Sazuna/UAT_keywords huggingface dataset:
Energy Dissipation in Electron-only Reconnection. Magnetic reconnection is a fundamental process in space and astrophysical plasmas that converts magnetic energy to particle energy. Recently, a novel kind of reconnection, called electron-only reconnection, has been observed in Earth's magnetosheath plasma. A defining characteristic of electron-only reconnection is that electron jets are observed but ion jets are absent. This is in contrast with traditional ion-coupled reconnection, where both ions and electrons exhibit outflowing velocity jets. Findings from the Magnetospheric Multiscale mission observations and particle-in-cell simulations show clear signatures of electron heating in electron-only reconnection events, while ions are not heated or cooled in these events. This result is unlike ion-coupled reconnection, where both ions and electrons are heated to varying degrees. The ratio of electron to ion dissipation increases with the local magnetic curvature, indicating that the partition of heat into ions and electrons is dependent on the current-sheet thickness.

Keywords: Space plasmas, Plasma astrophysics, Plasma physics
GRB 220304A: Another Gamma-Ray Burst Dominated by Thermal Radiation. We report a recently detected long-duration gamma-ray burst (GRB) event by Fermi-GBM, GRB 220304A. The spectral analysis of the burst by the Band function shows that both the time-integrated and time-resolved spectra are very narrow, with low-energy spectral index &lt;α&gt; = ‑0.05 ± 0.30 and high-energy spectral index &lt;β&gt; = ‑3.53 ± 0.30. It is reminiscent of GRB 090902B, a special GRB with photosphere radiation characteristics. Then, we perform spectral analysis using the Planck function (blackbody, BB) and the multicolor BB model. It is found that the spectra within ‑1 ∼ 3 s is well fit by the BB model, indicating that the observation within the first 4 s is a pure thermal event. Apart from that most of the spectra can be well modeled as a multicolor BB. We conclude that GRB 220304A is a GRB dominated by thermal radiation. We also find that the spectral widths of the time-resolved spectrum of the burst gradually increase with time. Based on the Amati relation, we infer the redshift to be 0.23, the physical properties of the relativistic outflow, and find that the relationship between the bulk Lorentz factor and the isotropic luminosity Γ–L iso,52 still exists.

Keywords: Gamma-ray bursts
Disk-induced Binary Precession: Implications for Dynamics and Multimessenger Observations of Black Hole Binaries. Many studies have recently documented the orbital response of eccentric binaries accreting from thin circumbinary disks, characterizing the change in the binary semimajor axis and eccentricity. We extend these calculations to include the precession of the binary's longitude of periapse induced by the circumbinary disk, and we characterize this precession continuously with binary eccentricity e  b  for equal mass components. This disk-induced apsidal precession is prograde with a weak dependence on the binary eccentricity when e  b  ≲ 0.4 and decreases approximately linearly for e  b  ≳ 0.4; yet at all e  b  binary precession is faster than the rates of change to the semimajor axis and eccentricity by an order of magnitude. We estimate that such precession effects are likely most important for subparsec separated binaries with masses ≲107 M ⊙, like LISA precursors. We find that accreting, equal-mass LISA binaries with M &lt; 106 M ⊙ (and the most massive M ∼ 107 M ⊙ binaries out to z ∼ 3) may acquire a detectable phase offset due to the disk-induced precession. Moreover, disk-induced precession can compete with general relativistic precession in a vacuum, making it important for observer-dependent electromagnetic searches for accreting massive binaries—like Doppler boost and binary self-lensing models—after potentially only a few orbital periods.

