adsabs/SciX_UAT_keywords huggingface dataset:
DR 21 South Filament: A Parsec-sized Dense Gas Accretion Flow onto the DR 21 Massive Young Cluster

DR 21 south filament (DR21SF) is a unique component of the giant network of filamentary molecular clouds in the north region of the Cygnus X complex. Unlike the highly fragmented and star-forming active environment wherein it resides, DR21SF exhibits a coherent profile in the column density map with very few star formation signposts, even though the previously reported linear density of the filament is an order of magnitude higher than the thermal stable threshold. We derive the size (3.6 pc by 0.13 pc), temperature (10-15 K), and mass (1048 M⊙) of DR21SF from our single-dish observations of NH3 (1, 1) and (2, 2) inversion lines in conjunction with the column density map from our previous work. Star-forming sites are identified along the filament where gas temperature is excessive. We find clear gradients in radial velocity and intrinsic line width along the spine of the filament. The gradients can be well interpreted by a scenario of an accretion flow feeding DR 21 at a mass transfer rate of 1.1 × 10-3M⊙ yr-1. Based on the analysis of its kinematic temperature, intrinsic line width, and mass distribution, we conclude that DR21SF is in an overall trans-critical status, which indicates an early evolutionary stage.

Keywords: interstellar filaments
A Distant Fast Radio Burst Associated with Its Host Galaxy by the Very Large Array

We present the discovery and subarcsecond localization of a new fast radio burst (FRB) by the Karl G. Jansky Very Large Array (VLA) and realfast search system. The FRB was discovered on 2019 June 14 with a dispersion measure of 959 $\mathrm{pc}\,{\mathrm{cm}}^{-3}$. This is the highest DM of any localized FRB and its measured burst fluence of 0.6 Jy ms is less than nearly all other FRBs. The source is not detected to repeat in 15 hr of VLA observing and 153 hr of CHIME/FRB observing. We describe a suite of statistical and data quality tests we used to verify the significance of the event and its localization precision. Follow-up optical/infrared photometry with Keck and Gemini associate the FRB with a pair of galaxies with $r\sim 23$ mag. The false-alarm rate for radio transients of this significance that are associated with a host galaxy is roughly $3\times {10}^{-4}\,{\mathrm{hr}}^{-1}$. The two putative host galaxies have similar photometric redshifts of ${z}_{\mathrm{phot}}\sim 0.6$, but different colors and stellar masses. Comparing the host distance to that implied by the dispersion measure suggests a modest ($\sim 50\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$) electron column density associated with the FRB environment or host galaxy/galaxies.

Keywords: radio transient sources; radio interferometry; extragalactic astronomy; radio bursts
Observed Rate Variations in Superflaring G-type Stars

Flare occurrence on the Sun is highly variable, exhibiting both short-term variation due to the emergence and evolution of active regions, and long-term variation from the solar cycle. On solar-like stars, more energetic stellar flares (superflares) have been observed, and it is of interest to determine whether the observed rates of superflare occurrence exhibit similar variability to solar flares. We analyze 274 G-type stars using data from the Transiting Exoplanet Survey Satellite and identify seven stars which exhibit statistically significant changes in the rate of superflare occurrence by fitting a piecewise constant-rate model with the Bayesian blocks algorithm. We investigate the properties of these stars and their flaring rates, and discuss the possible reasons for the low number of stars with detectable rate variation.

Keywords: stellar flares; stellar activity; stellar rotation; g dwarf stars
Does Nature Allow the Formation of Ultra-compact Black Hole X-Ray Binaries via the Accretion-induced Collapse of Neutron Stars?

