER, Swift, and XMM-Newton. Prominent blueshifted absorption features were detected exclusively during the intermediate phase of the event, occurring between days 172 and 212 within the first 300 days postdiscovery. During this period, the UFO appeared no earlier than day 74, strengthened between days 172 and 194, and disappeared after day 215. This marks the first time that the full evolutionary sequence of X-ray outflows has been observed in a TDE. Moreover, the outflows exhibited a dramatic deceleration from ∼0.19c to ∼0.0097c over a span of approximately 10 days. Photoionization spectral analysis reveals an inverse correlation between outflow velocity and ionization parameter, in contradiction to the predictions from radiation-pressure-driven wind. Finally, we propose that the delayed onset of the outflows may result from an increase in the wind opening angle and/or metal enrichment, particularly iron and oxygen, during the disk formation phase.

Keywords: Accretion, Black hole physics, Tidal disruption
Waiting Time Distribution of Supra-arcade Downflows. Supra-arcade downflows (SADs) are dark, sunward-moving structures above the arcade of flare loops. Naturally, they are considered to be associated with outflows resulting from magnetic reconnection at the vertical current sheet beneath the eruptive structure. Despite extensive investigations on the SAD properties, the timing information, particularly the waiting time between consecutive SADs, has not been systematically examined. Here, using the 131 Å passband of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we studied the waiting time distribution (WTD) of SADs in seven eruptive flares. In six of the seven flares, the SADs are identified and tracked in previous studies by two different methods, and in the seventh flare, they are identified and tracked by our optimized manual method. Based on statistical evaluations, we found that most of the WTDs are best fitted by a power-law function with the slope ranging from 1.7 to 2.4, in accordance with the prediction of nonstationary Poisson processes or self-organized criticality; but often they can also be fitted almost equally well by a log-normal function. These results rule out linear random or quasiperiodic processes to be responsible for the generation of SADs but suggest that several nonlinear mechanisms be coupled together in the reconnection outflow region to shape the heavy-tailed WTD of SADs.

Keywords: Active solar corona, Solar flares, Solar magnetic reconnection
Uniform Reanalysis of JWST MIRI 15 μm Exoplanet Eclipse Observations Using Frame-normalized Principal Component Analysis. James Webb Space Telescope (JWST) MIRI 15 μm time-series eclipse photometry presents a powerful way to probe for the presence of atmospheres on low-temperature rocky exoplanets orbiting nearby stars. Here, we introduce a novel technique, frame-normalized principal component analysis (FN-PCA), to analyze and detrend these MIRI time-series observations. Using the FN-PCA technique, we perform a uniform reanalysis of the published MIRI 15 μm observations of LHS 1478 b, TOI-1468 b, LHS 1140c, TRAPPIST-1 b, and TRAPPIST-1 c using our new data reduction pipeline (Erebus) and compare them to different potential atmospheric and surface compositions. We also investigate additional public data sets with the sole purpose of understanding the instrument systematics affecting MIRI. We identify and categorize important detector-level systematics in the observations that are generally present across all 17 analyzed eclipse observations, which we illustrate as eigenimage/eigenvalue pairs in the FN-PCA. One of these eigenimage/eigenvalue pairs corresponds to the prominent ramp effect at the beginning of the time-series observations, which has widely been reported for JWST and Spitzer photometry. For JWST/MIRI, we show that the detector settling timescales exponentially with the apparent magnitude of the target star  Tset[hr]=0.063exp0.427·mK‑0.657 . This uniform reanalysis and investigation of JWST/MIRI systematics is done in preparation for the 500 hr Rocky Worlds Director's Discretionary Time survey to demonstrate a data-driven systematic model usable across all MIRI 15 μm data sets.

