Sazuna/UAT_keywords huggingface dataset:
Shock and Discontinuity Formation in the Front of an Expanding Coronal Magnetic Arcade in Two-fluid Simulations. The dynamic evolution of a magnetic arcade associated with footpoint shearing motions is investigated by an ideal two-fluid (electron-ion) code. The two-fluid numerical simulations produce conspicuous differences compared to earlier MHD simulations beyond the inner arcade region. The decoupling motion between electrons and heavier ions during the arcade expansion induces a growing charge separation and strong electric field in the front of the expanding arcade. The presence of this electric field provides an additional force, along with the magnetic and thermal pressures, that drives the growth of an outwardly expanding wave that steepens into a propagating discontinuity in the plasma and magnetic field. The propagation speed of the discontinuity eventually exceeds the local phase velocity of the MHD fast mode and becomes a perpendicular fast-like shock. There is significant heating at the shock due to adiabatic compression, with preferential heating of the ion fluid also being observed. In addition, parameter tests indicate that (1) the propagation speed of the shock before exiting the inner arcade is independent of the maximum shear speed; (2) slower shearing speeds produce weaker shocks with weaker adiabatic heating; (3) the ion-to-electron mass ratio, mi/me, impacts the strength of the charge separation linearly but has a moderate effect on the propagation speed; and (4) the normalized value of the ion inertial length does not affect the formation and speed of the shock as a whole.

Keywords: Hydrodynamical simulations, Solar coronal loops, Solar coronal heating, Solar coronal waves, Shocks, Magnetic fields
A Model-insensitive Baryon Acoustic Oscillation Feature in the 21 cm Signal from Reionization. We examine the impact of baryon-dark matter relative velocities on intergalactic small-scale structure and the 21 cm signal during reionization. Streaming velocities reduced clumping in the intergalactic medium on mass scales of ∼104-108 M⊙. This effect produced a distinct baryon acoustic oscillation (BAO) feature in the 21 cm power spectrum at wavenumbers k ∼ 0.1 h/Mpc, near which forthcoming surveys will be most sensitive. In contrast to the highly uncertain impact of streaming velocities on star formation, the effect on clumping is better constrained because it is set mainly by cosmology and straightforward gas dynamics. We quantify the latter using coupled radiation-hydrodynamic simulations that capture the Jeans scale of pre-reionization gas. The clumping factor of ionized gas is reduced by 5%-10% in regions with rms streaming velocities. The suppression peaks ≈5 Myr after a region is reionized, but disappears within 200 Myr due to pressure smoothing. We model the corresponding impact on the 21 cm signal and find that the BAO feature is most likely to appear at ≈10% ionization. During this phase, the feature may appear at the 1% (5%) level at k ∼ 0.1 (0.06) h/Mpc with an amplitude that varies by a factor of &lt;10 across a range of reionization histories. We also provide a model for the signal originating from streaming velocity's impact on ionizing sources, which can vary by 4 orders of magnitude depending on highly uncertain source properties. We find that the clumping signal probably dominates the source one unless Population III star formation in 106-108 M⊙ halos contributed significantly to the first 10% of reionization.

Keywords: Reionization, Observational cosmology, Intergalactic medium
The Energetics of Launching the Most Powerful Jets in Quasars: A Study of 3C 82. 3C 82 at a redshift of 2.87 is the most distant 3C (Third Cambridge Catalogue) quasar. Thus, it is a strong candidate to have the most-luminous radio lobes in the universe. 3C 82 belongs to the class of compact steep-spectrum radio sources. We use single-dish and interferometric radio observations in order to model the plasma state of these powerful radio lobes. It is estimated that the long-term time-averaged jet power required to fill these lobes with leptonic plasma is $\overline{Q}\approx 2.66\pm 1.33\times {10}^{47}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , among the largest time-averaged jet powers from a quasar. Positing protonic lobes is not tenable as they would require two orders of magnitude more mass transport to the lobes than was accreted to the central black hole during their formation. The first high signal-to-noise optical spectroscopic observation obtained of this object indicates that there is a powerful high-ionization broad-line wind with a kinetic power of ∼1045 erg s-1 and a velocity of ∼0.01c. We also estimate from the broad lines in 2018 and the UV continuum in three epochs spread out over three decades that the accretion flow bolometric luminosity is Lbol ≈ 3.2-5.8 × 1046 erg s-1. The ratio of $\bar{Q}/{L}_{{\rm{bol}}}\approx 5.91\pm 3.41$ is perhaps the largest of any known quasar. Extremely powerful jets tend to strongly suppress powerful winds of ionized baryonic matter. Consequently, 3C 82 provides a unique laboratory for studying the dynamical limits of the central engine of outflow initiation in quasars.

