Sazuna/UAT_keywords huggingface dataset:
Implications of Symmetry and Pressure in Friedmann Cosmology. II. Stellar Remnant Black Hole Mass Function. We consider some observational consequences of replacing all black holes (BHs) with a class of non-singular solutions that mimic BHs but with dark energy (DE) interiors; GEneric Objects of DE (GEODEs). We focus on the BH mass function and chirp-mass redshift distribution of mergers visible to gravitational-wave observatories. We incorporate the GEODE blueshift into an initially Salpeter stellar remnant distribution, and model the binary population by evolving synthesized binary remnant distributions, published before LIGO's first measurements. We find that a GEODE produced between 20 ≲ z ≲ 40, and observed at z ∼ 7, will have its initial mass amplified by ∼20-140×. This can relieve tension between accretion-only growth models and the inferred masses of BHs in quasars at z ≳ 6. Moreover, we find that merger rates of GEODE binaries increase by a factor of ∼2× relative to classical BHs. The resulting GEODE mass function is consistent with the most recent LIGO constraints at &lt;0.5σ. In contrast, a Salpeter stellar distribution that evolves into classical remnants is in tension at ≳2σ. This agreement occurs without low-metallicity regions, abnormally massive progenitor stars, novel formation channels, or primordial object formation at extreme rates. In particular, we find that solar metallicity progenitors, which produce 1.1-1.8M⊙ remnants, overlap with many LIGO observations when evolved as GEODEs.

Keywords: Intermediate-mass black holes, Quasars, Compact binary stars, Stellar mass black holes, Astrophysical black holes, Dark energy
Rankine-Hugoniot Relations Including Pickup Ions. The Rankine-Hugoniot relations are consequences of the global, magnetohydrodynamic conservation laws of mass, momentum, energy, and magnetic flux at shocks in plasma. They provide us with the boundary conditions, although these are insufficient to quantify the energy partition in substantially non-Maxwellian plasmas in the presence of nonthermal, pickup ions (PUIs). Ion dynamics inside the shock front is essentially nonadiabatic and gyrophase-dependent. The shock jump conditions are typically evaluated using the upstream and downstream distributions in the regions where they already become gyrotropic. The relation between the gyrophase-dependent motion inside the shock front and the gyrophase-averaged moments of the ion distributions is established using numerical ion tracing across a model shock profile, which includes the major basic features of a collisionless shock. The upstream distribution of PUIs is taken to be a filled shell. The obtained moments of the PUI distribution function are used to construct the Rankine-Hugoniot relations for a gyrotropic plasma regime. The quality of numerical ion tracing is checked by comparing it with full particle simulations. The moments of the distribution in the isotropic region are estimated.

Keywords: Termination shock, Shocks, Space plasmas, Pickup ions
Hot Subdwarf Stars Identified in Gaia DR2 with Spectra of LAMOST DR6 and DR7. I. Single-lined Spectra. 182 single-lined hot subdwarf stars are identified by using spectra from the sixth and seventh data releases (DR6 and DR7) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope survey. We classified all the hot subdwarf stars using a canonical classification scheme, and got 89 sdB, 37 sdOB, 26 sdO, 24 He-sdOB, 3 He-sdO, and 3 He-sdB stars, respectively. Among these stars, 108 hot subdwarfs are newly discovered, while 74 stars were reported by previous catalogs. The atmospheric parameters of these stars were obtained by fitting the hydrogen (H) and helium (He) lines with non-local thermodynamic equilibrium model atmospheres. The atmospheric parameters confirm the two He sequences and the two subgroups of He-sdOB stars in our samples, which were found by previous studies in the Teff- $\mathrm{log}(n\mathrm{He}/n{\rm{H}})$ diagram. Our results demonstrate different origins of field hot subdwarf stars and extreme horizontal branch stars in globular clusters, and provide strict observational limits on the formation and evolution models of the different sub-types of these evolved objects. Based on the results, we evaluated the completeness of the Geier et al. catalog. We found the fraction of hot subwarf stars is between 10% and 60%, depending on the brightness of the sample. A more accurate estimation for the hot subdwarf fraction can be obtained when similar results from composite spectra will become available.

