Sazuna/UAT_keywords huggingface dataset:
GRB 211211A: a Prolonged Central Engine under a Strong Magnetic Field Environment. Recently, a kilonova-associated gamma-ray burst (GRB 211211A), whose light curve consists of a precursor (~0.2 s), a hard spiky emission (~10 s), and a soft long extended emission (~40 s), has attracted great attention. Kilonova association could prove its merger origin, while the detection of the precursor can be used to infer at least one highly magnetized neutron star (NS) being involved in the merger. In this case, a strong magnetic flux Φ is expected to surround the central engine of GRB 211211A. Here we suggest that when Φ is large enough, the accretion flow could be halted far from the innermost stable radius, which will significantly prolong the lifetime of the accretion process, and so the GRB duration. For example, we show that as long as the central black hole (BH) is surrounded by a strong magnetic flux Φ ~ 1029cm2 G, an accretion flow with ${\dot{M}}_{\mathrm{ini}}\simeq 0.1{M}_{\odot }\,{{\rm{s}}}^{-1}$ could be halted at 40 times the gravitational radius and be slowly transferred into the black hole on the order of ~10 s, which naturally explains the duration of hard spiky emission. After most of the disk mass has been accreted onto the BH, the inflow rate will be reduced, so a long and soft extended emission is expected when a new balance between the magnetic field and the accretion current is reconstructed at a larger radius. Our results further support that the special behavior of GRB 211211A is mainly due to the strong magnetic field of its progenitor stars.

Keywords: Gamma-ray bursts
HST/WFC3 Hα Direct-imaging Detection of a Pointlike Source in the Disk Cavity of AB Aur. Accreting protoplanets enable the direct characterization of planet formation. As part of a high-contrast imaging search for accreting planets with the Hubble Space Telescope (HST) Wide Field Camera 3, we present Hα images of AB Aurigae (AB Aur), a Herbig Ae/Be star harboring a transition disk. The data were collected in two epochs of direct-imaging observations using the F656N narrowband filter. After subtracting the point-spread function of the primary star, we identify a pointlike source located at a position angle of 182.°5 ± 1.°4 and a separation of 600 ± 22 mas relative to the host star. The position is consistent with the recently identified protoplanet candidate AB Aur b. The source is visible in two individual epochs separated by ~50 days, and the Hα intensities in the two epochs agree. The Hα flux density is F  ν  = 1.5 ± 0.4 mJy, 3.2 ± 0.9 times the optical continuum determined by published HST/STIS photometry. In comparison to PDS 70 b and c, the Hα excess emission is weak. The central star is accreting and the stellar Hα emission has a similar line-to-continuum ratio as seen in AB Aur b. We conclude that both planetary accretion and scattered stellar light are possible sources of the Hα emission, and the Hα detection alone does not validate AB Aur b as an accreting protoplanet. Disentangling the origin of the emission will be crucial for probing planet formation in the AB Aur disk.

Keywords: Accretion, Exoplanets, Hubble Space Telescope, HST photometry, Direct imaging, Protoplanetary disks, Spectroscopy, Exoplanet formation
Water UV-shielding in the Terrestrial Planet-forming Zone: Implications for Oxygen-18 Isotope Anomalies in {{H}}_{2}(18}{O) Infrared Emission and Meteorites. An understanding of abundance and distribution of water vapor in the innermost region of protoplanetary disks is key to understanding the origin of habitable worlds and planetary systems. Past observations have shown H2O to be abundant and a major carrier of elemental oxygen in disk surface layers that lie within the inner few astronomical units of the disk. The combination of high abundance and strong radiative transitions leads to emission lines that are optically thick across the infrared spectral range. Its rarer isotopologue ${{\rm{H}}}_{2}^{18}{\rm{O}}$ traces deeper into this layer and will trace the full content of the planet-forming zone. In this work, we explore the relative distribution of ${{\rm{H}}}_{2}^{16}{\rm{O}}$ and ${{\rm{H}}}_{2}^{18}{\rm{O}}$ within a model that includes water self-shielding from the destructive effects of ultraviolet radiation. In this Letter we show that there is an enhancement in the relative ${{\rm{H}}}_{2}^{18}{\rm{O}}$ abundance high up in the warm molecular layer within 0.1-10 au due to self-shielding of CO, C18O, and H2O. Most transitions of ${{\rm{H}}}_{2}^{18}{\rm{O}}$ that can be observed with JWST will partially emit from this layer, making it essential to take into account how H2O self-shielding may effect the H2O to ${{\rm{H}}}_{2}^{18}{\rm{O}}$ ratio. Additionally, this reservoir of ${{\rm{H}}}_{2}^{18}{\rm{O}}$ -enriched gas in combination with the vertical "cold finger" effect might provide a natural mechanism to account for oxygen isotopic anomalies found in meteoritic material in the solar system.

