Sazuna/UAT_keywords huggingface dataset:
Eight Years of Light from ASASSN-15oi: Toward Understanding the Late-time Evolution of TDEs. We present results from an extensive follow-up campaign of the tidal disruption event (TDE) ASASSN-15oi spanning δt ∼ 10–3000 days, offering an unprecedented window into the multiwavelength properties of a TDE during its first ≈8 yr of evolution. ASASSN-15oi is one of the few TDEs with strong detections at X-ray, optical/UV, and radio wavelengths and it also featured two delayed radio flares at δt ∼ 180 days and δt ∼ 1400 days. Our observations at δt &gt; 1400 days reveal an absence of thermal X-rays, a late-time variability in the nonthermal X-ray emission, and sharp declines in the nonthermal X-ray and radio emission at δt ∼ 2800 days and ∼3000 days, respectively. The UV emission shows no significant evolution at δt &gt; 400 days and remains above the pre-TDE level. We show that a cooling envelope model can explain the thermal emission consistently across all epochs. We also find that a scenario involving episodic ejection of material due to stream–stream collisions can possibly explain the first radio flare. Given the peculiar spectral and temporal evolution of the late-time emission, however, constraining the origins of the second radio flare and the nonthermal X-rays remains challenging. Our study underscores the critical role of long-term, multiwavelength follow-up to fully characterize the extended evolutionary phases of a TDE.

Keywords: Accretion, Tidal disruption, X-ray transient sources, Ultraviolet transient sources, Radio transient sources
EPOCHS. I. The Discovery and Star-forming Properties of Galaxies in the Epoch of Reionization at 6.5 &lt; z &lt; 18 with PEARLS and Public JWST Data. We present in this paper the discovery, properties, and a catalog of 1165 high-redshift 6.5 &lt; z &lt; 18 galaxies found in deep JWST NIRCam imaging from the GTO PEARLS survey combined with data from JWST public fields. We describe our bespoke homogeneous reduction process and our analysis of these areas including the NEP, CEERS, GLASS, NGDEEP, JADES, and ERO SMACS-0723 fields with over 214 arcmin2 imaged to depths of ∼30 mag. We describe our rigorous methods for identifying these galaxies, involving the use of Lyman-break strength, detection significance criteria, visual inspection, and integrated photometric redshift probability distributions predominately at high redshift. Our sample is a robust and highly pure collection of distant galaxies from which we also remove brown dwarf stars, and calculate completeness and contamination from simulations. We include a summary of the basic properties of these z &gt; 6.5 galaxies, including their redshift distributions, UV absolute magnitudes, and star formation rates. Our study of these young galaxies reveals a wide range of stellar population properties as seen in their colors and SED fits, which we compare to stellar population models, indicating a range of star formation histories (SFHs), dust, active galactic nuceli, and/or nebular emission. We find that a strong trend exists between stellar mass and (U − V) color, as well as the existence of the "main-sequence" of star formation for galaxies as early as z ∼ 12. This indicates that stellar mass, or an underlying variable correlating with stellar mass, is driving galaxy formation, in agreement with simulation predictions. We also discover ultra-high-redshift candidates at z &gt; 12 in our sample and describe their properties. Finally, we note a significant observed excess of galaxies compared to models at z &gt; 12, revealing a tension between predictions and our observations.

Keywords: Extragalactic astronomy, Galaxy evolution
The Distance of Quasar Outflows from the Central Source: The First Consistent Values from Emission and Absorption Determinations. Measuring the distance of quasar outflows from the central source (R) is essential for determining their importance for active galactic nucleus feedback. There are two methods to measure R: (1) a direct determination using spatially resolved integral field spectroscopy (IFS) of the outflow in emission and (2) an indirect method that uses the absorption troughs from ionic excited states. The column density ratio between the excited and resonance states yields the outflow number density. Combined with a knowledge of the outflow's ionization parameter, R can be determined. Generally, the IFS method probes an R range of several kiloparsecs or more, while the absorption method usually yields R values of less than 1 kpc. There is no inconsistency between the two methods as the determinations come from different objects. Here we report the results of applying both methods to the same quasar outflow, where we derive consistent determinations of R ≍ 5 kpc. This is the first time that the indirect absorption R determination is verified by a direct spatially resolved IFS observation. In addition, the velocities (and energetics) from the IFS and absorption data are found to be consistent. Therefore, these are two manifestations of the same outflow. In this paper we concentrate on the absorption R determination for the outflow seen in quasar 3C 191 using Very Large Telescope/X-shooter observations. We also reanalyze an older absorption determination for the outflow based on Keck/High Resolution Echelle Spectrometer data and find the revised measurement to be consistent with ours. Our companion paper details the IFS analysis of the same object.

