Sazuna/UAT_keywords huggingface dataset:
"Extended Emission" from Fallback Accretion onto Merger Remnants. Using a set of general-relativistic magnetohydrodynamics simulations that include proper neutrino transfer, we assess for the first time the role played by the fallback accretion onto the remnant from a binary neutron star merger over a timescale of hundreds of seconds. In particular, we find that, independently of the equation of state, the properties of the binary, and the fate of the remnant, the fallback material reaches a total mass of ≳10‑3 M ⊙, i.e., about 50% of the unbound matter, and that the fallback accretion rate follows a power law in time with slope ∼t ‑5/3. Interestingly, the timescale of the fallback and the corresponding accretion luminosity are in good agreement with the so-called "extended emission" observed in short gamma-ray bursts (GRBs). Using a simple electromagnetic emission model based on the self-consistent thermodynamical state of the fallback material heated by r-process nucleosynthesis, we show that this fallback material can shine in gamma and X-rays with luminosities ≳1048 erg s‑1 for hundreds of seconds, thus making it a good and natural candidate to explain the extended emission in short GRBs. Additionally, our model for fallback emission reproduces well and rather naturally some of the phenomenological traits of extended emission, such as its softer spectra with respect to the prompt emission and the presence of exponential cutoffs in time. Our results clearly highlight that fallback flows onto merger remnants cannot be neglected, and the corresponding emission represents a very promising and largely unexplored avenue to explain the complex phenomenology of GRBs.

Keywords: Neutron stars, Gamma-ray bursts, Compact objects, Magnetohydrodynamical simulations
X-Rays from a Central "Exhaust Vent" of the Galactic Center Chimney. Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of linear X-ray-emitting features located within the southern portion of the Galactic center chimney and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.°08, b = ‑1.°42. The surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology, which may have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the feature's spectra favor a complex two-component model consisting of thermal and recombining plasma components, possibly a sign of shock compression or heating of the interstellar medium by outflowing material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a sequence of accretion events onto the Galactic black hole may be a plausible quasi-continuous energy source to sustain the observed morphology.

Keywords: Galactic center, Diffuse x-ray background
Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman. The first-generation metal-free stars, referred to as Population III (Pop III) stars, are believed to be the first objects to form out of the pristine gas in the very early Universe. Pop III stars have different structures from the current generation of stars and are important for generating heavy elements and shaping subsequent star formation. However, it is very challenging to directly detect Pop III stars given their high redshifts and short lifetimes. In this Letter, we propose a novel method for detecting Pop III stars through their tidal disruption events (TDEs) by massive black holes. We model the emission properties and calculate the expected rates for these unique TDEs in the early Universe at z ∼ 10. We find that Pop III star TDEs have much higher mass fallback rates and longer evolution timescales compared to solar-type star TDEs in the local Universe, which enhances the feasibility of their detection, although a good survey strategy will be needed for categorizing these sources as transients. We further demonstrate that a large fraction of the flare emissions are redshifted to infrared wavelengths, which can be detected by the JWST and the Nancy Grace Roman Space Telescope (Roman). Last but not least, we find a promising Pop III star TDE detection rate of up to a few tens per year using Roman, based on our current understanding of the black hole mass function in the early Universe.

Keywords: Tidal disruption, Population III stars
CLEANing Cygnus A Deep and Fast with R2D2. A novel deep-learning paradigm for synthesis imaging by radio interferometry in astronomy was recently proposed, dubbed "Residual-to-Residual DNN series for high-Dynamic range imaging" (R2D2). In this work, we start by shedding light on R2D2's algorithmic structure, interpreting it as a learned version of CLEAN with minor cycles substituted with a deep neural network (DNN) whose training is iteration-specific. We then proceed with R2D2's first demonstration on real data, for monochromatic intensity imaging of the radio galaxy Cygnus A from S-band observations with the Very Large Array. We show that the modeling power of R2D2's learning approach enables delivering high-precision imaging, superseding the resolution of CLEAN, and matching the precision of modern optimization and plug-and-play algorithms, respectively uSARA and AIRI. Requiring few major-cycle iterations only, R2D2 provides a much faster reconstruction than uSARA and AIRI, known to be highly iterative, and is at least as fast as CLEAN.

Keywords: Aperture synthesis, Neural networks, Computational methods, Radio galaxies, Radio interferometry, Astronomy image processing
Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State. Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2–8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system.

