adsabs/SciX_UAT_keywords huggingface dataset:
GN-z11-flash in the Context of Gamma-Ray Burst Afterglows

The recently discovered rapid transient GN-z11-flash has been suggested to be the prompt-emission ultraviolet (UV) flash associated with a gamma-ray burst (GRB) serendipitously exploding in the ultra-high-z galaxy GN-z11. We here place the flash into the context of the early UV emission of GRBs, and find it is in agreement with the luminosity distribution of these events.

Keywords: gamma-ray bursts; high-redshift galaxies
Formulating and Critically Examining the Assumptions of Global 21 cm Signal Analyses: How to Avoid the False Troughs That Can Appear in Single-spectrum Fits

The assumptions inherent to global 21 cm signal analyses are rarely delineated. In this paper, we formulate a general list of suppositions underlying a given claimed detection of the global 21 cm signal. Then, we specify the form of these assumptions for two different analyses: (1) the one performed by the team for the Experiment to Detect the Global Epoch-of-Reionization Signature (EDGES) showing an absorption trough in brightness temperature that they modeled separately from the sky foreground and (2) a new, so-called minimum assumption analysis (MAA) that makes the most conservative assumptions possible for the signal. We show fits using the EDGES analysis on various beam-weighted foreground simulations from the EDGES latitude with no signal added. Depending on the beam used, these simulations produce large false troughs because of the invalidity of the foreground model in describing the combination of beam chromaticity and the shape of the Galactic plane in the sky, the residuals of which are captured by the ad hoc flattened Gaussian signal model. On the other hand, the MAA provides robust fits by including many spectra at different time bins and allowing any possible 21 cm spectrum to be modeled exactly. We present uncertainty levels and example signal reconstructions found with the MAA for different numbers of time bins. With enough time bins, one can determine the true 21 cm signal with the MAA to <10 times the noise level.

Keywords: reionization; astronomy data analysis; computational methods
The Empirical Limits of Gyrochronology

The promise of gyrochronology is that, given a star's rotation period and mass, its age can be inferred. The reality of gyrochronology is complicated by effects other than ordinary magnetized braking that alter stellar rotation periods. In this work, we present an interpolation-based gyrochronology framework that reproduces the time- and mass-dependent spin-down rates implied by the latest open cluster data, while also matching the rate at which the dispersion in initial stellar rotation periods decreases as stars age. We validate our technique for stars with temperatures of 3800-6200 K and ages of 0.08-2.6 gigayears (Gyr), and use it to reexamine the empirical limits of gyrochronology. In line with previous work, we find that the uncertainty floor varies strongly with both stellar mass and age. For Sun-like stars (≈5800 K), the statistical age uncertainties improve monotonically from ±38% at 0.2 Gyr to ±12% at 2 Gyr, and are caused by the empirical scatter of the cluster rotation sequences combined with the rate of stellar spin-down. For low-mass K dwarfs (≈4200 K), the posteriors are highly asymmetric due to stalled spin-down, and ±1σ age uncertainties vary non-monotonically between 10% and 50% over the first few gigayears. High-mass K dwarfs (5000 K) older than ≈1.5 Gyr yield the most precise ages, with limiting uncertainties currently set by possible changes in the spin-down rate (12% systematic), the calibration of the absolute age scale (8% systematic), and the width of the slow sequence (4% statistical). An open-source implementation, gyro-interp, is available online at github.com/lgbouma/gyro-interp.

Keywords: stellar ages; stellar rotation; field stars; bayesian statistics
A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows

We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.

Keywords: stellar accretion; magnetohydrodynamics; galactic center; black holes; very long baseline interferometry
MHD Wave Propagation and the Kelvin-Helmholtz Instability in an Asymmetric Magnetic Slab System

Magnetohydrodynamic waves are ubiquitously detected in the finely structured solar atmosphere. At the same time, our Sun is a highly dynamic plasma environment, giving rise to flows of various magnitudes, which can lead to the instability of waveguides. Recent studies have employed the method of introducing waveguide asymmetry to generalize "classical" symmetric descriptions of the fine structuring within the solar atmosphere, with some of them introducing steady flows as well. Building on these recent studies, here we investigate the magnetoacoustic waves guided by a magnetic slab within an asymmetric magnetic environment, in which the slab is under the effect of a steady flow. We provide an analytical investigation of how the phase speeds of the guided waves are changed, and where possible, determine the limiting flow speeds required for the onset of the Kelvin-Helmholtz instability. Furthermore, we complement the study with initial numerical results, which allows us to demonstrate the validity of our approximations and extend the investigation to a wider parameter regime. This configuration is part of a series of studies aimed to generalize, step-by-step, well-known symmetric waveguide models and understand the additional physics stemming from introducing further sources of asymmetry.

