adsabs/SciX_UAT_keywords huggingface dataset:
A Large Jet Narrow-line Seyfert 1 Galaxy: Observations from Parsec to 100 kpc Scales

We present new 1.5–8.5 GHz Very Long Baseline Array (VLBA) observations and 0.32–1.26 GHz Giant Meterwave Radio Telescope (GMRT) observations of J0354‑1340, which is the only known radio-quiet (RQ) or radio-intermediate (RI) narrow-line Seyfert 1 galaxy with a 100 kpc, two-sided radio jet. A parsec-scale, one-sided jet in the southeastern direction from the core emission is found in the VLBA observations, while the kiloparsec-scale jet observed with the Karl G. Jansky Very Large Array (VLA) and GMRT is in the south–north direction. Core spectra on parsec and kiloparsec scales are presented in combination with archival VLA Sky Survey observations at 3.0 GHz and VLA C-configuration observations at 5.5 GHz. The parsec-scale emission dominates the kiloparsec-scale emission above ∼5 GHz, and the spectrum is inverted due to synchrotron self-absorption. This indicates a compact synchrotron source with a size of ∼0.04 pc, which is associated with either the jet base or the corona. A subkiloparsec-scale jet, which is unresolved on scales of ∼3″, probably dominates the emission below ∼5 GHz. Future radio observations can explore the jet structure between the parsec and 100 kpc scales, the origin of their direction mismatch, and the parsec-scale jet proper motion. It remains to be explored how common such large-scale jets are in RQ or RI active galactic nuclei.

Keywords: active galactic nuclei; seyfert galaxies; radio continuum emission; radio jets; radio lobes
Two-dimensional Inflow-Outflow Solution of Supercritical Accretion Flow

We present the two-dimensional inflow-outflow solutions of radiation hydrodynamic equations of supercritical accretion flows. Compared with prior studies, we include all components of the viscous stress tensor. We assume steady-state flow and use self-similar solutions in the radial direction to solve the equations in the r-θ domain of spherical coordinates. The set of differential equations have been integrated from the rotation axis to the equatorial plane. We find that the self-similarity assumption requires that the radial profile of density is described by ρ(r) ∝ r -0.5. Correspondingly, the radial profile of the mass inflow rate decreases with decreasing radius as {\dot{M}}in}\propto r. An inflow-outflow structure has been found in our solution. Inflow exists in the region θ > 65°, while above that the flow moves outward and outflow could launch. The driving forces of the outflow are analyzed and it is found that the radiation force is dominant and pushes the gas particles outward with poloidal velocity ∼0.25c. The properties of the outflow are also studied. The results show that the mass flux-weighted angular momentum of the inflow is lower than that of the outflow, thus the angular momentum of the flow can be transported by the outflow. We also analyze the convective stability of the supercritical disk and find that in the absence of a magnetic field, the flow is convectively unstable. Our analytical results are fully consistent with the previous numerical simulations of supercritical accretion flow.

Keywords: high energy astrophysics; active galactic nuclei; black hole physics; black holes; seyfert galaxies
Radiation Magnetohydrodynamic Simulations of Sub-Eddington Accretion Flows in AGNs: Origin of Soft X-Ray Excess and Rapid Time Variabilities

We investigate the origin of the soft X-ray excess component in Seyfert galaxies observed when their luminosity exceeds 0.1% of the Eddington luminosity ( ${L}_{\mathrm{Edd}}$ ). The evolution of a dense blob in radiatively inefficient accretion flow (RIAF) is simulated by applying a radiation magnetohydrodynamic code, CANS+R. When the accretion rate onto a ${10}^{7}\,{M}_{\odot }$ black hole exceeds 10% of the Eddington accretion rate ( ${\dot{M}}_{\mathrm{Edd}}={L}_{\mathrm{Edd}}/{c}^{2}$ , where c is the speed of light), the dense blob shrinks vertically because of radiative cooling and forms a Thomson thick, relatively cool (∼107-8 K) region. The cool region coexists with the optically thin, hot ( $T\sim {10}^{11}\,{\rm{K}}$ ) RIAF near the black hole. The cool disk is responsible for the soft X-ray emission, while hard X-rays are emitted from the hot inner accretion flow. Such a hybrid structure of hot and cool accretion flows is consistent with the observations of both hard and soft X-ray emissions from "changing-look" active galactic nuclei (CLAGNs). Furthermore, we find that quasi-periodic oscillations (QPOs) are excited in the soft X-ray-emitting region. These oscillations can be the origin of rapid X-ray time variabilities observed in CLAGNs.