Keywords: X-ray astronomy, Black hole physics, Polarimetry, Stellar mass black holes
The Most Distant H I Galaxies Discovered by the 500 m Dish FAST. Neutral hydrogen (H I) is the primary component of the cool interstellar medium (ISM) and is the reservoir of fuel for star formation. Owing to the sensitivity of existing radio telescopes, our understanding of the evolution of the ISM in galaxies remains limited, as it is based on only a few hundred galaxies detected in H I beyond the local Universe. With the high sensitivity of the Five-hundred-meter Aperture Spherical radio Telescope (FAST), we carried out a blind H I search, the FAST Ultra-Deep Survey, which extends to redshifts up to 0.42 and a sensitivity of 50 μJy beam‑1. Here, we report the first discovery of six galaxies in H I at z &gt; 0.38. For these galaxies, the FAST angular resolution of ∼4' corresponds to a mean linear size of   $\sim 1.3\,{h}_{70}^{-1}\,$   Mpc. These galaxies are among the most distant H I emission detections known, with one having the most massive H I content (  ${10}^{10.93\pm 0.04}\,{h}_{70}^{-2}\,{M}_{\odot }$  ). Using recent data from the DESI survey and new observations with the Hale, Big Telescope Alt-azimuth, and Keck telescopes, optical counterparts are detected for all galaxies within the 3σ positional uncertainty (  $0.5\,{h}_{70}^{-1}\,$  Mpc) and 200 km s‑1 in recession velocity. Assuming that the dominant source of H I is the identified optical counterpart, we find evidence of evolution in the H I content of galaxies over the last 4.2 Gyr. Our new high-redshift H I galaxy sample provides the opportunity to better investigate the evolution of cool gas in galaxies. A larger sample size in the future will allow us to refine our knowledge of the formation and evolution of galaxies.

Keywords: High-redshift galaxies, Galaxy evolution, H I line emission
Possibility of Secondary i- and s-processes Following r-process in the Collapsar Jet. The slow and intermediate neutron-capture processes, s- and i-processes, are believed to occur in asymptotic giant branch stars to provide half of the heavy atomic nuclei with A ≥ 90. We suggest a possibility that certain types of outflows found in the collapsar, which is a supernova generated by a rapidly rotating massive star undergoing core collapse, leaving behind a black hole and emitting relativistic jets, can provide conditions that are viable for s- and i-processes as secondary processes following the rapid neutron-capture process, r-process. We propose that the pronounced odd–even effect in the mass abundance pattern near rare earth elements in metal-deficient halo stars could be an observational hint for the s- and i-processes in the collapsar.

Keywords: Explosive nucleosynthesis, R-process, Solar abundances, CEMP stars, S-process
Expected Impact of Glints from Space Debris in the LSST. We examine the simple model put forth in a recent note by Loeb regarding the brightness of space debris in the size range of 1–10 cm and their impact on the Rubin Observatory Legacy Survey of Space and Time (LSST) transient object searches. Their main conclusion was that "image contamination by untracked space debris might pose a bigger challenge [than large commercial satellite constellations in Low-Earth orbit]." Following corrections and improvements to this model, we calculate the apparent brightness of tumbling low-Earth orbit (LEO) debris of various sizes, and we briefly discuss the likely impact and potential mitigations of glints from space debris in LSST. We find the majority of the difference in predicted signal-to-noise ratio (S/N), about a factor of 6, arises from the defocus of LEO objects due to the large Simonyi Survey Telescope primary mirror and finite range of the debris. The largest change from the Loeb estimates is that 1–10 cm debris in LEO pose no threat to LSST transient object alert generation because their S/N for detection will be much lower than estimated by Loeb due to defocus. We find that only tumbling LEO debris larger than 10 cm or with significantly greater reflectivity, which give 1 ms glints, might be detected with high confidence (S/N &gt; 5). We estimate that only one in five LSST exposures low on the sky during twilight might be affected. More slowly tumbling objects of larger size can give flares in brightness that are easily detected; however, these will not be cataloged by the LSST Science Pipelines because of the resulting long streak.

Keywords: Sky surveys, Light pollution, Transient sources, Artificial satellites, Ground-based astronomy
The HI Mass Function of Star-forming Galaxies at z ≈ 1. We present the first estimate, based on direct HI 21 cm observations, of the HI mass function (HIMF) of star-forming galaxies at z ≈ 1, obtained by combining our measurement of the scaling relation between HI mass (M HI ) and B-band luminosity (M  B ) of star-forming galaxies with a literature estimate of the B-band luminosity function at z ≈ 1. We determined the M HI –M  B  relation by using the GMRT-CATz1 survey of the DEEP2 fields to measure the average HI mass of blue galaxies at z = 0.74–1.45 in three separate M  B  subsamples. This was done by separately stacking the HI 21 cm emission signals of the galaxies in each subsample to detect, at (3.5–4.4)σ significance, the average HI 21 cm emission of each subsample. We find that the M HI –M  B  relation at z ≈ 1 is consistent with that at z ≈ 0. We combine our estimate of the M HI –M  B  relation at z ≈ 1 with the B-band luminosity function at z ≈ 1 to determine the HIMF at z ≈ 1. We find that the number density of galaxies with M HI  &gt; 1010 M ⊙ (higher than the knee of the local HI mass function) at z ≈ 1 is a factor of ≈4–5 higher than that at z ≈ 0, for a wide range of assumed scatters in the M HI –M  B  relation. We rule out the hypothesis that the number density of galaxies with M HI  &gt; 1010 M ⊙ remains unchanged between z ≈ 1 and z ≈ 0 at ≳99.7% confidence. This is the first statistically significant evidence for evolution in the HIMF of galaxies from the epoch of cosmic noon.

