Sazuna/UAT_keywords huggingface dataset:
Swift Multiwavelength Follow-up of LVC S200224ca and the Implications for Binary Black Hole Mergers. On 2020 February 24, during their third observing run ("O3"), the Laser Interferometer Gravitational-wave Observatory and Virgo Collaboration detected S200224ca: a candidate gravitational wave (GW) event produced by a binary black hole (BBH) merger. This event was one of the best-localized compact binary coalescences detected in O3 (with 50%/90% error regions of 13/72 deg2), and so the Neil Gehrels Swift Observatory performed rapid near-UV/X-ray follow-up observations. Swift-XRT and UVOT covered approximately 79.2% and 62.4% (respectively) of the GW error region, making S200224ca the BBH event most thoroughly followed-up in near-UV (u-band) and X-ray to date. No likely EM counterparts to the GW event were found by the Swift BAT, XRT, or UVOT, nor by other observatories. Here, we report on the results of our searches for an EM counterpart, both in the BAT data near the time of the merger, and in follow-up UVOT/XRT observations. We also discuss the upper limits we can place on EM radiation from S200224ca, as well as the implications these limits have on the physics of BBH mergers. Namely, we place a shallow upper limit on the dimensionless BH charge, $\hat{q}\lt 1.4\times {10}^{-4}$ , and an upper limit on the isotropic-equivalent energy of a blast wave E &lt; 4.1 × 1051 erg (assuming typical GRB parameters).

Keywords: X-ray astronomy, Gamma-ray bursts, Black holes, High energy astrophysics, Near ultraviolet astronomy, Gravitational waves, Gamma-ray astronomy
Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of r-process Dynamics. Lanthanide element signatures are key to understanding many astrophysical observables, from merger kilonova light curves to stellar and solar abundances. To learn about the lanthanide element synthesis that enriched our solar system, we apply the statistical method of Markov Chain Monte Carlo to examine the nuclear masses capable of forming the r-process rare-earth abundance peak. We describe the physical constraints we implement with this statistical approach and demonstrate the use of the parallel chains method to explore the multidimensional parameter space. We apply our procedure to three moderately neutron-rich astrophysical outflows with distinct types of r-process dynamics. We show that the mass solutions found are dependent on outflow conditions and are related to the r-process path. We describe in detail the mechanism behind peak formation in each case. We then compare our mass predictions for neutron-rich neodymium and samarium isotopes to the latest experimental data from the CPT at CARIBU. We find our mass predictions given outflows that undergo an extended (n,γ)⇄(γ,n) equilibrium to be those most compatible with both observational solar abundances and neutron-rich mass measurements.

Keywords: Neutron stars, Bayesian statistics, Nucleosynthesis, Solar abundances, Chi-squared statistic, Nuclear astrophysics
Bright, Months-long Stellar Outbursts Announce the Explosion of Interaction-powered Supernovae. Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude -13 occur prior to 25% (5-69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 1049 erg, precursors could eject ∼1 M⊙ of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

