Sazuna/UAT_keywords huggingface dataset:
An Exploration of Tensor Virial Equilibrium in Magnetized Molecular Cloud Cores. PolCat is a software package designed to generate and constrain models of triaxial, magnetized molecular cloud cores using submillimeter polarization and continuum intensity data. Such models often compare well with observational data, but they are mathematically degenerate. As a result, many allowed models are either very elongated or flattened, and far from virial equilibrium. We present a tensor virial analysis of PolCat models with the aim of developing an optional new regularization constraint that can be used on the fly during the PolCat modeling process. This constraint is intended to guide PolCat toward models that are in or close to equilibrium on all three principal axes. While we have found the expected families of spheroidal solutions in tensor virial balance, we have also found a population of triaxial cores that are in three-axis tensor virial equilibrium. We find that models generated using the virial constraint have much more realistic shapes, with very elongated or flattened solutions now absent. Thus, these show that the tensor virial constraint may be useful for restricting PolCat's solution space to more realistic models, thereby also reducing the degeneracy inherent in our approach. We also perform a Monte Carlo analysis to predict the range of projected axis ratios present in the population of equilibrium solutions to suggest how these cores may appear when observed.

Keywords: Gravitational equilibrium, Astronomical models, Molecular clouds, Computational methods, Submillimeter astronomy, Magnetic fields
X-Ray Hotspots in the Northwest Shell of the Supernova Remnant RX J1713.7-3946. The supernova remnant (SNR) RX J1713.7-3946 is one of the best-studied accelerators of cosmic rays because of its strong nonthermal X-ray and gamma-ray radiation. We have analyzed accumulated Chandra observations with a total exposure time of ∼266 ks in the northwest rim of RX J1713.7-3946. We detect a substantially large number of point-like sources, referred to as "hotspots," which are likely associated with the remnant. The spectra of the hotspots are well described by an absorbed power-law model. The spectral properties ( ${10}^{21}\ {\mathrm{cm}}^{-2}\lesssim {N}_{{\rm{H}}}\,\lesssim {10}^{23}\ {\mathrm{cm}}^{-2}$ and 0.5 ≲ Γ ≲ 6) are different from diffuse X-ray emission in RX J1713.7-3946, and the harder hotspot tends to have the larger NH. We also confirm yearly and monthly variabilities of flux for some hotspots. We propose that RX J1713.7-3946 is embedded in a complex surroundings where some dense molecular clumps and cores exist inside a wind-blown cavity, and that the hotspot traces synchrotron emission caused by an interaction of shock waves of the SNR and dense molecular cores with a number density of 105-107 cm-3. The X-ray radiation of the hotspot might be emitted both from primary electrons accelerated at the shocks and secondary electrons produced by the interaction of accelerated protons with the cores.

Keywords: Supernova remnants, X-ray sources, Non-thermal radiation sources, Interstellar medium
Gigayear-timescale Destruction of High-eccentricity Asteroids by Spin and Why 2006 HY51 Has Been Spared. Asteroids and other small celestial bodies have markedly prolate shapes, and the perturbative triaxial torques that are applied during pericenter passages in highly eccentric orbits trigger and sustain a state of chaotic rotation. Because the prograde spin rate around the principal axis of inertia is not bounded from above, it can accidentally reach the threshold value corresponding to rotational breakup. Previous investigations of this process were limited to integrations of ∼103 orbits because of the stiff equation of motion. We present here a fast 1D simulation method to compute the evolution of this spin rate over ∼109 orbits. We apply the method to the most eccentric solar system asteroid known, 2006 HY51 (with e = 0.9684), and find that for any reasonably expected shape parameters it can never be accelerated to breakup speed. However, primordial solar system asteroids on more eccentric orbits may have already broken up from this type of rotational fission. The method also represents a promising opportunity to investigate the long-term evolution of extremely eccentric triaxial exo-asteroids (e &gt; 0.99), which are thought to be common in white dwarf planetary systems.

