Sazuna/UAT_keywords huggingface dataset:
Limiting Rotation Rate of Neutron Stars from Crust Breaking and Gravitational Waves. Neutron stars are not observed to spin faster than about half their breakup rate. This limiting rotational frequency may be related to the strength of their crusts. As a star spins up from accretion, centrifugal forces stress the crust. We perform finite-element simulations of rotating neutron stars and find that the crust fails at rotation rates about half the breakup rate. Given uncertainties in microphysics, we have not determined the crust configuration after this failure. Instead, we argue that the crust may fail in an asymmetric way and could produce a configuration with a significant ellipticity (fractional difference in moments of inertia). If the ellipticity is large, a rotating star will radiate gravitational waves that may limit further spin-up. These stars may be promising sources for LIGO/VIRGO and next-generation gravitational-wave detectors.

Keywords: Neutron stars, Gravitational wave sources, Pulsars
Three-dimensional Global Hybrid Simulation of Magnetosheath Jets at Mercury. Plasma high-speed jets are common in Earth's magnetosheath, and they significantly perturb the magnetosheath and affect the magnetosphere. The space environment of Mercury, characterized by the bow shock, magnetosheath, and magnetosphere, shares many similarities with that of Earth, so high-speed jets may also be formed in Mercury's magnetosheath. Here we examine the formation of magnetosheath jets using a three-dimensional global hybrid simulation. The simulation results demonstrate that magnetosheath jets may be formed by the passage of upstream compressive structures through the bow shock. The number and size of the jets are significantly smaller than those at Earth because of Mercury's smaller magnetosphere size. Under the impact of magnetosheath jets, Mercury's magnetopause undergoes significant deformation up to  0.19RM  ( RM  is Mercury's radius). These simulation results are expected to be tested by the BepiColombo mission.

Keywords: Planetary boundary layers, Solar-planetary interactions, Planetary bow shocks, Mercury (planet), Planetary magnetospheres
MLody—Deep Learning–generated Polarized Synchrotron Coefficients. Polarized synchrotron emission is a fundamental process in high-energy astrophysics, particularly in the environments around black holes and pulsars. Accurate modeling of this emission requires precise computation of the emission, absorption, rotation, and conversion coefficients, which are critical for radiative transfer simulations. Traditionally, these coefficients are derived using fit functions based on precomputed ground truth values. However, these fit functions often lack accuracy, particularly in specific plasma conditions not well represented in the data sets used to generate them. In this work, we introduce MLody, a deep neural network designed to compute polarized synchrotron coefficients with high accuracy across a wide range of plasma parameters. We demonstrate MLody's capabilities by integrating it with a radiative transfer code to generate synthetic polarized synchrotron images for an accreting black hole simulation. Our results reveal significant differences, up to a factor of 2, in both linear and circular polarization compared to traditional methods. These differences could have important implications for parameter estimation in Event Horizon Telescope observations, suggesting that MLody could enhance the accuracy of future astrophysical analyses.

Keywords: Accretion, Computational astronomy, Astronomy software, Astrophysical black holes
Termination Shock Particle Streaming Upstream at New Horizons. A couple years before Voyager 1 and Voyager 2 (V2) crossed the termination shock (TS), instruments on board both spacecraft observed high intensities of accelerated termination shock particles (TSPs) beaming in opposite directions. This phenomenon was explained by magnetic field lines connecting the spacecraft to the TS prior to the crossings. The opposite streaming of TSPs is due to an east–west asymmetry of the TS caused by the interstellar magnetic field building up on the outside of the heliopause. Here, we examine the magnetic connectivity for New Horizons (NH) ahead of the TS with a global MHD model with steady solar wind conditions. Our model predicts that NH will observe particles streaming in the same direction as V2 (+T direction in the RTN coordinate system), 1.0 ± 0.7 au from the TS. We then estimate the average speed of the TS during the V2 TS crossing to be 2.5 au yr‑1 outward, based on the timing and distance of the TS at the onset of the TSP observations and the crossing itself. Using this speed, we find that NH will have a 0.2 yr warning prior to crossing the TS if the TS is moving inward at the time of the crossing and a 2.4 yr warning if the TS is moving outward.

