Sazuna/UAT_keywords huggingface dataset:
Propagation-induced Frequency-dependent Polarization Properties of Fast Radio Burst. Frequency-dependent polarization properties provide crucial insights into the radiation mechanisms and magnetic environments of fast radio bursts (FRBs). We explore an analytical solution of radiative transfer of the polarization properties of FRBs as a strong incoming wave propagates in a homogeneous magnetized plasma. The cases of a thermal plasma are studied in detail. The rotational axis of the polarization spectrum undergoes precession with frequency on the Poincaré sphere when the medium has both strong Faraday rotation and conversion. Such precession on the Poincaré sphere could occur in hot or cold plasma with a strong magnetic field component perpendicular to the line of sight. Significant absorption can exist in a dense plasma medium, which may give rise to a highly circularly polarized outgoing wave. We apply the analytical solution with the mixing Faraday case to fit the observations of frequency-dependent Stokes parameters for FRB 20180301A and FRB 20201124A. The analytical solution offers a more physical description of FRBs' magnetic environment properties than the empirical "generalized Faraday rotation" method commonly adopted in the literature. The frequency-dependent Stokes parameters may be associated with reversing rotation measures or the presence of a persistent radio source around an FRB.

Keywords: Plasma astrophysics, Radiative transfer equation, Radio bursts, Radiative processes, Radio transient sources
Kinematic Confirmation of a Remarkable Linear Trail of Galaxies in the NGC 1052 Field, Consistent with Formation in a High-speed Bullet Dwarf Collision. A unique linear trail of diffuse galaxies was recently identified in the NGC 1052 field. This trail includes the remarkable, ultradiffuse galaxies DF2 and DF4, which lack dark matter and host unusually luminous globular clusters. It has been proposed that the trail formed via a high-speed collision between two gas-rich dwarf galaxies. This scenario predicts that the trail galaxies are kinematically connected and follow a specific trend in radial velocity as a function of position, based on the known velocities and positions of DF2 and DF4. To test this hypothesis, we measured radial velocities for seven additional galaxies on the trail. While the galaxies' low surface brightnesses presented observational challenges, we employ several methods to obtain measurements for galaxies with effective surface brightnesses up to 28.6 mag arcsec−2, including a narrow slit placed over globular clusters and a novel wide slit mode on Keck/Low Resolution Imaging Spectrometer (LRIS), as well as a "light bucket" mode on Keck/Keck Cosmic Web Imager (KCWI). We find that five of our seven targets follow the precise velocity trend predicted by DF2 and DF4, to a degree with just a 2% chance of randomly occurring. Moreover, the trail galaxies' radial velocities are significantly higher than those of the NGC 1052 group, setting it apart as a separate, kinematically connected system. Our findings support the theory that this trail of galaxies, including DF2 and DF4, formed together in a single event. A "bullet dwarf" collision remains the only known explanation for all the unusual properties of DF2, DF4, and the associated trail of galaxies.

Keywords: Galaxy formation, Galaxy collisions, Dwarf galaxies, Dark matter, Low surface brightness galaxies
Discovery and Multiwavelength Analysis of a New Dissociative Galaxy Cluster Merger: The Champagne Cluster. We report the discovery of a new binary galaxy cluster merger, the Champagne Cluster (RM J130558.9+263048.4), using a detection method that identifies dynamically active clusters in the redMaPPer Sloan Digital Sky Survey DR8 photometric galaxy cluster catalog. The Champagne Cluster exhibits the classic X-ray morphology of a post-pericenter dissociative galaxy cluster merger: an X-ray peak located between two galaxy overdensities at the same redshift. We conducted a Keck/DEIMOS survey and obtained redshifts for 102 member galaxies. The redshift analysis indicates a relative velocity of 411 ± 180 km s‑1 between the two subclusters, which suggests that the merger is happening near the plane of the sky. We estimated the bulk temperature (8.20 ± 1.2 keV) and total X-ray luminosity (7.29 ± 0.19 × 1044 erg s‑1) of the intracluster medium using Chandra archival data. We used the ClusterPyXT software to make a temperature map, and we compared it to hydrodynamic simulations to constrain the time since pericenter (TSP), the impact parameter, and the mass ratio. We found two scenarios that matched our data: a returning system with an impact parameter of 0 and TSP of 2.2 Gyr, and an outbound system with an impact parameter of 500 kpc and TSP of 0.4 Gyr. Both scenarios have a mass ratio of 1:10.