Keywords: Accretion, Hydrodynamical simulations, Supermassive black holes, Orbits, Gravitational waves
The Metallicity–Electron Temperature Relationship in H II Regions. H II region heavy-element abundances throughout the Galactic disk provide important constraints to theories of the formation and evolution of the Milky Way. In LTE, radio recombination line (RRL) emission and free–free continuum emission are accurate extinction-free tracers of the H II region electron temperature. Since metals act as coolants in H II regions via the emission of collisionally excited lines, the electron temperature is a proxy for metallicity. Shaver et al. found a linear relationship between metallicity and electron temperature with little scatter. Here we use CLOUDY H II region simulations to (1) investigate the accuracy of using RRLs to measure the electron temperature and (2) explore the metallicity–electron temperature relationship. We model 135 H II regions with different ionizing radiation fields, densities, and metallicities. We find that electron temperatures derived under the assumption of LTE are about 20% systematically higher owing to non-LTE effects, but overall LTE is a good assumption for centimeter-wavelength RRLs. Our CLOUDY simulations are consistent with the Shaver et al. metallicity–electron temperature relationship, but there is significant scatter since earlier spectral types or higher electron densities yield higher electron temperatures. Using RRLs to derive electron temperatures assuming LTE yields errors in the predicted metallicity as large as 10%. We derive correction factors for log(O/H) + 12 in each CLOUDY simulation. For lower metallicities the correction factor depends primarily on the spectral type of the ionizing star and ranges from 0.95 to 1.10, whereas for higher metallicities the correction factor depends on the density and is between 0.97 and 1.05.

Keywords: Radio astronomy, H II regions, Chemical abundances, Astronomical simulations
An Extremely Young Protostellar Core, MMS 1/OMC-3: Episodic Mass Ejection History Traced by the Micro SiO Jet. We present ∼0.″2 (∼80 au) resolution observations of the CO(2–1) and SiO(5–4) lines made with the Atacama large millimeter/submillimeter array toward an extremely young intermediate-mass protostellar source (t dyn &lt; 1000 yr), MMS 1 located in the Orion Molecular Cloud-3 region. We have successfully imaged a very compact CO molecular outflow associated with MMS 1, having deprojected lobe sizes of ∼1800 au (redshifted lobe) and ∼2800 au (blueshifted lobe). We have also detected an extremely compact (≲1000 au) and collimated SiO protostellar jet within the CO outflow. The maximum deprojected jet speed is measured to be as high as 93 km s‑1. The SiO jet wiggles and displays a chain of knots. Our detection of the molecular outflow and jet is the first direct evidence that MMS 1 already hosts a protostar. The position–velocity diagram obtained from the SiO emission shows two distinct structures: (i) bow shocks associated with the tips of the outflow, and (ii) a collimated jet, showing the jet velocities linearly increasing with the distance from the driving source. Comparisons between the observations and numerical simulations quantitatively share similarities such as multiple-mass ejection events within the jet and Hubble-like flow associated with each mass ejection event. Finally, while there is a weak flux decline seen in the 850 μm light curve obtained with the James Clerk Maxwell Telescope/SCUBA 2 toward MMS 1, no dramatic flux change events are detected. This suggests that there has not been a clear burst event within the last 8 yr.

Keywords: Stellar jets, Shocks, Stellar winds, Star formation, Protostars
An Outbursting Protostar: The Environment of L1251 VLA 6. Young protostars that undergo episodic accretion can provide insight into the impact on their circumstellar environments while matter is accreted from the disk onto the protostar. IRAS 22343+7501 is a four-component protostar system with one of those being a fading outbursting protostar, which was obseved with the Karl G. Jansky Very Large Array (VLA) and is referred to as L1251 VLA 6. Given the rarity of young stellar objects undergoing this type of accretion, L1251 VLA 6 can elucidate the fading phase of the post-outburst process. Here, we examine structure in the disk around L1251 VLA 6 at frequencies of 10 and 33 GHz with the VLA. We model the disk structure using Markov Chain Monte Carlo (MCMC). This method is then combined with a parametric ray-tracing code to generate synthetic model images of an axisymmetric disk, allowing us to characterize the radial distribution of dust in the system. The results of our MCMC fit show that the most probable values for the mass and radius are consistent with values typical of Class I objects. We find that the total mass of the disk is ${0.070}_{-0.2}^{+0.031}\,{M}_{\odot }$ and investigate the conditions that could cause the accretion outburst. We conclude that the eruption is not caused by gravitational instability and consider alternative explanations and trigger mechanisms.

