Sazuna/UAT_keywords huggingface dataset:
ALMA Observations Reveal No Preferred Outflow-filament and Outflow-magnetic Field Orientations in Protoclusters. We present a statistical study of the orientation of outflows with respect to large-scale filaments and magnetic fields. Although filaments are widely observed toward Galactic star-forming regions, the exact role of filaments in star formation is unclear. Studies toward low-mass star-forming regions revealed both preferred and random orientations of outflows with respect to the filament long axes, while outflows in massive star-forming regions are mostly oriented perpendicular to the host filaments and parallel to the magnetic fields at similar physical scales. Here, we explore outflows in a sample of 11 protoclusters in H II regions, a more evolved stage compared to infared dark clouds, using Atacama Large Millimeter/submillimeter Array CO (3-2) line observations. We identify a total of 105 outflow lobes in these protoclusters. Among the 11 targets, 7 are embedded within parsec-scale filamentary structures detected in 13CO line and 870 μm continuum emissions. The angles between outflow axes and corresponding filaments (γFil) do not show any hint of preferred orientations (I.e., orthogonal or parallel as inferred in numerical models) with respect to the position angle of the filaments. Identified outflow lobes are also not correlated with the magnetic fields and Galactic plane position angles. Outflows associated with filaments aligned along the large-scale magnetic fields are also randomly oriented. Our study presents the first statistical results of outflow orientation with respect to large-scale filaments and magnetic fields in evolved massive star-forming regions. The random distribution suggests a lack of alignment of outflows with filaments, which may be a result of the evolutionary stage of the clusters.

Keywords: Interstellar filaments, Stellar jets, Protoclusters, Star formation, Interstellar medium, Submillimeter astronomy, H II regions
A Photometric Analysis of the Relationship between the UV flux of Type Ia Supernovae and Host-galaxy Metallicity. The effect of progenitor metallicity on Type Ia supernovae (SNe Ia) has important cosmological implications due to the need for these standardizable candles to be compared across large spans of cosmic time in which the progenitor stars might have different properties. Theoretical models have come to different conclusions as to the wavelength range impacted by metallicity differences, leading to differing interpretations of the growing sample of UV observations. Recent work has claimed a correlation between the mid-UV flux of SNe Ia measured from Swift grism spectra and the gas-phase metallicities measured for their host galaxies. Here we examine UV photometry for the same objects. We find no significant correlations between the UV-optical colors (or UV/optical count rate ratios) of the SNe Ia and the host-galaxy properties of mass or metallicity. The lack of a significant correlation with host-galaxy metallicity implies that a physical difference other than progenitor metallicity dominates the UV flux differences. Understanding the existing observations requires improved theoretical models and a larger parameter space of physical differences.

Keywords: Metallicity, Type Ia supernovae
Superflares on Solar-type Stars from the First Year Observation of TESS. Superflares, which are strong explosions on stars, have been well studied with the progress of spacetime-domain astronomy. In this work, we present the study of superflares on solar-type stars using Transiting Exoplanet Survey Satellite (TESS) data. Thirteen sectors of observations during the first year of the TESS mission covered the southern hemisphere of the sky, containing 25,734 solar-type stars. We verified 1216 superflares on 400 solar-type stars through automatic search and visual inspection with 2 minute cadence data. Our result suggests a higher superflare frequency distribution than the result from Kepler. This may be because the majority of TESS solar-type stars in our data set are rapidly rotating stars. The power-law index γ of the superflare frequency distribution ( ${dN}/{dE}\propto {E}^{-\gamma }$ ) is constrained to be γ = 2.16 ± 0.10, which is a little larger than that of solar flares but consistent with the results from Kepler. Because only seven superflares of Sun-like stars are detected, we cannot give a robust superflare occurrence frequency. Four stars were accompanied by unconfirmed hot planet candidates. Therefore, superflares may possibly be caused by stellar magnetic activities instead of planet-star interactions. We also find an extraordinary star, TIC43472154, which exhibits about 200 superflares per year. In addition, the correlation between the energy and duration of superflares ( ${T}_{\mathrm{duration}}\propto {E}^{\beta }$ ) is analyzed. We derive the power-law index to be β = 0.42 ± 0.01, which is a little larger than β = 1/3 from the prediction according to magnetic reconnection theory.

