Sazuna/UAT_keywords huggingface dataset:
A DECam Search for Explosive Optical Transients Associated with IceCube Neutrino Alerts. In this work, we investigate the likelihood of association between real-time, neutrino alerts with teraelectronvolt to petaelectronvolt energy from IceCube and optical counterparts in the form of core-collapse supernovae (CC SNe). The optical follow-up of IceCube alerts requires two main instrumental capabilities: (1) deep imaging, since 73% of neutrinos would come from CC SNe at redshifts z &gt; 0.3, and (2) a large field of view (FoV), since typical IceCube muon neutrino pointing accuracy is on the order of ∼1 deg. With Blanco/DECam (gri to 24th magnitude and 2.2 deg diameter FoV), we performed a triggered optical follow-up observation of two IceCube alerts, IC170922A and IC171106A, on six nights during the three weeks following each alert. For the IC170922A (IC171106A) follow-up observations, we expect that 12.1% (9.5%) of coincident CC SNe at z ≲ 0.3 are detectable, and that, on average, 0.23 (0.07) unassociated SNe in the neutrino 90% containment regions also pass our selection criteria. We find two candidate CC SNe that are temporally coincident with the neutrino alerts in the FoV, but none in the 90% containment regions, a result that is statistically consistent with expected rates of background CC SNe for these observations. If CC SNe are the dominant source of teraelectronvolt to petaelectronvolt neutrinos, we would expect an excess of coincident CC SNe to be detectable at the 3σ confidence level using DECam observations similar to those of this work for ∼60 (∼200) neutrino alerts with (without) redshift information for all candidates.

Keywords: Neutrino astronomy, Optical observation, Core-collapse supernovae
Constraints on Gamma-Ray and Neutrino Emission from NGC 1068 with the MAGIC Telescopes. Starburst galaxies and star-forming active galactic nuclei are among the candidate sources thought to contribute appreciably to the extragalactic gamma-ray and neutrino backgrounds. NGC 1068 is the brightest of the star-forming galaxies found to emit gamma-rays from 0.1 to 50 GeV. Precise measurements of the high-energy spectrum are crucial to study the particle accelerators and probe the dominant emission mechanisms. We have carried out 125 hr of observations of NGC 1068 with the MAGIC telescopes in order to search for gamma-ray emission in the very-high-energy band. We did not detect significant gamma-ray emission, and set upper limits at the 95% confidence level to the gamma-ray flux above 200 GeV f &lt; 5.1 × 10-13 cm-2 s-1. This limit improves previous constraints by about an order of magnitude and allows us to put tight constraints on the theoretical models for the gamma-ray emission. By combining the MAGIC observations with the Fermi-LAT spectrum we limit the parameter space (spectral slope, maximum energy) of the cosmic ray protons predicted by hadronuclear models for the gamma-ray emission, while we find that a model postulating leptonic emission from a semi-relativistic jet is fully consistent with the limits. We provide predictions for IceCube detection of the neutrino signal foreseen in the hadronic scenario. We predict a maximal IceCube neutrino event rate of 0.07 yr-1.

Keywords: Gamma-ray sources, Starburst galaxies, Active galaxies
Validating Time-Distance Helioseismic Inversions for Nonseparable Subsurface Profiles of an Average Supergranule. Supergranules are divergent 30 Mm-sized cellular flows observed everywhere at the solar photosphere. Their place in the hierarchy of convective structures and their origin remain poorly understood. Estimating supergranular depth is of particular interest because this may help point to the underlying physics. However, their subsurface velocity profiles have proven difficult to ascertain. Birch et al. suggested that helioseismic inferences would benefit from an ensemble average over multiple realizations of supergranules due to the reduction in realization noise. Bhattacharya et al. used synthetic forward-modeled seismic wave travel times and demonstrated the potential of helioseismic inversions to recover the flow profile of an average supergranule that is separable in the horizontal and vertical directions, although the premise of this calculation has since been challenged by Ferret. In this work we avoid this assumption and carry out a validation test of helioseismic travel-time inversions starting from plausible synthetic nonseparable profiles of an average supergranule. We compute seismic wave travel times and sensitivity kernels by simulating wave propagation through this background. We find that, while the ability to recover the exact profile degrades based on the number of parameters involved, we are nevertheless able to recover the peak depth of our models in a few iterations where the measurements are presumably above the noise cutoff. This represents an important step toward unraveling the physics behind supergranules, as we start appreciating the parameters that we may reliably infer from a time-distance helioseismic inversion.

