Sazuna/UAT_keywords huggingface dataset:
Acceleration of Heavy Ions at Nonrelativistic Collisionless Shocks. We investigate the process of diffusive shock acceleration of particles with mass number to charge number ratios A/Q &gt; 1, e.g., partially ionized heavy ions. To this end, we introduce helium- and carbon-like ions at solar abundances into two-dimensional hybrid (kinetic ions─fluid electrons) simulations of nonrelativistic collisionless shocks. This study yields three main results: (1) Heavy ions are preferentially accelerated compared to hydrogen. For typical solar abundances, the energy transferred to accelerated helium ions is comparable to, or even exceeds, that of hydrogen, thereby enhancing the overall shock acceleration efficiency. (2) Accelerated helium ions contribute to magnetic field amplification, which increases the maximum attainable particle energy and steepens the spectra of accelerated particles. (3) The efficient acceleration of helium significantly enhances the production of hadronic γ-rays and neutrinos, likely dominating the one due to hydrogen. These effects should be taken into account, especially when modeling strong space and astrophysical shocks.

Keywords: Plasma astrophysics, Supernova remnants, Cosmic ray sources, Shocks, Particle astrophysics
Outflow─Cloud Interaction as the Possible Origin of the Peculiar Radio Emission in the Tidal Disruption Event AT2018cqh. AT2018cqh is a unique optical tidal disruption event (TDE) discovered in a dwarf galaxy exhibiting delayed X-ray and radio flares. We present the results from high-resolution Very Long Baseline Array and enhanced Multi Element Remotely Linked Interferometer Network radio observations of AT2018cqh extending to δt ∼ 2250 days postdiscovery, which reveal a compact radio emission, unresolved at a scale of ≲0.13 pc at 7.6 GHz, with a high brightness temperature of Tb ≳ 4.03 × 109 K. The radio spectral energy distribution (SED) is found to gradually shift toward a higher peak flux density and frequency over a period of ∼1000 days. An equipartition analysis suggests that there is little change in the radio-emitting region over this period, while the electron density increases by a factor of 3. The radio light curve at 0.89 GHz continues to rise, with a bump feature lasting for 240 days. These properties are in contrast to the predictions of the standard shock-wave model from a diffuse circumnuclear medium but could be explained if dense clouds exist in the circumnuclear environment. The latter scenario is supported by our hydrodynamic simulations of the interaction of the TDE outflow with a cloud, which can reproduce the temporal evolution in the radio SED. This work highlights the importance of outflow─cloud interaction in explaining the delayed fast-rising radio emission observed in some TDEs, especially those occurring in galaxies with preexisting active galactic nucleus activity.

Keywords: Accretion, Tidal disruption, Active galactic nuclei, Radio transient sources
On-sky Demonstration of Subdiffraction-limited Astronomical Measurement Using a Photonic Lantern. Resolving fine details of astronomical objects provides critical insights into their underlying physical processes. This drives in part the desire to construct ever-larger telescopes and interferometer arrays and to observe at shorter wavelengths to lower the diffraction limit of angular resolution. Alternatively, one can aim to overcome the diffraction limit by extracting more information from a single telescope's aperture. A promising way to do this is spatial-mode-based imaging, which projects a focal-plane field onto a set of spatial modes before detection, retaining focal-plane phase information that is crucial at small angular scales but typically lost in intensity imaging. However, the practical implementation of mode-based imaging in astronomy from the ground has been challenged by atmospheric turbulence. Here, we present the first on-sky demonstration of a subdiffraction-limited mode-based measurement, using a photonic-lantern-fed spectrometer installed on the Subaru Coronagraphic Extreme Adaptive Optics instrument at the Subaru Telescope. We introduce a novel calibration strategy that mitigates time-varying wave-front error and misalignment effects, leveraging simultaneously recorded focal-plane images and using a spectral-differential technique that self-calibrates the data. Observing the classical Be star β CMi, we detect spectral-differential spatial signals and reconstruct images of its Hα-emitting disk. We achieve an unprecedented Hα photocenter precision of ∼50 μas in about 10 minutes of observation with a single telescope, measuring the disk's nearside─farside asymmetry for the first time. This work demonstrates the high precision, efficiency, and practicality of photonic mode-based imaging techniques in recovering subdiffraction-limited information, opening new avenues for high-angular-resolution spectroscopic studies in astronomy.

