Sazuna/UAT_keywords huggingface dataset:
Direct Measurements of Activation Energies for Surface Diffusion of CO and CO<SUB>2</SUB> on Amorphous Solid Water Using In Situ Transmission Electron Microscopy. The importance of the activation energy of surface diffusion (Esd) of adsorbed molecules on amorphous solid water (ASW) has been widely discussed in terms of chemical reactions on ASW at low temperatures. However, in previous work, Esd has not been measured directly but estimated from indirect experiments. It has been assumed in chemical network calculations that Esd is between 0.3 and 0.8 of the desorption energies of a molecule. It remains important to obtain direct measurements of Esd. We performed in situ observations of the deposition process of CO and CO2 on ASW using transmission electron microscopy (TEM) and deduced the Esd of CO and CO2 on ASW to be 350 ± 50 and 1500 ± 100 K, respectively. The value of Esd of CO is approximately 0.3 of the total adsorption energy of CO on ASW, I.e., much smaller than assumed in chemical network calculations, where the corresponding figure is 575 K, assuming approximately 0.5 of the desorption energy. We demonstrated that TEM is very useful not only for the observation of ices but also for the measurement of some physical properties that are relevant in astrochemistry and astrophysics. Using the Esd of CO measured in the present study (350 K), we have updated the chemical network model of Furuya et al., confirming that CO2 could be efficiently formed by the reaction CO + OH → CO2 + H in the initial stages of the evolution of molecular clouds.

Keywords: Interstellar molecules, Theoretical models, Ice formation, Laboratory astrophysics, Experimental techniques, Reaction rates, Astrochemistry, Dense interstellar clouds, Interdisciplinary astronomy
The Blue Compact Dwarf Galaxy VCC 848 Formed by Dwarf-Dwarf Merging. It has long been speculated that many starburst or compact dwarf galaxies are resulted from dwarf-dwarf galaxy merging, but unequivocal evidence for this possibility has rarely been reported in the literature. We present the first study of deep optical broadband images of a gas-dominated blue compact dwarf galaxy (BCD) VCC 848 (M⋆ ≃ 2 × 108M⊙) that hosts extended stellar shells and thus is confirmed to be a dwarf-dwarf merger. VCC 848 is located in the outskirts of the Virgo Cluster. By analyzing the stellar light distribution, we found that VCC 848 is the result of a merging between two dwarf galaxies with a primary-to-secondary mass ratio ≲5 for the stellar components and ≲2 for the presumed dark matter halos. The secondary progenitor galaxy has been almost entirely disrupted. The age-mass distribution of photometrically selected star cluster candidates in VCC 848 implies that the cluster formation rate (CFR, ∝ star formation rate) was enhanced by a factor of ∼7-10 during the past ∼1 Gyr. The merging-induced enhancement of CFR peaked near the galactic center a few hundred Myr ago and has started declining in the last few tens of Myr. The current star formation activities, as traced by the youngest clusters, mainly occur at large galactocentric distances (≳1 kpc). The fact that VCC 848 is still (atomic) gas-dominated after the period of the most violent collision suggests that gas-rich dwarf galaxy merging can result in BCD-like remnants with extended atomic gas distribution surrounding a blue compact center, in general agreement with previous numerical simulations.

Keywords: Dwarf irregular galaxies, Starburst galaxies, Amorphous irregular galaxies, Late-type galaxies, Blue compact dwarf galaxies, N galaxies, Irregular galaxies, Dwarf galaxies, Galaxy pairs, Galaxy evolution, Interacting galaxies, Galaxies
Neutrino Process in Core-collapse Supernovae with Neutrino Self-interaction and MSW Effects. We calculate the abundances of 7Li, 11B, 92Nb, 98Tc, 138La, and 180Ta produced by neutrino (ν)-induced reactions in a core-collapse supernova explosion. We consider the modification by ν self-interaction (ν-SI) near the neutrinosphere and the Mikheyev-Smirnov-Wolfenstein (MSW) effect in the outer layers based on time-dependent neutrino energy spectra. Abundances of 7Li and the heavy isotopes 92Nb, 98Tc, and 138La are reduced by a factor of 1.5-2.0 by the ν-SI. In contrast, 11B is relatively insensitive to the ν-SI. We find that the abundance ratio of heavy to light nuclei, 138La/11B, is sensitive to the neutrino mass hierarchy, and the normal mass hierarchy is more likely to be consistent with the solar meteoritic abundances.

