Sazuna/UAT_keywords huggingface dataset:
Special Supernova Signature from BH-NS/BH Progenitor Systems. The gravitational-wave detection by the LIGO-Virgo scientific collaboration shows that black hole and neutron star (BH-NS) or BH-BH systems with a BH mass of tens of solar masses widely exist in the universe. Two main types of scenarios have been invoked for the formation of BH-NS/BH systems, including isolated binary evolution in galactic fields and dynamical interactions in dense environments. Here we propose that if the BH-NS/BH systems are formed from isolated binary evolution, the supernova (SN) signal associated with the second core collapse would show some identifiable features, due to the accretion feedback from the companion BH. Depending on the binary properties, we show that the SN lightcurve could present a sharp peak around ∼10 days, with luminosity even at the level of the super luminous SNe (e.g., $\sim {10}^{44}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ) or present a plateau feature lasting for several tens of days with regular luminosity of core collapse SNe. Comparing the event rate density of these special SN signals with the event rate density of LIGO-Virgo detected BH-NS/BH systems could help to distinguish the BH-NS/BH formation channel.

Keywords: Neutron stars, Gravitational waves, Supernovae, Black holes
Evidence for Sulfur-bearing Species on Callisto's Leading Hemisphere: Sourced from Jupiter's Irregular Satellites or Io?. We investigated whether sulfur-bearing species are present on the icy Galilean moon Callisto by analyzing eight near-infrared reflectance spectra collected over a wide range of sub-observer longitudes. We measured the band areas and depths of a 4 μm feature in these spectra, which has been attributed to sulfur dioxide (SO2), as well as carbonates, in previously collected data sets of this moon. All eight spectra we collected display the 4 μm band. The four spectra collected over Callisto's leading hemisphere display significantly stronger 4 μm bands compared to the four trailing hemisphere spectra (&gt;3σ difference). We compared the central wavelength position and shape of Callisto's 4 μm band to laboratory spectra of various sulfur-bearing species and carbonates. Our comparison demonstrates that Callisto's 4 μm band has a spectral signature similar to thermally altered sulfur, as well as a 4.025 μm feature attributed to disulfanide (HS2). Our analysis therefore supports the presence of S-bearing species on Callisto but is not consistent with the presence of SO2. The significantly stronger 4 μm band detected on Callisto's leading hemisphere could result from collisions with H2S-rich dust grains that originate on Jupiter's retrograde irregular satellites or implantation of magnetospheric S ions that originate from volcanic activity on Io. Alternatively, S-bearing species could be native to Callisto and are exposed by dust collisions and larger impacts that drive regolith overturn, primarily on its leading side.

Keywords: Surface processes, Surface composition, Planetary surfaces, Surface ices
The Lyman Continuum Escape Survey: Connecting Time-dependent [O III] and [O II] Line Emission with Lyman Continuum Escape Fraction in Simulations of Galaxy Formation. Escaping Lyman continuum photons from galaxies likely reionized the intergalactic medium at redshifts z ≳ 6. However, the Lyman continuum is not directly observable at these redshifts and secondary indicators of Lyman continuum escape must be used to estimate the budget of ionizing photons. Observationally, at redshifts z ∼ 2-3 where the Lyman continuum is observationally accessible, surveys have established that many objects that show appreciable Lyman continuum escape fractions fesc also show enhanced [O III]/[O II] (O32) emission line ratios. Here, we use radiative transfer analyses of cosmological zoom-in simulations of galaxy formation to study the physical connection between fesc and O32. Like the observations, we find that the largest fesc values occur at elevated O32 ∼ 3-10 and that the combination of high fesc and low O32 is extremely rare. While high fesc and O32 often are observable concurrently, the timescales of the physical origin for the processes are very different. Large O32 values fluctuate on short (∼1 Myr) timescales during the Wolf-Rayet-powered phase after the formation of star clusters, while channels of low absorption are established over tens of megayears by collections of supernovae. We find that while there is no direct causal relation between fesc and O32, high fesc most often occurs after continuous input from star formation-related feedback events that have corresponding excursions to large O32 emission. These calculations are in agreement with interpretations of observations that large fesc tends to occur when O32 is large, but large O32 does not necessarily imply efficient Lyman continuum escape.

