Sazuna/UAT_keywords huggingface dataset:
Simulating Solar Flare Irradiance with Multithreaded Models of Flare Arcades. Understanding how energy is released in flares is one of the central problems of solar and stellar astrophysics. Observations of high-temperature flare plasma hold many potential clues as to the nature of this energy release. It is clear, however, that flares are not composed of a few impulsively heated loops, but are the result of heating on many small-scale threads that are energized over time, making it difficult to compare observations and numerical simulations in detail. Several previous studies have shown that it is possible to reproduce some aspects of the observed emission by considering the flare as a sequence of independently heated loops, but these studies generally focus on small-scale features while ignoring the global features of the flare. In this paper, we develop a multithreaded model that encompasses the time-varying geometry and heating rate for a series of successively heated loops composing an arcade. To validate, we compare with spectral observations of five flares made with the MinXSS CubeSat, as well as light curves measured with GOES/XRS and SDO/AIA. We show that this model can successfully reproduce the light curves and quasi-periodic pulsations in GOES/XRS, the soft X-ray spectra seen with MinXSS, and the light curves in various AIA passbands. The AIA light curves are most consistent with long-duration heating, but elemental abundances cannot be constrained with the model. Finally, we show how this model can be used to extrapolate to spectra of extreme events that can predict irradiance across a wide wavelength range, including unobserved wavelengths.

Keywords: Hydrodynamical simulations, Solar flares, Solar x-ray flares
Discovery and Rapid Follow-up Observations of the Unusual Type II SN 2018ivc in NGC 1068. We present the discovery and high-cadence follow-up observations of SN 2018ivc, an unusual SNe II that exploded in NGC 1068 (D = 10.1 Mpc). The light curve of SN 2018ivc declines piecewise-linearly, changing slope frequently, with four clear slope changes in the first 30 days of evolution. This rapidly changing light curve indicates that interaction between the circumstellar material and ejecta plays a significant role in the evolution. Circumstellar interaction is further supported by a strong X-ray detection. The spectra are rapidly evolving and dominated by hydrogen, helium, and calcium emission lines. We identify a rare high-velocity emission-line feature blueshifted at ∼7800 $\mathrm{km}\,{{\rm{s}}}^{-1}$ (in Hα, Hβ, Pβ, Pγ, He I, and Ca II), which is visible from day 18 until at least day 78 and could be evidence of an asymmetric progenitor or explosion. From the overall similarity between SN 2018ivc and SN 1996al, the Hα equivalent width of its parent H II region, and constraints from pre-explosion archival Hubble Space Telescope images, we find that the progenitor of SN 2018ivc could be as massive as 52 ${M}_{\odot }$ but is more likely &lt;12 ${M}_{\odot }$ . SN 2018ivc demonstrates the importance of the early discovery and rapid follow-up observations of nearby supernovae to study the physics and progenitors of these cosmic explosions.

Keywords: Type II supernovae, Core-collapse supernovae, Circumstellar gas
The Zwicky Transient Facility Bright Transient Survey. I. Spectroscopic Classification and the Redshift Completeness of Local Galaxy Catalogs. The Zwicky Transient Facility (ZTF) is performing a three-day cadence survey of the visible northern sky (∼3π) with newly found transient candidates announced via public alerts. The ZTF Bright Transient Survey (BTS) is a large spectroscopic campaign to complement the photometric survey. BTS endeavors to spectroscopically classify all extragalactic transients with mpeak ≤ 18.5 mag in either the gZTF or rZTF filters, and publicly announce said classifications. BTS discoveries are predominantly supernovae (SNe), making this the largest flux-limited SN survey to date. Here we present a catalog of 761 SNe, classified during the first nine months of ZTF (2018 April 1-2018 December 31). We report BTS SN redshifts from SN template matching and spectroscopic host-galaxy redshifts when available. We analyze the redshift completeness of local galaxy catalogs, the redshift completeness fraction (RCF; the ratio of SN host galaxies with known spectroscopic redshift prior to SN discovery to the total number of SN hosts). Of the 512 host galaxies with SNe Ia, 227 had previously known spectroscopic redshifts, yielding an RCF estimate of 44% ± 4%. The RCF decreases with increasing distance and decreasing galaxy luminosity (for z &lt; 0.05, or ∼200 Mpc, RCF ≍ 0.6). Prospects for dramatically increasing the RCF are limited to new multifiber spectroscopic instruments or wide-field narrowband surveys. Existing galaxy redshift catalogs are only ∼50% complete at r ≍ 16.9 mag. Pushing this limit several magnitudes deeper will pay huge dividends when searching for electromagnetic counterparts to gravitational wave events or sources of ultra-high-energy cosmic rays or neutrinos.

