adsabs/SciX_UAT_keywords huggingface dataset:
Improving Coronal Magnetic Field Models Using Image Optimization

We have reported previously on our development and testing of a new method for using coronal images to improve coronal magnetic field models. In this technique, which we call image-optimization, coronal magnetic field models are extrapolated from synoptic photospheric magnetograms. The resulting models are then compared to morphological constraints derived from images of the solar corona, and the photospheric magnetograms are perturbed iteratively via an optimization algorithm to achieve optimal agreement with the image-based constraints. Here we present results from the first application of this technique using Mauna Loa Solar Observatory K-Coronagraph images and Global Oscillation Network Group synoptic magnetograms to create optimized models for two time periods, 2014 November 16-29 and 2016 May 16-29. We find that for both time periods the optimization algorithm converges well and results in better agreement between the model and the images, relatively small changes to the synoptic magnetogram, and an overall increase in the amount of open magnetic flux.

Keywords: solar corona; solar magnetic fields
GW190425: Observation of a Compact Binary Coalescence with Total Mass ∼ 3.4 M⊙

On 2019 April 25, the LIGO Livingston detector observed a compact binary coalescence with signal-to-noise ratio 12.9. The Virgo detector was also taking data that did not contribute to detection due to a low signal-to-noise ratio, but were used for subsequent parameter estimation. The 90% credible intervals for the component masses range from 1.12 to 2.52 M⊙ (1.46-1.87 M⊙ if we restrict the dimensionless component spin magnitudes to be smaller than 0.05). These mass parameters are consistent with the individual binary components being neutron stars. However, both the source-frame chirp mass 1.44-0.02+0.02 M⊙ and the total mass 3.4-0.1+0.3 M⊙ of this system are significantly larger than those of any other known binary neutron star (BNS) system. The possibility that one or both binary components of the system are black holes cannot be ruled out from gravitational-wave data. We discuss possible origins of the system based on its inconsistency with the known Galactic BNS population. Under the assumption that the signal was produced by a BNS coalescence, the local rate of neutron star mergers is updated to 250-2810 Gpc-3yr-1.

Keywords: neutron stars; gravitational waves
The Destruction and Recreation of the X-Ray Corona in a Changing-look Active Galactic Nucleus

We present the drastic transformation of the X-ray properties of the active galactic nucleus (AGN) 1ES 1927+654, following a changing-look event. After the optical/ultraviolet outburst the power-law component, produced in the X-ray corona, disappeared, and the spectrum of 1ES 1927+65 instead became dominated by a blackbody component (kT ∼ 80-120 eV). This implies that the X-ray corona, ubiquitously found in AGNs, was destroyed in the event. Our dense ∼450 days long X-ray monitoring shows that the source is extremely variable in the X-ray band. On long timescales the source varies up to ∼4 dex in ∼100 days, while on short timescales up to ∼2 dex in ∼8 hr. The luminosity of the source is found to first show a strong dip down to $\sim {10}^{40}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , and then a constant increase in luminosity to levels exceeding the pre-outburst level ≳300 days after the optical event detection, rising up asymptotically to $\sim 2\times {10}^{44}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ . As the X-ray luminosity of the source increases, the X-ray corona is recreated, and a very steep power-law component (Γ ≃ 3) reappears, and dominates the emission for 0.3-2 keV luminosities $\gtrsim {10}^{43.7}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , ∼300 days after the beginning of the event. We discuss possible origins of this event, and speculate that our observations could be explained by the interaction between the accretion flow and debris from a tidally disrupted star. Our results show that changing-look events can be associated with dramatic and rapid transformations of the innermost regions of accreting supermassive black holes.