Keywords: AGN host galaxies, Quasar absorption line spectroscopy, Quasars, Active galactic nuclei, Galaxies
Anisotropic Velocity Fluctuations in Galaxy Mergers: A Probe of the Magnetic Field. Magnetic fields and turbulence are fundamental to the evolutions of galaxies, yet their precise measurement and analysis present significant challenges. The recently developed Velocity Gradient Technique (VGT), which capitalizes on the anisotropy inherent in magnetohydrodynamic (MHD) turbulence, represents a new method for mapping magnetic fields in galaxies using spectroscopic observations. Most validations of VGT thus far have relied upon idealized MHD turbulence simulations, however, which lack the more complex dynamics found in galaxies and galaxy mergers. In this study, we scrutinize VGT using an AREPO-based cosmological galaxy merger simulation, testing its effectiveness across pre-merger, merging, and post-merger stages. We examine the underlying assumptions of VGT and probe the statistics of gas density, velocity, and magnetic fields over time. We find that the velocity fluctuations are indeed anisotropic at each stage, being larger in the direction perpendicular to the local magnetic field, as required by VGT. We find additionally that galaxy mergers substantially intensify the velocity and density fluctuations and amplify the magnetic fields at all scales. The observed scaling of the velocity fluctuations shows a steeper trend than r1/2 between 0.6 and 3 kpc and a shallower trend at larger scales. The scaling of the magnetic field and density fluctuations at scales ≲1.0 kpc also predominantly aligns with r1/2. Finally, we compare results from VGT to those derived from polarization-like mock magnetic field measurements, finding consistent and statistically significant global agreement in all cases.

Keywords: Galaxy magnetic fields, Galaxy mergers, Galaxy evolution, Magnetohydrodynamical simulations
Two Phases of Particle Acceleration of a Solar Flare Associated with In Situ Energetic Particles. How impulsive solar energetic particle (SEP) events are produced by magnetic-reconnection-driven processes during solar flares remains an outstanding question. Here we report a short-duration SEP event associated with an X-class eruptive flare on 2021 July 3, using a combination of remote sensing observations and in situ measurements. The in situ SEPs were recorded by multiple spacecraft including the Parker Solar Probe. The hard X-ray (HXR) light curve exhibits two impulsive periods. The first period is characterized by a single peak with a rapid rise and decay, while the second period features a more gradual HXR light curve with a harder spectrum. Such observation is consistent with in situ measurements: the energetic electrons were first released during the early impulsive phase when the eruption was initiated. The more energetic in situ electrons were released several minutes later during the second period of the impulsive phase when the eruption was well underway. This second period of energetic electron acceleration also coincides with the release of in situ energetic protons and the onset of an interplanetary type III radio burst. We conclude that these multimessenger observations favor a two-phase particle acceleration scenario: the first, less energetic electron population was produced during the initial reconnection that triggers the flare eruption, and the second, more energetic electron population was accelerated in the region above the loop-top below a well-developed, large-scale reconnection current sheet induced by the eruption.

