Sazuna/UAT_keywords huggingface dataset:
Neutron Star–White Dwarf Merger as One Possible Optional Source of Kilonova-like Emission: Implications for GRB 211211A. Long-duration GRB 211211A, which lacked an associated supernova at very a low redshift z = 0.076 but was associated with a possible kilonova emission, has attracted great attention. The neutron star–white dwarf (NS–WD) merger is proposed as a possible progenitor of GRB 211211A, and it could naturally explain the long duration of the prompt emission. However, the NS–WD merger is not an ideal site for producing heavy elements via r-process nucleosynthesis. In this Letter, we investigate the heavy elements produced in NS–WD mergers based on numerical simulations of nucleosynthesis via SkyNet and then calculate the resulting kilonova-like emission to compare with the solidly observed case of possible kilonova emission associated with GRB 211211A. By adopting three models (i.e., Model-A, Model-B, and Model-C) from M. A. R. Kaltenborn et al. at different temperatures (T = 4, 5, and 6 GK), which are treated as free parameters, we find that the mass number of the heaviest element produced in our simulations is less than 90 (A &lt; 90). Moreover, by comparing the calculated kilonova-like emission with the afterglow-subtracted observations of the possible kilonova associated with GRB 211211A, it is found that the merger of an NS and WD cannot be ruled out as the origin of GRB 211211A to produce the possible kilonova emission if the remnant of the WD–NS merger is a supramassive or stable magnetar. Otherwise, it is difficult to explain the early possible kilonova emission following GRB 211211A by invoking the merger of a WD and an NS.

Keywords: Gamma-ray bursts
The Probable Direct-imaging Detection of the Stellar Companion to Betelgeuse. Betelgeuse—the closest M-supergiant to the Sun—has recently been predicted to host a lower-mass stellar companion that orbits the primary with a period of ∼6 yr. The putative stellar companion is thought to cause the long photometric modulation observed in Betelgeuse, which cannot be explained by stellar pulsations. Additionally, radial velocity and astrometric data also point to a stellar companion. Here we present diffraction-limited optical speckle imaging observations obtained on the 8.1 m Gemini North telescope in 2020 and 2024. The 2020 observations were taken during the Great Dimming event and at a time when the stellar companion was predicted to be unobservable because it was directly in line with Betelgeuse itself. The 2024 observations were taken 3 days after the predicted time of greatest elongation for the companion. A comparison of the 2020 and 2024 data reveals no companion in 2020 (as expected) and the probable detection of a companion in 2024. The presumed stellar companion has an angular separation and position angle of 52 mas and 115° east of north, respectively, which is in excellent agreement with predictions from dynamical considerations. The detected companion is roughly 6 magnitudes fainter than Betelgeuse at 466 nm. While this is only a 1.5σ detection, five results are in reasonable agreement with the predictions: the appearance of the companion at quadrature; the angular separation from Betelgeuse; the position angle with respect to Betelgeuse; the magnitude difference; and the estimated mass of the companion.

Keywords: Late-type supergiant stars, Astronomical techniques, Binary stars, High angular resolution
JWST's First View of Tidal Disruption Events: Compact, Accretion-driven Emission Lines and Strong Silicate Emission in an Infrared-selected Sample. Mid-infrared (MIR) emission from tidal disruption events (TDEs) is a powerful probe of the circumnuclear environment around dormant supermassive black holes. This emission arises from the reprocessing of intrinsic emission into thermal MIR emission by circumnuclear dust. While the majority of optical- and X-ray-selected TDEs show only weak dust echoes consistent with primarily unobscured sight lines, there have been growing efforts aimed at finding TDEs in obscured environments using MIR selection methods. In this work, we present the first JWST observations of four MIR-selected TDEs with the JWST Mid-Infrared Instrument (MIRI) Medium-Resolution Spectrometer (MRS). Two of these sources show flares in other wavelength bands (one in optical, one in X-ray), while the other two are MIR-only transients. None of these TDEs showed pre-outburst nuclear activity, but all of the MIRI/MRS observations reveal emission lines associated with highly ionized gas in the nucleus, implying ionization from TDE accretion. Additionally, all four sources show silicate emission features around 10 and 18 μm that are much stronger than the features seen in active galactic nuclei. We suggest that the emitting dust is optically thin to its own emission and show that the MIR spectrum is consistent with emission from optically thin dust in the nucleus. All four sources show an excess at short wavelengths (λ &lt; 8 μm), which could arise from a late-time plateau in the intrinsic flare, akin to what is seen in late-time UV observations of unobscured TDEs, although self-consistent dust modeling is required to fully assess the strength of this late-time plateau.