Keywords: Galaxy clusters, Galactic and extragalactic astronomy
Detecting Stellar Coronal Mass Ejections via Coronal Dimming in the Extreme Ultraviolet. Stellar flares and coronal mass ejections (CMEs) can strip planetary atmospheres, reducing the potential habitability of terrestrial planets. While flares have been observed for decades, stellar CMEs remain elusive. Extreme-ultraviolet (EUV) emissions are sensitive to both flares and CME-induced coronal dimming. We assess the detectability of stellar CME-induced EUV dimming events by adapting a known "Sun-as-a-star" dimming technique—validated by the Solar Dynamics Observatory's EUV Variability Experiment (EVE)—to stellar conditions. We adapt the solar data to reflect a range of stellar intensities, accounting for intrinsic brightness, distance, and interstellar medium (ISM) attenuation. We generate synthetic light curves for two different missions: the legacy EUV Explorer (EUVE) and the proposed ESCAPE mission. Our results indicate that dimming detections are well within reach. EUVE's broadband imager was capable of detecting stellar CMEs—albeit with limited spectral (temperature) resolution—but that was not part of the observing plan. EUVE's spectroscopic survey lacked sufficient sensitivity for CME detections. Optimizing modern instrument design for this task would make the observation fully feasible. In this work, we present a tool to explore the stellar-CME detection parameter space. Our tool shows that with an instrument with performance similar to ESCAPE, setting a 600 s integration period, and integrating the spectra into bands, any star with a X-ray flux ≥2.51 × 10‑12 erg s‑1 cm‑2 should have a ≥3σ detection even for a modest few-percent dimming profile, regardless of ISM attenuation. Such measurements would be crucial for understanding the space weather environments of exoplanet host stars and, ultimately, for evaluating planetary habitability.

Keywords: Astronomical instrumentation, Extreme ultraviolet astronomy, Astronomy image processing, Stellar coronal mass ejections
Long-term Astrometric Monitoring of the Galactic Center Magnetar PSR J1745‑2900. We present new astrometric observations of the Galactic center magnetar PSR J1745‑2900 with the Very Long Baseline Array. Combined with previously published measurements in 10 epochs that spanned 477 days, the complete data set consists of 25 epochs and 41 independent measurements that span 1984 days. These data constrain the proper motion to an accuracy of ≲2% and set an upper limit on the absolute value of the magnetar's acceleration of ≲(0.4, 0.2) mas yr‑2 in the two celestial coordinates, consistent with the maximum value of ∼0.03 mas yr‑2 expected for an orbit around Sgr A*. Future measurements have the potential to detect the acceleration of PSR J1745‑2900 due to Sgr A* should PSR J1745‑2900 rebrighten. We consider several potential sources of systematic variations in the astrometric residuals after fitting for standard parameters, including refractive wander, changes in the structure of Sgr A*, and the presence of an unseen binary companion. While a stellar companion model can be fit to the astrometric data, pulse period measurements are inconsistent with that model. No changes in the apparent image size of the magnetar were detected over the duration of these observations, indicating a lack of change in the properties of the line-of-sight scattering during this period. We also show that the upper limit to the mean core shift of Sgr A* is consistent with expectations for a compact jet or symmetric accretion flow.