Keywords: Stellar flares, G stars
Strong Soft X-Ray Excess in 2015 XMM-Newton Observations of BL Lac OJ 287. We report a strong soft X-ray excess in the BL Lacartae γ-ray blazar OJ 287 during long exposure in 2015 May, among two of the latest XMM-Newton observations performed in 2015 and 2018 May. In the case of the 2015 May observation, a log parabola model fits the EPIC-pn data well, while a log parabola plus a power law describes the overall simultaneous optical to X-ray spectra, suggesting the excess as the synchrotron tail. This interpretation, however, is inconsistent with the observed spectral break between near-infrared (NIR) and optical spectra, attributed to a standard disk around a supermassive black hole (SMBH). Based on this, we considered two commonly invoked accretion-disk-based models in active galactic nuclei (AGNs) to explain the soft excess: the cool Comptonization component in the accretion disk and the blurred reflection from the partially ionized accretion disk. We found that both cool Comptonization and blurred reflection models provide an equally good fit to the data, and favor a super-heavy SMBH of mass ∼1010 M☉. Further investigation of about a month-long simultaneous X-ray and ultraviolet (UV) pointing observations revealed a delayed UV emission with respect to the 1.5-10 keV band, favoring X-ray reprocessing phenomenon as the dominant mechanism. The results suggest that the soft excess is probably caused by strong light bending close to the SMBH. The detected soft excess in the 2015 data and its disappearance in the 2018 data is also consistent with the presence of accretion-disk emission, inferred from the NIR-optical spectral break between 2013 May and 2016 March.

Keywords: Supermassive black holes, BL Lacertae objects, High energy astrophysics, Blazars, Active galaxies, Galaxy jets, Galaxy nuclei, X-ray active galactic nuclei, Relativistic disks
Energy Power Spectra Measured at an Interplanetary Shock by the New Horizon's SWAP Experiment: 1D Full Particle Simulations versus Observations. One-dimensional particle-in-cell (PIC) simulations are used to analyze the energy spectra measured by the New Horizons' Solar Wind Around Pluto (SWAP) instrument in the upstream region of an interplanetary shock observed at a distance of ∼34 au from the Sun. The use of individual populations simulating the different solar wind ion and pick-up ion (PUI) populations allows us to clearly identify the contribution of each population to the global energy spectra. The important role of shock front obliquity is stressed in the formation of PUIs streaming back along the magnetic field into the upstream region far from the front. Energy spectra measured by the SWAP experiment are well reproduced in the present simulations. A detailed analysis shows that (1) the highest-energy part of the spectrum is formed primarily by both backstreaming PUI-H+ and PUI-He+; (2) the middle-energy part of the energy spectrum is composed of both solar wind SW-H+ and SW-He2+ incoming ions that are superimposed on the PUI-H+ population; and (3) the low-energy range is composed of incoming PUI-H+. The agreement between experimental and simulation results is improved by using an initially filled-shell distribution for the PUI-H+ population (instead of a zero-thickness shell), as this affects the low-energy part of the spectrum strongly. This means that PUI-H+ ions have sufficient time to diffuse onto and fill out a shell distribution after their initial pick-up in the heliosphere, indicating that the subsequent cooling has an important impact on the global energy spectrum.

