Sazuna/UAT_keywords huggingface dataset:
Massive Star Formation Starts in Subvirial Dense Clumps Unless Resisted by Strong Magnetic Fields. Knowledge of the initial conditions of high-mass star formation is critical for theoretical models, but are not well observed. Built on our previous characterization of a Galaxy-wide sample of 463 candidate high-mass starless clumps (HMSCs), here we investigate the dynamical state of a representative subsample of 44 HMSCs (radii 0.13–1.12 pc) using Green Bank Telescope NH3 (1,1) and (2,2) data from the Radio Ammonia Mid-Plane Survey pilot data release. By fitting the two NH3 lines simultaneously, we obtain velocity dispersion, gas kinetic temperature, NH3 column density and abundance, Mach number, and virial parameter. Thermodynamic analysis reveals that most HMSCs have Mach number &lt;5, inconsistent with what have been considered in theoretical models. All but one (43 out of 44) of the HMSCs are gravitationally bound with virial parameter α vir &lt; 2. Either these massive clumps are collapsing or magnetic field strengths of 0.10–2.65 mG (average 0.51 mG) would be needed to prevent them from collapsing. The estimated B-field strength correlates tightly with density,  Best/mG=0.269(nH2/104cm‑3)0.61 , with a similar power-law index as found in observations but a factor of 4.6 higher in strength. For the first time, the initial dynamical state of high-mass formation regions has been statistically constrained to be subvirial, in contradiction to theoretical models in virial equilibrium and in agreement with the lack of observed massive starless cores. The findings urge future observations to quantify the magnetic field support in the prestellar stage of massive clumps, which has rarely been explored so far, toward a full understanding of the physical conditions that initiate massive star formation.

Keywords: Infrared dark clouds, Star forming regions, Interstellar magnetic fields, Star formation, Interstellar medium
Lava Worlds Surface Measurements at High Temperatures. First measurements of the emission of lava worlds with the James Webb Space Telescope (JWST) probe the conditions on worlds so hot that their surfaces are likely molten or partially molten. These observations provide a unique opportunity to explore rocky planets' evolution. Surfaces of lava world exoplanets can give insights into their composition and their interior workings. However, data of spectral emissivity of a wide range of potential exoplanet surface compositions and temperatures is required to understand JWST data. Here, we chose eight synthetic, potential exoplanet surfaces that span a wide range of chemical compositions to provide observers with a tool for the interpretation of JWST data for the exploration of lava worlds. We present the measured infrared emissivity spectra (2.5–20 μm) of these materials for temperatures between 800° C and 1350° C. Our data comprise the first spectral library of possible high-temperature exoplanet surfaces. From these measurements, we establish the link between composition and a strong spectral feature at around 9 μm, the Christiansen frequency (CF) for different temperatures. Additionally, we report that the shift in the CF associated with the bulk composition of the material is significantly more important than its temperature. This provides a critical tool to aid in interpreting future spectra of lava worlds that will be collected by the JWST and future missions.

Keywords: Exoplanet surfaces, Infrared spectroscopy, Exoplanets, Exoplanet surface composition
A Pileup of Coronal Mass Ejections Produced the Largest Geomagnetic Storm in Two Decades. The largest geomagnetic storm in two decades occurred in 2024 May with a minimum D st of ‑412 nT. We examine its solar and interplanetary origins by combining multipoint imaging and in situ observations. The source active region, NOAA AR 13664, exhibited extraordinary activity and produced successive halo eruptions, which were responsible for two complex ejecta observed at the Earth. In situ measurements from STEREO A, which was 12.°6 apart, allow us to compare the "geo-effectiveness" at the Earth and STEREO A. We obtain key findings concerning the formation of solar superstorms and how mesoscale variations of coronal mass ejections affect geo-effectiveness: (1) the 2024 May storm supports the hypothesis that solar superstorms are "perfect storms" in nature, i.e., a combination of circumstances resulting in an event of an unusual magnitude; (2) the first complex ejecta, which caused the geomagnetic superstorm, shows considerable differences in the magnetic field and associated "geo-effectiveness" between the Earth and STEREO A, despite a mesoscale separation; and (3) two contrasting cases of complex ejecta are found in terms of the geo-effectiveness at the Earth, which is largely due to different magnetic field configurations within the same active region.

