Sazuna/UAT_keywords huggingface dataset:
The New Magnetar SGR J1830-0645 in Outburst. The detection of a short hard X-ray burst and an associated bright soft X-ray source by the Swift satellite in 2020 October heralded a new magnetar in outburst, SGR J1830-0645. Pulsations at a period of ∼10.4 s were detected in prompt follow-up X-ray observations. We present here the analysis of the Swift/Burst Alert Telescope burst, of XMM-Newton and the Nuclear Spectroscopic Telescope Array observations performed at the outburst peak, and of a Swift/X-ray Telescope monitoring campaign over the subsequent month. The burst was single-peaked, lasted ∼6 ms, and released a fluence of ≍5 × 10-9 erg cm-2 (15-50 keV). The spectrum of the X-ray source at the outburst peak was well described by an absorbed double-blackbody model plus a power-law component detectable up to ∼25 keV. The unabsorbed X-ray flux decreased from ∼5 × 10-11 to ∼2.5 × 10-11 erg cm-2 s-1 one month later (0.3-10 keV). Based on our timing analysis, we estimate a dipolar magnetic field ≍5.5 × 1014 G at pole, a spin-down luminosity ≍2.4 × 1032 erg s-1, and a characteristic age ≍24 kyr. The spin modulation pattern appears highly pulsed in the soft X-ray band, and becomes smoother at higher energies. Several short X-ray bursts were detected during our campaign. No evidence for periodic or single-pulse emission was found at radio frequencies in observations performed with the Sardinia Radio Telescope and Parkes. According to magneto-thermal evolutionary models, the real age of SGR J1830-0645 is close to the characteristic age, and the dipolar magnetic field at birth was slightly larger, ∼1015 G.

Keywords: X-ray point sources, Pulsars, X-ray transient sources, Magnetars, Magnetic fields, X-ray bursts
Icy Exomoons Evidenced by Spallogenic Nuclides in Polluted White Dwarfs. We present evidence that excesses in Be in polluted white dwarfs (WDs) are the result of accretion of icy exomoons that formed in the radiation belts of giant exoplanets. Here we use excess Be in the white dwarf GALEX J2339-0424 as an example. We constrain the parent body abundances of rock-forming elements in GALEX J2339-0424 and show that the overabundance of beryllium in this WD cannot be accounted for by differences in diffusive fluxes through the WD outer envelope nor by chemical fractionations during typical rock-forming processes. We argue instead that the Be was produced by energetic proton irradiation of ice mixed with rock. We demonstrate that the MeV proton fluence required to form the high Be/O ratio in the accreted parent body is consistent with irradiation of ice in the rings of a giant planet within its radiation belt, followed by accretion of the ices to form a moon that is later accreted by the WD. The icy moons of Saturn serve as useful analogs. Our results provide an estimate of spallogenic nuclide excesses in icy moons formed by rings around giant planets in general, including those in the solar system. While excesses in Be have been detected in two polluted WDs to date, including the WD described here, we predict that excesses in the other spallogenic elements Li and B, although more difficult to detect, should also be observed, and that such detections would also indicate pollution by icy exomoons formed in the ring systems of giant planets.

Keywords: White dwarf stars, Natural satellites (Extrasolar), Cosmic rays
A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c. Strongly irradiated exoplanets develop extended atmospheres that can be utilized to probe the deeper planet layers. This connection is particularly useful in the study of small exoplanets, whose bulk atmospheres are challenging to characterize directly. Here, we report the 3.4σ detection of C II ions during a single transit of the super-Earth π Men c in front of its Sun-like host star. The transit depth and Doppler velocities are consistent with the ions filling the planet's Roche lobe and moving preferentially away from the star, an indication that they are escaping the planet. We argue that π Men c possesses a thick atmosphere with abundant heavy volatiles (≳ 50% by mass of atmosphere) but that needs not be carbon rich. Our reasoning relies upon cumulative evidence from the reported C II detection, the nondetection of H atoms in a past transit, modeling of the planet's interior, and the assumption that the atmosphere, having survived the most active phases of its Sun-like host star, will survive another 0.2-2 Gyr. Depending on the current mass of atmosphere, π Men c may still transition into a bare rocky core. Our findings confirm the hypothesized compositional diversity of small exoplanets, and represent a milestone toward understanding the planets' formation and evolution paths through the investigation of their extended atmospheres.