Keywords: Exoplanet atmospheres, Planetary atmospheres, Exoplanets
The Physical Nature of the Off-center Extended Emission Associated with the Little Red Dots. A significant fraction of little red dots (LRDs) exhibit nearby extended emission of unknown origin. If physically associated with the LRD, this component may trace stellar emission from an off-center host galaxy, neighboring companions, or nebular gas illuminated by the active nucleus. We investigate the detailed spectral energy distribution (SED) of the extended emission near four LRDs in the JWST UNCOVER and MegaScience surveys. We accurately decompose the extended emission from the dominant point source by simultaneously fitting the images in eight broadband and nine medium-band filters. After considering both the results from photometric redshift fitting and the probability of galaxies at different redshifts overlapping, we confirm that the off-center blobs in three sources are physically associated with the LRDs, with two of them showing strong [O III] λλ4959, 5007 emission captured by the medium-band filters. While the SEDs of all three blobs can be modeled assuming star-forming galaxies with stellar mass ∼108 M⊙, the exceptionally strong [O III] emission of two sources is best interpreted as pure nebular emission from low-density (n &lt; 10 cm‑3), low-metallicity (Z ≈ 0.05‑1 Z⊙) gas photoionized by the ultraviolet radiation from the nearby LRD. Adopting LRD halo masses constrained by clustering measurements and theoretical considerations, we estimate a typical baryonic halo mass accretion rate of ∼2‑9 M⊙ yr‑1. If the halo accretion rate is sustained to z = 4 and stars form with an efficiency of 10%, the accreted gas would build a galaxy with stellar mass ∼109 M⊙, potentially rendering them spatially resolved at lower redshift.

Keywords: AGN host galaxies, Early universe, Active galactic nuclei, High-redshift galaxies
A Recent Reacceleration of the Local Bubble Revealed by Kinematics of Young Star Associations. The low-density region of the interstellar medium where the Sun is located is known as the Local Bubble, a cavity filled with high-temperature and low-density plasma that may be created by a series of supernova (SN) explosions over the past 14 Myr. However, the effects of these SN explosions on the formation and evolution of the Local Bubble, as well as on nearby star formation, remain not fully understood. To study the expansion history of the Local Bubble, we use the kinematic data of the young stars obtained by cross-matching the pre-main-sequence star catalog of E. Zari et al. with the high-precision astrometric and photometric data from the Gaia DR3 database. We perform a 3D spatial clustering analysis on these young stars to identify star associations. We discover three unique star associations that exhibit a wiggle-like velocity pattern. The distances of these star associations are 108.5308, 141.5284, and 176.0318 pc, respectively. Their radial velocities in the local standard of rest are 10.0622, 5.4982, and 9.0581 km s‑1, showing a pattern of decreasing and then increasing. This velocity pattern, as predicted by M. G. H. Krause and R. Diehl, is caused by a recent reacceleration affected by the SN explosion, reinforcing the picture of the Local Bubble as an evolving entity.

Keywords: Pre-main sequence stars, Solar neighborhood
Dark Star Clusters or Ultrafaint Dwarf Galaxies? Revisiting UMa3/U1. Owing to sparse spectroscopic observations, the classification of faint satellites as either dark-matter-dominated dwarf galaxies or self-gravitating star clusters remains unresolved. The recently discovered Ursa Major III/UNIONS 1 (UMa3/U1) object, with its measured velocity dispersion, provides a rare observational anchor in this regime. Despite its cluster-like compactness, its inferred dynamical mass-to-light ratio (MDyn/L) suggests a dark-matter-dominated nature, prompting interpretations of UMa3/U1 as a microgalaxy, though current measurements remain inconclusive. Thousand-level MDyn/L values are not unique to galaxies; self-gravitating dark star clusters (DSCs) can reach comparable levels via energy injection driven by a centrally segregated black hole subsystem (BHSub), which accelerates the evaporation of luminous stars and leads to a supervirial appearance with elevated velocity dispersion. To assess whether UMa3/U1 is a DSC, we conducted direct N-body simulations and identified a model that successfully reproduces both its compact structure and elevated MDyn/L, supporting a self-gravitating cluster origin. We find the cluster entered the DSC phase around 4 Gyr ago, with its luminous stars expected to be depleted within the next 1 Gyr, followed by the gradual disruption of the central BHSub over the subsequent Gyr. We broaden our analysis by mapping DSC evolutionary tracks in the size versus total luminosity (L) and MDyn/L–L spaces, showing that DSCs occupy a region overlapping with faint, ambiguous satellites. In the MDyn/L–L diagram, DSCs trace a transitional channel bridging globular clusters and dwarf galaxies as they rise from MDyn/L ≈ 2 to 104 M⊙/L⊙.