Keywords: Shocks, Solar wind, Solar coronal mass ejections, Solar-terrestrial interactions
Late Jets, Early Sparks: Illuminating the Premaximum Bumps in Superluminous Supernovae. Superluminous supernovae (SLSNe) radiate ≳10–100 times more energy than ordinary stellar explosions, implicating a novel power source behind these enigmatic events. One frequently discussed source, particularly for hydrogen-poor (Type I) SLSNe, is a central engine such as a millisecond magnetar or accreting black hole. Both black hole and magnetar engines are expected to channel a fraction of their luminosity into a collimated relativistic jet. Using 3D relativistic hydrodynamical simulations, we explore the interaction of a relativistic jet, endowed with a luminosity L  j  ≈ 1045.5 erg s‑1 and duration t eng ≈ 10 days compatible with those needed to power SLSNe, launched into the envelope of the exploding star. The jet successfully breaks through the expanding ejecta, and its shocked cocoon powers ultraviolet/optical emission lasting several days after the explosion and reaching a peak luminosity ≳1044 erg s‑1, corresponding to a sizable fraction of L j . This high radiative efficiency is the result of the modest adiabatic losses the cocoon experiences owing to the low optical depths of the enlarged ejecta at these late times, e.g., compared to the more compact stars in gamma-ray bursts. The luminosity and temperature of the cocoon emission match those of the "bumps" in SLSN light curves observed weeks prior to the optical maximum in many SLSNe. Confirmation of jet breakout signatures by future observations (e.g., days-long to weeks-long internal X-ray emission from the jet for on-axis observers, spectroscopy confirming large photosphere velocities v/c ≳ 0.1, or detection of a radio afterglow) would offer strong evidence for central engines powering SLSNe.

Keywords: Type Ic supernovae, Gamma-ray bursts, Jets, Near ultraviolet astronomy, Optical astronomy, Type Ib supernovae, Visible sources, Relativistic jets, Transient sources, Ultraviolet astronomy, Transient detection, Ultraviolet transient sources
JWST/NIRISS Reveals the Water-rich "Steam World" Atmosphere of GJ 9827 d. With sizable volatile envelopes but smaller radii than the solar system ice giants, sub-Neptunes have been revealed as one of the most common types of planet in the galaxy. While the spectroscopic characterization of larger sub-Neptunes (2.5–4 R ⊕) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6–2.5 R ⊕) could either host thin, rapidly evaporating, hydrogen-rich atmospheres or be stable, metal-rich "water worlds" with high mean molecular weight atmospheres and a fundamentally different formation and evolutionary history. Here, we present the 0.6–2.8 μm JWST/NIRISS/SOSS transmission spectrum of GJ 9827 d, the smallest (1.98 R ⊕) warm (T eq,A=0.3 ∼ 620 K) sub-Neptune where atmospheric absorbers have been detected to date. Our two transit observations with NIRISS/SOSS, combined with the existing HST/WFC3 spectrum, enable us to break the clouds–metallicity degeneracy. We detect water in a highly metal-enriched "steam world" atmosphere (O/H of ∼4 by mass and H2O found to be the background gas with a volume mixing ratio of &gt;31%). We further show that these results are robust to stellar contamination through the transit light source effect. We do not detect escaping metastable He, which, combined with previous nondetections of escaping He and H, supports the steam atmosphere scenario. In water-rich atmospheres, hydrogen loss driven by water photolysis happens predominantly in the ionized form, which eludes observational constraints. We also detect several flares in the NIRISS/SOSS light curves with far-UV energies of the order of 1030 erg, highlighting the active nature of the star. Further atmospheric characterization of GJ 9827 d probing carbon or sulfur species could reveal the origin of its high metal enrichment.

