Sazuna/UAT_keywords huggingface dataset:
Gravitational-wave Kicks Impact the Spins of Black Holes from Hierarchical Mergers. One proposed black hole formation channel involves hierarchical mergers, where black holes form through repeated binary mergers. Previous studies have shown that such black holes follow a near-universal spin distribution centered around 0.7. However, gravitational-wave kicks can eject remnants from their host environments, meaning only retained black holes can participate in subsequent mergers. We calculate the spin distribution of retained black holes in typical globular clusters, accounting for remnant kick velocities. Since the kick magnitude depends on the binary's mass ratio and spin orientations, certain configurations are more likely to be retained than others. This preferentially selects certain remnant spin magnitudes, skewing the spin distribution of second-generation black holes away from the universal distribution. In low escape velocity environments, the distribution can become bimodal, as remnants with spins of 0.7 typically receive larger kicks than in other configurations. Regarding higher-generation black holes, their spin distribution does not converge to a unique form, and can span a broad range of spins, af ∈ (0.4, 1), depending on their merger history, birth spins, and the escape velocity. Additionally, we find that the presence of a small fraction of binaries with near-aligned spins can produce a second, more dominant peak, whose position depends on the birth spin magnitude. Our findings identify observable features of hierarchical merger black holes, which is essential for understanding their contribution to the gravitational-wave population. Moreover, the dependence of the spin distribution on astrophysical parameters means that precise spin measurements could provide insights into their formation environments.

Keywords: Gravitational wave astronomy, Gravitational waves, Black holes
New Symbiotic Stars from LAMOST DR10 Spectra and Multiband Photometry. The Symbiotic star (SySt) is a long-period interacting binary system, typically consisting of a white dwarf (WD) and a red giant surrounded by a nebula. These systems are natural astrophysical laboratories for investigating binary star evolution. In this paper, we identified nine SySts from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR10 low-resolution spectra survey, seven of which were previously known, while two are newly identified. Initially, we selected LAMOST spectra exhibiting typical SySt emission lines (e.g., Hα, Hβ, Hγ, and He II). Subsequently, we utilized the distribution of known SySts on the Hertzsprung–Russell diagram to select SySt candidates, and visually inspected their spectra. Ultimately, we classified all nine as S-type SySts using the J ‑ H versus H ‑ Ks diagram. Additionally, based on multiband photometric data from GALEX, Gaia, Two Micron All Sky Survey, ALLWISE, and several X-ray catalogs, we found 12 accreting-only SySt (acc-SySt) candidates, characterized by concurrent ultraviolet and infrared excess and accretion process. Furthermore, we estimated the WD temperatures by fitting their observed spectral energy distributions using a combination of the Kurucz stellar atmosphere model and the Koester WD model. We compared the accretion rates of acc-SySt candidates and confirmed SySts, and found they have similar accretion rate distributions, providing evidence that these acc-SySt candidates constitute bona fide SySts.

Keywords: Symbiotic binary stars, Emission line stars
Numerical Simulation of Oscillatory Magnetic Reconnection Modulated by Solar Convective Motions. Oscillatory magnetic reconnection is a periodic magnetic reconnection process, during which the current sheet's orientation and the magnetic connections change periodically. This periodic variation is generally considered to originate from the magnetic reconnection itself rather than from external driving processes. We conduct 2.5D radiative magnetohydrodynamic simulations to investigate the emergence of a magnetic flux tube from the convection zone into the lower corona, where the emerging magnetic fields reconnect with background ones. During the reconnection process, within 5771 s the current sheet's orientation has been reversed 41 times, corresponding to 40 oscillation periods. Notably, the longest period is 30 minutes, which is consistent with the previous observational results. We find that the main factor leading to the reversal of the current sheet's orientation is the quasi-periodic external force provided by the emergence of plasma and magnetic fields from the convection zone. We also find the shifting of the upward outflows from the reconnection region along the horizontal direction due to the alternating changes of the reconnection inflow and outflow regions. In addition to the quasi-periodic change of the current sheet orientation, the reconnection rate at the main X-point also oscillates with a period between 100 and 400 s, which corresponds to the period of p-mode oscillations.