Keywords: Small Solar System bodies, Asteroids, Astronomical simulations, Celestial mechanics, Computational methods, Eccentricity
Pulsar Candidate Sifting Using Multi-input Convolution Neural Networks. Pulsar candidate sifting is an essential process for discovering new pulsars. It aims to search for the most promising pulsar candidates from an all-sky survey, such as the High Time Resolution Universe (HTRU), Green Bank Northern Celestial Cap (GBNCC), Five-hundred-meter Aperture Spherical Radio Telescope, etc. Recently, machine learning (ML) has become a hot topic in investigations of pulsar candidate sifting. However, one typical challenge in ML for pulsar candidate sifting comes from the learning difficulty arising from the high class imbalance between the observed numbers of pulsars and non-pulsars. Therefore, this work proposes a novel framework for candidate sifting, named Multi-input Convolutional Neural Networks (MICNN). MICNN is an architecture of deep learning with four diagnostic plots of a pulsar candidate as its inputs. To train our MICNN on a highly class-imbalanced data set, a novel image augmentation technique is proposed, as well as a three-stage training strategy. Experiments on observations from HTRU and GBNCC show the effectiveness and robustness of these proposed techniques. In the experiments on HTRU, our MICNN model achieves a recall rate of 0.962 and a precision rate of 0.967 even in a highly class-imbalanced test data set.

Keywords: Convolutional neural networks, Astronomy data analysis, Pulsars
GRB 170817A as a Refreshed Shock Afterglow Viewed Off-axis. Energy injection into the external shock system that generates the afterglow to a gamma-ray burst (GRB) can result in a rebrightening of the emission. Here we investigate the off-axis view of a rebrightened refreshed shock afterglow. We find that the afterglow light curve, when viewed from outside of the jet opening angle, could be characterized by a slow rise, or long plateau, with a maximum flux determined by the total system energy. Using the broadband afterglow data for GRB 170817A, associated with the gravitational-wave-detected binary neutron star merger GW170817, we show that a refreshed shock model with a simple top-hat jet can reproduce the observed afterglow features. We consider two refreshed shock models: a single episode of energy injection, and an episode of continuous energy injection. The best-fit model parameters give a jet opening angle for our first and second models, respectively, of θj = 5° ${2}_{-0.6}^{+1.1}\,$ and 6° ${3}_{-1.1}^{+1.7}$ , an inclination to the line of sight ι = 16° ${0}_{-1.1}^{+3.4}\,$ and 17° ${8}_{-2.9}^{+4.5}$ , an initial on-axis isotropic equivalent kinetic energy ${E}_{1}=({0.3}_{-0.3}^{+3.5}\,$ and $\,{0.5}_{-0.2}^{+6.7})\times {10}^{52}$ erg, and a total/final, on-axis isotropic equivalent refreshed shock energy ${E}_{\mathrm{total}}=({0.42}_{-0.4}^{+5.6}\,$ and $\,{1.26}_{-0.7}^{+18.2})\times {10}^{53}$ erg. The first model fitting prefers an initial bulk Lorentz factor Γ0,1 &lt; 60, with a comparatively low central value of Γ0,1 = 19.5, indicating that, in this case, the on-axis jet could have been a "failed GRB." Alternatively, our second model is consistent with a bright GRB for an on-axis observer, with ${{\rm{\Gamma }}}_{\mathrm{0,1}}={162.2}_{-122.1}^{+219.7}$ . Due to the low Lorentz factor and/or the jet opening angles at θj ∼ ι/3, both models are unable to reproduce the γ-ray emission observed in GRB 170817A, which would therefore require an alternative explanation such as cocoon shock breakout.

Keywords: Gamma-ray bursts, Transient sources
GRB 200415A: A Short Gamma-Ray Burst from a Magnetar Giant Flare?. The giant flares of soft gamma-ray repeaters (SGRs) have long been proposed to contribute to at least a subsample of the observed short gamma-ray bursts (GRBs). In this paper, we perform a comprehensive analysis of the high-energy data of the recent bright short GRB 200415A, which was located close to the Sculptor galaxy. Our results suggest that a magnetar giant flare provides the most natural explanation for most observational properties of GRB 200415A, including its location, temporal and spectral features, energy, statistical correlations, and high-energy emissions. On the other hand, the compact star merger GRB model is found to have difficulty reproducing such an event in a nearby distance. Future detections and follow-up observations of similar events are essential to firmly establish the connection between SGR giant flares and a subsample of nearby short GRBs.

