Sazuna/UAT_keywords huggingface dataset:
A Data-constrained Analysis for Joule Heating as a Solar Active Region Atmosphere Heating Mechanism. I. Sunspot Umbral Light Bridge. Understanding the mechanisms underlying the heating of the solar atmosphere is a fundamental problem in solar physics. The lower atmosphere of the Sun (i.e., photosphere and chromosphere) is composed of weakly ionized plasma. This results in anisotropic dissipation of electric currents by Coulomb and Cowling resistivities. Joule heating due to dissipation of currents perpendicular to the magnetic field by Cowling resistivity has been demonstrated to be the main mechanism for the heating of a sunspot umbral light bridge located in NOAA AR 12002 on 2014 March 13. Here, we focus on the same target region and demonstrate the importance of further constraining our Joule heating model using observational data in addition to magnetic field, namely plasma temperature calculated from the inversion of spectroscopic data obtained from the Interferometric BI-dimensional Spectrometer instrument of the ground-based Dunn Solar Telescope. As a parameter in our analysis, temperature is demonstrated to have the highest sensitivity after magnetic field. We show that the heating of the light bridge is a highly dynamic event that necessitates utilization of 3D spatially resolved observational data for temperature rather than a 1D temperature stratification based on theoretical/semiempirical solar atmosphere models. Our improved data-constrained analysis using spatially resolved temperatures shows that the entire light bridge is heated by the proposed mechanism, and yields heating rate values that are consistent with our previous study.

Keywords: Solar chromospheric heating, Solar active region magnetic fields, Solar chromosphere
Phase-resolved Spectroscopy of Low-frequency Quasiperiodic Oscillations from the Newly Discovered Black Hole X-Ray Binary Swift J1727.8-1613. Low-frequency quasiperiodic oscillations (LFQPOs) are commonly observed in X-ray light curves of black hole X-ray binaries (BHXRBs); however, their origin remains a topic of debate. In order to thoroughly investigate variations in spectral properties on the quasiperiodic oscillation (QPO) timescale, we utilized the Hilbert–Huang transform technique to conduct phase-resolved spectroscopy across a broad energy band for LFQPOs in the newly discovered BHXRB Swift J1727.8–1613. This is achieved through quasi-simultaneous observations from Neutron Star Interior Composition Explorer, Nuclear Spectroscopic Telescope Array, and Hard X-ray Modulation Telescope. Our analysis reveals that both the nonthermal and disk–blackbody components exhibit variations on the quasiperiodic oscillation (QPO) timescale, with the former dominating the QPO variability. For the spectral parameters, we observe modulation of the disk temperature, spectral indices, and reflection fraction with the QPO phase with high statistical significance (≳5σ). Notably, the variation in the disk temperature is found to precede the variations in the nonthermal and disk fluxes by ∼0.4–0.5 QPO cycles. We suggest that these findings offer further evidence that the type-C QPO variability is a result of geometric effects of the accretion flow.

Keywords: Accretion, Black hole physics, X-ray binary stars, Stellar mass black holes
A Tale of Two Molecules: The Underprediction of CO<SUB>2</SUB> and Overprediction of PH<SUB>3</SUB> in Late T and Y Dwarf Atmospheric Models. The sensitivity and spectral coverage of JWST are enabling us to test our assumptions of ultracool dwarf atmospheric chemistry, especially with regards to the abundances of phosphine (PH3) and carbon dioxide (CO2). In this paper, we use Near Infrared Spectrograph PRISM spectra (∼0.8‑5.5 μm, R ∼ 100) of four late T and Y dwarfs to show that standard substellar atmosphere models have difficulty replicating the 4.1‑4.4 μm wavelength range, as they predict an overabundance of phosphine and an underabundance of carbon dioxide. To help quantify this discrepancy, we generate a grid of models using PICASO, based on the Elf Owl chemical and temperature profiles, where we include the abundances of these two molecules as parameters. The fits to these PICASO models show a consistent preference for orders-of-magnitude higher CO2 abundances and a reduction in PH3 abundance as compared to the nominal models. This tendency means that the claimed phosphine detection in UNCOVER‑BD‑3 could instead be explained by a CO2 abundance in excess of standard atmospheric model predictions; however, the signal-to-noise ratio of the spectrum is not high enough to discriminate between these cases. We discuss atmospheric mechanisms that could explain the observed underabundance of PH3 and overabundance of CO2, including a vertical eddy diffusion coefficient (K zz) that varies with altitude, incorrect chemical pathways, or elements condensing out in forms such as NH4H2PO4. However, our favored explanation for the required CO2 enhancement is that the quench approximation does not accurately predict the CO2 abundance, as CO2 remains in chemical equilibrium with CO after CO quenches.

