Sazuna/UAT_keywords huggingface dataset:
A Study of the Overall Evolution Behaviors of Pulses and Flares within Gamma-Ray Bursts. Many studies have shown that the X-ray flares in gamma-ray bursts (GRBs) have similar properties to the prompt emission pulses that occur in GRBs, suggesting that they may come from the same origin. We attempt to extend the evolution behavior that exists among GRBs to within individual GRBs. By selecting 12 GRBs with both multipulses and multiflares, we systematically study the overall evolution behaviors of the pulses and flares that occur within GRBs, including the width (w), peak time (t peak), rise time (t rise), decay time (t decay), and spectral lag. We find that correlated relationships exist within the GRBs, even if the overall evolution slopes of the pulses and flares in different GRBs are different. We also study the relations between the full pulse width (ω), the ratio of the rising width to the decay width (r/d), and the energy (E) of multipulses and multiflares within GRBs. It is found that there is a power-law anticorrelation between ω and E and a power-law correlation between r/d and E, with the mean values of the two power-law indexes being -0.42 and 0.07, respectively, which are very close to the values that are obtained for the prompt emission pulses. In addition, we find that the percentages of the positive lags for pulses and flares are 83% and 92%, respectively, with the lags of the flares being much larger than those of the pulses. Our results indicate that the overall evolution behaviors of the pulses and flares within individual GRBs are similar to the evolution behavior among GRBs, and that flares are low-energy extensions of pulses, providing further evidence that both come from the same origin.

Keywords: Gamma-ray bursts
Structure of the Plasma near the Heliospheric Current Sheet as Seen by WISPR/Parker Solar Probe from inside the Streamer Belt. Parker Solar Probe (PSP) crossed the heliospheric current sheet (HCS) near the perihelion on encounters E8 and E11, enabling the Wide-field Imager for Solar Probe (WISPR) to image the streamer belt plasma in high resolution while flying through it. With perihelia of 16 R ⊙ and 13 R ⊙ for E8 and E11, respectively, WISPR images enable investigation of the structure of density encasing the HCS at much higher resolution than reported previously. As PSP flies closer to the Sun, fine-scale structures are resolved within the coronal rays of the streamer belt. Near the HCS, WISPR observes a fan of rays of various sizes and brightnesses, indicating large density variations in the HCS plasma sheet transverse to the radial direction. Near the perihelion, when PSP's speed exceeds the solar corotation speed, some rays exhibit large changes in apparent latitude as the HCS is encountered, and rays pass over and under the spacecraft. The multiple viewpoints provided during the HCS crossing enable us to extract the coordinates of a few rays in a heliocentric frame. The rays were found to lie near the HCS from a PFSS model. We compare their locations to the location of the streamers as seen in synoptic maps from the Large Angle and Spectrometric Coronagraph, and find that the rays generally fall within the bright streamer bands seen in these maps, which confirms that they are features of the streamer belt plasma. We speculate that the density variations in the helmet streamer plasma result from continuous interchange reconnection along the coronal hole boundaries.

Keywords: Solar K corona, Solar coronal streamers
Simulations of Precessing Jets and the Formation of X-shaped Radio Galaxies. Jet precession is sometimes invoked to explain asymmetries in radio galaxy (RG) jets and "X/S/Z-shaped" RGs, caused by the presence of a binary black hole companion to the source active galactic nucleus or by accretion instabilities. We present a series of simulations of RG jet precession to examine how these sources would evolve over time, including a passive distribution of cosmic-ray electrons so we can model radio synchrotron emissions and create synthetic radio maps of the sources. We find that a single source viewed from different angles can result in differing RG morphological classifications, confusing physical implications of these classifications. Additionally, the jet trajectories can become unstable due to their own self-interactions and lead to "reorientation events" that may look like the effects of external dynamics such as shocks, winds, or cold fronts in the medium. Finally, something akin to an "Odd Radio Circle" may be observed in the case of viewing the radio remnant of such a precessing source from a line of sight near the precession axis.

