adsabs/SciX_UAT_keywords huggingface dataset:
The Case of the Missing Very High-energy Gamma-Ray Bursts: A Retrospective Study of Swift Gamma-Ray Bursts with Imaging Atmospheric Cherenkov Telescopes

Gamma-ray bursts (GRBs) are particle acceleration sites that can emit photons in the very high-energy (VHE) domain through nonthermal processes. From 2004 until 2018, the current generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) did not detect any GRB in the VHE domain. However, from 2018 to 2020, five detections were reported. In this work, we try to solve the case of the missing VHE GBRs prior to 2018. We aim to identify GRBs that might have eluded VHE detection in past years by the H.E.S.S., MAGIC, and VERITAS IACTs. To do so, we study GRBs with known redshift detected by Swift from 2004 until June 2022. We first identify all GRBs that could have been observed by these IACTs since 2004, considering observation conditions and visibility constraints. We assume a relation between the X-rays and the VHE gamma rays based on the VHE GRBs detected to date and combine this with the redshift measurements, instrument response information, and observation conditions to predict the observed VHE gamma-ray flux from the Swift X-Ray Telescope measurements. We report findings on 12 bright low-redshift GRBs that we identify as most likely to have been detected in the VHE domain by current IACTs. The rate of IACT-detectable GRBs with ideal observation conditions is <1 VHE GRB per year with the current configuration. With its lower energy threshold and higher sensitivity, this rate increases to ∼4 VHE GRBs per year with the Cherenkov Telescope Array.

Keywords: gamma-ray bursts; transient sources; gamma-ray observatories; gamma-ray transient sources; gamma-ray telescopes; gamma-ray astronomy; high energy astrophysics
3D Kinematics of Stellar SiO Masers in the Galactic Center

We present 3D velocity measurements and acceleration limits for stars within a few parsec of the Galactic Center (GC) black hole, Sgr A*, based on observations of 43 and 86 GHz circumstellar maser emission. Observations were taken with the Very Large Array in 2013, 2014, and 2020 and with the Atacama Large Millimeter/submillimeter Array in 2015 and 2017. We detect 28 masers in total, of which four are new detections. Combining these data with extant maser astrometry, we calculate stellar proper motions and accelerations with uncertainties as low as ~10 μas yr-1 and 0.5 μas yr-2, respectively, corresponding to approximately 0.5 km s-1 and 0.04 km s-1 yr-1 at a distance of 8 kpc. We measure radial velocities from maser spectra with ~0.5 km s-1 uncertainties, though the precision and accuracy of such measurements for deducing the underlying stellar velocities are limited by the complex spectral profiles of some masers. We therefore measure radial acceleration limits with typical uncertainties of ~0.1 km s-1 yr-1. We analyze the resulting 3D velocities and accelerations with respect to expected motions resulting from models of the mass distribution in the GC.

Keywords: silicon monoxide masers; astrophysical masers; galactic center; stellar kinematics
Turbulence Transport Modeling and First Orbit Parker Solar Probe (PSP) Observations

The Parker Solar Probe (PSP) achieved its first orbit perihelion on 2018 November 6, reaching a heliocentric distance of about 0.165 au (35.55 R⊙). Here, we study the evolution of fully developed turbulence associated with the slow solar wind along the PSP trajectory between 35.55 R⊙ and 131.64 R⊙ in the outbound direction, comparing observations to a theoretical turbulence transport model. Several turbulent quantities, such as the fluctuating kinetic energy and the corresponding correlation length, the variance of density fluctuations, and the solar wind proton temperature are determined from the PSP Solar Wind Electrons Alphas and Protons (SWEAP) plasma data along its trajectory between 35.55 R⊙ and 131.64 R⊙. The evolution of the PSP derived turbulent quantities are compared to the numerical solutions of the nearly incompressible magnetohydrodynamic (NI MHD) turbulence transport model recently developed by Zank et al. We find reasonable agreement between the theoretical and observed results. On the basis of these comparisons, we derive other theoretical turbulent quantities, such as the energy in forward and backward propagating modes, the total turbulent energy, the normalized residual energy and cross-helicity, the fluctuating magnetic energy, and the correlation lengths corresponding to forward and backward propagating modes, the residual energy, and the fluctuating magnetic energy.

