Sazuna/UAT_keywords huggingface dataset:
Energetic Electron Distribution of the Coronal Acceleration Region: First Results from Joint Microwave and Hard X-Ray Imaging Spectroscopy. Nonthermal sources located above bright flare arcades, referred to as the "above-the-loop-top" sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the Expanded Owens Valley Solar Array and the Reuven Ramaty High Energy Solar Spectroscopic Imager, respectively. By combining the microwave and HXR imaging spectroscopy observations with multifilter extreme ultraviolet and soft X-ray imaging data, we derive the coronal magnetic field and energetic electron distribution of the source over a broad energy range from &lt;10 keV up to ∼MeV during the early impulsive phase of the flare. The source has a strong magnetic field of over 800 G. The best-fit electron distribution consists of a thermal "core" from ∼25 MK plasma. A nonthermal power-law "tail" joins the thermal core at ∼16 keV with a spectral index of ∼3.6, which breaks down at above ∼160 keV to &gt;6.0. Temporally resolved analysis suggests that the electron distribution above the break energy rapidly hardens with the spectral index decreasing from &gt;20 to ∼6.0 within 20 s, or less than ∼10 Alfvén crossing times in the source. These results provide strong support for the above-the-loop-top source as the primary site where an ongoing bulk acceleration of energetic electrons is taking place very early in the flare energy release.

Keywords: Solar flares, Solar magnetic reconnection, Solar energetic particles, Solar x-ray emission, Solar radio emission, Non-thermal radiation sources, Solar coronal mass ejections
A Theoretical Framework for the Mass Distribution of Gas Giant Planets Forming through the Core Accretion Paradigm. This paper constructs a theoretical framework for calculating the distribution of masses for gas giant planets forming via the core accretion paradigm. Starting with known properties of circumstellar disks, we present models for the planetary mass distribution over the range 0.1MJ ≤ Mp &lt; 10MJ. If the circumstellar disk lifetime is solely responsible for the end of planetary mass accretion, the observed (nearly) exponential distribution of disk lifetime would imprint an exponential falloff in the planetary mass function. This result is in apparent conflict with observations, which suggest that the mass distribution has a (nearly) power-law form of ${dF}/{{dM}}_{{\rm{p}}}\sim {M}_{{\rm{p}}}^{-p}$ , with an index of p ≈ 1.3, over the relevant planetary mass range (and for stellar masses ∼0.5-2M⊙). The mass accretion rate onto the planet depends on the fraction of the (circumstellar) disk accretion flow that enters the Hill sphere, and on the efficiency with which the planet captures the incoming material. Models for the planetary mass function that include distributions for these efficiencies, with uninformed priors, can produce nearly power-law behavior, consistent with current observations. The disk lifetimes, accretion rates, and other input parameters depend on the mass of the host star. We show how these variations lead to different forms for the planetary mass function for different stellar masses. Compared to stars with masses M* = 0.5-2M⊙, stars with smaller masses are predicted to have a steeper planetary mass function (fewer large planets).

Keywords: Exoplanet astronomy, Exoplanet formation
LOFAR Observations of a Jet-driven Piston Shock in the Low Solar Corona. The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite the large number of type II radio burst observations, the precise origin of coronal shocks is still subject to investigation. Here, we present a well-observed solar eruptive event that occurred on 2015 October 16, focusing on a jet observed in the extreme ultraviolet by the Atmospheric Imaging Assembly (SDO/AIA), a streamer observed in white light by the Large Angle and Spectrometric Coronagraph (SOHO/LASCO), and a metric type II radio burst observed by the LOw Frequency Array (LOFAR). LOFAR interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be cospatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model that accounts for scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5R⊙ above the jet and propagated at a speed of ∼1000 km s-1, which was significantly faster than the jet speed of ∼200 km s-1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

