Sazuna/UAT_keywords huggingface dataset:
Prospects for Detecting γ-Ray Bursts at Very High Energies with the HADAR Experiment. Recent ground-based observations of TeV photons have significantly deepened our understanding of the nature of gamma-ray bursts (GRBs). However, many fundamental problems remain unsolved concerning the physical mechanisms behind GRBs, necessitating the need for sufficient statistical data. The High Altitude Detection of Astronomical Radiation (HADAR) experiment utilizes a wide-angle water Cherenkov telescope, presenting a novel approach to measure the spectra and variability of GRBs from 10 GeV to 10 TeV energy ranges with unprecedented photon statistics and thereby break new ground in elucidating the physics of GRBs, which is still poorly understood. In this study, a time-dependent numerical modeling technique is utilized to simulate extensive light curves and spectral energy distributions of synthetic GRB afterglow emissions. By harnessing the remarkable capabilities of HADAR, we evaluate its potential in detecting GRB afterglow emissions at energies &gt;10 GeV. Through our analysis, we unveil the prospect of detecting an estimated 5.8 GRBs annually, facilitating a systematic investigation into their reliance on model parameters. Future HADAR observations would offer valuable insights into the magnetic field and the environmental conditions surrounding GRBs.

Keywords: Gamma-ray bursts, Non-thermal radiation sources, Experimental techniques
Effect of Spherical Polarization on the Magnetic Spectrum of the Solar Wind. Magnetic fluctuations in the solar wind are often observed to maintain constant magnitude of the magnetic field in a manner consistent with spherically polarized large-amplitude Alfvén waves. We investigate the effect of spherical polarization on the magnetic spectral index through a statistical survey of magnetic fluctuations observed by Parker Solar Probe between 20 R ⊙ and 200 R ⊙. We find that deviations from spherical polarization, i.e., changes in ∣ B ∣ (compressive fluctuations) and one-dimensional discontinuities, have a dramatic effect on the scaling behavior of the turbulent fluctuations. We show that shallow k -3/2 spectra are only observed for three-dimensional structures of constant magnetic field strength, which we identify as large-amplitude Alfvén waves. The presence of compressive fluctuations coincides with a steepening of the spectrum up to k -5/3. Steeper power-law scalings approaching k -2 are observed when the fluctuations are dominated by discontinuities. Near-Sun fluctuations are found to be the most spherically polarized, suggesting that this spherical state is fundamental to the generation of the solar wind. With increasing distance from the Sun, fluctuations are found to become less three-dimensional and more compressive, which may indicate the breakdown of the Alfvénic equilibrium state.

Keywords: Space plasmas, Interplanetary turbulence, Solar wind, Solar physics, Alfven waves
CAHA/PPAK Integral-field Spectroscopic Observations of M81. II. Testing Photoionization Models in a Spatially Resolved LINER. The origin of the low-ionization nuclear emission-line region (LINER) prevalent in local galaxies and its relationship with supermassive black holes have been debated for decades. We perform a comprehensive evaluation of traditional photoionization models against the circumnuclear ionized gas in M81, for which recent CAHA/PPAK integral-field spectroscopic observations reveal a LINER characteristic out to a galactocentric radius of ~1 kpc. Constructed with the photoionization code CLOUDY, the models have the novel aspect of their primary parameters being well constrained by extensive observations of a prototypical low-luminosity active galactic nucleus (LLAGN) and an old stellar bulge in M81. Additionally, these models incorporate a reasonably broad range of uncertain nebular properties. It is found that the integrated photoionization by the LLAGN and hot, low-mass stars distributed in the bulge can roughly reproduce the observed radial intensity distributions of the Hα, Hβ, and [N II] lines, with the bulge stars dominating the ionizing flux at radii ≳200 pc. However, the models generally fail to reproduce a similarly declining profile of the [O III] line or an accordingly flat profile of the [O III]/Hβ ratio. This clearly points to a deficiency of ionizing photons in the outer regions despite an extended photoionization source. The discrepancy might be alleviated if much of the observed [O III] line arose from a bulge-filling, low-density gas surrounding a denser, Hα-emitting disk, or by a higher AGN luminosity in the recent past. The case of M81 has important implications for the ionization mechanism of LINERs and low-ionization emission-line regions in general.