Keywords: Space plasmas, Interplanetary particle acceleration, Interplanetary shocks, Heliosphere
Mars: Quantitative Evaluation of Crocus Melting behind Boulders. The possibility of liquid water on present-day Mars has been debated for half a century. Melting is physically difficult under Martian environmental conditions, because with the total pressure of the atmosphere near the triple point pressure of water, evaporative cooling of ice is high near the melting point. Here, a suite of quantitative models is used to investigate whether melting of seasonal water frost can occur on present-day Mars. An updated and generalized parameterization is derived for the turbulent convective heat flux that results from the buoyancy of water vapor. A three-dimensional surface energy balance model is used to calculate surface temperatures; it includes terrain shadowing, self heating, and subsurface conduction. Protruding topography creates locations that experience a rapid transition from conditions where water frost accumulates to high solar energy input. Beyond the pole-facing side of a boulder, CO2 and ${{\rm{H}}}_{2}{\rm{O}}$ frost can accumulate seasonally, and once the Sun reemerges and the CO2 frost disappears, the water frost is heated to near melting temperature within one or two sols. Dust contained in the CO2 frost facilitates the formation of a protective sublimation lag. Temperatures within about 10 K of the melting point are reached within one or two sols after the end of water frost accumulation. For expected sublimation lag thicknesses, evaporative cooling is not significantly reduced. Overall, melting of pure water ice is not expected under present-day Mars conditions. However, at temperatures that are readily reached, seasonal water frost can melt on a salt-rich substrate. Hence, crocus melting behind boulders can lead to the formation of brines under present-day Mars conditions.

Keywords: Water vapor, Theoretical models, Mars, Planetary science, Astrophysical fluid dynamics
The Explosion of Helium Stars Evolved with Mass Loss. Light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss. These presupernova stars should approximate the results of binary evolution for stars in interacting systems that lose their envelopes close to the time of helium core ignition. Initial helium star masses are in the range 2.5-40 M⊙, which corresponds to main-sequence masses of about 13-90 M⊙. Common SNe Ib and Ic result from stars whose final masses are approximately 2.5-5.6 M⊙. For heavier stars, a large fraction of collapses lead to black holes, though there is an island of explodability for presupernova masses near 10 M⊙. The median neutron star mass in binaries is 1.35-1.38 M⊙, and the median black hole mass is between 9 and 11 M⊙. Even though black holes less massive than 5 M⊙ are rare, they are predicted down to the maximum neutron star mass. There is no empty "gap," only a less populated mass range. For standard assumptions regarding the explosions and nucleosynthesis, the models predict light curves that are fainter than the brighter common SNe Ib and Ic. Even with a very liberal but physically plausible increase in 56Ni production, the highest-energy models are fainter than 1042.6 erg s-1 at peak, and very few approach that limit. The median peak luminosity ranges from 1042.0 to 1042.3 erg s-1. Possible alternatives to the standard neutrino-powered and radioactive-illuminated models are explored. Magnetars are a promising alternative. Several other unusual varieties of SNe I at both high and low mass are explored.

Keywords: Light curves, Explosive nucleosynthesis, Core-collapse supernovae, Compact objects
The Strikingly Metal-rich Halo of the Sombrero Galaxy. The nature of the Sombrero galaxy (M104 = NGC 4594) has remained elusive despite many observational studies at a variety of wavelengths. Here we present Hubble Space Telescope imaging of two fields at ∼16 and 33 kpc along the minor axis to examine stellar metallicity gradients in the extended spheroid. We use this imaging, extending more than 2 mag below the tip of the red giant branch, in combination with artificial star tests to forward model observed color-magnitude diagrams, measuring metallicity distribution functions (MDFs) at different radii along the minor axis. An important and unexpected result is that the halo of the Sombrero is strikingly metal-rich: even the outer field, located at ∼17 effective radii of the bulge, has a median metallicity [Z/H] ∼ -0.15, and the fraction of stars with [Z/H] &lt; -1.0 is negligible. This is unprecedented among massive galaxy halos studied to date, even among giant ellipticals. We find significant radial metallicity gradients, characterized by an increase in the fraction of metal-poor stars with radius and a gradient in median metallicity of ∼0.01 dex kpc-1. The density profile is well fit by power laws with slopes that exhibit a dependence on metallicity, with flatter slopes for more metal-poor stars. We discuss our results in the context of recent stellar MDF studies of other nearby galaxies and potential formation scenarios for the Sombrero galaxy.

