Sazuna/UAT_keywords huggingface dataset:
The Kangaroo's First Hop: The Early Fast Cooling Phase of EP250108a/SN 2025kg. Fast X-ray transients are a rare and poorly understood population of events. Previously difficult to detect in real time, the launch of the Einstein Probe with its Wide-field X-ray Telescope has led to a rapid expansionof the sample and allowed the exploration of these transients across the electromagnetic spectrum. EP250108a is a recently detected example linked to an optical counterpart, SN 2025kg, or "the kangaroo." Together with a companion Letter we present our observing campaign and analysis of this event. In this letter, we focus on the early evolution of the optical counterpart over the first 6 days, including our measurement of the redshift of z = 0.17641. We compare to other supernovae and fast transients showing similar features, finding significant similarities with SN 2006aj and SN 2020bvc, and show that the source is well modelled by a rapidly expanding cooling blackbody. We show the observed X-ray and radio properties are consistent with a collapsar-powered jet that is low energy (≲1051 erg) and/or fails to break out of the dense material surrounding it. While we examine the possibility that the optical emission emerges from the shock produced as the supernova ejecta expand into a dense shell of circumstellar material, due to our X-ray and radio inferences, we favour a model where it arises from a shocked cocoon resulting from a trapped jet. This makes SN 2025 one of the few examples of this currently observationally rare event.

Keywords: Type Ic supernovae, X-ray transient sources, Gamma-ray bursts, High energy astrophysics
Inertial-range Turbulence Anisotropy of the Young Solar Wind from Different Source Regions. We investigate the wavevector and variance anisotropies in the inertial range of the young solar wind observed by the Parker Solar Probe (PSP). Using the first 19 encounters of PSP measurements, we identify the young solar wind from different source regions: coronal hole (CH) interiors, streamers, and low Mach-number boundary layers (LMBLs), i.e., the peripheral region inside CHs. We assess the wavevector anisotropy with the 2D and slab turbulence model for the CH wind and streamer wind and the nearly incompressible MHD turbulence model for the LMBL wind, where Taylor's hypothesis becomes questionable. Unlike the ∼80% 2D contribution typically reported at 1 au, our results show that only 26% of the inertial range energy is associated with 2D fluctuations in the CH wind, and this fraction increases to 45% in the streamer wind. As a representation of the LMBL wind, similarly, the oblique sub-Alfvénic intervals and near-subsonic intervals are characterized by the dominance of slab fluctuations. All the results suggest that slab fluctuations are more abundant in the young solar wind below 0.3 au than at 1 au. Furthermore, we find a dependence of the variance anisotropy in the inertial range on proton plasma beta βp. The variance anisotropy is the strongest in the LMBL wind with the lowest βp and the weakest in the streamer wind with the highest βp. This contrast can be interpreted as the remnant of fluctuations from the coronal sources.

Keywords: Slow solar wind, Fast solar wind, Interplanetary turbulence, Solar wind, Solar corona
Solar Alfvénic Pulses and Mesoscale Solar Wind. Large-scale solar ejections are well understood, but the extent to which small-scale solar features directly influence the solar wind remains an open question, primarily due to the challenges of tracing these small-scale ejections and their impact. Here, we measure the fine-scale motions of network bright points along a coronal hole boundary in high-resolution Hα images from the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory to quantify the agitation of open flux tubes into generating Alfvénic pulses. We combine the motion, magnetic flux, and activity duration of the flux tubes to estimate the energy content carried by individual Alfvénic pulses, which is ∼1025 erg, adequately higher than the energies ∼1023 erg estimated for the magnetic switchbacks observed by the Parker Solar Probe (PSP). This implies the possibility that the surface-generated Alfvénic pulses could reach the solar wind with sufficient energy to generate switchbacks, even though some of then are expected to be reflected back in the stratified solar atmosphere. Alfvénic pulses further reproduce for the first time other properties of switchbacks, including the filling factor above ∼8% at granular and supergranular scales, which correspond best to the lower end of the mesoscale structure. This quantitative result for solar energy output in the form of Alfvénic pulses through magnetic funnels provides a crucial clue to the ongoing debate about the dynamic cycle of energy exchange between the Sun and the mesoscale solar wind that has been raised, but has not been adequately addressed, by PSP near-Sun observations.