Keywords: Galactic center, Black holes, Very long baseline interferometry, Radio astrometry, Pulsars, Astrometry, Interstellar scattering, Magnetars, Binary pulsars, Radio pulsars
The Gravity Collective: A Comprehensive Analysis of the Electromagnetic Search for the Binary Neutron Star Merger GW190425. We present an ultraviolet to infrared search for the electromagnetic (EM) counterpart to GW190425, the second ever binary neutron star merger discovered by the LIGO-Virgo-KAGRA Collaboration. GW190425 was more distant and had a larger localization area than GW170817, so we use a new tool, Teglon, to redistribute the GW190425 localization probability in the context of galaxy catalogs within the final localization volume. We derive a 90th percentile area of 6688 deg2, a ∼1.5× improvement relative to the LIGO/Virgo map, and show how Teglon provides an order-of-magnitude boost to the search efficiency of small (≤1 deg2) field-of-view instruments. We combine our data with a large, publicly reported imaging data set, covering 9078.59 deg2 of unique area and 48.13% of the LIGO/Virgo-assigned localization probability, to calculate the most comprehensive kilonova (KN), short gamma-ray burst (sGRB) afterglow, and model-independent constraints on the EM emission from a hypothetical counterpart to GW190425 to date under the assumption that no counterpart was found in these data. If the counterpart were similar to AT 2017gfo, there would be a 28.4% chance of it being detected in the combined data set. We are relatively insensitive to an on-axis sGRB, and rule out a generic transient with a similar peak luminosity and decline rate as AT 2017gfo to 30% confidence. Finally, across our new imaging and publicly reported data, we find 28 candidate optical counterparts that we cannot rule out as being associated with GW190425, finding that four such counterparts discovered within the localization volume and within 5 days of merger exhibit luminosities consistent with a KN.

Keywords: Neutron stars, Black holes, Astronomy software, Astronomy databases, Gravitational waves, Transient detection
Low-energy Measurement of the <SUP>86</SUP>Kr(α, n)<SUP>89</SUP>Sr Reaction Cross Section and Its Impact on Weak R-process Nucleosynthesis. The cross section of the 86Kr(α, n)89Sr reaction was measured at low energies using the activation technique via the detection of the β‑ emission from the residual 89Sr nuclei. The theoretical analysis of the measured cross sections shows that the new data can be well described in the statistical model using several recent α-nucleus potentials. The resulting astrophysical reaction rate has small uncertainties between about 15% at higher temperatures and up to a factor of 2 at low temperatures. Using this new reaction rate of the 86Kr(α, n)89Sr reaction for the nucleosynthesis in neutrino-driven outflows in core-collapse supernovae leads to well-constrained production ratios for the nuclei slightly above krypton (Z = 36) like Sr/Zr, Y/Zr, and Mo/Zr. A comparison to observational ratios in metal-poor stars allows to constrain the astrophysical conditions for this weak r-process.

Keywords: R-process, Nuclear astrophysics, Explosive nucleosynthesis
GNHeII J1236+6215: A He II λ1640 Emitting and Potentially LyC Leaking Galaxy at z = 2.9803 Unveiled through JWST and Keck Observations. He II λ1640 emission in galaxies indicates the presence of sources that produce extreme ionizing photons. Here we report the discovery of a He II λ1640 emitting galaxy, GNHeII J1236+6215, at z = 2.9803 in the GOODS-north field. We use photometry in 17 wave bands from near-UV to infrared to characterize the galaxy spectral energy distribution (SED) and combine Keck Low-resolution Imaging Spectrometer and JWST NIRSpec spectra to identify 15 emission lines including He II λ1640. We infer that the He+ ionization in the galaxy could be driven by small pockets of young Population III stars or low-metallicity very massive stars rather than active galactic nuclei or metal-rich Wolf─Rayet stars. The galaxy has a highly ionized interstellar medium (ISM) ([O III]5007/[O II]3727 = 7.28 ± 0.11, [S III]/[S II] = 1.97 ± 0.48, and detected Lyα, Hα, Hβ, Hγ lines), little reddening by dust (E(B − V) = 0.04 ± 0.12), low metallicity (12 + log(O/H) = 7.85 ± 0.22), and high star formation rate (SFRSED = 12.2 ± 2.0 M⊙ yr−1). In addition to these ISM conditions, we also notice a significant [S II] deficiency ([S II]6718,6732/Hα = 0.08 ± 0.02, ∆[S II] = −0.12), which may indicate the presence of density-bounded optically thin H II regions that, combined with the low-dust extinction, favor leaking of ionizing Lyman continuum photons. Our best-fit SED model also infers a high nebular ionization (log U = −2.0) and a low stellar mass M = 7.8 ± 3.1 × 108M⊙. This discovery not only adds one important object to the known sample of high-redshift He II emitters but also highlights a potential connection between He+ ionization and favorable ISM conditions for the leakage of ionizing photons from galaxies.