Keywords: Helioseismology, Solar physics, Supergranulation, Solar interior
Turbulence Dynamo in the Stratified Medium of Galaxy Clusters. The existence of microgauss magnetic fields in galaxy clusters has been established through observations of synchrotron radiation and Faraday rotation. They are conjectured to be generated via small-scale dynamo by turbulent flow motions in the intracluster medium (ICM). The microgauss magnetic fields of giant radio relics, show structures of synchrotron polarization vectors, organized over scales of megaparsecs, challenging the turbulence origin of cluster magnetic fields. Unlike turbulence in the interstellar medium, turbulence in the ICM is subsonic. And it is driven sporadically in highly stratified backgrounds, when major mergers occur during the hierarchical formation of clusters. To investigate quantitatively the characteristics of a turbulence dynamo in such an ICM environment, we performed a set of turbulence simulations using a high-order-accurate, magnetohydrodynamic (MHD) code. We find that turbulence dynamo could generate the cluster magnetic fields up to the observed level from the primordial seed fields of 10-15 G or so within the age of the universe, if the MHD description of the ICM could be extended down to kiloparsec scales. However, highly organized structures of polarization vectors, such as those observed in the Sausage relic, are difficult to reproduce through the shock compression of turbulence-generated magnetic fields. This implies that the modeling of giant radio relics may require pre-existing magnetic fields organized over megaparsec scales.

Keywords: Galaxy clusters, Shocks, Magnetic fields
Brown Dwarf Atmospheres as the Potentially Most Detectable and Abundant Sites for Life. We show that the total habitable volume in the atmospheres of cool brown dwarfs with effective temperatures of ∼250-350 K is possibly larger by 2 orders of magnitude than that of Earth-like planets. We also study the role of aerosols, nutrients, and photosynthesis in facilitating life in brown dwarf atmospheres. Our predictions might be testable through searches for spectral edges in the near-infrared and chemical disequilibrium in the atmospheres of nearby brown dwarfs that are either free-floating or within several au of stars. For the latter category, we find that the James Webb Space Telescope may be able to achieve a signal-to-noise ratio of ∼5 after a few hours of integration time per source for the detection of biogenic spectral features in ∼103 cool brown dwarfs.

Keywords: Biosignatures, Brown dwarfs, Astrobiology, Exoplanet atmospheres
Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs. When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e &gt; 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳100 Gpc-3 yr-1 for e &gt; 0.1, assuming a black hole mass spectrum with a power-law index ≲2.

Keywords: Elliptical orbits, Gravitational waves, Astrophysical black holes
Three-dimensional Density Structure of a Solar Coronal Streamer Observed by SOHO/LASCO and STEREO/COR2 in Quadrature. Helmet streamers are a prominent manifestation of magnetic structures with current sheets in the solar corona. These large-scale structures are regions with high plasma density, overlying active regions and filament channels. We investigate the three-dimensional (3D) structure of a coronal streamer, observed simultaneously by white-light coronagraphs from two vantage points near quadrature (the Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph Experiment (LASCO) and the Solar Terrestrial Relations Observatory (STEREO)/Coronagraph 2 (COR2)). We design a forward model based on plausible assumptions about the 3D streamer structure taken from physical models (a plasma slab centered around a current sheet). The streamer stalk is approximated by a plasma slab, with an electron density that is characterized by three separate functions describing the radial, transverse, and face-on profiles, respectively. For the first time, we simultaneously fit the observational data from SOHO and STEREO using a multivariate minimization algorithm. The streamer plasma sheet contains a number of brighter and darker ray-like structures with the density contrast up to about a factor of 3 between them. The densities derived using polarized and unpolarized data are similar. We demonstrate that our model corresponds well to the observations.