Keywords: Solar energetic particles, Solar radio emission, Solar flares, Solar x-ray emission
Subphotospheric Emission from Short Gamma-Ray Bursts. II. Signatures of Nonthermal Dissipation in the Multi-messenger Signals. Building on a general relativistic magnetohydrodynamic simulation of a short gamma-ray burst (sGRB) jet with initial magnetization σ0 = 150, propagating through the dynamical ejecta from a binary neutron star merger, we identify regions of energy dissipation driven by magnetic reconnection and collisionless subshocks within different scenarios. We solve the transport equations for photons, electrons, protons, neutrinos, and intermediate particles up to the photosphere, accounting for all relevant radiative processes, including electron and proton acceleration, and investigate the potential impact of magnetic reconnection occurring in different regions along the jet. We find the photon spectra undergo nonthermal modifications below the photosphere, observable in both on-axis and off-axis emission directions, as well as across different scenarios of energy dissipation and subsequent particle acceleration. Interestingly, the spectral index of the photon energy distribution can vary at most by ∼20% across all different dissipation scenarios. Depending on the dissipation mechanism at play, neutrino signatures may accompany the photon signal, pointing to efficient proton acceleration and shedding light on jet physics. Although our findings are based on one jet simulation, they point to a potential universal origin of the nonthermal features of the Band spectrum observed in sGRBs.

Keywords: Gamma-ray bursts, Transient sources, Particle astrophysics
Follow-up of Neutron Star Mergers with CTA and Prospects for Joint Detection with Gravitational-wave Detectors. The joint gravitational wave (GW) and electromagnetic observations of the binary neutron star (BNS) merger GW170817 marked a giant leap in multimessenger astrophysics. The extensive observation campaign of the associated gamma-ray burst (GRB) and its afterglow has strengthened the hypothesis associating GRBs with BNS mergers and provided insights into mass ejection, particularly the relativistic outflow launched in BNS mergers. In this paper, we investigate the joint detection probabilities of BNS mergers by GW detectors and the upcoming ground-based very-high-energy (VHE) γ-ray instrument, the Cherenkov Telescope Array (CTA). Using an empirical relation that constrains the distance–inclination angle plane, we simulated BNS mergers detectable in the O5 run of the LIGO/Virgo/Kagra network with a 300 Mpc BNS horizon. Assuming Gaussian structured jets and ignoring the large sky localization challenges of GW detectors, we estimated probability of detection of the VHE afterglow by CTA. We have explored the afterglow parameter space to identify conditions favourable for detecting synchrotron self-Compton emission by CTA. Our study reveals that events viewed at angles ≲3 times the jet core angle are detectable by CTA when the initial bulk Lorentz factor at the jet axis ranges between 100 and 800. We find high kinetic energy (Ek &gt; 1050 erg), ambient density (n0 &gt; 10‑1 cm‑3), and energy content in nonthermal electrons significantly enhance the likelihood of CTA detection within 300 Mpc. The joint detection rate varies significantly with afterglow parameter distributions, ranging from 0.003 to 0.5 per year.

Keywords: Gamma-ray bursts, Jets, Gravitational waves
On the Extremely X-Ray Variable Active Galactic Nuclei in the XMM-LSS Field. We present a systematic investigation of extremely X-ray variable active galactic nuclei (AGNs) in the ≈5.3 deg2 XMM-SERVS XMM-LSS region. Eight variable AGNs are identified with rest-frame 2 keV flux density variability amplitudes around 6–12. We comprehensively analyze the X-ray and multiwavelength data to probe the origin of their extreme X-ray variability. It is found that their extreme X-ray variability can be ascribed to changing accretion state or changing obscuration from dust-free absorbers. For five AGNs, their X-ray variability is attributed to changing accretion state, supported by contemporaneous multiwavelength variability and the absence of X-ray absorption in the low-state spectra. With new Multiple Mirror Telescope (MMT) spectra for four of these sources, we confirm one changing-look AGN. One MMT AGN lacks multiepoch spectroscopic observations, while the other two AGNs do not exhibit changing-look behavior, likely because the MMT observations did not capture their high states. The X-ray variability of the other three AGNs is explained by changing obscuration, and they show only mild long-term optical/IR variability. The absorbers of these sources are likely clumpy accretion-disk winds, with variable column densities and covering factors along the lines of sight.

