Sazuna/UAT_keywords huggingface dataset:
Spectral Features of the Energy-containing Range and the Inertial Range in Fast Solar Wind Turbulence. Power spectra of the fluctuations provide a baseline to interpret the solar wind turbulence in the magnetohydrodynamic scale. The magnetic spectra show a typical index of ‑1 in the low-frequency range, which is regarded as the energy-containing region. Recent studies show that it can be much shallower than 1/f in the near-Sun solar wind, indicating that there is a dynamic origin for the 1/f range formation. However, the nature of the energy-containing range remains unanswered. Here we investigate 97 fast solar wind intervals, each with time durations ≥2 days at 1 au observed by the Wind spacecraft from 2005 to 2018. We perform the spectral analyses and find that the spectral index in the energy-containing range is ‑0.78 ± 0.22 for the magnetic field and ‑1.49 ± 0.30 for the velocity. To compare, the spectral index in the inertial range is ‑1.60 ± 0.04 for the magnetic field and ‑1.51 ± 0.04 for the velocity. In both ranges, the indices for the magnetic field and the velocity are correlated. The cross helicity σc grows to the saturation level before the break between the two ranges. The saturation level is correlated with the magnetic spectral index in the inertial range and the velocity spectral index in the energy-containing range. Our findings provide new clues for the origin of the energy source and help understand the evolution from the energy-containing range to the inertial range.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Solar wind, Fast solar wind
Radiation Signatures of Electron Acceleration in the Decelerating Jet of MAXI J1348-630. A discrete jet component (blob) ejection and its subsequent deceleration were observed in the 2019/2020 outburst of the low-mass X-ray binary MAXI J1348-630. A first kinematic analysis of the deceleration due to an abrupt transition from an evacuated cavity to the interstellar medium (ISM) suggested a kinetic energy exceeding 1046 erg, surpassing estimates of the available total ejection energy. However, incorporating a transition layer with exponential density growth between the cavity and the ISM recently enabled a kinematic analysis with much more realistic energy requirements of approximately 1044 erg. Here, we study the expected radiative signatures of electrons accelerated within the decelerating blob by introducing a model akin to the relativistic blast wave model for gamma-ray bursts, considering radiative energy losses and radiation drag, to simulate the deceleration of a relativistically moving plasmoid. This model yields snapshot spectral energy distributions and multiwavelength light curves from synchrotron and synchrotron-self-Compton emission. Notably, the synchrotron emission peaks in the X-rays, but the predicted X-ray flux is negligible compared to thermal emission from the accretion disk. The predicted radio light curve closely resembles the observed one during the jet deceleration phase following the outburst in 2019/2020.

Keywords: X-ray binary stars, Relativistic jets
Loop I/NPS Morphology Predictions in the Ultralong-wavelength Band. Loop I/North Polar Spur (NPS) is the giant arc structure above the Galactic plane observed at radio wavelengths (≲10 GHz). There has been long-standing debate about its origin. While many people believe that it consists of nearby supernova remnants (SNRs), some others consider it as a giant bubble close to the Galactic Center (GC), associated with the Fermi Bubble and the eROSITA X-ray bubble. At ultralong wavelengths (wavelength ≳10 m or frequency ≲30 MHz), particularly below ∼10 MHz, the free–free absorption of the radio signal by diffuse electrons in the interstellar medium (ISM) becomes significant, resulting in different sky morphologies from those at higher frequencies. In this paper, we develop emissivity models for the two Loop I/NPS origin scenarios, and predict the Loop I/NPS morphology at ultralong wavelengths in both scenarios, taking into account the free–free absorption effect. We find that in the SNRs model, the full Loop I/NPS will still be a bright arc, even at ∼1 MHz. In the GC model, the arc is fully visible only above ∼3 MHz. While below this frequency, it is visible only at Galactic latitudes b ≳ 30°; the b ≲ 30° part becomes invisible due to the absorption by the ISM electrons between the GC and the Sun. The upcoming space missions aiming at ultralong wavelengths, such as the Discovering Sky at the Longest wavelength and the Farside Array for Radio Science Investigations of the Dark ages and Exoplanets, can potentially distinguish these two scenario and provide decisive information about the origin of the Loop I/NPS.