Keywords: Protoplanetary disks, Astrochemistry
First Report of a Solar Energetic Particle Event Observed by China's Tianwen-1 Mission in Transit to Mars. Solar energetic particles (SEPs) associated with flares and/or coronal mass ejection (CME)-driven shocks can impose acute radiation hazards on space explorations. To measure energetic particles in near-Mars space, the Mars Energetic Particle Analyzer (MEPA) instrument on board China's Tianwen-1 (TW-1) mission was designed. Here, we report the first MEPA measurements of the widespread SEP event occurring on 2020 November 29 when TW-1 was in transit to Mars. This event occurred when TW-1 and Earth were magnetically well connected, known as the Hohmann-Parker effect, thus offering us a rare opportunity to understand the underlying particle acceleration and transport process. Measurements from TW-1 and near-Earth spacecraft show similar double-power-law spectra and a radial dependence of the SEP peak intensities. Moreover, the decay phases of the time-intensity profiles at different locations clearly show the reservoir effect. We conclude that the double-power-law spectrum is likely generated at the acceleration site and that a small but finite cross-field diffusion is crucial to understanding the formation of the SEP reservoir phenomenon. These results provide insight into particle acceleration and transport associated with CME-driven shocks, which may contribute to the improvement of relevant physical models.

Keywords: Solar energetic particles
PSR J0952-0607: The Fastest and Heaviest Known Galactic Neutron Star. We describe Keck-telescope spectrophotometry and imaging of the companion of the "black widow" pulsar PSR J0952-0607, the fastest known spinning neutron star (NS) in the disk of the Milky Way. The companion is very faint at minimum brightness, presenting observational challenges, but we have measured multicolor light curves and obtained radial velocities over the illuminated "day" half of the orbit. The model fits indicate system inclination i = 59.°8 ± 1.°9 and a pulsar mass M NS = 2.35 ± 0.17 M ⊙, the largest well-measured mass found to date. Modeling uncertainties are small, since the heating is not extreme; the companion lies well within its Roche lobe and a simple direct-heating model provides the best fit. If the NS started at a typical pulsar birth mass, nearly 1 M ⊙ has been accreted; this may be connected with the especially low intrinsic dipole surface field, estimated at 6 × 107 G. Joined with reanalysis of other black widow and redback pulsars, we find that the minimum value for the maximum NS mass is ${M}_{\max }\gt 2.19\,{M}_{\odot }$ (2.09 M ⊙) at 1σ (3σ) confidence. This is ~ 0.15 M ⊙ heavier than the lower limit on ${M}_{\max }$ implied by the white dwarf-pulsar binaries measured via radio Shapiro-delay techniques.

Keywords: Pulsars
Direct-imaging Discovery and Dynamical Mass of a Substellar Companion Orbiting an Accelerating Hyades Sun-like Star with SCExAO/CHARIS. We present the direct-imaging discovery of a substellar companion in orbit around a Sun-like star member of the Hyades open cluster. So far, no other substellar companions have been unambiguously confirmed via direct imaging around main-sequence stars in Hyades. The star HIP 21152 is an accelerating star as identified by the astrometry from the Gaia and Hipparcos satellites. We detected the companion, HIP 21152 B, in multiple epochs using the high-contrast imaging from SCExAO/CHARIS and Keck/NIRC2. We also obtained the stellar radial-velocity data from the Okayama 188 cm telescope. The CHARIS spectroscopy reveals that HIP 21152 B's spectrum is consistent with the L/T transition, best fit by an early T dwarf. Our orbit modeling determines the semimajor axis and the dynamical mass of HIP 21152 B to be 17.5 ${}_{-3.8}^{+7.2}$ au and 27.8 ${}_{-5.4}^{+8.4}$ M Jup, respectively. The mass ratio of HIP 21152 B relative to its host is ≍2%, near the planet/brown dwarf boundary suggested by recent surveys. Mass estimates inferred from luminosity-evolution models are slightly higher (33-42 M Jup). With a dynamical mass and a well-constrained age due to the system's Hyades membership, HIP 21152 B will become a critical benchmark in understanding the formation, evolution, and atmosphere of a substellar object as a function of mass and age. Our discovery is yet another key proof of concept for using precision astrometry to select direct-imaging targets. *Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: Brown dwarfs, Exoplanet detection methods, Exoplanets, Coronagraphic imaging, Direct imaging, Astrometry, Astronomical instrumentation, Open star clusters
Standing Solitary Waves as Transitions to Spiral Structures in Gravitationally Unstable Accretion Disks. Astrophysical disks that are sufficiently cold and dense are linearly unstable to the formation of axisymmetric rings as a result of the disk's gravity. In practice, spiral structures are formed, which may in turn produce bound fragments. We study a nonlinear dynamical path that can explain the development of spirals in a local model of a gaseous disk on the subcritical side of the gravitational instability bifurcation. Axisymmetric equilibria can be radially periodic or localized, in the form of standing solitary waves. The solitary solutions have energy slightly larger than a smooth disk. They are further unstable to nonaxisymmetric perturbations with a wide range of azimuthal wavenumbers. The solitary waves may act as a pathway to spirals and fragmentation.