Keywords: Solar flares, Solar extreme ultraviolet emission, Plasma jets, Shocks, Radio bursts, Solar radio emission, Active solar corona, Solar coronal streamers
Harmonic Electron Cyclotron Maser Emission Excited by Energetic Electrons Traveling inside a Coronal Loop. A complete understanding of solar radio bursts requires developing numerical techniques that can connect large-scale activities with kinetic plasma processes. As a starting point, this study presents a numerical scheme combining three different techniques: (1) extrapolation of the magnetic field overlying a specific active region in order to derive the background field, (2) guiding-center simulation of the dynamics of millions of particles within a selected loop to reveal the integral velocity distribution function (VDF) around certain sections of the loop, and (3) particle-in-cell simulation of kinetic instabilities driven by energetic electrons initiated by the obtained distributions. Scattering effects at various levels (weak, moderate, and strong) due to wave turbulence-particle interaction are considered using prescribed timescales of scattering. It was found that the obtained VDFs contain strip-like and loss-cone features with positive gradient, and both features are capable of driving electron cyclotron maser emission, which is a viable radiation mechanism for some solar radio bursts, in particular, solar radio spikes. The strip-like feature is important in driving the harmonic X mode, while the loss-cone feature can be important in driving the fundamental X mode. In the weak-scattering case, the rate of energy conversion from energetic electrons to X2 can reach up to $\sim 2.9\times {10}^{-3}\,{E}_{{k}_{0}}$ , where ${E}_{{k}_{0}}$ is the initial kinetic energy of energetic electrons. The study demonstrates a novel way of exciting the X2 mode in the corona during solar flares and provides new sight into how escaping radiation can be generated within a coronal loop.

Keywords: Solar coronal radio emission, Plasma astrophysics, Radio bursts, Solar corona, Solar activity
Charging and Electromagnetic Radiation during the Inspiral of a Black Hole-Neutron Star Binary. Because mergers of black hole-neutron star (BH-NS) binaries are widely argued to produce both gravitational and electromagnetic waves, these binaries are among the most attractive systems in the era of multi-messenger astronomy. In this paper we explore the charging processes of a moving BH in two types of charged surroundings and propose a new charging scenario differing from the elegant mechanism of Wald. During the inspiral of such a binary, the NS is strongly magnetized and the BH is moving inward. By considering this moving BH charging scenario, we find that the BH will increasingly accumulate enough net charge to light up the binary system at the inspiral stage. This charging process is universal no matter whether the BH spins or not. We show that our BH charging scenario can physically explain the BH's unipolar inductor mechanism in a BH-NS binary system. We calculate electromagnetic emission luminosities due to various energy dissipation mechanisms and find that the electric dipole radiation of the BH makes a dominant contribution to electromagnetic emission at the final stage of inspiral if the BH spins slowly.

Keywords: Neutron stars, Black holes, Non-thermal radiation sources, General relativity, Compact objects
Possible Periodic Dips in the Pulsating Ultraluminous X-Ray Source M51 ULX-7. We report the discovery of possible periodic X-ray dips in a pulsating ultraluminous X-ray source, M51 ULX-7, with archival Chandra observations. With ∼20 days of monitoring in the superorbital descending state, we discovered three dips with separations of ∼2 and ∼8 days via the Bayesian block technique. A phase-dispersion minimization and a ${\chi }^{2}$ test suggest that the dip is likely recurrent with a period of ∼2 days, consistent with the orbital period of M51 ULX-7. We interpret the dip as an obscuring of the emission from the pulsar by the vertical structure on the stream-disk interaction region or the atmosphere of the companion star. Both interpretations suggest the viewing angle to be ∼60°. Given that the magnetic field of M51 ULX-7 is moderately high, B ∼ 1013 G, a low geometric beaming with $b\gtrsim 1/2$ is sufficient to explain the observed flux and the presence of dips. Obscuration of the stellar wind remains an alternative possible origin and further monitoring of the dips will be required.