Keywords: Exoplanet structure, Exoplanet atmospheres
Rapidly Spinning Compact Stars with Deconfinement Phase Transition. We study rapidly spinning compact stars with equations of state featuring a first-order phase transition between strongly coupled nuclear matter and deconfined quark matter by employing the gauge/gravity duality. We consider a family of models that allow purely hadronic uniformly rotating stars with masses up to approximately 2.9 M⊙, and are therefore compatible with the interpretation that the secondary component ( ${2.59}_{-0.09}^{+0.08}\,{M}_{\odot }$ ) in GW190814 is a neutron star. These stars have central densities that are several times the nuclear saturation density, so that strong coupling and non-perturbative effects become crucial. We construct models where the maximal mass of static (rotating) stars MTOV (Mmax) is either determined by the secular instability or a phase-transition induced collapse. We find the largest values for Mmax/MTOV in cases where the phase transition determines Mmax, which shifts our fit result to ${M}_{\max }/{M}_{\mathrm{TOV}}={1.227}_{-0.016}^{+0.031}$ , a value slightly above the Breu-Rezzolla bound ${1.203}_{-0.022}^{+0.022}$ inferred from models without phase transition.

Keywords: Neutron stars, Nuclear astrophysics, Neutron star cores
Water Production Rate of C/2020 F3 (NEOWISE) from SOHO/SWAN over Its Active Apparition. C/2020 F3 (NEOWISE) was discovered in images from the Near Earth Object program of the Wide-Field Infrared Survey Explorer (NEOWISE) taken on 2020 March 27 and has become the Great Comet of 2020. The Solar Wind ANisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO) spacecraft, located in a halo orbit around the Earth-Sun L1 Lagrange point, makes daily full-sky images of hydrogen Lyα. Water production rates were determined from the SWAN hydrogen Lyα brightness and spatial distribution of the comet measured over a 4 month period of time on either side of the comet's perihelion on 2020 July 3. The water production rate in s-1 was moderately asymmetric around perihelion and varied with the heliocentric distance, r, in au as (6.9 ± 0.5) × 1028 r-2.5±0.2 and (10.1 ± 0.5) × 1028 r-3.5±0.1 before and after perihelion, respectively. This is consistent with the comet having been through the planetary region of the solar system on one or more previous apparitions. Water production rates as large as 5.27 × 1030 s-1 were determined shortly after perihelion, once the comet was outside the solar avoidance area of SWAN, when the comet was 0.324 au from the Sun.

Keywords: Comae, Oort cloud, Neutral coma gases, Long period comets, Comets, Comet origins
Cluster Analysis of Presolar Silicon Carbide Grains: Evaluation of Their Classification and Astrophysical Implications. Cluster analysis of presolar silicon carbide grains based on literature data for 12C/13C, 14N/15N, δ30Si/28Si, and δ29Si/28Si including or not inferred initial 26Al/27Al data, reveals nine clusters agreeing with previously defined grain types but also highlighting new divisions. Mainstream grains reside in three clusters probably representing different parent star metallicities. One of these clusters has a compact core, with a narrow range of composition, pointing to an enhanced production of SiC grains in asymptotic giant branch (AGB) stars with a narrow range of masses and metallicities. The addition of 26Al/27Al data highlights a cluster of mainstream grains, enriched in 15N and 26Al, which cannot be explained by current AGB models. We defined two AB grain clusters, one with 15N and 26Al excesses, and the other with 14N and smaller 26Al excesses, in agreement with recent studies. Their definition does not use the solar N isotopic ratio as a divider, and the contour of the 26Al-rich AB cluster identified in this study is in better agreement with core-collapse supernova models. We also found a cluster with a mixture of putative nova and AB grains, which may have formed in supernova or nova environments. X grains make up two clusters, having either strongly correlated Si isotopic ratios or deviating from the 2/3 slope line in the Si 3-isotope plot. Finally, most Y and Z grains are jointly clustered, suggesting that the previous use of 12C/13C = 100 as a divider for Y grains was arbitrary. Our results show that cluster analysis is a powerful tool to interpret the data in light of stellar evolution and nucleosynthesis modeling and highlight the need of more multi-element isotopic data for better classification.