Keywords: Solar atmosphere, Solar wind, Solar surface, Solar granulation, Solar magnetic fields
Nonstandard Collapse of Strong Langmuir Turbulence: Constraints on Its Occurrence and Observation in the Solar Corona. We present fully kinetic simulations of strong Langmuir turbulence (SLT) excited by electron beams with solar coronal conditions. We study two different collapsing processes within the parameter regimes of classical modulational instability (MI) and electron MI (EMI). For the first time, we simulated the EMI-induced collapse of moving multiple packets that is referred to as the non-Zakharov (or nonstandard) process here. We also simulated the classical Zakharov collapse of SLT induced by MI. During the early stage of the nonstandard collapse, the propagating packets get localized to form density cavities with depths of less than 0.1 n0 (the background electron density) that are too shallow to trap the packets. As a result, a majority of the packet energy runs away, undergoes a secondary collapse, and generates stationary packets with cavities. During the damping stage, the packets accelerate the background electrons to form numerous bidirectional propagating jets that distribute asymmetrically. This study reveals novel features of SLT collapse under coronal conditions.

Keywords: Space plasmas, Plasma astrophysics, Solar corona
JWST Coronagraphic Images of 14 Her c: A Cold Giant Planet in a Dynamically Hot Multiplanet System. Most observed multiplanet systems are coplanar, in a dynamically "cold" configuration of concentric orbits like our own solar system. With the James Webb Space Telescope, we have detected 14 Her c, the first mature and cold exoplanet directly imaged in a dynamically "hot" multiplanet system. With large eccentricities and a nonzero mutual inclination, the present-day architecture of this system points to a turbulent past and ongoing angular momentum exchange between the planetary orbits of 14 Her b and c. The temperature of 14 Her c rivals both the coldest imaged exoplanet and the coldest known brown dwarf. Moreover, its photometry at 4.4 μm is consistent with the presence of carbon disequilibrium chemistry and water-ice clouds in its atmosphere. 14 Her c presents a unique laboratory to study giant planet formation, the dynamical evolution of multiplanet system architectures, and atmospheric composition and dynamics in extremely cold worlds.

Keywords: Exoplanet dynamics, Exoplanets, James Webb Space Telescope, Direct imaging, Extrasolar gaseous giant planets, Exoplanet atmospheres
Explaining Ultramassive Quiescent Galaxies at 3 &lt; z &lt; 5 in the Context of Their Environments. The swift assembly of the earliest galaxies poses a significant challenge to our understanding of galaxy formation. Ultramassive quiescent galaxies at intermediate redshifts (3 &lt; z &lt; 5) currently present one of the most pressing problems for theoretical modeling, since very few mechanisms can be invoked to explain how such galaxies formed so early in the history of the Universe. Here, we exploit the fact that these galaxies all reside within significant overdensities to explain their masses. To this end, we construct a modified version of the Extreme Value Statistics (EVS) code, which takes into account galaxy environment by incorporating clustering in the calculation. With this new version of EVS, we find that ultramassive quiescent galaxies at 3 &lt; z &lt; 5 do not present as serious a tension with simple models of galaxy formation when the analysis of a given galaxy is conditioned on its environment.

Keywords: Galaxy formation, High-redshift galaxies, Galaxies, Astrostatistics
Measuring Emission Lines with JWST MegaScience Medium Bands: A New Window into Dust and Star Formation at Cosmic Noon. We demonstrate the power of JWST-NIRCam medium-band photometry to measure emission line fluxes and study the dust and star formation properties of galaxies at cosmic noon. In this work, we present photometric emission line measurements and spatially resolved maps of Hα and Paβ for 14 galaxies at 1.3 ≤ z ≤ 2.4, observed by the MegaScience medium-band survey and the UNCOVER spectroscopic survey. We measure line fluxes directly from medium-band photometry and compare with spectroscopic measurements from UNCOVER. We find reasonable agreement between the photometric and spectroscopic emission line fluxes for both Hα and Paβ, with scatter &lt;0.15 dex down to emission line equivalent widths of 10 Å. We also make a nebular dust measurement from the ratio Paβ/Hα, finding an average nebular attenuation in the V band, AV, of 1.4 with a standard deviation of 0.8. Our photometric AV measurements show a slightly larger scatter of 0.5 mag when compared to spectroscopic measurements; however, this scatter may be partially caused by aperture effects. Finally, we produce spatially resolved maps of Hα emission, Paβ emission, and the stellar continuum. We find offsets between Hα and Paβ emission, especially for galaxies with high AV, indicating dusty substructures. Furthermore, the correlation between Hα and continuum emission decreases with increasing AV, suggesting that the dustiest objects have clumpy dust and star formation distributions. Our study demonstrates the power of medium-band photometry to directly probe emission line strengths, star formation, and dust attenuation for hundreds of galaxies in UNCOVER and thousands of galaxies in upcoming JWST medium-band surveys.