Keywords: Selenology, Gamma-ray bursts, Gamma-ray transient sources, Magnetars
The Solar Origin of Particle Events Measured by Parker Solar Probe. During the second solar encounter phase of Parker Solar Probe (PSP), two small solar energetic particle (SEP) events were observed by the Integrated Science Investigation of the Sun, on 2019 April 2 and 4. At the time, PSP was approaching its second perihelion at a distance of ∼24.8 million kilometers from the solar center, it was in near-radial alignment with STEREO-A and in quadrature with Earth. During the two SEP events multiple narrow ejections and a streamer-blowout coronal mass ejection (SBO-CME) originated from a solar region situated eastward of PSP. We analyze remote-sensing observations of the solar corona, and model the different eruptions and how PSP was connected magnetically to the solar atmosphere to determine the possible origin of the two SEP events. We find that the SEP event on April 2 was associated with the two homologous ejections from active region 12738 that included two surges and EUV waves occurring in quick succession. The EUV waves appear to merge and were fast enough to form a shock in the low corona. We show that the April 4 SEP event originates in the SBO-CME. Our modeling work suggests that formation of a weak shock is likely for this CME.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Solar particle emission, Solar coronal mass ejections
Massive Galaxies Impede Massive Outflows. A set of 66 3D hydrodynamical simulations explores how galactic stellar mass affects three-phase, starburst-driven outflows. Simulated velocities are compared to two basic analytic models: with and without a gravitational potential. For stellar mass &lt;1010M⊙, simulated velocities match those of both analytical models and are unaffected by the potential; above they reduce significantly as expected from the analytic model with gravity. Gravity also affects total outflow mass and each of the three phases differently. Outflow masses in the hot, warm, and cold phases each scale with stellar mass as $\mathrm{log}{M}_{* }\,=$ -0.25, -0.97, and -1.70, respectively. Thus, the commonly used Chevalier &amp; Clegg analytic model should be modified to include gravity when applied to higher-mass galaxies. In particular, using M82 as the canonical galaxy to interpret hydrodynamical simulations of starburst-driven outflows from higher-mass galaxies will underestimate the retarding effect of gravity. Using the analytic model of Johnson &amp; Axford with realistic thermalization efficiency and mass loading, I find that only galaxy masses ≲1011.5M⊙ can outflow.

Keywords: Starburst galaxies, Hydrodynamical simulations, Galactic winds, Galaxy properties, Active galaxies, Scaling relations, Galaxy winds, Galaxy kinematics, Galaxy processes
On the Magnetospheric Origin of Repeating Fast Radio Bursts. A bright radio burst was newly discovered in SGR 1935+2154, which exhibits some fast radio burst (FRB)-like temporal and frequency properties, suggesting a neutron star (NS)/magnetar magnetospheric origin of FRBs. We propose an explanation of the temporal and frequency properties of sub-pulses of repeating FRBs based on the generic geometry within the framework of charged-bunching coherent curvature radiation in the magnetosphere. The sub-pulses in a radio burst come from bunches of charged particles moving along different magnetic field lines. Their radiation beams sweep across the line of sight at different times, and those radiating at the more curved part tend to be seen earlier and at higher frequency. However, by considering bunches generated at slightly different times, we find there is also a small probability that the emission from the less curved part can be seen earlier. We simulate the time-frequency structures by deriving various forms of the electric acceleration field in the magnetosphere. This structure of sub-pulses is a natural consequence of coherent curvature radiation from an NS/magnetar magnetosphere with suddenly and violently triggered sparks. We apply this model to explain the time-frequency structure within a specific dipolar configuration by invoking the transient pulsar-like sparking from the inner gap of a slowly rotating NS, and we have also applied it to more generic configurations.