Keywords: Galaxy formation, Interstellar line emission, Star forming regions, High time resolution astrophysics, Emission nebulae, Radiative transfer simulations, High-redshift galaxies
An Exact, Generalized Laplace Resonance in the HR 8799 Planetary System. A system of four super-Jupiter planets around HR 8799 is the first multiplanet configuration discovered via the direct imaging technique. Despite over a decade of research, the system's architecture is still not fully resolved. The main difficulty comes from a still narrow observing window of ∼20 yr that covers small arcs of orbits with periods from roughly 50 to 500 yr. Soon after the discovery, it became clear that unconstrained best-fitting astrometric configurations self-disrupt rapidly due to strong mutual gravitational interactions between the companions of ≃10 Jupiter mass. Recently, we showed that the HR 8799 system may be long-term stable when locked in a generalized Laplace 8:4:2:1 mean-motion resonance (MMR) chain, and we constrained its orbits through the planetary migration. Here we qualitatively improve this approach by considering the MMR in terms of an exactly periodic configuration. This assumption enables us to construct for the first time the self-consistent N-body model of the long-term stable orbital architecture using only available astrometric positions of the planets relative to the star. We independently determine the planetary masses, which are consistent with thermodynamic evolution, and the parallax overlapping to 1σ with the most recent Gaia DR2 value. We also determine the global structure of the inner and outer debris disks in the [8, 600] au range, consistent with the updated orbital solution.

Keywords: Exoplanet dynamics, Exoplanet detection methods, Exoplanet systems
Oscillations of Hypermassive Compact Stars with Gravitational Radiation and Viscosity. Binary neutron star mergers, such as the multimessenger GW170817 event, may produce hypermassive compact objects that are supported against collapse by the internal circulation of the fluid within the star. We compute their unstable modes of oscillations driven by gravitational-wave radiation and shear viscosity, modeling them as triaxial Riemann ellipsoids. We work in a perturbative regime, where the gravitational radiation-reaction force is taken into account at 2.5-post-Newtonian order and find unstable modes with dissipation timescales ≳1 ms that are relevant to the transient state of a hypermassive remnant of a merger. We show that the secular instabilities are dominated by gravitational-wave radiation. If the shear viscosity is included, it can increase the growth times or even stabilize the unstable modes, but it must have values several orders of magnitude larger than predicted for cold neutron stars.

Keywords: Neutron stars, Stellar oscillations, Gravitational waves
Stringent Search for Precursor Emission in Short GRBs from Fermi/GBM Data and Physical Implications. We perform a stringent search for precursor emission of short gamma-ray bursts (SGRBs) from the Fermi/GBM data and find 16 precursor events with ≳4.5σ significance. We find that the durations of the main SGRB emission ( ${T}_{\mathrm{GRB}}$ ) and the precursor emission ( ${T}_{\mathrm{pre}}$ ), as well as the waiting time ( ${T}_{\mathrm{wt}}$ ) in between, are roughly comparable to each other, with ${T}_{\mathrm{wt}}$ ≈ 2.8 ${T}_{\mathrm{GRB}}$ 1.2 approximately satisfied for most cases except one significant outlier. We also perform spectral analyses to the precursors and SGRBs, and find that the spectra of precursor emission can be fitted with the blackbody, nonthermal cutoff power law and/or power-law models. We consider several possible models for precursor emission in SGRBs and find that the luminosity and spectral shape may be explained by the the shock breakout or the photospheric radiation of a fireball launched after the merger for thermal precursors, or magnetospheric interaction between two neutron stars prior to the merger for nonthermal precursors. For the fireball photospheric model, a matter-dominated jet is preferred and a constraint on the fireball Lorentz factor can be placed as Γ ∼ 30. For the magnetospheric interaction model, the jet launching mechanism may be constrained. In particular, those events with ${T}_{\mathrm{wt}}$ / ${T}_{\mathrm{GRB}}$ ≫ 1 (e.g., GRB191221802) require the formation of a supramassive or stable neutron star after the merger, with the delay time defined by the timescale for an initially baryon-loaded jet to become magnetically dominated and relativistic.

