adsabs/SciX_UAT_keywords huggingface dataset:
Physical Implications of the Subthreshold GRB GBM-190816 and Its Associated Subthreshold Gravitational-wave Event

The LIGO/Virgo and Fermi collaborations recently reported a possible joint detection of a subthreshold gravitational-wave (GW) event and a subthreshold gamma-ray burst (GRB), GBM-190816, that occurred 1.57 s after the merger. We perform an independent analysis of the publicly available data and investigate the physical implications of this potential association. By carefully studying the following properties of GBM-190816 using Fermi/GBM data, including signal-to-noise ratio, duration, f-parameter, spectral properties, energetic properties, and its compliance with some GRB statistical correlations, we confirm that this event is likely a typical short GRB. Assuming its association with the subthreshold GW event, the inferred luminosity is ${1.47}_{-1.04}^{+3.40}\times {10}^{49}$ erg s-1. Based on the available information of the subthreshold GW event, we infer the mass ratio q of the compact binary as $q={2.26}_{-1.43}^{+2.75}$ (90% confidence interval) according to the reported range of luminosity distance. If the heavier compact object has a mass >3 solar masses, q can be further constrained to $q={2.26}_{-0.12}^{+2.75}$ . The leading physical scenario invokes an NS-BH merger system with the NS tidally disrupted. Within this scenario, we constrain the physical properties of such a system (including mass ratio q, the spin parameters, and the observer's viewing angle) to produce a GRB. The GW data may also allow an NS-BH system with no tidal disruption of the NS (the plunge events) or a BH-BH merger. We apply the charged compact binary coalescence theory (for both a constant charge and an increasing charge for the merging members) to derive the model parameters to account for GBM-190816 and found that the required parameters are extreme. Finally, we argue that the fact that the observed GW-GRB delay timescale is comparable to that of GW170817/GRB 170817A suggests that the GW-GRB time delay of these two cases is mainly defined by the timescale for the jet to propagate to the energy dissipation/GRB emission site.

Keywords: gamma-ray bursts; gravitational waves; relativistic jets; compact objects; black holes; neutron stars; gamma-ray transient sources
Radiatively Driven Clumpy X-Ray Absorbers in the NLS1 Galaxy IRAS 13224-3809

Recent radiation-magnetohydrodynamic simulations of active galactic nuclei predict the presence of the disk winds, which may become unstable and turn into fragmented clumps far from the central black hole. These inner winds and the outer clumps may be observed as ultrafast outflows (UFOs) and partial absorbers, respectively. However, it is challenging to observationally constrain their origins because of the complicated spectral features and variations. To resolve such degeneracies of the clumpy absorbers and other components, we developed a novel spectral-ratio model fitting technique that estimates the variable absorbing parameters from the ratios of the partially absorbed spectra to the non-absorbed one, canceling the complex non-variable spectral features. We applied this method to the narrow-line Seyfert 1 galaxy IRAS 13224-3809 observed by XMM-Newton in 2016 for ~1.5 Ms. As a result, we found that the soft spectral variation is mostly caused by changes in the partial covering fraction of the mildly ionized clumpy absorbers, whose outflow velocities are similar to those of the UFO (~0.2-0.3c). Furthermore, the velocities of the clumpy absorbers and UFOs increase similarly with the X-ray fluxes, consistent with the change in the UV-dominant continuum flux. We also discovered a striking correlation between the clump covering fraction and the equivalent width of the UFO absorption lines, which indicates that increasing the outflow in the line of sight leads to more prominent UFOs and more partial absorption. These findings strongly suggest that the clumpy absorbers and the UFO share the same origin, driven by the same UV-dominant continuum radiation.

Keywords: active galactic nuclei; seyfert galaxies; x-ray astronomy
Universal Scaling Laws for Solar and Stellar Atmospheric Heating: Catalog of Power-law Index between Solar Activity Proxies and Various Spectral Irradiances

The formation of extremely hot outer atmospheres is one of the most prominent manifestations of magnetic activity common to late-type dwarf stars, including the Sun. It is widely believed that these atmospheric layers, the corona, transition region, and chromosphere, are heated by the dissipation of energy transported upwards from the stellar surface by the magnetic field. This is signified by the spectral line fluxes at various wavelengths, scaled with power-law relationships against the surface magnetic flux over a wide range of formation temperatures, which are universal to the Sun and Sunlike stars of different ages and activity levels. This study describes a catalog of power-law indices between solar activity proxies and various spectral line fluxes. Compared to previous studies, we expanded the number of proxies, which now includes the total magnetic flux, total sunspot number, total sunspot area, and the F10.7 cm radio flux, and further enhanced the number of spectral lines by a factor of 2. This provides the data to study in detail the flux-flux scaling laws from the regions specified by the temperatures of the corona (log(T/K) = 6-7) to those of the chromosphere (log(T/K) ~ 4), as well as the reconstruction of various spectral line fluxes of the Sun in the past, F-, G-, and K-type dwarfs, and the modeled stars.