Keywords: Astronomical techniques, Astronomical instrumentation, Circumstellar disks, Be stars, High angular resolution
Limits on Stellar Flybys in the Solar Birth Cluster. The orbits of small bodies in the outer solar system are particularly sensitive to gravitational perturbations, including stellar flybys. Stellar clusters, with low velocity dispersions and high number densities, can be the source of strong and frequent flybys. As a result, we can infer what properties of the solar birth environment would be incompatible with the structure of the outer solar system observed today. Here, we explore with n-body simulations the implications of the low inclinations (i &lt; 20∘) of the distant sednoids (objects with perihelia q &gt; 40 au and semimajor axes a &gt; 400 au) for the properties of the solar birth cluster. We find that the existence of these orbits, if they were in place in the Sun's birth cluster phase, would limit the product of the stellar number density and the Sun's residence time in the birth cluster to ≲5 × 103 Myr pc−3, as compared to the weaker limit ≲5 × 104 Myr pc−3 implied by the low inclinations of the cold classical Kuiper Belt.

Keywords: Solar system, Kuiper belt, Trans-Neptunian objects
First Temperature Profile of a Stellar Flare Using Differential Chromatic Refraction. We present the first derivation of a stellar flare temperature profile from single-band photometry. Stellar flare DWF 030225.574−545707.45129 was detected in 2015 by the Dark Energy Camera as part of the Deeper, Wider, Faster program. The brightness (∆mg = −6.12) of this flare, combined with the high air mass (1.45 ≲ X ≲ 1.75) and blue filter (DES g, 398─548 nm) in which it was observed, provided ideal conditions to measure the zenithward apparent motion of the source due to differential chromatic refraction (DCR) and, from that, infer the effective temperature of the event. We model the flare's spectral energy distribution as a blackbody to produce the constraints on flare temperature and geometric properties derived from single-band photometry. We additionally demonstrate how simplistic assumptions on the flaring spectrum, as well as on the evolution of flare geometry, can result in solutions that overestimate the effective temperature. Exploiting DCR enables studying chromatic phenomena with ground-based astrophysical surveys, and stellar flares on M dwarfs are a particularly enticing target for such studies due to their ubiquity across the sky and the heightened color contrast between their red quiescent photospheres and the blue flare emission. Our novel method will enable similar temperature constraints for a large sample of objects in upcoming photometric surveys like the Vera C. Rubin Legacy Survey of Space and Time.

Keywords: Astronomical methods, Atmospheric refraction, Red dwarf flare stars
The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the X-Rays and Radio. We present X-ray (0.3─79 keV) and radio (0.25─203 GHz) observations of the most luminous fast blue optical transient (LFBOT) AT 2024wpp at z = 0.0868, spanning 2─280 days after first light. AT 2024wpp shows luminous (LX ≍ 1.5 × 1043 erg s−1), variable X-ray emission with a Compton hump peaking at δt ≍ 50 days. The X-ray spectrum evolves from a soft (Fν ∝ ν−0.6) to an extremely hard state (Fν ∝ ν1.26) accompanied by a rebrightening at δt ≍ 50 days. The X-ray emission properties favor an embedded high-energy source shining through asymmetric expanding ejecta. We detect radio emission peaking at L9 GHz ≍ 1.7 × 1029 erg s−1 Hz−1 at δt ≍ 73 days. The spectral evolution is unprecedented: the early millimeter fluxes rise nearly an order of magnitude during δt ≍ 17─32 days, followed by a decline in spectral peak fluxes. We model the radio emission as synchrotron radiation from an expanding blast wave interacting with a dense environment ( Ṁ∼10−3M⊙yr−1  for vw = 1000 km s−1). The inferred outflow velocities increase from Γβc ≍ 0.07c to 0.42c during δt ≍ 32─73 days, indicating an accelerating blast wave. We interpret these observations as a shock propagating through a dense shell of radius ≍1016 cm and then accelerating into a steep density profile ρCSM(r) ∝ r−3.1. All radio-bright LFBOTs exhibit similar circumstellar medium (CSM) density profiles (ρCSM ∝ r−3), suggesting similar progenitor processes. The X-ray and radio properties favor a progenitor involving super-Eddington accretion onto a compact object launching mildly relativistic disk wind outflows.