Keywords: Globular star clusters, Dark matter, Compact dwarf galaxies, N-body simulations
Evidence of a Fraction of LIGO/Virgo/KAGRA Events Coming from Active Galactic Nuclei. The formation channels of the gravitational-wave (GW) sources detected by LIGO/Virgo/KAGRA (LVK) remain poorly constrained. Active galactic nucleus (AGN) has been proposed as one of the potential hosts, but the fraction of GW events originating from AGNs has not been quantified. Here, we constrain the AGN-origin fraction fagn by analyzing the spatial correlation between GW source localizations (O1–O4a) and AGNs (Sloan Digital Sky Survey 16th data release). We report preliminary evidence of an excess of lower-luminosity (1044.5 ≲ Lbol ≤ 1045 erg s‑1) as well as lower-Eddington ratio (0.01 ≲ λEdd ≤ 0.05) AGNs around the LVK events, the explanation of which requires  fagn=0.39‑0.32+0.41  and  0.29‑0.25+0.40  (90% confidence level) of the LVK events originating from these respective AGN populations. Monte Carlo simulations confirm that this correlation is unlikely to arise from random coincidence, further supported by anomalous variation of the error of fagn with GW event counts. These results support the theoretical speculation that some LVK events come from lower-luminosity or lower-accretion-rate AGNs, offering critical insights into the environmental dependencies of the formation of GW sources.

Keywords: Sky surveys, Active galactic nuclei, Black holes, Gravitational wave sources
Puzzling Variation of Gamma Rays from the Sun over the Solar Cycle Revealed with Fermi-LAT. The steady-state gamma-ray emission from the Sun is thought to consist of two emission components due to interactions with Galactic cosmic rays: (1) a hadronic disk component, and (2) a leptonic extended component peaking at the solar edge and extending into the heliosphere. The flux of these components is expected to vary with the 11 yr solar cycle, being highest during solar minimum and lowest during solar maximum, as it varies with the cosmic-ray flux. No study has yet analyzed the flux variation of each component over solar cycles. In this work, we measure the temporal variations of the flux of each component over 15 yr of Fermi Large Area Telescope observations and compare them with the sunspot number and Galactic cosmic-ray flux from AMS-02 near Earth. We find that the flux variation of the disk anticorrelates with the sunspot number and correlates with cosmic-ray protons, as expected, confirming its emission mechanism. In contrast, the extended component exhibits a more complex variation: despite an initial anticorrelation with the sunspot number, we find neither anticorrelation with the sunspot number nor correlation with cosmic-ray electrons over the full 15 yr period. This most likely suggests that cosmic-ray transport and modulation in the inner heliosphere are unexpectedly complex and may differ for electrons and protons or, alternatively, that there is an additional, unknown component of gamma rays or cosmic rays. These findings impact space weather research and emphasize the need for close monitoring of Cycle 25 and the ongoing polarity reversal.