Keywords: Late stellar evolution, Core-collapse supernovae, Stellar mass loss, Circumstellar matter, Eruptive phenomena, Stellar flares
STARCNET: Machine Learning for Star Cluster Identification. We present a machine learning (ML) pipeline to identify star clusters in the multicolor images of nearby galaxies, from observations obtained with the Hubble Space Telescope as part of the Treasury Project LEGUS (Legacy ExtraGalactic Ultraviolet Survey). STARCNET (STAR Cluster classification NETwork) is a multiscale convolutional neural network (CNN) that achieves an accuracy of 68.6% (four classes)/86.0% (two classes: cluster/noncluster) for star cluster classification in the images of the LEGUS galaxies, nearly matching human expert performance. We test the performance of STARCNET by applying a pre-trained CNN model to galaxies not included in the training set, finding accuracies similar to the reference one. We test the effect of STARCNET predictions on the inferred cluster properties by comparing multicolor luminosity functions and mass-age plots from catalogs produced by STARCNET and by human labeling; distributions in luminosity, color, and physical characteristics of star clusters are similar for the human and ML classified samples. There are two advantages to the ML approach: (1) reproducibility of the classifications: the ML algorithm's biases are fixed and can be measured for subsequent analysis; and (2) speed of classification: the algorithm requires minutes for tasks that humans require weeks to months to perform. By achieving comparable accuracy to human classifiers, STARCNET will enable extending classifications to a larger number of candidate samples than currently available, thus increasing significantly the statistics for cluster studies. * Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: Young massive clusters, Young star clusters, Galactic and extragalactic astronomy, Stellar astronomy, Interacting galaxies, Star clusters
A Blueprint for the Milky Way's Stellar Populations. II. Improved Isochrone Calibration in the SDSS and Pan-STARRS Photometric Systems. We improve the identification and isolation of individual stellar populations in the Galactic halo based on an updated set of empirically calibrated stellar isochrones in the Sloan Digital Sky Survey and Pan-STARRS 1 photometric systems. Along the Galactic prime meridian (l = 0° and 180°), where proper motions and parallaxes from Gaia DR2 can be used to compute rotational velocities of stars in the rest frame of the Milky Way, we use the observed double color-magnitude sequences of stars having large transverse motions, which are mostly attributed to groups of stars in the metal-poor halo and the thick disk with halo-like kinematics, respectively. The Gaia sequences directly constrain color-magnitude relations of model colors, and help to improve our previous calibration using Galactic star clusters. Based on these updated sets of stellar isochrones, we confirm earlier results on the presence of distinct groups of stars in the metallicity versus rotational-velocity plane, and find that the distribution of the most metal-poor ([Fe/H] &lt; -2) stars in our sample can be modeled using two separate groups on prograde and retrograde orbits, respectively. At 4-6 kpc from the Galactic plane, we find approximately equal proportions of the Splashed Disk, and the metal-rich (⟨[Fe/H]⟩ ∼ -1.6) and metal-poor (⟨[Fe/H]⟩ ∼ -2.5) halos on prograde orbits. The Gaia-Sausage-Enceladus, the metal-weak thick disk, and the retrograde halo structure(s) (⟨[Fe/H]⟩ ∼ -2.2) constitute approximately 10% of the rest of the stellar populations at these distances.

Keywords: Stellar abundances, Stellar evolutionary models, Milky Way dynamics, Milky Way stellar halo, Stellar atmospheres
Sunspot Simulations: Penumbra Formation and the Fluting Instability. The fluting instability has been suggested as the driver of the subsurface structure of sunspot flux tubes. We conducted a series of numerical experiments where we used flux tubes with different initial curvatures to study the effect of the fluting instability on the subsurface structure of spots. We used the MURaM code, which has previously been used to simulate complete sunspots, to first compute four sunspots in the slab geometry and then two complete circular spots of opposite polarities. We find that the curvature of a flux tube indeed determines the degree of fluting the flux tube will undergo—the more curved a flux tube is, the more fluted it becomes. In addition, sunspots with strong curvature have strong horizontal fields at the surface and therefore readily form penumbral filaments. The fluted sunspots eventually break up from below, with lightbridges appearing at the surface several hours after fluting commences.

Keywords: Starspots, Stellar interiors, Radiative magnetohydrodynamics, Solar interior, Sunspots, Solar physics
Discovery of a Low-redshift Damped Lyα System in a Foreground Extended Disk Using a Starburst Galaxy Background Illuminator. We present the discovery of a low-redshift damped Lyα (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 (z = 0.17514). The DLA is at an impact parameter of ρ = 36 kpc from the star-forming galaxy, SDSS J111324.08+293051.2 (z = 0.17077). We measure an H column density of N(H ) = 3.47 × 1020 cm-2 along with multiple low-ionization species such as N , N II, Si II, C II, and Si III. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be ADLA ≥ 3.3 kpc2. Assuming a uniform column density over the entire DLA system, we estimate its mass to be MDLA ≥ 5.3 × 106 M⊙. The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s-1 from the systemic velocity of the host for the DLA. This velocity is -84 km s-1 from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the H column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the H disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.

Keywords: Starburst galaxies, Damped Lyman-alpha systems, Galaxy disks, Interstellar absorption, Galaxy evolution, Interstellar medium, Circumgalactic medium, Extragalactic astronomy
The Decline and Fall of the Youngest Planetary Nebula. The Stingray Nebula, a.k.a. Hen3-1357, appeared for the first time in 1990 when bright nebular lines and radio emission that had not been observed before were unexpectedly discovered. In the ensuing years, the nebula faded precipitously. We report changes in shape and large decreases in its nebular emission-line fluxes based on well-calibrated images obtained by the Hubble Space Telescope in 1996 and 2016. Hen3-1357 is now a "recombination nebula."