Keywords: Galaxy spectroscopy, Photoionization, Active galactic nuclei, Galaxy nuclei
Coronal Magnetic Field Extrapolation and Topological Analysis of Fine-scale Structures during Solar Flare Precursors. Magnetic field plays an important role in various solar eruption phenomena. The formation and evolution of the characteristic magnetic field topology in solar eruptions are critical problems that will ultimately help us understand the origin of these eruptions in the solar source regions. With the development of advanced techniques and instruments, observations with higher resolutions in different wavelengths and fields of view have provided more quantitative information for finer structures. It is therefore essential to improve the method with which we study the magnetic field topology in the solar source regions by taking advantage of high-resolution observations. In this study, we employ a nonlinear force-free field extrapolation method based on a nonuniform grid setting for an M-class flare eruption event (SOL2015-06-22T17:39) with embedded vector magnetograms from the Solar Dynamics Observatory (SDO) and the Goode Solar Telescope (GST). The extrapolation results for which the nonuniform embedded magnetogram for the bottom boundary was employed are obtained by maintaining the native resolutions of the corresponding GST and SDO magnetograms. We compare the field line connectivity with the simultaneous GST/Hα and SDO/Atmospheric Imaging Assembly observations for these fine-scale structures, which are associated with precursor brightenings. Then we perform a topological analysis of the field line connectivity corresponding to fine-scale magnetic field structures based on the extrapolation results. The analysis results indicate that when we combine the high-resolution GST magnetogram with a larger magnetogram from the SDO, the derived magnetic field topology is consistent with a scenario of magnetic reconnection among sheared field lines across the main polarity inversion line during solar flare precursors.

Keywords: Solar active region magnetic fields, Solar flares, Solar magnetic fields
Modeling a Coronal Mass Ejection from an Extended Filament Channel. II. Interplanetary Propagation to 1 au. We present observations and modeling results of the propagation and impact at Earth of a high-latitude, extended filament channel eruption that commenced on 2015 July 9. The coronal mass ejection (CME) that resulted from the filament eruption was associated with a moderate disturbance at Earth. This event could be classified as a so-called "problem storm" because it lacked the usual solar signatures that are characteristic of large, energetic, Earth-directed CMEs that often result in significant geoeffective impacts. We use solar observations to constrain the initial parameters and therefore to model the propagation of the 2015 July 9 eruption from the solar corona up to Earth using 3D magnetohydrodynamic heliospheric simulations with three different configurations of the modeled CME. We find the best match between observed and modeled arrival at Earth for the simulation run that features a toroidal flux rope structure of the CME ejecta, but caution that different approaches may be more or less useful depending on the CME-observer geometry when evaluating the space weather impact of eruptions that are extreme in terms of their large size and high degree of asymmetry. We discuss our results in the context of both advancing our understanding of the physics of CME evolution and future improvements to space weather forecasting.

Keywords: Quiet sun, Space weather, Interplanetary magnetic fields, Solar coronal mass ejections, Solar filament eruptions, Solar-terrestrial interactions, Magnetohydrodynamical simulations
Unraveling the Thermodynamic Enigma between Fast and Slow Coronal Mass Ejections. Coronal mass ejections (CMEs) are the most energetic expulsions of magnetized plasma from the Sun that play a crucial role in space weather dynamics. This study investigates the diverse kinematics and thermodynamic evolution of two CMEs (CME1: 2011 September 24 and CME2: 2018 August 20) at coronal heights where thermodynamic measurements are limited. The peak 3D propagation speed of CME1 is high (1885 km s-1) with two-phase expansion (rapid and nearly constant), while the peak 3D propagation speed of CME2 is slow (420 km s-1) with only a gradual expansion. We estimate the distance-dependent variations in the polytropic index, heating rate, temperature, and internal forces implementing the revised FRIS model, taking inputs of 3D kinematics estimated from the graduated cylindrical shell model. We find CME1 exhibiting heat release during its early-rapid acceleration decrease and jumps to the heat-absorption state during its constant acceleration phase. In contrast to CME1, CME2 shows a gradual transition from the near-adiabatic to the heat-absorption state during its gradually increasing acceleration. Our analysis reveals that although both CMEs show differential heating, they experience heat absorption during their later propagation phases, approaching the isothermal state. The faster CME1 achieves an adiabatic state followed by an isothermal state at smaller distances from the Sun than the slower CME2. We also find that the expansion of CMEs is primarily influenced by centrifugal and thermal pressure forces, with the Lorentz force impeding expansion. Multiwavelength observations of flux-ropes at source regions support the FRIS-model-derived findings at initially observed lower coronal heights.