Keywords: Neutron stars, Gamma-ray bursts, Gravitational waves, Astrostatistics
Fermi/GBM View of the 2019 and 2020 Burst Active Episodes of SGR J1935+2154. We present temporal and time-integrated spectral analyses of 148 bursts from the latest activation of SGR J1935+2154, observed with the Fermi/Gamma-ray Burst Monitor from 2019 October 4 through 2020 May 20, excluding an ∼130 s segment with a very high burst density on 2020 April 27. The 148 bursts presented here are slightly longer and softer than bursts from earlier activations of SGR J1935+2154, as well as from other magnetars. The long-term spectral evolution trend is interpreted as being associated with an increase in the average plasma loading of the magnetosphere during bursts. We also find a trend of increased burst activity from SGR J1935+2154 since its discovery in 2014. Finally, we find no association of typical radio bursts with X-ray bursts from the source. This contrasts the association of FRB 200428 with an SGR J1935+2154 X-ray burst, which is to-date unique among the magnetar population.

Keywords: Magnetars, Soft gamma-ray repeaters
Neon Cluster Formation and Phase Separation during White Dwarf Cooling. Recent observations of Galactic white dwarfs (WDs) with Gaia suggest there is a population of massive crystallizing WDs exhibiting anomalous cooling—the Q branch. While single-particle 22Ne sedimentation has long been considered a possible heat source, recent work suggests that 22Ne must separate into clusters, enhancing diffusion, in order for sedimentation to provide heating on the observed timescale. We show definitively that 22Ne cannot separate to form clusters in C/O WDs using molecular dynamics simulations, and we further present a general C/O/Ne phase diagram showing that strong 22Ne enrichment is not achievable for 22Ne abundance ≲30%. We conclude that the anomalous heating cannot be due to 22Ne cluster sedimentation and that Q branch WDs may have an unusual composition, possibly rich with heavier elements.

Keywords: Stellar interiors, White dwarf stars, N-body simulations, Degenerate matter
Heliospheric Maps from Cassini INCA Early in the Cruise to Saturn. We present new energetic neutral atom (ENA) maps from the Ion and Neutral Camera (INCA) instrument on Cassini from the year 2000, prior to Cassini's encounter with Jupiter. These maps are the first produced for the year 2000 and are the only maps with comprehensive spatial coverage from the peak of solar cycle 23. These ENA maps span the energy range from 5.2 to 55 keV covering the pickup to suprathermal energy range. These maps represent a novel glimpse into the influence of the solar cycle on the structure of the outer heliosphere, specifically on the heliosheath where pickup and suprathermal ions dominate. The observations are consistent with the picture of the heliosheath from previous observations by the Cassini, Interstellar Boundary Explorer (IBEX), and Voyager missions. These maps have some consistent spatial features to maps produced by Cassini during solar cycle 24 such as reduced intensities in the mid-latitude basins. These maps also have distinct spatial features such as enhanced intensities at the poles and reduced intensities at the low-latitude flanks. These maps do not indicate a strong intensity increase in the regions adjacent to the nose and also show an intensity increase in the regions adjacent to the tailward direction.

Keywords: Heliosheath, Solar wind, Heliosphere
Discovery of a Gamma-Ray Black Widow Pulsar by GPU-accelerated Einstein@Home. We report the discovery of 1.97 ms period gamma-ray pulsations from the 75 minute orbital-period binary pulsar now named PSR J1653-0158. The associated Fermi Large Area Telescope gamma-ray source 4FGL J1653.6-0158 has long been expected to harbor a binary millisecond pulsar. Despite the pulsar-like gamma-ray spectrum and candidate optical/X-ray associations—whose periodic brightness modulations suggested an orbit—no radio pulsations had been found in many searches. The pulsar was discovered by directly searching the gamma-ray data using the GPU-accelerated Einstein@Home distributed volunteer computing system. The multidimensional parameter space was bounded by positional and orbital constraints obtained from the optical counterpart. More sensitive analyses of archival and new radio data using knowledge of the pulsar timing solution yield very stringent upper limits on radio emission. Any radio emission is thus either exceptionally weak, or eclipsed for a large fraction of the time. The pulsar has one of the three lowest inferred surface magnetic-field strengths of any known pulsar with Bsurf ≍ 4 × 107 G. The resulting mass function, combined with models of the companion star's optical light curve and spectra, suggests a pulsar mass ≳2 M☉. The companion is lightweight with mass ∼0.01 M☉, and the orbital period is the shortest known for any rotation-powered binary pulsar. This discovery demonstrates the Fermi Large Area Telescope's potential to discover extreme pulsars that would otherwise remain undetected.