Keywords: Neutron stars, X-ray binary stars, X-ray sources
Timing of Eight Binary Millisecond Pulsars Found with Arecibo in Fermi-LAT Unidentified Sources. We present timing solutions for eight binary millisecond pulsars (MSPs) discovered by searching unidentified Fermi-Large Area Telescope (LAT) source positions with the 327 MHz receiver of the Arecibo 305 m radio telescope. Five of the pulsars are "spiders" with orbital periods shorter than 8.1 hr. Three of these are in "black widow" systems (with degenerate companions of 0.02-0.03 M⊙), one is in a "redback" system (with a non-degenerate companion of ≳0.3 M⊙), and one (J1908+2105) is an apparent middle-ground case between the two observational classes. The remaining three pulsars have white dwarf companions and longer orbital periods. With the initially derived radio timing solutions, we detected γ-ray pulsations from all MSPs and extended the timing solutions using photons from the full Fermi mission, thus confirming the identification of these MSPs with the Fermi-LAT sources. The radio emission of the redback is eclipsed during 50% of its orbital period, which is typical for this kind of system. Two of the black widows exhibit radio eclipses lasting for 10%-20% of the orbit, while J1908+2105 eclipses for 40% of the orbit. We investigate an apparent link between gamma-ray emission and a short orbital period among known binary MSPs in the Galactic disk, and conclude that selection effects cannot be ruled out as the cause. Based on this analysis we outline how the likelihood of new MSP discoveries can be improved in ongoing and future pulsar searches.

Keywords: Millisecond pulsars, Binary pulsars, Pulsars
Inferred Linear Stability of Parker Solar Probe Observations Using One- and Two-component Proton Distributions. The hot and diffuse nature of the Sun's extended atmosphere allows it to persist in non-equilibrium states for long enough that wave-particle instabilities can arise and modify the evolution of the expanding solar wind. Determining which instabilities arise, and how significant a role they play in governing the dynamics of the solar wind, has been a decades-long process involving in situ observations at a variety of radial distances. With new measurements from the Parker Solar Probe (PSP), we can study what wave modes are driven near the Sun, and calculate what instabilities are predicted for different models of the underlying particle populations. We model two hours-long intervals of PSP/SPAN-i measurements of the proton phase-space density during the PSP's fourth perihelion with the Sun using two commonly used descriptions for the underlying velocity distribution. The linear stability and growth rates associated with the two models are calculated and compared. We find that both selected intervals are susceptible to resonant instabilities, though the growth rates and kinds of modes driven unstable vary depending on whether the protons are modeled using one or two components. In some cases, the predicted growth rates are large enough to compete with other dynamic processes, such as the nonlinear turbulent transfer of energy, in contrast with relatively slower instabilities at larger radial distances from the Sun.

Keywords: Space plasmas, Solar wind, Plasma physics
Molybdenum Isotope Dichotomy in Meteorites Caused by s-Process Variability. Molybdenum isotopes measured in most individual presolar silicon carbide grains are dominated by s-process contributions from the helium intershells of asymptotic giant branch (AGB) stars. The much smaller isotopic variations in molybdenum in meteorites and their components are largely controlled by s-process enrichments or depletions relative to terrestrial composition but lie along two parallel s-process mixing lines separated by what has been suggested to be an r-process contribution. The two mixing lines are populated by carbonaceous-chondrite- and noncarbonaceous-chondrite-related meteorites (CC and NC groups, respectively). We have compared molybdenum isotopic data for presolar grains with those from meteorites and renormalized the meteorite data in a way that is consistent with s-, r-, and p-process contributions observed in presolar SiC grains. The results indicate that (1) there seems to be a fixed ratio between p- and r-process contributions in all data, (2) the dichotomy in molybdenum isotopes between the CC and NC groups can be explained by variations in the isotope makeup of the s-process contribution to the meteoritic samples, (3) this variability is similar to the variations in s-process molybdenum from different AGB stars deduced from presolar grain analyses, and (4) the larger range of isotopic compositions found in refractory inclusions is also consistent with s-process isotope variability.