Keywords: Star forming regions, Galaxy structure, Galaxy evolution, Galaxy photometry
Stellar Distributions around Supermassive Black Holes in Gas-rich Nuclear Star Clusters. We study the stellar distribution around supermassive black holes in gas-rich nuclear star clusters (NSCs). NSCs could contain vast amounts of gas, which contribute significantly to shaping the stellar distribution, typically altering the stellar density cusp from the usual J. N. Bahcall &amp; R. A. Wolf solution and consequently affecting the dynamics in the NSC. The dense gaseous environment in NSCs gives rise to dynamical phenomena that are otherwise rare in other gas-free environments. Here we extend the derivation introduced in J. N. Bahcall &amp; R. A. Wolf to include an additional energy dissipation term associated with gas drag. We examine the effects of different forms of gas drag on the stellar density distribution. Finally, we discuss implications on the rates of tidal disruption events and other transients triggered by stellar interactions in gas-rich galactic nuclei.

Keywords: Supermassive black holes, Star clusters
Little Red Dots as the Very First Activity of Black Hole Growth. The James Webb Space Telescope has detected massive black holes (BHs) with masses of ∼106‑8 M⊙ within the first billion years of the Universe. One of the remarkable findings is the identification of "little red dots" (LRDs), a unique class of active galactic nuclei (AGNs) with distinct characteristics representing a key phase in the formation and growth of early BHs. Here, we analyze the occurrence rate of LRDs, which emerge around redshifts z ∼ 6–8 and sharply decline at z &lt; 4. We find that this trend follows a log-normal distribution, commonly observed in phenomena driven by stochastic and random factors. We propose a hypothesis that the first one or two AGN events associated with newly formed seed BHs are observed as LRDs, and their unique features fade in the subsequent episodes. This naturally explains the cosmic evolution of AGN abundance over 0 &lt; z &lt; 5, which follows ∝(1 + z)‑5/2 due to the cumulative effect of recurring AGN activity. The unique characteristics of LRDs are likely linked to the dense gas environments around the seed BHs, which create strong absorption features in the broad-line emission and enable super-Eddington accretion bursts, ultimately yielding the observed overmassive nature of BHs compared to the local relationship. An analytical expression for the redshift evolution of LRD abundance is provided for direct comparison with future observational constraints.

Keywords: Supermassive black holes, Galaxy formation, High-redshift galaxies, Quasars
Langmuir-wave Excitation in Solar Wind Magnetic Holes. Magnetic holes (MHs) are structures commonly observed in various space plasma environments throughout the solar system, including the solar wind. These structures are characterized by a localized decrease in magnetic field strength, coincident with an increase in plasma density. Previous observational studies in the solar wind link the presence of Langmuir waves to MHs, suggesting a strong correlation between these phenomena. We develop a model based on magnetic-moment conservation and its violation to explain the excitation of Langmuir waves in MHs. Our model illustrates that MHs induce changes in the electron velocity distribution function that emit electrostatic Langmuir waves due to the bump-on-tail instability. Using data from the Solar Orbiter spacecraft, we provide a comprehensive analysis of this process and test our predictions with observations. The consistency between our model and observations indicates that the proposed process is a viable mechanism for producing Langmuir waves in MHs in the solar wind.