Keywords: Interstellar dust, Clustering, Nucleosynthesis, Stellar evolution
Measuring Turbulence with Young Stars in the Orion Complex. Stars form in molecular clouds in the interstellar medium (ISM) with a turbulent kinematic state. Newborn stars therefore should retain the turbulent kinematics of their natal clouds. Gaia DR2 and APOGEE-2 surveys in combination provide three-dimensional (3D) positions and 3D velocities of young stars in the Orion Molecular Cloud Complex. Using the full 6D measurements, we compute the velocity structure functions (VSFs) of the stars in six different groups within the Orion Complex. We find that the motions of stars in all diffuse groups exhibit strong characteristics of turbulence. Their first-order VSFs have a power-law exponent ranging from ∼0.2-0.5 on scales of a few to a few tens of parsecs, generally consistent with Larson's relation. On the other hand, dense star clusters, such as the Orion Nebula Cluster (ONC), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. The VSFs of several individual groups and the whole Complex all show features supporting local energy injection from supernovae. The measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of the groups. Our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics of the ISM. Unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6D information of stars, presenting a more complete picture of the 3D interstellar turbulence.

Keywords: Stellar feedback, Stellar motion, Young star clusters, Stellar dynamics, Molecular clouds, Supernova remnants, Interstellar medium
First Detection of Interaction between a Magnetic Disk Wind and an Episodic Jet in a Protostellar System. Rotating outflows from protostellar disks might trace extended magnetohydrodynamic (MHD) disk winds (DWs), providing a solution to the angular momentum problem in disk accretion for star formation. In the jet system HH 212, a rotating outflow was detected in SO around an episodic jet detected in SiO. Here we spatially resolve this SO outflow into three components: a collimated jet aligned with the SiO jet, the wide-angle disk outflow, and an evacuated cavity in between created by a large jet-driven bow shock. Although it was theoretically predicted, this is the first time that such a jet-DW interaction has been directly observed and resolved, and it is crucial for the proper interpretation and modeling of non-resolved DW candidates. The resolved kinematics and brightness distribution both support the wide-angle outflow to be an extended MHD DW dominating the local angular momentum extraction out to 40 au, but with an inner launching radius truncated to ≳4 au. Inside 4 au, where the DW may not exist, the magnetorotational instability might be transporting angular momentum outward. The jet-DW interaction in HH 212, potentially present in other similar systems, opens an entirely new avenue to probe the large-scale magnetic field in protostellar disks.

Keywords: Accretion, Jets, Herbig-Haro objects, Stellar jets, Young stellar objects, Star formation
Discovery of a Candidate Hypervelocity Star Originating from the Sagittarius Dwarf Spheroidal Galaxy. In this Letter, we report the discovery of an intriguing hypervelocity star (HVS; J1443+1453) candidate that is probably from the Sagittarius Dwarf Spheroidal galaxy (Sgr dSph). The star is an old and very metal-poor low-mass main-sequence turn-off star (age ∼14.0 Gyr and [Fe/H] = -2.23 dex) and has a total velocity of ${559.01}_{-87.40}^{+135.07}$ km s-1 in the Galactic rest frame and a heliocentric distance of ${2.90}_{-0.48}^{+0.72}$ kpc. The velocity of J1443+1453 is larger than the escape speed at its position, suggesting that it is a promising HVS candidate. By reconstructing its trajectory in the Galactic potential, we find that the orbit of J1443+1453 intersects closely with that of Sgr dSph ${37.8}_{-6.0}^{+4.6}$ Myr ago, when the latter has its latest pericentric passage through the Milky Way. The encounter occurs at a distance ${2.42}_{-0.77}^{+1.80}$ kpc from the center of Sgr dSph, a distance that is smaller than the size of the Sgr dSph. The chemical properties of this star are also consistent with those of an Sgr dSph-associated globular cluster, or of the Sgr stream member stars. Our finding suggests that J1443+1453 is an HVS that is either tidally stripped from the Sgr dSph or ejected from the Sgr dSph by the gravitational slingshot effect, requiring a (central) massive/intermediate-mass black hole or a (central) massive primordial black hole in the Sgr dSph.