Keywords: Spiral arms, Gravitational instability, Spiral galaxies, Circumstellar disks
Molecules with ALMA at Planet-forming Scales (MAPS): A Circumplanetary Disk Candidate in Molecular-line Emission in the AS 209 Disk. We report the discovery of a circumplanetary disk (CPD) candidate embedded in the circumstellar disk of the T Tauri star AS 209 at a radial distance of about 200 au (on-sky separation of 1.″4 from the star at a position angle of 161°), isolated via 13CO J = 2-1 emission. This is the first instance of CPD detection via gaseous emission capable of tracing the overall CPD mass. The CPD is spatially unresolved with a 117 × 82 mas beam and manifests as a point source in 13CO, indicating that its diameter is ≲14 au. The CPD is embedded within an annular gap in the circumstellar disk previously identified using 12CO and near-infrared scattered-light observations and is associated with localized velocity perturbations in 12CO. The coincidence of these features suggests that they have a common origin: an embedded giant planet. We use the 13CO intensity to constrain the CPD gas temperature and mass. We find that the CPD temperature is ≳35 K, higher than the circumstellar disk temperature at the radial location of the CPD, 22 K, suggesting that heating sources localized to the CPD must be present. The CPD gas mass is ≳0.095 M Jup ≃ 30 M ⊕ adopting a standard 13CO abundance. From the nondetection of millimeter continuum emission at the location of the CPD (3σ flux density ≲26.4 μJy), we infer that the CPD dust mass is ≲0.027 M ⊕ ≃ 2.2 lunar masses, indicating a low dust-to-gas mass ratio of ≲9 × 10-4. We discuss the formation mechanism of the CPD-hosting giant planet on a wide orbit in the framework of gravitational instability and pebble accretion.

Keywords: Millimeter astronomy, Protoplanetary disks, Submillimeter astronomy, Exoplanet formation, Radio interferometry, Planet formation
Radio Detection of an Elusive Millisecond Pulsar in the Globular Cluster NGC 6397. We report the discovery of a new 5.78 ms period millisecond pulsar (MSP), PSR J1740-5340B (NGC 6397B), in an eclipsing binary system discovered with the Parkes radio telescope (now also known as Murriyang) in Australia and confirmed with the MeerKAT radio telescope in South Africa. The measured orbital period, 1.97 days, is the longest among all eclipsing binaries in globular clusters (GCs) and consistent with that of the coincident X-ray source U18, previously suggested to be a "hidden MSP." Our XMM-Newton observations during NGC 6397B's radio-quiescent epochs detected no X-ray flares. NGC 6397B is either a transitional MSP or an eclipsing binary in its initial stage of mass transfer after the companion star left the main sequence. The discovery of NGC 6397B potentially reveals a subgroup of extremely faint and heavily obscured binary pulsars, thus providing a plausible explanation for the apparent dearth of binary neutron stars in core-collapsed GCs as well as a critical constraint on the evolution of GCs.