Keywords: Lyman-break galaxies, Population III stars, Galaxy evolution, Galaxy spectroscopy, High-redshift galaxies
The Centre of Attention: A Powerful Radio Galaxy Pinpoints a Near-infrared-dark Protocluster at z ∼ 3.9. We report the discovery of a z ∼ 3.9 protocluster identified from Atacama Large Millimeter/submillimeter Array Band 3 spectral scans of a bright radio source selected from the Galactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. Extended CO(4─3) and [C I] (3P1 → 3P0) line emission was detected in GLEAM J005332−325630 confirming it to be a z = 3.879 powerful radio galaxy with luminosity L500 MHz = 1.3 × 1028 W Hz−1. This source is part of a sample of candidate high-redshift radio galaxies with bright radio fluxes, S150 MHz &gt; 0.1 Jy, but host galaxies with Ks(AB) ≳ 23 mag. The molecular gas associated with the radio galaxy host has two kinematically separate components, likely infalling and indicative of a recent interaction or merger with another galaxy. One 100 GHz continuum source ∼120 pkpc away is found to have both CO(4─3) and [C I] (3P1 → 3P0) emission lines and a further five protocluster members are identified from CO(4─3) emission alone, all at a similar redshift (∆v &lt; 700 km s−1) and within a radius of  1.'1 . Using photometry from the High Acuity Widefield K-band Imager Ks band and the Dark Energy Survey g, r, i, z, and Y bands, we find this protocluster harbours a rare, optically dark, very massive M* ∼ 1012 M⊙ galaxy. Comparisons with the TNG300 cosmological simulation puts this galaxy in a dark matter (DM) halo of MDM ∼ 3 × 1013 M⊙, which will evolve into a Coma-like DM halo (MDM ∼ 1015 M⊙) by the present day.

Keywords: Molecular gas, High-redshift galaxy clusters, Millimeter-wave spectroscopy, Radio galaxies, CO line emission, High-redshift galaxies
Gaussian Mixtures in Solar Wind Plasma Turbulence. Based on previous analyses of data from a fleet of space exploration missions, we argue that plasma fluctuations in the turbulent solar wind are consistently described by normal variance mixtures on a broad range of scales encompassing the inertial and kinetic scales. In the inertial range, the normal variance mixture distributions are derived from conditioning the Elsässer field increments either on fluctuations of the energy transfer rate or on fluctuations of the singularity strength. The two kinds of description can be linked to each other via bridging relations. An exact analytical expression for the even-order structure functions is obtained from a normal inverse Gaussian fit, accurate from inertial to dissipative scales in the plasma. The self-similar kappa distributions describing the kinetic scales result from an inverse χ2 distribution of the variance in the Gaussian mixture model.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Solar wind
High-resolution Observations of a Flare Associated with a Partial Filament Eruption on 2023 April 21. We investigate an eruptive M-class flare on 2023 April 21 (SOL2023-04-21T18:12) with observations from the Solar Dynamics Observatory and the Chinese Hα Solar Explorer. We discuss two stages of energy release, the preflare activity and the eruptive flare. The preflare phase features some brightening of the lower atmosphere, the rising motion of filament materials, and a brightening ribbon structure. We suggest that low-altitude magnetic reconnection triggers the eruptive activity. The reconnection between the ambient loops and continuously rising thread-like structures produced the well-formed parallel-ribbon flare. In the main flare phase, the filament experienced a partial eruption with significant plasma motion in the constrained part. We propose a double-decker filament structure based on the multiwavelength observations and analysis of the magnetic field.

Keywords: Solar activity, Solar atmosphere, Solar flares
Polarization Position Angle Swing and the Rotating Vector Model of Repeating Fast Radio Bursts. Fast radio bursts (FRBs), typically highly polarized, usually have a nearly constant polarization position angle (PA) during each burst. Some bursts show significant PA variations, and one of them was claimed to have a PA variation pattern consistent with the prediction of the rotating vector model (RVM) commonly adopted to fit the PA variations in radio pulsars. We systematically study the PA evolution pattern of 1727 bursts from three active repeating FRB sources monitored by the Five-hundred-meter Aperture Spherical Radio Telescope. We identify 46 bursts whose PA variations are fully consistent with the RVM. However, the inferred geometrical parameters and rotation periods derived from these RVM fittings are inconsistent from each other. This suggests that the magnetosphere of the FRB central engine is constantly distorted by the FRB emitter and the magnetic configuration is dynamically evolving.