Keywords: galaxy accretion disks; active galactic nuclei; radiative magnetohydrodynamics
On the Nature of the Photospheric Horizontal Magnetic Field Increase in Major Solar Flares

The rapid increase of the horizontal magnetic field (B h ) around the flaring polarity inversion line is the most prominent photospheric field change during flares. It is considered to be caused by the contraction of flare loops, the details behind which is still not fully understood. Here we investigate the B h increase in 35 major flares using HMI high-cadence vector magnetograms. We find that the B h increase is always accompanied by the increase of field inclination. It usually initiates near the flare ribbons, showing a step-like change in between the ribbons. In particular, its evolution in the early flare phase shows a close spatiotemporal correlation to flare ribbons. We further find that the B h increase tends to have similar intensity in confined and eruptive flares but a larger spatial extent in eruptive flares in a statistical sense. Its intensity and timescale have inverse and positive correlations to the initial ribbon separations, respectively. The results altogether are well consistent with a recent proposed scenario that suggests that the reconnection-driven contraction of flare loops enhances the photospheric B h according to the ideal induction equation, providing statistical evidence of the reconnection-driven origin for the B h increase for the first time.

Keywords: solar flares; solar activity; solar magnetic fields
Determining the Nanoflare Heating Frequency of an X-Ray Bright Point Observed by MaGIXS

Nanoflares are thought to be one of the prime candidates that can heat the solar corona to its multimillion kelvin temperature. Individual nanoflares are difficult to detect with the present generation of instruments, but their presence can be inferred by comparing simulated nanoflare-heated plasma emissions with the observed emission. Using HYDRAD coronal loop simulations, we model the emission from an X-ray bright point (XBP) observed by the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS), along with the nearest available observations from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) and the X-Ray Telescope (XRT) on board the Hinode observatory. The length and magnetic field strength of the coronal loops are derived from the linear force-free extrapolation of the observed photospheric magnetogram by the Helioseismic and Magnetic Imager on board SDO. Each loop is assumed to be heated by random nanoflares, whose magnitude and frequency are determined by the loop length and magnetic field strength. The simulation results are then compared and matched against the measured intensity from AIA, XRT, and MaGIXS. Our model results indicate the observed emission from the XBP under study could be well matched by a distribution of nanoflares with average delay times 1500–3000 s. Further, we demonstrate the high sensitivity of MaGIXS and XRT for diagnosing the heating frequency using this method, while AIA passbands are found to be the least sensitive.

Keywords: solar coronal heating; solar coronal loops; solar x-ray emission; x-ray bright point
Revisiting Newly Large Magellanic Cloud Age-gap Star Clusters

Recently, a noticeable number of new star clusters was identified in the outskirts of the Large Magellanic Cloud (LMC) populating the so-called star-cluster age gap, a space of time (∼4-12 Gyr) where the only known star cluster is up-to-date ESO 121-SC 03. We used Survey of the Magellanic Stellar History DR2 data sets, as well as those employed to identify these star-cluster candidates, to produce relatively deep color-magnitude diagrams (CMDs) of 17 out of 20 discovered age-gap star clusters with the aim of investigating them in detail. Our analysis relies on a thorough CMD cleaning procedure of the field-star contamination, which presents variations in its stellar density and astrophysical properties, such as luminosity and effective temperature, around the star-cluster fields. We built star-cluster CMDs from stars with membership probabilities assigned from the cleaning procedure. These CMDs and their respective spatial distribution maps favor the existence of LMC star field density fluctuations rather than age-gap star clusters, although a definitive assessment on them will be possible from further deeper photometry.