Keywords: interplanetary turbulence; slow solar wind; solar wind
Evidence for Gas-phase Metal Deficiency in Massive Protocluster Galaxies at z ∼2.2

We study the mass-metallicity relation for 19 members of a spectroscopically confirmed protocluster in the COSMOS field at z = 2.2 (CC2.2), and compare it with that of 24 similarly selected field galaxies at the same redshift. Both samples are Hα emitting sources, chosen from the HiZELS narrowband survey, with metallicities derived from the ${\rm{N}}2\ \left(\tfrac{[\mathrm{NII}]\lambda 6584}{{\rm{H}}\alpha }\right)$ line ratio. For the mass-matched samples of protocluster and field galaxies, we find that protocluster galaxies with 109.9 M⊙ ≤ M* ≤ 1010.9 M⊙ are metal deficient by 0.10 ± 0.04 dex (2.5σ significance) compared to their coeval field galaxies. This metal deficiency is absent for low-mass galaxies, M* < 109.9 M⊙. Moreover, relying on both spectral energy distribution derived and Hα (corrected for dust extinction based on M*) star formation rates (SFRs), we find no strong environmental dependence of the SFR-M* relation; however, we are not able to rule out the existence of small dependence due to inherent uncertainties in both SFR estimators. The existence of 2.5σ significant metal deficiency for massive protocluster galaxies favors a model in which funneling of the primordial cold gas through filaments dilutes the metal content of protoclusters at high redshifts (z ≳ 2). At these redshifts, gas reservoirs in filaments are dense enough to cool down rapidly and fall into the potential well of the protocluster to lower the gas-phase metallicity of galaxies. Moreover, part of this metal deficiency could be originated from galaxy interactions that are more prevalent in dense environments. * Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Keywords: metallicity; galaxy evolution; protoclusters; high-redshift galaxy clusters; large-scale structure of the universe
The Warm Neptune GJ 3470b Has a Polar Orbit

The warm Neptune GJ 3470b transits a nearby (d = 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter-McLaughlin effect, yielding a sky-projected obliquity of $\lambda ={98}_{-12}^{+15\ \circ }$ and a $v\sin i={0.85}_{-0.33}^{+0.27}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of $\psi ={95}_{-8}^{+9\ \circ }$ , revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope of $\dot{\gamma }=-0.0022\pm 0.0011\,{\rm{m}}\,{{\rm{s}}}^{-1}\,{\mathrm{day}}^{-1}$ over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b's mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ~1.5-1.7, which could help account for its evaporating atmosphere.

Keywords: exoplanet astronomy
A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth

Enhanced emission from the dense gas tracer HCN (relative to HCO+) has been proposed as a signature of active galactic nuclei (AGN). In a previous single-dish millimeter line survey we identified galaxies with HCN/HCO+ (1-0) intensity ratios consistent with those of many AGN but whose mid-infrared spectral diagnostics are consistent with little to no (≲15%) contribution of an AGN to the bolometric luminosity. To search for putative heavily obscured AGN, we present and analyze NuSTAR hard X-ray (3-79 keV) observations of four such galaxies from the Great Observatories All-sky LIRG Survey. We find no X-ray evidence for AGN in three of the systems and place strong upper limits on the energetic contribution of any heavily obscured ( ${N}_{{\rm{H}}}\gt {10}^{24}$ ${\mathrm{cm}}^{-2}$ ) AGN to their bolometric luminosity. The upper limits on the X-ray flux are presently an order of magnitude below what XDR-driven chemistry models predict are necessary to drive HCN enhancements. In a fourth system we find a hard X-ray excess consistent with the presence of an AGN, but contributing only ∼3% of the bolometric luminosity. It is also unclear if the AGN is spatially associated with the HCN enhancement. We further explore the relationship between HCN/HCO+ (for several Jupper levels) and ${L}_{\mathrm{AGN}}$ / ${L}_{\mathrm{IR}}$ for a larger sample of systems in the literature. We find no evidence for correlations between the line ratios and the AGN fraction derived from X-rays, indicating that HCN/HCO+ intensity ratios are not driven by the energetic dominance of AGN, nor are they reliable indicators of ongoing supermassive black hole accretion.