Keywords: Magnetohydrodynamics, Radiative transfer, Solar magnetic reconnection
Multiphase Shock Cooling Emission in Ultrastripped Supernovae. Ultrastripped and Type Ibn supernovae (USSNe and SNe Ibn, respectively) are fast-evolving, hydrogen-poor transients that often show signs of interaction with dense circumstellar material (CSM). S. C. Wu &amp; J. Fuller identify a mass range for helium-core stars in which they expand significantly during core oxygen/neon burning, resulting in extreme late-stage mass loss in tight binaries (P ∼ 1–100 days). Here we explore the resulting light curves from a subset of models from S. C. Wu &amp; J. Fuller and find that in some cases they can exhibit two phases of shock cooling emission (SCE). The first SCE is attributed to the circumbinary material, and the second is from the extended helium-burning envelope of the exploding star. Since SCE luminosity is roughly proportional to the initial radius of the emitting material, events that exhibit both phases of SCE provide the exciting opportunity of measuring both the extent of the CSM and the radius of the exploding star. These light curves are explored with both analytic arguments and numerical modeling, and from this we identify the parameter space of CSM mass, helium envelope (HE) mass, and nickel mass, for which the HE SCE will be visible. We provide a qualitative comparison of these models to two fast-evolving, helium-rich transients, SN 2019kbj and SN 2019dge. The similarity between these events and our models demonstrates that this extreme binary mass loss mechanism may explain some SNe Ibn and USSNe.

Keywords: Type Ib supernovae, Radiative transfer, Core-collapse supernovae
A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST. Increasingly precise space-based photometry uncovers higher-order effects in transits, eclipses, and phase curves that can be used to characterize exoplanets in novel ways. The subtle signature induced by a rotationally deformed exoplanet is determined by the planet's oblateness and rotational obliquity, which provide a wealth of information about a planet's formation, internal structure, and dynamical history. However, oblateness and obliquity are often strongly degenerate and require sophisticated methods to convincingly constrain. We develop a new semianalytic model for an ellipsoidal object occulting a spherical body with arbitrary surface maps expressed in terms of spherical harmonics. We implement this model in an open-source JAX-based Python package eclipsoid (https://github.com/shishirdholakia/eclipsoid), allowing just-in-time compilation and automatic differentiation. We then estimate the precision obtainable with JWST observations of the long-period planet population and demonstrate the best current candidates for studies of oblateness and obliquity. We test our method on the JWST NIRSpec transit of the inflated warm Neptune WASP-107 b and place an upper bound on its projected oblateness of f &lt; 0.23, which corresponds to a rotation period of Prot &gt; 13 hr if the planet is not inclined to our line of sight. Further studies of long-period exoplanets will necessitate discarding the assumption of planets as spherical bodies. Eclipsoid provides a general framework allowing rotational deformation to be modeled in transits, occultations, phase curves, transmission spectra, and more. ✎ ✎

Keywords: Open source software, Exoplanets, Planetary alignment, Exoplanet systems, Oblateness, Exoplanet astronomy, James Webb Space Telescope, Exoplanet structure, Transit photometry
Simulation of Solar Energetic Particle Events Originated from Coronal Mass Ejection Shocks with a Data-driven Physics-based Transport Model. Solar energetic particle (SEP) events are associated with coronal mass ejections (CMEs) and/or solar flares. SEPs travel through the corona and interplanetary space to reach Earth, posing a radiation hazard to spacecraft and astronauts working in space and the electronics on spacecraft. Due to the distinct magnetic field configuration and solar eruption kinematic properties associated with each event, the use of a data-driven model becomes essential for predicting SEP hazards. In this study, we use a developed model that utilizes photospheric magnetic field measurements and CME-driven shock observations as inputs to simulate several historical SEP events associated with fast CME speeds (&gt;700 km s−1). The model includes an SEP source term aligned with the theory of diffusive shock acceleration by the CME-driven shock. The performance of the model is assessed by comparing simulations and observations of SEP intensity-time profiles at Solar and Heliospheric Observatory, ACE, STEREO-A, and STEREO-B. The results generally match the observations well, particularly for protons below 40.0 MeV. However, discrepancies arose for higher-energy protons, notably for the events on 2011 March 7 and 2014 February 25, where the simulation tends to overestimate the proton flux. At STEREO-A, the modeled proton intensities for the SEP events on 2013 April 11 and 2011 March 7 display a very different behavior compared to observations because of the efficient transport in longitude caused by the weak magnetic field.