The formation path to ultracompact X-ray binaries (UCXBs) with black hole (BH) accretors is still unclear. In the classical formation scenario, it is difficult to eject the massive envelope of the progenitor star of the BH via the common envelope process. Given that some neutron stars (NSs) in binary systems evidently have birth masses close to ~2.0 M ⊙, we explore here the possibility that BH-UCXBs may form via the accretion-induced collapse (AIC) of accreting NSs, assuming that these previously evolved in low-mass X-ray binaries to masses all the way up to the maximum limit of an NS. We demonstrate this formation path by modeling a few cases of NS-UCXBs with initial NS masses close to the maximum mass of an NS that evolve into BH-UCXBs after the NS accretes material from its He white dwarf (WD) companion. We follow the evolution of the post-AIC BH-UCXB and, based on simple arguments, we anticipate that there is about one BH-UCXB with an AIC origin and a He WD donor within the current sample of known UCXBs and that two to five such BH-UCXBs may be detected in gravitational waves by LISA. In addition, we find that the X-ray luminosity of NS-UCXBs near their orbital period minimum exceeds ~1039 erg s-1, and thus, such systems may appear as ultraluminous X-ray sources.

Keywords: compact binary stars; x-ray binary stars; black holes; neutron stars; white dwarf stars; gravitational wave sources
Meterwavelength Single-pulse Polarimetric Emission Survey. V. Flux Density, Component Spectral Variation, and Emission States

We present the flux density measurements of the pulsars observed in the Meterwavelength Single-pulse Polarimetric Emission Survey. The average flux densities were estimated in 113 pulsars at two frequencies of 325 and 610 MHz using interferometric imaging. The average profile and single-pulse emission in each pulsar were calibrated using the estimated flux density. We have used the flux-calibrated average profile to study the variation of the spectral index across the emission beam in 21 pulsars where the core, inner cone, and the outer conal components could be clearly identified. The central core component showed a steeper increase in emission at the lower frequency compared with conal emission, with an average difference in spectral index δαcore-cone ~ -0.7 between the core and the conal components in this frequency range. In contrast, the inner conal components had positive difference in their spectral index compared to the outer cones with average difference δαin-out ~ +0.3. The variation in the spectral index across the pulse window should provide valuable inputs for constraining the radio emission processes. The single-pulse emission showed the presence of emission mode changing in 12 pulsars, with three cases where the phenomenon is being reported for the first time. In addition, we have also detected enhanced emission for short durations or flaring, in parts or across the entire emission window in 14 pulsars. The sudden changes in the emission during mode changing, as well as these bursting states, are unrelated to the emission mechanism and suggest the presence of rapid and repetitive changes during the plasma generation process.

Keywords: radio pulsars
Physics of Nonuniversal Larson's Relation

From a new perspective, we reexamine self-gravity and turbulence jointly, in hopes of understanding the physical basis for one of the most important empirical relations governing clouds in the interstellar medium (ISM), the Larson's relation relating velocity dispersion (σR) to cloud size (R). We report on two key new findings. First, the correct form of the Larson's relation is ${\sigma }_{R}={\alpha }_{v}^{1/5}{\sigma }_{\mathrm{pc}}{(R/1\mathrm{pc})}^{3/5}$ , where αv is the virial parameter of clouds and σpc is the strength of the turbulence, if the turbulence has the Kolmogorov spectrum. Second, the amplitude of Larson's relation, σpc, is not universal, differing by a factor of about 2 between clouds on the Galactic disk and those at the Galactic center, as evidenced by observational data.

Keywords: interstellar medium; diffuse interstellar clouds; gravitational interaction; interstellar clouds; interstellar dynamics; gravitational equilibrium; gravitational collapse; star formation; interstellar magnetic fields; dark interstellar clouds; dense interstellar clouds
Statistics and Polarization of Type III Radio Bursts Observed in the Inner Heliosphere

We present initial results from the Radio Frequency Spectrometer, the high-frequency component of the FIELDS experiment on the Parker Solar Probe (PSP). During the first PSP solar encounter (2018 November), only a few small radio bursts were observed. During the second encounter (2019 April), copious type III radio bursts occurred, including intervals of radio storms where bursts occurred continuously. In this paper, we present initial observations of the characteristics of type III radio bursts in the inner heliosphere, calculating occurrence rates, amplitude distributions, and spectral properties of the observed bursts. We also report observations of several bursts during the second encounter that display circular polarization in the right-hand-polarized sense, with a degree of polarization of 0.15-0.38 in the range from 8 to 12 MHz. The degree of polarization can be explained either by depolarization of initially 100% polarized o-mode emission or by direct generation of emission in the o-mode and X-mode simultaneously. Direct in situ observations in future PSP encounters could provide data that can distinguish these mechanisms.