Keywords: Isotopic abundances, Solar system formation, Nucleosynthesis, R-process, P-process, Circumstellar grains, Meteorites, S-process
Diurnal Variability and Detectability of Vegetation Red Edge of Earth-like Exoplanets. The vegetation red edge (VRE) is a unique spectral fingerprint of light-harvesting vegetation on Earth and provides a robust remote detectable surface biosignature of exoplanets. To improve the detectability and sensitivity, we have studied the diurnal variability of VRE in the disk-integrated spectra of Earth and also Earth analogs in the case of different observing geometry conditions. Simulation results show that the VRE index varies from &lt;-0.4 to &gt;0.6 at a diurnal timescale for both present and also Late Triassic Earth, and the maximum variation of VRE in 1 day changes by &gt;3 times with different observing geometry conditions. This means that the extraterrestrial light-harvesting vegetation (even if it really exists) will not be efficiently detectable without proper observing geometry conditions and time, especially in the case of the exoplanets covered with thick clouds. The VRE temporal variation curve can also be used to retrieve the cloud cover fraction and continent distribution of exoplanets with relatively high precision. Several observational strategies are proposed to detect the light-harvesting vegetation and retrieve the planetary information from the planet's VRE variation signals, and a mock observation is also demonstrated.

Keywords: Exoplanet surface variability, Astrobiology, Exoplanet surface characteristics, Spectroscopy, Biosignatures
Effects of Pseudostreamer Boundary Dynamics on Heliospheric Field and Wind. Interchange reconnection has been proposed as a mechanism for the generation of the slow solar wind, and a key contributor to determining its characteristic qualities. In this paper we study the implications of interchange reconnection for the structure of the plasma and field in the heliosphere. We use the Adaptively Refined Magnetohydrodynamic Solver to simulate the coronal magnetic evolution in a coronal topology containing both a pseudostreamer and helmet streamer. We begin with a geometry containing a low-latitude coronal hole that is separated from the main polar coronal hole by a pseudostreamer. We drive the system by imposing rotating flows at the solar surface within and around the low-latitude coronal hole, which leads to a corrugation (at low altitudes) of the separatrix surfaces that separate open from closed magnetic flux. Interchange reconnection is induced both at the null points and separators of the pseudostreamer, and at the global helmet streamer. We demonstrate that a preferential occurrence of interchange reconnection in the "lanes" between our driving cells leads to a filamentary pattern of newly opened flux in the heliosphere. These flux bundles connect to but extend far from the separatrix-web (S-Web) arcs at the source surface. We propose that the pattern of granular and supergranular flows on the photosphere should leave an observable imprint in the heliosphere.

Keywords: Slow solar wind, Solar corona, Magnetohydrodynamics, Solar magnetic reconnection
25 au Angular Resolution Observations of HH 211 with ALMA: Jet Properties and Shock Structures in SiO, CO, and SO. HH 211 is a highly collimated jet with a chain of knots and a wiggle structure on both sides of a young Class 0 protostar. We used two epochs of Atacama Large Millimeter/submillimeter Array (ALMA) data to study its inner jet in the CO(J = 3-2), SiO(J = 8-7), and SO(NJ = 89-78) lines at ∼25 au resolution. With these ALMA and previous 2008 Submillimeter Array data, the proper motion of 8 knots within ∼250 au of the central source is found to be ∼0"068 per year (∼102 km s-1), consistent with previous measurements in the outer jet. At about four times higher resolution, the reflection-symmetric wiggle can be still fitted by a previously proposed orbiting jet source model. Previously detected continuous structures in the inner jet are now resolved, containing at least 5 subknots. These subknots are interpreted in terms of a variation in the ejection velocity of the jet with a period of ∼4.5 yr, shorter than that of the outer knots. In addition, backward and forward shocks are resolved in a fully formed knot, BK3, and signatures of internal working surface and sideways ejection are identified in position-velocity diagrams. In this knot, low-density SO and CO layers are surrounded by a high-density SiO layer.