Keywords: active galactic nuclei; active galaxies; high energy astrophysics; x-ray active galactic nuclei; quasars; x-ray quasars; supermassive black holes
A Double-decker Filament Formation Driven by Sunspot Rotation and Magnetic Reconnection

In this paper, through analyzing data from the Solar Dynamics Observatory (SDO) and the Global Oscillation Network Group (GONG), we present a study on the formation of a double-decker filament in NOAA Active Region 12665 from 2017 July 8 to 14. We find that magnetic reconnection occurs between two smaller filaments to form a longer filament. According to the evolution of the leading sunspot, it is obvious that the sunspot experiences a continuous rotation around its umbra. During the period from 03:00 UT on July 11 to 10:00 UT on July 14, the average speed of sunspot rotation is about 3.°7 hr-1. The continuous rotation of sunspot stretches the filament and results in the formation of a reversed S-shaped filament. Due to the motion of the magnetic field and internal magnetic reconnection, the filament splits into two branches and forms a double-decker filament structure. In the process of filament separation, internal magnetic reconnection can also accelerate the filament separation. Nonlinear force-free field extrapolation indicates that there are two magnetic flux ropes, which are consistent with the observed results. Eventually, the upper filament erupts and produces an M-class flare and a halo coronal mass ejection.

Keywords: solar magnetic reconnection; solar filaments
Extreme Variability Quasars in Their Various States. II. Spectral Variation Revealed with Multiepoch Spectra

We previously built a sample of 14,012 extremely variable quasars (EVQs) based on Sloan Digital Sky Survey (SDSS) and Pan-STARRS1 photometric observations. In this work we present the spectral fitting to their SDSS spectra and study the spectral variation in 1259 EVQs with multiepoch SDSS spectra (after prudently excluding spectra with potentially unreliable spectroscopic photometry). We find a clear "bluer-when-brighter" trend in EVQs, consistent with previous findings of normal quasars and active galactic nuclei. We detect significant intrinsic Baldwin effect (iBeff, i.e., smaller line equivalent width at higher continuum flux in individual active galactic nuclei) in the broad Mg II and C IV lines of EVQs. Meanwhile, no systematical iBeff is found for the broad Hβ line, which could be attributed to strong host contamination at longer wavelengths. Remarkably, by comparing the iBeff slope of EVQs with archived changing-look quasars, we show that the changing-look quasars identified in the literature are most likely a biased (due to its definition) subpopulation of EVQs, rather than a distinct population of quasars. We also found no significant broad line breathing of Hβ, Mg II, or C IV, suggesting the broad line breathing in quasars may disappear at longer timescales (∼3000 days).

Keywords: quasars; time domain astronomy; active galactic nuclei; black hole physics
Dynamical Model of the Milky Way Using APOGEE and Gaia Data

We construct a dynamical model of the Milky Way disk from a data set that combines Gaia EDR3 and APOGEE data throughout galactocentric radii in the range 5.0 kpc ≤ R ≤ 19.5 kpc. We make use of the spherically aligned Jeans anisotropic method to model the stellar velocities and their velocity dispersions. Building upon our previous work, our model is now fitted to kinematic maps that have been extended to larger galactocentric radii due to the expansion of our data set, probing the outer regions of the Galactic disk. Our best-fitting dynamical model suggests a logarithmic density slope of αDM = -1.602 ± 0.079syst for the dark matter halo and a dark matter density of ρDM(R⊙) = (8.92 ± 0.56syst) × 10-3 M⊙ pc-3 (0.339 ± 0.022syst GeV cm3). We estimate a circular velocity at the solar radius of vcirc = (234.7 ± 1.7syst) km s-1 with a decline toward larger radii. The total mass density is ρtot(R⊙) = (0.0672 ± 0.0015syst) M⊙ pc-3 with a slope of αtot = -2.367 ± 0.047syst for 5 kpc ≤ R ≤ 19.5 kpc, and the total surface density is Σ(R⊙, ∣z∣ ≤ 1.1 kpc) = (55.5 ± 1.7syst) M⊙ pc-2. While the statistical errors are small, the error budget of the derived quantities is dominated by the three to seven times larger systematic uncertainties. These values are consistent with our previous determination, but the systematic uncertainties are reduced due to the extended data set covering a larger spatial extent of the Milky Way disk. Furthermore, we test the influence of nonaxisymmetric features on our resulting model and analyze how a flaring disk model would change our findings.