Keywords: Time domain astronomy, Transient sources, High energy astrophysics
The Extended Stellar Distribution in the Outskirts of the Ursa Minor Dwarf Spheroidal Galaxy. We discover an extended distribution of main-sequence (MS) stars along the minor axis of the Ursa Minor (UMi) dwarf spheroidal galaxy (dSph). This study is enabled by deep, wide Subaru/Hyper Suprime-Cam data, reaching photometric uncertainties below 0.1 mag at g, i ∼ 26 mag. Color─magnitude diagrams along the major and minor axes reveal a clear excess of MS stars beyond the nominal tidal radius along the minor axis. To characterize this structure, we derive radial number density profiles in seven azimuthal directions and fit them with an exponential+power-law function to assess the symmetry of the extended component. The power-law slopes tend to be shallower toward the minor axis, though the symmetry remains inconclusive within 1σ uncertainties. This may indicate that the extended component is preferentially distributed along the minor axis and could be different from the previously suggested tidal features along the major axis. Comparing with simulations, we find that the fraction of stars beyond five effective radii is consistent with expectations from an intermediate mass ratio merger scenario with a stellar mass ratio around 6:1. While these findings provide new insights into the structural complexity and dynamical history of the UMi dSph, alternative mechanisms such as stellar or supernova feedback have also been proposed for extended stellar halos in dwarfs and cannot be ruled out.

Keywords: Stellar feedback, Galactic archaeology, Dwarf galaxies, Galaxy stellar halos, Ursa Minor dwarf spheroidal galaxy, Galaxy mergers, Tidal interaction
Dual-band Ion-scale Waves in the Solar Wind: Statistical Properties and Comparison with Single-band Ion-scale Waves. We present a comprehensive statistical analysis of ion-scale waves including dual-band ion-scale waves (DBIWs) observed by the Parker Solar Probe in the solar wind. DBIWs are characterized by the simultaneous occurrence of distinct left- and right-handed polarized wave packets at higher and lower frequencies, respectively, in the spacecraft frame, implying the presence of bidirectionally propagating L-mode waves. We identify and compare DBIWs to single-band ion-scale waves (SBIWs) and investigate their spatial distributions, background magnetic field conditions, and associated inertial range turbulence characteristics. We find that DBIWs exhibit a strong preferential occurrence at heliocentric distances between 0.2 and 0.25 au (equivalently 43 and 54 RS) in contrast to SBIWs, the occurrence rate of which peaks closer to the Sun and decreases with the heliocentric distance. DBIWs are also preferentially observed under conditions of strong Alfvénic turbulence, characterized by low magnetic compressibility and perpendicular-dominant fluctuations. These findings support a scenario in which stochastic ion heating via sufficiently large perpendicular Alfvénic fluctuation generates the ion temperature anisotropies required to excite bidirectional ion cyclotron waves. This work advances our understanding of kinetic wave generation in the solar wind and its connection to large-scale turbulence.

Keywords: Interplanetary turbulence, Solar wind, Alfven waves
Radiation Forces and Trajectory of Hayabusa2♯ Target 1998 KY<SUB>26</SUB>. Small near-Earth asteroid 1998 KY26 has recently become an object of interest because it is the target of the Hayabusa2♯ mission and because challenges in fitting its astrometric data have led to classifying it as a dark comet. Data acquired during the favorable apparition in 2024 helped significantly improve the physical characterization of 1998 KY26 but also led to increased orbit determination challenges. We develop a high-fidelity force model of solar radiation pressure and thermal emission of 1998 KY26 that accounts for a nonspherical shape of the asteroid and results in an excellent orbital fit. Thanks to its close ties to the physical properties of the asteroid, the model removes the degeneracy in the orientation of the rotation pole stemming from lightcurve analysis and constrains 1998 KY26's bulk density to  2.8−1.0+1.6  g cm−3 (90% confidence level), which is consistent with the asteroid's taxonomic type. Our model does not require the contribution of undetected cometary activity of 1998 KY26, which alleviates safety concerns for the Hayabusha2♯ mission and has broader implications for the dark comet hypothesis.

