Sazuna/UAT_keywords huggingface dataset:
A Sandwich Model for Changing-look Active Galactic Nuclei. The spectral variability of changing-look active galactic nuclei (CL-AGNs) occurred on timescales of years to tens of years, posing a significant challenge to the standard thin disk model. In this work, we propose a sandwich model, including an optically thick disk in the mid-plane (Disk 1) and two disks of low effective optical depth on both sides (Disk 2). These two types of disks are coupled with magnetic fields, which allow viscous torque interaction between them. As a consequence, the radial velocity of Disk 1 can increase by up to 3 orders of magnitude compared to the standard thin disk, leading to an equivalent decrease in the accretion timescale. Therefore, such a sandwich model can account for the rapid variability in CL-AGNs. In addition, we also discuss the influence of the magnetic pressure on Disk 2. When Disk 2 is dominated by the magnetic pressure, it resembles a "warm corona," which is responsible for the soft X-ray excess.

Keywords: Accretion, Black hole physics, Galaxy accretion disks, Active galactic nuclei
The Magnetic Keys to Massive Star Formation: The Western η Carinae Giant Molecular Cloud. We present SOFIA/HAWC+ continuum polarization data on the magnetic fields (B fields) threading 17 pc-scale massive molecular clumps at the western end of the η Carinae giant molecular cloud (Region 9 of the Galactic Census of High- and Medium-mass Protostars, or CHaMP, representing all stages of star formation from pre-stellar to dispersing via feedback), revealing important details about the field morphology and role in the gas structures of this clump sample. We performed Davis–Chandrasekhar–Fermi (DCF) and histogram of relative orientation (HRO) analyses tracing column densities 25.0 &lt; log(N/m‑2) &lt; 27.2. With HRO, B fields change from mostly parallel to column density structures to mostly perpendicular at a threshold Ncrit = (3.7 ± 0.6) × 1026 m‑2, indicating that gravitational forces exceed magnetic forces above this value. The same analysis in 10 individual clumps gives similar results, with the same clear trend in alignments and a threshold Ncrit = (1.9 ‑0.8+1.5 ) × 1026 m‑2. In the other seven clumps, the alignment trend with N is much flatter or even reversed, inconsistent with the usual HRO pattern. Instead, these clumps' fields reflect external environmental forces from the nearby H II region NGC 3324. DCF analysis reveals field strengths somewhat higher than typical of nearby clouds, with the B–n data lying mostly above the R. M. Crutcher relation. The mass-to-flux ratio λ across all clumps has a Gaussian distribution, logλDCF = –0.75 ± 0.45; only small areas are dominated by gravity. However, a significant trend of rising logλ with falling Tdust parallels R. L. Pitts et al.'s result: Tdust falls as  NH2  rises toward clump centres. In this massive clump sample, B fields provide enough support against gravity to explain their overall low star formation rate.

Keywords: Star forming regions, Magnetic fields, Magnetohydrodynamics, Dense interstellar clouds
Deciphering Sub-Neptune Atmospheres: New Insights from Geochemical Models of TOI-270 d. The nature of sub-Neptunes is one of the hottest topics in exoplanetary science. Temperate sub-Neptunes are of special interest because some could be habitable. Here, we consider whether these planets might instead be rocky worlds with thick, hot atmospheres. Can recent James Webb Space Telescope observations of TOI-270 d be understood in terms of such a model? We perform thermochemical equilibrium calculations to infer conditions of quenching of C–H–O–N species. Our results indicate apparent CO2–CH4 equilibrium between ∼900 and ∼1100 K. The CO abundance should be quenched higher in the atmosphere where the equilibrium CO/CO2 ratio is lower, potentially explaining a lack of CO. N2 is predicted to dominate the nitrogen budget. We confirm that the atmosphere of TOI-270 d is strongly enriched in both C and Ogas relative to protosolar H, whereas N is likely to be less enriched or even depleted. We attempt to reproduce these enrichments by modeling the atmosphere as nebular gas that extracted heavy elements from accreted solids. This type of model can explain the C/H and Ogas/H ratios, but despite supersolar C/N ratios provided by solids, the NH3 abundance will probably be too high unless there is a nitrogen sink in addition to N2. A magma ocean may be implied, and indeed the oxygen fugacity of the deep atmosphere seems sufficiently low to support the sequestration of reduced N in silicate melt. The evaluation presented here demonstrates that exoplanetary geochemistry now approaches a level of sophistication comparable to that achieved within our own solar system.