Keywords: Radio loud quasars, Black hole physics, Relativistic jets, Radio jets
FIREBall-2: The Faint Intergalactic Medium Redshifted Emission Balloon Telescope. The Faint Intergalactic Medium Redshifted Emission Balloon (FIREBall) is a mission designed to observe faint emission from the circumgalactic medium of moderate-redshift (z ∼ 0.7) galaxies for the first time. FIREBall observes a component of galaxies that plays a key role in how galaxies form and evolve, likely contains a significant amount of baryons, and has only recently been observed at higher redshifts in the visible. Here we report on the 2018 flight of the FIREBall-2 Balloon telescope, which occurred on 2018 September 22 from Fort Sumner, New Mexico. The flight was the culmination of a complete redesign of the spectrograph from the original FIREBall fiber-fed integral field unit to a wide-field multiobject spectrograph. The flight was terminated early owing to a hole in the balloon, and our original science objectives were not achieved. The overall sensitivity of the instrument and telescope was 90,000 LU, due primarily to increased noise from stray light. We discuss the design of the FIREBall-2 spectrograph, including modifications from the original FIREBall payload, and provide an overview of the performance of all systems. We were able to successfully flight-test a new pointing control system, a UV-optimized, delta-doped, and coated electron multiplying CCD, and an aspheric grating. The FIREBall-2 team is rebuilding the payload for another flight attempt in the fall of 2021, delayed from 2020 as a result of COVID-19.

Keywords: Ultraviolet telescopes, Ultraviolet astronomy, High altitude balloons, Spectroscopy, Circumgalactic medium
CLEAR. II. Evidence for Early Formation of the Most Compact Quiescent Galaxies at High Redshift. The origin of the correlations between mass, morphology, quenched fraction, and formation history in galaxies is difficult to define, primarily due to the uncertainties in galaxy star formation histories (SFHs). SFHs are better constrained for higher redshift galaxies, observed closer to their formation and quenching epochs. Here we use "nonparametric" SFHs and a nested sampling method to derive constraints on the formation and quenching timescales of quiescent galaxies at $0.7\lt z\lt 2.5$ . We model deep HST grism spectroscopy and photometry from the CLEAR (CANDELS Lyα Emission at Reionization) survey. The galaxy formation redshifts, z50 (defined as the point where they had formed 50% of their stellar mass) range from ${z}_{50}\sim 2$ (shortly prior to the observed epoch) up to ${z}_{50}\simeq 5-8$ . We find that early formation redshifts are correlated with high stellar-mass surface densities, $\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }\,{\mathrm{kpc}}^{-2})\gt 10.25$ , where Σ1 is the stellar mass within 1 pkpc (proper kpc). Quiescent galaxies with the highest stellar-mass surface density, $\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }{\mathrm{kpc}}^{-2})\gt 10.25$ , show a minimum formation redshift: all such objects in our sample have ${z}_{50}\gt 2.9$ . Quiescent galaxies with lower surface density, $\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }\,{\mathrm{kpc}}^{-2})=9.5-10.25$ , show a range of formation epochs ( ${z}_{50}\simeq 1.5\mbox{--}8$ ), implying these galaxies experienced a range of formation and assembly histories. We argue that the surface density threshold $\mathrm{log}{{\rm{\Sigma }}}_{1}/({M}_{\odot }\,{\mathrm{kpc}}^{-2})\gt 10.25$ uniquely identifies galaxies that formed in the first few Gyr after the big bang, and we discuss the implications this has for galaxy formation models.