Keywords: Interstellar plasma, Interstellar absorption, Interstellar medium, Radio interferometers, Milky Way Galaxy
An Increase in the Prevalence of Ionized Outflows in Galaxies with Coronal Line Emission: Feedback in Action?. Coronal lines (CLs), which arise from collisionally excited forbidden transitions from highly ionized species, are a powerful diagnostic tool in uncovering active galactic nuclei (AGNs) and constraining their properties. However, recent optical surveys are finding that coronal lines are rarely detected in the majority of local AGNs, possibly as a result of the depletion of elements from the interstellar gas onto dust grains. Prominent CL emission may therefore only arise when dust is being destroyed in the highly ionized gas in AGNs. To explore the possibility that dust destruction may be caused by ionized gas outflows in galaxies with prominent CLs, we present the first large-scale systematic study of ionized outflows, as traced by the [O III] λ5007 emission, in galaxies displaying CL emission relative to a robust control sample of non-CL-emitting galaxies. We find that (1) galaxies that display CL emission have a significantly elevated outflow incidence rate compared to their matched controls, (2) the outflow luminosity is significantly higher in the CL emitters, (3) the CL emitters have systematically lower intrinsic extinction toward the ionized gas compared with the controls, and (4) there are significant correlations between the CL luminosity and outflow velocity for the iron CLs, with similar relationships found between the CL FWHM and outflow luminosity. These observations are consistent with dust destruction in an outflowing wind from a dusty torus causing efficient CL emission.

Keywords: Active galactic nuclei, Galaxy winds
Mitigating Polarization Leakage in Gas Pixel Detectors through Hybrid Machine Learning and Analytic Event Reconstruction. Spatially resolved polarization measurements of extended X-ray sources are expanding our understanding of the emission mechanisms and magnetic field properties involved. Such measurements have been possible in the past few years thanks to the Imaging X-ray Polarimetry Explorer (IXPE). However, the analysis of extended sources suffers a systematic effect known as polarization leakage, which artificially affects the measured polarization signal. To address this issue, we built a hybrid reconstruction algorithm, which combines machine learning and analytic techniques to improve the reconstruction of photoelectron tracks in the Gas Pixel Detector and to significantly mitigate polarization leakage. This work presents the first application of this hybrid method to experimental data, including both calibration lab measurements and IXPE observational data. We confirmed the reliable performance of the hybrid method for both cases. Additionally, we demonstrated the algorithm's effectiveness in reducing the polarization leakage effect through the analysis of the IXPE observation of the supernova remnant G21.5-0.9. By enabling more reliable polarization measurements, this method can potentially yield deeper insights into the magnetic field structures, particle acceleration processes, and emission mechanisms at work within extended X-ray sources.

Keywords: Convolutional neural networks, Polarimetry, X-ray sources, X-ray telescopes
A Machine Learning Method for Monte Carlo Calculations of Radiative Processes. Radiative processes such as synchrotron radiation and Compton scattering play an important role in astrophysics. Radiative processes are fundamentally stochastic in nature, and the best tools currently used for resolving these processes computationally are Monte Carlo (MC) methods. These methods typically draw a large number of samples from a complex distribution such as the differential cross section for electron–photon scattering, and then use these samples to compute the radiation properties such as angular distribution, spectrum, and polarization. In this work, we propose a machine learning (ML) technique for efficient sampling from arbitrary known probability distributions that can be used to accelerate MC calculation of radiative processes in astrophysical scenarios. In particular, we apply our technique to inverse Compton radiation and find that our ML method can be up to an order of magnitude faster than traditional methods currently in use.