Keywords: milky way dynamics; milky way disk
Global Energetics of Solar Flares. X. Petschek Reconnection Rate and Alfvén Mach Number of Magnetic Reconnection Outflows

We investigate physical scaling laws for magnetic energy dissipation in solar flares, in the framework of the Sweet-Parker model and the Petschek model. We find that the total dissipated magnetic energy Ediss in a flare depends on the mean magnetic field component Bf associated with the free energy Ef, the length scale L of the magnetic area, the hydrostatic density scale height λ of the solar corona, the Alfvén Mach number MA = V1/VA (the ratio of the inflow speed V1 to the Alfvénic outflow speed VA), and the flare duration τf, I.e., ${E}_{\mathrm{diss}}=(1/4\pi ){B}_{f}^{2}\ L\ \lambda \ {V}_{{\rm{A}}}\ {M}_{{\rm{A}}}\ {\tau }_{f}$ , where the Alfvén speed depends on the nonpotential field strength Bnp and the mean electron density ne in the reconnection outflow. Using MDI/Solar Dynamics Observatory (SDO) and AIA/SDO observations and 3D magnetic field solutions obtained with the vertical-current approximation non-linear force-free field code we measure all physical parameters necessary to test scaling laws, which represents a new method to measure Alfvén Mach numbers MA, the reconnection rate, and the total free energy dissipated in solar flares.

Keywords: solar coronal heating; solar coronal loops; solar flares; solar magnetic reconnection; solar magnetic fields
The California Legacy Survey. III. On the Shoulders of (Some) Giants: The Relationship between Inner Small Planets and Outer Massive Planets

We use a high-precision radial velocity survey of FGKM stars to study the conditional occurrence of two classes of planets: close-in small planets (0.023-1 au, 2-30 M ⊕) and distant giant planets (0.23-10 au, 30-6000 M ⊕). We find that ${41}_{-13}^{+15} \% $ of systems with a close-in, small planet also host an outer giant, compared to ${17.6}_{-1.9}^{+2.4} \% $ for stars irrespective of small planet presence. This implies that small planet hosts may be enhanced in outer giant occurrences compared to all stars with 1.7σ significance. Conversely, we estimate that ${42}_{-13}^{+17} \% $ of cold giant hosts also host an inner small planet, compared to ${27.6}_{-4.8}^{+5.8} \% $ of stars irrespective of cold giant presence. We also find that more massive and close-in giant planets are not associated with small inner planets. Specifically, our sample indicates that small planets are less likely to have outer giant companions more massive than approximately 120 M ⊕ and within 0.3-3 au, than to have less massive or more distant giant companions, with ~2.2σ confidence. This implies that massive gas giants within 0.3-3 au may suppress inner small planet formation. Additionally, we compare the host-star metallicity distributions for systems with only small planets and those with both small planets and cold giants. In agreement with previous studies, we find that stars in our survey that only host small planets have a metallicity distribution that is consistent with the broader solar-metallicity-median sample, while stars that host both small planets and gas giants are distinctly metal rich with ~2.3σ confidence.

Keywords: exoplanets
Morphology of TeV Gamma-Ray Emission from the Kiloparsec-scale Jets in Radio Galaxies

TeV γ rays are observed from a few nearby radio galaxies whose jets are viewed at relatively large angles toward the observer. This emission can be produced in kiloparsec-scale jets whose Lorentz factors are decelerated from values of the order of several at parsec-scale distances. We consider in detail the model in which TeV γ-ray emission is produced by the relativistic electrons in kiloparsec-scale jets that comptonize strongly beamed radiation from inner (parsec-scale) jets. As an example, we study the morphology of the TeV γ-ray emission from the decelerated kiloparsec-scale jet in the nearby radio galaxy Cen A. We show that TeV γ-ray emission can extend throughout kiloparsec-scale distances, as it is relatively smoothly distributed along jets for some parameters of the model we consider. Investigation of the morphological structure of such specific γ-ray emission by the future Cerenkov Telescope Array should provide important constraints on the content and dynamics of the kiloparsec-scale jet in Cen A.

Keywords: gamma-ray sources; active galactic nuclei
Energetic Neutral Atom Fluxes from the Heliosheath: Constraints from in situ Measurements and Models

Voyager 2 observations throughout the heliosheath from the termination shock to the heliopause are used to normalize and constrain model pickup ion (PUI) fluxes. Integrating normalized PUI fluxes along the Voyager 2 trajectory through the heliosheath, and combining these integral fluxes with the energy-dependent charge-exchange cross section and the neutral hydrogen density, produces semi-empirical estimates of the energetic neutral atom (ENA) fluxes from the heliosheath. These estimated ENA fluxes are compared with observed ENA fluxes from the Interstellar Boundary Explorer (IBEX) to determine what percentage of the observed fluxes at each IBEX energy are from the heliosheath. These percentages are a maximum of ~10% for most energies and depend strongly on termination shock properties, plasma density, bulk plasma flow characteristics, the shape of the heliopause, and turbulent energy diffusion in the heliosheath.