Keywords: Near-Earth objects, Asteroids, Asteroid dynamics, Asteroid rotation, Astrometry
Threading the Magellanic Needle: Hypervelocity Stars Trace the Past Location of the LMC. Recent discoveries have shown that a population of hypervelocity stars (HVSs) originates from the Large Magellanic Cloud (LMC). We use three such HVSs as dynamical tracers to constrain the past orbit of the LMC. Since each star was ejected at a finite time in the past, it must intersect the past position of the LMC's central black hole at its ejection time. We model the LMC's orbit under the influence of dynamical friction and extended mass distributions for both the LMC and the Milky Way, generating a large ensemble of orbital realizations. By evaluating which orbits intersect the back-integrated HVS trajectories, we compute posterior distributions over the LMC's orbital history. This approach provides significantly tighter constraints on the past motion of the LMC than previously possible. We find two previously published orbital models that are consistent with these new constraints: a first-passage trajectory from a self-consistent hydrodynamic simulation, and a second-passage trajectory from a collisionless N-body simulation. In parallel, we infer the present-day ejection site of the HVSs—likely tracing the LMC's dynamical center and supermassive black hole—independent of conventional methods.

Keywords: Galaxy dynamics, Large Magellanic Cloud
Comparing XRISM Cluster Velocity Dispersions with Predictions from Cosmological Simulations: Are Feedback Models Too Ejective?. The dynamics of the intracluster medium (ICM), the hot plasma that fills galaxy clusters, are shaped by gravity-driven cluster mergers and feedback from supermassive black holes (SMBHs) in the cluster cores. XRISM measurements of ICM velocities in several clusters offer insights into these processes. We compare XRISM measurements for nine galaxy clusters (Virgo, Perseus, Centaurus, Hydra-A, PKS 0745─19, A2029, Coma, A2319, and Ophiuchus) with predictions from three state-of-the-art cosmological simulation suites, TNG-Cluster, the Three Hundred Project GADGET-X, and GIZMO-SIMBA, that employ different models of feedback. In cool cores, XRISM reveals systematically lower velocity dispersions than the simulations predict, with all 10 measurements below the median simulated values by a factor of 1.5─1.7 on average and all falling within the bottom 10% of the predicted distributions. The observed kinetic-to-total pressure ratio is also lower, with a median value of 2.2%, compared to the predicted 5.0%─6.5% for the three simulations. Outside the cool cores and in non-cool-core (NCC) clusters, simulations show better agreement with XRISM measurements, except for the outskirts of the relaxed, cool-core cluster A2029, which exhibits an exceptionally low kinetic pressure support (&lt;1%), with none of the simulated systems in either of the three suites reaching such low levels. The NCC Coma and A2319 exhibit dispersions at the lower end but within the simulated spread. Our comparison suggests that the three numerical models may overestimate the kinetic effects of SMBH feedback in cluster cores. Additional XRISM observations of NCC clusters will clarify if there is a systematic tension in the gravity-dominated regime as well.

Keywords: Galaxy clusters, Hydrodynamical simulations, High resolution spectroscopy, Intracluster medium
Escape Fractions from Unattenuated Lyα Emitters around Luminous z &gt; 6 Quasars. Ionized proximity zones around luminous quasars provide a unique laboratory to characterize the Lyα emission lines from z &gt; 6 galaxies without significant attenuation from the intergalactic medium (IGM). However, Lyα line measurements for galaxies within high-redshift quasars' proximity zones have been rare so far. Here we present deep spectroscopic observations obtained with the NIRSpec/Micro-Shutter Assembly (MSA) instrument on the James Webb Space Telescope of galaxies in two z &gt; 6 quasar fields. We measure the Lyα line fluxes for 50 galaxies at 6 &lt; z &lt; 7 with UV absolute magnitude MUV &lt; −19 (median MUV = −19.97), among which 15 are located near the luminous quasars, i.e., within ∆v &lt; 2500 km s−1. We find that galaxies near the quasars show significant flux blueward of the systemic Lyα wavelength, and have higher Lyα equivalent width compared to galaxies at similar redshifts that are not located within the quasars' environment. Our result indicates little or no redshift evolution for the Lyα emitter fraction from z ∼ 6.4 to z ∼ 5. Leveraging the low IGM opacity in the quasars' vicinity, we evaluate the Lyα escape fraction ( fescLyα ) of high-redshift galaxies. Our analysis suggests that galaxies at &lt;z&gt; ≍ 6.4 have an average  fescLyα=0.14±0.04 . This value is consistent with reionization models where the Lyman continuum escape fraction is low  (fescLyC≲0.1)  for luminous galaxies, and where the most luminous galaxies have only a minor contribution to the total ionizing photon budget.