Keywords: Supermassive black holes, Infrared spectroscopy, High energy astrophysics, Transient sources, Infrared astronomy
An Energy Perspective of Core Erosion in Gas Giant Planets. Juno and Cassini have shown that Jupiter and Saturn likely contain extended gradients of heavy elements. Yet, how these gradients can survive over billions of years remains an open question. Classical convection theories predict rapid mixing and homogenization, which would erase such gradients on timescales far shorter than the planets' ages. To address this, we estimate the energy required to erode both dense and fuzzy cores, and compare it to what the planet can realistically supply. If the entire cooling budget is available to drive mixing, then even a compact core can, in principle, be destroyed. But if mixing is limited to the thermal energy near the core, which is another plausible scenario, the energy falls short. In that case, Jupiter can erode a fuzzy core by up to approximately 10 M⊕, but a compact one remains intact. Saturn's core is more robust. Even in the fuzzy case, only about 1 M⊕ is lost, and if the core is compact, erosion is negligible. The outcome depends sensitively on the assumed initial temperature and entropy profiles. Hotter and more superadiabatic interiors are more prone to mixing. We suggest that 3D simulations of convection driven from above, with realistic stratification and enough depth (i.e., many density scale heights) would be of great interest to further constrain the energy budget for core erosion.

Keywords: Planetary cores, Planetary interior, Solar system gas giant planets, Planetary thermal histories
Contemporaneous X-Ray and Optical Polarization of Extremely High-synchrotron-peaked Blazar H 1426+428. We present the first contemporaneous X-ray and optical polarimetric measurement of the extremely high-synchrotron-peaked (HSP) blazar H 1426+428. The X-ray polarimetric observations were undertaken using the Imaging X-ray Polarimetry Explorer (IXPE) on 2024 May 27 and 2024 July 5. The IXPE pointings were accompanied by contemporaneous optical observations of the Observatorio de Sierra Nevada, Calar Alto Observatory, and the Perkins Telescope Observatory. While we observed the X-ray degree of polarization to be &gt;20%, the polarization in the optical band was found to be only 1%–3%. This trend has been observed in several HSP blazars with available optical and X-ray polarimetric data and is typically explained in terms of energy stratification downstream of a shock. However, we observed a significant difference between the optical and X-ray polarization angles, a feature that has been observed in certain HSP blazars, such as Mrk 421, but remains a relatively rare or underreported phenomenon. We discuss possible scenarios for these findings within the framework of a partially turbulent jet model.

Keywords: Blazars
Near-horizon Polarization as a Diagnostic of Black Hole Spacetime. A key challenge in imaging supermassive black holes is disentangling gravitational effects from plasma physics in order to accurately determine spacetime properties, particularly black hole spin. In this Letter, we present a fully covariant and rigorous analysis of the synchrotron emission from accreting plasma in the equatorial plane in the stationary, axisymmetric, high-conductivity regime and identify—for the first time—a distinctive near-horizon polarization pattern that remains robust across different flow structures. This pattern arises from strong frame dragging near the event horizon, which induces a degeneracy among plasma flow and magnetic field configurations, yielding a polarization signature determined solely by the spacetime geometry and the observer's inclination. The near-horizon polarization thus offers a clean and precise probe of black hole spin and other fundamental parameters. If future space-based millimeter very long baseline interferometry observations can resolve synchrotron emission originating within approximately 1% of the event horizon radius in M87* or Sgr A*, this universal polarization pattern may become observable.

