Sazuna/UAT_keywords huggingface dataset:
Magnetic Reconnection in a Compact Magnetic Dome: Chromospheric Emissions and High-velocity Plasma Flows. Magnetic reconnection at small spatial scales is a fundamental driver of energy release and plasma dynamics in the lower solar atmosphere. We present observations of a brightening in an active region, captured in high-resolution data from the Daniel K. Inouye Solar Telescope using the Visible Broadband Imager and the Visible Spectro-Polarimeter (ViSP). The event exhibits Ellerman bomb‑like morphology in the Hβ filter, associated with flux cancellation between a small negative-polarity patch and an opposite polarity plage. Additionally, it displays enhanced emissions in Ca II K, hot elongated features containing Alfvénic plasma flows, and cooler blueshifted structures. We employ multiline, nonlocal thermodynamic equilibrium inversions of the spectropolarimetric data to infer the stratification of the physical parameters of the atmosphere. Furthermore, we use the photospheric vector magnetogram inferred from the ViSP spectra as a boundary condition for nonlinear force-free field extrapolations, revealing the three-dimensional distribution of squashing factors. We find significant enhancements in temperature, velocity, and microturbulence confined to the upper photosphere and low chromosphere. Our findings provide observational evidence of low-altitude magnetic reconnection along quasi-separatrix layers in a compact fan-spine-type configuration, highlighting the complex interplay between magnetic topology, energy release, and plasma flows.

Keywords: Solar atmosphere, Solar chromosphere, Spectropolarimetry, Solar magnetic fields
Temporal Variation of Flare Occurrence Rates via the Spot Evolution on the Sun and Solar-type Stars. The spot evolution on the Sun and solar-type stars is important for understanding the nature of consequential flaring activity. This study statistically investigates the variance of flare occurrence rate through the time evolution of spots on the Sun and solar-type stars. We have compiled the 28 yr catalogs of solar flares and their source sunspots obtained from solar surface observations by NOAA and GOES for the Sun. Also, we combined the cataloged stellar flares with the time evolution of starspots estimated by light curves obtained by the 4 yr Kepler mission for solar-type stars. For the obtained 24,124 solar flares and 180 stellar flares, we calculate the flare occurrence distribution with respect to  tflare‑tmax , which represents the timing of flare through the spot evolution, where  tflare  is the flare occurrence time and  tmax  is the time when the source spot takes its maximum area. When normalized by the spot lifetime, we found that the flare occurrence distribution for  tflare‑tmax  shows a similar distribution regardless of spot size or flare energy, suggesting that the Sun and the solar-type star share the same physical process in the spot-to-flare activity. On this basis, we propose a formula for the time variation of the flare occurrence rate per spot. Also, the correlation between the temporal variation of flare occurrence rate and the time evolution of spot area and the lack of difference in flare occurrence rate between the emergence and decaying phases provide a milestone for the nature of flare-productive spots.

Keywords: Starspots, Solar flares, Solar analogs, Sunspots, Flare stars, Stellar flares
Physics of Pair-producing Gaps in Black Hole Magnetospheres: Two-dimensional General Relativistic Particle-in-cell Simulations. Black holes can launch powerful jets through the Blandford─Znajek process. This relies on enough plasma in the jet funnel to conduct the necessary current. However, in some low-luminosity active galactic nuclei, the plasma supply near the jet base may be an issue. It has been proposed that spark gaps—local regions with unscreened electric field—can form in the magnetosphere, accelerating particles to initiate pair cascades, thus filling the jet funnel with plasma. In this paper, we carry out 2D general relativistic particle-in-cell (GRPIC) simulations of the gap, including self-consistent treatment of inverse Compton scattering and pair production. We observe gap dynamics that is fully consistent with our earlier 1D GRPIC simulations. We find strong dependence of the gap power on the soft photon spectrum and energy density, as well as the strength of the horizon magnetic field. We derive physically motivated scaling relations, and applying to M87, we find that the gap may be energetically viable for the observed TeV flares. For Sgr A*, the energy dissipated in the gap may also be sufficient to power the X-ray flares.