Keywords: Solar energetic particles, Solar particle emission, Solar coronal mass ejections
Dynamical Inference from Polarized Light Curves of Sagittarius A<SUP>*</SUP>. Polarimetric light curves of Sagittarius A* (Sgr A*) sometimes exhibit loops in the Stokes Q and U plane over time, often interpreted as orbiting hotspot motion. In this work, we apply the differential geometry of planar curves to develop a new technique for estimating polarimetric rotation rates. Applying this technique to 230 GHz light curves of Sgr A*, we find evidence of clockwise motion not only during a postflare period on 2017 April 11, as previously discovered, but also during the quiescent days imaged by the Event Horizon Telescope (EHT). The data exhibit a clockwise fraction of 0.65 ± 0.09 and an overall Q−U rotation rate of  −2.6±0.6degtg−1 . We analyze a library of general relativistic magnetohydrodynamic simulations and find that face-on, clockwise-rotating models with strong magnetic fields are most likely to be consistent with the observations. These results are consistent with EHT and GRAVITY Collaboration studies and indirectly support an interpretation in which the polarized image of Sgr A* has been rotated by an external Faraday screen. This technique offers a novel probe of event-horizon-scale dynamics that complements dynamical reconstructions.

Keywords: Accretion, Supermassive black holes, Radiative transfer simulations, Polarimetry, Magnetohydrodynamical simulations
Resistive Tearing Mode Instability in Generalized Harris Current Sheets. The widely adopted initial force-balanced equilibrium prior to the occurrence of magnetic reconnection (MR) is the so-called Harris sheet model with antiparallel magnetic field. This study examines the tearing mode instability of the recently developed generalized Harris sheet equilibrium based on two-dimensional, resistive, isotropic, linear, and nonlinear MHD models. The generalized Harris equilibrium incorporating the nonthermal Kappa-like velocity distributions in the Vlasov–Maxwell equations may give rise to a family of plasma and magnetic field profiles with various current layer thicknesses which may be used to study various plasma instabilities and MR. It is shown that the linear growth rate is proportional to  δ‑2/5Rm‑2/5 , where  δ  and  Rm  are the current layer thickness and magnetic Reynolds number, respectively. The linear eigenmode solutions are used as the initial perturbations of the nonlinear MHD simulations to allow the full evolution of the tearing instability. It is shown that the cases with small  Rm  may not be nonlinearly unstable, and the cases with relatively thinner current sheets and larger  Rm  may grow faster with larger aspect ratios of magnetic islands. In the generalized kinetic Harris models, the thinning of current sheets may be achieved by the decrease of central temperature or the increase of the drift velocity of charged particles. The asymptotic magnetic field of the equilibrium profiles seems to play a minor role in the linear and nonlinear growth of resistive tearing mode instability.

Keywords: Space plasmas, Magnetohydrodynamics, Plasma physics, Plasma astrophysics, Planetary science, Planetary magnetospheres, Magnetohydrodynamical simulations
Growth of Massive Molecular Cloud Filament by Accretion Flows. II. New Mechanism to Support a Supercritical Filament Against Radial Collapse. Observations indicate that dense molecular filamentary clouds are sites of star formation. The filament width determines the most unstable scale for self-gravitational fragmentation and influences the stellar mass. Therefore, constraining the evolution of filaments and the origin of their properties is important for understanding star formation. Although some observations show a universal width of 0.1 pc, many theoretical studies predict the contraction of thermally supercritical filaments (&gt;17 M⊙ pc‑1) due to radial collapse. Through nonideal magnetohydrodynamics simulations with ambipolar diffusion, we explore the formation and evolution of filaments via slow-shock instability at the front of accretion flows. We reveal that ambipolar diffusion allows the gas in the filament to flow across the magnetic fields around the shock front, forming dense blobs behind the concave points of the shock front. The blobs transfer momentum that drives internal turbulence. We name this mechanism "the STORM"(Slow-shock-mediated Turbulent flOw Reinforced by Magnetic diffusion). The persistence and efficiency of the turbulence inside the filament are driven by the magnetic field and the ambipolar diffusion effect, respectively. The STORM mechanism sustains the width even when the filament reaches very large line masses (∼100 M⊙ pc‑1).