Keywords: Exoplanet atmospheric composition , Planetary atmospheres, Exoplanet astronomy, Exoplanet structure, Exoplanet atmospheres, Exoplanet atmospheric evolution
JWST/NIRCam 4─5 μm Imaging of the Giant Planet AF Lep b. With a dynamical mass of 3 M Jup, the recently discovered giant planet AF Lep b is the lowest-mass imaged planet with a direct mass measurement. Its youth and spectral type near the L/T transition make it a promising target to study the impact of clouds and atmospheric chemistry at low surface gravities. In this work, we present JWST/NIRCam imaging of AF Lep b. Across two epochs, we detect AF Lep b in F444W (4.4 μm) with signal-to-noise ratios of 9.6 and 8.7, respectively. At the planet's separation of 320 mas during the observations, the coronagraphic throughput is ≍7%, demonstrating that NIRCam's excellent sensitivity persists down to small separations. The F444W photometry of AF Lep b affirms the presence of disequilibrium carbon chemistry and enhanced atmospheric metallicity. These observations also place deep limits on wider-separation planets in the system, ruling out 1.1 M Jup planets beyond 15.6 au (0.″58), 1.1 M Sat planets beyond 27 au (1″), and 2.8 M Nep planets beyond 67 au (2.″5). We also present new Keck/NIRC2   imaging of AF Lep b; combining this with the two epochs of F444W photometry and previous Keck   photometry provides limits on the long-term 3─5 μm variability of AF Lep b on timescales of months to years. AF Lep b is the closest-separation planet imaged with JWST to date, demonstrating that planets can be recovered well inside the nominal (50% throughput) NIRCam coronagraph inner working angle.

Keywords: James Webb Space Telescope, Direct imaging, Extrasolar gaseous giant planets, Exoplanet atmospheres
Monster Shocks, Gamma-Ray Bursts, and Black Hole Quasi-normal Modes from Neutron-star Collapse. We perform the first magnetohydrodynamic simulation tracking the magnetosphere of a collapsing magnetar. The collapse is expected for massive rotating magnetars formed in merger events and may occur many hours after the merger. Our simulation suggests a novel mechanism for a gamma-ray burst (GRB), which is uncollimated and forms a delayed high-energy counterpart of the merger gravitational waves. The simulation shows that the collapse launches an outgoing magnetospheric shock, and a hot magnetized outflow forms behind the shock. The outflow is baryon free and uncollimated, and its power peaks on a millisecond timescale. Then, the outflow becomes modulated by the ring-down of the nascent black hole, imprinting its kilohertz quasi-normal modes on the GRB tail.

Keywords: Neutron stars, Black hole physics, Gamma-ray bursts, Plasma astrophysics, General relativity, Magnetars, Magnetohydrodynamical simulations
Sun-as-a-star Analysis of the X1.6 Flare on 2023 August 5: Dynamics of Postflare Loops in Spatially Integrated Observational Data. Postflare loops are loop-like plasmas observed during the decay phase of solar flares, and they are expected to exist for stellar flares. However, it is unclear how postflare loops are observed in stellar flares' cases. To clarify behaviors of postflare loops in spatially integrated data, we performed the Sun-as-a-star analysis of the X1.6 flare that occurred on 2023 August 5, using GOES X-ray flux (∼107 K), extreme ultraviolet (EUV) images taken by Atmospheric Imaging Assembly on board the Solar Dynamic Observatory (≥104.9 K), and Hα data taken by Solar Dynamics Doppler Imager on board the Solar Magnetic Activity Research Telescope at Hida Observatory, Kyoto University (∼104 K). As a result, we found that this flare showed signatures corresponding to the important dynamics of the postflare loops even in the spatially integrated data: (1) The Hα light curve showed two distinct peaks corresponding to the flare ribbons and the postflare loops. The plasma cooling in the postflare loops generated different peak times in soft X-rays, EUV, and Hα light curves. (2) Downflows were confirmed as simultaneous redshifted/blueshifted absorptions in the Hα spectra. (3) The apparent rise of postflare loops was recognized as a slowing of the decay for the Hα light curve. These results are the key to investigating stellar postflare loops with spatially integrated data. We also discuss the dependence of our results on flare locations and their possible applications to stellar observations.

Keywords: Solar flares, Stellar flares
The AMS-02 Cosmic-Ray Deuteron Flux is Consistent with a Secondary Origin. The recent measurements of cosmic-ray (CR) deuteron fluxes by AMS-02 show that the rigidity dependence of deuterons is similar with that of protons but flatter than 3He, which has been attributed to the existence of primary deuterons with abundance much higher than that from the Big Bang nucleosynthesis. The requirement of highly deuteron-abundant sources imposes a serious challenge to modern astrophysics since there is no known process to produce a large amount of deuterons without violating other constraints. In this work we demonstrate that the fragmentation of heavy nuclei up to nickel plays a crucial role in shaping/enhancing the spectrum/flux of the CR deuterons. Based on the latest CR data, the predicted secondary fluxes of deuterons and 3He are found to be reasonably consistent with the AMS-02 measurements, and a primary deuteron component is not needed. The observed differences between the spectra of D and 3He, as well as those between the D/4He (D/p) and 3He/4He (3He/p) flux ratios, measured in the rigidity space, is probably due to the kinetic-energy-to-rigidity conversion and the solar modulation, given different charge-to-mass ratios of D and 3He. More precise measurements of the fragmentation cross sections of various nuclei to produce deuterons, tritons, and 3He in a wide energy range will be very helpful in further testing the secondary origin of cosmic-ray deuterons.