Keywords: Surveys, Redshift surveys, Supernovae, Galaxies
A New Method to Measure Hubble Parameter H(z) Using Fast Radio Bursts. The Hubble parameter H(z) is directly related to the expansion of our universe. It can be used to study dark energy and constrain cosmology models. In this paper, we propose that H(z) can be measured using fast radio bursts (FRBs) with redshift measurements. We use dispersion measures contributed by the intergalactic medium, which is related to H(z), to measure the Hubble parameter. We find that 500 mocked FRBs with dispersion measures and redshift information can accurately measure Hubble parameters using Monte Carlo simulation. The maximum deviation of H(z) from the standard ΛCDM model is about 6% at redshift z = 2.4. We also test our method using Monte Carlo simulation. A Kolmogorov-Smirnov (K-S) test is used to check the simulation. The p-value of the K-S test is 0.23, which confirms internal consistency of the simulation. In the future, more localizations of FRBs make it an attractive cosmological probe.

Keywords: Radio bursts, Cosmological parameters
The Parameter-free Finger-of-God Model and Its Application to 21 cm Intensity Mapping. Using the galaxy catalog built from ELUCID N-body simulation and the semianalytical galaxy formation model, we have built a mock H I intensity mapping map. We have implemented the Finger-of-God (FoG) effect in the map by considering the galaxy H I gas velocity dispersion. By comparing the H I power spectrum in redshift space with a measurement from the IllustrisTNG simulation, we have found that the FoG effect can explain the discrepancy between current mock maps built from the N-body simulation and the IllustrisTNG simulation. Then we built a parameter-free FoG model and a shot-noise model to calculate the H I power spectrum. We found that our model can accurately fit both the monopole and quadrupole moments of the H I matter power spectrum. Our approach to building the mock H I intensity map and the parameter-free FoG model will be useful for upcoming 21 cm intensity mapping experiments, such as CHIME, Tianlai, BINGO, FAST, and SKA. It is also vital for studying nonlinear effects in 21 cm intensity mapping.

Keywords: Line intensities, Large-scale structure of the universe
Constraints on the Circumnuclear Disk through Free-Free Absorption in the Nucleus of 3C 84 with KaVA and KVN at 43 and 86 GHz. The nearby bright radio galaxy 3C 84 at the center of the Perseus cluster is an ideal target to explore the jet in an active galactic nucleus and its parsec-scale environment. The recent research of Fujita &amp; Nagai revealed the existence of the northern counter-jet component (N1) located 2 mas north from the central core in very long baseline interferometer (VLBI) images at 15 and 43 GHz and they are explained by the free-free absorption (FFA) due to an ionized plasma foreground. Here we report a new quasi-simultaneous observation of 3C 84 with the Korean VLBI Network (KVN) at 86 GHz and the KVN and VLBI Exploration of Radio Astrometry Array (KaVA) at 43 GHz in 2016 February. We succeeded the first detection of N1 at 86 GHz and the data show that N1 still has an inverted spectrum between 43 and 86 GHz with its spectral index &amp;agr; ( ${S}_{\nu }\propto {\nu }^{\alpha }$ ) of 1.19 ± 0.43, while the approaching lobe component has a steep spectrum with an index of -0.54 ± 0.30. Based on the measured flux asymmetry between the counter and approaching lobes, we constrain the averaged number density of the FFA foreground ne as $1.8\times {10}^{4}\,{\mathrm{cm}}^{-3}\lesssim {n}_{{\rm{e}}}\lesssim 1.0\times {10}^{6}\,{\mathrm{cm}}^{-3}$ . Those results suggest that the observational properties of the FFA foreground can be explained by the dense ionized gas in the circumnuclear disk and/or assembly of clumpy clouds at the central ∼1 pc region of 3C 84.