Keywords: solar radio emission; radio bursts; heliosphere; space vehicle instruments
A Candidate Dual QSO at Cosmic Noon

We report the discovery of a candidate dual QSO at z = 1.889, a redshift that is in the era known as "cosmic noon" where most of the universe's black hole and stellar mass growth occurred. The source was identified in Hubble Space Telescope WFC3/IR images of a dust-reddened QSO that showed two closely separated point sources at a projected distance of 0.″26, or 2.2 kpc. This red QSO was targeted for imaging to explore whether red QSOs are hosted by merging galaxies. We subsequently obtained a spatially resolved Space Telescope Imaging Spectrograph spectrum of the system, covering the visible spectral range, and verifying the presence of two distinct QSO components. We also obtained high-resolution radio continuum observations with the Very Long Baseline Array at 1.4 GHz (21 cm L band) and found two sources coincident with the optical positions. The sources have similar black hole masses, bolometric luminosities, and radio-loudness parameters. However, their colors and reddenings differ significantly. The redder QSO has a higher Eddington ratio, consistent with previous findings. We consider the possibility of gravitational lensing and find that it would require extreme and unlikely conditions. If confirmed as a bona fide dual QSO, this system would link dust reddening to galaxy and supermassive black hole mergers, opening up a new population in which to search for samples of dual active galactic nuclei.

Keywords: quasars; double quasars
Dynamical Analysis of the Dark Matter and Central Black Hole Mass in the Dwarf Spheroidal Leo I

We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and previously published data. We find a steady rise in the velocity dispersion from 300″ into the center. The integrated-light kinematics provide a velocity dispersion of 11.76 ± 0.66 km s-1 inside 75″. After applying appropriate corrections to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars. Crowding corrections need to be applied when targeting individual stars in high-density stellar environments. From integrated light, we measure the surface brightness profile and find a shallow cusp toward the center. Axisymmetric, orbit-based models measure the stellar mass-to-light ratio, black hole mass, and parameters for a dark matter halo. At large radii it is important to consider possible tidal effects from the Milky Way, so we include a variety of assumptions regarding the tidal radius. For every set of assumptions, models require a central black hole consistent with a mass (3.3 ± 2) × 106 M⊙. The no-black-hole case for any of our assumptions is excluded at over 95% significance, with 6.4 < Δχ2 < 14. A black hole of this mass would have significant effects on dwarf galaxy formation and evolution. The dark halo parameters are heavily affected by the assumptions for the tidal radii, with the circular velocity only constrained to be above 30 km s-1. Reasonable assumptions for the tidal radius result in stellar orbits consistent with an isotropic distribution in the velocities. These more realistic models have little need for a dark matter halo.

Keywords: dwarf galaxies; supermassive black holes; galaxy kinematics
Greater Climate Sensitivity and Variability on TRAPPIST-1e than Earth