Keywords: Magnetohydrodynamics, 53 Persei stars, Star formation, Interstellar medium
The Sloan Digital Sky Survey Reverberation Mapping Project: Insights on Maximizing Efficiency in Lag Measurements and Black Hole Masses. Multiyear observations from the Sloan Digital Sky Survey (SDSS) Reverberation Mapping (RM) project have significantly increased the number of quasars with reliable RM lag measurements. We statistically analyze target properties, light-curve characteristics, and survey design choices to identify factors crucial for successful and efficient RM surveys. Analyzing 172 high-confidence ("gold") lag measurements from SDSS-RM for the Hβ, Mg II, and C IV emission lines, we find that the Durbin─Watson statistic (a statistical test for residual correlation) is the most significant predictor of light curves suitable for lag detection. The variability signal-to-noise ratio and emission-line placement on the detector also correlate with successful lag measurements. We further investigate the impact of the observing cadence on the survey design by analyzing the effect of reducing observations in the first year of SDSS-RM. Our results demonstrate that a modest reduction in the observing cadence to ∼1.5 weeks between observations can retain approximately 90% of the lag measurements compared to twice-weekly observations in the initial year. Provided similar and uniform sampling in subsequent years, this adjustment has a minimal effect on the overall recovery of lags across all emission lines. These results provide valuable inputs for optimizing future RM surveys.

Keywords: Light curves, Reverberation mapping, Surveys, Quasars
Modeling Polarized Radio Sounding Observations of a Coronal Mass Ejection. Coronal mass ejections (CMEs) evolve significantly as they propagate from the Sun to the Earth, so remote observations of their changes in speed, strength of the magnetic field, density, and overall structure are critical for predicting their arrival time and geoeffectiveness. Radio line-of-sight observations of Faraday rotation and total electron content (TEC) combined with white-light observations enable the measurement of these properties with careful analyses. This paper describes the analysis techniques and evaluates their accuracy with regard to measuring a CME's complex evolving structure and speed. The approach utilizes the layout of the Faraday effect tracker of coronal and heliospheric structures, a purely space-based instrument concept, with Alfvén Wave Solar atmosphere Model (AWSoM) simulations as input for evaluating these radio-based measures. Focusing on density and velocity/speed, we find that in situ measurements of CME properties observe similar but different aspects of the distinct CME structure. The AWSoM model suggests that Faraday rotation may be a more sensitive measure of structure than TEC. Finally, we discuss the difficulty the simulation reveals in determining the trailing edge location of a magnetic flux rope.

Keywords: Heliosphere, Plasma physics, Interplanetary scintillation, Solar wind, Solar physics, Interplanetary magnetic fields, Solar coronal mass ejections, Solar corona, Solar magnetic fields, Radio astronomy
On the Accuracy and Uncertainty of Coronal Mass Ejection 3D Reconstructions Depending on the Number of Viewpoints in the Heliosphere. This paper presents a systematic study that focuses on how the number of viewpoints distributed in the heliosphere affects the accuracy and uncertainty of the 3D geometric coronal mass ejection (CME) measurements. An efficient nonmanual minimization-based fitting technique that is different from the manual methods widely used in the community is developed. It uses the MPFIT minimization IDL routine and searches for the optimized model point clouds that best fit the observed CME leading edges from one, two, or three viewpoints using a set of combinations of observations provided by the Solar Terrestrial Relations Observatory and Solar and Heliospheric Observatory. The technique also provides a robust calculation of uncertainties of the CME geometric parameters that is lacking in manual methods. Three well-known geometric models, the cone, graduated cylindrical shell, and spheroid shock, are used. All three models depend on geometric parameters that govern the CME propagation direction and size. Sample cases of a halo, partial halo, and limb CMEs as seen from the Earth are used in the fitting and uncertainty calculation. It is found that, after adding a second viewpoint off the Sun–Earth line, the uncertainties drop significantly, while the addition of the third viewpoint adds limited benefits. This study shows that the minimization fitting method provides a robust, fast, and straightforward way to define the CME geometric parameters along with their uncertainties for individual events, which shall provide the necessary data constraints for ensemble predictions of CME evolution. It also underlines the importance of having a permanent observatory off the Sun–Earth line for operational space weather prediction.

