Sazuna/UAT_keywords huggingface dataset:
Characterization of the Alfvén Transition in the Young Solar Wind using Parker Solar Probe Observations Approaching Solar Maximum. Close to Earth, the solar wind is usually super-Alfvénic, i.e., the speed of the solar wind is much larger than the Alfvén speed. However, in the lower coronal regions, the solar wind is mostly sub-Alfvénic. With the Parker Solar Probe (PSP) crossing the boundary between the sub- and super-Alfvénic flow, R. Bandyopadhyay et al. performed a turbulence characterization of the sub-Alfvénic solar wind with initial data from encounters 8 and 9. In this study, we reexamine the turbulence properties such as turbulence amplitude, anisotropy of the magnetic field variance, intermittency, and switchback strength using PSP data from encounters 8─19. The later orbits probe lower altitudes and experience sub-Alfvénic conditions more frequently, providing a greater statistical coverage to contrast sub- and super-Alfvénic solar wind. These later orbits also extend the observations from near solar minimum at launch to near solar maximum conditions. Also, by isolating the intervals where the solar wind speed is approximately equal to the Alfvén speed, we explore the transition in more detail. We show that the amplitude of the normalized magnetic field fluctuation is smaller for the sub-Alfvénic samples. While solar wind turbulence in general is shown to be anisotropic, the sub-Alfvénic samples are more anisotropic than the super-Alfvénic samples, in general. Further, we show that the sub- and super-Alfvénic samples do not show much distinction in terms of intermittency strength. Finally, consistent with prior results, we find no evidence for polarity reversing &gt;90° switchbacks in the sub-Alfvénic solar wind.

Keywords: Space plasmas, Alfven waves, Solar wind, Interplanetary magnetic fields
A Complete Theory for Nondiffusive Field Line Random Walk in Magnetic Turbulence. Previous analytical and numerical investigations of the stochastic properties of field lines in magnetic turbulence have been based on determining the running field-line diffusion coefficient. The latter transport parameter is directly related to the second moment of the field-line distribution function. For the normal diffusive case, this distribution function should be a Gaussian where the width increases linearly with distance. The corresponding transport equation is a usual heat transport or diffusion equation. However, such an equation is no longer valid for nondiffusive cases. In this paper, we systematically develop a theory for obtaining a nondiffusive transport equation. The derived equation has the same structure as a generalized master equation. In the latter equation, we employ a so-called rapid decorrelation approximation to achieve a strong simplification. Its solution is a Gaussian regardless of whether the transport is subdiffusive, normal diffusive, or superdiffusive. For slab turbulence, where the theory of field line random walk is exact, we determine the running diffusion coefficient and the mean squared displacement for a general spectrum in the energy range. The same quantities are then computed by employing numerical simulations. It is demonstrated that the simulations agree perfectly with the analytically obtained distribution functions, and those are indeed Gaussian distributions. The derivations presented in this study can also be used to derive transport equations in other areas of physics such as the theory of energetic particles interacting with magnetohydrodynamic turbulence.

Keywords: Interplanetary turbulence, Non-Gaussianity, Interplanetary magnetic fields
The New Status Qvo? SN 2021qvo Is Another 2003fg-like Type Ia Supernova with a Rising Light-curve Bump. In recent years, multiple Type Ia supernovae (SNe Ia) have been observed with "bumps" in their rising light curves shortly after the explosion. Here, we present SN 2021qvo: an SN Ia that exhibits a clear early bump in photometry obtained by the Young Supernova Experiment. Photometric and spectroscopic observations of SN 2021qvo show that it has a broader light curve, higher peak luminosity, shallower Si II λ5972 pseudoequivalent width, and lower ejecta velocities than normal SNe Ia, which are all consistent with the characteristics of the 2003fg-like (often called "super-Chandrasekhar") SN subtype. Including SN 2021qvo, just four known 2003fg-like SNe Ia have sufficient prepeak data to reveal a rising light-curve bump, and all four have bump detections. A host-galaxy analysis reveals that SN 2021qvo exploded in a low-mass galaxy  log(M*/M⊙)=7.83−0.24+0.17 , also consistent with other members of this class. The current leading early bump 2003fg-like SN Ia progenitor model involves an interaction between the circumstellar material (CSM) and the SN ejecta. We test the validity of this theory by modeling the early bump and subsequent light-curve evolution of SN 2021qvo with the Modular Open Source Fitter for Transients. We find that the bump can be modeled with a best-fit CSM mass in the range MCSM = 3.31−8.51 × 10−3M⊙. SN 2021qvo adds to the small but growing number of 2003fg-like SNe Ia with rising light-curve bumps; as the number of these SNe Ia with CSM estimates continues to grow, population-level inferences about the CSM distribution will be able to constrain the progenitor scenario for these SNe Ia.