Keywords: Black hole physics, Non-thermal radiation sources, Plasma astrophysics, High energy astrophysics
Narrowband Imaging of a z = 3.24 Protocluster: Insights from [O III]-emitting Galaxies. We present narrowband imaging of a spectroscopically confirmed protocluster "D4UD01" at z = 3.24 using CFHT/WIRCam. We identify a sample of 24 [O III] emission-line galaxies in the field, which forms a large overdensity in the protocluster region. The protocluster is expected to evolve into a Virgo-like cluster by z = 0. Utilizing multiwavelength data, we derive the physical properties of these [O III] emitters and find that they are intermediate-mass normal star-forming galaxies (∼1010 M⊙) roughly following the star-forming main sequence. The [O III] emitters trace an overdensity spatially offset from that of photometric-redshift and quiescent galaxies, suggesting that these distinct galaxy populations may inhabit dark matter halos that formed at different epochs. A comparative analysis of [O III]-emitter properties shows similar characteristics in both protocluster and field environments. This protocluster likely represents an evolved structure that has progressed beyond its peak star formation phase, although our limited sample size may prevent detection of subtle environmental effects.

Keywords: Protoclusters
Structure and Dynamics of Erupting Solar Prominences Using the Rolling Hough Transform: Toward a Feature-oriented Classification. The classification of solar prominences has proven to be challenging, due to their diverse morphologies and dynamical behavior. Complexity is heightened when considering eruptive prominences, where the dynamics demand methods capable of capturing detailed structural information. While there exist a range of line-of-sight and plane-of-sky (POS) techniques that have advanced our understanding of prominence motions, they are subject to limitations, emphasizing the need for effective methods of extracting structural information from prominence dynamics. We present a proof of concept for the spatial Rolling Hough Transform (RHT) algorithm, which identifies fine-scale structural orientation in the POS, applied to prominence structure and dynamics. We demonstrate the RHT approach using two contrasting prominence dynamics events using Solar Dynamics Observatory/Atmospheric Imaging Assembly 304 Å observations: (1) a quiet-Sun eruption, and (2) activation (swirl) of a polar crown prominence. By analyzing the light curves and movies from each event, we divide the events into distinct dynamical phases: from slow rise to drainage. The spatial RHT method enables us to extract structural information and localized dynamics for both events and the different evolution phases. We develop a classification to label the prominences as either radially or tangentially oriented structures. The quiet-Sun eruption has a predominately tangential structure in the slow-rise phase but displays greater radial features during/after the eruption. The polar swirl activation initially shows a strong radial contribution, which diminishes as more tangential structures appear during/after the activation. Our results demonstrate the successful application of the spatial RHT to prominences, leading to the classification of individual prominences and an insight into their dynamics.

Keywords: Solar activity, Solar prominences, Solar filament eruptions
Unraveling the Mysteries of KS 1947+300: Multiwavelength Observations in a Low-eccentricity Be/X-Ray Binary. KS 1947+300, a Be/X-ray binary system, has been observed to experience both type I and type II X-ray outbursts despite its nearly circular orbit, which is atypical according to the viscous decretion disk model. To understand the variations in optical and X-ray, we have analyzed data covering more than 20 yr of observations. In the optical band, we analyzed spectra and light curves, measuring the strength of the Hα and He I λ6678 lines. In the X-ray band, we studied the long-term light curves provided by several all-sky monitors. KS 1947+300 exhibits changes in brightness and Hα emission on timescales from months to years. The optical and IR variability shows small amplitude changes during the active X-ray state, and a long, smooth decrease during the quiescent state. The fact that the amplitude of variability increased with wavelength suggests that the long-term decrease in the optical emission is due to weakening of the circumstellar disk. Structural changes in the disk may also be the origin of the periodic signals with periods ∼200 days detected in the Zwicky Transient Facility (ZTF)-g and ZTF-r band light curves. These changes could be attributed to the mechanism that ejects matter from the photosphere of the Be star into the disk. In conclusion, the long-term changes in optical continuum and line emission, as well as the X-ray variability patterns, are attributed to an evolving and distorted decretion disk.