Keywords: Solar corona, Space weather, Solar coronal mass ejections, The Sun
A Comparative Study of the Ground State Transitions of CO and C I as Molecular Gas Tracers at High Redshift. The CO(1─0) and [C I](1─0) emission lines are well-established tracers of cold molecular gas mass in local galaxies. At high redshift, where the interstellar medium is likely to be denser, there have been limited direct comparisons of both ground-state transitions. We present a comparison of [C I](1─0) and CO(1─0) emission in 20 unlensed dusty, star-forming galaxies at z ≥ 2─5. The CO(1─0)/[C I](1─0) ratio remains constant up to z = 5, supporting the reliability of [C I](1─0) as a gas─mass tracer. We use the CO(1─0), [C I](1─0), and 3 mm dust continuum measurements to cross─calibrate their respective gas mass conversion factors, finding no dependence of these factors on either redshift or infrared luminosity. Radiative transfer modeling shows that the warmer cosmic microwave background (CMB) at high redshift can significantly affect the [C I] as well as CO emission, which can change the derived molecular gas masses by up to 70% for the coldest kinetic gas temperatures expected. Nevertheless, the magnitude of the CMB effect on the CO/[C I] ratio is within the known scatter of the  LCO'−L[CI]'  relation. Precisely determining the CMB effect on individual line intensities would require well-sampled spectral line energy distributions to robustly model the gas excitation conditions. Finally, we note that adopting a variable CO gas─mass conversion factor for different galaxy populations implies [C I](1─0) and dust conversion factors that differ from canonically assumed values. However, the revised conversion factors are consistent with expectations for (super)solar metallicities likely to be found in high-redshift dusty galaxies.

Keywords: Submillimeter astronomy, Molecular gas, High-redshift galaxies, Interstellar medium
Radiative Relativistic Turbulence as an In Situ Pair-plasma Source in Blazar Jets. As powerful gamma-ray engines, blazars—relativistic plasma jets launched toward Earth from active galactic nuclei—are manifestly high-energy particle accelerators. Yet, exactly how these jets accelerate particles as well as what they are made of both remain largely mysterious. In this work, we argue that these issues may be linked through the gamma-ray emission for which blazars are renowned. Namely, high-energy photons produced at sites of intense particle acceleration could be absorbed by soft radiation within the jet, enriching it with electron–positron pairs. We explore this possibility in the specific context of particle acceleration by magnetized radiative relativistic turbulence. Using a combination of theory, particle-in-cell simulations, and Fokker–Planck modeling, we identify and characterize a novel pair-production-mediated equilibration mechanism in such turbulence. Initially, turbulent energy injection outpaces radiative cooling, leading to runaway particle acceleration and gamma-ray radiation. Then, gamma-ray absorption begets copious newborn pairs, slowing subsequent particle acceleration. This eventually brings particle acceleration into balance with radiative cooling and shuts down pair production: a pair-enriched final equilibrium. We estimate that this process could significantly load jets of flat-spectrum radio quasars with fresh pairs. These results represent an important connection between particle acceleration and plasma composition in blazar jets.

Keywords: Relativistic mechanics, Blazars, Flat-spectrum radio quasars, Plasma astrophysics, Magnetic fields