adsabs/SciX_UAT_keywords huggingface dataset:
Multiwavelength Study of an X-Ray Tidal Disruption Event Candidate in NGC 5092

We present multiwavelength studies of a transient X-ray source, XMMSL1 J131952.3+225958, associated with the galaxy NGC 5092 at z = 0.023 detected in the XMM-Newton SLew survey (XMMSL). The source brightened in the 0.2-2 keV band by a factor of > 20 in 2005 as compared with previous flux limits and then faded by a factor of >200 as observed with XMM-Newton in 2013 and with Swift in 2018. At the flaring state the X-ray spectrum can be modeled with a blackbody at a temperature of ∼60 eV and an overall luminosity of ∼ 1.5× {10}43 erg s-1. A UV flare and optical flare were also detected with the Galaxy Evolution Explorer and the Sloan Digital Sky Survey, respectively, within several months of the X-ray flare, whose nonstellar UV-optical spectrum can be described with a blackbody at a temperature of ∼ (1-2)× {10}4 K and a luminosity of ∼ (2-6)× 1043 erg s-1. Interestingly, mid-infrared monitoring observations of NGC 5092 with the Wide-field Infrared Survey Explorer 5-13 yr later show a continuous flux decline. These dramatic variability properties, from the X-ray through UV and optical to infrared, appear to be orderly, suggestive of a stellar tidal disruption event (TDE) by a massive black hole, confirming the postulation by Kanner et al. This TDE candidate belongs to a rare sample with contemporaneous bright emission detected in the X-ray, UV, and optical, which are later echoed by dust-reprocessed light in the mid-infrared. The black hole has a mass of ∼ 5 × 107 M⊙, residing in a galaxy that is dominated by a middle-aged stellar population of 2.5 Gyr.

Keywords: tidal disruption; galaxy nuclei
Doppler Imaging and Differential Rotation of σ2 Coronae Borealis Using SONG

We present new Doppler images of both components of the double-lined binary σ2 CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March-April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of σ2 CrB simultaneously. The surfaces of both F9 and G0 components are dominated by pronounced polar spots. The F9 component exhibits a weak spot at latitude 30° and its mid-to-low latitudes are relatively featureless. The G0 star shows an extended spot structure at latitude 30°, and its surface spot coverage is larger than that of the F9 star, which suggests a higher level of magnetic activity. With the cross-correlation method, we derive a solar-like surface differential rotation on the G0 star of σ2 CrB for the first time, and the surface shear rate is ΔΩ = 0.180 ± 0.004 rad days-1 and α = ΔΩ/Ωeq = 0.032 ± 0.001. We do not obtain a clear surface shear law for the F9 star due to the lack of mid-to-low latitude features, but detect a systematic longitude shift of high-latitude spots, which indicates a slower rotation with respect to the corotating frame.

Keywords: stellar activity; close binary stars; doppler imaging; starspots
Characterizing Magnetic Reconnection Regions Using Gaussian Mixture Models on Particle Velocity Distributions

We present a method based on unsupervised machine learning to identify and characterize regions of interest using particle velocity distributions as a signature pattern. An automatic density estimation technique is applied to particle distributions provided by particle-in-cell simulations to study magnetic reconnection regions. Its application to magnetic reconnection is new. The key components of the method involve (I) a Gaussian mixture model determining the presence of a given number of subpopulations within an overall population, and (II) a model selection technique with a Bayesian information criterion to estimate the appropriate number of subpopulations. Thus, this method automatically identifies the presence of complex distributions, such as beams or other non-Maxwellian features, and can be used as a detection algorithm able to identify reconnection regions. The approach is demonstrated for a specific double Harris sheet simulation, but it can in principle be applied to any other type of simulation data on the particle distribution function.