Keywords: Exoplanet atmospheric composition , Cosmochemistry, Abundance ratios, James Webb Space Telescope, Mini Neptunes, Exoplanet formation, Exoplanet atmospheric structure
Viewing Global Changes in the Heliosheath with IMAP's Energetic Neutral Atom Imagers. We present a simulation analysis of NASA's upcoming Interstellar Mapping and Acceleration Probe (IMAP) energetic neutral atom (ENA) instrument capabilities in viewing "global" changes in the heliosheath (HS) plasma, and the resulting ENA flux changes detected near Earth. This is done by simulating ENA emissions produced by charge exchange in a simulated heliosphere, utilizing the instruments' energy coverage, and calculating the time it takes for the SW to travel from 1 au to the HS and for ENAs to travel back. We aim to answer the following: (i) What are the time delays as a function of energy and direction; (ii) at what energies can we observe changes the soonest; and (iii) what might the ENA source distributions affecting the time delays look like? We find the following: (i) The time delay depends on energy and direction in the sky, taking from &gt;20 yr to &lt;2 yr to see a response. The time delay does not decrease monotonically with increasing ENA energy, because of the energy-dependent, H+p charge exchange cross section. (ii) The quickest changes can be observed at ∼15 keV (without HS energy diffusion), intersecting IMAP-Hi and IMAP-Ultra energies. (iii) The ENA source distributions, and how far out IMAP can "see" the heliosphere, strongly depend on energy: IMAP-Lo and IMAP-Ultra should be able to view the farthest back in the heliotail but with long delay times. Finally, we show how energy diffusion in the HS affects the time delays and ENA source distributions, increasing ENA fluxes and prolonging time delays.

Keywords: Space plasmas, Heliosphere, Solar wind, Solar wind termination, Pickup ions, Ion-neutral reactions, Solar activity
A Multimechanism Hybrid Model of Peaked-spectrum Radio Sources. Peaked-spectrum (PS) sources exhibit turnover characteristics in their broad radio spectra. However, the mechanism underlying this phenomenon remains elusive. The two most common hypotheses are synchrotron self-absorption (SSA) and free–free absorption (FFA). By incorporating multiple absorption scenarios, we propose a multimechanism hybrid model, which aligns well with current observational data and provides a good physical explanation. Using data from the GLEAM survey, we identified a sample of 4315 sources with peak frequencies between approximately 72 and 3000 MHz, most of which are MHz-peaked-spectrum sources. Our analysis shows that FFA rather than SSA is the dominant mechanism in producing the spectral turnover for most of the sources in this sample. The index of the optically thick spectrum αthick has a lower boundary due to FFA, and the steeper αthick indicates a complex multiabsorption mechanism. In particular, the external FFA produces substantial αthick, which exhibits a weak correlation with the peak frequency. Future ultralong-wavelength observations would also provide data on the spectrum of these sources at even lower frequencies. Determining the absorption mechanism that shaped the spectrum of these sources would be a crucial part of understanding their nature.

Keywords: Extragalactic radio sources, Active galaxies, Radio continuum emission, Radio galaxies, Circumgalactic medium, Extragalactic astronomy
The Sun's Open–Closed Flux Boundary and the Origin of the Slow Solar Wind. The Sun's open–closed flux boundary (OCB) separates closed and open magnetic field lines, and is the site for interchange magnetic reconnection processes thought to be linked to the origin of the slow solar wind (SSW). We analyze the global magnetic field structure and OCB from 2010 December to 2019 December using three coronal magnetic field models: a potential-field source-surface (PFSS) model, a static equilibrium magnetofrictional model, and a time-dependent magnetofrictional model. We analyze the model and cycle dependence of the OCB length on the photosphere, as well as the magnetic flux in the vicinity of the OCB. Near solar maximum, the coronal magnetic field for each model consists predominantly of long, narrow coronal holes, and nearly all the open flux lies within 1 supergranule diameter (25 Mm) of the OCB. By comparing to interplanetary scintillation measurements of SSW speeds, we argue that the fraction of open flux within this 25 Mm band is a good predictor of the amount of SSW in the heliosphere. Importantly, despite its simplicity, we show that the PFSS model estimates this fraction as well as the time-dependent model. We discuss the implications of our results for understanding SSW origins and interchange reconnection at the OCB.