Keywords: Reionization, High-redshift galaxies, Quasars
Return of the Clocked Burster: Exceptionally Short Recurrence Time in GS 1826−238. We report the discovery of an exceptionally short burst recurrence time in the well-known clocked burster GS 1826−238, observed with the CubeSat X-ray observatory NinjaSat. In 2025 May, GS 1826−238 underwent a soft-to-hard state transition for the first time in 10 yr. On June 23, NinjaSat began monitoring GS 1826−238 in the hard state and continued until it returned to a steady soft state. During this period, we detected 19 X-ray bursts: 14 during the hard state, 4 in the transitional state, and 1 in the soft state. In the hard state, we identified a new clocked bursting epoch, during which the burst recurrence time remained highly stable and unprecedentedly short among the clocked bursting phases of GS 1826−238, with trec = 1.603 ± 0.040 hr (1σ error). Previous observations showed that the burst recurrence time in GS 1826−238 decreased with increasing mass accretion rate, reached its minimum value of trec ∼ 3 hr, and then increased again. The observed 1.6 hr recurrence time is therefore exceptionally short, indicating anomalous ignition conditions. We propose that this phenomenon reflects fuel accumulation over a smaller fraction of the neutron star surface, resulting in a higher local accretion rate compared to earlier epochs. This scenario naturally accounts for the exceptionally short recurrence time, together with the observed reductions during bursts in blackbody normalization (proportional to the emitting area) and fluence. We also discuss possible contributions from residual heat in the neutron star crust or the presence of an additional soft spectral component.

Keywords: Low-mass x-ray binary stars, Neutron stars, Nuclear astrophysics, X-ray bursts
Caught in the Cosmic Web: Evidence for Ram Pressure Stripping of a Low-mass Galaxy by the Cosmic Web. We present interferometric radio observations of the neutral atomic gas in AGC 727130, a low-mass, gas-rich field galaxy lacking significant star formation. The atomic gas in AGC 727130 displays a pronounced asymmetry, extending well beyond the stellar disk in one direction while remaining relatively undisturbed in the other. Despite proximity to a pair of interacting dwarfs, tidal analysis suggests these neighboring galaxies are not responsible for this pronounced asymmetry. Instead, using a topological cosmic web filament finder on spectroscopic catalog data, we find AGC 727130 lies at the intersection of several large-scale cosmic web filaments, environments predicted to host diffuse, shock-heated gas. We propose that an interaction with this ambient medium is stripping gas from the galaxy via cosmic web ram pressure stripping. This mechanism, supported by recent simulations, may quench low-mass galaxies outside of massive halos and must be accounted for when comparing observed numbers of dwarf galaxies to theoretical predictions.

Keywords: Dwarf galaxies, Cosmic web, Interstellar medium, Ram pressure stripped tails
Distinct Solar Energetic Particle Shock Intensity─Diffusion Coefficient Relationships in the Inner Heliosphere. It has been inferred from theory that the spatial diffusion coefficient (κ) upstream of shocks is anticorrelated with the intensity of solar energetic particles (SEPs) at the shock (jshock) motivated by quasi-linear theory (QLT). This is because a lower κ along the magnetic field (κ∥) implies that particles are trapped for longer, providing more acceleration and resulting in a higher jshock. However, the simplest version of DSA predicts that jshock is determined by the source of the injected population at the shock and plasma density jump with no relation to κ for low-energy SEPs. Here, we identify the relationship between κ and jshock, whose form is unknown, using Parker Solar Probe observations of eight shocks within 1 au. We estimate a characteristic κfit along the shock normal by fitting the upstream SEP intensity profiles with a 1D steady-state transport model for acceleration and escape assuming pitch-angle isotropy in the plasma frame. Also, we estimate κ∥ based on the magnetic power spectral density using QLT for comparison with κfit. Our results show that both quantities are anticorrelated with jshock. Instead of a uniform relationship between κ and jshock, we find distinct relationships appearing as potential power laws manifested across SEP events with no obvious radial dependence from 0.07 to 0.74 au. These relationships may be grouped by similar shock parameters (in terms of speed, strength, and orientation). Our findings raise questions about SEP transport and its radial dependence within 1 au and provide important observational constraints for models of shock-accelerated particles.

Keywords: Solar energetic particles, Shocks, Solar wind