Keywords: stellar coronae; stellar chromospheres; solar spectral irradiance; solar corona; solar transition region; solar chromosphere; solar magnetic fields; solar analogs; g dwarf stars
Infrared Echoes of Optical Tidal Disruption Events: ∼1% Dust-covering Factor or Less at Subparsec Scale

The past decade has experienced an explosive increase of optically discovered tidal disruption events (TDEs) with the advent of modern time-domain surveys. However, we still lack a comprehensive observational view of their infrared (IR) echoes in spite of individual detections. To this end, we have conducted a statistical study of the IR variability of the 23 optical TDEs discovered between 2009 and 2018 using the full public data set of the Wide-field Infrared Survey Explorer. The detection of variability is performed on the difference images, yielding 11 objects with significant (>3σ) variability in at least one band, while dust emission can be only fit in 8 objects. Their peak dust luminosity is around 1041-1042 erg s-1, corresponding to a dust-covering factor fc ∼ 0.01 at a subparsec scale. The only exception is the disputed source ASASSN-15lh, which shows an ultra-high dust luminosity (∼1043.5 erg s-1), and this makes its nature even more elusive. Other nondetected objects show even lower fc, which could be lower by one more order of magnitude. The derived fc is generally much lower than those of dusty tori in active galactic nuclei, suggesting either a dearth of dust or a geometrically thin and flat disk in the vicinity of supermassive black holes. Our results also indicate that the optical TDE sample (post-starburst galaxies overrepresented) is seriously biased to events with little dust at subparsec scale, while TDEs in dusty star-forming systems could be more efficiently unveiled by IR echoes.

Keywords: supermassive black holes; tidal disruption; time domain astronomy; galaxy nuclei; active galactic nuclei; dust continuum emission; interstellar medium; infrared astronomy
First Resolved Scattered-light Images of Four Debris Disks in Scorpius-Centaurus with the Gemini Planet Imager

We present the first spatially resolved scattered-light images of four debris disks around members of the Scorpius-Centaurus (Sco-Cen) OB association with high-contrast imaging and polarimetry using the Gemini Planet Imager (GPI). All four disks are resolved for the first time in polarized light, and one disk is also detected in total intensity. The three disks imaged around HD 111161, HD 143675, and HD 145560 are symmetric in both morphology and brightness distribution. The three systems span a range of inclinations and radial extents. The disk imaged around HD 98363 shows indications of asymmetries in morphology and brightness distribution, with some structural similarities to the HD 106906 planet-disk system. Uniquely, HD 98363 has a wide comoving stellar companion, Wray 15-788, with a recently resolved disk with very different morphological properties. HD 98363 A/B is the first binary debris disk system with two spatially resolved disks. All four targets have been observed with ALMA, and their continuum fluxes range from one nondetection to one of the brightest disks in the region. With the new results, a total of 15 A/F stars in Sco-Cen have resolved scattered-light debris disks, and approximately half of these systems exhibit some form of asymmetry. Combining the GPI disk structure results with information from the literature on millimeter fluxes and imaged planets reveals a diversity of disk properties in this young population. Overall, the four newly resolved disks contribute to the census of disk structures measured around A/F stars at this important stage in the development of planetary systems.

Keywords: circumstellar disks; debris disks; direct imaging; planetary system formation; near infrared astronomy; circumstellar dust; circumstellar matter
Low-resolution Optical Spectroscopy of Recently Discovered Accreting-only Symbiotic Star THA 15-31

Recently, the discovery and characterization of a new accreting-only symbiotic star THA 15-31 was presented. Motivated by the suggestion that the optical spectrum of the star might show the emission lines with higher ionization potential in comparison with previously studied epochs, we have obtained a low-resolution spectrum of this target. The spectrum does not reveal the presence of suggested He II emission lines. Moreover, the near-UV excess seems to be even less prominent now in comparison with the previous observations, suggesting a decrease in mass transfer and accretion rate. The search for He II emission lines should be repeated when the accretion rate is higher.