Keywords: Galaxy quenching, Quenched galaxies, Galaxy evolution, Compact galaxies
Probing the Physical Conditions and Star Formation Processes in the Galactic H II Region S305. We present multiscale and multiwavelength observations of the Galactic H II region S305, which is excited by massive O8.5V and O9.5V stars. Infrared images reveal an extended sphere-like shell (extension ∼7.5 pc; at Td = 17.5-27 K) enclosing the S305 H II region (size ∼5.5 pc; age ∼1.7 Myr). The extended structure observed in the Herschel temperature map indicates that the molecular environment of S305 is heated by the massive O-type stars. Regularly spaced molecular condensations and dust clumps are investigated toward the edges of the infrared shell, where the polycyclic aromatic hydrocarbon (PAH) and H2 emission is also observed. The molecular line data show a signature of an expanding shell of molecular gas in S305. Giant Metrewave Radio Telescope 610 and 1280 MHz continuum maps reveal overdensities of the ionized emission distributed around two O-type stars, which are surrounded by the horseshoe envelope (extension ∼2.3 pc). A molecular gas deficient region/cavity is identified toward the center of the horseshoe envelope, which is well traced with PAH, H2, molecular, and dust emission. The edges of the infrared shell are found to be located in the front of the horseshoe envelope. All these outcomes provide the observational evidence of the feedback of O-type stars in S305. Moreover, nonthermal radio emission is detected in S305 with an average spectral index α ∼ -0.45. The variations in α, ranging from -1.1 to 1.3, are explained due to soft synchrotron emission and either optically thicker thermal emission at high frequencies or a suppression of the low-frequency emission by the Razin-Tsytovich effect.

Keywords: Extinction, Pre-main sequence stars, Star formation, Interstellar medium, H II regions
Rotation of Solar Analogs Crossmatching Kepler and Gaia DR2. A major obstacle to interpreting the rotation period distribution for main-sequence stars from Kepler mission data has been the lack of a precise evolutionary status for these objects. We address this by investigating the evolutionary status based on Gaia Data Release 2 parallaxes and photometry for more than 30,000 Kepler stars with rotation period measurements. Many of these are subgiants and should be excluded in future work on dwarfs. We particularly investigate a 193-star sample of solar analogs and report newly determined rotation periods for 125 of these. These include 54 stars from a prior sample, of which we can confirm the periods for 50. The remainder are new, and 10 of them longer than a solar rotation period, suggesting that Sun-like stars continue to spin down on the main sequence past solar age. Our sample of solar analogs could potentially serve as a benchmark for future missions, such as PLAnetary Transits and Oscillations of stars, and emphasizes the need for additional astrometric, photometric, and spectroscopic information before interpreting the stellar populations and results from time series surveys.

Keywords: Stellar photometry, Starspots, Fundamental parameters of stars, Stellar activity, Stellar rotation, Stellar evolution
The Slow Heartbeats of an Ultraluminous X-Ray Source in NGC 3621. We report on the results of X-ray observations of 4XMM J111816.0-324910, a transient ultraluminous X-ray source located in the galaxy NGC 3621. This system is characterized by a transient nature and marked variability with a characteristic timescale of ≍3500 s, in contract with other ultraluminous X-ray sources, which in the vast majority show limited intra-observation variability. Such a behavior is very reminiscent of the so-called heartbeats sometimes observed in the Galactic black hole binary GRS 1915+105, where the variability timescale is ∼10-1000 s. We study the spectral and timing properties of this object and find that overall, once the differences in the variability timescales are taken into account, they match quite closely those of both GRS 1915+105 and of a number of objects showing heartbeats in their light curves, including a confirmed neutron star and a supermassive black hole powering an active galactic nucleus. We investigate the nature of the compact object in 4XMM J111816.0-324910 by searching for typical neutron star signatures and by attempting a mass estimate based on different methods and assumptions. Based on the current available data, we are not able to unambiguously determine the nature of the accreting compact object responsible for the observed phenomenology.