Keywords: astronomical methods; large magellanic cloud; star clusters
NuSTAR Hard X-Ray Monitoring of Gravitationally Lensed Quasar RX J1131-1231

The X-ray emission from active galactic nuclei is believed to come from a combination of inverse Compton scattering of photons from the accretion disk and reprocessing of the direct X-ray emission by reflection. We present hard (10-80 keV) and soft (0.5-8 keV) X-ray monitoring of a gravitationally lensed quasar RX J1131-1231 (hereafter RXJ1131) with NuSTAR, Swift, and XMM-Newton between 2016 June 10 and 2020 November 30. Comparing the amplitude of quasar microlensing variability at the hard and soft bands allows a size comparison, where larger sources lead to smaller microlensing variability. During the period between 2018 June 6 and 2020 November 30, where both the hard and soft light curves are available, the hard and soft bands varied by factors of 3.7 and 5.5, respectively, with rms variability of 0.40 ± 0.05 and 0.57 ± 0.02. Both the variability amplitude and rms are moderately smaller for the hard X-ray emission, indicating that the hard X-ray emission is moderately larger than the soft X-ray emission region. We found the reflection fraction from seven joint hard and soft X-ray monitoring epochs is effectively consistent with a constant with low significance variability. After decomposing the total X-ray flux into direct and reprocessed components, we find a smaller variability amplitude for the reprocessed flux compared to the direct emission. The power-law cutoff energy is constrained at ${96}_{-24}^{+47}$ keV, which positions the system in the allowable parameter space due to the pair production limit.

Keywords: gravitational lensing; x-ray quasars; quasar microlensing; supermassive black holes
Contemporaneous Multiwavelength and Precovery Observations of the Active Centaur P/2019 LD2 (ATLAS)

The Gateway Centaur and Jupiter co-orbital P/2019 LD2 (ATLAS) provides the first opportunity to observe the migration of a solar system small body from a Centaur orbit to a Jupiter Family Comet (JFC) four decades from now. The Gateway transition region is beyond where water ice can power cometary activity, and coma production there is as poorly understood as in all Centaurs. We present contemporaneous multiwavelength observations of LD2 from 2020 July 2-4: Gemini North visible imaging, NASA IRTF near-infrared spectroscopy, and ARO Submillimeter Telescope millimeter-wavelength spectroscopy. Precovery DECam images limit the nucleus's effective radius to ≤1.2 km and no large outbursts were seen in archival Catalina Sky Survey observations. LD2's coma has $g^{\prime} -r^{\prime} =0.70\pm 0.07$ , $r^{\prime} -i^{\prime} =0.26\pm 0.07$ , a dust-production rate of ∼10-20 kg s-1, and an outflow velocity between v ∼ 0.6-3.3 m s-1. We did not detect CO toward LD2 on 2020 July 2-3, with a 3σ upper limit of Q(CO) < 4.4 × 1027 mol s-1 (⪅ 200 kg s-1). Near-infrared spectra show evidence for water ice at the 1%-10% level depending on grain size. Spatial profiles and archival data are consistent with sustained activity. The evidence supports the hypothesis that LD2 is a typical small Centaur that will become a typical JFC, and thus, it is critical to understanding the transition between these two populations. Finally, we discuss potential strategies for a community-wide, long-baseline monitoring effort.

Keywords: comet nuclei; comets; short period comets; comet volatiles; centaur group; astronomy web services; ccd photometry; spectroscopy
The Quadruple Image Configurations of Asymptotically Circular Gravitational Lenses

The quadruple image configurations of gravitational lenses with vanishing ellipticity are examined. Even though such lenses asymptotically approach circularity, the configurations are stable if the position of the source relative to the vanishing diamond caustic is held constant. The configurations are the solutions of a quartic equation, an "asymptotically circular lens equation," parameterized by a single complex quantity. Several alternative parameterizations are examined. Relative magnifications of the images are derived. When a nonvanishing quadrupole, in the form of an external shear (XS), is added to the singular isothermal sphere (SIS), its configurations emerge naturally as stretched and squeezed versions of the circular configurations. And as the SIS+XS model is a good first approximation for most quadruply lensed quasars, their configurations likewise have only 2 + 1 salient dimensions. The asymptotically circular configurations can easily be adapted to the problem of solar system "occultation flashes."