Keywords: Gamma-ray sources, Neutron stars, Binary pulsars, Millisecond pulsars
Confirming the Explosive Outflow in G5.89 with ALMA. The explosive molecular outflow detected decades ago in the Orion BN/KL region of massive star formation was considered to be a bizarre event. This belief was strengthened by the nondetection of similar cases over the years with the only exception of the marginal case of DR21. Here, we confirm a similar explosive outflow associated with the UCHII region G5.89-0.39 that indicates that this phenomenon is not unique to Orion or DR21. Sensitive and high angular resolution (∼0"1) Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) and SiO(5-4) observations show that the molecular outflow in the massive star-forming region G5.89-0.39 is indeed an explosive outflow with an age of about 1000 yr and a liberated kinetic energy of 1046-49 erg. Our new CO(2-1) ALMA observations revealed over 30 molecular filaments, with Hubble-like expansion motions, pointing to the center of UCHII region. In addition, the SiO(5-4) observations reveal warmer and strong shocks very close to the origin of the explosion, confirming the true nature of the flow. A simple estimation for the occurrence of these explosive events during the formation of the massive stars indicates an event rate of once every ∼100 yr, which is close to the supernovae rate.

Keywords: Stellar-interstellar interactions, Aperture synthesis, Massive stars, Stellar jets, Star formation
The Origin of Switchbacks in the Solar Corona: Linear Theory. The origin, structure, and propagation characteristics of a switchback are compelling questions posed by Parker Solar Probe (PSP) observations of velocity spikes and magnetic field reversals. By assuming interchange reconnection between coronal loop and open magnetic field, we show that this results in the generation of upward (into the heliosphere) and downward complex structures propagating at the fast magnetosonic speed (i.e., the Alfvén speed in the low plasma beta corona) that can have an arbitrary radial magnetic field deflection, including "S-shaped." We derive the evolution equation for the switchback radial magnetic field as it propagates through the inhomogeneous supersonic solar corona. An analytic solution for arbitrary initial conditions is used to investigate the properties of a switchback propagating from launch ∼6 to ∼35 R⊙ where PSP observed switchbacks during its first encounter. We provide a detailed comparison to an example event, showing that the magnetic field and plasma solutions are in accord with PSP observations. For a simple single switchback, the model predicts either a single or a double-humped structure; the former corresponding to PSP observing either the main body or the flanks of the switchback. The clustering of switchbacks and their sometimes complicated structure may be due to the formation of multiple closely spaced switchbacks created by interchange reconnection with numerous open and loop magnetic field lines over a short period. We show that their evolution yields a complex, aggregated group of switchbacks that includes "sheaths" with large-amplitude radial magnetic field and velocity fluctuations.

Keywords: Interplanetary turbulence, Active solar corona, Solar coronal waves
Turbulence and Energetic Particles in Radiative Shock Waves in the Cygnus Loop. II. Development of Postshock Turbulence. Radiative shock waves in the Cygnus Loop and other supernova remnants show different morphologies in [O III] and Hα emission. We use HST spectra and narrowband images to study the development of turbulence in the cooling region behind a shock on the west limb of the Cygnus Loop. We refine our earlier estimates of shock parameters that were based upon ground-based spectra, including ram pressure, vorticity, and magnetic field strength. We apply several techniques, including Fourier power spectra and the Rolling Hough Transform, to quantify the shape of the rippled shock front as viewed in different emission lines. We assess the relative importance of thermal instabilities, the thin shell instability, upstream density variations, and upstream magnetic field variations in producing the observed structure.

Keywords: Interplanetary turbulence, Plasma astrophysics, Supernova remnants, Interstellar magnetic fields, Shocks
Probing the Physics of Mechanical AGN Feedback with Radial Elongations of X-Ray Cavities. Mechanical active galactic nucleus (AGN) feedback plays a key role in massive galaxies, galaxy groups, and clusters. However, the energy content of AGN jets that mediate this feedback process is still far from clear. Here we present a preliminary study of radial elongations τ of a large sample of X-ray cavities, which are apparently produced by mechanical AGN feedback. All of the cavities in our sample are elongated along the angular (type I) or jet directions (type II), or nearly circular (type III). The observed value of τ roughly decreases as the cavities rise buoyantly, confirming the same trend found in hydrodynamic simulations. For young cavities, both type-I and type-II cavities exist, and the latter dominates. Assuming a spheroidal cavity shape, we derive an analytical relation between the intrinsic radial elongation $\bar{\tau }$ and the inclination-angle-dependent value of τ, showing that projection effect makes cavities appear more circular, but does not change type-I cavities into type-II ones, or vice versa. We summarize radial elongations of young cavities in simulations, finding that $\bar{\tau }$ increases with the kinetic fraction of AGN jets. While mild jets always produce type-II cavities, thermal-energy-dominated strong jets produce type-I cavities, and kinetic-energy-dominated strong jets produce type-II cavities. Our results suggest that some AGN jets are strong and dominated by thermal energy (or cosmic rays). However, these jets do not dominate in AGN feedback. If most jets are dominated by nonkinetic energies, they should be mainly mild jets. If most jets are strong, they must be mainly dominated by the kinetic energy.