Keywords: Solar cycle, Heliosphere, Termination shock, Solar wind, Heliosheath
The CIViL* Survey: The Discovery of a C IV Dichotomy in the Circumgalactic Medium of L* Galaxies. This paper investigates C IV absorption in the circumgalactic medium (CGM) of L⋆ galaxies and its relationship with galaxy star formation rates. We present new observations from the C IV in L⋆ galaxies survey (PID#17076) using the Hubble Space Telescope/Cosmic Origins Spectrograph. By combining these measurements with archival C IV data (46 observations total), we estimate detection fractions for star-forming (sSFR &gt; 10‑11 yr‑1) and passive galaxies (sSFR ≤ 10‑11 yr‑1 ) to be 72 ‑18+14 % [21/29] and 23 ‑15+27 % [3/13], respectively. This indicates a significant dichotomy in C IV presence between L⋆ star-forming and passive galaxies, with over 99% confidence. This finding aligns with J. Tumlinson et al., which noted a similar dichotomy in O VI absorption. Our results imply a substantial carbon reservoir in the CGM of L⋆ galaxies, suggesting a minimum carbon mass of ≳3.03 × 106 M⊙ out to 120 kpc. Together, these findings highlight a strong connection between star formation in galaxies and the state of their CGM, providing insight into the mechanisms governing galaxy evolution.

Keywords: Galaxy evolution, Quasar absorption line spectroscopy, Circumgalactic medium
First Calculations of Starspot Spectra Based on 3D Radiative Magnetohydrodynamics Simulations. Accurate calculations of starspot spectra are essential for multiple applications in astronomy. The current standard is to represent starspot spectra by spectra of stars that are cooler than the quiet star regions. This implies approximating a starspot as a nonmagnetic 1D structure in radiative–convective equilibrium, parametrizing convective energy transport by mixing-length theory. It is the inhibition of convection by the starspot magnetic field that is emulated by using a lower spot temperature relative to the quiet stellar regions. Here, we take a different approach, avoiding the approximate treatment of convection and instead self-consistently accounting for the interaction between matter, radiation, and the magnetic field. We simulate spots on G2V, K0V, and M0V stars with the 3D radiative magnetohydrodynamics code MURaM and calculate spectra (R ≈ 500 from 250 to 6000 nm) using ray-by-ray radiative transfer with the MPS-ATLAS code. We find that the 1D models fail to return accurate umbral and penumbral spectra on K0V and M0V stars, where convective and radiative transfer of energy is simultaneously important over a broad range of atmospheric heights, rendering mixing-length theory inaccurate. However, 1D models work well for G2V stars, where both radiation and convection significantly contribute to energy transfer only in a narrow region near the stellar surface. Quantitatively, the 1D approximation leads to errors longward of 500 nm of about 50% for both umbral and penumbral flux contrast relative to quiet star regions on M0V stars and less than 2% (for umbrae) and 10% (for penumbrae) for G2V stars.

Keywords: Starspots, Radiative magnetohydrodynamics, Solar analogs, Stellar magnetic fields, Transmission spectroscopy, Stellar atmospheres
Equation of State Independent Determination on the Radius of a 1.4 M<SUB>⊙</SUB> Neutron Star Using Mass–Radius Measurements. Traditional methods for determining the radius of a 1.4 M⊙ neutron star (R1.4) rely on specific equation-of-state (EOS) models that describe various types of dense nuclear matter. This dependence on EOS models can introduce substantial systematic uncertainties, which may exceed the measurement uncertainties when constraining R1.4. In this study, we explore a novel approach to constraining R1.4 using data from Neutron Star Interior Composition Explorer observations of PSR J0030+0451 (J0030) and PSR J0437-4715 (J0437). However, this work presents a more data-driven analysis framework, substantially decreasing the need for EOS assumptions. By analyzing the mass–radius measurements of these two neutron stars, we infer R1.4 using statistical methods based mostly on observational data. We examine various hotspot configurations for J0030, along with new J0437 observations, and their effects on the inferred radius. Our results are consistent with X-ray timing, gravitational-wave, and nuclear physics constraints, while avoiding EOS-related biases. The same method has also been applied to a simulated mass–radius data set, based on our knowledge of future X-ray telescopes, demonstrating the model's ability to recover the injected R1.4 value in certain cases. This method provides a data-driven pathway for extracting neutron star properties and offers a new approach for future observational efforts in neutron star astrophysics.