Keywords: Accretion, Black hole physics, Supermassive black holes, Kerr black holes, Polarimetry, Astrophysical black holes
Intermingled Open and Closed Magnetic Field Lines near the Radial Origin of the Heliospheric Current Sheet. On 2024 March 30, the Parker Solar Probe crossed the heliospheric current sheet at 13 solar radii while encountering two distinctly different regions at sharp boundaries on several occasions. The two regions had very different plasma densities, electric-field spectra, and magnetic-field geometries. In one region the strahl flowed only along the direction from the Sun, and there were relatively few particles at pitch angles near 90°, while in the other region the strahl flowed both toward and away from the Sun, and there were relatively many particles at pitch angles near 90°. These different properties are interpreted as being due to the spacecraft being in the heliospheric current sheet on long open magnetic field lines in the case of unidirectional strahl flow and the spacecraft being in coronal loops having much shorter closed magnetic field lines in the case with bidirectional strahl flow. The two regions intermingled on time scales less than 100 ms to create a complex magnetic field geometry. Broadband waves were observed in the open field-line regions, while narrowband electrostatic harmonic waves were observed in both regions. These harmonic frequencies correlated with the proton plasma frequency, fpp, with the lowest frequency at ∼0.1fpp. This result, plus the field-aligned electric field waves and plasma density fluctuations, requires that the observed electrostatic mode and associated harmonics were ion acoustic waves.

Keywords: Solar magnetic fields
Inferring a Dense Confined Circumstellar Medium around Supernova Progenitors via Long-term Hydrodynamical Evolution. Circumstellar interaction of supernova (SN) ejecta is an essential process in its evolution, and observations of SNe have found the signature of circumstellar interaction in both the early and late evolutionary phases of SNe. In this Letter, we show that if the SN forward shock plunges into a tenuous stellar wind from a dense circumstellar medium (CSM) in the vicinity of the progenitor (i.e., confined CSM), the subsequent time evolutions of the SN–CSM interaction system deviate from the prediction of a self-similar solution. In this case, after all of the confined CSM is swept up by the SN forward shock (roughly 10 days after the explosion), the propagation of the shocked shell will be driven by the freely expanding ram pressure of the confined CSM component, instead of the SN ejecta. Meanwhile, the forward shock decelerates faster than the prediction of thin-shell approximation once the confined CSM component reaches homologous expansion. This lasts until the reverse shock in the confined CSM component reaches the head of the SN ejecta, leading to the restoration of the system into the evolutionary model without confined CSM, where the SN ejecta drives the expansion of the system. We also show that this peculiar evolution will be reflected in observational signatures originating from SN–CSM interaction, taking rapid decline and rebrightening of radio emission as examples. Our results shed light on the importance of taking into account the effect of initial SN–CSM interaction even when we focus on observational properties of SNe a few years after the explosion.

Keywords: Circumstellar matter, Supernova dynamics, Supernovae, Hydrodynamics
XRISM Spectroscopy of Accretion-driven Wind Feedback in NGC 4151. The hottest, most ionized, and fastest winds driven by accretion onto massive black holes have the potential to reshape their host galaxies. Calorimeter-resolution X-ray spectroscopy is the ideal tool to understand this feedback mode, as it enables accurate estimates of the physical characteristics needed to determine the wind's kinetic power. We report on a photoionization analysis of five observations of the Seyfert 1.5 galaxy NGC 4151, obtained with XRISM/Resolve in 2023 and 2024. In the Fe K band, individual spectra require as many as six wind absorption components. Slow "warm absorbers" (WAs; vout ∼ 100–1000 km s‑1), "very fast outflows" (VFOs; vout ∼ 103–104 km s‑1), and "ultrafast outflows" (UFOs; vout ∼ 104–105 km s‑1 or 0.033–0.33c) are detected simultaneously and indicate a stratified, multiphase wind. Fast and variable emission components suggest that the wind is axially asymmetric. All of the wind components have mass flow rates comparable to or in excess of the mass accretion rate, though the slowest zones may be "failed" winds that do not escape. Two UFO components have kinetic luminosities that exceed the theoretical threshold of Lkin ≥ 0.5% LEdd necessary to strip the host bulge of gas and halt star formation, even after corrections for plausible filling factors. The bulk properties of the observed winds are consistent with magnetocentrifugal driving, where the density depends on the radius as n ∝ r‑1.5, but radiative driving and other mechanisms may also be important. Numerous complexities and variability require further analysis.