Keywords: astrosphere interstellar medium interactions; solar wind; solar wind termination; interstellar medium; pickup ions; space plasmas
A Focused Transport-based Kinetic Fractional Diffusion-advection Equation for Energetic Particle Trapping and Reconnection-related Acceleration by Small-scale Magnetic Flux Ropes in the Solar Wind

Analysis of energetic particle inner heliospheric spacecraft data increasingly suggests the existence of anomalous diffusion phenomena that should be addressed to achieve a better understanding of energetic particle transport and acceleration in the expanding solar wind medium. Related to this is fast-growing observational evidence supporting the long-standing prediction from magnetohydrodynamic (MHD) theory and simulations of the presence of an inner heliospheric, dominant quasi-two-dimensional MHD turbulence component that contains coherent contracting and merging (reconnecting) small-scale magnetic flux rope (SMFR) structures. This suggests that energetic particle trapping in SMFRs should play a role in anomalous diffusion in the solar wind that warrants further investigation. However, progress in studying such anomalous energetic particle transport phenomena in the solar wind is hampered by the lack of a fundamental derivation of a general fractional kinetic transport equation linking macroscopic energetic particle fractional transport to the microscopic physics of energetic particle interaction with SMFR structures. Here, we outline details of how one can derive a closed ensemble-averaged focused transport equation in the form of a general kinetic fractional diffusion-advection equation from first principles following the nonlinear Eulerian correlation function closure approach of Sanchez et al. With this equation one can model the anomalous diffusion of energetic particles in ordinary, momentum, and pitch-angle space in response to particle trapping in numerous SMFRs advected with the solar wind flow.

Keywords: interplanetary particle acceleration; solar wind; solar magnetic reconnection
SDSS-IV MaNGA: Kinematic Asymmetry as an Indicator of Galaxy Interaction in Paired Galaxies

The interaction between galaxies is believed to be the main origin of the peculiarities of galaxies, which disturbs not only the morphology but also their kinematics. These disturbed and asymmetric features are the indicators of galaxy interaction. We study the velocity field of the ionized gas of the paired galaxies in the SDSS-IV MaNGA IFU survey. Using the kinemetry package, we fit the velocity field of the ionized gas to quantify the degree of kinematic asymmetry. We find that the star formation rate (SFR) of the paired galaxies with high kinematic asymmetry is significantly enhanced even when the projected separation between the pair members is quite large (dp ∼ 100 h-1 kpc. On the contrary, no significant SFR enhancement is found for the paired galaxies with low kinematic asymmetry even when their projected separation is small (dp < 30 h-1 kpc). Moreover, we also find that the fraction of galaxies with high kinematic asymmetry is much higher in close pairs (dp < 30 h-1 kpc) than those with larger d<SUB<p, which explains well the early statistical finding of the significant SFR enhancement in close pairs. Our new findings illustrate that the kinematic asymmetry is an excellent indicator of galaxy-galaxy interaction strength, which helps us better understand the merging stage of the observed galaxy pairs.

Keywords: galaxy pairs; galaxy mergers; interacting galaxies; galaxy kinematics; star formation
MAVEN Observations of the Interloop Magnetic Reconnections at Mars

Magnetic reconnection between neighboring magnetic field loops, the so-called interloop reconnection, is a common process to drive flares in the solar atmosphere. However, there is no direct evidence that a similar but less explosive process can take place on planets. The strong crustal fields on Mars generate plenty of magnetic loops in the near-Mars regions, providing a unique environment to research the interloop reconnection on a planet. Here, we report magnetic reconnection events between crustal field loops in the Martian ionosphere observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) for the first time. During the current layer crossing, MAVEN recorded the characteristic signals of collisionless magnetic reconnection, including the Hall magnetic field, Alfvénic outflow, and electron energization. This finding implies that the interloop reconnection in the Martian ionosphere could contribute to the localized energy deposition and particle energization, which provides the seed source for aurora in the Martian atmosphere.