Keywords: Neutron stars, Bayesian statistics
Fire and Ice in the Whirlpool: Spatially Resolved Scaling Relations between X-Ray-emitting Hot Gas and Cold Molecular Gas in M51. The cold and hot interstellar medium in star-forming galaxies resembles the reservoir for star formation and associated heating by stellar winds and explosions during stellar evolution, respectively. We utilize data from deep Chandra observations and archival millimeter surveys to study the interconnection between these two phases and the relation to star formation activities in M51 on kiloparsec scales. A sharp radial decrease is present in the hot gas surface brightness profile within the inner 2 kpc of M51. The ratio between the total infrared luminosity (LIR) and the hot gas luminosity ( ) shows a positive correlation with the galactic radius in the central region. For the entire galaxy, a twofold correlation is revealed in the  –LIR diagram, where   sharply increases with LIR in the center but varies more slowly in the disk. The best fit gives a steep relation of   for the center of M51. The similar twofold correlations are also found in the  –molecular line luminosity ( ) relations for the four molecular emission lines CO(1–0), CO(2–1), HCN(1–0), and HCO+(1–0). We demonstrate that the core-collapse supernovae (SNe) are the primary source of energy for heating gas in the galactic center of M51, leading to the observed steep  –LIR and  –  relations, as their X-ray radiation efficiencies (η ≡  / ) increase with the star formation rate surface densities (ΣSFR), where   is the SN mechanical energy input rate.

Keywords: Spiral galaxies, Star formation, Interstellar medium, Scaling relations
Superstrong Magnetic Fields in Sunspot Bipolar Light Bridges. Recent solar observations of bipolar light bridges (BLBs) in sunspots have, in a few individual cases, revealed magnetic fields up to 8.2 kG, which is at least twice as strong as typical values measured in sunspot umbrae. However, the small number of such observations hinted that such strong fields in these bright photospheric features that separate two opposite-polarity umbrae are a rare phenomenon. We determine the field strength in a large sample of BLBs with the aim of establishing how prevalent such strong fields are in BLBs. We apply a state-of-the-art inversion technique that accounts for the degradation of the data by the intrinsic point-spread function of the telescope, to the so far largest set of spectropolarimetric observations, by Hinode/Solar Optical Telescope spectropolarimeter, of sunspots containing BLBs. We identified 98 individual BLBs within 51 distinct sunspot groups. Since 66.3% of the BLBs were observed multiple times, a total of 630 spectropolarimetric scans of these 98 BLBs were analyzed. All analyzed BLBs contain magnetic fields stronger than 4.5 kG at unit optical depth. The field strengths decrease faster with height than the fields in umbrae and penumbrae. BLBs display a unique continuum intensity and field strength combination, forming a population well separated from umbrae and the penumbrae. The high brightness of BLBs in spite of their very strong magnetic fields points to the presence of a so far largely unexplored regime of magnetoconvection.

Keywords: Solar magnetic fields, Sunspot groups, Solar photosphere
Alpha–Proton Relative Drift: Implications for the Origins and Dynamics of the Solar Wind. Helium nuclei (alpha particles) strongly influence the momentum and energy balance in the solar wind, comprising up to 20% of the solar wind mass density. In fast Alfvénic wind at heliocentric distances greater than 0.3 au, the alpha particles' bulk flow speed is systematically different to that of the protons. This relative drift speed is of unknown origin and is often close to the local Alfvén wave speed. Novel Parker Solar Probe measurements of the solar wind below 0.3 au show that, closer to the Sun, the alpha–proton drift speed remains on the order of 100–200 km s‑1, even where the Alfvén speed is greater than 600 km s‑1. This relative speed is quantitatively similar to oxygen–hydrogen drift speeds observed in the transition region by remote sensing, suggesting similar selective acceleration processes in the corona. Due to the relative speed of the Alfvén wave to each particle population close to the Sun, the alphas fluctuate with velocity amplitudes comparable to those of the protons, altering the energy balance of the wave. As a result, alpha particles carry a significant fraction of the total kinetic energy in Alfvénic fluctuations in the near-Sun solar wind. The alpha–proton drift speed is comparable to the proton speed in the near-Sun wind, making the bulk flow of the alpha particles a significant contribution to the kinetic energy flux. These heavy-ion dynamics provide new observational constraints on quantifying the energy budget of the solar wind and the magnetic field evolution through the heliosphere.