Keywords: symbiotic binary stars; emission line stars; spectroscopy; red giant stars
Mg II and Fe II Fluxes of Luminous Quasars at z ∼ 2.7 and the Evaluation of the Baldwin Effect in the Flux-to-abundance Conversion Method for Quasars

To investigate the chemical abundance of broad-line region clouds in quasars at high redshifts, we performed near-infrared spectroscopy of six luminous quasars at z ∼ 2.7 with the WINERED spectrograph mounted on the New Technology Telescope at the La Silla Observatory, Chile. The measured Fe II/Mg II flux ratios nearly matched with the published data for 0.7 ≲ z ≲ 1.6, suggesting that there is no evolution over a long period of cosmic time, which is consistent with previous studies. To derive the chemical abundances from the measured equivalent widths (EWs), their dependence on nonabundance factors must be corrected. In our previous paper, we proposed a method to derive the [Mg/Fe] abundance ratio and the [Fe/H] abundance by correcting the dependence of EW(Mg II) and EW(Fe II) on the Eddington ratio. To the best of our knowledge, that was the first report to discuss the star formation history through a direct comparison with chemical evolution models. In the present study, we further investigated the dependence of EWs on luminosity, which is known as the Baldwin effect (BEff). Additional correction for the BEff significantly affects the derived chemical abundances for the six luminous quasars at z ∼ 2.7, and the resultant abundances agree well with the prediction of chemical evolution models. Given that most distant quasars found thus far are biased toward luminous ones, the correction of the measured EWs for the BEff is crucial for extending the chemical evolution study to higher redshifts.

Keywords: quasars; chemical abundances
Types of Transients in the Centers of Post-starburst and Quiescent Balmer-strong Galaxies

Tidal disruption events (TDEs) have been found to show a preference for post-starburst (PS) and quiescent Balmer-strong (QBS) galaxies. This preference can be used to help find TDEs in transient surveys. But what other transients might "contaminate" such a search, and by how much? We examine all reported transients coincident with the centers of galaxies in the French & Zabludoff (2018) catalog of spectroscopically confirmed PS and QBS galaxies and photometrically identified PS and QBS galaxy candidates. We find that TDEs and Type Ia supernovae (SNe) are the only types of transients classified in the centers of these galaxies (aside from one active galactic nucleus flare), with Type Ia SNe being 8.3 ± 0.2 times more prevalent than TDEs (1σ confidence bounds). This factor is ~2.7 times lower than in a control sample of quiescent galaxies. Narrowing the sample to spectroscopically confirmed QBS galaxies does not change these statistics much. In spectroscopically confirmed PS galaxies, however, TDEs are the ones that outnumber Type Ia SNe 2 ± 0.6 to 1. Unfortunately, there are few such galaxies in the catalog. By classifying transients from the entire catalog, three times more TDEs are expected to be found, but with a ~16 times larger Type Ia SN contamination. We use the public ZTF photometric archive to search for possibly missed TDEs in the French & Zabludoff (2018) galaxies. We find three unclassified clear transients-none of which are likely missed TDEs based on their light-curve colors.

Keywords: e+a galaxies; supernovae; tidal disruption
Shape Modeling of Dimorphos for the Double Asteroid Redirection Test (DART)

The Double Asteroid Redirection Test (DART) is the first planetary defense test mission. It will demonstrate the kinetic impactor technique by intentionally colliding the DART spacecraft with the near-Earth asteroid Dimorphos. The main DART spacecraft is accompanied by the Italian Space Agency Light Italian CubeSat for Imaging of Asteroids (LICIACube). Shape modeling efforts will estimate the volume of Dimorphos and constrain the nature of the impact site. The DART mission uses stereophotoclinometry (SPC) as its primary shape modeling technique. DART is essentially a worst-case scenario for any image-based shape modeling approach because images taken by the camera on board the DART spacecraft, called the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), possess little stereo and no lighting variation; they simply zoom in on the asteroid. LICIACube images add some stereo, but the images are substantially lower in resolution than the DRACO images. Despite the far-from-optimal imaging conditions, our tests indicate that we can identify the impact site to an accuracy and precision better than 10% the size of the spacecraft core, estimate the volume of Dimorphos to better than 25%, and measure tilts at the impact site over the scale of the spacecraft with an accuracy better than 7°. In short, we will know with excellent accuracy where the DART spacecraft hit, with reasonable knowledge of local tilt, and determine the volume well enough that uncertainties in the density of Dimorphos will be comparable to or dominate the uncertainty in the estimated mass. The tests reported here demonstrate that SPC is a robust technique for shape modeling, even with suboptimal images.

Keywords: asteroids; near-earth objects; asteroid satellites; impact phenomena; planetary science
Maser Investigation toward Off-Plane Stars (MIOPS): Detection of SiO Masers in the Galactic Thick Disk and Halo

Studying stars that are located off the Galactic plane is important for understanding the formation history of the Milky Way. We searched for SiO masers toward off-plane O-rich asymptotic giant branch (AGB) stars from the catalog presented by Mauron et al. in order to shed light on the origins of these objects. A total of 102 stars were observed in the SiO J = 1‑0, v = 1 and 2 transitions with the Effelsberg 100 m and Tianma 65 m telescopes. SiO masers were discovered in eight stars, all first detections. The measured maser velocities allow for initial estimates of the host AGB stars' radial velocities. We find that the radial velocities of three stars (namely G068.881‑24.615, G070.384‑24.886, and G084.453‑21.863) significantly deviate from the values expected from Galactic circular motion. The updated distances and 3D motions indicate that G068.881‑24.615 is likely located in the Galactic halo, while G160.648‑08.846 is probably located in the Galactic thin disk, and the other six stars are probably part of the Galactic thick disk.