Keywords: Solar coronal mass ejections
A Chandra Study of the NGC 7618/UGC 12491 Major Group Merger at Apogee: Multiple Cold Fronts, Boxy Wings, Filaments, and Arc-shaped Slingshot Tails. Analyses of major group mergers are key to understanding the evolution of large-scale structure in the Universe and the microphysical properties of the hot gas in these systems. We present imaging and spectral analyses of deep Chandra observations of hot gas structures formed in the major merger of the NGC 7618 and UGC 12491 galaxy groups and compare the observed hot gas morphology, temperatures, and abundances with recent simulations. The morphology of the observed multiple cold front edges and boxy wings are consistent with those expected to be formed by Kelvin-Helmholtz instabilities and gas sloshing in inviscid gas. The arc-shaped slingshot tail morphologies seen in each galaxy suggest that the dominant galaxies are near their orbital apogee after having experienced at least one core passage at a large impact parameter.

Keywords: X-ray astronomy, Galaxy environments, Cool intergalactic medium, Galaxy groups, Galaxy mergers
CWISE J105512.11+544328.3: A Nearby Y Dwarf Spectroscopically Confirmed with Keck/NIRES. Y dwarfs, the coolest known spectral class of brown dwarfs, overlap in mass and temperature with giant exoplanets, providing unique laboratories for studying low-temperature atmospheres. However, only a fraction of Y dwarf candidates have been spectroscopically confirmed. We present Keck/NIRES near-infrared spectroscopy of the nearby (d ≈ 6-8 pc) brown dwarf CWISE J105512.11+544328.3. Although its near-infrared spectrum aligns best with the Y0 standard in the J band, no standard matches well across the full YJHK wavelength range. The CWISE J105512.11+544328.3 NH3-H = 0.427 ± 0.0012 and CH4-J = 0.0385 ± 0.0007 absorption indices and absolute Spitzer [4.5] magnitude of 15.18 ± 0.22 are also indicative of an early-Y dwarf rather than a late-T dwarf. CWISE J105512.11+544328.3 additionally exhibits the bluest Spitzer [3.6]-[4.5] color among all spectroscopically confirmed Y dwarfs. Despite this anomalously blue Spitzer color given its low luminosity, CWISE J105512.11+544328.3 does not show other clear kinematic or spectral indications of low metallicity. Atmospheric model comparisons yield a log(g) ≤ 4.5 and T eff ≈ 500 ± 150 K for this source. We classify CWISE J105512.11+544328.3 as a Y0 (pec) dwarf, adding to the remarkable diversity of the Y-type population. JWST spectroscopy would be crucial to understanding the origin of this Y dwarf's unusual preference for low-gravity models and blue 3-5 μm color.

Keywords: Near infrared astronomy, Brown dwarfs, Y dwarfs, T dwarfs
Ejecta, Rings, and Dust in SN 1987A with JWST MIRI/MRS. Supernova (SN) 1987A is the nearest supernova in ~400 yr. Using the JWST MIRI Medium Resolution Spectrograph, we spatially resolved the ejecta, equatorial ring (ER), and outer rings in the mid-infrared 12,927 days (35.4 yr) after the explosion. The spectra are rich in line and dust continuum emission, both in the ejecta and the ring. The broad emission lines (280-380 km s-1 FWHM) that are seen from all singly-ionized species originate from the expanding ER, with properties consistent with dense post-shock cooling gas. Narrower emission lines (100-170 km s-1 FWHM) are seen from species originating from a more extended lower-density component whose high ionization may have been produced by shocks progressing through the ER or by the UV radiation pulse associated with the original supernova event. The asymmetric east-west dust emission in the ER has continued to fade, with constant temperature, signifying a reduction in dust mass. Small grains in the ER are preferentially destroyed, with larger grains from the progenitor surviving the transition from SN into SNR. The ER dust is fit with a single set of optical constants, eliminating the need for a secondary featureless hot dust component. We find several broad ejecta emission lines from [Ne II], [Ar II], [Fe II], and [Ni II]. With the exception of [Fe II] 25.99 μm, these all originate from the ejecta close to the ring and are likely to be excited by X-rays from the interaction. The [Fe II] 5.34 to 25.99 μm line ratio indicates a temperature of only a few hundred K in the inner core, which is consistent with being powered by 44 Ti decay.