Keywords: Quiet sun, Gamma-rays, Cosmic rays
Overcast Mornings and Clear Evenings in Hot Jupiter Exoplanet Atmospheres. Aerosols are an old topic in the young field of exoplanet atmospheres. Understanding what they are, how they form, and where they go has long provided a fertile playground for theorists. For observers, however, aerosols have been a multidecade migraine, as their chronic presence hides atmospheric features. For hot Jupiters, the large day–night temperature contrast drives inhomogeneous thermal structures and aerosol distribution, leading to different limb properties probed by transit spectra. We present JWST NIRISS/SOSS spectra of morning and evening limbs for nine gas giants with equilibrium temperatures of ∼800–1700 K. By measuring feature size of the 1.4 μm water band for both limbs, we found three planets (WASP-39 b, WASP-94 Ab, and WASP-17 b) show prominent (&gt;5σ) limb–limb atmospheric opacity difference with muted morning and clear evening limbs. The heavily muted water features on morning limbs indicate high-altitude (0.1–0.01 mbar) aerosols. To simultaneously have clear evening limbs requires processes with timescales (∼day) comparable to advection to remove these lofted grains, and we found that both downwelling flow and dayside cloud evaporation could be plausible mechanisms. We hypothesize an empirical boundary—termed the "asymmetry horizon"—in temperature–gravity space that marks the transition where inhomogeneous aerosol coverage begins to emerge. Heterogeneous aerosol coverage is common among hot Jupiters. If unrecognized, limb averaging suppresses spectral features, mimicking high-mean-molecular-weight atmospheres, inflating inferred metallicity by up to 2 dex, and underestimating limb temperatures by as much as half. Finally, we introduce the Limb Spectroscopy Metric to predict limb spectral feature size based on planet parameters.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheres
Discovery of an [Fe/H] ∼ −4.8 Star in Gaia XP Spectra. We report on the discovery of GDR3_526285 (Gaia DR3 Source ID 5262850721755411072), a star with [Fe/H] = −4.82 ± 0.25 and one of the lowest metal (atomic number &gt; 2) mass fractions ever found (ZGDR3_526585 ≲ 1.0 × 10−6). We first identified it as an ultra-metal-poor (UMP; [Fe/H] &lt; −4) red-giant branch (RGB) star candidate in the Gaia Blue (BP) and Red (RP) Photometer (XP) spectrophotometric catalog (Gaia G magnitude ≍ 15). A combination of multiband photometry and high-resolution spectroscopic analysis under local thermodynamic equilibrium confirmed the status of GDR3_526285 as a distant (≍24 kpc from the Sun) RGB star (Teff = 4596 K,  logg=0.88 ) in the Milky Way's outer halo. We obtain only an upper limit for the carbon abundance of [C/H] &lt; −4.32, resulting in [C/Fe] &lt; +0.50. A correction for the evolutionary carbon depletion (∆[C/Fe] = +0.68) brings the nominal carbon-to-iron ratio upper limit to [C/Fe]cor &lt; +1.18. Given its extraordinarily low [C/H], GDR3_526285 likely formed from gas cooled via dust grains rather than fine structure line cooling. The kinematics of GDR3_526285 suggests that this star was either dynamically perturbed by the infall of the Magellanic system or was formerly a member of the Magellanic Clouds and was later stripped by the Milky Way. Our results showcase the potential of an all-sky search for low-metallicity targets with Gaia XP and confirm that the methodology described here is a useful "treasure map" for finding additional UMP stars. *Based on observations gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: High resolution spectroscopy, Population III stars, Gaia, Chemical abundances, Halo stars, Population II stars, Metallicity
Cosmic Outliers: Low-spin Halos Explain the Abundance, Compactness, and Redshift Evolution of the Little Red Dots. The little red dots (LRDs) are high-redshift galaxies uncovered by JWST, characterized by small effective radii (Reff ∼ 80–300 pc), number densities intermediate between typical galaxies and quasars, and a redshift distribution peaked at z ∼ 5. We present a theoretical model in which the LRDs descend from dark matter halos in the extreme low-spin tail of the angular momentum distribution. Within this framework, we explain their three key observational signatures: (i) abundance, (ii) compactness, and (iii) redshift distribution. Our model focuses on observed, not modeled, properties; it is thus independent of whether they are powered primarily by a black hole or stars. We find that the assumption that the prototypical LRD at z ∼ 5 originates from halos in the lowest ∼1% of the spin distribution is sufficient to reproduce both their observed number densities and physical sizes. The redshift evolution of their observability is driven by the interplay between the evolving compact disk fraction and cosmological surface brightness dimming. This effect leads to a well-defined "LRD era" at 4 &lt; z &lt; 8, during which the LRDs are common and detectable; at z &lt; 4, they are bright but rare, while at z &gt; 8, they are common but faint. Finally, we test the predicted redshift trend against observational data, finding excellent agreement. Additional observational support comes from their excess small-scale clustering and spectral signatures of extreme core densities, both of which are expected outcomes of galaxy formation in low-spin halos. These findings suggest that the LRDs are not a fundamentally distinct population but the natural manifestation of galaxies forming in the rarest, lowest angular momentum environments.