Keywords: Surveys, Stellar classification, Subdwarf stars
A Neutral Beam Model for High-energy Neutrino Emission from the Blazar TXS 0506+056. The IceCube collaboration reported an ∼3.5σ excess of 13 ± 5 neutrino events in the direction of the blazar TXS 0506+056 during an ∼6 month period in 2014-2015, as well as the (∼3σ) detection of a high-energy muon neutrino during an electromagnetic flare in 2017. We explore the possibility that the 2014-2015 neutrino excess and the 2017 multimessenger flare are both explained in a common physical framework that relies on the emergence of a relativistic neutral beam in the blazar jet due to interactions of accelerated cosmic rays (CRs) with photons. We demonstrate that the neutral beam model provides an explanation for the 2014-2015 neutrino excess without violating X-ray and γ-ray constraints and yields results consistent with the detection of one high-energy neutrino during the 2017 flare. If both neutrino associations with TXS 05065+056 are real, our model requires that (I) the composition of accelerated CRs is light, with a ratio of helium nuclei to protons ≳5; (II) a luminous external photon field (∼1046 erg s-1) variable (on yearlong timescales) is present; and (III) the CR injection luminosity, as well as the properties of the dissipation region (I.e., Lorentz factor, magnetic field, and size), vary on yearlong timescales.

Keywords: Jets, High energy astrophysics, High-energy cosmic radiation, Blazars, Neutrino astronomy, Active galactic nuclei, Gamma-ray astronomy, Particle astrophysics, Cosmic rays
r-process Enrichment in the Galactic Halo Characterized by Nucleosynthesis Variation in the Ejecta of Coalescing Neutron Star Binaries. A large star-to-star variation in the abundances of r-process elements, as seen in the [Eu/Fe] ratio for Galactic halo stars, is a prominent feature that is distinguishable from other heavy elements. It is, in part, caused by the presence of highly r-process-enriched stars, classified as r-II stars ([Eu/Fe] ≥ + 1). In parallel, halo stars show that the ratio of a light r-process element (Y) to Eu is tightly correlated with [Eu/Fe], giving the lowest [Y/Eu] ratio that levels off at r-II stars. On the other hand, recent hydrodynamical simulations of coalescing double neutron stars (cNSNSs) have suggested that r-process sites may be separated into two classes providing different electron-fraction distributions: tidally driven dynamical ejecta and (dynamical or postmerger) nontidal ejecta. Here, we show that a widely spanning feature of [Eu/Fe] can be reproduced by models that consider the different masses of tidally driven dynamical ejecta from both cNSNSs and coalescing black hole/neutron star binaries (cBHNSs). In addition, the observed [Y/Eu] trend is explained by the combined nucleosynthesis in two kinds of ejecta with varying mass asymmetry in double NS systems. Our scenario suggests that massive tidally driven dynamical ejecta accompanied by massive nontidal part from cNSNSs or cBHNSs could alone accommodate r-II abundances, including an actinide boost in some cases. The event rate for cNSNSs estimated from our study agrees with the latest result of ∼1000 (90% confidence interval of 110-3840) Gpc-3yr-1 by gravitational-wave detection, and a few events per Gpc3 per year of cBHNSs associated with r-process production are predicted to emerge.

Keywords: Neutron stars, Galaxy chemical evolution, Nucleosynthesis, Abundance ratios, Stellar mergers, R-process, Compact binary stars, Stellar mass black holes, Gravitational wave astronomy, Milky Way stellar halo, Galactic abundances
Two-year Cosmology Large Angular Scale Surveyor (CLASS) Observations: A First Detection of Atmospheric Circular Polarization at Q band. The Earth's magnetic field induces Zeeman splitting of the magnetic dipole transitions of molecular oxygen in the atmosphere, which produces polarized emission in the millimeter-wave regime. This polarized emission is primarily circularly polarized and manifests as a foreground with a dipole-shaped sky pattern for polarization-sensitive ground-based cosmic microwave background experiments, such as the Cosmology Large Angular Scale Surveyor (CLASS), which is capable of measuring large angular scale circular polarization. Using atmospheric emission theory and radiative transfer formalisms, we model the expected amplitude and spatial distribution of this signal and evaluate the model for the CLASS observing site in the Atacama Desert of northern Chile. Then, using two years of observations at 32°3 to 43.7 GHz from the CLASS Q-band telescope, we present a detection of this signal and compare the observed signal to that predicted by the model. We recover an angle between magnetic north and true north of -5°5 ± 0°6, which is consistent with the expectation of -5°9 for the CLASS observing site. When comparing dipole sky patterns fit to both simulated and data-derived sky maps, the dipole directions match to within a degree, and the measured amplitudes match to within ∼20%.