Keywords: X-ray transient sources, Circular orbits, Be stars, High mass x-ray binary stars
Simultaneous Construction of Fast Equator, Poleward Meridional Flow, and Near-surface Shear Layer in Solar Magnetohydrodynamic Calculation. We carry out an unprecedented high-resolution simulation for the solar convection zone. Our calculation reproduces the fast equator and near-surface shear layer (NSSL) of differential rotation and the near-surface poleward meridional flow simultaneously. The NSSL is located in a complex layer where the spatial and time scales of thermal convection are significantly small compared with the deep convection zone. While there have been several attempts to reproduce the NSSL in numerical simulation, the results are still far from reality. In this study, we succeed in reproducing an NSSL in our new calculation. Our analyses led to a deeper understanding of the construction mechanism of the NSSL, which is summarized as: (1) rotationally unconstrained convection in the near-surface layer transports the angular momentum radially inward; (2) sheared poleward meridional flow around the top boundary is constructed; (3) the shear causes a positive kinetic  &lt;vr'vθ'&gt;  and negative magnetic &lt;BrBθ&gt; correlations; and (4) the turbulent viscosity and magnetic tension are latitudinally balanced with the Coriolis force in the NSSL. We emphasize the importance of the magnetic field in the solar convection zone.

Keywords: Solar convective zone, Solar meridional circulation, Solar differential rotation, Solar interior
The 230 GHz Variability of Numerical Models of Sagittarius A*. II. The Physical Origins of the Variability. We continue our previous work, H.-S. Chan et al., to investigate how variations in the electron temperature prescription parameter, RLow, influence the 3 hr variability at 230 GHz, MΔT, in magnetically arrested disk (MAD) models of Sagittarius A* (Sgr A*), through analyzing a series of general-relativistic magnetohydrodynamics and ray-tracing simulations. For models with a black hole spin a &gt; 0, we discovered that increasing RLow renders the photon ring more optically thick, obscuring the varying accretion flows that contribute to the variability. However, as RLow increases further, MAD flux eruptions become more pronounced, compensating for the decrease in MΔT. For models with spin a &lt; 0, although a higher RLow also increases the optical thickness of the fluid, voids within the optically thick gas fail to cover the entire photon ring. Similarly, flux eruptions become more prominent as RLow increases further, contributing to the observed rise in MΔT relative to RLow. For black holes with spin a = 0, although the effect of increasing optical depth is still present, their 230 GHz light curves, and hence MΔT, are insensitive to changes in RLow. Furthermore, we found that the variability of the 230 GHz light curves at RLow = 1 might correlate with fluctuations in the internal energy of the gas near the black hole, and we listed potential causes and solutions to the over-variability problem. Our findings highlight potential approaches for refining MΔT to better align with observations when modeling Sgr A*.

Keywords: Black hole physics, Galactic center, Black holes, High energy astrophysics, Plasma astrophysics, Radiative transfer, Radio astronomy
The EMPI Code for Plasma-induced Effects on Radio Waves. I. Nonmagnetized Media and Applications to Fast Radio Bursts. Electromagnetic waves undergo modifications as they propagate through plasma. We present electromagnetic wave–plasma interaction (EMPI), a three-dimensional numerical framework designed to simulate the interaction between radio signals and cold plasma. With input plasma density profiles, intrinsic radio signals, and the time and frequency resolutions of the telescope, the code synthesizes observed signals using first-principles calculations. EMPI is capable of modeling a wide range of plasma distributions, spanning analytically described smooth functions (e.g., Gaussian or exponential profiles), statistical models (e.g., turbulent screens), and discrete macroscopic structures like isolated plasma clumps, which are difficult to model both analytically and statistically. Validation tests demonstrate excellent agreement with established plasma propagation effects, such as dispersion, lensing, scintillation, and scattering. This code provides an efficient method for handling both analytical and statistical scenarios, bridging the gap between these descriptions. Thanks to its comprehensive capabilities, EMPI is particularly useful for studying radio sources of cosmological origin, especially pulse-like signals such as fast radio bursts. As these signals travel through diverse and complex plasma environments across the universe, their properties are inevitably altered, resulting in observable changes. In this context, EMPI serves as a valuable tool for studying the propagation effects of these sources, helping to advance the understanding of their essence and the intervening plasma environments.