Keywords: Neutron stars, Radio bursts, Non-thermal radiation sources, Magnetars, Radio transient sources
Differential Rotation of the Halo Traced by K-giant Stars. We use K-giant stars selected from the LAMOST DR5 to study the variation of the rotational velocity of the Galactic halo at different space positions. Modeling the rotational velocity distribution with both the halo and disk components, we find that the rotational velocity of the halo population decreases almost linearly with increasing vertical distance to the Galactic disk plane, Z, at fixed galactocentric radius, R. The samples are separated into two parts with $6\lt R\lt 12\,\mathrm{kpc}$ and $12\lt R\lt 20\,\mathrm{kpc}$ . We derive that the decreasing rates along Z for the two subsamples are -3.07 ± 0.63 and -1.89 ± 0.37 km s-1 kpc-1, respectively. Comparing with the TNG simulations, we suggest that this trend is caused by the interaction between the disk and halo. The results from the simulations show that only an oblate halo can provide a decreasing rotational velocity with increasing Z. This indicates that the Galactic halo is oblate with galactocentric radius $R\lt 20\,\mathrm{kpc}$ . On the other hand, the flaring of the disk component (mainly the thick disk) is clearly traced by this study; with R between 12 and 20 kpc, the disk can vertically extend to $6\sim 10\,\mathrm{kpc}$ above the disk plane. What is more interesting is that we find the Gaia-Enceladus-Sausage component has a significant contribution only in the halo with $R\lt 12\,\mathrm{kpc}$ , i.e., a fraction of 23%-47%, while in the outer subsample, the contribution is too low to be well constrained.

Keywords: K giant stars, Milky Way dynamics, Milky Way rotation, Milky Way disk, Milky Way stellar halo, Milky Way evolution, Milky Way Galaxy
Photospheric Emission in Gamma-Ray Bursts. I. Variability. It is generally believed that the variability of photospheric emission in gamma-ray bursts (GRBs) traces that of the jet power. This work further investigates the variability of photospheric emission in a variable jet. By setting a constant η (dimensionless entropy of the jet), we find that the light curve of the photospheric emission shows a "tracking" pattern on the time profile of jet power. However, the relative variability is significantly low in the photospheric emission compared with that in the jet power. If the η is genetic variable, the variability of the photospheric emission is not only limited by the jet power but also affected by η strongly. It becomes complex and is generally different from that of the jet power. Moreover, the opposite phase may stand in the variabilities of the photospheric emission at different photon energies. We also find that the relative variability does not remain constant over the photon energies with an obvious reduction at a certain energy. This is consistent with the analysis of GRB 090902B in which an appreciable thermal component has been detected in a wide energy range. For several other GRBs coupling with the thermal component, we conservatively evaluate the variability of the thermal and nonthermal emission, respectively. Our results show that the relative variability of the thermal emission is likely comparable to that of the nonthermal emission for these bursts. In addition, the analysis of GRB 120323A reveals that the variability of the photospheric emission may be of the opposite phase from that of the nonthermal emission.

Keywords: Non-thermal radiation sources, Gamma-ray bursts, Jets, Astronomy data analysis
AGN Feedback and Star Formation of Quasar Host Galaxies: Insights from the Molecular Gas. Molecular gas serves as a key probe of the complex interplay between black hole accretion and star formation in the host galaxies of active galactic nuclei (AGNs). We use CO(2-1) observations from a new Atacama Large Millimeter/submillimeter Array survey, in conjunction with literature measurements, to investigate the molecular gas properties of a representative sample of 40 z &lt; 0.3 Palomar-Green quasars, the largest and most sensitive study of molecular gas emission to date for nearby quasars. We find that the AGN luminosity correlates with both the CO luminosity and black hole mass, suggesting that AGN activity is loosely coupled to the cold gas reservoir of the host. The observed strong correlation between host galaxy total infrared luminosity and AGN luminosity arises from their common dependence on the molecular gas. We argue that the total infrared luminosity, at least for low-redshift quasars, can be used to derive reliable star formation rates for the host galaxy. The host galaxies of low-redshift quasars have a molecular gas content similar to that of star-forming galaxies of comparable stellar mass. Moreover, they share similar gas kinematics, as evidenced by their CO Tully-Fisher relation and the absence of detectable molecular outflows down to sensitive limits. There is no sign that AGN feedback quenches star formation for the quasars in our sample. On the contrary, the abundant gas supply forms stars prodigiously, at a rate that places most of them above the star-forming main sequence and with an efficiency that rivals that of starburst systems.