Keywords: Astronomy software, High energy astrophysics, Plasma astrophysics, Computational methods, Radiative processes
Reflection Spectra of Accretion Disks Illuminated by an Off-axis Corona. Relativistic reflection features in the X-ray spectra of accreting black holes are considered to be generated by the illumination of the accretion disk by the hot corona. In this work, we present a numerical method for the emission line profile and the reflection spectrum produced by an off-axis X-ray source. The X-ray source is considered as a point source, as in the lamppost scenario, except that it is located off-axis and moves at arbitrary velocity. The observed flux for the distant observer is calculated directly without priority evaluation of the emissivity on the accretion disk, which allows our model to be applicable to the point source that deviates from the axis of the black hole spins and moves with a velocity. To study the impact of the off-axis geometry on the measurement of source properties, we simulate observations for a black hole binary with NuSTAR and eXTP. We compare the simulation with the observation of the phase-resolved spectra of the low-frequency quasiperiodic oscillation observed by the Insight Hard X-ray Modulation Telescope. Due to the nonaxisymmetric illumination on the accretion disk, parameters of the model are not reproduced by the lamppost model, including the corona height, radial velocity, and the reflection fraction. On the other hand, all the model parameters are recovered through the off-axis model.

Keywords: Black hole physics, X-ray binary stars, High energy astrophysics
Partially Ionized Gas at Equilibrium Powered by Ultraviolet Irradiation. We study the formation of a partially ionized zone behind the usual H II zone in photoionized gas for a density intermediate between ordinary H II regions and active galactic nucleus broad-line regions, and without X-rays. While Lyman continuum photons are depleted before reaching this zone, Balmer continuum photons can ionize the n = 2 hydrogen atoms as those are pumped by scattering-trapped Lyα photons. Lyα photons need to be replenished in a steady state, but fast radiative cooling at high gas temperature makes replenishment through electron collisional excitation of n = 2 inefficient. Independent of the temperature, Raman scattering of incident continuum photons on the Lyman-series damping wings injects Lyα photons in the line core and pumps the n = 2 state, which helps realize a partially ionized equilibrium at 5000–7000 K. Since the ratio between the incident radiation flux and gas density is limited by the dynamic effects of radiation pressure, significant ionization fraction is only realized at densities nH ≳ 107 cm‑3. A large Hα/Hβ line ratio results from such partially ionized gas, as large Balmer line optical depths enhance the n = 3 population relative to higher n states. Partial ionization also provides the ideal condition for internally forming an intense and very broad Lyα line, which can power strong fluorescent metal emission lines observed from the Weigelt blobs of η Carinae in the Galaxy, and from a candidate young super star cluster in the Cosmic Noon Sunburst galaxy. This phenomenon may also have implications for understanding the spectra of high-z galaxies that show unusually dense ionized gas.

Keywords: Interstellar dust, Photoionization, Interstellar atomic gas, Young star clusters, Luminous blue variable stars, Interstellar plasma
Searching for R-process-enhanced Stars in the LAMOST Survey. II. Two New r-II Stars in the Milky Way Disk. R-process-enhanced (RPE) stars are rare and typically metal-poor ([Fe/H] &lt; ‑1.0), primarily found in the Milky Way halo system and dwarf galaxies. This study reports the discovery of two relatively bright, highly RPE stars ([Eu/Fe] &gt; +0.70) located in the Milky Way disk, with [Fe/H] of ‑0.34 and ‑0.80, respectively. These two stars are selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope medium-resolution (R ∼ 7500) spectroscopic survey. Follow-up high-resolution (R ∼ 25,000) observations were conducted with the High Optical Resolution Spectrograph installed on the 10.4 m Gran Telescopio Canarias. We perform the determination of elemental abundances and calculate the orbital parameters. We find that they are r-II stars with elemental abundances in agreement with the solar r-process pattern. These two objects are chemically and dynamically consistent with membership in the Galactic disk and exhibit no evidence of being part of accreted systems.

Keywords: Stellar abundances, R-process, Milky Way disk, Nucleosynthesis
FAST Drift-scan Survey for H I Intensity Mapping: Simulation on Hunting H I Filament with Pairwise Stacking. Filaments stand as pivotal structures within the cosmic web. However, direct detection of the cold gas content of the filaments remains challenging owing to its inherently low brightness temperature. With the TNG hydrodynamical simulations, we demonstrate the effectiveness of isolating faint filament H I signal from the FAST H I intensity mapping (IM) survey through pairwise stacking of galaxies, which yields an average H I filament signal amplitude of ∼0.29 μK at z ≃ 0.1. However, our simulations reveal a nonnegligible contribution from H I-rich galaxies within or near the filaments. Particularly, the faint galaxies dominantly contribute to the extra filament H I signal. Our simulation also shows that the measurement uncertainty is produced by both thermal noise and background variation caused by brightness leakage from surrounding random galaxies. Given a fixed total observation time, a wide-field H I IM survey, which includes a large number of galaxy pairs, can simultaneously reduce thermal noise to below the filament signal level and minimize background variation to a negligible level. Through the end-to-end simulation, this work demonstrates the critical role of the galaxy pairwise stacking method in future filament H I detection, outlining a road map for filament H I detection in the next-generation H I IM surveys.

