Sazuna/UAT_keywords huggingface dataset:
Constraining the Equation of State of Hybrid Stars Using Recent Information from Multidisciplinary Physics. At the ultrahigh densities existing in the core of neutron stars (NSs), it is expected that a phase transition from baryonic to deconfined quark matter may occur. Such a phase transition would affect the underlying equation of state (EoS) as well as the observable astrophysical properties of NSs. Comparison of EoS model predictions with astronomical data from multimessenger signals then provides us an opportunity to probe the behavior of dense matter. In this work, we restrict the allowed parameter space of EoS models in NSs for both nucleonic (relativistic mean field model) and quark matter (MIT bag model) sectors by imposing state-of-the-art constraints from nuclear calculations, multimessenger astrophysical data, and perturbative quantum chromodynamics (pQCD). We systematically investigate the effect of each constraint on the parameter space of uncertainties using a cutoff filter scheme, as well as the correlations among the parameters and with NS astrophysical observables. Using the constraints, we obtain limits for maximum NS mass, maximum central density, as well as for NS radii and tidal deformability. Although pQCD constraints are only effective at very high densities, they significantly reduce the parameter space of the quark model. We also conclude that astrophysical data supports high values of the bag parameter B and disfavors the existence of a pure quark matter core in hybrid stars.

Keywords: Neutron stars, Neutron star cores, High energy astrophysics, Gravitational waves, Particle astrophysics
A Statistical Study of Short-period Decayless Oscillations of Coronal Loops in an Active Region. Coronal loop oscillations are common phenomena in the solar corona, which are often classified as decaying and decayless oscillations. Using the high-resolution observation measured by the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter, we statistically investigate small-scale transverse oscillations with short periods (&lt;200 s) of coronal loops in an active region (AR), i.e., NOAA AR 12965. A total of 111 coronal loops are identified in EUI 174 Å images, and they all reveal transverse oscillations without any significant decaying, regarded as decayless oscillations. Oscillatory periods are measured from ~11 to ~185 s, with a median period of 40 s. Thus, they are also termed short-period oscillations. The corresponding loop lengths are measured from ~10.5 to ~30.2 Mm, and a strong dependence of oscillatory periods on loop lengths is established, indicating that the short-period oscillations are standing kink-mode waves in nature. Based on the coronal seismology, kink speeds are measured to be ~330-1910 km s-1, and magnetic field strengths in coronal loops are estimated to be ~4.1-25.2 G, while the energy flux carried by decayless kink oscillations lies in the range from roughly 7 to 9220 W m-2. Our estimations suggest that the wave energy carried by short-period decayless kink oscillations cannot support the coronal heating in the AR.

Keywords: Magnetohydrodynamics, Solar ultraviolet emission, Solar coronal loops, Solar oscillations, Solar coronal seismology
Orbital- and Spin-phase Variability in the X-Ray Emission from the Accreting Pulsar Centaurus X-3. We present a time-resolved analysis using 39 ks NuSTAR observation data of the X-ray pulsar Centaurus X-3, covering an orbital-phase interval of Φ = 0.199-0.414. The orbital- and spin-phase variabilities are investigated through time-resolved spectra, light curves, and pulse profiles. The orbital-phase variability was due to the mixture of two comparable effects: intrinsic flux variability of ~10% and obscuration by the clumpy stellar wind. The typical size and number density of the clumps are ~9 × 1010 cm and ~3 × 1012 cm-3, respectively. In the spin-phase-resolved analysis, we detected variations in the spectral features of the continuum, the Fe line, and the cyclotron resonance scattering feature (CRSF). The photon index ranged from 0.72 to 1.06, corresponding to the difference in the Comptonization optical depth by a factor of ~1.6. The equivalent width and intensity of the Fe line had negative correlations with the continuum flux. The central energy and the strength of the CRSF increased at the pulse maximum. The former ranged from 26.0 to 28.7 keV, while the latter varied by a factor of ~1.9. The pulse profile was double-peaked in the low-energy band, and it gradually shifted to being single-peaked with energy, indicating the existence of two distinct emission patterns, corresponding to the pencil and fan beams. Finally, we found that the pulse profiles were highly stable along the orbital phase, within a variation degree of ~20%, which provides evidence of the highly stable accretion stream of the binary system.