Keywords: quiet solar corona; quiet solar chromosphere; solar atmosphere; solar magnetic fields; solar physics
S-type Stars from LAMOST DR10: Classification of Intrinsic and Extrinsic Stars

In this paper, we found 2939 S-type stars from LAMOST Data Release 10 using two machine-learning methods, and 2306 of them were reported for the first time. The main purpose of this work is to study how to divide S-type stars into intrinsic and extrinsic stars with photometric data and LAMOST spectra. Using infrared photometric data, we adopted two methods to distinguish S-type stars, i.e., the XGBoost algorithm and color-color diagrams. We trained the XGBoost model with 15 input features consisting of colors and absolute magnitudes from Two Micron All Sky Survey (2MASS), AllWISE, AKARI, and IRAS, and found that the model trained by input features with 2MASS, AKARI, and IRAS data has the highest accuracy of 95.52%. Furthermore, using this XGBoost model, we found four color-color diagrams with six infrared color criteria to divide S-type stars, which have an accuracy of about 90%. Applying the two methods to the 2939 S-type stars, 381 (XGBoost)/336 (color-color diagrams) intrinsic and 495 (XGBoost)/82 (color-color diagrams) extrinsic stars were classified, respectively. Using these photometrically classified intrinsic and extrinsic stars, we retrained the XGBoost model with their blue and red medium-resolution spectra, and the 2939 stars were divided into 855 intrinsic and 2056 extrinsic stars from spectra with an accuracy of 94.82%. In addition, we also found the four spectral regions of Zr I (6451.6 Å), Ne II (6539.6 Å), H α (6564.5 Å), and Fe I (6609.1 Å) and C I (6611.4 Å) are the most important features, which can reach an accuracy of 92.1% when using them to classify S-type stars.

Keywords: s stars
Gravitational-wave Radiation from the Magnetar-driven Supernovae

Rapidly spinning magnetars are potential candidates for the energy source of supernovae (SNe) and gamma-ray bursts and the most promising sources for continuous gravitational waves (GWs) detected by ground-based GW detectors. Continuous GWs can be radiated from magnetars due to magnetic-induced deformation or fluid oscillations, compatible with magnetic dipole (MD) radiation for spin-down energy. In this paper, we investigate the diverse light curves of magnetar-driven SNe in the scenario that the spin-down is dominated by GW radiation and/or MD radiation. By simulating the light curves of SNe and employing the Markov Chain Monte Carlo method, we constrain the parameters of the magnetars and SN explosions and show that the signature of GW radiation may be indicated by the bolometric luminosity curves of SNe Ic-BL 2007ru and 2009bb. We find that the ellipticity of magnetars in the order of 10‑3 can be induced by the magnetic field of ∼1016 G. If such continuous GWs associated with SNe can be detected in the future by the Advanced LIGO and Virgo detectors, this would be a smoking gun for a magnetar engine powering SNe.

Keywords: gravitational waves; supernovae; magnetars
Accretion Properties of PDS 70b with MUSE

We report a new evaluation of the accretion properties of PDS 70b obtained with the Very Large Telescope/Multi Unit Spectroscopic Explorer. The main difference from the previous studies of Haffert et al. and Aoyama & Ikoma is in the mass accretion rate. Simultaneous multiple line observations, such as Hα and Hβ, can better constrain the physical properties of an accreting planet. While we clearly detected Hα emissions from PDS 70b, no Hβ emissions were detected. We estimate the line flux of Hβ with a 3σ upper limit to be 2.3 × 10-16 erg s-1 cm-2. The flux ratio FHβ/FHα for PDS 70b is <0.28. Numerical investigations by Aoyama et al. suggest that FHβ/FHα should be close to unity if the extinction is negligible. We attribute the reduction of the flux ratio to the extinction, and estimate the extinction of Hα (AHα) for PDS 70b to be >2.0 mag using the interstellar extinction value. By combining with the Hα linewidth and the dereddening line luminosity of Hα, we derive the PDS 70b mass accretion rate to be ≳5 × 10-7 MJup yr-1. The PDS 70b mass accretion rate is an order of magnitude larger than that of PDS 70. We found that the filling factor ff (the fractional area of the planetary surface emitting Hα) is ≳0.01, which is similar to the typical stellar value. The small value of ff indicates that the Hα emitting areas are localized at the surface of PDS 70b.