Keywords: Planetary nebulae, Post-asymptotic giant branch stars, Ionization
Gaussian Process Modeling Fermi-LAT γ-Ray Blazar Variability: A Sample of Blazars with γ-Ray Quasi-periodicities. Blazar variability may be driven by stochastic processes. On the other hand, quasi-periodic oscillation (QPO) behaviors were recently reported to be detected in the Fermi-LAT data of blazars. However, the significances of these QPO signals given by traditional Fourier-like methods are still questioned. We analyze γ-ray light curves of the QPO blazars with two Gaussian process methods, CARMA and celerite, to examine the appropriateness of Gaussian processes for characterizing γ-ray light curves of blazars and the existence of the reported QPOs. We collect a sample of 27 blazars with possible γ-ray periodicity and generate their ∼11 yr Fermi-LAT light curves. We apply the Gaussian process models to the γ-ray light curves, and build their intrinsic power spectral densities (PSDs). The results show that in general the γ-ray light curves can be characterized by CARMA and celerite models, indicating that γ-ray variabilities of blazars are essentially Gaussian processes. The resulting PSDs are generally the red noise shapes with slopes between -0.6 and -1.7. Possible evidence for the γ-ray QPOs in PKS 0537-441 and PG 1553+113 are found in the Gaussian process modelings.

Keywords: Blazars, Period search , Gaussian Processes regression, Gamma-rays, Time series analysis
Stellar Feedback on the Earliest Stage of Massive Star Formation. We report SOFIA/GREAT observations of high-J CO lines and [C II] observations of the super star cluster candidate H72.97-69.39 in the Large Magellanic Cloud (LMC), which is in its very early formation stage. We use our observations to determine if shocks are heating the gas or if photon-dominated regions (PDRs) are being heated by local far-UV radiation. We use a PDR model and a shock model to determine whether the CO and [C II] lines arise from PDRs or shocks. We can reproduce the observed high-J CO and [C II] emission with a clumpy PDR model with the following properties: a density of 104.7 cm-3, a mass of 104 M⊙, and UV radiation of 103.5 in units of Draine field. Comparison with the ALMA beam-filling factor suggests a higher density within the uncertainty of the fit. We find the lower-limit [C II]/total infrared (TIR) ratio (ɛ) traced by [C II]/TIR to be 0.026%, lower than other known young star-forming regions in the LMC. Our shock models may explain the CO (16-15) and CO (11-10) emission lines with shock velocity of 8-11 km s-1, pre-shock density of 104-105 cm-3, and GUV = 0 in units of Draine field. However, the [C II] line emission cannot be explained by a shock model, thus it is originating in a different gas component. Observations of [O ] 63 μm predicted to be 1.1 × 10-13 W m-2 by PDR models and 7.8 × 10-15 W m-2 by shock models will help distinguish between the PDR and shock scenarios.

Keywords: Shocks, Photodissociation regions, Young stellar objects, Star formation, Protostars
Reheating after an Inflationary Universe from a Perfect Fluid and Its Comparison with Observational Data. We present the reheating constraints on an inflationary universe induced by perfect fluid models. Starting with the descriptions for the observables of the scalar field inflationary models in the reconstructed methods, we outline the procedure of perfect fluid inflationary models through these methods to calculate the inflationary observables and reheating. We show that the reheating e-folds number Nre and the reheating final temperature Tre are bound depending on the finite range of reasonable values of ${\omega }_{{re}}$ . By restricting the equation-of-state parameter in the reheating stage, $-\tfrac{1}{3}\lt {\omega }_{{re}}\lt 1$ , more stringent constraints can be derived for the model's parameter space of perfect fluid. These constraints correspond to viable values of the scalar spectral index ns and tensor-to-scalar ratio r, released by Planck2018 observational data.

Keywords: Observational cosmology, Cosmic inflation
Identification of Methyl Isocyanate and Other Complex Organic Molecules in a Hot Molecular Core, G31.41+0.31. G31.41+0.31 is a well known chemically rich hot molecular core (HMC). Using Band 3 observations from the Atacama Large Millimeter Array (ALMA), we have analyzed the chemical and physical properties of the source. We have identified methyl isocyanate (CH3NCO), a precursor of prebiotic molecules, toward the source. In addition to this, we have reported the presence of complex organic molecules (COMs) like methanol (CH3OH), methanethiol (CH3SH), and methyl formate (CH3OCHO). Additionally, we have used transitions from molecules like HCN, H13CO+, and SiO to trace the presence of infall and outflow signatures around the star-forming region. For the COMs, we have estimated the column densities and kinetic temperatures, assuming molecular excitation under local thermodynamic equilibrium (LTE) conditions. From the estimated kinetic temperatures of certain COMs, we found that multiple temperature components may be present in the HMC environment. Comparing the obtained molecular column densities between the existing observational results around other HMCs, it seems that the COMs are favorably produced in the hot core environment (∼100 K or higher). Though the spectral emissions toward G31.41+0.31 are not fully resolved, we find that CH3NCO and other COMs are possibly formed on grain/ice phase and populate the gas environment similar to other hot cores like Sgr B2, Orion KL, and G10.47+0.03.