Keywords: Accretion, Neutron stars
Rotational Fingerprints of Vinylketene for Astronomical Observations. A high degree of isomerism in the realm of interstellar molecules stimulates systematic astronomical investigations of members of different families of isomers. Among them, vinyl-bearing compounds have kindled considerable interest due to recent detections of vinylamine, vinylacetylene, and vinylcyanoacetylene. Herein, we open the possibility to search for vinylketene in the interstellar space by means of its rotational transitions. The pure rotational spectrum of the title molecule was recorded in the frequency regions 195-218 and 293-324 GHz and an improved and extended set of spectroscopic parameters has been obtained for the most stable trans conformer. In addition, rotational signatures and molecular constants for the less stable cis form are reported for the first time. We provide a catalog of precise transition frequencies and intensities of vinylketene to the astronomical community and pave the way toward interstellar explorations of C4H4O isomer family.

Keywords: Interstellar molecules, Experimental data, Molecular spectroscopy, Laboratory astrophysics, Catalogs
Boundary Conditions in Hydrodynamic Simulations of Isolated Galaxies and Their Impact on the Gas-loss Processes. Three-dimensional hydrodynamic simulations are commonly used to study the evolution of the gaseous content in isolated galaxies, besides its connection with galactic star formation histories. Stellar winds, supernova blasts, and black hole feedback are mechanisms usually invoked to drive galactic outflows and decrease the initial galactic gas reservoir. However, any simulation imposes the need of choosing the limits of the simulated volume, which depends, for instance, on the size of the galaxy and the required numerical resolution, besides the available computational capability to perform it. In this work, we discuss the effects of boundary conditions on the evolution of the gas fraction in a small-sized galaxy (tidal radius of ~1 kpc), like classical spheroidal galaxies in the Local Group. We found that open boundaries with sizes smaller than approximately 10 times the characteristic radius of the galactic dark-matter halo become unappropriated for this kind of simulation after ~0.6 Gyr of evolution, since they act as an infinity reservoir of gas due to dark-matter gravity. We also tested two different boundary conditions that avoid gas accretion from numerical frontiers: closed and selective boundary conditions. Our results indicate that the later condition (that uses a velocity threshold criterion to open or close frontiers) is preferable since it minimizes the number of reversed shocks due to closed boundaries. Although the strategy of putting computational frontiers as far as possible from the galaxy itself is always desirable, simulations with a selective boundary condition can lead to similar results at lower computational costs.

Keywords: Hydrodynamical simulations, Computational methods, Dwarf galaxies, Galaxy evolution
A Special State Transition in the Blazar OT 081: Implication for the Unified State Transition Paradigm of Different-scale Black Hole Systems. Exploring the similar behavior of black hole systems with different scales will provide insight into the unified physical laws of black hole systems. Here, we report a special spectral state transition process in blazar OT 081, which is driven by a supermassive black hole. Based on the X-ray flux versus photon index distribution, stacked average X-ray spectra, L 2500Å  - α ox parameters, and broadband spectral energy distributions, we conducted a pilot study on the spectral state transition for this blazar system. The analysis results suggest that the source transitions through a steady-state point from a strong corona, weak jet unsteady state to a weak corona, strong jet unsteady state. This state transition behavior is similar to that observed in the much smaller Galactic black hole binary systems, providing further observational evidence for the possible existence of a unified state transition paradigm for black hole systems with different scales.