Keywords: Brown dwarfs, Y dwarfs, Carbon dioxide, Chemical abundances, James Webb Space Telescope, Spectroscopy, Near infrared astronomy
Examining the Nature of the Starless Dark Matter Halo Candidate Cloud-9 with Very Large Array Observations. Observations with the Five-hundred-meter Aperture Spherical Telescope recently detected H I 21 cm emission near M94, revealing an intriguing object, Cloud-9, without an optical counterpart. Subsequent analysis suggests that Cloud-9 is consistent with a gas-rich (M H I ≈ 106 M ⊙), starless, dark matter (DM) halo of mass M 200 ≈ 5 × 109 M ⊙. Using the Karl G. Jansky Very Large Array in D-array configuration, we present interferometric observations of Cloud-9, revealing it as a dynamically cold (W 50 ≈ 12 km s‑1), nonrotating, and spatially asymmetric system, exhibiting gas compression on one side and a tail-like structure toward the other—features likely originating from ram pressure. Our observations suggest Cloud-9 is consistent with a starless ΛCDM DM halo if the gas is largely isothermal. If interpreted as a faint dwarf, Cloud-9 is similar to Leo T, a nearby gas-rich galaxy that would fall below current optical detection limits at Cloud-9's distance (d ≈ 5 Mpc). Further observations with the Hubble Space Telescope reaching magnitudes m  g  ≈ 30 would help identify such a galaxy or dramatically lower the current limits on its stellar mass (M gal ≲ 105 M ⊙). Cloud-9 thus stands as the firmest starless DM halo candidate to date or the faintest galaxy known at its distance.

Keywords: Cosmology, Reionization, Dark matter
Observational Evidence of Particle Acceleration by Relativistic Magnetic Reconnection in Gamma-Ray Bursts. Gamma-ray bursts (GRBs) as the most energetic explosions in the modern universe have been studied for over half a century, but the physics of the particle acceleration and radiation responsible for their observed spectral behaviors are still not well understood. Based on the comprehensive analysis of the pulse properties in both bright GRB 160625B and GRB 160509A, for the first time, we identify evidence of particle acceleration by relativistic magnetic reconnection from the evolutionary behavior of the two spectral breaks E p and E cut. Meanwhile, the adiabatic cooling process of the emitting particles in the magnetic reconnection regions produces a relation between the spectral index and the flux. We also discuss the physics behind spectral energy correlations. Finally, we argue that the identification of an anticorrelation between E cut and L iso may open a new avenue for diagnostics of the physics of the particle acceleration and radiation in a variety of astrophysical sources.

Keywords: Gamma-ray bursts
A New Deep Learning Model to Detect Gamma-Ray Bursts in the AGILE Anticoincidence System. The AGILE space mission was launched in 2007 to study X-ray and gamma-ray astrophysics. AGILE operated in spinning mode from 2009 until 2024 February 14, when it re-entered the Earth's atmosphere. This work uses data acquired from the AGILE anticoincidence system (ACS) from 2019 January 1 to 2022 December 31. The ACS is designed to reject charged background particles. It also detects X-ray photons in the 50–200 KeV energy range and saves each panel count rate in the telemetry as ratemeter data, a time series with a resolution of 1.024 s. We developed a method that uses a deep learning model to predict the background count rates of the AGILE ACS top panel (perpendicular to the pointing direction of the payload detectors) using the satellite's orbital parameters as input. Then, we use the difference between predicted and acquired count rates to detect gamma-ray bursts (GRB). We trained the model with a background-only data set. After the training, the model can predict the ACS count rates with a mean reconstruction error of 3.8%. We used the GRBs listed in the GRBweb catalog to search for significant anomalies in the ACS data. We extracted light curves of 140 bins of 1.024 s for each GRB from the AGILE ACS to cover the trigger time of the GRBs. The model detected 39 GRBs with a significance of σ ≥ 3. The results contain four GRBs detected for the first time in the AGILE data.