Keywords: Radio lobes, Very long baseline interferometers, Radio galaxies, Active galactic nuclei, Radio continuum emission, Perseus Cluster
Magnetic Field Geometry and Composition Variation in Slow Solar Winds: The Case of Sulfur. We present an examination of the first ionization potential (FIP) fractionation scenario, invoking the ponderomotive force in the chromosphere and its implications for the source(s) of slow-speed solar winds by using observations from The Advanced Composition Explorer (ACE). Following a recent conjecture that the abundance enhancements of intermediate FIP elements, S, P, and C, in slow solar winds can be explained by the release of plasma fractionated on open fields, though from regions of stronger magnetic field than usually associated with fast solar wind source regions, we identify a period in 2008 containing four solar rotation cycles that show repeated pattern of sulfur abundance enhancement corresponding to a decrease in solar wind speed. We identify the source regions of these slow winds in global magnetic field models, and find that they lie at the boundaries between a coronal hole and its adjacent active region, with origins in both closed and open initial field configurations. Based on magnetic field extrapolations, we model the fractionation and compare our results with element abundances measured by ACE to estimate the solar wind contributions from open and closed fields, and to highlight potentially useful directions for further work.

Keywords: Solar abundances, Solar wind, Alfven waves, Solar chromosphere
Resolving the Soft X-Ray Ultrafast Outflow in PDS 456. Past X-ray observations of the nearby luminous quasar PDS 456 (at z = 0.184) have revealed a wide-angle accretion disk wind with an outflow velocity of ∼-0.25c, as observed through observations of its blueshifted iron K-shell absorption line profile. Here we present three new XMM-Newton observations of PDS 456: one in 2018 September where the quasar was bright and featureless and two in 2019 September, 22 days apart, occurring when the quasar was five times fainter and where strong blueshifted lines from the wind were present. During the second 2019 September observation, three broad (σ = 3000 km s-1) absorption lines were resolved in the high-resolution Reflection Grating Spectrometer spectrum that are identified with blueshifted O VIII Lyα, Ne IX Heα, and Ne X Lyα. The outflow velocity of this soft X-ray absorber was found to be V/c = -0.258 ± 0.003, fully consistent with an iron K absorber with V/c = -0.261 ± 0.007. The ionization parameter and column density of the soft X-ray component (log ξ = 3.4, NH = 2 × 1021 cm-2) outflow was lower by about 2 orders of magnitude when compared to the high-ionization wind at iron K (log ξ = 5, NH = 7 × 1023 cm-2). Substantial variability was seen in the soft X-ray absorber between the 2019 observations, declining from NH = 1023 to 1021 cm-2 over 20 days, while the iron K component was remarkably stable. We conclude that the soft X-ray wind may originate from an inhomogeneous wind streamline passing across the line of sight that, due to its lower ionization, is located further from the black hole, on parsec scales, than the innermost disk wind.

Keywords: Black hole physics, Radio quiet quasars, Active galactic nuclei, X-ray quasars, X-ray active galactic nuclei
Detection of PAH Absorption and Determination of the Mid-infrared Diffuse Interstellar Extinction Curve from the Sight Line toward Cyg OB2-12. The sight line toward the luminous blue hypergiant Cyg OB2-12 is widely used to study interstellar dust on account of its large extinction (AV ≃ 10 mag) and the fact that this extinction appears to be dominated by dust typical of the diffuse interstellar medium. We present a new analysis of archival Infrared Space Observatory Short Wavelength Spectrometer and Spitzer IRS observations of Cyg OB2-12 using a model of the emission from the star and its stellar wind to determine the total extinction Aλ from 2.4 to 37 μm. In addition to the prominent 9.7 and 18 μm silicate features, we robustly detect absorption features associated with polycyclic aromatic hydrocarbons, including the first identification of the 7.7 μm feature in absorption. The 3.3 μm aromatic feature is found to be much broader in absorption than is typically seen in emission. The 3.4 and 6.85 μm aliphatic hydrocarbon features are observed with relative strengths that are consistent with observations of these features on sight lines toward the Galactic center. We identify and characterize more than 60 spectral lines in this wavelength range, which may be useful in constraining models of the star and its stellar wind. Based on this analysis, we present an extinction curve ${A}_{\lambda }/{A}_{2.2\mu {\rm{m}}}$ that extrapolates smoothly to determinations of the mean Galactic extinction curve at shorter wavelengths and to dust opacities inferred from emission at longer wavelengths, providing a new constraint on models of interstellar dust in the mid-infrared.