Keywords: Neutrino oscillations, Supernova neutrinos, Explosive nucleosynthesis
Plasma Emission Induced by Electron Cyclotron Maser Instability in Solar Plasmas with a Large Ratio of Plasma Frequency to Gyrofrequency. In plasmas with a large ratio of plasma frequency to gyrofrequency (ωpe/Ωce), energetic electrons characterized by \partial f/\partial {V}_{\perp }&gt; 0 can excite electron cyclotron maser instability (ECMI), generating waves of upper hybrid (UH), Z, and W modes. It has been presumed that these ECMI waves can somehow convert to escaping X-O modes as fundamental (F) or harmonic (H) plasma emission. Here we perform a fully kinetic, electromagnetic particle-in-cell simulation to investigate the proposed radiation process. ECMI is driven by energetic electrons with a Dory-Guest-Harris distribution representative of a double-sided loss cone, and ωpe/Ωce is set to be 10. We find that the electrostatic UH mode is the fastest-growing mode. Around the time when its energy starts to decline, the W mode grows to be dominant. During this stage, we observe significant F and H plasma emission. The F emission is in the O mode with a bandwidth around 0.1-0.2 Ωce, and the H emission is contributed by both X and O modes with a narrower bandwidth. We suggest that the O-F emission is caused by coalescence of almost counterpropagating Z and W modes, while the H emission arises from coalescence of an almost counterpropagating UH mode at relatively large wave number. Thus the plasma emission investigated here is induced by a combination of wave growth due to ECMI and further nonlinear wave-coupling processes. The result is relevant to understanding solar radio bursts as well as other astronomical radio sources that are excited by energetic electrons trapped within certain magnetic structures.

Keywords: Solar coronal radio emission, Plasma astrophysics, Radio bursts, Solar corona, Solar activity
Shock Drift Acceleration of Ions in an Interplanetary Shock Observed by MMS. An interplanetary (IP) shock wave was recorded crossing the Magnetospheric Multiscale constellation on 2018 January 8. Plasma measurements upstream of the shock indicate efficient proton acceleration in the IP shock ramp: 2-7 keV protons are observed upstream for about three minutes (∼8000 km) ahead of the IP shock ramp, outrunning the upstream waves. The differential energy flux of 2-7 keV protons decays slowly with distance from the ramp toward the upstream region (dropping by about half within 8 Earth radii from the ramp) and is lessened by a factor of about four in the downstream compared to the ramp (within a distance comparable to the gyroradius of ∼keV protons). Comparison with test-particle simulations has confirmed that the mechanism accelerating the solar wind protons and injecting them upstream is classical Shock Drift Acceleration (SDA). This example of observed proton acceleration by a low-Mach, quasi-perpendicular shock may be applicable to astrophysical contexts, such as supernova remnants or the acceleration of cosmic rays.

Keywords: Shocks, Interplanetary shocks, Space plasmas
Picky Partners: The Pairing of Component Masses in Binary Black Hole Mergers. We examine the relationship between individual black hole (BH) masses in merging binary black hole (BBH) systems. Analyzing the 10 BBH detections from LIGO/Virgo's first two observing runs, we find that the masses of the component BHs comprising each binary are unlikely to be randomly drawn from the same underlying distribution. Instead, the two BHs of a given binary prefer to be of comparable mass. We show that it is ∼5 times more likely that the component BHs in a given binary are always equal (to within 5%) than that they are randomly paired. If we assume that the probability of a merger between two BHs scales with the mass ratio q as qβ, so that β = 0 corresponds to random pairings, we find β &gt; 0 is favored at credibility 0.987. By modeling the mass distribution, we find that the median mass ratio is q_{50 %}= 0.91-0.17+0.05 at 90% credibility. While the pairing between BHs depends on their mass ratio, we find no evidence that it depends on the total mass of the system. We predict that 99% of BBHs detected by LIGO/Virgo will have mass ratios q &gt; 0.5. We conclude that merging black holes do not form random pairings; instead they are selective about their partners, preferring to mate with black holes of a similar mass. The details of these selective pairings provide insight into the underlying formation channels of merging binaries.