Keywords: High energy astrophysics, Plasma physics, Plasma astrophysics, Radio bursts, Computational methods, Radio sources, Radio transient sources
Early Planet Formation in Embedded Disks (eDisk). XXI. Limited Role of Streamers in Mass Supply to the Disk in the Class 0 Protostar IRAS 16544-1604. Asymmetric and narrow infalling structures, often called streamers, have been observed in several Class 0/I protostars, which is not expected in the classical star formation picture. Their origin and impact on the disk formation remain observationally unclear. By combining data from the James Clerk Maxwell Telescope (JCMT) and Atacama Large Millimeter/submillimeter Array (ALMA), we investigate the physical properties of the streamers and parental dense core in the Class 0 protostar, IRAS 16544─1604. Three prominent streamers associated to the disk with lengths between 2800 and 5800 au are identified on the northern side of the protostar in the C18O emission. Their mass and mass infalling rates are estimated to be in the range of (1─4) × 10−3 M⊙ and (1─5) × 10−8 M⊙ yr−1, respectively. Infall signatures are also observed in the more diffuse extended protostellar envelope observed with the ALMA from the comparison to the infalling and rotating envelope model. The parental dense core detected by the JCMT observation has a mass of ∼0.5 M⊙, a subsonic to transonic turbulence of  M  = 0.8─1.1, and a mass-to-flux ratio of 2─6. Our results show that the streamers in IRAS 16544─1604 only possess 2% of the entire dense core mass and contribute less than 10% of the mass infalling rate of the protostellar envelope. Therefore, the streamers in IRAS 16544─1604 play a minor role in the mass accretion process onto the disk, in contrast to those streamers observed in other sources and those formed in numerical simulations of collapsing dense cores with similar turbulence and magnetic field strengths.

Keywords: Circumstellar envelopes, Star formation, Low mass stars, Protoplanetary disks, Protostars
Image Instabilities and Polarization Crosstalk. We expand on our previous study of the impact of atmospheric seeing on polarization crosstalk, and show how the formalism that was developed in that work can be applied to treat the case of spatial modulators of polarization. Beside formally demonstrating how the problem of crosstalk is fully eliminated in such devices, we also gain insight on the meaning of polarimetric noise of temporal modulation schemes in the limit of very high modulation frequency. We also describe the problem of spectrograph instabilities, and how the spectral gradients that are naturally associated with a line spectrum feed into the problem of polarimetric errors induced by mechanical vibrations, thermal drifts, and pointing jitter. Finally, we show how this formalism can be used to estimate the contribution of polarization crosstalk to the errors on the elements of the 4 × 4 Stokes response matrix, for the purpose of producing realistic error budgets for polarimetric instrumentation.

Keywords: Spectropolarimetry
Fundamental Understanding of Magnetic Reconnection via Spiral CT Scan. III. Electron Agyrotropy and Temperature Anisotropy. For the first time, we reveal the distribution of electron agyrotropy and electron temperature anisotropy around a reconnection X-line by using the spiral CT scan technique, which is a novel technique analogous to that in the hospital. This X-line was detected by the Magnetospheric Multiscale (MMS) spacecraft and has been widely believed to host a magnetic reconnection without a guide field. With the help of such an advanced technique, we find that: (1) the electron agyrotropy is weak in the magnetosheath-side inflow region, medium in the magnetosphere-side inflow region, and strong near the X point; (2) the electron temperature is isotropic near the current sheet center but is parallel-dominant in both the magnetosheath-side and magnetosphere-side inflow regions, with the anisotropy on the magnetosphere side more prominent than on the magnetosheath side. Quantitatively, the strongest electron agyrotropy is within a scale of 10 km (0.1 di) around the X point. Interestingly, there is no enhancement of electron agyrotropy near the magnetosheath-side separatrix line. Both the electron agyrotropy and temperature anisotropy exhibit asymmetric distributions in the two inflow regions, providing different conditions for wave generation and instability growth, which may affect the reconnection rate.