Keywords: Interstellar dust, Silicate grains, Polycyclic aromatic hydrocarbons, Interstellar dust extinction, Stellar winds, Carbonaceous grains
X-Ray Afterglows from the Gamma-Ray Burst "Large-angle" Emission. We derive basic analytical results for the timing and decay of the gamma-ray burst (GRB) counterpart and delayed afterglow light curves for a brief emission episode from a relativistic surface endowed with angular structure, consisting of a uniform core of size ${\theta }_{c}$ (Lorentz factor ${{\rm{\Gamma }}}_{c}$ and surface emissivity ${I}_{\nu ^{\prime} }^{{\prime} }$ are angle independent) and an axially symmetric power-law envelope ( ${\rm{\Gamma }}\sim {\theta }^{-g}$ ). In this "large-angle emission" model, radiation produced during the prompt emission phase (GRB) at angles $\theta \gt {\theta }_{c}$ arrives at the observer well after the burst (delayed emission). The dynamical time range of the very fast decaying GRB "tail" and of the flat afterglow "plateau" and the morphology of the GRB counterpart/afterglow are all determined by two parameters: the core's parameter ${{\rm{\Gamma }}}_{c}{\theta }_{c}$ and the envelope's Lorentz factor index g, leading to three types of light curves that display three post-GRB phases (type 1: tail, plateau/slow decay, post-plateau/normal decay), two post-GRB phases (type 2: tail and fast decay), or just one (type 3: normal decay). We show how X-ray light-curve features can be used to determine core and envelope dynamical and spectral parameters. Testing of the large-angle emission model is done using the Swift/XRT X-ray emission of two afterglows of type 1 (GRB 060607A, GRB 061121), one of type 2 (GRB 061110A), and one of type 3 (GRB 061007). We find that the X-ray afterglows with plateaus require an envelope Lorentz factor ${\rm{\Gamma }}\sim {\theta }^{-2}$ and a comoving-frame emissivity ${I}_{\nu ^{\prime} }^{{\prime} }\sim {\theta }^{2}$ ; thus, for a typical afterglow spectrum ${F}_{\nu }\sim {\nu }^{-1}$ , the lab-frame energy release is uniform over the emitting surface.

Keywords: Gamma-ray bursts, Non-thermal radiation sources, High energy astrophysics
Evaluation of Automated Fermi GBM Localizations of Gamma-Ray Bursts. The capability of the Fermi Gamma-ray Burst Monitor (GBM) to localize gamma-ray bursts (GRBs) is evaluated for two different automated algorithms: the GBM Team's RoboBA algorithm and the independently developed BALROG algorithm. Through a systematic study utilizing over 500 GRBs with known locations from instruments like Swift and the Fermi Large Area Telescope, we directly compare the effectiveness of, and accurately estimate the systematic uncertainty for, both algorithms. We show that simple adjustments to the GBM Team's RoboBA, in operation since early 2016, yield significant improvement in the systematic uncertainty, removing the long tail identified in the systematic, and improve the overall accuracy. The systematic uncertainty for the updated RoboBA localizations is 1°8 for 52% of GRBs and 4°1 for the remaining 48%. Both from public reporting by BALROG and our systematic study, we find the systematic uncertainty of 1°-2° quoted in circulars for bright GRBs is an underestimate of the true magnitude of the systematic, which we find to be 2°7 for 74% of GRBs and 33° for the remaining 26%. We show that, once the systematic uncertainty is considered, the RoboBA 90% localization confidence regions can be more than an order of magnitude smaller in area than those produced by BALROG.

Keywords: Gamma-ray bursts, Astronomy data analysis
Outbursts in Global Protoplanetary Disk Simulations. While accreting through a circumstellar disk, young stellar objects are observed to undergo sudden and powerful accretion events known as FUor or EXor outbursts. Although such episodic accretion is considered to be an integral part of the star formation process, the triggers and mechanisms behind them remain uncertain. We conducted global numerical hydrodynamics simulations of protoplanetary disk formation and evolution in the thin-disk limit, assuming both magnetically layered and fully magnetorotational instability (MRI)-active disk structure. In this paper, we characterize the nature of the outbursts occurring in these simulations. The instability in the dead zone of a typical layered disk results in "MRI outbursts." We explore their progression and their dependence on the layered disk parameters as well as cloud core mass. The simulations of fully MRI-active disks showed an instability analogous to the classical thermal instability. This instability manifested at two temperatures—above approximately 1400 K and 3500 K—due to the steep dependence of Rosseland opacity on the temperature. The origin of these thermally unstable regions is related to the bump in opacity resulting from molecular absorption by water vapor and may be viewed as a novel mechanism behind some of the shorter duration accretion events. Although we demonstrated local thermal instability in the disk, more investigations are needed to confirm that a large-scale global instability will ensue. We conclude that the magnetic structure of a disk, its composition, as well as the stellar mass, can significantly affect the nature of episodic accretion in young stellar objects.