Keywords: Blazars
Pre-acceleration in the Electron Foreshock. II. Oblique Whistler Waves. Thermal electrons have gyroradii many orders of magnitude smaller than the finite width of a shock, thus need to be pre-accelerated before they can cross it and be accelerated by diffusive shock acceleration. One region where pre-acceleration may occur is the inner foreshock, which upstream electrons must pass through before any potential downstream crossing. In this paper, we perform a large-scale particle-in-cell simulation that generates a single shock with parameters motivated from supernova remnants. Within the foreshock, reflected electrons excite the oblique whistler instability and produce electromagnetic whistler waves, which comove with the upstream flow and as nonlinear structures eventually reach radii of up to 5 ion-gyroradii. We show that the inner electromagnetic configuration of the whistlers evolves into complex nonlinear structures bound by a strong magnetic field around four times the upstream value. Although these nonlinear structures do not in general interact with cospatial upstream electrons, they resonate with electrons that have been reflected at the shock. We show that they can scatter, or even trap, reflected electrons, confining around 0.8% of the total upstream electron population to the region close to the shock where they can undergo substantial pre-acceleration. This acceleration process is similar to, yet approximately three times more efficient than, stochastic shock drift acceleration.

Keywords: Supernova remnants, Shocks
Pegasus W: An Ultrafaint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization. We report the discovery of an ultrafaint dwarf (UFD) galaxy, Pegasus W, located on the far side of the Milky Way-M31 system and outside the virial radius of M31. The distance to the galaxy is ${915}_{-91}^{+60}$ kpc, measured using the luminosity of horizontal branch stars identified in Hubble Space Telescope optical imaging. The galaxy has a half-light radius (r  h ) ${100}_{-13}^{+11}$ pc, ${M}_{V}=-{7.20}_{-0.16}^{+0.17}$ mag, and a present-day stellar mass ${6.5}_{-1.4}^{+1.1}\times {10}^{4}$ M ⊙. We identify sources in the color-magnitude diagram (CMD) that may be younger than ~500 Myr, suggesting late-time star formation in the UFD galaxy, although further study is needed to confirm these are bona fide young stars in the galaxy. Based on fitting the CMD with stellar evolution libraries, Pegasus W shows an extended star formation history. Using the τ 90 metric (defined as the timescale by which the galaxy formed 90% of its stellar mass), the galaxy was quenched only ${7.4}_{-2.6}^{+2.2}$ Gyr ago, which is similar to the quenching timescale of a number of UFD satellites of M31 but significantly more recent than the UFD satellites of the Milky Way. Such late-time quenching is inconsistent with the more rapid timescale expected by reionization and suggests that, while not currently a satellite of M31, Pegasus W was nonetheless slowly quenched by environmental processes.

Keywords: Local Group, Hertzsprung Russell diagram
Phase-space Energization of Ions in Oblique Shocks. Examining energization of kinetic plasmas in phase space is a growing topic of interest, owing to the wealth of data in phase space compared to traditional bulk energization diagnostics. Via the field-particle correlation (FPC) technique and using multiple means of numerically integrating the plasma kinetic equation, we have studied the energization of ions in phase space within oblique collisionless shocks. The perspective afforded to us with this analysis in phase space allows us to characterize distinct populations of energized ions. In particular, we focus on ions that reflect multiple times off the shock front through shock-drift acceleration, and how to distinguish these different reflected populations in phase space using the FPC technique. We further extend our analysis to simulations of three-dimensional shocks undergoing more complicated dynamics, such as shock ripple, to demonstrate the ability to recover the phase-space signatures of this energization process in a more general system. This work thus extends previous applications of the FPC technique to more realistic collisionless shock environments, providing stronger evidence of the technique's utility for simulation, laboratory, and spacecraft analysis.