Keywords: Radio astronomy, High-redshift galaxies, Neutral hydrogen clouds
Forming Mercury from Excited Initial Conditions. Mercury is notoriously difficult to form in Solar System simulations, due to its small mass and iron-rich composition. Smooth particle hydrodynamics simulations of collisions have found that a Mercury-like body could be formed by one or multiple giant impacts, but due to the chaotic nature of collisions, it is difficult to create a scenario where such impacts will take place. Recent work has found more success forming Mercury analogues by adding additional embryos near Mercury's orbit. In this work, we aim to form Mercury by simulating the formation of the Solar System in the presence of the giant planets Jupiter and Saturn. We test out the effect of an inner disk of embryos added on to the commonly used narrow annulus of initial material. We form Mercury analogues with core-mass fractions (CMFs) &gt; 0.4 in ∼10% of our simulations, and twice that number of Mercury analogues form during the formation process but are unstable and do not last to the end of the simulations. Mercury analogues form at similar rates for both disks with and without an inner component, and most of our Mercury analogues have lower CMFs than that of Mercury, ∼0.7, due to significant accretion of debris material. We suggest that a more in-depth understanding of the fraction of debris mass that is lost to collisional grinding is necessary to understand Mercury's formation, or some additional mechanism is required to stop this debris from accreting.

Keywords: Collisional processes, Solar system formation, Solar system terrestrial planets, Mercury (planet)
Oscillating Dark Energy in Light of the Latest Observations and Its Impact on the Hubble Tension. In this paper, we have performed a comparative study of different types of oscillating dark energy (DE) models using the Metropolis algorithm of Markov Chain Monte Carlo. Eight different oscillating parameterizations are examined herein that have demonstrated considerable ability to fit the overall cosmological observations, including the Pantheon sample of Type Ia supernovae, baryon acoustic oscillations, cosmic chronometer Hubble data, and distance priors of the Planck cosmic microwave background. In order to compare the consistency of these models with observations, we have used both the Akaike and deviance information criteria. Although the values of the Akaike information criterion for different models indicate that there is no support for oscillating DE models, the deviance information criterion showed that there is significant support for some of these models. Our results showed that these models are capable of solving the cosmic coincidence problem and alleviating the Hubble tension. Comparing the H 0 values obtained for different oscillating scenarios with that of ΛCDM, we observed that our oscillating models led to   $\bar{{H}_{0}}=69.78$  , which is 0.29 greater than H 0,Λ and thus reduces the Hubble tension. Among all of the models, model 1, with H 0 = 70.00 ± 0.71, is the most capable of alleviating the H 0 tension. Furthermore, we examined our models assuming H 0 = 73.0 ± 1.4 from SHoES measurements. We find that adding this data point to our data combination led to a   ${\rm{\Delta }}\bar{{H}_{0}}=0.95$   increase in the H 0 value for different models.

Keywords: Cosmology, Cosmological models, Cosmological parameters, Observational cosmology, Hubble constant, Dark energy
Relativistic Jet Ejections from Slim Disks. A mechanism for the ejection of relativistic jets from slim disks is studied. Since radiation pressure is dominant in the slim disk, radiative energy flows along the pressure gradient in the vertical direction. The divergence of the radiative flux tells us that the flow of radiative energy from a bottom layer near the equatorial plane is absorbed by another layer above the boundary surface. The absorbed energy accumulates in the upper layer as the matter advances inward, and calculations show that the specific energy of the flow in the upper layer can be as large as ∼c 2 near the black hole when the accretion rate through the upper layer is relatively low. Since the specific energy ∼c 2 is much larger than the gravitational energy, the height of the upper layer could significantly increase then. Hence, the innermost part of the upper layer after almost all the angular momentum has been removed could have a much greater height than the size of the black hole, and the flow could collide with itself around the central axis of the disk, bouncing back from the axis while simultaneously expanding along it. The flow is expected to go outward along the central axis and to become supersonic due to the change in its cross section, finally producing relativistic jets.