Keywords: Observational cosmology, Cosmic microwave background radiation, Astronomical instrumentation, Polarimeters, Atmospheric effects
Clusters of Galaxies Masquerading as X-Ray Quasars. Inspired by the discovery of the Phoenix cluster by the South Pole Telescope team, we initiated a search for other massive clusters of galaxies missing from the standard X-ray catalogs. We began by identifying 25 cluster candidates not included in the Meta-Catalog of X-ray Clusters of galaxies cluster compilation through cross-identification of the central galaxies of optically identified clusters in the Sloan Digital Sky Survey GMBCG catalog with bright X-ray sources in the ROSAT Bright Source Catalog. Those candidates were mostly unidentified or previously classified as X-ray active galactic nucleus (AGN). We analyzed brief Chandra X-ray Observatory observations of 14 of these X-ray sources and found that eight are X-ray luminous clusters of galaxies, only one showing evidence for a central X-ray point source. The remaining six candidates turned out to be point-source dominated, with faint detections or upper limits on any extended emission. We were not able to rule out the presence of extended X-ray emission from any of the point sources. The levels of extended emission around the six point sources are consistent with expectations based on optical richness, but could also be contaminated by scattered X-ray light from the central point source or extended nonthermal emission from possible radio lobes. We characterize the extended components of each of the well-detected cluster sources, finding that six of the eight X-ray clusters are consistent with being compact cool-core clusters. One of the newly identified low-luminosity X-ray clusters may have had an X-ray-luminous AGN 20 yr prior to the recent Chandra observations, based on the 4σ difference between its Chandra and ROSAT fluxes.

Keywords: Galaxy clusters, X-ray identification, X-ray quasars, X-ray sources
Toward the Detection of Relativistic Image Doubling in Imaging Atmospheric Cherenkov Telescopes. Cosmic gamma-ray photons incident on the upper atmosphere create air showers that move to the Earth's surface with superluminal speed, relative to the air. Even though many of these air showers remain superluminal all along their trajectories, the shower's velocity component toward a single Imaging Atmospheric Cherenkov Telescope (IACT) may drop from superluminal to subluminal. When this happens, an IACT that is able to resolve the air shower both in time and angle should be able to document an unusual optical effect known as relativistic image doubling (RID). The logic of RID is that the shower appears to precede its own Cherenkov radiation when its speed component toward the IACT is superluminal, but appears to trail its own Cherenkov radiation when its speed component toward the IACT is subluminal. The result is that the IACT will see the shower start not at the top of the atmosphere but in the middle—at the point along the shower's path where its radial velocity component drops to subluminal. Images of the shower would then be seen by the IACT to go both up and down simultaneously. A simple simulation demonstrating this effect is presented. Clear identification of RID would confirm in the atmosphere a novel optical imaging effect caused not by lenses but solely by relativistic kinematics, and may aid in the accuracy of path and speed reconstructions of the relativistic air shower.

Keywords: Cosmic ray showers, Special relativity, Astronomical optics
Interpolation of Turbulent Magnetic Fields and Its Consequences on Cosmic Ray Propagation. Numerical simulations of the propagation of charged particles through magnetic fields solving the equation of motion often leads to the usage of an interpolation in the case of discretely defined magnetic fields, typically given on a homogeneous grid structure. However, the interpolation method influences the magnetic field properties and, therefore, also the propagation of particles through these fields. To determine the resulting error, we compare three different interpolation routines—trilinear, tricubic, and nearest neighbor interpolation—in the case of isotropic, turbulent magnetic fields. First, we analyze the impact of the different interpolation methods on the root mean square field strength, the divergence, and the spectrum of the turbulent magnetic field. Here, the nearest neighbor interpolation shows some clear benefits compared with the trilinear method; however, that changes significantly if we consider the particle propagation. In principle, a better interpolation method also yields a better description of the particle transport. In the case of field line random walk, it is shown that none of these methods, especially not the nearest neighbor interpolation, is able to yield an accurate description of the diffusion coefficient, exposing the need for a continuous, grid-less turbulent magnetic field. We optimize the performance of an algorithm that generates such a magnetic field by more than an order of magnitude. Further, the necessary number of wave-modes is determined, so that this continuous method supports realistic simulations over a larger energy range without limitations by the available memory.