Keywords: Convolutional neural networks, Gamma-ray bursts
The Environments of Fast Radio Bursts Viewed Using Adaptive Optics. We present observations from the Gemini Multi-Conjugate Adaptive Optics System/Gemini South Adaptive Optics Imager at Gemini South of five fast radio burst (FRB) host galaxies of FRBs with subarcsecond localizations. We examine and quantify the spatial distributions and locations of the FRBs with respect to their host galaxy light distributions, finding a median host-normalized offset of 2.09 half-light radii (r  e ) and the trend that these FRBs occur in fainter regions of their host galaxies. When combined with the FRB host galaxy sample from Mannings et al., we find that FRBs are statistically distinct from Ca-rich transients in terms of light at the source location and from SGRBs and LGRBs in terms of host-normalized offset. We further find that most FRBs are in regions of elevated local stellar mass surface densities in comparison to the mean global values of their hosts. This, along with the finding that the FRB locations trace the distribution of stellar mass, points toward a possible similarity of the environments of CCSNe and FRBs. We also find that four out of five FRB hosts exhibit distinct spiral arm features, and the bursts originating from such hosts tend to appear on or close to their host's spiral structure, with a median distance of 0.53 ± 0.27 kpc. With many well-localized FRB detections looming on the horizon, we will be able to better characterize the properties of FRB environments relative to their host galaxies and other transient classes. Such insights may only require us to double the number of FRBs with subarcsecond localizations.

Keywords: Galaxy photometry, Radio transient sources
Shocking and Mass Loss of Compact Donor Stars in Type Ia Supernovae. Type Ia supernovae arise from thermonuclear explosions of white dwarfs accreting from a binary companion. Following the explosion, the surviving donor star leaves at roughly its orbital velocity. The discovery of the runaway helium subdwarf star US 708, and seven hypervelocity stars from Gaia data, all with spatial velocities ≳900 km s‑1, strongly support a scenario in which the donor is a low-mass helium star or a white dwarf. Motivated by these discoveries, we perform three-dimensional hydrodynamical simulations with the Athena++ code, modeling the hydrodynamical interaction between a helium star or helium white dwarf and the supernova ejecta. We find that ≈0.01–0.02 M ⊙ of donor material is stripped, and explain the location of the stripped material within the expanding supernova ejecta. We continue the postexplosion evolution of the shocked donor stars with the MESA code. As a result of entropy deposition, they remain luminous and expanded for ≈105–106 yr. We show that the postexplosion properties of our helium white dwarf donor agree reasonably with one of the best-studied hypervelocity stars, D6-2.

Keywords: White dwarf stars, Hypervelocity stars, Type Ia supernovae, Binary stars
Direct Imaging of a Prolonged Plasma/Current Sheet and Quasiperiodic Magnetic Reconnection on the Sun. Magnetic reconnection is widely believed to be the fundamental process in the solar atmosphere that underlies magnetic energy release and particle acceleration. This process is responsible for the onset of solar flares, coronal mass ejections, and other explosive events (e.g., jets). Here, we report direct imaging of a prolonged plasma/current sheet along with quasiperiodic magnetic reconnection in the solar corona using ultra-high-resolution observations from the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory and the Solar Dynamics Observatory/Atmospheric Imaging Assembly. The current sheet appeared near a null point in the fan–spine topology and persisted over an extended period (≈20 hr). The length and apparent width of the current sheet were about 6″ and 2″, respectively, and the plasma temperature was ≈10–20 MK. We observed quasiperiodic plasma inflows and outflows (bidirectional jets with plasmoids) at the reconnection site/current sheet. Furthermore, quasiperiodic reconnection at the long-lasting current sheet produced recurrent eruptions (small flares and jets) and contributed significantly to the recurrent impulsive heating of the active region. Direct imaging of a plasma/current sheet and recurrent null-point reconnection for such an extended period has not been reported previously. These unprecedented observations provide compelling evidence that supports the universal model for solar eruptions (i.e., the breakout model) and have implications for impulsive heating of active regions by recurrent reconnection near null points. The prolonged and sustained reconnection for about 20 hr at the breakout current sheet provides new insights into the dynamics and energy release processes in the solar corona.