Keywords: Space plasmas, Solar wind
Radio Emission from Tidal Disruption Events Produced by the Collision between Super-Eddington Outflows and the Circumnuclear Medium. In this Letter, we simulate the collision between outflows from the tidal disruption of a 1 M⊙ main-sequence star around a 106 M⊙ black hole and an initially spherically symmetric circumnuclear cloud. We launch super-Eddington outflows self-consistently by simulating the disruption of stars on both bound and unbound initial orbits using general relativistic smoothed particle hydrodynamics. We find that shocks formed as early as ∼10 days after the initial stellar disruption produce prompt radio emission. The shock radius (≈1017 cm), velocity (∼0.15c), and total energy (∼1051 erg) in our simulations match those inferred from radio observations of tidal disruption events (TDEs). We ray-trace to produce synthetic radio images and spectra to compare with the observations. While the TDE outflow is quasi-spherical, the synchrotron emitting region is aspherical but with reflection symmetry above and below the initial orbital plane. Our synthetic spectra show a continuous decay in peak frequency, matching prompt radio TDE observations. Our model supports the hypothesis that synchrotron radio flares from TDEs result from the collision between outflows and the circumnuclear material.

Keywords: Supermassive black holes, Hydrodynamical simulations, Tidal disruption, Radiative transfer, Interstellar synchrotron emission, Radio transient sources
Impact of Two-population α-particle Distributions on Plasma Stability. The stability of weakly collisional plasmas is well represented by linear theory, and the generated waves play an essential role in the thermodynamics of these systems. The velocity distribution functions (VDFs) characterizing kinetic particle behavior are commonly represented as a sum of anisotropic bi-Maxwellians. A three bi-Maxwellian model is commonly applied for the ions, assuming that the VDF consists of a proton core, a proton beam, and a single He (α) particle population, each with its own density, bulk velocity, and anisotropic temperature. Resolving a secondary α-beam component was generally not possible due to instrumental limitations. The Solar Orbiter Solar Wind Analyser Proton and Alpha Sensor (SWA-PAS) resolves velocity space with sufficient coverage and accuracy to consistently characterize secondary α populations. This design makes the SWA-PAS ideal for examining the effects of α-particle beams on the plasma's kinetic stability. We test the wave signatures observed in the magnetic field power spectrum at ion scales and compare them to the predictions from linear plasma theory, Doppler-shifted into the spacecraft reference frame. We find that taking into account the α-particle beam component is necessary to predict the coherent wave signatures in the observed power spectra, emphasizing the importance of separating the α-particle populations as is traditionally done for protons. Moreover, we demonstrate that the drifts of beam components are responsible for the majority of the modes that propagate in the oblique direction to the magnetic field, while their temperature anisotropies are the primary source of parallel fast magnetosonic modes.

Keywords: Space plasmas, Solar wind
Understanding the Magnetic Field and Plasma-β along Umbral Fan Loops Traced Using 3 Minute Slow Waves. Plasma-β is an important fundamental physical quantity in solar plasma physics, which determines the dominating process in the solar atmosphere, i.e., magnetic or thermodynamic processes. Here, for the first time, we provide variations of magnetic field and plasma-β along magnetically structured loops from the photosphere to the corona. We have selected several fan loops rooted in sunspot umbra observed simultaneously by the Interface Region Imaging Spectrograph and Solar Dynamics Observatory. The 3 minute slow waves enabled us to trace and analyze several fan loops with cross-sectional areas in the lower atmosphere and locate their footpoints at the photosphere. We find the rms magnetic field strengths in the range 1596–2269 G at the photospheric footpoints of the fan loops, which decrease rapidly to 158–236 G at the coronal footpoints. We estimated the plasma-β at the photospheric and coronal footpoints in the range 0.2–0.5 and 0.0001–0.001, respectively. We found plasma-β &lt; 1 along the whole loop, whereas the plasma-β ≈ 1 layer is found to be at subphotospheric heights. We compared our findings for isolated individual fan loops with a previously established model for active regions and found an almost similar pattern in variations with height, but with different plasma-β values. Our results demonstrate the seismological potential of 3 minute slow waves omnipresent in the umbral sunspot atmosphere to probe and map isolated loops and determine magnetic field and plasma-β along these loops. The obtained parameters provide crucial ingredients for the theoretical modeling of the umbral atmosphere and wave dynamics along loops.