Keywords: AGN host galaxies, Active galactic nuclei, Interstellar medium, Quasars
Comprehensive Multimessenger Modeling of the Extreme Blazar 3HSP J095507.9+355101 and Predictions for IceCube. 3HSP J095507.9+355101 is an extreme blazar that has been possibly associated with a high-energy neutrino (IceCube-200107A) detected 1 day before the blazar was found to undergo a hard X-ray flare. We perform a comprehensive study of the predicted multimessenger emission from 3HSP J095507.9+355101 during its recent X-ray flare, but also in the long term. We focus on one-zone leptohadronic models, but we also explore alternative scenarios: (i) a blazar-core model, which considers neutrino production in the inner jet, close to the supermassive black hole; (ii) a hidden external-photon model, which considers neutrino production in the jet through interactions with photons from a weak broad line region; (iii) a proton-synchrotron model, where high-energy protons in the jet produce γ-rays via synchrotron; and (iv) an intergalactic cascade scenario, where neutrinos are produced in the intergalactic medium by interactions of a high-energy cosmic-ray beam escaping the jet. The Poisson probability to detect a single muon neutrino in 10 years from 3HSP J095507.9+355101 with the real-time IceCube alert analysis is ∼1% (3%) for the most optimistic one-zone leptohadronic model (the multi-zone blazar-core model). Meanwhile, detection of a single neutrino during the 44-day-long high X-ray flux-state period following the neutrino detection is 0.06%, according to our most optimistic leptohadronic model. The most promising scenarios for neutrino production also predict strong intrasource γ-ray attenuation above ∼100 GeV. If the association is real, then IceCube-Gen2 and other future detectors should be able to provide additional evidence for neutrino production in 3HSP J095507.9+355101 and other extreme blazars.

Keywords: BL Lacertae objects, High energy astrophysics, Blazars, Neutrino astronomy, Gamma-rays
Anomalous Extinction toward NGC 1938. Intrigued by the extended red giant clump (RC) stretching across the color-magnitude diagram of the stars in a 50 × 50 pc2 region of the Large Magellanic Cloud (LMC) containing the clusters NGC 1938 and NGC 1939, we have studied the stellar populations to learn about the properties of the interstellar medium (ISM) in this area. The extended RC is caused by a large and uneven amount of extinction across the field. Its slope reveals anomalous extinction properties, with AV/E(B - V) ≃ 4.3, indicating the presence of an additional gray component in the optical contributing about 30% of the total extinction in the field and requiring big grains to be about twice as abundant as in the diffuse ISM. This appears to be consistent with the number of big grains injected into the surrounding ISM by the about 70 SN II explosions estimated to have occurred during the lifetime of the ∼120 Myr old NGC 1938. Although this cluster appears relatively small today and would be hard to detect beyond the distance of M31, with an estimated initial mass of ∼4800 M⊙, NGC 1938 appears to have seriously altered the extinction properties in a wide area. This has important implications for the interpretation of luminosities and masses of star-forming galaxies both nearby and in the early universe.

Keywords: Star forming regions, Large Magellanic Cloud, Interstellar dust extinction
Nonlinear Turbulent Dynamo during Gravitational Collapse. Via amplification by turbulent dynamo, magnetic fields can be potentially important for the formation of the first stars. To examine the dynamo behavior during the gravitational collapse of primordial gas, we extend the theory of the nonlinear turbulent dynamo to include the effect of gravitational compression. The relative importance between dynamo and compression varies during contraction, with the transition from dynamo- to compression-dominated amplification of magnetic fields with the increase of density. In the nonlinear stage of magnetic field amplification with the scale-by-scale energy equipartition between turbulence and magnetic fields, reconnection diffusion of magnetic fields in ideal magnetohydrodynamic turbulence becomes important. It causes the violation of the flux-freezing condition and accounts for (a) the small growth rate of the nonlinear dynamo, (b) the weak dependence of magnetic energy on density during contraction, (c) the saturated magnetic energy, and (d) the large correlation length of magnetic fields. The resulting magnetic field structure and the scaling of magnetic field strength with density are radically different from the expectations of flux freezing.

Keywords: Magnetohydrodynamics, Population III stars, Magnetic fields