Keywords: Massive stars, Spectral line identification, Chemical abundances, Astronomy data analysis, Astrochemistry, Interstellar medium
Dynamics and Emission of Wind-powered Afterglows of Gamma-Ray Bursts: Flares, Plateaus, and Steep Decays. We have developed a model of early X-ray afterglows of gamma-ray bursts originating from the reverse shock (RS) propagating through ultrarelativistic, highly magnetized pulsar-like winds produced by long-lasting central engines. We first performed fluid and magnetohydrodynamic numerical simulations of relativistic double explosions. We demonstrate that even for constant properties of the wind a variety of temporal behaviors can be produced, depending on the energy of the initial explosion and the wind power, the delay time for the switch-on of the wind, and the magnetization of the wind. X-ray emission of the highly magnetized RS occurs in the fast-cooling regime—this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that (i) RS emission naturally produces light curves, showing power-law temporal evolution with various temporal indices; (ii) mild wind power, of the order of ∼1046 erg s-1 (equivalent isotropic), can reproduce the afterglows' plateau phase; (iii) termination of the wind can produce sudden steep decays; and (iv) short-duration afterglow flares are due to mild variations in the wind luminosity, with small total injected energy.

Keywords: X-ray transient sources, Magnetohydrodynamics, Gamma-ray bursts, Non-thermal radiation sources
Evolution of Galaxy Star Formation and Metallicity: Impact on Double Compact Object Mergers. In this paper, we study the impact of different galaxy statistics and empirical metallicity scaling relations on the merging rates and properties of compact object binaries. Firstly, we analyze the similarities and differences of using the star formation rate functions versus stellar mass functions as galaxy statistics for the computation of cosmic star formation rate density. We then investigate the effects of adopting the Fundamental Metallicity Relation versus a classic Mass Metallicity Relation to assign metallicity to galaxies with given properties. We find that when the Fundamental Metallicity Relation is exploited, the bulk of the star formation occurs at relatively high metallicities, even at high redshift; the opposite holds when the Mass Metallicity Relation is employed, since in this case the metallicity at which most of the star formation takes place strongly decreases with redshift. We discuss the various reasons and possible biases giving rise to this discrepancy. Finally, we show the impact of these different astrophysical prescriptions on the merging rates and properties of compact object binaries; specifically, we present results for the redshift-dependent merging rates and for the chirp mass and time delay distributions of the merging binaries.

Keywords: Luminosity function, Neutron stars, Stellar mergers, Astrophysical black holes, Gravitational wave sources, Stellar mass functions, Star formation, Galaxy evolution, Compact objects, Gravitational waves, Metallicity, Early-type galaxies
Dispersion and Rotation Measures from the Ejecta of Compact Binary Mergers: Clue to the Progenitors of Fast Radio Bursts. Since the discovery of FRB 200428 associated with the Galactic SGR 1935+2154, magnetars have been considered to power fast radio bursts (FRBs). It is widely believed that magnetars could form by core-collapse (CC) explosions and compact binary mergers, such as binary neutron stars (BNSs), binary white dwarfs (BWDs), and neutron star-white dwarf (NSWD) mergers. Therefore, it is important to distinguish the various progenitors. The expansion of the merger ejecta produces a time-evolving dispersion measure (DM) and rotation measure (RM) that can probe the local environments of FRBs. In this paper, we derive the scaling laws for the DM and RM from ejecta with different dynamical structures (the mass and energy distribution) in the uniform ambient medium (merger scenario) and wind environment (CC scenario). We find that the DM and RM will increase in the early phase, while DM will continue to grow slowly but RM will decrease in the later phase in the merger scenario. We fit the DM and RM evolution of FRB 121102 simultaneously for the first time in the BNS merger scenario and find that the source age is ∼9-10 yr when it was first detected in 2012, and the ambient medium density is ∼2.5-3.1 cm-3. The large offsets of some FRBs are consistent with the BNS/NSWD channel. The population synthesis method is used to estimate the rate of compact binary mergers. The rate of BWD mergers is close to the observed FRB rate. Therefore, the progenitors of FRBs may not be unique.

Keywords: Magnetars, Radio bursts, Radio transient sources