The atmospheres of rocky exoplanets are close to being characterized by astronomical observations, in part due to the commissioning of the JWST. These observations compel us to understand exoplanetary atmospheres, in the voyage to find habitable planets. With this aim, we investigate the effect that CO2 partial pressure (pCO2) has on exoplanets' climate variability, by analyzing results from ExoCAM model simulations of the tidally locked TRAPPIST-1e exoplanet, an Earth-like aqua-planet, and Earth itself. First, we relate the differences between the planets to their elementary parameters. Then, we compare the sensitivity of the Earth analog and TRAPPIST-1e's surface temperature and precipitation to pCO2. Our simulations suggest that the climatology and extremes of TRAPPIST-1e's temperature are ~1.5 times more sensitive to pCO2 relative to Earth. The precipitation sensitivity strongly depends on the specific region analyzed. Indeed, the precipitation near mid-latitude and equatorial substellar regions of TRAPPIST-1e is more sensitive to pCO2, and the precipitation sensitivity is ~2 times larger in TRAPPIST-1e. A dynamical systems perspective, which provides information about how the atmosphere evolves in phase space, provides additional insights. Notably, an increase in pCO2 results in an increase in atmospheric persistence on both planets, and the persistence of TRAPPIST-1e is more sensitive to pCO2 than Earth. We conclude that the climate of TRAPPIST-1e may be more sensitive to pCO2, particularly on its dayside. This study documents a new pathway for understanding the effect that varying planetary parameters have on the climate variability of potentially habitable exoplanets and on Earth.

Keywords: exoplanet atmospheric variability; exoplanet dynamics; exoplanet atmospheres; exoplanet atmospheric composition; atmospheric variability; atmospheric composition; planetary climates; habitable planets; extrasolar rocky planets
Dark Matter Admixed Neutron Star Properties in the Light of X-Ray Pulse Profile Observations

The distribution of the dark matter (DM) in DM-admixed neutron stars (DANSs) is supposed to result in either a dense dark core or an extended dark halo, subject to the DM fraction of the DANS (f χ ) and the DM properties, such as the mass (m χ ) and the strength of the self-interaction (y). In this paper, we perform an in-depth analysis of the formation criterion for dark cores/dark halos, and point out that the relative distribution of these two components is essentially determined by the ratio of the central enthalpy of the DM component to that of the baryonic matter component inside the DANSs. For the critical case where the radii of the DM and the baryonic matter are the same, we further derive an analytical formula to describe the dependence of ${f}_{\chi }^{\mathrm{crit}}$ on m χ and y for a given DANS mass. The relative distribution of the two components in DANSs can lead to different observational effects. We here focus on the modification of the pulsar pulse profile, due to the extra light-bending effect in the case of a dark halo existence, and conduct the first investigation into the dark halo effects on the pulse profile. We find that the peak flux deviation is strongly dependent on the ratio of the halo mass to the radius of the DM component. Last, we perform Bayesian parameter estimation on the DM particle properties, based on the recent X-ray observations of PSR J0030+0451 and PSR J0740+6620 by the Neutron Star Interior Composition Explorer.

Keywords: dark matter; neutron stars; pulsars
Theoretical Analysis of the RX J0209.6‑7427 X-Ray Spectrum during a Giant Outburst

We model the spectral formation occurring in the binary X-ray pulsar (XRP) RX J0209.6‑7427 during the 2019 super-Eddington outburst. Using a theoretical model previously developed by the authors, we are able to produce spectra that closely resemble the phase-averaged X-ray spectra observed using the Nuclear Spectroscopic Telescope Array and Insight-HXMT during low- and high-luminosity states of the outburst, respectively. The theoretical model simulates the accretion of fully ionized gas in a dipole magnetic field and includes a complete description of the radiation hydrodynamics, matter distribution, and spectral formation. Type II X-ray outbursts provide an opportunity to study accretion over a large range of luminosities for the same neutron star. The analysis performed here represents the first time both the outburst low and high states of an accretion-powered XRP are modeled using a physics-based model rather than standard phenomenological fitting with arbitrary mathematical functions. We find that the outer polar cap radius remains constant and the column is more fully filled with increasing luminosity, Comptonized bremsstrahlung dominates the formation of the phase-averaged X-ray spectrum, and a negative correlation exists between cyclotron centroid energy and luminosity, as expected. The super-Eddington nature of the outburst is rendered possible owing to the low scattering cross section for photons propagating parallel to the magnetic field. We also find that emission through the column top dominates in both the low and high states, implying that the pulse profiles should have a roughly sinusoidal shape, which agrees with observed properties of ultraluminous XRPs.