Keywords: Space plasmas, Fast solar wind, Solar wind, Solar physics, Alfven waves
Resolving Turbulence Drivers in Two Luminous Obscured Quasars with JWST/NIRSpec Integral Field Unit. In this Letter, we investigate the turbulence and energy injection in the extended nebulae surrounding two luminous obscured quasars, WISEA J100211.29+013706.7 (z = 1.5933) and SDSS J165202.64+172852.3 (z = 2.9489). Utilizing high-resolution data from the NIRSpec integral field unit onboard the James Webb Space Telescope, we analyze the velocity fields of line-emitting gas in and around these quasars and construct the second-order velocity structure functions (VSFs) to quantify turbulent motions across different spatial scales. Our findings reveal a notable flattening in the VSFs from ≈ 3 kpc up to a scale of 10–20 kpc, suggesting that energy injection predominantly occurs at a scale ≲ 10 kpc, likely powered by quasar outflows and jet-driven bubbles. The extended spatial range of flat VSFs may also indicate the presence of multiple energy injection sources at these scales. For J1652, the turbulent energy in the host interstellar medium (ISM) is significantly higher than in tidally stripped gas, consistent with the expectation of active galactic nucleus (AGN) activities stirring up the host ISM. Compared to the VSFs observed on spatial scales of 10–50 kpc around lower-redshift UV-bright quasars, these obscured quasars exhibit higher turbulent energies in their immediate surroundings, implying different turbulence drivers between the ISM and halo-scale gas. Future studies with an expanded sample are essential to elucidate further the extent and the pivotal role of AGNs in shaping the gas kinematics of host galaxies and beyond.

Keywords: AGN host galaxies, Interstellar medium, Circumgalactic medium
X-Ray and Optical Polarization Aligned with the Radio Jet Ejecta in GX 339─4. We present the first X-ray polarization measurements of GX 339─4. IXPE observed this source twice during its 2023─2024 outburst, once in the soft-intermediate state and again during a soft state. The observation taken during the intermediate state shows a significant (4σ) polarization degree PX = 1.3% ± 0.3% and polarization angle θX = −74° ± 7° only in the 3─8 keV band. FORS2 at the Very Large Telescope observed the source simultaneously, detecting optical polarization in the B, V, R, and I bands (between ∼0.1% and ∼0.7%), all roughly aligned with the X-ray polarization. We also detect a discrete jet knot from radio observations with the Australia Telescope Compact Array taken later in time; this knot would have been ejected from the system around the same time as the hard-to-soft X-ray state transition, and a bright radio flare occurred ∼3 months earlier. The proper motion of the jet knot provides a direct measurement of the jet orientation angle on the plane of the sky at the time of the ejection. We find that both the X-ray and optical polarization angles are aligned with the direction of the ballistic jet.

Keywords: Accretion, X-ray astronomy, Low-mass x-ray binary stars, Radio astronomy, Astrophysical black holes
Detection of Extended X-Ray Emission around the PeVatron Microquasar V4641 Sgr with XRISM. A recent report on the detection of very-high-energy gamma rays from V4641 Sagittarii (V4641 Sgr) up to ≈0.8 PeV has made it the second confirmed "PeVatron" microquasar. Here we report on the observation of V4641 Sgr with X-Ray Imaging and Spectroscopy Mission (XRISM) in 2024 September. Thanks to the large field of view and low background, the CCD imager Xtend successfully detected for the first time X-ray extended emission around V4641 Sgr with a significance of ≳4.5σ and &gt;10σ based on our imaging and spectral analysis, respectively. The spatial extent is estimated to have a radius of 7' ± 3' (13 ± 5 pc at a distance of 6.2 kpc) assuming a Gaussian-like radial distribution, which suggests that the particle acceleration site is within ~10 pc of the microquasar. If the X-ray morphology traces the diffusion of accelerated electrons, this spatial extent can be explained by either an enhanced magnetic field (∼80 μG) or a suppressed diffusion coefficient (∼1027 cm2 s‑1 at 100 TeV). The integrated X-ray flux, (4–6) × 10‑12 erg s‑1 cm‑2 (2–10 keV), would require a magnetic field strength higher than the Galactic mean (≳8 μG) if the diffuse X-ray emission originates from synchrotron radiation and the gamma-ray emission is predominantly hadronic. If the X-rays are of thermal origin, the measured extension, temperature, and plasma density can be explained by a jet with a luminosity of ∼2 × 1039 erg s‑1, which is comparable to the Eddington luminosity of this system.