Keywords: Supermassive black holes, Active galactic nuclei, X-ray active galactic nuclei
Atmospheric C/O Ratios of Sub-Neptunes with Magma Oceans: Homemade rather than Inherited. Recently, the James Webb Space Telescope has enabled detailed spectroscopic characterization of sub-Neptune atmospheres. With detections of carbon- and oxygen-bearing species such as CO, CO2, CH4, and H2O, a central question is whether the atmospheric C/O ratio, commonly used to trace formation location in giant planets, can serve a similar diagnostic role for sub-Neptunes. We use the global chemical equilibrium framework of H. E. Schlichting &amp; E. D. Young to quantify how magma ocean–atmosphere interactions affect the atmospheric C/O ratio. We find that the resulting C/O ratios range from several orders of magnitude below solar to a few times solar. The atmospheric C/O ratio in sub-Neptunes is therefore not inherited from the protoplanetary disk, but instead emerges from chemical equilibrium between the atmosphere and the underlying magma ocean. Planetary mass, atmospheric mass fraction, and thermal state all strongly influence the atmospheric C/O ratio. In addition, carbon partitioning into the metal phase typically reduces the atmospheric C/O ratio substantially, particularly for atmospheric mass fractions less than a few percent. Finally, we couple the deep equilibrium compositions to 1D atmospheric models that self-consistently solve for the pressure–temperature structure and chemical composition, including photochemistry. We find that the C/O ratio varies with altitude under low vertical mixing conditions (Kzz = 104 cm2 s‑1) but remains constant under strong mixing (Kzz = 107 cm2 s‑1). Our results imply that observed C/O ratios of sub-Neptunes can be used to probe their interiors. Specifically, C/O ratios much lower than host star values would imply an underlying magma ocean with iron metal having sequestered significant amounts of carbon.

Keywords: Exoplanet structure, Exoplanet atmospheric composition , Exoplanet atmospheric structure
High-resolution Observations of an X6.4 Solar Flare in the Mid-infrared. We present a unique observation of the X6.4-class flare SOL2024-02-22T22:34 using the Mid-InfraRed Imager (MIRI) at the Goode Solar Telescope. Three ribbon-like flare sources and one unidentified source were detected in MIRI's two mid-infrared (mid-IR) bands at 5.2 and 8.2 μm. The two stronger ribbons displayed maximum mid-IR enhancements of 21% and 18% above quiet-Sun levels and 10% in Helioseismic and Magnetic Imager (HMI) continuum intensity (Ic). The weak ribbon and the unidentified source had maximum mid-IR enhancements of 7% but showed HMI/Ic dimmings, instead of excess emissions. Our result suggests that mid-IR emission forms in a higher layer during the flare and is more sensitive to flare heating than HMI/Ic emission. The MIRI observations have high temporal resolution (2.6 s cadence in these observations) and show apparent source motions. One flare ribbon extends along weak vertical magnetic-field channels in the sunspot umbra, light bridge, and penumbra, with an approximately 30 s delay between HMI/Ic and 8.2 μm emissions. Meanwhile, the unidentified source moved at an apparent speed of 130 km s‑1 from a mixed-polarity area to one flare ribbon with a strong HMI/Ic enhancement. We studied available hard X-ray/microwave imaging spectroscopy and used nonlinear force-free field extrapolation modeling to identify flare structures. The observational evidence strongly favors the chromospheric origin of the unidentified mid-IR source. Comparison with the X1.0 flare SOL2022-10-02T20:25 indicates that the total amount of high-energy electron (&gt;60 keV) flux density is a key factor in determining the total brightening area and the maximum intensity enhancement in HMI/Ic emissions.