Keywords: Protostars, Young stellar objects, Stellar accretion, Circumstellar disks
Using Bright Point Shapes to Constrain Wave Heating of the Solar Corona: Predictions for DKIST. Magnetic bright points on the solar photosphere mark the footpoints of kilogauss magnetic flux tubes extending toward the corona. Convective buffeting of these tubes is believed to excite magnetohydrodynamic waves, which can propagate to the corona and deposit heat there. Measuring wave excitation via bright point motion can thus constrain coronal and heliospheric models, and this has been done extensively with centroid tracking, which can estimate kink-mode wave excitation. DKIST is the first telescope to provide well-resolved observations of bright points, allowing shape and size measurements to probe the excitation of other wave modes that have been difficult, if not impossible, to study to date. In this work, we demonstrate a method of automatic bright point tracking that robustly identifies the shapes of bright points, and we develop a technique for interpreting measured bright point shape changes as the driving of a range of thin-tube wave modes. We demonstrate these techniques on a MURaM simulation of DKIST-like resolution. These initial results suggest that modes other than the long-studied kink mode could increase the total available energy budget for wave heating by 50%. Pending observational verification as well as modeling of the propagation and dissipation of these additional wave modes, this could represent a significant increase in the potency of wave-turbulence heating models.

Keywords: Magnetohydrodynamics, Solar photosphere, Solar coronal heating, Alfven waves, Solar magnetic bright points
The Role of the Third Dredge-up and Mass Loss in Shaping the Initial–Final Mass Relation of White Dwarfs. The initial–final mass relation (IFMR) plays a crucial role in understanding stellar structure and evolution by linking a star's initial mass to the mass of the resulting white dwarf. This study explores the IFMR in the initial mass range 0.8 ≤ M ini/M ⊙ ≤ 4 using full PARSEC evolutionary calculations supplemented with COLIBRI computations to complete the ejection of the envelope and obtain the final core mass. Recent works have shown that the supposed monotonicity of the IFMR is interrupted by a kink in the initial mass range M ini ≈ 1.65–2.10 M ⊙, due to the interaction between recurrent dredge-up episodes and stellar winds in carbon stars evolving on the thermally pulsing asymptotic giant branch phase. To reproduce the IFMR nonmonotonic behavior we investigate the role of convective overshooting efficiency applied to the base of the convective envelope (f env) and to the borders of the pulse-driven convective zone (f pdcz), as well as its interplay with mass loss. We compare our models to observational data and find that f env must vary with initial mass in order to accurately reproduce the IFMR's observed kink and slopes. We find some degeneracy between the overshooting parameters when only the IFMR information is used. Nonetheless, this analysis provides valuable insights into the internal mixing processes during the TP-AGB phase.

Keywords: Stellar convective zones, White dwarf stars, Carbon stars, Asymptotic giant branch stars, Stellar winds
Millimeter-wave CO and SiO Observations toward the Broad-velocity-width Molecular Feature CO 16.134–0.553: A Smith Cloud Scenario?. We report the results of the CO J = 1–0 and SiO J = 2–1 mapping observations toward the broad-velocity-width molecular feature (BVF) CO 16.134–0.553 with the Nobeyama Radio Observatory 45 m telescope. The high-quality CO map shows that the 5 pc size BVF bridges two separate velocity components at V LSR ≃ 40 km s‑1 and 65 km s‑1 in the position–velocity space. The kinetic power of CO 16.134–0.553 amounts to 7.8 × 102 L ⊙, whereas no apparent driving sources were identified. Prominent SiO emission was detected from the BVF and its root in the V LSR ≃ 40 km s‑1 component. In the CO Galactic plane survey data, CO 16.134–0.553 appears to correspond to the Galactic eastern rim of a 15 pc diameter expanding CO shell. A 1° diameter H I emission void and 4° long vertical H I filament were also found above and below the CO shell, respectively. We propose that the high-velocity plunge of a dark matter subhalo with a clump of baryonic matter was responsible for the formation of the H I void, CO 16.134–0.553/CO shell, and the H I filament.