Keywords: Jets, Radio jets, Extragalactic radio sources, Galaxy jets, Radio galaxies, Astronomical simulations, Magnetohydrodynamical simulations
The Dark Side of Using Dark Sirens to Constrain the Hubble-Lemaître Constant. Dark sirens, i.e., gravitational-wave (GW) sources without electromagnetic counterparts, are new probes of the expansion of the universe. The efficacy of this method relies on correctly localizing the host galaxies. However, recent theoretical studies have shown that astrophysical environments could mislead the spatial localization by distorting the GW signals. It is unclear whether and to what degree the incorrect spatial localizations of dark sirens would impair the accuracy of the measurement of the cosmological parameters. To address this issue, we consider the future observations of dark sirens using the Cosmic Explorer and the Einstein Telescope, and we design a Bayesian framework to access the precision of measuring the Hubble-Lemaître constant H 0. Interestingly, we find that the precision is not compromised when the number of well-localized dark sirens is significantly below 300, even in the extreme scenario that all the dark sirens are localized incorrectly. As the number exceeds 300, the incorrect spatial localizations start to produce statistically noticeable effects, such as a slow convergence of the posterior distribution of H 0. We propose several tests that can be used in future observations to verify the spatial localizations of dark sirens. Simulations of these tests suggest that incorrect spatial localizations will dominate a systematic error of H 0 if as much as 10% of a sample of 300 well-localized dark sirens are affected by their environments. Our results have important implications for the long-term goal of measuring H 0 to a precision of &lt;1% using dark sirens.

Keywords: Sky surveys, Bayesian statistics, Stellar mass black holes, Hubble constant, Gravitational waves
Carnegie Supernova Project. II. Near-infrared Spectral Diversity and Template of Type Ia Supernovae. We present the largest and most homogeneous collection of near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia): 339 spectra of 98 individual SNe obtained as part of the Carnegie Supernova Project-II. These spectra, obtained with the FIRE spectrograph on the 6.5 m Magellan Baade telescope, have a spectral range of 0.8-2.5 μm. Using this sample, we explore the NIR spectral diversity of SNe Ia and construct a template of spectral time series as a function of the light-curve-shape parameter, color stretch s  BV . Principal component analysis is applied to characterize the diversity of the spectral features and reduce data dimensionality to a smaller subspace. Gaussian process regression is then used to model the subspace dependence on phase and light-curve shape and the associated uncertainty. Our template is able to predict spectral variations that are correlated with s  BV , such as the hallmark NIR features: Mg II at early times and the H-band break after peak. Using this template reduces the systematic uncertainties in K-corrections by ~90% compared to those from the Hsiao template. These uncertainties, defined as the mean K-correction differences computed with the color-matched template and observed spectra, are on the level of 4 × 10-4 mag on average. This template can serve as the baseline spectral energy distribution for light-curve fitters and can identify peculiar spectral features that might point to compelling physics. The results presented here will substantially improve future SN Ia cosmological experiments, for both nearby and distant samples.

Keywords: Type Ia supernovae, Infrared spectroscopy, Time domain astronomy, High energy astrophysics
CLASSY. VI. The Density, Structure, and Size of Absorption-line Outflows in Starburst Galaxies. Galaxy formation and evolution are regulated by the feedback from galactic winds. Absorption lines provide the most widely available probe of winds. However, since most data only provide information integrated along the line of sight, they do not directly constrain the radial structure of the outflows. In this paper, we present a method to directly measure the gas electron density in outflows (n  e ), which in turn yields estimates of outflow cloud properties (e.g., density, volume filling factor, and sizes/masses). We also estimate the distance (r  n ) from the starburst at which the observed densities are found. We focus on 22 local star-forming galaxies primarily from the COS Legacy Archive Spectroscopic SurveY (CLASSY). In half of them, we detect absorption lines from fine-structure excited transitions of Si II (i.e., Si II*). We determine n  e  from relative column densities of Si II and Si II*, given Si II* originates from collisional excitation by free electrons. We find that the derived n  e  correlates well with the galaxy's star formation rate per unit area. From photoionization models or assuming the outflow is in pressure equilibrium with the wind fluid, we get r  n  ~ 1-2r * or ~5r *, respectively, where r * is the starburst radius. Based on comparisons to theoretical models of multiphase outflows, nearly all of the outflows have cloud sizes large enough for the clouds to survive their interaction with the hot wind fluid. Most of these measurements are the first ever for galactic winds detected in absorption lines and, thus, will provide important constraints for future models of galactic winds.