Keywords: Hypervelocity stars, Chemical abundances, Galaxy stellar halos, Galaxy kinematics, Sagittarius dwarf spheroidal galaxy
Extending the Frequency Reach of Pulsar Timing Array-based Gravitational Wave Search without High-cadence Observations. Gravitational wave (GW) searches using pulsar timing arrays (PTAs) are assumed to be limited by the typical average observational cadence of 1/(2 weeks) for a single pulsar to GW frequencies ≲4 × 10-7 Hz. We show that this assumption is incorrect and that a PTA can detect signals with much higher frequencies, which are preserved in the data due to aliasing, by exploiting asynchronous observations from multiple pulsars. This allows an observation strategy that is scalable to future large-scale PTAs containing O(103) pulsars, enabled by the Five-hundred meter Aperture Spherical Telescope and the Square Kilometer Array, without requiring a higher per-pulsar observation cadence. We show that higher frequency GW observations, reaching up to 4 × 10-4 Hz with an Square Kilometer Array-era PTA, have significant astrophysical implications, such as (i) a three orders of magnitude better constraint than current high-cadence observations on GW strain in the [10, 400] μHz band, and (ii) sensitive tests of the no-hair theorem in the mass range of supermassive black hole binaries using their inspiral, merger, and ringdown signals.

Keywords: Gravitational wave astronomy, Pulsar timing method
Reconnection-driven Particle Acceleration in Relativistic Shear Flows. Particle energization in shear flows is invoked to explain nonthermal emission from the boundaries of relativistic astrophysical jets. Yet the physics of particle injection, i.e., the mechanism that allows thermal particles to participate in shear-driven acceleration, remains unknown. With particle-in-cell simulations, we study the development of Kelvin-Helmholtz (KH) instabilities seeded by the velocity shear between a relativistic magnetically dominated electron-positron jet and a weakly magnetized electron-ion ambient plasma. We show that, in their nonlinear stages, KH vortices generate kinetic-scale reconnection layers, which efficiently energize the jet particles, thus providing a first-principles mechanism for particle injection into shear-driven acceleration. Our work lends support to spine-sheath models of jet emission—with a fast core/spine surrounded by a slower sheath—and can explain the origin of radio-emitting electrons at the boundaries of relativistic jets.

Keywords: Non-thermal radiation sources, Relativistic jets, Plasma astrophysics, High energy astrophysics
Bounds on Velocity-dependent Dark Matter-Proton Scattering from Milky Way Satellite Abundance. We use the latest measurements of the Milky Way satellite population from the Dark Energy Survey and Pan-STARRS1 to infer the most stringent astrophysical bound to date on velocity-dependent interactions between dark matter particles and protons. We model the momentum-transfer cross section as a power law of the relative particle velocity v with a free normalizing amplitude, σMT = σ0vn, to broadly capture the interactions arising within the nonrelativistic effective theory of dark matter-proton scattering. The scattering leads to a momentum and heat transfer between the baryon and dark matter fluids in the early universe, ultimately erasing structure on small physical scales and reducing the abundance of low-mass halos that host dwarf galaxies today. From the consistency of observations with the cold collisionless dark matter paradigm, using a new method that relies on the most robust predictions of the linear perturbation theory, we infer an upper limit on σ0 of 1.4 × 10-23, 2.1 × 10-19, and 1.0 × 10-12 cm2, for interaction models with n = 2, 4, and 6, respectively, for a dark matter particle mass of 10 MeV. These results improve observational limits on dark matter-proton scattering by orders of magnitude and thus provide an important guide for viable sub-GeV dark matter candidates.

Keywords: Galaxy dark matter halos, Dark matter
Atmosphere Escape Inferred from Modeling the Hα Transmission Spectrum of WASP-121b. The escaping atmospheres of hydrogen driven by stellar X-ray and extreme ultraviolet (XUV) have been detected around some exoplanets by the excess absorption of Lyα in the far-ultraviolet band. In the optical band the excess absorption of Hα is also found by ground-based instruments. However, it is not certain if the escape of the atmosphere driven by XUV can result in such absorption. Here we present the XUV-driven hydrodynamic simulation coupled with the calculation of detailed level population and the process of radiative transfer for WASP-121b. Our fiducial model predicts a mass-loss rate of ∼1.28 × 1012 g s-1 for WASP-121b. Due to the high temperature and Lyα intensity predicted by the fiducial model, many hydrogen atoms are populated into the first excited state. As a consequence, the transmission spectrum of Hα simulated by our model is broadly consistent with the observation. Compared with the absorption of Hα at different observation times, the stellar XUV emission varies in the range of 0.5-1.5 times fiducial value, which may reflect the variation of the stellar activity. Finally, we find that the supersonic regions of the planetary wind contribute a prominent portion to the absorption of Hα by comparing the equivalent width of Hα, which hints that a transonic outflow of the upper atmosphere driven by XUV irradiation of the host star can be detected by a ground-based telescope and that Hα can be a good indicator of escaping atmosphere.