Keywords: Solar coronal streamers, Solar corona
A Flaring AGN in a ULIRG Candidate in Stripe 82. We report the discovery of a mid-infrared variable AGN that is hosted by an ultraluminous infrared galaxy (ULIRG) in the Sloan Stripe 82 field. WISE J030654.88+010833.6 is a red, extended galaxy, which we estimate to be at a photometric redshift of 0.28 ≤ z ≤ 0.31, based on its optical and near-infrared spectral energy distribution (SED). The factor of two variability over 8 yr seen in the Wide-field Infrared Survey Explorer (WISE) 3.4 and 4.6 μm wavelength channels is not clearly correlated with optical variability in archival data. Based on our estimation of the physical parameters of the host galaxy, J030654.88+010833.6 is possibly a composite AGN/starburst ULIRG in a phase where high star formation ∼70 M ⊙ yr-1 is occurring. Our estimate of the black hole mass to stellar mass ratio also appears to be consistent with that of broad line AGN in the local universe. The long-term variability of J030654.88+010833.6 as seen in the WISE W1 and W2 light curves is likely due to variations in the accretion rate, with the energy being reprocessed by dust in the vicinity of the AGN.

Keywords: AGN host galaxies, Black holes, Surveys, Light curves, Active galactic nuclei
Turbulence Driven by Stellar Jets, the Possibility and the Efficiency. We investigate the feedback of the stellar jets on the surrounding interstellar gas based on 2D and 3D simulations applying HD and MHD modules of the PLUTO 4.2 code. The main question we address is whether the stellar jet can be considered as a turbulence driver into the interstellar gas. In addition, we investigate the most effective circumstances in which the driven turbulence is larger and can survive for a longer timescale in the ambient gas. We present a case study of different parameter runs including the jet Mach number, the initial jet velocity field, the background magnetic field geometries and the interacting jets. We also study the environmental effects on the jet-gas interaction by considering the non-homogeneous surrounding gas containing the clumps in the model setup. Among different setups, we find (1) a higher jet Mach number, (2) a rotating jet, (3) a jet propagating in a magnetized environment, (4) a jet propagating in a non-homogeneous environment, and (5) the interacting jets produce more fluctuations and random motions in the entrained gas, which can survive for a longer timescale. In addition, we perform the 3D simulations of jet-ambient gas interaction and we find that the amount of (subsonic-supersonic) fluctuation increases compared to the axisymmetric run, and the entrained gas gains higher velocities in a 3D run. In total, we confirm the previous finding that the stellar jets can transfer the turbulence on neighboring regions and are not sufficient drivers of the large-scale supersonic turbulence in molecular clouds.

Keywords: Hydrodynamical simulations, Stellar jets, Computational methods, Interstellar medium, Magnetohydrodynamical simulations
Synchrotron Self-Compton as a Likely Mechanism of Photons beyond the Synchrotron Limit in GRB 190114C. GRB 190114C, a long and luminous burst, was detected by several satellites and ground-based telescopes from radio wavelengths to GeV gamma-rays. In the GeV gamma-rays, the Fermi Large Area Telescope detected 48 photons above 1 GeV during the first 100 s after the trigger time, and the MAGIC telescopes observed for more than 1000 s very high-energy (VHE) emission above 300 GeV. Previous analysis of the multi-wavelength observations showed that, although these are consistent with the synchrotron forward-shock model that evolves from a stratified stellar-wind to a homogeneous ISM-like medium, photons above a few GeV can hardly be interpreted in the synchrotron framework. In the context of the synchrotron forward-shock model, we derive the light curves and spectra of the synchrotron self-Compton (SSC) model in a stratified and homogeneous medium. In particular, we study the evolution of these light curves during the stratified-to-homogeneous afterglow transition. Using the best-fit parameters reported for GRB 190114C we interpret the photons beyond the synchrotron limit in the SSC framework and model its spectral energy distribution. We conclude that low-redshift gamma-ray bursts described under a favorable set of parameters as found in the early afterglow of GRB 190114C could be detected at hundreds of GeV, and also afterglow transitions would allow that VHE emission could be observed for longer periods.