Keywords: accretion; exoplanet formation; direct imaging
Identification of 4FGL Uncertain Sources at Higher Resolutions with Inverse Discrete Wavelet Transform

In the forthcoming era of big astronomical data, it is a burden to find target sources from ground-based and space-based telescopes. Although machine-learning methods have been extensively utilized to address this issue, the incorporation of in-depth data analysis can significantly enhance the efficiency of identifying target sources when dealing with massive volumes of astronomical data. In this work, we focused on the task of finding active galactic nucleus (AGN) candidates and identifying BL Lacertae objects (BL Lac) or flat spectrum radio quasar (FSRQ) candidates from the 4FGL_DR3 uncertain sources. We studied the correlations among the attributes of the 4FGL_DR3 catalog and proposed a novel method, named fractal dimension-inverse discrete wavelet transform (FDIDWT), to transform the original data. The transformed data set is characterized as low-dimensional and feature-highlighted, with the estimation of correlation features by fractal dimension theory and the multi-resolution analysis by inverse discrete wavelet transform (IDWT). Combining the FDIDWT method with an improved lightweight MatchboxConv1D model, we accomplished two missions: (1) to distinguish the AGNs from others (non-AGNs) in the 4FGL_DR3 uncertain sources with an accuracy of 96.65% ± 1.32%, namely Mission A; and (2) to classify blazar candidates of uncertain type into BL Lacs or FSRQs with an accuracy of 92.03% ± 2.2%, namely Mission B. There are 1354 AGN candidates in Mission A, and 482 BL Lacs candidates and 128 FSRQ candidates were found in Mission B. The results show a high consistency of greater than 98% with the results in previous works. In addition, our method has the advantage of finding less variable and relatively faint sources than ordinary methods.

Keywords: blazars; classification; active galactic nuclei; wavelet analysis
Strong Near-infrared Spectral Variability of the Young Cloudy L Dwarf Companion VHS J1256-1257 b

Rotationally modulated variability of brown dwarfs and giant planets provides unique information about their surface brightness inhomogeneities, atmospheric circulation, cloud evolution, vertical atmospheric structure, and rotational angular momentum. We report results from Hubble Space Telescope/Wide Field Camera 3 near-infrared time-series spectroscopic observations of three companions with masses in or near the planetary regime: VHS J125601.92-125723.9 b, GSC 6214-210 B, and ROXs 42 B b. VHS J1256-1257 b exhibits strong total intensity and spectral variability with a brightness difference of 19.3% between 1.1 and 1.7 μm over 8.5 hr and even higher variability at the 24.7% level at 1.27 μm. The light curve of VHS J1256-1257 b continues to rise at the end of the observing sequence so these values represent lower limits on the full variability amplitude at this epoch. This observed variability rivals (and may surpass) the most variable brown dwarf currently known, 2MASS J21392676+0220226. The implied rotation period of VHS J1256-1257 b is ≈21-24 hr assuming sinusoidal modulations, which is unusually long for substellar objects. No significant variability is evident in the light curves of GSC 6214-210 B (<1.2%) and ROXs 42 B b (<15.6%). With a spectral type of L7, an especially red spectrum, and a young age, VHS J1256-1257 b reinforces emerging patterns between high variability amplitude, low surface gravity, and evolutionary phase near the L/T transition.

Keywords: brown dwarfs; exoplanet atmospheric variability
Deep Very Long Baseline Interferometry Observations Challenge Previous Evidence of a Binary Supermassive Black Hole Residing in Seyfert Galaxy NGC 7674

Previous Ku-band (15 GHz) imaging with data obtained from the Very Long Baseline Array (VLBA) had shown two compact, subparsec components at the location of a presumed kiloparsec-scale radio core in Seyfert galaxy NGC 7674. It was then presumed that these two unresolved and compact components were dual radio cores corresponding to two supermassive black holes (SMBHs) accreting surrounding gas and launching radio-bright relativistic jets. However, utilizing the original VLBA data set used to claim the detection of a binary SMBH, in addition to later multiepoch/multifrequency data sets obtained from both the VLBA and the European very long baseline interferometry (VLBI) network, we find no evidence to support the presence of a binary SMBH. We place stringent upper limits to the flux densities of any subparsec-scale radio cores that are at least an order of magnitude lower than the original VLBI radio-core detections, directly challenging the original binary SMBH detection claim. With this in mind, we discuss the possible reasons for the nondetection of any VLBI radio cores in our imaging, the possibility of a binary SMBH still residing in NGC 7674, and the prospect of future observations shedding further light on the true nature of this active galactic nucleus.