Keywords: gravitational lensing; strong gravitational lensing; caustic curve; critical curve
VALENTInE: A Concept for a New Frontiers-Class Long-duration In Situ Balloon-based Aerobot Mission to Venus

Described here is a concept for a variable-altitude aerobot mission to Venus developed as part of the 2020 NASA Planetary Science Summer School in collaboration with NASA Jet Propulsion Laboratory. The Venus Air and Land Expedition: a Novel Trailblazer for in situ Exploration (VALENTInE) is a long-duration New Frontiers-class mission to Venus in alignment with the goals recommended by the 2013 Planetary Science Decadal Survey. VALENTInE would have five science objectives: (1) determine the driving force of atmospheric superrotation, (2) determine the source of D/H and noble gas inventory, (3) determine the properties that govern how light is reflected within the lower cloud later, (4) determine whether the tesserae are felsic, and (5) determine whether there is evidence of a recent dynamo preserved in the rock record. The proposed mission concept has a total duration of 15 Earth days and would float at an altitude of 55 km, along with five dips to a lower altitude of 45 km to study Venus's lower atmosphere. The instrument payload allows for measurements of the atmosphere, surface, and interior of Venus and includes six instruments: an atmospheric weather suite, a mass spectrometer, a multispectral imager, a near-infrared spectrometer, light detection and ranging, and a magnetometer. Principle challenges included a limitation caused by battery lifetime and low technology readiness levels for aerobots that can survive the harsh conditions of Venus's atmosphere. This preliminary mission was designed to fit within an assumed New Frontiers 5 (based on inflated New Frontiers 4) cost cap.

Keywords: venus; high altitude balloons; planetary probes; planetary atmospheres
JWST and ALMA Discern the Assembly of Structural and Obscured Components in a High-redshift Starburst Galaxy

We present observations and analysis of the starburst PACS-819 at z = 1.45 (M * = 1010.7 M ⊙), using high-resolution (0.″1; 0.8 kpc) Atacama Large Millimeter/submillimeter Array (ALMA) and multiwavelength JWST images from the COSMOS-Web program. Dissimilar to Hubble Space Telescope (HST) ACS images in the rest-frame UV, the redder NIRCam and MIRI images reveal a smooth central mass concentration and spiral-like features, atypical for such an intense starburst. Through dynamical modeling of the CO (J = 5–4) emission with ALMA, PACS-819 is rotation dominated and thus consistent with having a disk-like nature. However, kinematic anomalies in CO and asymmetric features in the bluer JWST bands (e.g., F150W) support a more disturbed nature likely due to interactions. The JWST imaging further enables us to map the distribution of stellar mass and dust attenuation, thus clarifying the relationships between different structural components not discernible in the previous HST images. The CO (J = 5–4) and far-infrared dust continuum emission are cospatial with a heavily obscured starbursting core (<1 kpc) that is partially surrounded by much less obscured star-forming structures including a prominent arc, possibly a tidally distorted dwarf galaxy, and a massive clump (detected in CO), likely a recently accreted low-mass satellite. With spatially resolved maps, we find a high molecular gas fraction in the central area reaching ∼3 (M gas/M *) and short depletion times (M gas/SFR ∼ 120 Myr, where SFR is star formation rate) across the entire system. These observations provide insights into the complex nature of starbursts in the distant Universe and underscore the wealth of complementary information from high-resolution observations with both ALMA and JWST.

Keywords: star formation; starburst galaxies; high-redshift galaxies; interstellar medium
Global 21 cm Signal Extraction from Foreground and Instrumental Effects. III. Utilizing Drift-scan Time Dependence and Full Stokes Measurements

When using valid foreground and signal models, the uncertainties on extracted signals in global 21 cm signal experiments depend principally on the overlap between signal and foreground models. In this paper, we investigate two strategies for decreasing this overlap: (I) utilizing time dependence by fitting multiple drift-scan spectra simultaneously, and (II) measuring all four Stokes parameters instead of only the total power, Stokes I. Although measuring polarization requires different instruments than are used in most existing experiments, all existing experiments can utilize drift-scan measurements merely by averaging their data differently. In order to evaluate the increase in constraining power from using these two techniques, we define a method for connecting root-mean-square (rms) uncertainties to probabilistic confidence levels. Employing simulations, we find that fitting only one total power spectrum leads to rms uncertainties at the few K level, while fitting multiple time-binned, drift-scan spectra yields uncertainties at the ≲10 mK level. This significant improvement only appears if the spectra are modeled with one set of basis vectors instead of using multiple sets of basis vectors that independently model each spectrum. Assuming that they are simulated accurately, measuring all four Stokes parameters also leads to lower uncertainties. These two strategies can be employed simultaneously, and fitting multiple time bins of all four Stokes parameters yields the most precise measurements of the 21 cm signal, approaching the noise level in the data.