Keywords: Accretion, Relativistic jets, Black holes, X-ray binary stars
Dynamical Properties of Magnetized Low-angular-momentum Accretion Flows around a Kerr Black Hole. An essential factor for determining the characteristics of an accretion flow is its angular momentum. According to the angular momentum of the flow, semi-analytical analysis suggests various types of accretion solutions. It is critical to test these with numerical simulations, using the most advanced framework available (general relativistic magnetohydrodynamics), to understand how the flow changes with different angular momentum. By changing the initial condition of the accretion torus minimally, we can simulate a steady, low-angular-momentum accretion flow around a Kerr black hole. We focus primarily on the lower limits of angular momentum and find that an accretion flow with an intermediate range of angular momentum differs significantly from high- or very-low-angular-momentum flows. The intermediate-angular-momentum accretion flow has the highest density, pressure, and temperature near the black hole, making it easier to observe. We find that the density and pressure have power-law scalings ρ ∝ r  n‑3/2 and p  g  ∝ r  n‑5/2, which only hold for very-low-angular-momentum cases. With the increase in flow angular momentum, it develops a nonaxisymmetric nature. In this case, simple self-similarity does not hold. We also find that the sonic surface moves away from the innermost stable circular orbit as the angular momentum decreases. Finally, we emphasize that an intermediate-angular-momentum flow could provide a possible solution to explaining the complex observation features of the supermassive black hole Sgr A* at our galactic center.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, Relativistic fluid dynamics, Magnetohydrodynamical simulations
Insights into the Galactic Bulge Chemodynamical Properties from Gaia Data Release 3. We explore the chemodynamical properties of the Galaxy in the azimuthal velocity V  ϕ  and metallicity [Fe/H] space using red giant stars from Gaia Data Release 3. The row-normalized V  ϕ –[Fe/H] maps form a coherent sequence from the bulge to the outer disk, clearly revealing the thin/thick disk and the Splash. The metal-rich stars display bar-like kinematics, while the metal-poor stars show dispersion-dominated kinematics. The intermediate-metallicity population (‑1 &lt; [Fe/H]&lt; ‑ 0.4) can be separated into two populations, one that is bar-like, i.e., dynamically cold (  ${\sigma }_{{V}_{R}}\sim 80$   km s‑1) and fast-rotating (V  ϕ  ≳ 100 km s‑1), and the Splash, which is dynamically hot (  ${\sigma }_{{V}_{R}}\sim 110$   km s‑1) and slow-rotating (V  ϕ  ≲ 100 km s‑1). We compare the observations in the bulge region with an Auriga simulation where the last major merger event occurred ∼10 Gyr ago: only stars born around the time of the merger reveal a Splash-like feature in the V  ϕ –[Fe/H] space, suggesting that the Splash is likely merger-induced, predominantly made up of heated disk stars and the starburst associated with the last major merger. Since the Splash formed from the proto-disk, its lower metallicity limit coincides with that of the thick disk. The bar formed later from the dynamically hot disk with [Fe/H] &gt; ‑ 1 dex, with the Splash not participating in the bar formation and growth. Moreover, with a set of isolated evolving N-body disk simulations, we confirm that a nonrotating classical bulge can be spun up by the bar and develop cylindrical rotation, consistent with the observations for the metal-poor stars.

Keywords: Milky Way evolution, Galaxy bulges, Galactic bulge
KFVM-WENO: A High-order Accurate Kernel-based Finite Volume Method for Compressible Hydrodynamics. This paper presents a fully multidimensional kernel-based reconstruction scheme for finite volume methods applied to systems of hyperbolic conservation laws, with a particular emphasis on the compressible Euler equations. Nonoscillatory reconstruction is achieved through an adaptive-order weighted essentially nonoscillatory (WENO) method cast into a form suited to multidimensional reconstruction. A kernel-based approach inspired by radial basis functions and Gaussian process modeling, which we call kernel-based finite volume method with WENO, is presented here. This approach allows the creation of a scheme of arbitrary order of accuracy with simply defined multidimensional stencils and substencils. Furthermore, the fully multidimensional nature of the reconstruction allows for a more straightforward extension to higher spatial dimensions and removes the need for complicated boundary conditions on intermediate quantities in modified dimension-by-dimension methods. In addition, a new simple yet effective set of reconstruction variables is introduced, which could be useful in existing schemes with little modification. The proposed scheme is applied to a suite of stringent and informative benchmark problems to demonstrate its efficacy and utility. A highly parallel multi-GPU implementation using Kokkos and the message-passing interface is also provided.

Keywords: Computational methods, Astrophysical fluid dynamics