Keywords: neutron stars; high mass x-ray binary stars; ultraluminous x-ray sources; hydrodynamics; radiative transfer
Comparing the Photometric Calibration of DESI Imaging and Gaia Synthetic Photometry

The relative photometric calibration errors in the DESI Legacy Imaging Surveys (LS), which are used for DESI target selection, can leave imprints on the DESI target densities and bias the resulting cosmological measurements. We characterize the LS calibration systematics by comparing the LS stellar photometry with Gaia DR3 synthetic photometry. We find the stellar photometry of LS DR9 and Gaia has an RMS difference of 4.7, 3.7, 4.4 mmag in DECam grz bands, respectively, when averaged over an angular scale of $27^{\prime} $ . There are distinct spatial patterns in the photometric offset resembling the Gaia scan patterns (most notably in the synthesized g-band) which indicate systematics in the Gaia spectrophotometry, as well as honeycomb patterns due to LS calibration systematics. We also find large and smoothly varying photometric offsets at decl. < -29.°25 in LS DR9 which are fixed in DR10.

Keywords: photometry; spectrophotometry; flux calibration; sky surveys
Three-dimensional Hydrodynamics Simulations of Precollapse Shell Burning in the Si- and O-rich Layers

We present 3D hydrodynamics simulations of shell burning in two progenitors with zero-age main-sequence masses of 22 and 27 M⊙ for ∼65 and 200 s up to the onset of gravitational collapse, respectively. The 22 and 27 M⊙ stars are selected from a suite of 1D progenitors. The former and the latter have an extended Si- and O-rich layer with a width of ∼109 cm and ∼5 × 109 cm, respectively. Our 3D results show that turbulent mixing occurs in both of the progenitors with the angle-averaged turbulent Mach number exceeding ∼0.1 at the maximum. We observe that an episodic burning of O and Ne, which takes place underneath the convection bases, enhances the turbulent mixing in the 22 and 27 M⊙ models, respectively. The distribution of nucleosynthetic yields is significantly different from that in 1D simulations, namely, in 3D more homogeneous and inhomogeneous in the radial and angular direction, respectively. By performing a spectrum analysis, we investigate the growth of turbulence and its role of material mixing in the convective layers. We also present a scalar spherical harmonics mode analysis of the turbulent Mach number. This analytical formula would be helpful for supernova modelers to implement the precollapse perturbations in core-collapse supernova simulations. Based on the results, we discuss implications for the possible onset of the perturbation-aided neutrino-driven supernova explosion.

Keywords: late stellar evolution
Electron Energy Partition across Interplanetary Shocks. III. Analysis

An analysis of model fit results of 15,210 electron velocity distribution functions (VDFs), observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented as the third and final part on electron VDFs near IP shocks. The core electrons and protons dominate in the magnitude and change in the partial-to-total thermal pressure ratio, with the core electrons often gaining as much or more than the protons. Only a moderate positive correlation is observed between the electron temperature and the kinetic energy change across the shock, while weaker, if any, correlations were found with any other macroscopic shock parameter. No VDF parameter correlated with the shock normal angle. The electron VDF evolves from a narrowly peaked core with flaring suprathermal tails in the upstream to either a slightly hotter core with steeper tails or much hotter flattop core with even steeper tails downstream of the weaker and strongest shocks, respectively. Both quasi-static and fluctuating fields are examined as possible mechanisms modifying the VDF, but neither is sufficient alone. For instance, flattop VDFs can be generated by nonlinear ion acoustic wave stochastic acceleration (I.e., inelastic collisions), while other work suggested they result from the combination of quasi-static and fluctuating fields. This three-part study shows that not only are these systems not thermodynamic in nature; even kinetic models may require modification to include things like inelastic collision operators to properly model electron VDF evolution across shocks or in the solar wind.

Keywords: solar wind; interplanetary shocks; solar coronal mass ejections; solar coronal mass ejection shocks; space plasmas; plasma astrophysics; plasma physics; interplanetary particle acceleration