Keywords: Galactic cosmic rays, Secondary cosmic rays
Constraining the Properties of the Multicomponent Local Interstellar Medium: MHD-kinetic Modeling Validated by Voyager and New Horizons Data. We introduce the first solar-cycle simulations from our 3D, global MHD-plasma/kinetic-neutrals model, where both hydrogen and helium atoms are treated kinetically, while electrons and helium ions are described as individual fluids. Using Voyager/PWS observations of electron density up to 160 au from the Sun for validation of several different global models, we conclude that the current estimates for the proton density in the local interstellar medium (LISM) need a revision. Our findings indicate that the commonly accepted value of 0.054 cm‑3 may need to be increased to values exceeding 0.07 cm‑3. We also show how different assumptions regarding the proton velocity distribution function in the outer heliosheath may affect the global solution. A new feature revealed by our simulations is that the helium ion flow may be significantly compressed and heated in the heliotail at heliocentric distances exceeding ∼400 au. Additionally, we identify a Kelvin–Helmholtz instability at the boundary of the slow and fast solar wind in the inner heliosheath, which acts as a driver of turbulence in the heliotail. These results are crucial for inferring the properties of the LISM and of the global heliosphere structure.

Keywords: Heliopause, Astrosphere interstellar medium interactions, Heliosphere, Interstellar plasma, Interstellar medium, Charge exchange ionization
Mitigating the Binary Viewing Angle Bias for Standard Sirens. The inconsistency between experiments in the measurements of the local Universe expansion rate, the Hubble constant, suggests unknown systematics in the existing experiments or new physics. Gravitational-wave standard sirens, a method to independently provide direct measurements of the Hubble constant, have the potential to address this tension. Before that, it is critical to ensure there are no substantial systematics in the standard siren method. A significant systematic has been identified when the viewing angle of the gravitational-wave sources, the compact binary coalescences, was inferred inaccurately from electromagnetic observations of the sources. Such a systematic has led to a more than 10% discrepancy in the standard siren Hubble constant measurements with the observations of binary neutron star merger, GW170817. In this Letter, we develop a new formalism to infer and mitigate this systematic. We demonstrate that the systematic uncertainty of the Hubble constant measurements can be reduced to a level smaller than their statistical uncertainty with 5, 10, and 20 binary neutron star merger observations. We show that our formalism successfully reduces the systematics even if the shape of the biased viewing angle distribution does not follow precisely the model we choose. Our formalism ensures unbiased standard siren Hubble constant measurements when the binary viewing angles are inferred from electromagnetic observations.

Keywords: Neutron stars, Gravitational waves, Cosmological parameters
Temporally Resolved Type III Solar Radio Bursts in the Frequency Range 3–13 MHz. Radio observations from space allow to characterize solar radio bursts below the ionospheric cutoff, which are otherwise inaccessible, but suffer from low, insufficient temporal resolution. In this Letter we present novel, high-temporal resolution observations of type III solar radio bursts in the range 3–13 MHz. A dedicated configuration of the Radio and Plasma Waves (RPW) High Frequency Receiver (HFR) on the Solar Orbiter mission, allowing for a temporal resolution as high as ∼0.07 s (up to 2 orders of magnitude better than any other spacecraft measurements), provides for the very first time resolved measurements of the typical decay time values in this frequency range. The comparison of data with different time resolutions and acquired at different radial distances indicates that discrepancies with decay time values provided in previous studies are only due to the insufficient time resolution not allowing to accurately characterize decay times in this frequency range. The statistical analysis on a large sample of ∼500 type III radio bursts shows a power low decay time trend with a spectral index of ‑0.75 ± 0.03 when the median values for each frequency are considered. When these results are combined with previous observations, referring to frequencies outside the considered range, a spectral index of ‑1.00 ± 0.01 is found in the range ∼0.05–300 MHz, compatible with the presence of radio-wave scattering between 1 and 100 R ☉.