Keywords: Supernova remnants, Circumstellar dust, High energy astrophysics, Core-collapse supernovae
Revisiting Galaxy Evolution in Morphology in the Cosmic Evolution Survey Field (COSMOS-ReGEM). I. Merging Galaxies. We revisit the evolution of galaxy morphology in the Cosmic Evolution Survey field over the redshift range 0.2 ≤ z ≤ 1, using a large and complete sample of 33,605 galaxies with a stellar mass of log(M */M ⊙) &gt; 9.5 with significantly improved redshifts and comprehensive nonparametric morphological parameters. Our sample has 13,881 (~41.3%) galaxies with reliable spectroscopic redshifts and more accurate photometric redshifts with a σ NMAD ~ 0.005. This paper is the first in a series that investigates merging galaxies and their properties. We identify 3594 major merging galaxies through visual inspection and find 1737 massive galaxy pairs with log(M */M ⊙) &gt;10.1. Among the family of nonparametric morphological parameters including C, A, S, Gini, M 20, A O, and D O, we find that the outer asymmetry parameter A O and the second-order momentum parameter M 20 are the best tracers of merging features compared to other combinations. Hence, we propose a criterion for selecting candidates of violently star-forming mergers: M 20 &gt; - 3A O + 3 at 0.2 &lt; z &lt; 0.6 and M 20 &gt; - 6A O + 3.7 at 0.6 &lt; z &lt; 1.0. Furthermore, we show that both the visual merger sample and the pair sample exhibit a similar evolution in the merger rate at z &lt; 1, with ${\mathfrak{R}}\sim {(1+z)}^{1.79\pm 0.13}$ for the visual merger sample and ${\mathfrak{R}}\sim {(1+z)}^{2.02\pm 0.42}$ for the pair sample. The visual merger sample has a specific star formation rate that is about 0.16 dex higher than that of nonmerger galaxies, whereas no significant star formation excess is observed in the pair sample. This suggests that the effects of mergers on star formation differ at different merger stages.

Keywords: Galaxy evolution, Galaxy pairs, Galaxy mergers, Galaxy classification systems
Predicting the Radiation Field of Molecular Clouds Using Denoising Diffusion Probabilistic Models. Accurately quantifying the impact of radiation feedback in star formation is challenging. To address this complex problem, we employ deep-learning techniques known as denoising diffusion probabilistic models (DDPMs) to predict the interstellar radiation field (ISRF) strength based on three-band dust emission at 4.5, 24, and 250 μm. We adopt magnetohydrodynamic simulations from the STARFORGE project that model star formation and giant molecular cloud (GMC) evolution. We generate synthetic dust emission maps matching observed spectral energy distributions in the Monoceros R2 (MonR2) GMC. We train DDPMs to estimate the ISRF using synthetic three-band dust emission. The dispersion between the predictions and true values is within a factor of 0.1 for the test set. We extended our assessment of the diffusion model to include new simulations with varying physical parameters. While there is a consistent offset observed in these out-of-distribution simulations, the model effectively constrains the relative intensity to within a factor of 2. Meanwhile, our analysis reveals a weak correlation between the ISRF solely derived from dust temperature and the actual ISRF. We apply our trained model to predict the ISRF in MonR2, revealing a correspondence between intense ISRF, bright sources, and high dust emission, confirming the model's ability to capture ISRF variations. Our model robustly predicts radiation feedback distribution, even in complex, poorly constrained ISRF environments like those influenced by nearby star clusters. However, precise ISRF predictions require an accurate training data set mirroring the target molecular cloud's unique physical conditions.