Keywords: Solar atmosphere, Magnetohydrodynamics, Solar coronal loops, Sunspots, Solar magnetic fields
CO<SUB>2</SUB> Infrared Spectra on Silicate Dust Grain Analogs: Implications for JWST Observations. Carbon dioxide is one of the three most abundant species within the ice mantles around dust grains inside molecular clouds. Since a substantial number of interstellar grains are made of siliceous materials, we have studied the infrared profile of CO2 deposited on top of a bare and ice-coated amorphous silicate (MgFeSiO4) film using reflection absorption infrared spectroscopy (RAIRS). In contrast to a metal surface, the CO2 IR profile shows a relaxation of the metal surface selection rule in the presence of the bare MgFeSiO4 dust grain analog, which brings the IR profile closer to the observational spectra while maintaining the sensitivity of RAIRS. Experiments with the underlying CO and CH4 ices show that their presence facilitates structural changes toward crystalline ice for the deposited CO2 at much lower temperatures than on the polar ice layers. Warming-up experiments of CO2 showed that it tends to stay on the silicate surface for much longer than on the gold surface without the silicate layer. We noticed for the first time a split in the 13CO2 IR feature on the pure or ice-covered silicate grain as a marker for the onset of diffusion. The laboratory 13CO2 profile then closely resembles recent JWST observations of this feature around young and embedded protostars, suggesting that it can be linked to the observed feature.

Keywords: Ice spectroscopy, Infrared spectroscopy, Astrochemistry
XRISM Spectroscopy of the Stellar-mass Black Hole 4U 1630-472 in Outburst. We report on XRISM/Resolve spectroscopy of the recurrent transient and well-known black hole candidate 4U 1630‑472 during its 2024 outburst. The source was captured at the end of a disk-dominated high/soft state at an Eddington fraction of λEdd ∼ 0.05 (10 M⊙/MBH). A variable absorption spectrum with unprecedented complexity is revealed with the Resolve calorimeter. This marks one of the lowest Eddington fractions at which highly ionized absorption has been detected in an X-ray binary. The strongest lines are fully resolved, with He-like Fe XXV separated into resonance and intercombination components and H-like Fe XXVI seen as a spin–orbit doublet. The depth of some absorption lines varied by almost an order of magnitude, far more than expected based on a 10% variation in apparent X-ray flux and ionization parameter. The velocity of some absorption components also changed significantly. Jointly modeling two flux segments with a consistent model including four photoionization zones, the spectrum can be described in terms of highly ionized but likely failed winds that sometimes show redshifts, variable obscuration that may signal asymmetric structures in the middle and outer accretion disk, and a tentative very fast outflow (v = 0.026–0.033c). We discuss the impact of these findings on our understanding of accretion and winds in stellar-mass black holes and potential consequences for future studies.

Keywords: Accretion, Black holes
CHIME/Fast Radio Burst Discovery of an Unusual Circularly Polarized Long-period Radio Transient with an Accelerating Spin Period. We report the discovery of CHIME J1634+44, a long-period radio transient (LPT) unique for two aspects: it is the first known LPT to emit fully circularly polarized radio bursts, and it is the first LPT with a significant spin-up. Given that high circular polarization (&gt;90%) has been observed in FRB 20201124A and in some giant pulses of PSR B1937+21, we discuss the implications of the high circular polarization of CHIME J1634+44 and conclude its emission mechanism is likely to be "pulsar-like." While CHIME J1634+44 has a pulse period of 841 s, its burst arrival patterns are indicative of a secondary 4206 s period, probably associated with binary activity. The timing properties suggest it has a significantly negative period derivative of  Ṗ=‑9.03(0.11)×10-12  s s‑1. Few systems have been known to spin up, most notably transitional millisecond pulsars and cataclysmic binaries, both of which seem unlikely progenitors for CHIME J1634+44. If the period was only associated with the spin of the object, then the spin-up is likely generated by accretion of material from a companion. If, however, the radio pulse period and the orbital period are locked, as appears to be the case for two other LPTs, the spin-up of CHIME J1634+44 could be driven by gravitational-wave radiation.

Keywords: White dwarf stars, Compact binary stars, Radio transient sources, Binary pulsars, Radio pulsars