Keywords: Shocks, Stellar winds, Stellar jets, Star formation
Systematic Difference between Ionized and Molecular Gas Velocity Dispersions in z ∼ 1-2 Disks and Local Analogs. We compare the molecular and ionized gas velocity dispersions of nine nearby turbulent disks, analogs to high-redshift galaxies, from the DYNAMO sample using new Atacama Large Millimeter/submillimeter Array and GMOS/Gemini observations. We combine our sample with 12 galaxies at z ∼ 0.5-2.5 from the literature. We find that the resolved velocity dispersion is systematically lower by a factor 2.45 ± 0.38 for the molecular gas compared to the ionized gas, after correcting for thermal broadening. This offset is constant within the galaxy disks and indicates the coexistence of a thin molecular gas disk and a thick ionized one. This result has a direct impact on the Toomre Q and pressure derived in galaxies. We obtain pressures ∼0.22 dex lower on average when using the molecular gas velocity dispersion, σ0,mol. We find that σ0,mol increases with gas fraction and star formation rate. We also obtain an increase with redshift and show that the EAGLE and FIRE simulations overall overestimate σ0,mol at high redshift. Our results suggest that efforts to compare the kinematics of gas using ionized gas as a proxy for the total gas may overestimate the velocity dispersion by a significant amount in galaxies at the peak of cosmic star formation. When using the molecular gas as a tracer, our sample is not consistent with predictions from star formation models with constant efficiency, even when including transport as a source of turbulence. Feedback models with variable star formation efficiency, ∊ff, and/or feedback efficiency, p*/m*, better predict our observations.

Keywords: Stellar feedback, Galaxy kinematics, Galaxy evolution, Star formation, Extragalactic astronomy, High-redshift galaxies
XMM Observation of the Supernova Remnant J0454-6713 and the Adjacent N9 Superbubble. The Large Magellanic Cloud supernova remnant J0454-6713 abutting the H II region N9 has been observed with XMM-Newton. Two groups of lines from Fe XVII account for half the emission and lines from Fe XVIII, O VII, and O VIII are also clearly detected with the XMM RGS. Isothermal equilibrium fits of the EPIC spectra reproduce the basic spectral form and show little variation throughout the remnant but are insensitive to the lines from the high-temperature ions. These are overwhelmed in the EPIC cameras by the dominant Fe XVII radiation and the EPIC best-fit spectra do not agree with the RGS data. Uncertainties in the atomic data used to determine Fe-line strength present a further complication which inhibits a good EPIC spectral fit. We build a two-temperature model which does fit both RGS and EPIC results and propose that the high-T component is from SN debris and the low from heated material in the H II region. The high ratio of Fe emission to that from O requires the remnant to be the product of a Type Ia supernova and points to a deflagration-detonation origin. Weak X-ray emission from the N9 superbubble is detected and briefly discussed. The abundance of Ne in N9 material seems higher than average for the LMC in both the superbubble spectrum and the low-temperature component of the remnant RGS spectrum.

Keywords: X-ray astronomy, Plasma astrophysics, Large Magellanic Cloud, Supernova remnants, Type Ia supernovae
Strange Quark Stars in 4D Einstein-Gauss-Bonnet Gravity. The existence of strange matter in compact stars may give rise to striking outcomes of the various physical phenomena. As an alternative to neutron stars, a new class of compact stars called strange stars should exist if the strange matter hypothesis is true. In this paper, we investigate the possible construction of strange stars in quark matter phases based on the MIT bag model. We consider scenarios in which strange stars have no crusts. Then we apply two types of equations of state to quantify the mass-radius diagram for static strange star models, performing the numerical calculation of the modified Tolman-Oppenheimer-Volkoff equations in the context of 4D Einstein-Gauss-Bonnet (EGB) gravity. It is worth noting that the GB term gives rise to a nontrivial contribution to the gravitational dynamics in the limit D → 4. However, the claim that the resulting theory is one of pure gravity has been cast in doubt on several grounds. Thus, we begin our discussion by showing the regularized 4D EGB theory has an equivalent action as the novel 4D EGB in a spherically symmetric spacetime. We also study the effects of coupling constant α on the physical properties of the constructed strange stars including the compactness and criterion of adiabatic stability. Finally, we compare our results to those obtained from standard general relativity.

Keywords: Neutron stars, Theoretical models, Compact objects
Photon-dominated Hydrodynamics. Some subtle distinctions between optically thin emission and optically thick emission (with a dynamically passive source of opacity) from an emitting surface are drawn. It is noted that photons may escape a region of high optical depth by dragging the opaque material with them, and that optically thick emission can have a shorter scale of variation than optically thin emission and less light echoing.

Keywords: Gamma-ray transient sources