Keywords: Gravitational wave sources, Massive stars, Stellar remnants, Astrophysical black holes
A Rapid Change in X-Ray Variability and a Jet Ejection in the Black Hole Transient MAXI J1820+070. We present Neutron Star Interior Composition Explorer X-ray and Arcminute Microkelvin Imager Large Array radio observations of a rapid hard-to-soft state transition in the black hole X-ray transient MAXI J1820+070. During the transition from the hard state to the soft state a switch between two particular types of quasiperiodic oscillations (QPOs) was seen in the X-ray power density spectra, from type-C to type-B, along with a drop in the strength of the broadband X-ray variability and a brief flare in the 7-12 keV band. Soon after this switch (∼2-2.5 hr) a strong radio flare was observed that corresponded to the launch of superluminal ejecta. Although hints of a connection between QPO transitions and radio flares have been seen in other black hole X-ray transients, our observations constitute the strongest observational evidence to date for a link between the appearance of type-B QPOs and the launch of discrete jet ejections.

Keywords: X-ray astronomy, Accretion, Radio jets, Timing variation methods, X-ray transient sources, Low-mass x-ray binary stars
The Splash without a Merger. The Milky Way's progenitor experienced several merger events that left their imprints on the stellar halo, including the Gaia-Sausage/Enceladus. Recently, it has been proposed that this event perturbed the proto-disk and gave rise to a metal-rich ([Fe/H] &gt; -1), low angular momentum (Vφ &lt; 100 km s-1) stellar population. These stars have dynamical and chemical properties different from the accreted stellar halo, but are continuous with the canonical thick disk. In this Letter, we use a hydrodynamical simulation of an isolated galaxy that develops clumps that produce a bimodal thin+thick disk chemistry to explore whether it forms such a population. We demonstrate that clump scattering forms a metal-rich, low angular momentum population, without the need for a major merger. We show that, in the simulation, these stars have chemistry, kinematics, and density distribution in good agreement with those in the Milky Way.

Keywords: Hydrodynamical simulations, Milky Way evolution, Milky Way dynamics, Milky Way formation
The Most Massive Binary Black Hole Detections and the Identification of Population Outliers. Advanced LIGO and Virgo detected 10 binary black holes (BBHs) in their first two observing runs (O1 and O2). Analysis of these events found evidence for a dearth of BBHs with component masses greater than ∼45 M⊙, as would be expected from pair-instability supernovae. Meanwhile, a standalone analysis of the merger GW170729 found its primary mass to be {m}1={51.2}-11.0+16.2 {M}⊙, which appears to be in contradiction with the existence of a limit at ∼45 M⊙. In this work, we argue that the masses of individual events can only be evaluated with reference to the full population. When GW170729 is analyzed jointly with the remaining detections, its inferred primary mass tightens considerably, to {m}1={38.9}-4.5+7.3 {M}⊙ . In the presence of noise, apparent outliers in the detected distribution are inevitable. We discuss methods of distinguishing between statistical fluctuations and true population outliers using posterior predictive tests. Applying these tests to O1 and O2, we find that the 10 detections are consistent with even the simplest power-law plus maximum-mass model considered by the LIGO-Virgo Collaboration, supporting the claim that GW170729 is not a population outlier. We also provide non-parametric constraints on the rate of high-mass mergers and conservatively bound the rate of mergers with m1 &gt; 45 M⊙ at {2.8}-2.0+5.4% of the total merger rate. After 100 detections like those of O1 and O2 from a population with a maximum primary mass of 45 M⊙, it would be common for the most massive system to have an observed maximum-likelihood mass m1 ≳ 70 M⊙.