Keywords: Interstellar molecules, Milky Way dark matter halo, Interstellar clouds
Constrain the Dark-matter Distribution of Ultra-diffuse Galaxies with Globular-cluster Mass Segregation: A Case Study with NGC5846-UDG1. The properties of globular clusters (GCs) contain valuable information of their host galaxies and dark-matter halos. In the remarkable example of ultra-diffuse galaxy, NGC5846-UDG1, the GC population exhibits strong radial mass segregation, indicative of dynamical-friction-driven orbital decay, which opens the possibility of using imaging data alone to constrain the dark-matter content of the galaxy. To explore this possibility, we develop a semianalytical model of GC evolution, which starts from the initial mass, structural, and spatial distributions of the GC progenitors, and follows the effects of dynamical friction, tidal evolution, and two-body relaxation. Using Markov Chain Monte Carlo, we forward-model the GCs in a UDG1-like potential to match the observed GC statistics, and to constrain the profile of the host halo and the origin of the GCs. We find that, with the assumptions of zero mass segregation when the star clusters were born, UDG1 is relatively dark-matter-poor compared to what is expected from stellar-to-halo–mass relations, and its halo concentration is lower than the cosmological average, irrespective of having a cuspy or a cored profile. Its GC population has an initial spatial distribution more extended than the smooth stellar distribution. We discuss the results in the context of scaling laws of galaxy–halo connections, and warn against naively using the GC-abundance–halo–mass relation to infer the halo mass of ultra-diffuse galaxies. Our model is generally applicable to GC-rich dwarf galaxies, and is publicly available.

Keywords: Globular star clusters, Galaxy dark matter halos, Dwarf galaxies, Dynamical friction, Low surface brightness galaxies
The Origins of Gas Accreted by Supermassive Black Holes: The Importance of Recycled Gas. We investigate the fueling mechanisms of supermassive black holes (SMBHs) by analyzing 10 zoom-in cosmological simulations of massive galaxies, with stellar masses 1011–12 M ⊙ and SMBH masses 108.9–9.7 M ⊙ at z = 0, featuring various major and minor merger events. By tracing the gas history in these simulations, we categorize the gas accreted by the central SMBHs based on its origin. Gas that belonged to a different galaxy before accretion onto the BH is labeled as (i) "external," while smoothly accreted cosmic gas is classified as (ii) "smooth." Gas produced within the primary halo through stellar evolution and subsequently accreted by the SMBH is classified as (iii) "recycled." Our analysis, which includes stellar feedback, reveals that the primary fuel source for SMBHs is the recycled gas from dying stars. This recycled gas from stars in the inner region of the galaxy readily collapses toward the center, triggering starbursts and simultaneously fueling the SMBH. Galaxy mergers also play a crucial role in fueling SMBHs in massive galaxies, as SMBHs in massive halos tend to accrete a higher fraction of external gas from mergers compared to smoothly accreted gas. However, on average, it takes approximately 1.85 Gyr for external gas to enter the main galaxy and accrete onto the SMBH. Considering the presence of various other gas triggers for active galactic nucleus (AGN) activity alongside this time delay, the association between AGNs and mergers may not always be obvious.

Keywords: AGN host galaxies, Hydrodynamical simulations, Supermassive black holes, Active galactic nuclei
Testing CCC+TL Cosmology with Observed Baryon Acoustic Oscillation Features. The primary purpose of this paper is to see how well a recently proposed new model fits (a) the position of the baryon acoustic oscillation (BAO) features observed in the large-scale distribution of galaxies and (b) the angular size measured for the sound horizon due to BAO imprinted in the cosmic microwave background (CMB) anisotropy. The new model is a hybrid model that combines the tired light (TL) theory with a variant of the ΛCDM model in which the cosmological constant is replaced with a covarying coupling constants' (CCC) parameter α. This model, dubbed the CCC+TL model, can fit the Type Ia supernovae Pantheon+ data as accurately as the ΛCDM model, and also fit the angular size of cosmic dawn galaxies observed by the James Webb Space Telescope, which is in tension with the ΛCDM model. The results we obtained are 151.0 (±5.1) Mpc for the absolute BAO scale at the current epoch, and the angular size of the sound horizon θ sh = 0.°60, matching Planck's observations at the surface of the last scattering when the baryon density is set to 100% of the matter density and ∣α∣ is increased by 5.6%. It remains to be seen if the new model is consistent with the CMB power spectrum, the Big Bang nucleosynthesis of light elements, and other critical observations.