Keywords: Radio bursts, Solar radio emission, Radio receivers
Impacts of Extreme Ultraviolet Late Phase of the Solar Flare on Ionospheric Electrodynamics. Previous investigations of ionospheric electrodynamical responses to solar flares primarily focused on the main phases (MPs) of solar flares. Typical solar irradiance models for driving global ionosphere models do not include the extreme ultraviolet (EUV) late phase (ELP) of flares, which was recently observed with new high-quality solar EUV spectra. Thus, it is still unclear how ionospheric electrodynamics respond to the flare ELP. Here, we analyzed the ionospheric electrodynamical response to the MP and ELP of the X9.3 flare on 2017 September 6, using observations from ground magnetometers, along with simulation results from an ionosphere–thermosphere coupled model. Observations indicated an intensification of the dayside eastward equatorial electrojet (EEJ) by approximately 12 nT at the ELP peak as compared to the quiet day reference. Additionally, the dayside eastward electric field increased due to the ELP, which is different from the reduction of dayside electric fields during MP. The upward E × B plasma drifts decreased by 2.5 m s–1 during MP but increased by 0.75 m s–1 during the ELP. Altitude-dependent responses of ionospheric conductivities to the ELP modulated the relative contribution of the E- and F-region wind dynamo to zonal electric fields, resulting in an overall increase in the daytime eastward electric fields. Furthermore, combined effects of electric fields and conductivities enhancements contributed to EEJ intensification during the ELP. This study enhances our understanding of how solar flares with ELP change global ionospheric electric fields and currents.

Keywords: Solar flares, Solar flare spectra, Solar extreme ultraviolet emission, Earth ionosphere
Lyman Continuum Leakers at z &gt; 3 in the GOODS-S Field: Starburst or Not?. We investigate the star-forming properties of 23 Lyman continuum (LyC) leakers at z &gt; 3 in the Great Observatories Origins Deep Survey-South field based on a systematic review of LyC observations from the literature. Using data from the Hubble Space Telescope and the James Webb Space Telescope, we construct the spectral energy distributions for these LyC leakers, covering the spectrum from rest-frame ultraviolet to near-infrared. Through the application of a unified modeling approach, we measure the ultraviolet slope (β), star formation rate, and stellar mass for these LyC leakers in a consistent manner. These high-redshift LyC leakers demonstrate statistically blue UV-continuum slopes (β), which is consistent with their high escape fraction of LyC photons. We find that these high-redshift LyC leakers span a wide range of specific star formation rate ( log(sSFR /yr) from ‑8.6 to ‑6.7). Ten of these LyC leakers are located on the star formation main sequence, instead of all being in the starburst mode. The results indicate that intense bursts of star formation are not necessarily required for the leakage of LyC photons for galaxies at z &gt; 3.

Keywords: Galaxies
Mechanism of Circular Polarization in Giant Pulses and Fast Radio Bursts. Some giant pulses and fast radio bursts (FRBs) exhibit notable circular polarization, which remains unexplained and carries significant implications for their emission mechanisms. In this study, we identify multiple nanoshot pairs uniformly spaced by approximately 21 μs within a giant pulse emitted by the Crab pulsar. Among these pairs, a subset displays left-hand and right-hand circular polarization in two distinct nanoshots. We propose that the occurrence of such nanoshot pairs with dual circular polarizations arises from the fragmentation of a linearly polarized nanoshot along the magnetic field lines under the extreme Faraday effect, leveraging highly asymmetrical pair plasma and the ultra-intense field of nanoshots. The asymmetry in pair plasmas is likely linked to discharge activities in pulsars. Moreover, the intense field of nanoshots induces cyclotron resonance within the magnetosphere, effectively slowing down the propagation velocity of the circularly polarized mode. Our findings suggest that Crab giant pulses composing nanoshots originate in its polar cap region and escape the magnetosphere along the polar magnetic field. This mechanism can also elucidate the origin of circular polarization in some FRBs and thus lends support to their magnetospheric origin.

Keywords: Radio bursts, Plasma astrophysics, Radio pulsars, Radio transient sources