Keywords: Gravitational wave astronomy, Hierarchical models, Astronomy data analysis, Astrophysical black holes
The Influence of Late-stage Nuclear Burning on Red Supergiant Supernova Light Curves. Many Type II supernovae (SNe) show hot early (∼30 days) emission, and a diversity in their light curves extending from the Type IIP to the Type IIL, which can be explained by interaction with dense and confined circumstellar material (CSM). We perform hydrodynamical simulations of red supergiants to model the ejection of CSM caused by wave heating during late-stage nuclear burning. Even a small amount of deposited energy (1046-1047 erg), which is roughly that expected due to waves excited by convection in the core, is sufficient to change the shapes of SN light curves and bring them into better agreement with observations. As a test case, we consider the specific example of supernova (SN) 2017eaw, which shows that a nuclear burning episode is able to explain the light curve if it occurs ∼150-450 days prior to core collapse. Due to the long timescale that it takes for the low-energy shock to traverse the star, this would manifest as a pre-SN outburst ∼50-350 days prior to the full-fledged SN. Applying work like this to other SNe will provide a direct connection between the SN and pre-SN outburst properties, which can be tested by future wide field surveys. In addition, we show that our models can qualitatively explain the short-lived "flash-ionization" lines seen in the early spectra of many Type II SNe.

Keywords: Core-collapse supernovae, Hydrodynamics, Type II supernovae, Radiative transfer, Supernovae
On the Origin of High-energy Neutrinos from NGC 1068: The Role of Nonthermal Coronal Activity. NGC 1068, a nearby type-2 Seyfert galaxy, is reported as the hottest neutrino spot in the 10 yr survey data of IceCube. Although there are several different possibilities for the generation of high-energy neutrinos in astrophysical sources, feasible scenarios allowing such emission in NGC 1068 have not yet been firmly defined. We show that the flux level of GeV and neutrino emission observed from NGC 1068 implies that the neutrino emission can be produced only in the vicinity of the supermassive black hole in the center of the galaxy. The coronal parameters, such as magnetic field strength and corona size, that make this emission possible, are consistent with the spectral excess registered in the millimeter range. The suggested model and relevant physical parameters are similar to those revealed for several nearby Seyferts. Due to the internal gamma-ray attenuation, the suggested scenario cannot be verified by observations of NGC 1068 in the GeV and TeV gamma-ray energy bands. However, the optical depth is expected to become negligible for MeV gamma-rays, thus future observations in this band will be able to validate our model.

Keywords: Accretion, Black hole physics, Supermassive black holes, Black holes, High energy astrophysics, Neutrino astronomy, Seyfert galaxies, Active galactic nuclei, Particle astrophysics, Astrophysical black holes
Accelerated Electrons Observed Down to &lt;7 keV in a NuSTAR Solar Microflare. We report the detection of emission from a nonthermal electron distribution in a small solar microflare (GOES class A5.7) observed by the Nuclear Spectroscopic Telescope Array, with supporting observation by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The flaring plasma is well accounted for by a thick-target model of accelerated electrons collisionally thermalizing within the loop, akin to the "coronal thick-target" behavior occasionally observed in larger flares. This is the first positive detection of nonthermal hard X-rays from the Sun using a direct imager (as opposed to indirectly imaging instruments). The accelerated electron distribution has a spectral index of 6.3 ± 0.7, extends down to at least 6.5 keV, and deposits energy at a rate of ∼2 × 1027 erg s-1, heating the flare loop to at least 10 MK. The existence of dominant nonthermal emission in X-rays down to &lt;5 keV means that RHESSI emission is almost entirely nonthermal, contrary to what is usually assumed in RHESSI spectroscopy. The ratio of nonthermal to thermal energies is similar to that of large flares, in contrast to what has been found in previous studies of small RHESSI flares. We suggest that a coronal thick target may be a common property of many small microflares based on the average electron energy and collisional mean free path. Future observations of this kind will enable understanding of how flare particle acceleration changes across energy scales, and will aid the push toward the observational regime of nanoflares, which are a possible source of significant coronal heating.