Keywords: Solar flares, Solar photosphere, Infrared astronomy, Solar white-light flares, Solar chromosphere
ODIN: Clustering Analysis of 14,000 Lyα-emitting Galaxies at z = 2.4, 3.1, and 4.5. Lyα emitters (LAEs) are star-forming galaxies that efficiently probe the spatial distribution of galaxies in the high-redshift Universe. The spatial clustering of LAEs reflects the properties of their individual host dark matter halos, allowing us to study the evolution of the galaxy–halo connection. We analyze the clustering of 5233, 5220, and 3706 LAEs at z = 2.4, 3.1, and 4.5, respectively, in the 9 deg2 COSMOS field from the One-hundred-deg2 DECam Imaging in Narrowbands survey. After correcting for redshift-space distortions, LAE contamination rates, and the integral constraint, the observed angular correlation functions imply linear galaxy bias factors of b =  1.72‑0.27+0.26,2.01‑0.29+0.26,  and  2.95‑0.46+0.40  for z = 2.4, 3.1, and 4.5, respectively. The median dark matter halo masses inferred from these measurements are  log(Mh/M⊙)  =  11.44‑0.28+0.30,11.13‑0.26+0.26,and10.85‑0.24+0.24  for the three samples, respectively. The analysis also reveals that LAEs occupy roughly 3%–7% of the halos whose clustering strength matches that of the LAEs.

Keywords: Lyman-alpha galaxies, High-redshift galaxies, Galaxy evolution, Large-scale structure of the universe
Kinematic Evidence for Bipolar Ejecta Flows in the Galactic Supernova Remnant W49B. W49B is a unique Galactic supernova remnant with centrally peaked, "bar"-like ejecta distribution, which was once considered evidence for a hypernova origin that resulted in a bipolar ejection of the stellar core. However, chemical abundance measurements contradict this interpretation. Closely connected to the morphology of the ejecta is its velocity distribution, which provides critical details for understanding the explosion mechanism. We report the first ever observational constraint on the kinematics of the ejecta in W49B using the Resolve microcalorimeter spectrometer on the X-ray Imaging and Spectroscopy Mission (XRISM). Using XRISM/Resolve, we measured the line-of-sight velocity traced by the Fe Heα emission, which is the brightest feature in the Resolve spectrum, to vary by ±300 km s‑1 with a smooth east-to-west gradient of a few tens of kilometers per second per parsec along the major axis. Similar trends in the line-of-sight velocity structure were found for other Fe-group elements Cr and Mn, traced by the Heα emission, and also for intermediate-mass elements Si, S, Ar, and Ca, traced by the Lyα emission. The discovery of the east–west gradient in the line-of-sight velocity, together with the absence of a twin-peaked line profile or enhanced broadening in the central region, clearly rejects the equatorially expanding disk model. In contrast, the observed velocity structure suggests bipolar flows reminiscent of a bipolar explosion scenario. An alternative scenario would be a collimation of the ejecta by an elongated cavity sculpted by bipolar stellar winds.

Keywords: Supernova remnants, High resolution spectroscopy, X-ray astronomy
Generation of Magnetic Fields around Black Hole Accretion Disks due to Nonconservative Radiation Fields. We investigate the generation of magnetic fields above black hole accretion disks due to the nonzero curl of the disk radiation field. By self-consistently computing the components of the radiation flux and their curl, we show that the rotational nature of the radiation field induces charge separation, leading to magnetic field generation in the plasma above the disk. Solving the magnetohydrodynamic equations, we derive the time evolution of these fields and demonstrate that they grow over astrophysically relevant timescales. For a standard Keplerian accretion disk, the produced magnetic fields remain weak, on the order of a few gauss, consistent with previous predictions. However, when a luminous corona is present in the inner disk region (rd &lt; 3rg–10rg), the generated fields reach dynamically significant strengths of up to 105 G, where the magnetic energy density approaches a few percentage of gas pressure. These fields develop within realistic growth timescales (such as the viscous timescale) and can be dynamically significant in governing disk and jet evolution. Our findings suggest that radiation-driven magnetic fields play a crucial role in accretion flow magnetization, influencing both disk dynamics and observational signatures. The predicted field strengths could affect the thermal emission, synchrotron radiation, and polarization properties of black hole accretion systems, with implications for X-ray binaries, active galactic nuclei, and jet formation. Future numerical simulations and high-resolution polarimetric observations, such as those from the Imaging X-ray Polarimetry Explorer, enhanced X-ray Timing and Polarimetry Mission, and the Event Horizon Telescope, may provide observational confirmation of our findings.

Keywords: High energy astrophysics, Stellar accretion, Stellar accretion disks, Magnetic fields, Astronomical radiation sources