Keywords: Hydrodynamical simulations, T Tauri stars, Young stellar objects, Protoplanetary disks, Circumstellar disks
A Solar Magnetic-fan Flaring Arch Heated by Nonthermal Particles and Hot Plasma from an X-Ray Jet Eruption. We have investigated an M1.3 limb flare, which develops as a magnetic loop/arch that fans out from an X-ray jet. Using Hinode/EIS, we found that the temperature increases with height to a value of over 107 K at the loop top during the flare. The measured Doppler velocity (redshifts of 100-500 km s-1) and the nonthermal velocity (≥100 km s-1) from Fe XXIV also increase with loop height. The electron density increases from 0.3 × 109 cm-3 early in the flare rise to 1.3 × 109 cm-3 after the flare peak. The 3D structure of the loop derived with Solar TErrestrial RElations Observatory/EUV Imager indicates that the strong redshift in the loop-top region is due to upflowing plasma originating from the jet. Both hard X-ray and soft X-ray emission from the Reuven Ramaty High Energy Solar Spectroscopic Imager were only seen as footpoint brightenings during the impulsive phase of the flare, then, soft X-ray emission moved to the loop top in the decay phase. Based on the temperature and density measurements and theoretical cooling models, the temperature evolution of the flare arch is consistent with impulsive heating during the jet eruption followed by conductive cooling via evaporation and minor prolonged heating in the top of the fan loop. Investigating the magnetic field topology and squashing factor map from Solar Dynamics Observatory/HMI, we conclude that the observed magnetic-fan flaring arch is mostly heated from low atmospheric reconnection accompanying the jet ejection, instead of from reconnection above the arch as expected in the standard flare model.

Keywords: Solar flares, Solar extreme ultraviolet emission, Solar flare spectra, Solar x-ray emission, Spectroscopy
The Physical Nature of Starburst-driven Galactic Outflows. We present the fourth simulation of the Cholla Galactic OutfLow Simulations suite. Using a physically motivated prescription for clustered supernova feedback, we successfully drive a multiphase outflow from a disk galaxy. The high resolution (&lt;5 pc) across a relatively large domain (20 kpc) allows us to capture the hydrodynamic mixing and dynamical interactions between the hot and cool (T ∼ 104 K) phases in the outflow, which in turn leads to direct evidence of a qualitatively new mechanism for cool gas acceleration in galactic winds. We show that mixing of momentum from the hot phase to the cool phase accelerates the cool gas to 800 km s-1 on kiloparsec scales, with properties inconsistent with the physical models of ram pressure acceleration or bulk cooling from the hot phase. The mixing process also affects the hot phase, modifying its radial profiles of temperature, density, and velocity from the expectations of radial supersonic flow. This mechanism provides a physical explanation for the high-velocity, blueshifted, low-ionization absorption lines often observed in the spectra of starburst and high-redshift galaxies.

Keywords: Local Group, Starburst galaxies, Hydrodynamical simulations, Stellar feedback, Active galaxies, Galaxy evolution, Circumgalactic medium
Detection of the 511 keV Galactic Positron Annihilation Line with COSI. The signature of positron annihilation, namely the 511 keV γ-ray line, was first detected coming from the direction of the Galactic center in the 1970s, but the source of Galactic positrons still remains a puzzle. The measured flux of the annihilation corresponds to an intense steady source of positron production, with an annihilation rate on the order of ∼1043 ${\text{}}{e}^{+}\,{{\rm{s}}}^{-1}$ . The 511 keV emission is the strongest persistent Galactic γ-ray line signal, and it shows a concentration toward the Galactic center region. An additional low-surface brightness component is aligned with the Galactic disk; however, the morphology of the latter is not well constrained. The Compton Spectrometer and Imager (COSI) is a balloon-borne soft γ-ray (0.2-5 MeV) telescope designed to perform wide-field imaging and high-resolution spectroscopy. One of its major goals is to further our understanding of Galactic positrons. COSI had a 46-day balloon flight in 2016 May-July from Wanaka, New Zealand, and here we report on the detection and spectral and spatial analyses of the 511 keV emission from those observations. To isolate the Galactic positron annihilation emission from instrumental background, we have developed a technique to separate celestial signals using the COMPTEL Data Space. With this method, we find a 7.2σ detection of the 511 keV line. We find that the spatial distribution is not consistent with a single point source, and it appears to be broader than what has previously been reported.

Keywords: Galactic center, Astronomy data modeling, Gamma-ray lines, Gamma-ray telescopes, High altitude balloons, Spectroscopy