Keywords: Gamma-ray bursts, High energy astrophysics, Non-thermal radiation sources, Astrophysical processes, Interstellar medium wind, Particle physics
The Evolution of O I over 3.2 &lt; z &lt; 6.5: Reionization of the Circumgalactic Medium. We present a survey for metal absorption systems traced by neutral oxygen over 3.2 &lt; z &lt; 6.5. Our survey uses Keck/ESI and VLT/X-Shooter spectra of 199 QSOs with redshifts up to 6.6. In total, we detect 74 O I absorbers, of which 57 are separated from the background QSO by more than 5000 km s-1. We use a maximum likelihood approach to fit the distribution of O I λ1302 equivalent widths in bins of redshift and from this determine the evolution in number density of absorbers with W 1302 &gt; 0.05 Å, of which there are 49 nonproximate systems in our sample. We find that the number density does not monotonically increase with decreasing redshift, as would naively be expected from the buildup of metal-enriched circumgalactic gas with time. The number density over 4.9 &lt; z &lt; 5.7 is a factor of 1.7-4.1 lower (68% confidence) than that over 5.7 &lt; z &lt; 6.5, with a lower value at z &lt; 5.7 favored with 99% confidence. This decrease suggests that the fraction of metals in a low-ionization phase is larger at z ∼ 6 than at lower redshifts. Absorption from highly ionized metals traced by C IV is also weaker in higher-redshift O I systems, supporting this picture. The evolution of O I absorbers implies that metal-enriched circumgalactic gas at z ∼ 6 is undergoing an ionization transition driven by a strengthening ultraviolet background. This in turn suggests that the reionization of the diffuse intergalactic medium may still be ongoing at or only recently ended by this epoch.

Keywords: Quasar absorption line spectroscopy, Intergalactic medium, Circumgalactic medium, Reionization, High-redshift galaxies
Can Reverberation-measured Quasars Be Used for Cosmology?. Quasars have been proposed as a new class of standard candles analogous to supernovae, since their large redshift range and high luminosities make them excellent candidates. The reverberation mapping (RM) method enables one to estimate the distance to the source from the time delay measurement of the emission lines with respect to the continuum, since the time delay depends on the absolute luminosity of the source. The radius-luminosity relation exhibits a low scatter and offers a potential use in cosmology. However, in recent years, the inclusion of new sources, particularly the super-Eddington accreting QSO, has increased the dispersion in the radius-luminosity relation, with many objects showing time delays shorter than the expected. Using 117 H β reverberation-mapped active galactic nuclei with 0.002 &lt; z &lt; 0.9 and 41.5 &lt; log L 5100 &lt; 45.9, we find a correction for the time delay based on the dimensionless accretion rate (\dot{{\mathscr{M}}}) considering a virial factor anticorrelated with the FWHM of H β. This correction decreases the scattering of the accretion parameters compared with the typical values used, which is directly reflected by suppressing the radius-luminosity relation dispersion. We also confirm the anticorrelation between the excess of variability and the accretion parameters. With this correction, we are able to build the Hubble diagram and estimate the cosmological constants Ω m  and ΩΛ, which are consistent with the Λ Cold Dark Matter model at 2σ confidence level. Therefore, reverberation mapping results can be used to constrain cosmological models in the future.

Keywords: Cosmology, Reverberation mapping, Active galaxies, Quasars
Bayesian Inference of High-density Nuclear Symmetry Energy from Radii of Canonical Neutron Stars. The radius R 1.4 of neutron stars (NSs) with a mass of 1.4 M ⊙ has been extracted consistently in many recent studies in the literature. Using representative R 1.4 data, we infer high-density nuclear symmetry energy E sym(ρ) and the associated nucleon specific energy E 0(ρ) in symmetric nuclear matter (SNM) within a Bayesian statistical approach using an explicitly isospin-dependent parametric equation of state (EOS) for nucleonic matter. We found the following. (1) The available astrophysical data can already significantly improve our current knowledge about the EOS in the density range of ρ 0 - 2.5ρ 0. In particular, the symmetry energy at twice the saturation density ρ 0 of nuclear matter is determined to be E sym(2ρ 0)={39.2}-8.2+12.1 MeV at a 68% confidence level. (2) A precise measurement of R 1.4 alone with a 4% 1σ statistical error but no systematic error will not greatly improve the constraints on the EOS of dense neutron-rich nucleonic matter compared to what we extracted from using the available radius data. (3) The R 1.4 radius data and other general conditions, such as the observed NS maximum mass and causality condition, introduce strong correlations for the high-order EOS parameters. Consequently, the high-density behavior of E sym(ρ) inferred depends strongly on how the high-density SNM EOS E 0(ρ) is parameterized, and vice versa. (4) The value of the observed maximum NS mass and whether it is used as a sharp cutoff for the minimum maximum mass or through a Gaussian distribution significantly affects the lower boundaries of both E 0(ρ) and E sym(ρ) only at densities higher than about 2.5ρ 0.