Keywords: Globular star clusters, Eclipsing binary stars, Millisecond pulsars
Spectral Analysis of GRB 220426A: Another Case of a Thermally Dominated Burst. We report a very bright, long-duration gamma-ray burst (GRB), GRB 220426A, observed by the Fermi satellite. GRB 220426A, with a total duration of T 90 = 6 s, is composed of two main pulses and some subpeaks. The spectral analysis of this burst with a Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with a high α ≳ 0.2 and low β ≲ -3.1. It is highly reminiscent of GRB 090902B, a special GRB with a photospheric emission identification. Then, we perform the spectral analysis of this burst based on nondissipated photospheric emission, which can be well modeled by a multicolor blackbody with a cutoff power-law distribution of the thermal temperature. The spectral fittings reveal that the photospheric emission can well describe the radiation spectrum of this burst. We conclude that this burst would be a second burst in the class of GRB 090902B observed by the Fermi satellite. We also discuss the physics of the photosphere and the origin of the high-energy component in GRB 220426A.

Keywords: Gamma-ray bursts
Faculae Cancel out on the Surfaces of Active Suns. Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance, they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots or faculae. Here, we utilize a surface flux transport model to show that more effective cancellation of diffuse magnetic flux associated with faculae leads to spot area coverages increasing faster with stellar magnetic activity than that by faculae. Our calculations explain the observed dependence between solar spot and facular area coverages and allow its extension to stars that are more active than the Sun. This extension enables anticipating the properties of stellar signal and its more reliable mitigation, leading to a more accurate characterization of exoplanets and their atmospheres.

Keywords: Stellar astronomy, Solar physics
10 Yr Transformation of the Obscuring Wind in NGC 5548. A decade ago, the archetypal Seyfert-1 galaxy NGC 5548 was discovered to have undergone major spectral changes. The soft X-ray flux had dropped by a factor of 30 while new broad and blueshifted UV absorption lines appeared. This was explained by the emergence of a new obscuring wind from the accretion disk. Here we report on the striking long-term variability of the obscuring disk wind in NGC 5548 including new observations taken in 2021-2022 with the Swift Observatory and the Hubble Space Telescope's Cosmic Origins Spectrograph. The X-ray spectral hardening as a result of obscuration has declined over the years, reaching its lowest in 2022, at which point we find the broad C IV UV absorption line to have nearly vanished. The associated narrow low-ionization UV absorption lines, produced previously when shielded from the X-rays, are also remarkably diminished in 2022. We find a highly significant correlation between the variabilities of the X-ray hardening and the equivalent width of the broad C IV absorption line, demonstrating that X-ray obscuration is inherently linked to disk winds. We derive for the first time a relation between the X-ray and UV covering fractions of the obscuring wind using its long-term evolution. The diminished X-ray obscuration and UV absorption are likely caused by an increasingly intermittent supply of outflowing streams from the accretion disk. This results in growing gaps and interstices in the clumpy disk wind, thereby reducing its covering fractions.

Keywords: Accretion, High resolution spectroscopy, Broad-absorption line quasar, X-ray active galactic nuclei, Active galactic nuclei
Water Shielding in the Terrestrial Planet-forming Zone: Implication for Inner Disk Organics. The chemical composition of the inner region of protoplanetary disks can trace the composition of planetary-building material. The exact elemental composition of the inner disk has not yet been measured and tensions between models and observations still exist. Recent advancements have shown UV shielding to be able to increase the emission of organics. Here, we expand on these models and investigate how UV shielding may impact chemical composition in the inner 5 au. In this work, we use the model from Bosman et al. and expand it with a larger chemical network. We focus on the chemical abundances in the upper disk atmosphere where the effects of water UV shielding are most prominent and molecular lines originate. We find rich carbon and nitrogen chemistry with enhanced abundances of C2H2, CH4, HCN, CH3CN, and NH3 by &gt;3 orders of magnitude. This is caused by the self-shielding of H2O, which locks oxygen in water. This subsequently results in a suppression of oxygen-containing species like CO and CO2. The increase in C2H2 seen in the model with the inclusion of water UV shielding allows us to explain the observed C2H2 abundance without resorting to elevated C/O ratios as water UV shielding induced an effectively oxygen-poor environment in oxygen-rich gas. Thus, water UV shielding is important for reproducing the observed abundances of hydrocarbons and nitriles. From our model result, species like CH4, NH3, and NO are expected to be observable with the James Webb Space Telescope (JWST).

Keywords: Protoplanetary disks, Chemical abundances, Astrochemistry
Lyα Halos around [O III]-selected Galaxies in HETDEX. We present extended Lyα emission out to 800 kpc of 1034 [O III]-selected galaxies at redshifts 1.9 &lt; z &lt; 2.35 using the Hobby-Eberly Telescope Dark Energy Experiment. The locations and redshifts of the galaxies are taken from the 3D-HST survey. The median-stacked surface brightness profile of the Lyα emission of the [O III]-selected galaxies agrees well with that of 968 bright Lyα-emitting galaxies (LAEs) at r &gt; 40 kpc from the galaxy centers. The surface brightness in the inner parts (r &lt; 10 kpc) around the [O III]-selected galaxies, however, is 10 times fainter than that of the LAEs. Our results are consistent with the notion that photons dominating the outer regions of the Lyα halos are not produced in the central galaxies but originate outside of them.