Keywords: mars; magnetic fields; plasma physics
Morphological-based Classifications of Radio Galaxies Using Supervised Machine-learning Methods Associated with Image Moments

With the advent of new high-resolution instruments for detecting and studying radio galaxies with different morphologies, the need for the use of automatic classification methods is undeniable. Here, we focused on the morphological-based classification of radio galaxies known as Fanaroff-Riley (FR) type I and type II via supervised machine-learning approaches. Galaxy images with a resolution of 5″ at 1.4 GHz provided by the Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey are employed. The radial Zernike polynomials are exploited to extract image moments. Then, the rotation, translation, and scale-invariant moments of images are used to form a training set (65% of the radio galaxy sample) and a test set (the remaining 35%). The classes of the test set are determined by two classifiers: a support vector machine and a twin support vector machine (TWSVM). In addition the genetic algorithm is employed to optimize the length of moment series and to find the optimum values of the parameters of the classifiers. The labels of outputs are compared to identify the best performance classifier. To do this the confidence level of classifications is estimated by four different metrics: precision, recall, F1 score, and accuracy. All tests show that implementing TWSVM with the radial basis function as a kernel achieves a confidence level of more than 95% in grouping galaxies.

Keywords: radio galaxies; support vector machine; classification; catalogs
Fossil Signatures of Main-sequence Convective Core Overshoot Estimated through Asteroseismic Analyses

Some physical processes that occur during a star's main-sequence evolution also affect its post-main-sequence evolution. It is well known that stars with masses above approximately 1.1 M ⊙ have well-mixed convective cores on the main sequence; however, the structure of the star in the neighborhood of the convective core regions is currently underconstrained. We use asteroseismology to study the properties of the stellar core, in particular convective boundary mixing through convective overshoot, in such intermediate-mass stars. These core regions are poorly constrained by the acoustic (p) mode oscillations observed for cool main-sequence stars. Consequently, we seek fossil signatures of main-sequence core properties during the subgiant and early first-ascent red giant phases of evolution. During these stages of stellar evolution, modes of mixed character that sample the deep interior can be observed. These modes sample the parts of the stars that are affected by the main-sequence structure of these regions. We model the global and near-core properties of 62 subgiant and early first-ascent red giant branch stars observed by the Kepler, K2, and TESS space missions. We find that the effective overshoot parameter, α ov,eff, increases from M = 1.0 M ⊙ to M = 1.2 M ⊙ before flattening out, although we note that the relationship between α ov,eff and mass will depend on the incorporated modeling choices of internal physics and nuclear reaction network. We also situate these results within existing studies of main-sequence convective core boundaries.

Keywords: asteroseismology; stellar physics; stellar evolution; stellar convective zones; subgiant stars
Virial Black Hole Masses for Active Galactic Nuclei behind the Magellanic Clouds

We use the spectroscopic data collected by the Magellanic Quasars Survey (MQS) and the photometric V- and I-band data from the Optical Gravitational Lensing Experiment (OGLE) to measure the physical parameters for active galactic nuclei (AGNs) located behind the Magellanic Clouds. The flux-uncalibrated MQS spectra were obtained with the 4 m Anglo-Australian Telescope and the AAOmega spectroscope (R = 1300) in a typical ∼1.5 hr visit. They span a spectral range of 3700–8500 Å and have signal-to-noise ratios in a range of 3–300. We report the discovery and observational properties of 161 AGNs in this footprint, which expands the total number of spectroscopically confirmed AGNs by MQS to 919. After the conversion of the OGLE mean magnitudes to the monochromatic luminosities at 5100, 3000, and 1350 Å, we were able to reliably measure the black hole masses for 165 out of 919 AGNs. The remaining physical parameters we provide are the bolometric luminosities and the Eddington ratios. A fraction of these AGNs have been observed by the OGLE survey since 1997 (all of them since 2001), enabling studies of correlations between the variability and physical parameters of these AGNs.

Keywords: active galactic nuclei; supermassive black holes; quasars