Keywords: Space plasmas, High energy astrophysics, Plasma physics, Plasma astrophysics, Shocks
Feature Identification and Statistical Characteristics of Quasi-periodic Pulsation in Solar Flares using the Markov-Chain-Monte-Carlo Approach. Quasi-periodic pulsation (QPP) is a common phenomenon in solar flares. Studying QPP is important to further our understanding of the physical processes operating in flares. However, detection of QPP is complicated by the presence of noise in flaring lightcurves. In this study, we apply the Bayesian-based Markov-Chain-Monte-Carlo (MCMC) technique to the QPP detection. We use MCMC to fit the Fourier power spectral density (PSD) profiles of flaring lightcurves, aiming to determine a quasi-periodic component by model comparison and test statistics. Two models fitting the PSD were compared: the first model consists of colored and white noise only, and the second model adds a spectral peak of a Gaussian shape representing a short-living oscillatory signal. To evaluate MCMC of the QPP detection, we test it on 100 synthetic signals with spectral properties similar to those observed in flares. Subsequently, we analyzed QPP events in 699 flare signals in the 1-8 Å channel recorded by the Geostationary Operational Environmental Satellite from 2010 to 2017, including 250 B-class, 250 C-class, 150 M-class, and 49 X-class flares. Approximately 57% X-class, 39% M-class, 20% C-class, and 16% B-class flares are found to show a strong evidence of QPP, whose periods range mainly from 6.2 to 75.3 s. The results demonstrate that QPP events are easier to detect in more powerful flares. The distribution of the detected QPP periods is found to follow a logarithmic normal distribution. The distributions in the four flare classes are similar. This suggests that the established distribution is a common feature for flares of different classes.

Keywords: Solar activity, Solar flares, Solar flare spectra, Solar oscillations
Modeling CO Line Profiles in Shocks of W28 and IC 443. Molecular emission arising from the interactions of supernova remnant (SNR) shock waves and molecular clouds provide a tool for studying the dispersion and compression that might kick-start star formation as well as understanding cosmic-ray production. Purely rotational CO emission created by magnetohydrodynamic shock in the SNR-molecular cloud interaction is an effective shock tracer, particularly for slow-moving, continuous shocks into cold inner clumps of the molecular cloud. In this work, we present a new theoretical radiative transfer framework for predicting the line profile of CO with the Paris-Durham 1D shock model. We generated line profile predictions for CO emission produced by slow, magnetized C shocks into gas of density ~104 cm-3 with shock speeds of 35 and 50 km s-1. The numerical framework to reproduce the CO line profile utilizes the large velocity gradient (LVG) approximation and the omission of optically thick plane-parallel slabs. With this framework, we generated predictions for various CO spectroscopic observations up to J = 16 in SNRs W28 and IC 443, obtained with SOFIA, IRAM-30 m, APEX, and KPNO. We found that CO line profile prediction offers constraints on the shock velocity and pre-shock density independent of the absolute line brightness and requires fewer CO lines than diagnostics using a rotational excitation diagram.

Keywords: Supernova remnants, Magnetohydrodynamics, Radiative transfer, Interstellar medium
Multistage Reconnection Powering a Solar Coronal Jet. Coronal jets are short-lived eruptive features commonly observed in polar coronal holes and are thought to play a key role in the transfer of mass and energy into the solar corona. We describe unique contemporaneous observations of a coronal blowout jet seen by the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter (SO) spacecraft and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The coronal jet erupted from the south polar coronal hole, and was observed with high spatial and temporal resolution by both instruments. This enabled identification of the different stages of a breakout reconnection process producing the observed jet. We find bulk plasma flow kinematics of ~100-200 km s-1 across the lifetime of its observed propagation, with a distinct kink in the jet where it impacted and was subsequently guided by a nearby polar plume. We also identify a faint faster feature ahead of the bulk plasma motion propagating with a velocity of ~715 km s-1, which we attribute to untwisting of newly reconnected field lines during the eruption. A differential emission measure (DEM) analysis using the SDO/AIA observations revealed a very weak jet signal, indicating that the erupting material was likely much cooler than the coronal passbands used to derive the DEM. This is consistent with the very bright appearance of the jet in the Lyα passband observed by SO/EUI. The DEM was used to estimate the radiative thermal energy of the source region of the coronal jet, finding a value of ~2 × 1024 erg, comparable to the energy of a nanoflare.