Keywords: Neutron stars, Accretion, Black holes, X-ray point sources, Compact objects, Extragalactic astronomy
Modeling MMS Observations at the Earth's Magnetopause with Hybrid Simulations of Alfvénic Turbulence. Magnetospheric Multiscale (MMS) observations of plasma turbulence generated by a Kelvin-Helmholtz (KH) event at the Earth's magnetopause are compared with a high-resolution two-dimensional (2D) hybrid direct numerical simulation of decaying plasma turbulence driven by large-scale balanced Alfvénic fluctuations. The simulation, set up with four observation-driven physical parameters (ion and electron betas, turbulence strength, and injection scale), exhibits a quantitative agreement on the spectral, intermittency, and cascade-rate properties with in situ observations, despite the different driving mechanisms. Such agreement demonstrates a certain universality of the turbulent cascade from magnetohydrodynamic to sub-ion scales, whose properties are mainly determined by the selected parameters, also indicating that the KH instability-driven turbulence has a quasi-2D nature. The fact that our results are compatible with the validity of the Taylor hypothesis, in the whole range of scales investigated numerically, suggests that the fluctuations at sub-ion scales might have predominantly low frequencies. This would be consistent with a kinetic Alfvén wave-like nature and/or with the presence of quasi-static structures. Finally, the third-order structure function analysis indicates that the cascade rate of the turbulence generated by a KH event at the magnetopause is an order of magnitude larger than in the ambient magnetosheath.

Keywords: Interplanetary turbulence, Space plasmas, Plasma astrophysics, Astronomical simulations
The Destruction and Recreation of the X-Ray Corona in a Changing-look Active Galactic Nucleus. We present the drastic transformation of the X-ray properties of the active galactic nucleus (AGN) 1ES 1927+654, following a changing-look event. After the optical/ultraviolet outburst the power-law component, produced in the X-ray corona, disappeared, and the spectrum of 1ES 1927+65 instead became dominated by a blackbody component (kT ∼ 80-120 eV). This implies that the X-ray corona, ubiquitously found in AGNs, was destroyed in the event. Our dense ∼450 days long X-ray monitoring shows that the source is extremely variable in the X-ray band. On long timescales the source varies up to ∼4 dex in ∼100 days, while on short timescales up to ∼2 dex in ∼8 hr. The luminosity of the source is found to first show a strong dip down to $\sim {10}^{40}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , and then a constant increase in luminosity to levels exceeding the pre-outburst level ≳300 days after the optical event detection, rising up asymptotically to $\sim 2\times {10}^{44}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ . As the X-ray luminosity of the source increases, the X-ray corona is recreated, and a very steep power-law component (Γ ≃ 3) reappears, and dominates the emission for 0.3-2 keV luminosities $\gtrsim {10}^{43.7}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ , ∼300 days after the beginning of the event. We discuss possible origins of this event, and speculate that our observations could be explained by the interaction between the accretion flow and debris from a tidally disrupted star. Our results show that changing-look events can be associated with dramatic and rapid transformations of the innermost regions of accreting supermassive black holes.

Keywords: Supermassive black holes, High energy astrophysics, Quasars, Active galaxies, X-ray active galactic nuclei, Active galactic nuclei, X-ray quasars
Isotopic Evolution of the Inner Solar System Inferred from Molybdenum Isotopes in Meteorites. The fundamentally different isotopic compositions of non-carbonaceous (NC) and carbonaceous (CC) meteorites reveal the presence of two distinct reservoirs in the solar protoplanetary disk that were likely separated by Jupiter. However, the extent of material exchange between these reservoirs, and how this affected the composition of the inner disk, are not known. Here we show that NC meteorites display broadly correlated isotopic variations for Mo, Ti, Cr, and Ni, indicating the addition of isotopically distinct material to the inner disk. The added material resembles bulk CC meteorites and Ca-Al-rich inclusions in terms of its enrichment in neutron-rich isotopes, but unlike the latter materials is also enriched in s-process nuclides. The comparison of the isotopic composition of NC meteorites with the accretion ages of their parent bodies reveals that the isotopic variations within the inner disk do not reflect a continuous compositional change through the addition of CC dust, indicating an efficient separation of the NC and CC reservoirs and limited exchange of material between the inner and outer disk. Instead, the isotopic variations among NC meteorites more likely record a rapidly changing composition of the disk during infall from the Sun's parental molecular cloud, where each planetesimal locks the instant composition of the disk when it forms. A corollary of this model is that late-formed planetesimals in the inner disk predominantly accreted from secondary dust that was produced by collisions among pre-existing NC planetesimals.