Keywords: molecular gas; active galactic nuclei; x-ray active galactic nuclei; luminous infrared galaxies; starburst galaxies
Discovery of Two TNO-like Bodies in the Asteroid Belt

Two extremely red main-belt asteroids, 203 Pompeja and 269 Justitia, were identified from combined visible and near-infrared spectroscopic observations collected at the Infra-red Telescope Facility (IRTF) and Seoul National University Astronomical Observatory (SAO). These two asteroids have a redder spectral slope than any other D-type body, which are the reddest objects in the asteroid belt, and similar to RR and IR-class objects found in the outer Solar System among trans-Neptunian objects (TNOs) and Centaurs. Spectroscopic results suggest the presence of complex organic materials on the surface layer of these asteroids, implying that they could have formed in the vicinity of Neptune and been transplanted to the main belt region during a phase of planetary migration. 203 Pompeja is the only very red asteroid known so far among the ~250 bodies with diameter larger than 110 km (i.e., presumably structurally intact) found in the asteroid belt. These discoveries provide more evidence that the main asteroid belt hosts a population of bodies that were formed in the outskirts of the Solar System.

Keywords: small solar system bodies; asteroids; trans-neptunian objects; solar system formation
Black Hole Mass Function of Coalescing Binary Black Hole Systems: Is there a Pulsational Pair-instability Mass Cutoff?

We analyze the LIGO/Virgo GWTC-2 catalog to study the primary mass distribution of the merging black holes. We perform hierarchical Bayesian analysis and examine whether the mass distribution has a sharp cutoff for primary black hole masses below 65 M⊙, as predicted in the pulsational pair-instability supernova model. We construct two empirical mass functions. One is a piece-wise function with two power-law segments joined by a sudden drop. The other consists of a main-truncated power-law component, a Gaussian component, and a third very massive component. Both models can reasonably fit the data and a sharp drop of the mass distribution is found at ∼50M⊙, suggesting that the majority of the observed black holes can be explained by the stellar evolution scenarios in which the pulsational pair-instability process takes place. On the other hand, the very massive subpopulation, which accounts for at most several percent of the total, may be formed through hierarchical mergers or other processes.

Keywords: astrophysical black holes; intermediate-mass black holes; bayesian statistics; hierarchical models
Born to Be Wide: The Distribution of Wide Binaries in the Field and Soft Binaries in Clusters

Most stars, binaries, and higher-multiplicity systems are thought to form in stellar clusters and associations that later dissociate. Very wide binaries can be easily disrupted in clusters due to dynamical evaporation (soft binaries) and/or tidal disruption by the gravitational potential of the cluster. Nevertheless, wide binaries are quite frequent in the field, where they can sometimes play a key role in the formation of compact binaries and serve as tools to study key physical processes. Here we use analytic tools to study the dynamical formation of soft binaries in clusters and their survival as field binaries following cluster dispersion. We derive the expected properties of very wide binaries both in clusters and in the field. We analytically derive their detailed distributions, including the wide binary fraction as a function of mass in different cluster environments, binary mass functions and mass ratios, and the distribution of their orbital properties. We show that our calculations agree well in most aspects with the results of N-body simulations but show some different binary fraction dependence on the cluster mass. We find that the overall fraction of wide binaries scales as $\propto {N}_{\star }^{-1}$ , where N ⋆ is the size of the cluster, even for non-equal-mass stars. More massive stars are more likely to capture wide companions, with most stars above 5 M ⊙ likely to capture at least one stellar companion, and formation of triples is found to be frequent.