Keywords: Slow solar wind, Solar coronal holes, Solar corona, Solar magnetic fields
Ground to Dust: Collisional Cascades and the Fate of Kardashev II Megaswarms. Extraterrestrial intelligences are speculated to surround stars with structures to collect their energy or to signal distant observers. If they exist, these most likely are megaswarms, vast constellations of satellites (elements) in orbit around the hosts. Although long-lived megaswarms are extremely powerful technosignatures, they are liable to be subject to collisional cascades once guidance systems start failing. The collisional time is roughly an orbital period divided by the covering fraction of the swarm. Structuring the swarm orbits does not prolong the initial collisional time as long as there is enough randomness to ensure collisions, although it can reduce collision velocities. I further show that once the collisional cascade begins, it can develop extremely rapidly for hypervelocity collisions. Companion stars or planets in the stellar system induce perturbations through the Lidov–Kozai effect among others, which can result in orbits crossing within some millions of years. Radiative perturbations, including the Yarkovsky effect, also can destabilize swarms. Most megaswarms are thus likely to be short-lived on cosmic timescales without active upkeep. I discuss possible mitigation strategies and implications for megastructure searches.

Keywords: Astrodynamics, Collisional processes, Technosignatures, Orbits, Search for extraterrestrial intelligence
Search for Continuous Gravitational Waves from Unknown Neutron Stars in Binary Systems with Long Orbital Periods in O3 Data. Gravitational waves emitted by asymmetric rotating neutron stars are the primary targets of continuous gravitational-wave searches. Neutron stars in binary systems are particularly interesting due to the potential for nonaxisymmetric deformations induced by a companion star. However, all-sky searches for unknown neutron stars in binary systems are very computationally expensive, and this limits their sensitivity and/or breadth. In this paper we present results of a search for signals with gravitational-wave frequencies between 50 and 150 Hz, from systems with orbital periods between 100 and 1000 days and projected semimajor axes between 40 and 200 lt-s. This parameter space region has never been directly searched before. We do not detect any signal, and our results exclude gravitational-wave amplitudes above 1.25 × 10‑25 at 144.32 Hz with 95% confidence. Our improved search pipeline is more sensitive than any previous all-sky binary search by about 75%.

Keywords: Neutron stars, Gravitational waves
Formation of Near-surface Atmospheric Inversion and Surface Inversion in Hothouse Climates. A hothouse climate may develop throughout Earth's history and its warming future, and on potentially habitable exoplanets near the inner edge of the habitable zone. Previous studies have suggested that near-surface atmospheric inversion (NAIV), with the planetary boundary air temperature being higher than the air temperature adjacent to the surface, is a pronounced phenomenon in hothouse climates. However, the underlying mechanisms are unclear. Here, we show that lower-tropospheric radiative heating is necessary but not independently sufficient in forming the NAIV. Instead, the dynamic heating induced by large-scale subsidence is essential. With the prescribed reasonable large-scale subsidence, NAIV appears in small-domain cloud-resolving simulations, which was not observed in previous studies. Surface evaporative cooling also contributes to the formation of the NAIV. Besides NAIV, we find that surface inversion (SIV), with the air adjacent to the surface being warmer than the underlying sea surface, is also a distinct phenomenon in hothouse climates. SIV is caused by strong surface evaporative cooling and large atmospheric shortwave absorption. These two types of inversion strongly stabilize the atmosphere, weaken atmospheric circulation, dry the free troposphere, and suppress the hydrological cycle.