Keywords: Cosmology, Early universe, Active galaxies, Galaxy evolution, Galaxies
An Eccentric Sub-Neptune Moving Into the Evaporation Desert. Though missions such as Kepler, K2, and TESS have discovered &gt;2000 sub-Neptune and Neptunian planets, there is a dearth of such planets at close-in (P ≲ 3 days) orbits. This feature, called the Neptune desert or the evaporation desert, is believed to be primarily shaped by planetary migration and photoevaporation. However, this region is not completely devoid of planets—a small number of very hot Neptunes reside within the desert. These planets provide an opportunity to directly probe the effects of migration and photoevaporation. We present confirmation of TOI-5800 b, an eccentric sub-Neptune on an ≈2.6 day period that is likely actively undergoing tidal migration. We use radial velocity measurements from the Carnegie Planet Finder Spectrograph to constrain TOI-5800 b's mass and eccentricity. We find that it has an unusually high eccentricity (0.39 ± 0.07) for its short orbit. TOI-5800 b is therefore currently experiencing high levels of tidal heating as it moves into the desert. Ranked as a top candidate for transmission and emission spectroscopy within its temperature and radius regime, TOI-5800 b is a prime target for atmospheric characterization with the James Webb Space Telescope. TOI-5800 b presents a unique opportunity to study the atmosphere of a planet undergoing tidal heating and to probe the composition of sub-Neptune planets. *This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Exoplanet astronomy, Exoplanet detection methods, Exoplanet migration, Exoplanet dynamics
Extending the Short Gamma-Ray Burst Population from Subthreshold Triggers in Fermi/GBM and GECAM Data and Its Implications. Detection of short gamma-ray bursts (SGRBs) is critically important for the research of compact object mergers and multimessenger astrophysics, but a significant part of SGRBs fall below the trigger threshold of GRB detectors, and thus are often missed. Here we present a systematic search for and verification of missed SGRBs using Fermi/Gamma-ray Burst Monitor (GBM) subthreshold triggers, jointly analyzing data from GBM, Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor (GECAM)-B, and GECAM-C. Among 466 Fermi/GBM subthreshold events (with reliability ≥5) from 2021 to 2024, 181 are within GECAM's field of view. We find that 49 out of 181 are confirmed astrophysical transients, and 41 can be classified as SGRBs. Thus, the SGRB detection rate of Fermi/GBM is increased to about 50 per year. Additionally, a complete multi-instrument monitoring and systematic verification of GBM subthreshold events is expected to further increase the SGRB rate to about 80 per year, which is ∼100% improvement relative to the GBM-triggered SGRBs. These results may have important implications on the local formation rate of SGRBs and the binary neutron star merger rate. We also searched for potential temporal coincidences between these SGRBs and gravitational waves from the LIGO–Virgo–KAGRA O4 run resulting in no detection.

Keywords: Gamma-ray observatories, Gamma-ray bursts, Gamma-ray telescopes
Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Centauri A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits. We report on coronagraphic observations of the nearest solar-type star, α Centauri A (α Cen A), using the MIRI instrument on the James Webb Space Telescope. The proximity of α Cen (1.33 pc) means that the star's habitable zone is spatially resolved at mid-infrared wavelengths, so sufficiently large planets or quantities of exozodiacal dust would be detectable via direct imaging. With three epochs of observation (2024 August, 2025 February, and 2025 April), we achieve a sensitivity sufficient to detect Teff ≍ 225─250 K (1─1.2 RJup) planets between 1″─2″ and exozodiacal dust emission at the level of &gt;5─8× the brightness of our own zodiacal cloud. The lack of exozodiacal dust emission sets an unprecedented limit of a few times the brightness of our own zodiacal cloud—a factor of ≳10 more sensitive than measured toward any other stellar system to date. In 2024 August, we detected an Fν(15.5 μm) = 3.5 mJy point source, called S1, at a separation of 1 .″ 5 from α Cen A at a contrast level of 5.5 × 10−5. Because the 2024 August epoch had only one successful observation at a single roll angle, it is not possible to unambiguously confirm S1 as a bona fide planet. Our analysis confirms that S1 is neither a background nor a foreground object. S1 is not recovered in the 2025 February and April epochs. However, if S1 is the counterpart of the object C1, seen by the Very Large Telescope/New Earths in Alpha Centauri Region program in 2019, we find that there is a 52% chance that the S1 + C1 candidate was missed in both follow-up JWST/MIRI observations due to orbital motion. Incorporating constraints from the nondetections, we obtain families of dynamically stable orbits for S1 + C1 with periods between 2 and 3 yr. These suggest that the planet candidate is on an eccentric (e ≍ 0.4) orbit significantly inclined with respect to the α Cen AB orbital plane (imutual ≍ 50∘, prograde, or ≍130∘, retrograde). Based on the photometry and inferred orbital properties, the planet candidate could have a temperature of 225 K, a radius of ≍1─1.1 RJup, and a mass between 90 and 150 M⊕, consistent with radial velocity limits. This Letter is first in a series of two papers: Paper II discusses the data reduction strategy and finds that S1 is robust as a planet candidate, as opposed to an image or detector artifact.

Keywords: Coronagraphic imaging, James Webb Space Telescope, Extrasolar gaseous giant planets, Exozodiacal dust