Keywords: Cosmology, Cosmic microwave background radiation, Baryon acoustic oscillations
Explosions in Roche-lobe Distorted Stars: Relativistic Bullets in Binaries. State-of-the-art surveys reveal that most massive stars in the Universe evolve in close binaries. Massive stars in such systems are expected to develop aspherical envelopes due to tidal interactions and/or rotational effects. Recently, it was shown that point explosions in oblate stars can produce relativistic equatorial ring-like outflows. Moreover, since stripped-envelope stars in binaries can expand enough to fill their Roche lobes anew, it is likely that these stars die with a greater degree of asphericity than the oblate spheroid geometry previously studied. We investigate the effects of this asymmetry by studying the gas dynamics of axisymmetric point explosions in stars in various stages of filling their Roche lobes. We find that point explosions in these pear-shaped stars produce transrelativistic ejecta that coalesce into bullets pointed both toward and away from the binary companion. We present this result and comment on key morphological differences between core-collapse explosions in spherical versus distorted stars in binary systems, effects on gravitational wave sources, and observational signatures that could be used to glean these explosion geometries from current and future surveys.

Keywords: Roche lobe, Binary stars, Relativistic fluid dynamics, Supernovae, Radio transient sources
The Case of the Missing Very High-energy Gamma-Ray Bursts: A Retrospective Study of Swift Gamma-Ray Bursts with Imaging Atmospheric Cherenkov Telescopes. Gamma-ray bursts (GRBs) are particle acceleration sites that can emit photons in the very high-energy (VHE) domain through nonthermal processes. From 2004 until 2018, the current generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) did not detect any GRB in the VHE domain. However, from 2018 to 2020, five detections were reported. In this work, we try to solve the case of the missing VHE GBRs prior to 2018. We aim to identify GRBs that might have eluded VHE detection in past years by the H.E.S.S., MAGIC, and VERITAS IACTs. To do so, we study GRBs with known redshift detected by Swift from 2004 until June 2022. We first identify all GRBs that could have been observed by these IACTs since 2004, considering observation conditions and visibility constraints. We assume a relation between the X-rays and the VHE gamma rays based on the VHE GRBs detected to date and combine this with the redshift measurements, instrument response information, and observation conditions to predict the observed VHE gamma-ray flux from the Swift X-Ray Telescope measurements. We report findings on 12 bright low-redshift GRBs that we identify as most likely to have been detected in the VHE domain by current IACTs. The rate of IACT-detectable GRBs with ideal observation conditions is &lt;1 VHE GRB per year with the current configuration. With its lower energy threshold and higher sensitivity, this rate increases to ∼4 VHE GRBs per year with the Cherenkov Telescope Array.

Keywords: Gamma-ray bursts, High energy astrophysics, Transient sources, Gamma-ray telescopes, Gamma-ray observatories, Gamma-ray astronomy, Gamma-ray transient sources
Preliminary Discussion on the Current Sheet. The current sheet is a characteristic structure of magnetic energy dissipation during the magnetic reconnection process. So far, the width and depth of the current sheet are still indefinite. Here we investigate 64 current sheets observed by four telescopes from 1999 to 2022, and all of them have been well identified in the previous literature. In each current sheet, three width values are obtained at the quartering points. Based on these investigated cases, we obtain 192 values, which are in a wide range from hundreds to tens of thousands of kilometers. By calculating the pixel width (PW: the ratio of the current sheet width to the pixel resolution of corresponding observed data) of these current sheets, we find that more than 80% of the PW values concentrate on 2–4 pixels, indicating that the widths of the current sheets are dependent strongly on the instrument resolutions and all the sheets have no observable three-dimensional information. To interpret this result, we suggest that there are two probabilities. One is that the width of the current sheet is smaller than the instrument resolution, and the other is that the detected current sheet is only a small segment of the real one. Furthermore, there is another possible scenario. The so-called current sheet is just an emission-enhanced region.

Keywords: Solar activity, Solar magnetic fields, Solar magnetic reconnection