Keywords: Galaxy spheroids, Galaxy stellar content, Galaxy stellar halos, Star formation, Metallicity
Evolution of the Accretion Disk-Corona during the Bright Hard-to-soft State Transition: A Reflection Spectroscopic Study with GX 339-4. We present the analysis of several observations of the black hole binary GX 339-4 during its bright intermediate states from two different outbursts (2002 and 2004), as observed by the RXTE/Proportional Counter Array. We perform a consistent study of its reflection spectrum by employing the relxill family of relativistic reflection models to probe the evolutionary properties of the accretion disk including the inner disk radius (Rin), ionization parameter (ξ), temperatures of the inner disk (Tin), corona (kTe), and its optical depth (τ). Our analysis indicates that the disk inner edge approaches the innermost stable circular orbit during the early onset of the bright hard state, and that the truncation radius of the disk remains low (&lt;9 Rg) throughout the transition from hard to soft state. This suggests that the changes observed in the accretion disk properties during the state transition are driven by variation in accretion rate, and not necessarily due to changes in the inner disk's radius. We compare the aforementioned disk properties in two different outbursts with state transitions occurring at dissimilar luminosities and find identical evolutionary trends in the disk properties, with differences only seen in the corona's kTe and τ. We also perform an analysis by employing a self-consistent Comptonized accretion disk model accounting for the scatter of disk photons by the corona, and measure the low inner disk truncation radius across the bright intermediate states, using the temperature-dependent values of the spectral hardening factor, thereby independently confirming our results from the reflection analysis.

Keywords: Accretion, Black hole physics, X-ray astronomy, Astronomy data modeling, High energy astrophysics, Gravitation, General relativity, Compact objects, Spectroscopy, Low-mass x-ray binary stars, X-ray sources, Astrophysical black holes
On the Wind-driven Relaxation Cycle in Accretion Disks. A disk wind can cause perturbations that propagate throughout the disk via diffusive processes. On reaching the inner disk, these perturbations can change the disk luminosity, which in turn, can change the wind mass loss rate, ${\dot{M}}_{w}$ . It has been argued that this so-called "wind-driven relaxation cycle" might explain the observed variability in some disk accreting objects. Here, we study the response of the innermost mass accretion rate ${\dot{M}}_{a}$ to the loss of matter at different rates and radii. We allow the wind launching radius, RL, to scale with ${\dot{M}}_{a}$ . We computed a grid of time-dependent models for various ${\dot{M}}_{w}$ - ${\dot{M}}_{a}$ and RL- ${\dot{M}}_{a}$ dependencies. We find that the disk behavior significantly differs for the "variable RL" case compared to the "fixed RL" case. In particular, much stronger winds are required to destabilize the disk in the former than the latter case. However, the ${\dot{M}}_{a}$ amplitude does not grow significantly even for unstable cases because the oscillations saturate at a low level either due to disk depletion or due to the wind being launched at very small radii, or both. This result implies that disk winds are unlikely to be responsible for state transitions as those require large changes in the inner disk. Despite modest changes at the inner disk regions, the disk surface density at large radii can vary with a large amplitude, I.e., from 0 to a few factors of the steady state value. This dramatic variation of the outer disk could have observable consequences.

Keywords: Accretion, Low-mass x-ray binary stars, Hydrodynamics
Nonlinear Reconnection in Magnetized Turbulence. Recent analytical works on strong magnetized plasma turbulence have hypothesized the existence of a range of scales where the tearing instability may govern the energy cascade. In this paper, we estimate the conditions under which such tearing may give rise to full nonlinear magnetic reconnection in the turbulent eddies. When those conditions are met, a new turbulence regime is accessed where reconnection-driven energy dissipation becomes common, rather than the rare feature that it must be when they are not. We conclude that while such conditions are very stringent for fluid-scale eddies, they are easily met for kinetic-scale eddies; in particular, we suggest that our arguments may help explain recent Magnetospheric Multiscale (MMS) observations of (so-called) electron-only reconnection and of energy dissipation via electron Landau damping in the Earth's magnetosheath.