Keywords: Interstellar dust, Magnetohydrodynamics, Interstellar radiation field, Astrostatistics techniques, Molecular clouds, Astrostatistics, Young stellar objects, Interstellar medium
Early Planet Formation in Embedded Disks (eDisk). XII. Accretion Streamers, Protoplanetary Disk, and Outflow in the Class I Source Oph IRS 63. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Class I source Oph IRS 63 in the context of the Early Planet Formation in Embedded Disks large program. Our ALMA observations of Oph IRS 63 show a myriad of protostellar features, such as a shell-like bipolar outflow (in 12CO), an extended rotating envelope structure (in 13CO), a streamer connecting the envelope to the disk (in C18O), and several small-scale spiral structures seen toward the edge of the dust continuum (in SO). By analyzing the velocity pattern of 13CO and C18O, we measure a protostellar mass of M ⋆ = 0.5 ± 0.2 M ☉ and confirm the presence of a disk rotating at almost Keplerian velocity that extends up to ~260 au. These calculations also show that the gaseous disk is about four times larger than the dust disk, which could indicate dust evolution and radial drift. Furthermore, we model the C18O streamer and SO spiral structures as features originating from an infalling rotating structure that continuously feeds the young protostellar disk. We compute an envelope-to-disk mass infall rate of ~10-6 M ☉ yr-1 and compare it to the disk-to-star mass accretion rate of ~10-8 M ☉ yr-1, from which we infer that the protostellar disk is in a mass buildup phase. At the current mass infall rate, we speculate that soon the disk will become too massive to be gravitationally stable.

Keywords: Star formation, Low mass stars, Protoplanetary disks, Stellar accretion, Protostars, Planet formation
HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow. Hubble Space Telescope (HST) images obtained in 2018 are combined with archival HST data taken in 1995 to detect changes and measure proper motions in the HH 80/81 shock complex, which is powered by the fastest known jet driven by a forming star, the massive object IRAS 18162-2048. Some persistent features close to the radio jet axis have proper motions of &gt;1000 km s-1 away from IRAS 18162-2048. About 3-5 pc downstream from the IRAS source and beyond HH 80/81, Hα emission traces the rim of a parsec-scale bubble blown by the jet. Lower speed motions are seen in [S II] away from the jet axis; these features have a large component of motion at right angles to the jet. We identify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The northeastern counterflow to HH 80/81 exhibits an extended but faint complex of 2.12 μm H2 shocks. The inner portion of the outflow is traced by dim 1.64 μm [Fe II] emission. The full extent of this outflow is at least 1500″ (~10 pc in projection at a distance of 1.4 kpc). We speculate about the conditions responsible for the production of the ultrafast jet and the absence of prominent large-scale molecular outflow lobes.

Keywords: Star forming regions, Star formation
Composite Bulges. III. A Study of Nuclear Star Clusters in Nearby Spiral Galaxies. We present photometric and morphological analyses of nuclear star clusters (NSCs)-very dense, massive star clusters present in the central regions of most galaxies-in a sample of 33 massive disk galaxies within 20 Mpc, part of the "Composite Bulges Survey." We use data from the Hubble Space Telescope including optical (F475W and F814W) and near-IR (F160W) images from the Wide Field Camera 3. We fit the images in 2D to take into account the full complexity of the inner regions of these galaxies (including the contributions of nuclear disks and bars), isolating the NSC and bulge components. We derive NSC radii and magnitudes in all three bands, which we then use to estimate NSC masses. Our sample significantly expands the sample of massive late-type galaxies with measured NSC properties. We clearly identify NSCs in nearly 80% of our galaxies, putting a lower limit on the nucleation fraction in these galaxies that is higher than previous estimates. We find that the NSCs in our massive disk galaxies are consistent with previous NSC mass-NSC radius and galaxy mass-NSC mass relations. However, we also find a large spread in NSC masses, with a handful of galaxies hosting very low-mass, compact clusters. Our NSCs are aligned in PA with their host galaxy disks but are less flattened. They show no correlations with bar or bulge properties. Finally, we find the ratio of NSC to BH mass in our massive disk galaxy sample spans a factor of ~300.

Keywords: Disk galaxies, Star clusters