Keywords: Type Ia supernovae
Hierarchical Interferometric Bayesian Imaging. Very long baseline interferometry (VLBI) achieves the highest angular resolution in astronomy. VLBI measures corrupted Fourier components, known as visibilities. Reconstructing on-sky images from these visibilities is a challenging inverse problem, particularly for sparse arrays such as the Event Horizon Telescope (EHT) and the Very Long Baseline Array, where incomplete sampling and severe calibration errors introduce significant uncertainty in the image. To help guide convergence and control the uncertainty in image reconstructions, regularization on the space of images is utilized, such as enforcing smoothness or similarity to a fiducial image. Coupled with this regularization is the introduction of a new set of parameters that modulate its strength. We present a hierarchical Bayesian imaging approach (hierarchical interferometric Bayesian Imaging, HIBI) that enables the quantification of uncertainty for all parameters. Incorporating instrumental effects within HIBI is straightforward, allowing for simultaneous imaging and calibration of data. To showcase HIBI's effectiveness and flexibility, we build a simple imaging model based on Markov random fields and demonstrate how different physical components can be included, e.g., black hole shadow size, and their uncertainties can be inferred. For example, while the original EHT publications were unable to constrain the ring width of M87*, HIBI measures a width of 9.3 ± 1.3 μas. We apply HIBI to image and calibrate EHT synthetic data, real EHT observations of M87*, and multifrequency observations of OJ 287. Across these tests, HIBI accurately recovers a wide variety of image structures and quantifies their uncertainties. HIBI is publicly available in the Comrade VLBI software repository.

Keywords: Aperture synthesis, Black holes, Bayesian statistics, Very long baseline interferometry, Astronomy data analysis, Active galactic nuclei
Multicolor Characterization of Optically Invisible FU Orionis-type Outbursts: Demonstration and Prospects for the WINTER Survey. Episodic mass accretion is the dominant mechanism for mass assembly in the protostellar phase. Although prior optical time-domain searches have allowed detailed studies of individual outbursts, these searches remain insensitive to the earliest stages of star formation. In this paper, we present the characterization of two FU Orionis (FUor) outbursts identified using the combination of the ground-based, near-infrared Wide-field Infrared Transient Explorer (WINTER) and the space-based, mid-infrared NEOWISE survey. Supplemented with near-infrared spectroscopic follow-up, we show that both objects are bona fide FUor type outbursts based on (i) their proximity to star-forming regions, (ii) large amplitude (2─4 magnitudes) infrared brightening over the last decade, (iii) progenitor colors consistent with embedded (Class I) protostars, and (iv) "mixed-temperature" infrared spectra exhibiting characteristic signatures of cool outer envelopes and a hot inner disk with a wind. While one source, WNTR24-cua, is a known FUor that we independently recover; the second source, WNTR24-egv, is a newly confirmed object. Neither source is detected in contemporaneous ground-based optical imaging, despite flux limits ≳100× fainter than their infrared brightness, demonstrating the capabilities of WINTER to identify heavily obscured young stellar object outbursts. We highlight the capabilities of the Galactic Plane Survey of the recently commissioned WINTER observatory in addressing the poorly understood FUor population with its unique combination of real-time detection capabilities, multicolor sensitivity, weekly cadence, and wide area coverage.