Keywords: Quasars, Active galaxies, Active galactic nuclei, X-ray active galactic nuclei, Galaxies
Digging Into the Interior of Hot Cores with ALMA (DIHCA). V. Deuterium Fractionation of Methanol. We have observed the 13CH3OH 51‑41 A+, 13CH3OH 141‑132 A‑, and CH2DOH 82,6‑81,7 e0 lines toward 24 high-mass star-forming regions by using Atacama Large Millimeter/submillimeter Array with an angular resolution of about 0 3. This resolution corresponds to a linear scale of 400–1600 au, allowing us to resolve individual cores properly. We detected the 13CH3OH and CH2DOH emission near the continuum peaks in many of these regions. From the two 13CH3OH lines, we calculated the temperature toward the 13CH3OH peaks, and confirm that the emission traces hot (&gt;100 K) regions. The N(CH2DOH)/N(12CH3OH) ratio in the observed high-mass star-forming regions is found to be lower than that in low-mass star-forming regions. We have found no correlation between the N(CH2DOH)/N(13CH3OH) or N(CH2DOH)/N(12CH3OH) ratios and either temperatures or distance to the sources, and have also found a source-to-source variation in these ratios. Our model calculations predict that the N(CH2DOH)/N(12CH3OH) ratio in hot cores depends on the duration of the cold phase; the shorter the cold phase, the lower the deuterium fractionation in the hot cores. We have suggested that the lower N(CH2DOH)/N(12CH3OH) ratio in high-mass star-forming regions compared to that in low-mass star-forming regions is due to the shorter duration of the cold phase and that the diversity in the N(CH2DOH)/N(12CH3OH) ratio in high-mass star-forming regions is due to the diversity in the length of the cold prestellar phase, and not the time that the objects have been in the hot core phase.

Keywords: Interstellar molecules, Star forming regions, Molecular clouds, Astrochemistry
Data-constrained Magnetohydrodynamic Simulation for Magnetic Flux Rope Eruptions Driven by Magnetic Reconnection. We conducted data-constrained magnetohydrodynamic (MHD) simulations for solar active region (AR) NOAA AR 11429, which produced two X-class flares within a span of 63 minutes. The simulations were performed using the zero-β MHD approximation, with the initial condition derived from the nonlinear force-free field extrapolated from the photospheric magnetograms taken 2 hr before the first X5.4 flare. During the simulation, we enhanced magnetic reconnection locally by applying anomalous resistivity in the induction equation within the regions of interest. As a result, the simulations successfully reproduced the expansion of two magnetic flux ropes (MFRs) corresponding to the two observed eruptions. The result shows that the difference in stability between the two MFRs is related to the location of the magnetic reconnection that triggers the solar eruptions. Furthermore, comparison with the analysis of failed MFR eruptions indicates that both the initiation reconnection and the subsequent driving mechanism, torus instability, are equally important for a successful eruption. This simulation reveals a new mechanism in which long loops, formed via tether-cutting reconnection, push up the overlying twisted field lines, leading to their destabilization by torus instability.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Solar flares, Magnetohydrodynamical simulations
Mass Transfer in Eccentric Orbits with Self-consistent Stellar Evolution. We investigate Roche lobe overflow mass transfer (MT) in eccentric binary systems between stars and compact objects (COs), modeling the coupled evolution of both the star and the orbit due to eccentric MT (eMT) in a self-consistent framework. We implement the analytic expressions for secular rates of change of the orbital semimajor axis and eccentricity, assuming a delta function MT at periapse, in the binary stellar evolution code MESA. Two scenarios are examined: (1) a simplified model isolating the effects of eMT on stellar and orbital evolution, and (2) realistic binary configurations that include angular momentum exchange (e.g., tides, mass loss, spin–orbit coupling, and gravitational-wave (GW) radiation). Unlike the ad hoc approach of instant circularization that is often employed, explicit modeling of eMT reveals that a large fraction of binaries can remain eccentric post-MT. Even binaries that naturally circularize during eMT have different properties (donor mass and orbital size) compared to predictions from instant circularization, with some showing fundamentally different evolutionary outcomes (e.g., stable vs. unstable MT). We demonstrate that a binary's initial mass ratio and eccentricity are predictive of whether it will remain eccentric or circularize after eMT. These findings underscore the importance of eMT in understanding CO-hosting binary populations, including X-ray binaries, GW sources, and other high-energy transients.