Keywords: solar magnetic reconnection; gaussian mixture model; plasma astrophysics
An Unsupervised Machine Learning-based Algorithm for Detecting Weak Impulsive Narrowband Quiet Sun Emissions and Characterizing Their Morphology

The solar corona is extremely dynamic. Every leap in observational capabilities has been accompanied by unexpected revelations of complex dynamic processes. The ever more sensitive instruments now allow us to probe events with increasingly weaker energetics. A recent leap in the low-frequency radio solar imaging ability has led to the discovery of a new class of emissions, namely weak impulsive narrowband quiet Sun emissions (WINQSEs). They are hypothesized to be the radio signatures of coronal nanoflares and could potentially have a bearing on the long standing coronal heating problem. In view of the significance of this discovery, this work has been followed up by multiple independent studies. These include detecting WINQSEs in multiple data sets, using independent detection techniques and software pipelines, and looking for their counterparts at other wavelengths. This work focuses on investigating morphological properties of WINQSEs and also improves upon the methodology used for detecting WINQSEs in earlier works. We present a machine learning-based algorithm to detect WINQSEs, classify them based on their morphology, and model the isolated ones using 2D Gaussians. We subject multiple data sets to this algorithm to test its veracity. Interestingly, despite the expectations of their arising from intrinsically compact sources, WINQSEs tend to be resolved in our observations. We propose that this angular broadening arises due to coronal scattering. Hence, WINQSEs can provide ubiquitous and ever-present diagnostic of coronal scattering (and, in turn, coronal turbulence) in the quiet Sun regions, which has not been possible until date.

Keywords: solar radio emission; quiet sun; solar coronal transients; solar coronal heating
The FUSE Spectrum of HD 215441 (Babcock's Star)

The analysis of the far-ultraviolet spectrum of the B9 Si HD 215441 recorded by the LWRS camera on board FUSE reveals a large deficiency of the flux when compared to the non-magnetic late B-type star HD 182308 of similar fundamental parameters. Most features can be identified using spectrum synthesis. The FUSE spectrum of HD 215441 contains mostly blends of low-excitation lines of Ti II, Mn II, Cr II, Fe II, a few lines of Ti III, Cr III and Fe III and interesting lines of C III, P II, S II and Cl I.

Keywords: chemically peculiar stars; magnetic stars
Adsorption-driven Gas Trapping in Cometary Ice Analogs

Icy planetary bodies carry volatiles in abundances that should reflect the conditions of their formation. However, the interpretation of volatile abundance data from comets is complicated by the fact that the governing parameters and underlying mechanism of volatile trapping are poorly constrained. To unravel the mechanism of gas trapping in water ice and shed light on the origin of comets, gas-trapping experiments were conducted under isothermal conditions with a focus on the relationship between adsorption properties and the quantities of trapped gas. The adsorption data suggest that the adsorption energies of ice surfaces are heterogeneous, and surface properties depend on initial ice-deposition temperatures as well as on the effect of thermal annealing. Sites with different adsorption energies result in temperature dependence of contributing adsorption sites. Moreover, adsorption sites characterized by higher energy contribute predominantly at low pressures, relevant to the protosolar nebula, and at higher temperatures. When new ice was added to the well-characterized ice surface under controlled Ar pressure, the amount of trapped gas was proportional to the amount of gas adsorbed on the newly generated external surface, suggesting the burial of adsorbed gas as the primary mechanism of gas trapping. The ratio of trapped to newly adsorbed gas reflecting the internal to external surface areas ranged between 5 and 20. Assuming the formation of comparable water ice under the pressure-temperature profile of the protosolar nebula, Ar/H2O~10-5 reported from 67P/Churyumov-Gerasimenko could have formed at about 40 K.

Keywords: laboratory astrophysics; ice formation
Globular Cluster Formation from Colliding Substructure

We investigate a scenario where the formation of globular clusters (GCs) is triggered by high-speed collisions between infalling atomic-cooling subhalos during the assembly of the main galaxy host, a special dynamical mode of star formation that operates at high gas pressures and is intimately tied to ΛCDM hierarchical galaxy assembly. The proposed mechanism would give origin to "naked" globular clusters as colliding dark matter subhalos and their stars will simply pass through one another while the warm gas within them clashes at highly supersonic speed and decouples from the collisionless component, in a process reminiscent of the Bullet galaxy cluster. We find that the resulting shock-compressed layer cools on a timescale that is typically shorter than the crossing time, first by atomic line emission and then via fine-structure metal-line emission, and is subject to gravitational instability and fragmentation. Through a combination of kinetic theory approximation and high-resolution N-body simulations, we show that this model may produce: (a) a GC number-halo mass relation that is linear down to dwarf galaxy scales and agrees with the trend observed over five orders of magnitude in galaxy mass; (b) a population of old globular clusters with a median age of 12 Gyr and an age spread similar to that observed; (c) a spatial distribution that is biased relative to the overall mass profile of the host; and (d) a bimodal metallicity distribution with a spread similar to that observed in massive galaxies.