Keywords: binary stars; multiple stars; wide binary stars
Coaxing the Eclipsing Binary V367 Cygni out of Its Shell

Spectra that cover 0.63-0.69 μm with a spectral resolution ~17,000 are presented of the W Serpentis system V367 Cygni. Absorption lines of Fe II and Si II that form in a circumsystem shell are prominent features, and the depths of these are stable with time, suggesting that the shell is smoothly distributed and well mixed. Further evidence of uniformity comes from modest radial velocity variations measured in the deepest parts of the shell lines. It is suggested that motions previously attributed to rotation of the shell are instead artifacts of contamination from the donor star spectrum. A donor star spectrum is extracted that is consistent with that of an early to mid-A giant. The depths of metallic lines in the donor spectrum vary with orbital phase, suggesting that spot activity covers a large fraction of the surface of that star. A spectrum of the accretion disk that surrounds the second star is also extracted, and similarities are noted with the emission spectra of Herbig Ae/Be stars. In addition to variations with orbital phase, Hα changes with time over timescales of no more than two orbits. A tentative detection of He I 6678 emission is made near primary minimum, but not at other phases. Finally, projected emission from hot dust in and around V367 Cyg is more or less symmetric and extends over 28″, or 0.09 pc at the distance of the system; V367 Cyg is thus expelling matter into a large volume of the surrounding space.

Keywords: close binary stars; semi-detached binary stars
Circumnuclear Medium around the Central AGN in a Cool-core Cluster, Abell 1644-South

We present the circumnuclear multiphase gas properties of the brightest cluster galaxy (BCG) in the center of Abell 1644-South (A1644-S). A1644-S is the main cluster in a merging system, which is well known for X-ray hot gas sloshing in its core. The sharply peaked X-ray profile of A1644-S implies the presence of a strongly cooling gas core. In this study, we analyze ALMA 12CO (1-0) data, JVLA H I data, and KaVA 22 GHz data for the central region of A1644-S to probe the potential origin of the cool gas and its role in (re)powering the central active galactic nucleus (AGN). We find CO clumps distributed in an arc shape along the X-ray gas sloshing, which is suggestive of a connection between the cold gas and the hot intracluster medium (ICM). H I and CN are detected in absorption against the AGN continuum emission. The absorption dip is observed at the systemic velocity of the BCG with an extended, redshifted tail. Based on the spatial and spectral configurations of the H I, CN, and CO gases, it is inferred that cool gas spirals into the core of the BCG, which is then fed to the central AGN. Indeed, our KaVA observation reveals a parsec-scale bipolar jet, implying that this AGN could have been (re)powered quite recently. Combining this, we suggest that some cold gas in A1644-S could have been formed from the cooling of the ICM, triggering the activity of the central AGN in the early development of a cool-core cluster.

Keywords: cooling flows; brightest cluster galaxies; molecular gas; interstellar atomic gas; radio jets
On Charon's Far-ultraviolet Surface Reflectance

We present the first measurements of Charon's far-ultraviolet (FUV) surface reflectance, obtained by the Alice spectrograph on New Horizons. We find no measurable flux shortward of 1650 Å, and Charon's geometric albedo is <0.019 (3σ) at 1600 Å. From 1650 to 1725 Å, Charon's geometric albedo increases to 0.166 ± 0.068 and remains nearly constant until 1850 Å. As this spectral shape is characteristic of H2O ice absorption, Charon is the first Kuiper Belt object with a H2O ice surface to be detected in the FUV. Charon's geometric albedo is ~3.7 times lower than Enceladus's at these wavelengths but has a very similar spectral shape. We attribute this to similarities in their surface compositions and the difference in absolute reflectivity to a high concentration or more-absorbing contaminants on Charon's surface. Finally, we find that Charon has different solar phase behavior in the FUV than Enceladus, Mimas, Tethys, and Dione, with a stronger opposition surge than Enceladus and a shallower decline at intermediate solar phase angles than any of these Saturnian satellites.