Keywords: Neutron stars, Binary stars, Black holes, Close binary stars, Stellar populations, Compact binary stars, Interacting binary stars, Gravitational wave sources, Stellar evolutionary models, Compact objects, Astronomical simulations
Radiation Transport Simulations of Quasiperiodic Eruptions from Star–Disk Collisions. Periodic collisions between a star on an inclined orbit around a supermassive black hole and its accretion disk offer a promising explanation for X-ray "quasiperiodic eruptions" (QPEs). Each passage through the disk midplane shocks and compresses gas ahead of the star, which subsequently re-expands above the disk as a quasi-spherical cloud. We present spherically symmetric Monte Carlo radiation transport simulations that follow the production of photons behind the radiation-mediated shock, Comptonization by hot electrons, and the eventual escape of the radiation through the expanding debris. Such 1D calculations are approximately justified for thin disks (scale-height h ≲ few × R⋆), through which the star of radius R⋆ passes more quickly than the shocked gas can flow around the star. For collision speeds vcoll ≳ 0.15c and disk surface densities Σ ∼ 103 g cm‑2 characteristic of those encountered by stellar orbits consistent with QPE recurrence times, the predicted transient light curves exhibit peak luminosities ≳1042 erg s‑1 and Comptonized quasi-thermal (Wien-like) spectra that peak at energies hν ∼ 100 eV, which is broadly consistent with QPE properties. For these conditions, gas and radiation are out of equilibrium, rendering the emission temperature harder than the blackbody value due to inefficient photon production behind the radiation-mediated shock. The predicted eruptions execute counterclockwise loops in hardness–luminosity space, qualitatively similar to QPE observations. Reproducing the observed eruption properties (duration, luminosity, temperature) requires a large radius R⋆ ≳ 10 R⊙, which may point to inflation of the star's atmosphere from repeated collisions.

Keywords: X-ray transient sources, Supermassive black holes, Tidal disruption
Lagrangian Perturbation Theory for Biased Tracers: Significance of the Number Conservation. The Lagrangian perturbation theory provides a simple yet powerful way of computing the nonlinear matter power spectrum, and it has been applied to biased tracers such as halos and galaxies. The number conservation of matter particles allows a simple relation between the fluctuations at the initial and late times, which is essential in deriving the exact expression for the nonlinear matter power spectrum. Here, we investigate the significance of the number conservation in the Lagrangian perturbation theory for biased tracers. We use N-body simulations to test the significance of the number conservation, by tracing dark matter halo samples in time. For the mass-bin sample   at z ≃ 3, the theoretical predictions for the halos overestimate the power spectrum at z = 0 by a factor of 3, while the simulation results match the theoretical predictions if the number conservation of halos is imposed in the simulations throughout the evolution. Starting with a halo sample at z = 0 as another test, we trace back in time the particles that belong to the halos at z = 0 and use their center-of-mass positions as halo positions at z &gt; 0. The halo power spectra at z &gt; 0 from the simulations agree with the theoretical predictions of the Lagrangian perturbation theory. This numerical experiment proves that the number conservation is crucial in the Lagrangian perturbation theory predictions. We discuss the implications for various applications of the Lagrangian perturbation theory for biased tracers.

Keywords: Cosmology, Large-scale structure of the universe
Nonlinear Evolution of the Kelvin–Helmholtz Instability in the Presence of Radiation and Parallel Magnetic Fields. The evolution of Kelvin–Helmholtz (KH) instability in the Orion Nebula is studied using a two-dimensional radiation magnetohydrodynamic (MHD) simulation in the presence of the in-plane magnetic field parallel to the flow direction. The linear results show that the parallel component of the magnetic field can stabilize the instability due to the increase of the field line tension, while the radiation field leads to the reduced compressibility of the system and enhances the growth of the instability. When the interface is subjected to more radiation pressure, it is found that a greater saturation magnetic energy is produced, and there is a transfer of the kinetic energy to the thermal energy in the nonlinear evolution of the KH instability. The radiation pressure also accelerates the development of instability at the interface, resulting in a large vortex structure in the nonlinear phase. The results also reveal the relaxation mechanism of the velocity profile caused by momentum transport in the nonlinear phase. The complete evolution of the KH instability as the result of a combination of dynamo effects and energy release is also discussed. Based on these results, a preliminary discussion of several events observed in star-forming regions is given.

Keywords: Magnetic fields, Astronomical radiation sources