Keywords: globular star clusters; cold dark matter; galaxy formation; hydrodynamics; n-body simulations
Longitudinally Modulated Dynamo Action in Simulated M-dwarf Stars

M-dwarf stars are well known for the intense magnetic activity that many of them exhibit. In cool stars with near-surface convection zones, this magnetic activity is thought to be driven largely by the interplay of convection and the large-scale differential rotation and circulations it establishes. The highly nonlinear nature of these flows yields a fascinatingly sensitive and diverse parameter space, with a wide range of possible dynamics. We report here on a set of three global MHD simulations of rapidly rotating M2 (0.4 M ⊙) stars. Each of these three models established nests of vigorous convection that were highly modulated in longitude at low latitudes. Slight differences in their magnetic parameters led each model to disparate dynamo states, but the effect of the convective nest was a unifying feature. In each case, the action of longitudinally modulated convection led to localized (and in one case, global) reversals of the toroidal magnetic field, as well as the formation of an active longitude, with enhanced poloidal field amplitudes and flux emergence.

Keywords: stellar convective zones; magnetohydrodynamics; stellar interiors; m dwarf stars; stellar magnetic fields
A New Constraint on the Simulation of the Intergalactic Medium through the Evolution of the Neutral Hydrogen Fraction in the Epoch of Reionization

The thermal history of the intergalactic medium is full of extremely useful data in the field of astrophysics and cosmology. In other words, by examining this environment in different redshifts, the effects of cosmology and astrophysics can be observed side by side. Therefore, simulation is a very powerful tool to reach a suitable model for the intergalactic medium, both in terms of cosmology and astrophysics. In this work, we have simulated the intergalactic medium with the help of the 21cmFAST code and compared the evolution of the neutral hydrogen fraction in different initial conditions. Considerable works have arbitrarily determined many important effective parameters in the thermal history of the intergalactic medium without any constraints, and usually, there is much flexibility in the modeling. Nonetheless, in this work, by focusing on the evolution of the neutral hydrogen fraction in different models and comparing it with observational data, we have eliminated many simulated models and introduced only limited simulation models that could confirm the observations with sufficient accuracy. This issue becomes thoroughly vital from the point of view that in addition to restricting the models through the neutral hydrogen fraction, it can also impose restrictions on the parameters affecting its changes. However, we hope that in future works, by enhancing the observational data and increasing their accuracy, more compatible models with the history of the intergalactic medium can be achieved.

Keywords: intergalactic medium; h i line emission
The Sunward Electron Deficit: A Telltale Sign of the Sun's Electric Potential

As the Parker Solar Probe explores new regions of the inner heliosphere, it travels ever deeper into the electric potential of the Sun. In the near-Sun environment, a new feature of the electron distribution emerges, in the form of a deficit in the sunward suprathermal population. The lower boundary of this deficit forms a cutoff in phase space, at an energy determined by the electric potential drop between the observation point and the outer heliosphere. We explore the characteristics of the sunward deficit and the associated cutoff, as well as the properties of the plasma in which we observe them. The deficit occurs in ~60%-80% of electron observations within ~0.2 au, and even more frequently in plasma with low β, low collisional age, and a more anisotropic electron core population. At greater distances, the deficit rapidly disappears, as the suprathermal halo grows, with these two trends likely related. The cutoff energy varies linearly with the local electron core temperature, confirming a direct relationship to the ambipolar electric potential. Meanwhile, the cutoff width varies with β and collisional age, suggesting that energy diffusion plays a role in erasing the deficit. The nearly ubiquitous occurrence of the sunward deficit in the inner heliosphere suggests that we may need to reconsider the functional forms commonly used to represent electron distributions in this environment.