Keywords: active galactic nuclei; radio cores; gravitational waves; supermassive black holes
Evolutionary Origins of Binary Neutron Star Mergers: Effects of Common Envelope Efficiency and Metallicity

The formation histories of compact binary mergers, especially stellar-mass binary black hole mergers, have recently come under increased scrutiny and revision. We revisit the question of the dominant formation channel and efficiency of forming binary neutron star (BNS) mergers. We use the stellar and binary evolution code MESA and implement a detailed method for common envelope and mass transfer. We perform simulations for donor masses between 7 M ⊙ and 20 M ⊙ with a neutron star (NS) companion of 1.4 M ⊙ and 2.0 M ⊙ at two metallicities, using varying common envelope efficiencies and two different prescriptions to determine if the donor undergoes core collapse or electron capture, given their helium and carbon-oxygen cores. In contrast to the case of binary black hole mergers, for an NS companion of 1.4 M ⊙, all BNS mergers are formed following a common envelope phase. For an NS mass of 2.0 M ⊙, we identify a small subset of mergers following only stable mass transfer if the NS receives a natal kick sampled from a Maxwellian distribution with velocity dispersion σ = 265 km s-1. Regardless of the supernova prescription, we find more BNS mergers at subsolar metallicity compared to solar.

Keywords: gravitational wave sources; neutron stars; common envelope evolution; stellar evolutionary models; roche lobe overflow
End-to-end Kilonova Models of Neutron Star Mergers with Delayed Black Hole Formation

We investigate the nucleosynthesis and kilonova properties of binary neutron star (NS) merger models that lead to intermediate remnant lifetimes of ~0.1-1 s until black hole (BH) formation and describe all components of the material ejected during the dynamical merger phase, NS remnant evolution, and final viscous disintegration of the BH torus after gravitational collapse. To this end, we employ a combination of hydrodynamics, nucleosynthesis, and radiative transfer tools to achieve a consistent end-to-end modeling of the system and its observables. We adopt a novel version of the Shakura-Sunyaev scheme allowing the approximate turbulent viscosity inside the NS remnant to vary independently of the surrounding disk. We find that asymmetric progenitors lead to shorter remnant lifetimes and enhanced ejecta masses, although the viscosity affects the absolute values of these characteristics. The integrated production of lanthanides and heavier elements in such binary systems is subsolar, suggesting that the considered scenarios contribute in a subdominant fashion to r-process enrichment. One reason is that BH tori formed after delayed collapse exhibit less neutron-rich conditions than typically found, and often assumed in previous BH torus models, for early BH formation. The outflows in our models feature strong anisotropy as a result of the lanthanide-poor polar neutrino-driven wind pushing aside lanthanide-rich dynamical ejecta. Considering the complexity of the models, the estimated kilonova light curves show promising agreement with AT 2017gfo after times of several days, while the remaining inconsistencies at early times could possibly be overcome in binary configurations with a more dominant neutrino-driven wind relative to the dynamical ejecta.

Keywords: hydrodynamical simulations; compact objects; gravitational wave astronomy; transient sources; r-process; nuclear astrophysics
A New Archive of Apollo's Lunar Seismic Data

The Apollo astronauts deployed seismic experiments on the nearside of the Moon between 1969 and 1972. Five stations collected passive seismic data. Apollo 11 operated for around 20 days, and stations 12, 14, 15, and 16 operated nearly continuously from their installation until 1977. Seismic data were collected and digitized on the Moon and transmitted to Earth. The data were recorded on magnetic reel-to-reel tapes, with timestamps representing the signal reception time on Earth. The taped data have been widely used for many applications and have previously been shared in various formats. The data have slightly varying sampling rates, due to random fluctuations of the data sampler and also its sensitivity to the significant temperature variations on the Moon's surface. Additionally, there were timing errors. Previously shared versions of the Apollo data were affected by these problems. We have reimported the passive data to SEED (Standard for the Exchange of Earthquake Data) format, and we make these data available via Incorporated Research Institutions for Seismology and the Planetary Data System. We have cleaned the timestamp series to reduce incorrectly recorded timestamps. The archive includes five tracks: three components of the mid-period seismometers, one short-period component, and a time track containing the timestamps. The seismic data are provided unprocessed in their raw format, and we provide instrument response files. We hope that the new archive will make it easier for a new generation of seismologists to use these data to learn more about the structure of the Moon.

Keywords: lunar seismology; lunar interior
Turbulence and Energetic Particles in Radiative Shock Waves in the Cygnus Loop. II. Development of Postshock Turbulence

Radiative shock waves in the Cygnus Loop and other supernova remnants show different morphologies in [O III] and Hα emission. We use HST spectra and narrowband images to study the development of turbulence in the cooling region behind a shock on the west limb of the Cygnus Loop. We refine our earlier estimates of shock parameters that were based upon ground-based spectra, including ram pressure, vorticity, and magnetic field strength. We apply several techniques, including Fourier power spectra and the Rolling Hough Transform, to quantify the shape of the rippled shock front as viewed in different emission lines. We assess the relative importance of thermal instabilities, the thin shell instability, upstream density variations, and upstream magnetic field variations in producing the observed structure.

Keywords: shocks; supernova remnants; plasma astrophysics; interstellar magnetic fields; interplanetary turbulence