Keywords: Solar coronal holes, Solar corona, Solar extreme ultraviolet emission, Solar filament eruptions
The Runaway Greenhouse on Sub-Neptune Waterworlds. The implications of the water vapor runaway greenhouse phenomenon for water-rich sub-Neptunes are developed. In particular, the nature of the postrunaway equilibration process for planets that have an extremely high water inventory is addressed. Crossing the threshold from subrunaway to superrunaway conditions leads to a transition from equilibrated states with cold, deep liquid oceans and deep interior ice-X phases to states with hot supercritical fluid interiors. There is a corresponding marked inflation of radius for a given mass, similar to the runaway greenhouse radius inflation effect noted earlier for terrestrial planets, but in the present case the inflation involves the entire interior of the planet. The calculation employs the AQUA equation-of-state database to simplify the internal structure calculation. Some speculations concerning the effect of H2 admixture, silicate cores, and hot- versus cold-start evolution trajectories are offered. Observational implications are discussed though the search for the mass-radius signature of the phenomena considered is limited by degeneracies and by lack of data.

Keywords: Exoplanet atmospheres
GRB 200829A: External-shock Origin of the Very Early Prompt Emission?. Long-duration GRB 200829A was detected by Fermi-GBM and Swift-BAT/XRT, and then rapidly observed by other ground-based telescopes. It has a weak γ-ray emission in the very early phase and is followed by a bright spiky γ-ray emission pulse. The radiation spectrum of the very early emission is best fitted by a power-law function with index ~-1.7. However, the bright spiky γ-ray pulse, especially the time around the peak, exhibits a distinct two-component radiation spectrum, i.e., Band function combined with a blackbody radiation spectrum. We infer the photospheric properties and reveal a medium magnetization at a photospheric position by adopting the initial size of the outflow as r 0 = 109 cm. It implies that the Band component in this pulse may be formed during the dissipation of the magnetic field. The power-law radiation spectra found in the very early prompt emission may imply the external-shock origination of this phase. Then, we perform the Markov Chain Monte Carlo method fitting on the light curves of this burst, where the jet corresponding to the γ-ray pulse at around 20 s is used to refresh the external shock. It is shown that the light curves of the very early phase and X-ray afterglow after 40 s, involving the X-ray bump at around 100 s, can be well modeled in the external-shock scenario. For the obtained initial outflow, we estimate the minimum magnetization factor of the jet based on the fact that the photospheric emission of this jet is missed in the very early phase.

Keywords: Gamma-ray bursts
The Origins of Calcium-rich Supernovae From Disruptions of CO White Dwarfs by Hybrid He-CO White Dwarfs. Calcium-rich explosions are very faint (M B ~ -15.5), type I supernovae (SNe) showing strong Ca lines, mostly observed in old stellar environments. Several models for such SNe have been explored and debated, but none were able to reproduce consistently the observed properties of Ca-rich SNe, nor their rates and host-galaxy distributions. Here we show that the disruptions of low-mass carbon-oxygen (CO) white dwarfs (WDs) by hybrid helium-CO (HeCO) WDs during their merger could explain the origin and properties of such SNe. We make use of detailed multidimensional hydrodynamical-thermonuclear (FLASH) simulations to characterize such explosions. We find that the accretion of CO material onto an HeCO-WD heats its He shell and eventually leads to its "weak" detonation and ejection and the production of a sub-energetic ~1049 erg Ca-rich SN, while leaving the CO core of the HeCO-WD intact as a hot remnant WD, possibly giving rise to X-ray emission as it cools down. We model the detailed light curves and spectra of such explosions and find excellent agreement with the observations of Ia/c Ca-rich, and potentially Ib Ca-rich, SNe. We thereby provide a viable, consistent model for the origins of Ca-rich SNe. These findings can shed new light on the role of Ca-rich SNe in the chemical evolution of galaxies and the intracluster medium, and their contribution to the observed 511 Kev signal in the galaxy originating from positrons produced from 44Ti decay. Finally, the origins of such SNe points to the key role of HeCO-WDs as SN progenitors and their potential role as progenitors of other thermonuclear SNe including normal Ia.

Keywords: Hydrodynamical simulations, White dwarf stars, Type Ia supernovae