Keywords: plutonian satellites; ultraviolet photometry
Opposition Observations of 162173 Ryugu: Normal Albedo Map Highlights Variations in Regolith Characteristics

On 2019 January 8, the Telescopic Optical Navigation Camera (ONC-T) on board the Hayabusa2 spacecraft observed the Cb-type asteroid 162173 Ryugu under near-opposition illumination and viewing conditions from approximately 20 km in distance. Although opposition observations have never been used for mapping purposes of a planetary body, we found three advantages for mapping under these conditions: (1) images are free of topographic shadows, (2) the reflectance is nearly independent of the orientation of the surface, and (3) spurious color artifacts that may appear near shadowed terrain are avoided. We present normal albedo maps, one for each of the seven filters (0.40-0.95 μm), using an empirical photometric correction. Global coverage of Ryugu is 99.4%. The 0.55 μm band average normal albedo is 4.06% ± 0.10%. Various spectral variations are derived from these maps. Spectral features of regions and boulders are quantified by examining the normal albedo-derived spectral slope and UV index (spectral slope from visible to ultraviolet wavelength) value. In terms of space weathering, three spectral characteristics are observed over the majority of Ryugu: (1) reddening, (2) increases in reflectance at ultraviolet wavelengths compared to visible, and (3) darkening. By contrast, the bright boulders ("type 3") show a different trend, with wide variations in the 0.95 μm albedo and UV index. Finally, principal component analysis (PCA) comparisons with other asteroids strongly suggest that the main components of Ryugu belong to the B-Cb-type populations. The PCA feature of the fresh material on Ryugu is close to the Eulalia family.

Keywords: asteroids; small solar system bodies; multi-color photometry; near-earth objects; photometry; surface photometry
A Comparison of Rotating and Binary Stellar Evolution Models: Effects on Massive Star Populations

Both rotation and interactions with binary companions can significantly affect massive star evolution, altering interior and surface abundances, mass loss rates and mechanisms, observed temperatures and luminosities, and their ultimate core-collapse fates. The Geneva and the Binary Population and Spectral Synthesis (BPASS) stellar evolution codes include detailed treatments of the effects of rotation and binary evolution, respectively, and can illustrate the impact of these phenomena on massive stars and stellar populations. However, a direct comparison of these two widely used codes is vital if we hope to use their predictions for interpreting observations. In particular, rotating and binary models will predict different young stellar populations, impacting the outputs of stellar population synthesis (SPS) and the resulting interpretation of large samples of massive stars based on commonly used tools such as star count ratios. Here we compare the Geneva and BPASS evolutionary models, using an interpolated SPS scheme introduced in our previous work and a novel Bayesian framework to present the first in-depth direct comparison of massive stellar populations produced from single, rotating, and binary nonrotating evolution models. We calculate both models' predicted values of star count ratios and compare the results to observations of massive stars in Westerlund 1, h + χ Persei, and both Magellanic Clouds. We also consider the limitations of both the observations and the models, and how to quantitatively include observational completeness limits in SPS models. We demonstrate that the methods presented here, when combined with robust stellar evolutionary models, offer a potential means of estimating the physical properties of massive stars in large stellar populations.

Keywords: stellar populations; local group; star counts; binary stars; stellar rotation; stellar types; massive stars; galaxy stellar content
Orbital Periods and Waveforms of Dwarf Novae Observed by Kepler

Kepler high cadence data are used to measure the orbital periods and to determine the orbital waveforms of five dwarf novae. A significant improvement of the period of V1504 Cyg is achieved, while for the other systems periods are derived which are compatible with previous determinations. The orbital waveforms of the short period systems V1504 Cyg, V344 Lyr and V516 Lyr are very nearly sinusoidal, while the longer period dwarf nova V447 Lyr appears almost to be a twin of U Gem. The unusual system KIC 9202990 exhibits distinct variations of its waveform as a function of brightness during its outburst cycle.

Keywords: close binary stars; variable stars; cataclysmic variable stars; dwarf novae
Gangotri Wave-A High Density Gas Ripple in the Inner Galaxy

Recently, we reported the discovery of a kpc-scale CO structure in the inner Galaxy which we named the Gangotri wave. The structure is at least 2 kpc in extent and its vertical distribution is wave-like in morphology. The analysis of the velocity data suggests Gangotri wave being a spur of the Milky Way or a sub-branch of the Norma arm. Following the discovery, there is a rebuttal published, expressing concerns on identifying the inner Galaxy CO emission features as a single coherent structure. In this article, we aim to address the concerns of the rebuttal article, hoping to clarify some of the criticisms.

Keywords: interstellar filaments; galaxy structure; spiral arms