Keywords: Exoplanet atmospheric dynamics, Exoplanet surfaces, Habitable planets, Exoplanet atmospheres
Traversing the Star-forming Main Sequence with Molecular Gas Stacks of z ∼ 1.6 Cluster Galaxies. The cluster environment has been shown to affect the molecular gas content of cluster members, yet a complete understanding of this often subtle effect has been hindered due to a lack of detections over the full parameter space of galaxy star formation rates (SFRs) and stellar masses. Here, we stack CO(2–1) spectra of z ∼ 1.6 cluster galaxies to explore the average molecular gas fractions of galaxies both at lower mass (log(M*/M⊙) ∼ 9.6) and further below the star-forming main sequence (SFMS; ΔMS ∼ ‑0.9) than other literature studies; this translates to a 3σ gas mass limit of ∼7 × 109 M⊙ for stacked galaxies below the SFMS. We divide our sample of 54 z ∼ 1.6 cluster galaxies, derived from the Spitzer Adaptation of the Red-Sequence Cluster Survey, into nine groupings, for which we recover detections in 8. The average gas content of the full cluster galaxy population is similar to coeval field galaxies matched in stellar mass and SFR. However, when further split by CO-undetected and CO-detected, we find that galaxies below the SFMS have statistically different gas fractions from the field scaling relations, spanning deficiencies to enhancements from 2σ below to 3σ above the expected field gas fractions, respectively. These differences between z = 1.6 cluster and field galaxies below the SFMS are likely due to environmental processes, though further investigation of spatially resolved properties and more robust field scaling relation calibration in this parameter space are required.

Keywords: Galaxy clusters, Molecular gas, High-redshift galaxy clusters, Galactic and extragalactic astronomy, Radio astronomy
Variabilities of Gamma-Ray Bursts from the Dynamics of Fallback Material after Tidal Disruption. The gamma-ray bursts GRB 211211A and GRB 060614, believed to originate from the merger of compact objects, exhibit similarities to the jetted tidal disruption event (TDE) Sw J1644+57, by showing violent variabilities in the light curve during the decay phase. Previous studies suggest that such fluctuations in TDE may arise from the fallback of tidal disrupted debris. In this paper, we introduce the fluctuations of the mass distribution dM/dE for the debris ejected during the tidal disruption (with energy E) and study their impact on jet power. Turbulence induced by tidal force and the self-gravity of the debris may imprint variabilities in dM/dE during fallback. We model these fluctuations with a power density spectrum  ∝fEβ , where fE = 1/E and β is the power-law index. We find that the resulting light curve can preserve the fluctuation characteristics from dM/dE. In addition, the observed fluctuations in the light curves can be reproduced for a given suitable β. Based on the observations, we find that the value of β should be around ‑1.

Keywords: Accretion, Tidal disruption, Gamma-ray bursts
New Insights into Lava Tube Formation: An Asymmetrical and Deep Case Observed by Yutu-2 Radar at Lunar Farside. This article reports a potential lava tube observed at ∼130 m depth of the lunar farside by Lunar Penetrating Radar data. However, a possible scenario with a kind of dry and low-density materials connected with a basaltic boulder or lava flow cannot be excluded. If the lava tube is valid, it is at the edge of a huge paleo-depression with a maximum width of ∼26 m and a height of ∼16 m. It presents bright and phase-reversed reflections, a depressed roof, and asymmetrical reflected power on the radargram. Estimation results of the loss tangent provide evidence for it and simultaneously reveal the residual basalt material in the western region of the tube. The ancient lava flow is thought to postdate the adjacent ejecta and has high FeO+TiO2 content. Comprehensive analyses demonstrate that the lava flow inflation, the looseness of the adjacent ejecta, and the depressed paleo-terrain may cause horizontal erosion, subsequent deceleration, and final residue of the lava. Subsequent differential compaction of overlying strata resulted in its deformation and the accumulation of pyroclastic materials in it. The results may provide unprecedented knowledge about the formation mechanisms and interior structures of lava tubes on the Moon.

Keywords: Lunar interior, Remote sensing, The Moon, Planetary science
Detecting Intermediate-mass Black Holes Using Quasar Microlensing. Recent studies suggest that numerous intermediate-mass black holes (IMBHs) may wander undetected across the Universe, emitting little radiation. These IMBHs largely preserve their birth masses, offering critical insights into the formation of heavy black hole seeds and the dynamical processes driving their evolution. We propose that such IMBHs could produce detectable microlensing effects on quasars. Their Einstein radii, comparable to the scale of quasar broad-line regions, magnify radiation from the accretion disk and broad emission lines, making these quasars outliers in flux scaling relations. Meanwhile, the microlensing causes long-term, quasi-linear variability that is distinguishable from the stochastic variability of quasars through its coherent multiwavelength behavior. We develop a matched-filtering technique that effectively separates the long-term lensing signal from the intrinsic quasar variability, with sensitivity tripling each time the observational time span doubles. Moreover, as IMBHs are often surrounded by dense star clusters, their combined gravitational field produces substantial extended, concentric caustics. These caustics induce significant variability in optical, ultraviolet, and X-ray bands over decade timescales, alongside hour-to-day-scale flux fluctuations in broad emission lines. We predict a substantial number of detectable events in the upcoming surveys by the Vera C. Rubin Observatory, considering recent IMBH mass density estimates. Even in the absence of positive detections, searches for these microlensing signals will place meaningful constraints on the cosmological mass density of IMBHs, advancing our understanding of their role in cosmic evolution.