Keywords: Galaxy clusters, Hydrodynamical simulations, X-ray astronomy, Radio jets, High energy astrophysics, Active galaxies, Radio lobes, Active galactic nuclei, Galaxy groups, Intracluster medium
The Magellan M2FS Spectroscopic Survey of High-redshift Galaxies: A Sample of 260 Lyα Emitters at Redshift z ≈ 5.7. We present a spectroscopic survey of Lyα emitters (LAEs) at z ≈ 5.7 using the multiobject spectrograph M2FS on the Magellan Clay telescope. This is part of a high-redshift galaxy survey carried out in several well-studied deep fields. These fields have deep images in multiple UV/optical bands, including a narrow NB816 band that has allowed an efficient selection of LAE candidates at z ≈ 5.7. Our sample consists of 260 LAEs and covers a total effective area of more than 2 deg2 on the sky. This is so far the largest (spectroscopically confirmed) sample of LAEs at this redshift. We use the secure redshifts and narrowband photometry to measure Lyα luminosities. We find that these LAEs span a Lyα luminosity range of $\sim 2\times {10}^{42}\mbox{--}5\times {10}^{43}$ erg s-1 and include some of the most luminous galaxies known at $z\geqslant 5.7$ in terms of Lyα luminosity. Most of them have rest-frame equivalent widths between 20 and 300 Å, and more luminous Lyα emission lines tend to have broader line widths. We detect a clear offset of ∼20 Å between the observed Lyα wavelength distribution and the NB816 filter transmission curve, which can be explained by the intergalactic medium absorption of continua blueward of Lyα in the high-redshift spectra. This sample is being used to study the Lyα luminosity function and galaxy properties at z ≈ 5.7.

Keywords: Lyman-alpha galaxies, High-redshift galaxies, Galaxy properties
Young Faithful: The Eruptions of EC 53 as It Cycles through Filling and Draining the Inner Disk. While young stellar objects sometimes undergo bursts of accretion, these bursts usually occur sporadically, making them challenging to study observationally and to explain theoretically. We build a schematic description of cyclical bursts of the young stellar object EC 53 (also known as V371 Ser) using near-IR and submillimeter monitoring obtained over six cycles, each lasting ≈530 days. EC 53 brightens over 0.12 yr by 0.3 mag at 850 μm, by 2 mag at 3.35 μm, and by 1.5 mag at near-IR wavelengths, to a maximum luminosity consistent with an accretion rate of ∼8 × 10-6 M⊙ yr-1. The emission then decays with an e-folding timescale of $\approx 0.74\,\mathrm{yr}$ until the accretion rate is ∼1 × 10-6 M⊙ yr-1. The next eruption then occurs, likely triggered by the buildup of a ∼5 × 10-6 M⊙ mass in the inner disk, enough for it to become unstable and drain onto the star. Just before outburst, when the disk is almost replenished, the near-IR colors become redder, indicating an increase in the geometrical height of the disk by this mass buildup. The reddening disappears soon after the initial burst, as much of the mass is drained from the disk. We quantify physical parameters related to the accretion process in EC 53 by assuming an α-disk formulation, constrained by the observed disk properties and accretion rate. While we can only speculate about the possible trigger for these faithful eruptions, we hope that our quantified schematic will motivate theorists to test the hypothesized mechanisms that could cause the cyclical buildup and draining of mass in the inner disk.

Keywords: Periodic variable stars, Young stellar objects, Star formation, Protoplanetary disks, Variable stars, Circumstellar disks, Stellar accretion, Protostars