Keywords: The Sun, Active sun, Solar flare spectra, Flare stars, Non-thermal radiation sources, Solar x-ray flares
Revealing the Dark Threads of the Cosmic Web. Modern cosmology predicts that matter in our universe today has assembled into a vast network of filamentary structures colloquially termed the "cosmic web." Because this matter is either electromagnetically invisible (I.e., dark) or too diffuse to image in emission, tests of this cosmic web paradigm are limited. Wide-field surveys do reveal web-like structures in the galaxy distribution, but these luminous galaxies represent less than 10% of baryonic matter. Statistics of absorption by the intergalactic medium (IGM) via spectroscopy of distant quasars support the model yet have not conclusively tied the diffuse IGM to the web. Here, we report on a new method inspired by the Physarum polycephalum slime mold that is able to infer the density field of the cosmic web from galaxy surveys. Applying our technique to galaxy and absorption-line surveys of the local universe, we demonstrate that the bulk of the IGM indeed resides in the cosmic web. From the outskirts of cosmic web filaments, at approximately the cosmic mean matter density (ρm) and ∼5 virial radii from nearby galaxies, we detect an increasing H I absorption signature toward higher densities and the circumgalactic medium, to ∼200ρm. However, the absorption is suppressed within the densest environments, suggesting shock-heating and ionization deep within filaments and/or feedback processes within galaxies.

Keywords: Quasar absorption line spectroscopy, Circumgalactic medium, Voids, Cosmic web, Galaxy evolution, Intergalactic medium, Galaxy quenching, Intergalactic filaments
A Nonthermal Bomb Explains the Near-infrared Superflare of Sgr A*. The Galactic center supermassive black hole, Sgr A*, has experienced a strong, unprecedented flare in 2019 May when its near-infrared luminosity reached much brighter levels than ever measured. We argue that an explosive event of particle acceleration to nonthermal energies in the innermost parts of the accretion flow—a nonthermal bomb—explains the near-infrared light curve. We discuss potential mechanisms that could explain this event such as magnetic reconnection and relativistic turbulence acceleration. Multiwavelength monitoring of such superflares in radio, infrared, and X-rays should allow a concrete test of the nonthermal bomb model and put better constraints on the mechanism that triggered the bomb.

Keywords: Accretion, Black hole physics, Galactic center, Non-thermal radiation sources
Betelgeuse Just Is Not That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse. We present optical spectrophotometry of the red supergiant (RSG) Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way RSGs, we conclude that Betelgeuse has a current effective temperature of 3600 ± 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that episodic mass loss and an increase in the amount of large-grain circumstellar dust along our sightline to Betelgeuse is the most likely explanation for its recent photometric evolution.

Keywords: Circumstellar dust, M supergiant stars, Stellar atmospheres
Spectropolarimetric Analysis of FRB 181112 at Microsecond Resolution: Implications for Fast Radio Burst Emission Mechanism. We have developed a new coherent dedispersion mode to study the emission of fast radio bursts (FRBs) that trigger the voltage capture capability of the Australian SKA Pathfinder (ASKAP) interferometer. In principle the mode can probe emission timescales down to 3 ns with full polarimetric information preserved. Enabled by the new capability, here we present a spectropolarimetric analysis of FRB 181112 detected by ASKAP, localized to a galaxy at redshift 0.47. At microsecond time resolution the burst is resolved into four narrow pulses with a rise time of just 15 μs for the brightest. The pulses have a diversity of morphology, but do not show evidence for temporal broadening by turbulent plasma along the line of sight, nor is there any evidence for periodicity in their arrival times. The pulses are highly polarized (up to 95%), with the polarization position angle varying both between and within pulses. The pulses have apparent rotation measures that vary by 15± 2 rad {m}-2 and apparent dispersion measures that vary by 0.041± 0.004 pc {cm}-3 . Conversion between linear and circular polarization is observed across the brightest pulse. We conclude that the FRB 181112 pulses are most consistent with being a direct manifestation of the emission process or the result of propagation through a relativistic plasma close to the source. This demonstrates that our method, which facilitates high-time-resolution polarimetric observations of FRBs, can be used to study not only burst emission processes, but also a diversity of propagation effects present on the gigaparsec paths they traverse.

Keywords: Radio interferometry, Astronomical instrumentation, Polarimetry, Radio transient sources