Keywords: Jets, Solar coronal heating, Solar flares, Solar magnetic reconnection
Constraining Wind-driven Accretion onto Gaia BH3 with Chandra. Gaia BH3 is the most massive known stellar-origin black hole in the Milky Way, with a mass M • ≈ 33 M ⊙. Detected from Gaia's astrometry, this black hole is in the mass range of those observed via gravitational waves, whose nature is still highly debated. Hosted in a binary system with a companion giant star that is too far away for Roche-lobe mass transfer, this black hole could nonetheless accrete at low levels due to wind-driven mass loss from its companion star, thus accreting in advection-dominated accretion flow, or ADAF, mode. Using stellar wind models, we constrain its Eddington ratio in the range 10‑9 &lt; f Edd &lt; 10‑7, corresponding to radiative efficiencies 5 × 10‑5 &lt; ϵ &lt; 10‑3, compatible with radiatively inefficient accretion modes. Chandra ACIS-S observed this object and obtained the most sensitive upper bound of its [2–10] keV flux: F  X  &lt; 3.25 × 10‑15 erg s‑1 cm‑2 at 90% confidence level corresponding to L [2–10] &lt; 2.10 × 1029 erg s‑1. Using ADAF emission models, we constrained its accretion rate to f Edd &lt; 4.91 × 10‑7 at the apastron, in agreement with our theoretical estimate. At the periastron, we expect fluxes ∼50 times larger. Because of the inferred low rates, accretion did not significantly contribute to black hole growth over the system's lifetime. Detecting the electromagnetic emission from Gaia BH3 will be fundamental to informing stellar wind and accretion disk models.

Keywords: X-ray photometry, Black holes, Bondi accretion, Spectral energy distribution, Astrophysical black holes
Observations of Kappa Distributions in Solar Energetic Protons and Derived Thermodynamic Properties. In this paper, we model the high-energy tail of observed solar energetic proton energy distributions with a kappa distribution function. We employ a technique for deriving the thermodynamic parameters of solar energetic proton populations measured by the Parker Solar Probe Integrated Science Investigation of the Sun EPI-Hi high-energy telescope, over energies from 10 to 60 MeV. With this technique, we explore, for the first time, the characteristic thermodynamic properties of the solar energetic protons associated with an interplanetary coronal mass ejection (ICME) and its driven shock. We find that: (1) the spectral index or, equivalently, the thermodynamic parameter kappa of solar energetic protons (κ EP) gradually increases, starting from the pre-ICME region (upstream of the CME-driven shock), reaching a maximum in the CME ejecta (κ EP ≈ 3.5), followed by a gradual decrease throughout the trailing portion of the CME; (2) the solar energetic proton temperature and density (T EP and n EP) appear anticorrelated, a behavior consistent with subisothermal polytropic processes; and (3) values of T EP and κ EP appear to be positively correlated, indicating an increasing entropy with time. Therefore, these proton populations are characterized by a complex and evolving thermodynamic behavior, consisting of multiple subisothermal polytropic processes, and a large-scale trend of increasing temperature, kappa, and entropy. This study and its companion study by Livadiotis et al. open up a new set of procedures for investigating the thermodynamic behavior of energetic particles and their shared thermal properties.

Keywords: Space plasmas, Heliosphere, Solar energetic particles, Solar wind, Solar coronal mass ejections
CANUCS: An Updated Mass and Magnification Model of A370 with JWST. We present an updated mass and magnification model of galaxy cluster A370 using new NIRCam, NIRISS, and NIRSpec data from the Canadian NIRISS Unbiased Cluster Survey (CANUCS). Using Lenstool and a combination of archival Hubble Space Telescope (HST) and MUSE data with new JWST data as constraints, we derive an improved gravitational lensing model and extract magnifications of background galaxies with uncertainties. Using our best fit model, we perform a search for new multiply imaged systems via predicted positions. We report no new multiply imaged systems with identifiable redshifts, likely due to already very deep HST and Spitzer data but confirm a z ∼ 8 multiply imaged system by measuring its redshift with NIRISS and NIRSpec spectra. We find that the overall shape of the critical curve for a source at z = 9.0 is similar to previous models of A370, with small changes. We investigate the z ∼ 8 galaxy with two images observable with an apparent magnitude in the F125W band of 26.0 ± 0.2 and 25.6 ± 0.1. After correcting for the magnifications of the images,  7.4−0.3+0.5  and  9.4−0.4+0.5 , we use spectral energy distribution fitting to find an intrinsic stellar mass of log(M */M ⊙) =  7.49−0.05+0.04 , intrinsic star formation rate of  2.8−0.3+0.4  M ⊙ yr−1, and M UV of −21.3 −0.2+0.2 , which is close to the knee of the luminosity function at that redshift. Our model, and corresponding magnification, shear, and convergence maps are available on request and will be made publicly available on MAST in a CANUCS data release (doi:10.17909/ph4n-6n76).