Keywords: Neutron star cores
In the Galactic Disk, Stellar [Fe/H] and Age Predict Orbits and Precise [X/Fe]. We explore the structure of the element abundance-age-orbit distribution of the stars in the Milky Way’s low-α disk, by (re-)deriving precise [Fe/H], [X/Fe], and ages, along with orbits, for red clump stars from the APOGEE survey. There has been a long-standing theoretical expectation and observational evidence that metallicity ([Fe/H]) and age are informative about a star’s orbit, e.g., about its angular momentum and the corresponding mean Galactocentric distance or its vertical motion. Indeed, our analysis of the APOGEE data confirms that [Fe/H] or age alone can predict the stars’ orbits far less well than a combination of the two. Remarkably, we find and show explicitly that, for known [Fe/H] and age, the other abundances [X/Fe] of Galactic disk stars can be predicted well (on average to 0.02 dex) across a wide range of Galactocentric radii, and therefore provide little additional information, e.g., for predicting their orbit. While the age-abundance space for metal-poor stars and potentially for stars near the Galactic center is rich or complex, for the bulk of the Galaxy’s low-α disk it is simple: [Fe/H] and age contain most information, unless [X/Fe] can be measured to 0.02 or better. Consequently, we do not have the precision with current (and likely near-future) data to assign stars to their individual (coeval) birth clusters, from which the disk is presumably formed. We can, however, place strong constraints on future models of Galactic evolution, chemical enrichment, and mixing.

Keywords: Milky Way disk, Milky Way formation, Milky Way Galaxy, Milky Way evolution
Fast-to-Alfvén Mode Conversion and Ambipolar Heating in Structured Media. II. Numerical Simulation. This paper studies the effectiveness of production of Alfvén waves in the solar atmosphere through the processes of mode conversion, taking into account several new effects that have not been considered before. We perform simulations of wave propagation and conversion from the photosphere to the corona. Both magnetic field and plasma parameters are structured in the form of small-scale flux tubes with characteristic scale significantly below the wavelength of the waves. The waves are allowed to dissipate through the ambipolar diffusion (AD) mechanism. We use an analytical magneto-static equilibrium model, which provides the AD coefficient values at the lower end of what is expected for the quiet solar regions. This work extends the simplified study of mode conversion by Cally and Cally &amp; Khomenko to the case of warm, partially ionized, and structured plasma. We conclude that interaction of waves with the flux tube ensemble produces a discrete spectrum of high-order harmonics. The scattering is a linear process: however, the nonlinear effects have considerable influence upon the amplitudes of the harmonics. The magnetic Poynting flux reaching the corona is enhanced by about 35% and the reflection of waves at the transition region is decreased by about 50% when the flux tubes structure is present, relative to the horizontally homogeneous case. The energy flux of Alfvén waves exceeds that of acoustic waves at coronal heights. Ambipolar diffusion decreases the magnetic Poynting flux in the corona because the fast waves entering the transformation region at chromospheric heights are degraded and have lower amplitudes. The effect of the enhancement of Alfvén wave production due to interaction with flux tubes is independent of the numerical resolution, while the effect of the AD is resolution-dependent and is not converged at the 10 km resolution of our best simulations.

Keywords: The Sun, Solar magnetic fields, Solar corona, Solar chromosphere, Magnetohydrodynamical simulations