Keywords: Space plasmas, Plasma physics, Interplanetary turbulence, Plasma astrophysics, Magnetic fields
Synchrotron Gamma-Ray Emission Model of the Giant Outburst of Quasar 3C 279 in 2015 June: Fast Reconnection or Stochastic Acceleration with Electromagnetic Cascade?. We test the synchrotron emission scenario for the very bright gamma-ray flare of blazar 3C 279 observed in 2015 June using time-dependent numerical simulations. A bulk Lorentz factor as high as 100 can bring the synchrotron maximum energy above the GeV energy range. We find two possible solutions for the X-ray to gamma-ray spectrum. One is a prompt electron injection model with a hard power-law index as magnetic reconnection models suggest. Too strong a magnetic field yields too bright a synchrotron X-ray flux due to secondary electron-positron pairs. Even in the prompt electron injection model, the Poynting flux luminosity is at most comparable to the gamma-ray or electron luminosity. Another model is the stochastic acceleration model, which leads to a very unique picture accompanying the electromagnetic cascade and reacceleration of the secondary electron-positron pairs. In this model, the energy budget of the magnetic field is very low compared to gamma-rays and electrons.

Keywords: Blazars
NuSTAR Observations of the Transient Galactic Black Hole Binary Candidate Swift J1858.6-0814: A New Sibling of V404 Cyg and V4641 Sgr?. Swift J1858.6-0814 was discovered by the Burst Alert Telescope on Swift on 2018 October 25. Here we report on the first follow-up Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the source, which shows variability spanning two orders of magnitude in count rate on timescales of ∼10-100 s. The power spectrum of the source does not show any quasi-periodic oscillations or periodicity, but has a large fractional rms amplitude of 147% ± 3%, exhibiting a number of large flares throughout the observation. The hardness ratio (defined as R10-79keV/R3-10keV) of the flares tends to be soft, while the source spans a range of hardness ratios during nonflaring periods. The X-ray spectrum of the source shows strong reflection features, which become more narrow and peaked during the nonflaring intervals. We fit an absorbed relativistic reflection model to the source spectra to place physical constraints on the system. Most notably, we find that the source exhibits a large and varying intrinsic absorbing column density (NH = (1.4-4.2) × 1023 cm-2). This large intrinsic absorption is further supported by the energy spectra extracted from two flares observed simultaneously by NuSTAR and the Neutron Star Interior Composition Explorer. We find that the inner accretion disk of the source has a low inclination, $I\lt 29^\circ $ (3σ upper limit), while the iron abundance in the disk is close to solar, AFe = 1.0 ± 0.3. We set a 90% confidence upper limit on the inner radius of the accretion disk of rin &lt; 8rISCO and, by fixing rin to be at rISCO, a 90% confidence lower limit on the spin of the black hole of ${a}^{* }\gt 0.0$ . Finally, we compare the properties of Swift J1858.6-0814 to those of V404 Cygni and V4641 Sgr, which both show rapid flaring and a strong and variable absorption.

Keywords: Low-mass x-ray binary stars, X-ray transient sources, Stellar mass black holes
Gauss-Bonnet Inflation after Planck2018. We study the primordial perturbations and reheating process in the models where the Gauss-Bonnet (GB) term is nonminimally coupled to the canonical and noncanonical (DBI and tachyon) scalar fields. We consider several potentials and GB coupling terms as power-law, dilaton-like, cosh-type, E-model, and T-model. To seek the observational viability of these models, we study the scalar perturbations numerically and compare the results with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at 68% CL and 95% CL. We also study the tensor perturbations in confrontation with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO, and Virgo2016 joint data at 68% CL and 95% CL. In this regard, we obtain some constraints on the GB coupling parameter β. Another important process in the early universe is the reheating phase after inflation, which is necessary to reheat the universe for subsequent evolution. In this regard, we study the reheating process in these models and find some expressions for the e-folds number and temperature during that era. Considering that from Planck TT, TE, EE+lowEB+lensing data and BICEP2/Keck Array 2014, based on the ΛCDM $+r+\tfrac{{{dn}}_{s}}{d\mathrm{ln}k}$ model, we have ns = 0.9658 ± 0.0038 and r &lt; 0.072, we obtain some constraints on the e-folds number and temperature. From the values of the e-folds number and the effective equation of state and also the observationally viable value of the scalar spectral index, we explore the capability of the models in explaining the reheating phase.

Keywords: Observational cosmology, Inflationary universe, Early universe