Keywords: Gravitational lensing, High-redshift galaxies
Fermi and eROSITA Bubbles as Persistent Structures of the Milky Way. The Fermi and eROSITA bubbles (FBs and eRBs), large diffuse structures in our Galaxy, can be the by-products of steady star formation activity. To simultaneously explain the star formation history of the Milky Way (MW) and the metallicity of ∼Z ⊙ at the Galactic disk, a steady Galactic wind driven by cosmic rays (CRs) is required. For tenuous gases with a density of ≲10‑3 cm‑3, CR heating dominates over radiative cooling, and the gas can maintain the virial temperature of ∼0.3 keV, ideal for escape from the Galactic system as the wind. A part of the wind falls back onto the disk like a Galactic fountain flow. We model the wind dynamics according to the Galactic evolution scenario and find that the scale height and surface brightness of the X-ray and the hadronic gamma-ray emissions from such fountain flow region can be consistent with the observed properties of the FBs and eRBs. This implies that the bubbles are persistent structures of the MW existing over (at least) the last ∼1 Gyr rather than evanescent structures formed by nontrivial, ∼10 Myr past Galactic center transient activities.

Keywords: Galactic winds, Galactic cosmic rays, X-ray sources, Circumgalactic medium, Milky Way evolution, Gamma-rays
Substructures within Substructures in the Complex Postmerging System A514 Unveiled by High-resolution Magellan/Megacam Weak Lensing. Abell 514 (A514) at z = 0.071 is an intriguing merging system exhibiting highly elongated (∼1 Mpc) X-ray features and three large-scale (300 ∼ 500 kpc) bent radio jets. To dissect this system with its multiwavelength data, it is critical to robustly identify and quantify its dark matter substructures. We present a weak-lensing analysis of A514 using deep Magellan/Megacam observations. Combining two optical band filter imaging data obtained under optimal seeing (∼0.″6) and leveraging the proximity of A514, we achieve a high source density of  ∼46arcmin−2  or ∼6940 Mpc−2, which enables high-resolution mass reconstruction. We unveil the complex dark matter substructures of A514, which are characterized by the NW and SE subclusters separated by ∼0.7 Mpc, each exhibiting a bimodal mass distribution. The total mass of the NW subcluster is estimated to be  M200cNW=1.08−0.22+0.25×1014M⊙  and is further resolved into the eastern ( M200cNWE=2.6−1.1+1.4×1013M⊙)  and western ( M200cNWW=7.1−2.0+2.3×1013M⊙ ) components. The mass of the SE subcluster is  M200cSE=1.55−0.26+0.28×1014M⊙ , which is also further resolved into the northern ( M200cSEN=2.9−1.3+1.8×1013M⊙ ) and southern ( M200cSES=8.5−2.6+3.1×1013M⊙ ) components. These four substructures coincide with the A514 brightest galaxies and are detected with significances ranging from 3.3σ to 4.7σ. Comparison of the dark matter substructures with the X-ray distribution suggests that A514 might have experienced an off-axis collision, and the NW and SE subclusters are currently near their apocenters.

Keywords: Weak gravitational lensing, Abell clusters, Galaxy clusters, Dark matter
Methane Formation Efficiency on Icy Grains: Role of Adsorption States. Methane (CH4) is one of the major components of the icy mantle of cosmic dust prevalent in cold, dense regions of interstellar media, playing an important role in the synthesis of complex organic molecules and prebiotic molecules. Solid CH4 is considered to be formed via the successive hydrogenation of C atoms accreting onto dust: C + 4H → CH4. However, most astrochemical models assume this reaction on the ice mantles of dust to be barrierless and efficient, without considering the states of adsorption. Recently, we found that C atoms exist in either the physisorbed or chemisorbed state on compact amorphous solid water, which is analogous to an interstellar ice mantle. These distinct adsorption states considerably affect the hydrogenation reactivity of the C atom. Herein, we elucidate the reactivities of physisorbed and chemisorbed C atoms with H atoms via sequential deposition and codeposition processes. The results indicate that only physisorbed C atoms can produce CH4 on ice. Combining this finding with a previous estimate for the fraction of physisorbed C atoms on ice, we determined the upper limit for the conversion of C atoms into CH4 to be 30%.

Keywords: Interstellar molecules, Interstellar dust, Laboratory astrophysics, Molecular clouds, Astrochemistry