Keywords: FU Orionis stars, Infrared astronomy, Young stellar objects, Pre-main sequence stars, Infrared telescopes, Infrared sources, Time domain astronomy, Protostars
Beyond the Local Void: A Data-driven Search for the Origins of the Amaterasu Particle. We introduce a simulation-based inference framework to constrain the origins of individual ultra-high-energy cosmic rays by combining realistic three-dimensional propagation modeling with Bayesian parameter estimation. Our method integrates CRPropa 3 simulations, including all relevant interactions and magnetic deflections in both Galactic and extragalactic fields, with approximate Bayesian computation to infer posterior distributions over key parameters such as source position, distance, energy, and magnetic field properties. This approach allows joint constraints from the observed energy and arrival direction to be applied simultaneously, naturally incorporating their correlations in addition to relevant modelling uncertainties. We demonstrate our method by applying it to the Amaterasu particle detected by the TA observatory, the second-highest-energy cosmic ray ever detected. The resulting posterior distributions quantify the regions of space consistent with its reconstructed properties under different energy and composition assumptions, revealing a broader set of nearby source candidates than found in previous analyses. This application highlights the framework's ability to translate individual ultra-high-energy cosmic-ray observations into directly interpretable source constraints and provides a foundation for future simulation-based analyses of cosmic rays at the highest energies.

Keywords: Cosmic rays, Bayesian statistics, Particle astrophysics, Ultra-high-energy cosmic radiation
Formation of Recycled Pulsars in Common Envelope Binaries. We present a systematic study of the evolution of low- and intermediate-mass X-ray binaries consisting of a 1.4 M⊙ neutron star (NS) and a donor star of mass 1─8 M⊙. Using grids of detailed MESA simulations, we show that for donor masses of 2─8 M⊙, mass transfer may be dynamically unstable, leading to a common envelope (CE) phase. By adopting CE ejection efficiencies in the range αCE = 0.3─3.0, we find that post-CE binaries frequently experience a CE decoupling phase (CEDP), which plays a critical role in determining their final orbital and compositional properties. Systems with initial donor masses ≳3.5 M⊙ predominantly evolve into NS binaries with carbon─oxygen or oxygen─neon white dwarfs (WDs) with masses between 0.5 and 1.4 M⊙. Comparison with the observed population of binary pulsars with a WD companion shows better agreement with higher CE ejection efficiencies (αCE = 3.0). Furthermore, we demonstrate that NSs can accrete a sufficient amount of matter (≳0.01 M⊙) during the CEDP and subsequent Case BA/BB/BC mass transfer phases to be effectively recycled into millisecond pulsars. We identify two distinct evolutionary channels capable of reproducing the observed characteristics of the millisecond pulsar PSR J1928+1815 with a helium-star companion. Our results highlight the importance of the CEDP in the formation of recycled pulsars and provide constraints on the CE ejection efficiency during binary evolution.

Keywords: Neutron stars, X-ray binary stars, Binary stars, White dwarf stars, Stellar evolution
Limits to Extracting Neutron-star Physics Constraints from NICER Pulse Profiles. Modeling energy-dependent X-ray pulse profiles from rotation-powered millisecond pulsars observed with Neutron Star Interior and Composition Explorer (NICER) has emerged as a promising avenue for measuring neutron-star radii and probing the equation of state of cold, ultradense matter. However, pulse profile models have often required an unwieldy number of parameters to account for complex surface emission geometries, introducing the risk of overfitting and degeneracies. To explore the number of model parameters that can be inferred uniquely, we perform a quantitative assessment of the information content in X-ray pulse profiles by applying Fourier methods. We determine the number of independent observables that can be reliably extracted from the pulse shapes, as well as from complementary X-ray spectral data obtained with XMM-Newton, for key NICER targets. Our analysis provides a framework for evaluating the match between model complexity and data constraints. It also demonstrates the importance of incorporating in the model the pulsed components of the magnetospheric nonthermal emission, which may often contribute significantly to the observed spectra. Our results highlight limitations in previous inferences of neutron-star radii from NICER observations, which may have incorporated model complexity not supported by the data.