Keywords: Extragalactic astronomy, Intergalactic filaments, Cosmic web, Large-scale structure of the universe
Synchronous and Asynchronous X-Ray Monitoring of FRB 20190520B with the Chandra X-Ray Observatory. We report on X-ray limits on observations of FRB 20190520B during simultaneous observations with the Green Bank Telescope and the Chandra X-ray Observatory. FRB 20190520B is an outlier in the fast radio burst (FRB) population due to its excess source-local dispersion, its association with compact persistent radio emission, and its high line-of-sight magnetic field variability. One radio burst was detected during the overlapping observing time, and no X-ray emission was detected. We find line-of-sight density and burst duration limits on FRB 20190520B's X-ray luminosity, interpreting the nondetection in the context of known X-ray populations that might serve as progenitors for FRB 20190520B. We place a direct limit on the presence of a massive black hole (MBH) in this system, limiting mass and the Eddington ratio λE to   (in a low-density line-of-sight limit) and   (high-density limit). These limits are both inconsistent with the scenario derived by Anna-Thomas et al. in which the FRB is viewed through a MBH wind; however, the model is still allowed if the wind luminosity has an X-ray emission fraction of less than 8%. Our observations would have been sensitive to the brightest ∼15% of the ultraluminous X-ray source (ULX) population and the brightest flares from soft gamma-ray repeaters, but the nondetection is consistent with expectations for SGR 1806-20–like flares, most ULX hypernebula models, and X-ray binaries.

Keywords: X-ray astronomy, Supermassive black holes, Black holes, Soft gamma-ray repeaters, Magnetars, Astrophysical black holes, Radio transient sources
Flux Variations and Torque Reversals of Cen X-3. Cen X-3 is an archetypical X-ray pulsar with strong flux variations and alternating torque reversals, both of which are similar to those of recently discovered pulsating ultraluminous X-ray sources. We study a low state of Cen X-3 that occurred in 2023, lasting for ∼100 days, with Chandra and Insight-HXMT observations, supplemented with MAXI and Fermi Gamma-ray Burst Monitor data. The Chandra spectrum during the eclipse of Cen X-3 in the low state is very similar to that in the high state, especially the Fe lines. The HXMT spectrum in the low state shows an enhanced Fe line, as do the MAXI data. The spin-up/spin-down trends of Cen X-3 are not affected by the low states. All these results indicate that the intrinsic emission in the low states is high, and the low states are just apparently low and are dominated by reprocessed emission. We found that the spin-up to spin-down reversals of Cen X-3 take a longer time than the spin-down to spin-up reversals, which provides a definite observation test of any possible torque-reversal models. We discuss insights from these results for understanding the pulsating ultraluminous X-ray sources.

Keywords: Ultraluminous x-ray sources, High mass x-ray binary stars, X-ray binary stars
Discovery and Timing of Four γ-Ray Millisecond Pulsars. We discovered four millisecond pulsars (MSPs) in searches of 80 γ-ray sources conducted from 2015 to 2017 with the Murriyang radio telescope of the Parkes Observatory. We provide an overview of the survey and focus on the results of a follow-up pulsar timing campaign. Using Fermi Large Area Telescope data, we have detected γ-ray pulsations from all four pulsars, and by combining radio and γ-ray data, we obtain improved timing solutions. We also provide flux density distributions for the radio pulsars and flux-calibrated and phase-aligned radio and γ-ray pulse profiles. Some of the pulsars may be suitable for radio pulsar timing array experiments. PSR J0646–5455, PSR J1803–4719, and PSR J2045–6837 are in typical, nearly circular white dwarf binaries with residual eccentricities proportional to their binary periods. PSR J1833–3840 is a black widow pulsar with the longest known period, Pb = 0.9 day, and a very soft radio spectrum. PSR J0646–5455 has a strong, Vela-like γ-ray pulse profile and is suitable for inclusion in the γ-ray pulsar timing array. Despite this, it is possibly one of the lowest-efficiency γ-ray MSPs known. Indeed, all four new γ-ray MSPs have lower-than-average efficiency, a potential indication of bias in earlier searches. Finally, we retrospectively evaluate the efficiency of this survey: while only four new MSPs were directly discovered, subsequent campaigns have found pulsars in a further 19 of our targets, an excellent 30% efficiency.