Keywords: Intergalactic medium, Galaxy environments, High-redshift galaxies, Circumgalactic medium
The ALMA REBELS Survey: The Cosmic H I Gas Mass Density in Galaxies at z ≍ 7. The neutral atomic gas content of individual galaxies at large cosmological distances has until recently been difficult to measure due to the weakness of the hyperfine H I 21 cm transition. Here we estimate the H I gas mass of a sample of main-sequence star-forming galaxies at z ~ 6.5-7.8 surveyed for [C II] 158 μm emission as part of the Reionization Era Bright Emission Line Survey (REBELS), using a recent calibration of the [C II]-to-H I conversion factor. We find that the H I gas mass excess in galaxies increases as a function of redshift, with an average of M HI /M ⋆ ≍ 10, corresponding to H I gas mass fractions of f HI  = M HI /(M ⋆ + M HI ) = 90%, at z ≍ 7. Based on the [C II] 158 μm luminosity function (LF) derived from the same sample of galaxies, we further place constraints on the cosmic H I gas mass density in galaxies (ρ HI ) at this redshift, which we measure to be ${\rho }_{{\rm{H}}{\rm\small{I}}}={7.1}_{-3.0}^{+6.4}\times {10}^{6}\,{M}_{\odot }\,{\mathrm{Mpc}}^{-3}$ . This estimate is substantially lower by a factor of ≍10 than that inferred from an extrapolation of damped Lyα absorber (DLA) measurements and largely depends on the exact [C II] LF adopted. However, we find this decrease in ρ HI  to be consistent with recent simulations and argue that this apparent discrepancy is likely a consequence of the DLA sight lines predominantly probing the substantial fraction of H I gas in high-z galactic halos, whereas [C II] traces the H I in the ISM associated with star formation. We make predictions for this buildup of neutral gas in galaxies as a function of redshift, showing that at z ≳ 5, only ≍10% of the cosmic H I gas content is confined in galaxies and associated with the star-forming ISM.

Keywords: High-redshift galaxies, Galaxy evolution, Interstellar medium
Third and Fourth Harmonics of Electromagnetic Emissions by a Weak Beam in a Solar Wind Plasma with Random Density Fluctuations. Electromagnetic emissions ${{ \mathcal H }}_{3}$ and ${{ \mathcal H }}_{4}$ at the third and fourth harmonics of the plasma frequency ω  p  were observed during the occurrence of type II and type III solar radio bursts. Two-dimensional particle-in-cell simulations are performed using a weak beam, high space and time resolutions, and a plasma with density fluctuations of a few percent, for parameters relevant to regions of type III bursts. For the first time, a detailed study of the different wave coalescence processes involved in the generation of ${{ \mathcal H }}_{3}$ and ${{ \mathcal H }}_{4}$ waves is presented and the impact of density fluctuations on the wave interaction mechanisms is demonstrated. Energy ratios between the second, third, and fourth harmonics ${{ \mathcal H }}_{2}$ , ${{ \mathcal H }}_{3}$ , and ${{ \mathcal H }}_{4}$ are consistent with space observations. It is shown that, in both homogeneous and inhomogeneous plasmas, the dominant processes generating ${{ \mathcal H }}_{3}$ ( ${{ \mathcal H }}_{4}$ ) are the coalescence of ${{ \mathcal H }}_{2}$ ( ${{ \mathcal H }}_{3}$ ) with a Langmuir wave, in spite of the random density fluctuations modifying the waves' resonance conditions by energy transport in the wavevector space and of the damping of Langmuir waves. The role of the backscattered (forward-propagating) Langmuir waves coming from the first (second) cascade of the electrostatic decay of beam-driven Langmuir waves is determinant in these processes. Understanding such wave coalescence mechanisms can provide indirect information on Langmuir and ion acoustic wave turbulence, the average level of density inhomogeneities, and suprathermal electron fluxes generated in solar wind regions where the harmonics manifest. Causes for the rarity of their observations are discussed.

Keywords: Radio bursts, Solar wind, Solar electromagnetic emission