Keywords: reionization; astronomy data analysis; cosmology
How Bar Fraction Depends on Baryon Fraction

We use Galaxy Zoo 2 morphologies (based on SDSS Legacy Imaging) alongside the completed Arecibo Legacy Fast ALFA survey measuring H I to investigate the correlation between bar fraction and an estimate of baryonic mass fraction for a sample of nearby (z < 0.06) disk galaxies (M ⋆ > 109 M ⊙). As expected from theoretical considerations, and as seen in previous work using different samples/morphological classifications, we find clear evidence of an increase in bar fraction, particularly strong bar fraction in galaxies with larger baryonic mass fractions (i.e., heavier discs for their dark matter halo).

Keywords: barred spiral galaxies
Planets Across Space and Time (PAST). IV. The Occurrence and Architecture of Kepler Planetary Systems as a Function of Kinematic Age Revealed by the LAMOST-Gaia-Kepler Sample

One of the fundamental questions in astronomy is how planetary systems form and evolve. Measuring the planetary occurrence and architecture as a function of time directly addresses this question. In the fourth paper of the Planets Across Space and Time series, we investigate the occurrence and architecture of Kepler planetary systems as a function of kinematic age by using the LAMOST-Gaia-Kepler sample. To isolate the age effect, other stellar properties (e.g., metallicity) have been controlled. We find the following results. (1) The fraction of stars with Kepler-like planets (F Kep) is about 50% for all stars; no significant trend is found between F Kep and age. (2) The average planet multiplicity ( ${\bar{N}}_{p}$ ) exhibits a decreasing trend (~2σ significance) with age. It decreases from ${\bar{N}}_{p}$ ~ 3 for stars younger than 1 Gyr to ${\bar{N}}_{p}$ ~ 1.8 for stars of about 8 Gyr. (3) The number of planets per star (η = F Kep× ${\bar{N}}_{p}$ ) also shows a decreasing trend (~2σ-3σ significance). It decreases from η ~ 1.6-1.7 for young stars to η ~ 1.0 for old stars. (4) The mutual orbital inclination of the planets (σ i,k ) increases from $1\buildrel{\circ}\over{.} {2}_{-0.5}^{+1.4}$ to $3\buildrel{\circ}\over{.} {5}_{-2.3}^{+8.1}$ as the stars age from 0.5 to 8 Gyr with a best fit of $\mathrm{log}{\sigma }_{i,k}=0.2+0.4\times \mathrm{log}\tfrac{\mathrm{Age}}{1\mathrm{Gyr}}$ . Interestingly, the solar system also fits such a trend. The fact that F Kep remains relatively constant at approximately ~ 50% across different ages suggests the robustness of planet formation throughout the history of the Galaxy. The age dependence of ${\bar{N}}_{p}$ and σ i,k demonstrates that the planetary architecture is evolving, and planetary systems generally become dynamically hotter with fewer planets as they age.

Keywords: planetary system evolution; exoplanets
Low-energy Measurement of the 96Zr(α,n)99Mo Reaction Cross Section and Its Impact on Weak r-process Nucleosynthesis

Lighter heavy elements beyond iron and up to around silver can form in neutrino-driven ejecta in core-collapse supernovae and neutron star mergers. Slightly neutron-rich conditions favor a weak r-process that follows a path close to stability. Therefore, the beta decays are slow compared to the expansion timescales, and (α,n) reactions become critical to move matter toward heavier nuclei. The rates of these reactions are calculated with the statistical model and their main uncertainty, at energies relevant for the weak r-process, is the α+nucleus optical potential. There are several sets of parameters to calculate the α+nucleus optical potential leading to large deviations for the reaction rates, exceeding even one order of magnitude. Recently the 96Zr(α,n)99Mo reaction has been identified as a key reaction that impacts the production of elements from Ru to Cd. Here, we present the first cross section measurement of this reaction at energies (6.22 MeV ≤ Ec.m. ≤ 12.47 MeV) relevant for the weak r-process. The new data provide a stringent test of various model predictions which is necessary to improve the precision of the weak r-process network calculations. The strongly reduced reaction rate uncertainty leads to very well-constrained nucleosynthesis yields for Z = 44-48 isotopes under different neutrino-driven wind conditions.

Keywords: explosive nucleosynthesis; r-process; nuclear physics; nuclear reaction cross sections