Keywords: Gravitational microlensing, Galaxy nuclei, Active galaxies, Quasars
Large Cold Dust Reservoir Revealed in Transitional SN Ib 2014C by James Webb Space Telescope Mid-infrared Spectroscopy. Supernova (SN) 2014C is a rare transitional event that exploded as a hydrogen-poor, helium-rich Type Ib SN and subsequently interacted with a hydrogen-rich circumstellar medium (CSM) a few months postexplosion. This unique interacting object provides an opportunity to probe the mass-loss history of a stripped-envelope SN progenitor. Using the James Webb Space Telescope (JWST), we observed SN 2014C with the Mid-Infrared Instrument Medium Resolution Spectrometer at 3477 days postexplosion (rest frame), and the Near-Infrared Spectrograph Integral Field Unit at 3568 days postexplosion, covering 1.7─25 μm. The bolometric luminosity indicates that the SN is still interacting with the same CSM that was observed with the Spitzer Space Telescope 40─1920 days postexplosion. JWST spectra and near-contemporaneous optical and near-infrared spectra show strong [Ne II] 12.831 μm, He 1.083 μm, Hα, and forbidden oxygen ([O I] λλ6300, 6364, [O II] λλ7319, 7330, and [O III] λλ4959, 5007) emission lines with asymmetric profiles, suggesting a highly asymmetric CSM. The mid-IR continuum can be explained by ∼0.036 M⊙ of carbonaceous dust at ∼300 K and ∼0.043 M⊙ of silicate dust at ∼200 K. The observed dust mass has increased tenfold since the last Spitzer observation 4 yr ago, with evidence suggesting that new grains have condensed in the cold dense shell between the forward and reverse shocks. This dust mass places SN 2014C among the dustiest SNe in the mid-IR and supports the emerging observational trend that SN explosions produce enough dust to explain the observed dust mass at high redshifts.

Keywords: Type Ib supernovae, Core-collapse supernovae, Dust formation
Search for Kink Events in Variable Fermi-LAT Blazars. This study explores the detection of quasiperiodic oscillations (QPOs) in blazars as a method to identify kink events within their jets, utilizing both γ-ray and polarized light observations. Focusing on a sample of nine blazars, we analyze γ-ray light curves to identify significant QPOs. In addition to γ-ray data, we incorporated polarized light data corresponding to the same temporal segments to cross-validate the presence of QPOs. However, the limited availability of comprehensive polarized data restricted our ability to perform a thorough analysis across all data sets. Despite these limitations, our analysis reveals a segment where QPOs in polarized light coincided with those observed in γ-rays, providing preliminary evidence supporting the kink origin of these oscillations.

Keywords: Gamma-ray astronomy, Astronomy data analysis, Blazars
Learning to See: Applying Inverse Recurrent Inference Machines to See through Refractive Scattering. The Event Horizon Telescope (EHT) has produced horizon-resolving images of Sagittarius A* (Sgr A*). Scattering in the turbulent plasma of the interstellar medium distorts the appearance of Sgr A* on scales only marginally smaller than the fiducial resolution of EHT. The scattering process both diffractively blurs and adds stochastic refractive substructures that limits the practical angular resolution of EHT images of Sgr A*. We explore the ability of a novel recurrent neural network machine learning framework to mitigate these scattering effects, after training on sample data that are agnostic to general relativistic magnetohydrodynamics (GRMHD). We demonstrate that if instrumental limitations are negligible, it is possible to nearly completely mitigate interstellar scattering at a wavelength of 1.3 mm. We validate and quantify the fidelity of this scattering mitigation scheme with physically relevant GRMHD simulations. We find that we can accurately reconstruct resolved structures at the scale of 3 μas, well below the nominal instrumental resolution of EHT, 24 μas.

Keywords: Supermassive black holes, Galactic center, Neural networks, Convolutional neural networks, Interstellar scattering