Keywords: solar wind; the sun
Galaxy Stellar Mass Functions from z 10 to z 6 using the Deepest Spitzer/Infrared Array Camera Data: No Significant Evolution in the Stellar-to-halo Mass Ratio of Galaxies in the First Gigayear of Cosmic Time

We present new stellar mass functions at z ~ 6, z ~ 7, z ~ 8, z ~ 9 and, for the first time, z ~ 10, constructed from ~800 Lyman-break galaxies previously identified over the eXtreme Deep Field and Hubble Ultra-Deep Field parallel fields and the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. Our study is distinctive due to (1) the much deeper (~200 hr) wide-area Spitzer/Infrared Array Camera (IRAC) imaging at 3.6 μm and 4.5 μm from the Great Observatories Origins Deep Survey Re-ionization Era Wide-area Treasury from Spitzer program (GREATS) and (2) consideration of z ~ 6-10 sources over a 3× larger area than those of previous Hubble Space Telescope+Spitzer studies. The Spitzer/IRAC data enable ≥2σ rest-frame optical detections for an unprecedented 50% of galaxies down to a stellar mass limit of $\sim {10}^{8}{{ \mathcal M }}_{\odot }$ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in the characteristic mass ${{ \mathcal M }}^{* }$ and normalization factor φ* between z ~ 6 and z ~ 8. The stellar mass density (SMD) increases by ~1000× in the ~500 Myr between z ~ 10 and z ~ 6, with indications of a steeper evolution between z ~ 10 and z ~ 8, similar to the previously reported trend of the star formation rate density. Strikingly, abundance matching to the Bolshoi-Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between z ~ 10 and z ~ 4. Our results show that the stellar-to-halo mass ratios, a proxy for the star formation efficiency, do not change significantly over the huge stellar mass buildup occurred from z ~ 10 to z ~ 6, indicating that the assembly of stellar mass closely mirrors the buildup in halo mass in the first ~1 Gyr of cosmic history. The James Webb Space Telescope is poised to extend these results into the "first galaxy" epoch at z ≳ 10.

Keywords: lyman-break galaxies; stellar mass functions
Deep Optical Emission-line Images of Nine Known and Three New Galactic Supernova Remnants

Deep optical emission-line images are presented for nine known plus three new Galactic supernova remnants (SNRs), all but one having at least one angular dimension >1°. Wide-field images taken in Hα and [O III] λ5007 reveal many new and surprising remnant structures including large remnant shock extensions and "breakout" features not seen in published optical or radio data. These images represent over 12,000 individual images totaling more than 1000 hr of exposure time taken over the last 2 yr mainly using small aperture telescopes, which detected fainter nebular line emissions than published emission-line images. During the course of this imaging program, we discovered three new SNRs, namely G107.5-5.1 (the Nereides Nebula), G209.9-8.2, and G210.5+1.3, two of which have diameters >1.°5. In addition to offering greater structural detail on the nine already known SNRs, a key finding of this study is the importance of [O III] emission-line imaging for mapping the complete shock emissions of Galactic SNRs.

Keywords: interstellar medium; supernova remnants
Deconvolving Pulsar Signals with Cyclic Spectroscopy: A Systematic Evaluation

Radio pulsar signals are significantly perturbed by their propagation through the ionized interstellar medium. In addition to the frequency-dependent pulse times of arrival due to dispersion, pulse shapes are also distorted and shifted, having been scattered by the inhomogeneous interstellar plasma, affecting pulse arrival times. Understanding the degree to which scattering affects pulsar timing is important for gravitational-wave detection with pulsar timing arrays (PTAs), which depend on the reliability of pulsars as stable clocks with an uncertainty of ∼100 ns or less over ∼10 yr or more. Scattering can be described as a convolution of the intrinsic pulse shape with an impulse response function representing the effects of multipath propagation. In previous studies, the technique of cyclic spectroscopy has been applied to pulsar signals to deconvolve the effects of scattering from the original emitted signals, increasing the overall timing precision. We present an analysis of simulated data to test the quality of deconvolution using cyclic spectroscopy over a range of parameters characterizing interstellar scattering and pulsar signal-to-noise ratio (S/N). We show that cyclic spectroscopy is most effective for high S/N and/or highly scattered pulsars. We conclude that cyclic spectroscopy could play an important role in scattering correction to distant populations of highly scattered pulsars not currently included in PTAs. For future telescopes and for current instruments such as the Green Bank Telescope upgraded with the ultrawide bandwidth receiver, cyclic spectroscopy could potentially double the number of PTA-quality pulsars.