Keywords: Extragalactic magnetic fields, Computational methods, Astrophysical processes, Cosmic magnetic fields theory, Cosmic rays
IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops. We observed rapid variability (≲60 s) at the footpoints of transient, hot (∼8-10 MK) coronal loops in active region cores, with the Interface Region Imaging Spectrograph (IRIS). The high spatial (∼0"33) and temporal (≲5-10 s) resolution of IRIS is often crucial for the detection of this variability. We show how, in combination with 1D RADYN loop modeling, these IRIS spectral observations of the transition region (TR) and chromosphere provide powerful diagnostics of the properties of coronal heating and energy transport (thermal conduction or nonthermal electrons, NTEs). Our simulations of nanoflare-heated loops indicate that emission in the Mg II triplet can be used as a sensitive diagnostic for nonthermal particles. In our events, we observe a large variety of IRIS spectral properties (intensity, Doppler shifts, broadening, chromospheric/TR line ratios, Mg II triplet emission) even for different footpoints of the same coronal events. In several events, we find spectroscopic evidence for NTEs (e.g., TR blueshifts and Mg II triplet emission), suggesting that particle acceleration can occur even for very small magnetic reconnection events, which are generally below the detection threshold of hard X-ray instruments that provide direct detection of emission of nonthermal particles.

Keywords: High resolution spectroscopy, Solar ultraviolet emission, Solar extreme ultraviolet emission, Solar energetic particles, Solar coronal loops, Solar coronal heating, Solar active regions, Solar corona, Solar transition region, Solar chromosphere
Quantifying the Toroidal Flux of Preexisting Flux Ropes of Coronal Mass Ejections. In past decades, much progress has been achieved in understanding the origin and evolution of coronal mass ejections (CMEs). In situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these properties in an erupting CME flux rope, in particular in a preexisting flux rope. In this work, we propose a model to estimate the toroidal flux of a preexisting flux rope by subtracting the flux contributed by magnetic reconnection during the eruption from the flux measured in the MC. The flux contributed by the reconnection is derived from geometric properties of two-ribbon flares based on a quasi-2D reconnection model. We then apply the model to four CME/flare events and find that the ratio of toroidal flux in the preexisting flux rope to that in the associated MC lies in the range 0.40-0.88. This indicates that the toroidal flux of the preexisting flux rope makes an important contribution to that of the CME flux rope and is usually at least as large as the flux arising from the eruption process for the selected events.

Keywords: Solar coronal mass ejections, Solar flares, Solar corona
Comparing Observed Stellar Kinematics and Surface Densities in a Low-latitude Bulge Field to Galactic Population Synthesis Models. We present an analysis of Galactic bulge stars from Hubble Space Telescope Wide Field Camera 3 observations of the Stanek window (l, b = [0.25, -2.15]) from two epochs approximately two years apart. This data set is adjacent to the provisional Wide-field Infrared Survey Telescope (WFIRST) microlensing field. Proper motions are measured for approximately 115,000 stars down to 28th mag in V band and 25th mag in I band, with accuracies of 0.5 mas yr-1 (20 km s-1) at I ≈ 21. A cut on the longitudinal proper motion μl allows us to separate disk and bulge populations and produce bulge-only star counts that are corrected for photometric completeness and efficiency of the proper-motion cut. The kinematic dispersions and surface density in the field are compared to the nearby SWEEPS sight line, finding a marginally larger-than-expected gradient in stellar density. The observed bulge star counts and kinematics are further compared to the Besançon, Galaxia, and GalMod Galactic population synthesis models. We find that most of the models underpredict low-mass bulge stars by ∼33% below the main-sequence turnoff, and upwards of ∼70% at redder J and H wavebands. While considering inaccuracies in the Galactic models, we give implications for the exoplanet yield from the WFIRST microlensing mission.