Keywords: Gamma-ray sources, Binary pulsars, Radio pulsars, Millisecond pulsars
The Climates and Thermal Emission Spectra of Prime Nearby Temperate Rocky Exoplanet Targets. Over the course of the past decade, advances in radial velocity and transit techniques have enabled the detection of rocky exoplanets in the habitable zones of nearby stars. Future observations with novel methods are required to characterize this sample of planets, especially those that are nontransiting. One proposed method is the Planetary Infrared Excess (PIE) technique, which would enable the characterization of nontransiting planets by measuring the excess IR flux from the planet relative to the star's spectral energy distribution. In this work, we predict the efficacy of future observations using the PIE technique by potential future observatories such as the MIRECLE mission concept. To do so, we conduct a broad suite of 21 general circulation model (GCM) simulations, with ExoCAM, of seven nearby habitable zone targets for three choices of atmospheric composition with varying partial pressure of CO2. We then construct thermal phase curves and emission spectra by post-processing our ExoCAM GCM simulations with the Planetary Spectrum Generator (PSG). We find that all cases have distinguishable carbon dioxide and water features assuming a 90° orbital inclination. Notably, we predict that CO2 is potentially detectable at 15 μm with MIRECLE for at least four nearby known nontransiting rocky planet candidate targets in the habitable zone: Proxima Centauri b, GJ 1061 d, GJ 1002 b, and Teegarden's Star c. Our ExoCAM GCMs and PSG post-processing demonstrate the potential to observationally characterize nearby nontransiting rocky planets and better constrain the potential for habitability in our solar neighborhood.

Keywords: Exoplanet atmospheric dynamics, Planetary atmospheres, Astrobiology, Planetary climates, Exoplanet atmospheres
Stellar- and AGN-driven Outflows in JWST Galaxies at z = 3–9: More Frequent, Wider Opening Angles, and Mostly Bounded. We study outflows in 130 galaxies with ‑22 &lt; MUV &lt; ‑16 at z = 3–9 identified in JWST NIRSpec and NIRCam WFSS data taken by the ERO, CEERS, FRESCO, GLASS, and JADES programs. We identify 30 out of the 130 galaxies with broad components of FWHM ∼ 200–700 km s‑1 in the emission lines of Hα and [O III] that trace ionized outflows. Four out of the 30 outflowing galaxies are Type 1 AGN whose Hα emission lines include line profile components as broad as FWHM ≳ 1000 km s‑1, while one galaxy is identified as a Type 2 AGN by high ionization emission lines. With the velocity shift and line widths of the outflow broad lines, we obtain ∼80–500 km s‑1 for the outflow velocities. We find that the outflow velocities are slower than low-z galaxies with similar star formation rates, which may be explained by the low stellar masses of high-z galaxies. The outflow velocities of AGNs are large but not significantly different from the others. Interestingly, these outflow velocities are typically not high enough to escape from the galactic potentials, possibly suggesting fountain-type outflows. We estimate mass loading factors η to be 0.1–1, which are not particularly large, but comparable with those of z ∼ 1 outflows. The large fraction of galaxies with outflows (30% with high-resolution data) provides constraints on outflow parameters, suggesting a wide opening angle of ≳45° and a large duty cycle of ≳30%, which gives a picture of more frequent and spherical outflows in high-z galaxies.

Keywords: Galaxy fountains, James Webb Space Telescope, Galaxy winds, Galaxy evolution, High-redshift galaxies