Keywords: astrophysical masers; silicon monoxide masers; asymptotic giant branch stars; galaxy structure
Void Galaxy Distribution: A Challenge for ΛCDM

We extract void catalogs from the Sloan Digital Sky Survey Data Release 16 (SDSS DR16) survey and also from the Millennium simulation. We focus our comparison on distribution of galaxies brighter than Mr < -18 inside voids and study the mean separation of void galaxies, distance from the void center, and the radial density profile. We find that mean separation of void galaxies depends on void size, as bigger voids have lower mean separation in both samples. However, void galaxies in the observation sample seem to have generally larger mean-distance than simulated ones at any given void size. In addition, observed void galaxies tend to reside closer to the void center than those in the simulation. This discrepancy is also shown in the density profile of voids. Regardless of the void size, the central densities of real void profiles are higher than the ones in the predicted simulated catalog.

Keywords: voids
Toward the IR Detection of Carbonic Acid: Absorption and Emission Spectra

With the recent radioastronomical detection of cis-trans-carbonic acid (H2CO3) in a molecular cloud toward the Galactic center, the more stable but currently unobserved cis-cis conformer is shown here to have strong IR features. While the higher-energy cis-trans-carbonic acid was detected at millimeter and centimeter wavelengths, owing to its larger dipole moment, the vibrational structure of cis-cis-carbonic acid is more amenable to its observation at micron wavelengths. Even so, both conformers have relatively large IR intensities, and some of these fall in regions not dominated by polycyclic aromatic hydrocarbons. Water features may inhibit observation near the 2.75 μm hydride stretches, but other vibrational fundamentals and even overtones in the 5.5–6.0 μm range may be discernible with JWST data. This work has employed high-level, accurately benchmarked quantum chemical anharmonic procedures to compute exceptionally accurate rotational spectroscopic data compared to experiment. Such performance implies that the IR absorption and even cascade emission spectral features computed in this work should be accurate and will provide the needed reference for observation of either carbonic acid conformer in various astronomical environments.

Keywords: astrochemistry; pre-biotic astrochemistry; interstellar molecules; small molecules; molecular spectroscopy; molecular data; molecular spectroscopic constants; complex organic molecules; quantum-chemical calculations; infrared spectroscopy; rotational spectroscopy
On the Diversity of Asymmetries in Gapped Protoplanetary Disks

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum caused by dust trapping in pressure bumps and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. First, we compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex, or spiral density waves. Second, we reassess the gas gap radii from the 13CO maps, which are about a factor of 2 smaller than the dust ring radii, suggesting that the companions in these disks are in the brown dwarf (∼15-50 MJup) or super-Jovian (∼3-15 MJup) mass regime on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions (q > 0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered-light images are primarily detected around high-luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass.

Keywords: protoplanetary disks; circumstellar disks; planet formation
A Molecular Gas Ring Hidden in the Sombrero Galaxy

We present Herschel, ALMA, and MUSE observations of the molecular ring of Messier 104, also known as the Sombrero galaxy. These previously unpublished archival data shed new light on the content of the interstellar medium of M104. In particular, molecular hydrogen measured by CO emission and dust measured by far-infrared light are uniformly distributed along the ring. The ionized gas revealed by Hα and [C II] emission is distributed in knots along the ring. Despite being classified as an SAa galaxy, M104 displays features typical of early-type galaxies. We therefore compared its [C II] and dust emission to a sample of early-type galaxies observed with Herschel and SOFIA. The [C II]/FIR ratio of M104 is much lower than that of typical star-forming galaxies and is instead much more similar to that of early-type galaxies. By classifying regions using optical emission line diagnostics, we also find that regions classified as H II lie closer to star-forming galaxies in the [C II]/FIR diagram than those classified as low-ionization emission regions. The good match between [C II] and Hα emission, in conjunction with the lack of correlation between CO emission and star formation, suggests that there is very limited active star formation along the ring and that most of the [C II] emission is from ionized and neutral atomic gas rather than molecular gas. From the total intensity of the CO line, we estimate a molecular hydrogen mass of 0.9 × 109 M ⊙, a value intermediate between those of early-type galaxies and the content of the molecular ring of our galaxy.

Keywords: infrared galaxies; molecular gas; galaxy environments; interstellar medium