Keywords: Luminosity function, Astronomical models, Stellar kinematics, Galactic bulge, HST photometry, Gravitational microlensing
Possible Evidence for the Gluon Condensation Effect in Cosmic Positron and Gamma-Ray Spectra. The gluon condensation (GC) effect in cosmic proton-proton collisions at high energy is used to explain an excess in the positron spectrum observed by the Alpha Magnetic Spectrometer. We find that this excess may originate from the GC effect in Tycho's supernova remnant.

Keywords: Galactic cosmic rays, Gamma-ray astronomy, High energy astrophysics
Probing the Origin of Diffuse Radio Emission in the Cool Core of the Phoenix Galaxy Cluster. Cool core galaxy clusters are considered to be dynamically relaxed clusters with regular morphology and highly X-ray luminous central region. However, cool core clusters can also be sites for merging events that exhibit cold fronts in X-ray and minihalos in radio. We present recent radio/X-ray observations of the Phoenix Cluster or South Pole Telescope (SPT)-CL J2344-4243 at the redshift of z = 0.596. Using archival Chandra X-ray observations, we detect spiraling cool gas around the cluster core as well as discover two cold fronts near the core. This is perhaps the most distant galaxy cluster to date known to host cold fronts. Also, we present JVLA8 1.52 GHz observations of the minihalo, previously discovered at 610 MHz with GMRT9 observations in the center of the Phoenix galaxy cluster. The minihalo flux density at 1.52 GHz is 9.65 ± 0.97 mJy with the spectral index between 610 MHz and 1.52 GHz being -0.98 ± 0.16.10 A possible origin of these radio sources is turbulence induced by sloshing of the gas in the cluster core.

Keywords: Galaxy clusters, Extended radiation sources, Cool cores, Non-thermal radiation sources, X-ray sources, Intracluster medium
Molecular Oxygen in the Nearest QSO Mrk 231. We report the detection of an emission feature at the 12σ level with FWHM line width of about 450 km s-1 toward the nearest quasi-stellar object, QSO Mrk 231. Based on observations with the IRAM 30 m telescope and the Northern Extended Millimeter Array Interferometer, the 11-10 transition of molecular oxygen is the likely origin of the line with rest frequency close to 118.75 GHz. The velocity of the O2 emission in Mrk 231 coincides with the red wing seen in CO emission, suggesting that it is associated with the outflowing molecular gas, located mainly at about 10 kpc away from the central active galactic nucleus (AGN). This first detection of extragalactic molecular oxygen provides an ideal tool to study AGN-driven molecular outflows on dynamic timescales of tens of megayears. O2 may be a significant coolant for molecular gas in such regions affected by AGN-driven outflows. New astrochemical models are needed to explain the implied high molecular oxygen abundance in such regions several kiloparsecs away from the center of galaxies.

Keywords: Interstellar medium, Quasars
Beyond Optical Depth: Future Determination of Ionization History from the Cosmic Microwave Background. We explore the fundamental limits to which reionization histories can be constrained using only large-scale cosmic microwave background (CMB) anisotropy measurements. The redshift distribution of the fractional ionization Xe(z) affects the angular distribution of CMB polarization. We project constraints on the reionization history of the universe using low-noise full-sky temperature and E-mode measurements of the CMB. We show that the measured TE power spectrum, ${\hat{C}}_{{\ell }}^{\mathrm{TE}}$ , has roughly one quarter of the constraining power of ${\hat{C}}_{{\ell }}^{\mathrm{EE}}$ on the reionization optical depth τ, and its addition improves the precision on τ by 20% over using ${\hat{C}}_{{\ell }}^{\mathrm{EE}}$ only. We also use a two-step reionization model with an additional high-redshift step, parameterized by an early ionization fraction ${X}_{e}^{\min }$ , and a late reionization step at zre. We find that future high signal-to-noise measurements of the multipoles 10 ≤ ℓ &lt; 20 are especially important for breaking the degeneracy between ${X}_{e}^{\min }$ and zre. In addition, we show that the uncertainties on these parameters determined from a map with sensitivity 10 μK arcmin are less than 5% larger than the uncertainties in the noiseless case, making this noise level a natural target for future large sky area E-mode measurements.

Keywords: Cosmological neutrinos, Reionization, Cosmology, Cosmic background radiation