Keywords: Neutron stars, X-ray stars
Mass Distribution of Binary Black Hole Mergers from Young and Old Dense Star Clusters. Dense star clusters are thought to contribute significantly to the merger rates of stellar-mass binary black holes (BBHs) detected by the LIGO─Virgo─KAGRA collaboration. We combine N-body dynamic models of realistic dense star clusters with cluster formation histories to estimate the merger rate distribution as a function of primary mass for merging BBHs formed in these environments. It has been argued that dense star clusters—most notably old globular clusters—predominantly produce BBH mergers with primary masses Mp ≍ 30 M⊙. We show that dense star clusters forming at lower redshifts—and thus having higher metallicities—naturally produce lower-mass BBH mergers. We find that cluster BBH mergers span a wide range of primary mass, from about 6 M⊙ to above 100 M⊙, with a peak near 8 M⊙, reproducing the overall merger rate distribution inferred from gravitational wave detections. Our results show that most low-mass BBH mergers (about 95% with Mp ≲ 20 M⊙) originate in metal-rich (Z ∼ Z⊙) dense star clusters, while more massive BBH mergers form predominately in metal-poor globular clusters. We also discuss the role of hierarchical mergers in shaping the BBH mass distribution. Gravitational wave detection of dynamically formed low-mass BBH mergers—potentially identifiable by features such as isotropic spin distributions—may serve as probes of cluster formation histories in metal-rich environments at low redshifts.

Keywords: Stellar mass black holes, N-body simulations, Gravitational wave sources, Star clusters
Discovery of a Rapidly Evolving Global Magnetic Field in the M Dwarf YZ Cet and Constraints on the Magnetic Field of Its Planet YZ Cet b. We present a spectropolarimetric study of the nearby M4.5V exoplanet host star YZ Cet, based on near-infrared observations obtained with the Spectropolarimètre Infrarouge at the Canada-France-Hawaii Telescope. We detect striking changes in the large-scale magnetic field strength and geometry over the course of just a few stellar rotations, a level of short-term global magnetic field evolution rarely reported in M dwarfs. We modeled the temporal variation of the longitudinal magnetic field using the Gaussian process regression, which allowed us to robustly determine the stellar rotation period and quantify the evolution timescale of the magnetic field. Independent Zeeman Doppler imaging reconstructions of the two epochs confirm a significant reconfiguration of the star's global magnetic strength and topology. The detection of a weaker complex axisymmetric magnetic field (mean ∣B∣ ∼ 201 G), which changes into a stronger nonaxisymmetric dipole-dominated field (Mean ∣B∣ ∼ 276 G) over a few rotation cycles, is in contrast to results from similar fully convective M dwarf stars. YZ Cet is known to exhibit polarized radio bursts potentially driven by auroral radio emission from star─planet interaction (SPI). By combining our magnetic maps with recent radio observations, we refine the constraints on the magnetic field strength of the innermost planet, YZ Cet b. These results underscore the importance of monitoring stellar magnetic variability to interpret multiwavelength SPI signatures and to characterize the magnetospheres of potentially habitable exoplanets.

Keywords: M dwarf stars, Zeeman-Doppler imaging, Stellar magnetic fields, Magnetic variable stars, Planetary magnetospheres
HST Confirms Sub-5 kpc Dual Quasar Pairs at Cosmic Noon. During cosmic noon (z ∼ 1─3), when both star formation and black hole growth peaked, galaxy mergers are predicted to trigger dual active galactic nuclei that eventually coalesce as supermassive black hole (SMBH) binaries. However, observations of dual quasars with sub-5 kpc separations—the critical phase preceding final coalescence—have remained challenging due to angular resolution limitations. We present the discovery and confirmation of two subarcsecond dual quasars at z &gt; 1, selected from 59,025 Sloan Digital Sky Survey (SDSS) quasars, which fall within the footprint of the Hyper Suprime-Cam Survey. Using high-resolution Hubble Space Telescope imaging and slitless spectroscopy, we confirmed SDSS J1625+4309 (z = 1.647, separation 0 .″ 55/4.7 kpc) and SDSS J0229−0514 (z = 3.174, separation 0 .″ 42/3.2 kpc), probing the sub-5 kpc separation regime. Through the novel combination of WFC3/IR direct imaging (F140W) and grism spectroscopy (G141), we resolve both components morphologically and spectroscopically confirm their dual nature via detection of Hβ+[O III] and Mg II emission lines in each nucleus. Two-dimensional image decomposition reveals distinct host galaxy morphologies: J1625+4309 shows an extended, disturbed structure (Re = 4.7 kpc) indicative of an ongoing major merger, while J0229−0514 exhibits a compact host (Re = 1.4 kpc) suggesting an advanced coalescence stage. Black hole mass estimates based on virial relations yield  MBH∼108.1─108.7M⊙ with line-of-sight velocity offsets of (0.7 ± 0.1) × 103 km s−1 and (1.0 ± 0.2) × 103 km s−1, respectively. These confirmations directly constrain the frequency and properties of close dual quasars, opening new avenues for studying SMBH mergers at cosmic noon.