Keywords: Accretion, Isotopic abundances, Meteorite composition, Nucleosynthesis, R-process, Carbonaceous chondrites, Protoplanetary disks, Planetesimals, Meteorites, S-process
Populating the Low-mass End of the M<SUB>BH</SUB>- {\sigma }_{* } Relation. We present high-resolution spectroscopy taken with the Keck Echellete Spectrograph and Imager to measure stellar velocity dispersions for eight active dwarf galaxies (M* &lt; 3 × 109 M⊙) with virial black hole masses. We double the number of systems in this stellar mass regime with measurements of both black hole mass (MBH) and stellar velocity dispersion (σ*), and place them on the MBH-σ* relation. The tight relation between MBH and σ* for higher mass galaxies is a strong piece of evidence for the coevolution of BHs and their host galaxies, but it has been unclear whether this relation holds in the dwarf galaxy regime. Our sample is in good agreement with the extrapolation of the MBH-σ* relation to low BH/galaxy masses, suggesting that the processes that produce MBH-σ* can also operate in dwarf galaxies. These results provide important constraints for massive black hole seed formation models and models exploring the impact of active galactic nucleus feedback in dwarf galaxies.

Keywords: Intermediate-mass black holes, Dwarf galaxies, Scaling relations, Active galactic nuclei, Astrophysical black holes
Searching for Black Holes in the Outer Solar System with LSST. Planet Nine has been proposed to potentially be a black hole (BH) in the outer solar system. We investigate the accretion flares that would result from impacts of small Oort Cloud objects, and find that the upcoming Legacy Survey of Space and Time (LSST) observing program will be able to either rule out or confirm Planet Nine as a BH within a year. We also find that LSST could rule out or confirm the existence of trapped planet-mass BHs out to the edge of the Oort Cloud, indirectly probing the dark matter fraction in subsolar mass BHs and potentially improving upon current limits by orders of magnitude.

Keywords: Accretion, Transient sources, Dark matter, Primordial black holes, Oort cloud objects
On the Distance of SGR 1935+2154 Associated with FRB 200428 and Hosted in SNR G57.2+0.8. Owing to the detection of an extremely bright fast radio burst (FRB) 200428 associated with a hard X-ray counterpart from the magnetar soft gamma-ray repeater (SGR) 1935+2154, the distance of SGR 1935+2154 potentially hosted in the supernova remnant (SNR) G57.2+0.8 can be revisited. Under the assumption that the SGR and the SNR are physically related, in this Letter, by investigating the dispersion measure (DM) of the FRB contributed by the foreground medium of our Galaxy and the local environments and combining other observational constraints, we find that the distance of SGR 1935+2154 turns out to be 9.0 ± 2.5 kpc and the SNR radius falls into 10-18 pc since the local DM contribution is as low as 0-18 pc cm-3. These results are basically consistent with previous studies. In addition, an estimate for the Faraday rotation measure of the SGR and SNR is also carried out.

Keywords: Supernova remnants, Soft gamma-ray repeaters, Radio bursts, Magnetars, X-ray bursts, Radio transient sources
Evidence for Gravitational-wave-dominated Emission in the Central Engine of Short GRB 200219A. GRB 200219A is a short gamma-ray burst (GRB) with extended emission (EE) lasting ∼90 s. By analyzing data observed with the Swift/BAT and Fermi/GBM, we find that a cutoff power-law model can adequately fit the spectra of the initial short pulse with ${E}_{{\rm{p}}}={1387}_{-134}^{+232}$ keV. More interestingly, together with the EE component and early X-ray data, it exhibits plateau emission smoothly connected with a ∼t-1 segment and followed by an extremely steep decay. The short GRB composed of those three segments is unique in the Swift era and is very difficult to explain with the standard internal/external shock model of a black hole central engine, but could be consistent with the prediction of a magnetar central engine from the merger of an NS binary. We suggest that the plateau emission followed by a ∼t-1 decay phase is powered by the spin-down of a millisecond magnetar, which loses its rotation energy via GW quadrupole radiation. Then, the abrupt drop decay is caused by the magnetar collapsing into a black hole before switching to EM-dominated emission. This is the first short GRB for which the X-ray emission has such an intriguing feature powered by a magnetar via GW-dominated radiation. If this is the case, one can estimate the physical parameters of a magnetar, the GW signal powered by a magnetar and the merger-nova emission are also discussed.

Keywords: Gamma-ray bursts, Gravitational waves