Keywords: Low-mass x-ray binary stars, Gamma-ray sources, Non-thermal radiation sources, Radio jets
Identification of the Optical Counterpart of the Fast X-Ray Transient EP240414a. Fast X-ray transients (FXTs) are extragalactic bursts of X-rays first identified in archival X-ray data and are now routinely discovered in real time by the Einstein Probe, which is continuously surveying the night sky in the soft (0.5─4 keV) X-ray regime. In this Letter, we report the discovery of the second optical counterpart (AT 2024gsa) to an FXT (EP 240414a). EP 240414a is located at a projected radial separation of 27 kpc from its likely host galaxy at z = 0.4018 ± 0.0010. The optical light curve of AT 2024gsa displays three distinct components. The initial decay from our first observation is followed by a rebrightening episode, displaying a rapid rise in luminosity to an absolute magnitude Mr ∼ −21 after two rest-frame days. While the early optical luminosity and decline rate are similar to those of luminous fast blue optical transients, the color temperature of AT 2024gsa is distinctly red and we show that the peak flux is inconsistent with a thermal origin. The third component peaks at Mi ∼ −19 at ≳16 rest-frame days post-FXT, and is compatible with an emerging supernova. We fit the riz-band data with a series of power laws and find that the decaying components are in agreement with gamma-ray burst afterglow models, and that the rebrightening may originate from refreshed shocks. By considering EP 240414a in context with all previously reported known-redshift FXT events, we propose that Einstein Probe FXT discoveries may predominantly result from (high-redshift) gamma-ray bursts, and thus appear to be distinct from the previously discovered lower-redshift, lower-luminosity population of FXTs.

Keywords: Gamma-ray bursts, Optical identification, Relativistic jets, Transient sources, X-ray transient sources
TOI-4504: Exceptionally Large Transit Timing Variations Induced by Two Resonant Warm Gas Giants in a Three-planet System. We present a joint analysis of transit timing variations (TTVs) and Doppler data for the transiting exoplanet system TOI-4504. TOI-4504 c is a warm Jupiter-mass planet that exhibits the largest known TTVs, with a peak-to-node amplitude of ∼2 days, the largest value ever observed, and a superperiod of ~930 days. TOI-4504 b and c were identified in public Transiting Exoplanet Survey Satellite (TESS) data, while the TTVs observed in TOI-4504 c, together with radial velocity (RV) data collected with FEROS, allowed us to uncover a third, nontransiting planet in this system, TOI-4504 d. We were able to detect transits of TOI-4504 b in the TESS data with a period of 2.4261 ± 0.0001 days and derive a radius of 2.69 ± 0.19 R⊕. The RV scatter of TOI-4504 was too large to constrain the mass of TOI-4504 b, but the RV signals of TOI-4504 c and d were sufficiently large to measure their masses. The TTV+RV dynamical model we apply confirms TOI-4504 c as a warm Jupiter planet with an osculating period of 82.54 ± 0.02 days, a mass of 3.77 ± 0.18 MJ, and a radius of 0.99 ± 0.05 RJ, while the nontransiting planet TOI-4504 d has an orbital period of 40.56 ± 0.04 days and a mass of 1.42  MJ. We present the discovery of a system with three exoplanets: a hot sub-Neptune and two warm Jupiter planets. The gas giant pair is stable and likely locked in a first-order 2:1 mean-motion resonance (MMR). The TOI-4504 system is an important addition to MMR pairs, whose increasing occurrence supports a smooth migration into a resonant configuration during the protoplanetary disk phase.

Keywords: Exoplanet dynamics, Radial velocity, Transit photometry, Transit timing variation method
The GD-1 Stellar Stream Perturber as a Core-collapsed Self-interacting Dark Matter Halo. The GD-1 stellar stream exhibits spur and gap structures that may result from a close encounter with a dense substructure. When interpreted as a dark matter subhalo, the perturber is denser than predicted in the standard cold dark matter (CDM) model. In self-interacting dark matter (SIDM), however, a halo could evolve into a phase of gravothermal collapse, resulting in a higher central density than its CDM counterpart. We conduct high-resolution controlled N-body simulations to show that a collapsed SIDM halo could account for the GD-1 perturber's high density. We model a progenitor halo with a mass of 3 × 108 M⊙, motivated by a cosmological simulation of a Milky Way analog, and evolve it in the Milky Way's tidal field. For a cross section per mass of σ/m ≈ 30–100 cm2 g‑1 at  , the enclosed mass of the SIDM halo within the inner 10 pc can be increased by more than 1 order of magnitude compared to its CDM counterpart, leading to a good agreement with the properties of the GD-1 perturber. Our findings indicate that stellar streams provide a novel probe into the self-interacting nature of dark matter.

Keywords: Galaxy dark matter halos, Dark matter, Stellar streams