Keywords: Double quasars, Galaxy mergers, Quasars
CN Trianguli: A W-type Contact Binary Exhibiting A-type Light Curve via Starspot-induced Dimming. We present comprehensive photometric observations and analysis of the totally eclipsing binary CN Tri. The photometric solutions suggest it as an extremely low mass ratio contact binary system with q ∼ 0.08. Multiband photometry obtained using the WH50 and XL85 telescopes, along with high-cadence time-series photometric data from the Transiting Exoplanet Survey Satellite (TESS), reveals that CN Tri is fundamentally a W-type contact binary. However, the light curve morphology from TESS observations exhibits characteristics typical of A-type systems. We successfully reconciled this apparent contradiction through modeling a time-evolving starspot near orbital phase 0.5, which provides a comprehensive explanation for the anomaly observation in this system. This case study demonstrates that starspot-induced light curve distortions can lead to misclassification of contact binary types, offering a valuable framework for interpreting similar anomalies in other W UMa systems with discrepant photometric classifications.

Keywords: Close binary stars, Late-type stars, Eclipsing binary stars, Contact binary stars
Hubble Space Telescope Imaging of Three Isolated Faint Dwarf Galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known; hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from the environmental effects of more massive galaxies. Our HST data reach ∼2─4 magnitudes below the tip of the red giant branch (TRGB) for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime (MV = −10.62 ± 0.08 and  D=2.16−0.07+0.08  Mpc for Pavo, MV = −10.91 ± 0.10 and D = 3.34 ± 0.11 Mpc for Corvus A, and MV = −12.02 ± 0.12 and  D=6.50−0.11+0.15  Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed ∼60% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies.

Keywords: Galaxy distances, Galaxy environments, Dwarf galaxies, Galaxy stellar content, HST photometry, Star formation, Galaxy evolution, Low surface brightness galaxies
INTEGRAL IBIS Catalog of Magnetar Bursts. One of the distinctive properties of magnetars, young neutron stars powered mainly by magnetic energy, is the emission of short (≲1 s) bursts of hard X-rays. Such bursts have been observed in nearly all the known magnetars, although at different and time-variable rates of occurrence. In the past two decades, the INTEGRAL satellite has extensively covered the Galactic plane with good imaging capabilities, where most magnetars reside. We present the results of a comprehensive search for magnetar bursts in more than 20 yr of archival data of the INTEGRAL IBIS instrument (15 keV─1 MeV). This led to the detection of 1349 bursts with 30─150 keV fluence in the ∼2 × 10−9 to 3 × 10−6 erg cm−2 range from 21 of the 34 examined magnetars and candidate magnetars with well-known positions. The durations of the bursts, in terms of T90, follow a lognormal distribution centered at ∼0.1 s. Most of the detected bursts originated from three particularly active sources: 1E 1547─5408, SGR 1806─20, and SGR 1935+2154. The integral distributions of their burst fluences follow power laws with slopes β = 0.76±0.04, 0.95±0.06, and 0.92±0.10, respectively. The burst spectra are generally well fit with an exponentially cutoff power law with peak energy Epeak in the range ∼20−60 keV for SGR 1806─20 and SGR 1935+2154, while the bursts of 1E 1547─5408 are slightly harder (Epeak ∼ 35−100 keV). A significant anticorrelation between Epeak and fluence is found for SGR 1806─20, which provided the largest number of bursts among the sources of our sample.

Keywords: Magnetars