Keywords: Space plasmas, Solar magnetic reconnection, Plasma physics
Exploring the Active Galactic Nucleus Fraction of a Sample of JWST's Little Red Dots at 4 &lt; z &lt; 8: Overmassive Black Holes Are Strongly Favored. JWST is revolutionizing our view of the early Universe by pushing the boundaries of detectable galaxies and black holes in redshift (upward) and mass (downward). The little red dots (LRDs), detected by several surveys at z &gt; 4, present a significant interpretational challenge, as their spectral energy distributions (SEDs) can mimic both active galactic nucleus (AGN) and stellar population templates. This study analyzes 19 LRDs from the JWST Advanced Deep Extragalactic Survey survey, utilizing NIRCam and MIRI photometry. By performing SED fitting across a vast parameter space, we explore a broad range of AGN fractions, defined as the ratio of the monochromatic luminosities (AGN, galaxy, and dust) over a specified wavelength range, 0.4–0.7 μm rest frame. We find that 17 of the 19 LRDs investigated are consistent with having significant AGN contributions, with best-fitting AGN fractions ranging between 20% and 70%, while one galaxy shows a low AGN contribution (2%) and another appears to be purely star forming. Moreover, assuming these LRDs do indeed host AGN, we can place limits on their black hole masses using the inferred AGN bolometric luminosities and adopting the Eddington limit. We find that, independent of the specific AGN fraction adopted, the LRDs' black holes are significantly overmassive relative to their host galaxies—by ∼1 dex, and up to ∼4 dex in the most extreme cases—compared to the local M•–M⋆ relation. The presence of overmassive black holes in the high-z Universe may provide the strongest evidence yet of heavy black hole seeding occurring during the cosmic dark ages.

Keywords: Supermassive black holes, Active galaxies, Scaling relations, Galaxy evolution, High-redshift galaxies
Impacts of Tidal Locking on Magnetospheric Energy Input to Exoplanet Atmospheres. We investigate the effect of planetary corotation on energy dissipation within the magnetosphere–ionosphere system of exoplanets. Using magnetohydrodynamic simulations, we find that tidally locked exoplanets have a higher cross polar cap potential (CPCP) compared to fast-rotating planets with the same magnetic field strength, confirming previous studies. Our simulations show that for a given interplanetary magnetic field, an increase in corotation period leads to a higher CPCP. Notably, this difference in CPCP between tidally locked and rotating planets persists across a range of solar wind conditions, including extreme environments such as those experienced by hot Jupiters. Furthermore, we observe that variations in corotation have little impact on CPCP for Earth-sized planets. These results underscore the significance of both corotation dynamics and planetary size in understanding how exoplanets interact with their stellar environments.

Keywords: Planetary magnetospheres, Solar-planetary interactions
Probing the Kinematics of Multiple- and Single-protostar Systems in Perseus with N<SUB>2</SUB>H<SUP>+</SUP>. We analyze the dense gas kinematics in two class 0/I protostellar cores, Per 30 and NGC 1333 IRAS 7, in the Perseus Molecular Cloud to determine whether their velocity structures are indicative of rotation. We examine the hyperfine structure of the N2H+ J = 1–0 transition by combining 3″ (900 au) Atacama Large Millimeter/submillimeter Array measurements with 9″ (2700 au) measurements from the Green Bank Telescope. We use the CASA Feather method to combine these data in order to maximize our sensitivity across spatial scales. We fit the N2H+ spectra to constrain the centroid velocity of the gas at each pixel and use these values to calculate the linear velocity gradient and specific angular momentum within apertures centered on each protostar with radii ranging from 5″ to 60″. Our results indicate that the velocity structure probed by the N2H+ emission is likely not a result of core rotation. These findings are consistent with other studies in the literature that indicate rotation is often not evident on scales ≲1000 au. We instead suggest that the velocity structure we see is a result of torques caused by irregular density distributions in these protostellar systems.

Keywords: Molecular gas, Multiple star evolution, Stellar kinematics, Star forming regions, Star formation, Protostars