Keywords: Neutron stars, Radio bursts, Radio transient sources
Distances of Supernova Remnants Associated with Neutron Stars in the Galaxy. Accurate distance measurements to supernova remnants (SNRs) are essential for determining their physical parameters, such as size, age, and explosion energy, and for constraining the properties of associated neutron stars (NSs). We present an extinction–distance method that combines precise Gaia DR3 photometry, parallax, and stellar parameters from the SHBoost catalog to homogeneously construct extinction–distance profiles for 44 NS-associated Galactic SNRs. Applying a statistical model, we identify clear extinction jumps along each sightline, corresponding to probable SNR distances. We classify the results into three reliability levels (A, B, and C), primarily based on comparisons with previously reported kinematic distances, supplemented by independent estimates from other methods. Our results show that the majority of reliable distances (17 Level A and 8 Level B) are located within 5 kpc, predominantly in the Local Arm. This study presents an independent and effective method for determining distances to SNRs, particularly for those with small angular sizes or located in the second and third Galactic quadrants. Although the current method is limited to within 5 kpc due to the precision constraints of Gaia parallax and photometry, the upcoming Gaia DR4 release, combined with complementary infrared data, will extend its applicability to more distant and heavily obscured SNRs and help resolve kinematic distance ambiguities.

Keywords: Interstellar dust, Neutron stars, Distance measure, Supernova remnants, Extinction
Refined Constraints on the Hubble Constant from Localized Fast Radio Bursts with Assessment of Systematic Effects. The dispersion measure─redshift relation of fast radio bursts (FRBs) provides a valuable cosmological probe for constraining the Hubble constant, offering an independent measurement that could help resolve the ongoing Hubble tension. In this paper, we begin with a sample of 117 localized FRBs and use 95 of them to constrain H0 to  71.28−2.08+1.90  km s−1 Mpc−1 within the standard Lambda cold dark matter model. The resulting statistical uncertainty is below 2.8%, improving previous FRB-based measurements and highlighting the promise of larger future samples. Beyond statistical improvements, we note that different parameter choices have been adopted in previous studies and some results show discrepancies in H0. To address this issue, we perform a systematic assessment of modeling uncertainties that can affect the inferred value of H0, including models of the Galactic electron density, the contribution of the Galactic halo, outliers such as FRB 20190520B located in extreme environments, and the other parameter selections. We also discuss possible approaches to mitigate these sources of uncertainty, emphasizing both the challenges and prospects of using FRBs as reliable cosmological tools.

Keywords: Hubble constant, Radio transient sources
Constraining the z ∼ 1 Initial Mass Function with HST and JWST Lensed Stars in MACS J0416.1−2403. Our understanding of galaxy properties and evolution is contingent on knowing the initial mass function (IMF), and yet to date the IMF is constrained only to local galaxies. Individual stars are now becoming routinely detected at cosmological distances, where luminous stars such as supergiants in background galaxies strongly lensed by galaxy clusters are temporarily further magnified by huge factors (up to 104) by intracluster stars, thus being detected as transients. The detection rate of these events depends on the abundance of luminous stars in the background galaxy and is thus sensitive to the IMF and the star formation history (SFH), especially for the blue supergiants detected as transients in the rest-frame ultraviolet/optical filters. As a proof of concept, we use simple SFH and IMF models constrained by spectral energy distributions (SEDs) to see how well we can predict the Hubble Space Telescope and James Webb Space Telescope transient detection rate in a lensed arc dubbed "Spock" (z = 1.0054). We find that demanding a simultaneous fit of the SED and the transient detection rate places constraints on the IMF, independent of the assumed simple SFH model. We conclude that our likelihood analysis indicates that the data definitively prefers the "Spock" galaxy to have a Salpeter IMF (α = 2.35) rather than a top-heavy IMF (α = 1)—which is thought to be the case in the early universe—with no clear excess of supergiants above the standard IMF.

Keywords: Gravitational microlensing, Galaxy clusters, Initial mass function