Keywords: millisecond pulsars; pulsars; radio pulsars; interstellar medium; interstellar plasma; radio astronomy; gravitational waves
Interplanetary Signatures during the 1972 Early August Solar Storms

In 1972, early August, a series of interplanetary shocks were observed in the heliosphere from 0.8 to 2.2 au. These shocks were attributed to a series of brilliant flares and plasma clouds since at that time coronal mass ejections (CMEs) and their interplanetary counterparts (ICMEs) were unknown to the scientific community. This paper aims to reinterpret the interplanetary data in light of the current understanding about interplanetary transients and to track the evolution of the ICMEs, taking advantage of the alignment of Pioneers 9 and 10 spacecraft. For this purpose, we reanalyze in situ data from these two Pioneers and also from Heos, Prognoz 1 and 2, and Explorer 41 spacecraft searching for ICMEs and high-speed streams. Then we assemble the interplanetary transients and solar activity and analyze the propagation of the ejections through the heliosphere. The evolution of four ICMEs and a high-speed stream from a low-latitude coronal hole is followed using the multipoint in situ observations. The first three ICMEs show clear signatures of ICME-ICME interaction in the interplanetary medium, suggesting the first observations of an ICME which developed into an ICME-in-the-sheath. For a non-perturbed ICME event, we obtain the evolution parameter, ζ, related to the local expansion of ICMEs, getting similar values for Pioneer 9 (ζ = 0.80) and Pioneer 10 (ζ = 0.78). These results support previous findings of ζ being independent of the heliocentric distance and the magnetic field strength decreasing as r -2ζ .

Keywords: solar activity; interplanetary shocks; solar flares; solar coronal mass ejections
JWST Constraints on the UV Luminosity Density at Cosmic Dawn: Implications for 21 cm Cosmology

An unprecedented array of new observational capabilities are starting to yield key constraints on models of the epoch of first light in the Universe. In this Letter we discuss the implications of the UV radiation background at cosmic dawn inferred by recent JWST observations for radio experiments aimed at detecting the redshifted 21 cm hyperfine transition of diffuse neutral hydrogen. Under the basic assumption that the 21 cm signal is activated by the Lyα photon field produced by metal-poor stellar systems, we show that a detection at the low frequencies of the EDGES and SARAS3 experiments may be expected from a simple extrapolation of the declining UV luminosity density inferred at z ≲ 14 from JWST early galaxy data. Accounting for an early radiation excess above the cosmic microwave background suggests a shallower or flat evolution to simultaneously reproduce low- and high-z current UV luminosity density constraints, which cannot be entirely ruled out, given the large uncertainties from cosmic variance and the faint-end slope of the galaxy luminosity function at cosmic dawn. Our findings raise the intriguing possibility that a high star formation efficiency at early times may trigger the onset of intense Lyα emission at redshift z ≲ 20 and produce a cosmic 21 cm absorption signal 200 Myr after the Big Bang.

Keywords: cosmology; james webb space telescope; radio interferometers; h i line emission; early universe
A UFO Seen Edge-on? Resolving Ultrafast Outflow Emission on 200 pc Scales with Chandra in the Active Nucleus of Mrk 34

We present Chandra ACIS imaging spectroscopy of the nucleus of the Seyfert 2 Galaxy Mrk 34. We identify spatially and spectrally resolved features in the band that includes Fe Kα, Fe XXV, and Fe XXVI. These features suggest high-velocity (≳15,000 km s-1 line-of-sight) material spanning ~0.″5, within ~200 pc of the nucleus. This outflow could have deprojected velocities ~12-28× greater than the [O III]-emitting outflows, and could potentially dominate the kinetic power in the outflow. This emission may point to the origins of the optical and X-ray winds observed at larger radii, and could indicate a link between ultrafast outflows and AGN feedback on ≳kiloparsec scales.

Keywords: agn host galaxies; x-ray active galactic nuclei; seyfert galaxies