Keywords: Upper atmosphere, Hot Jupiters, Exoplanets, Stellar activity, Atmospheric composition, Stellar spectral lines, Exoplanet atmospheres
Search for Black Hole Merger Families. The origin, environment, and evolution of stellar-mass black hole (BH) binaries are still a mystery. One of the proposed binary formation mechanisms is manifest in dynamical interactions between multiple BHs. A resulting framework of these dynamical interactions is the so-called hierarchical triple-merger scenario, which happens when three BHs become gravitationally bound, causing two successive BH mergers to occur. In such successive mergers, the BHs involved are directly related to each other, and hence this channel can be directly tested from the properties of the detected binary BH mergers. Here we present a search for hierarchical triple mergers among events within the first and second gravitational-wave transient catalogs of the Laser Interferometer Gravitational-Wave Observatory/Virgo, the eccentric localization of GW190521, and those found by the IAS-Princeton group. The search includes improved statistical quantification that also accounts for BH spins. We perform our analysis for different upper bounds on the mass distribution of first-generation BHs. Our results demonstrate the importance of the mass distributions' properties for constraining the hierarchical merger scenario. We present the individually significant merger pairs. The search yields interesting candidate families and hints of its future impact.

Keywords: Gravitational wave astronomy, Gravitational wave sources, Astrophysical black holes
Golden Galactic Binaries for LISA: Mass-transferring White Dwarf Black Hole Binaries. We study the evolution and gravitational wave emission of white dwarf-black hole accreting binaries with a semianalytical model. These systems will evolve across the mHz gravitational wave frequency band and potentially be detected by the Laser Interferometer Space Antenna (LISA). We identify new universal relations for this class of binaries, which relate the component masses to the gravitational wave frequency and its first derivative. Combined with the high precision measurements possible with LISA, these relations could allow us to infer the component masses and the luminosity distance of the source. LISA has therefore the potential to detect and characterize a virtually unexplored binary population.

Keywords: Accretion, White dwarf stars, Compact binary stars, Gravitational waves, Astrophysical black holes
Formation of Massive Star Clusters by Fast H I Gas Collision. Young massive clusters (YMCs) are dense aggregates of young stars, which are essential to galaxy evolution, owing to their ultraviolet radiation, stellar winds, and supernovae. The typical mass and radius of YMCs are M ∼ 104 M⊙ and R ∼ 1 pc, respectively, indicating that many stars are located in a small region. The formation of YMC precursor clouds may be difficult because a very compact massive cloud should be formed before stellar feedback blows off the cloud. Recent observational studies suggest that YMCs can be formed as a consequence of the fast H I gas collision with a velocity of ∼100 km s-1, which is the typical velocity of the galaxy-galaxy interaction. In this study, we examine whether the fast H I gas collision triggers YMC formation using three-dimensional magnetohydrodynamics simulations, which includes the effects of self-gravity, radiative cooling/heating, and chemistry. We demonstrate that massive gravitationally bound gas clumps with M &gt; 104 M⊙ and L ∼ 4 pc are formed in the shock compressed region induced by the fast H I gas collision, in which massive gas clumps can evolve into YMCs. Our results show that the YMC precursors are formed by the global gravitational collapse of molecular clouds, and YMCs can be formed even in low-metal environments, such as the Magellanic Clouds. Additionally, the very massive YMC precursor cloud, with M &gt; 105 M⊙, can be created when we consider the fast collision of H I clouds, which may explain the origin of the very massive stellar cluster R136 system in the Large Magellanic Cloud.

Keywords: Star formation, Young star clusters