Keywords: Starburst galaxies, Ultraviolet astronomy, Galaxy winds, Galaxy evolution, Galaxy kinematics, Galaxy spectroscopy
SCF-FDPS: A Fast N-body Code for Simulating Disk-Halo Systems. A fast N-body code has been developed for simulating a stellar disk embedded in a live dark matter halo. In generating its Poisson solver, a self-consistent field (SCF) code that inherently possesses perfect scalability is incorporated into a tree code that is parallelized using a library termed Framework for Developing Particle Simulators (FDPS). Thus, the code developed here is called SCF-FDPS. This code has realized the speedup of a conventional tree code by applying an SCF method not only to the calculation of the self-gravity of the halo but also to that of the gravitational interactions between the disk and halo particles. Consequently, in the SCF-FDPS code, a tree algorithm is applied only to calculate the self-gravity of the disk. On a many-core parallel computer, the SCF-FDPS code has performed at least 3 times (in one case, nearly an order of magnitude) faster than an extremely tuned tree code on it, if the numbers of disk and halo particles are, respectively, fixed for both codes. In addition, the SCF-FDPS code shows that the central processing unit cost scales almost linearly with the total number of particles and almost inversely with the number of cores. We find that the time evolution of a disk-halo system simulated with the SCF-FDPS code is, in large measure, similar to that obtained using the tree code. We suggest how the present code can be extended to cope with a wide variety of disk-galaxy simulations.

Keywords: Galaxy dark matter halos, Disk galaxies, Stellar dynamics, N-body simulations, Dynamical evolution
Photometric and Spectroscopic Observations of GRB 190106A: Emission from Reverse and Forward Shocks with Late-time Energy Injection. Early optical observations of gamma-ray bursts can significantly contribute to the study of the central engine and physical processes therein. However, of the thousands observed so far, only a few have data at optical wavelengths in the first minutes after the onset of the prompt emission. Here we report on GRB 190106A, whose afterglow was observed in optical bands just 36 s after the Swift/BAT trigger, i.e., during the prompt emission phase. The early optical afterglow exhibits a bimodal structure followed by a normal decay, with a faster decay after ~T 0 + 1 day. We present optical photometric and spectroscopic observations of GRB 190106A. We derive the redshift via metal absorption lines from Xinglong 2.16 m/BFOSC spectroscopic observations. From the BFOSC spectrum, we measure z = 1.861 ± 0.002. The double-peak optical light curve is a significant feature predicted by the reverse-forward external-shock model. The shallow decay followed by a normal decay in both the X-ray and optical light curves is well explained with the standard forward-shock model with late-time energy injection. Therefore, GRB 190106A offers a case study for GRB emission from both reverse and forward shocks.

Keywords: Gamma-ray bursts
A Search for OH 18 cm Emission from Intermediate-velocity Gas at High Galactic Latitudes. We present search results of 22 high-latitude (∣b∣ &gt; 25°) sightlines for OH 18 cm emission using the 305 m radio telescope at the Arecibo Observatory. These sightlines appear in neutral hydrogen emission at intermediate velocities -90 ≤ V LSR ≤ -20 km s-1 and are predicted to have a sufficient molecular composition so as to be detectable in molecular emission. Such objects, known as intermediate-velocity molecular clouds (IVMCs), have historically been detected through 12CO emission. Recent studies indicate that IVMCs may be widespread in the galaxy and have important implications for models of the interstellar medium and star formation. However, we report nondetections of OH emission toward the 22 sightlines and provide stringent upper limits on the OH column density. Using available H I and A  v  data in combination with existing state-of-the-art PDR models, we estimate H2 column densities and find that they are more than an order of magnitude lower than the predicted values. We also find that the hydrogen volume density of these clouds is ≲25 cm-3. In addition, we discuss the known IVMCs with previous 12CO detections in the context of the PDR models. Our analysis of these clouds indicates that the structure of molecular material in IVMCs is morphologically clumpy. These results motivate the need for future sensitive, on-the-fly searches (rather than targeted searches) for CO emission from IVMCs with resolutions on the order of ~1'. High angular resolution (~1') H I and A  v  data will also be helpful to better constrain the structure and composition of IVMCs.

Keywords: Interstellar molecules, Radio spectroscopy, Interstellar clouds, Interstellar medium, Electron impact ionization, Diffuse interstellar clouds
A Pilot Study of Nulling in 22 Pulsars Using Mixture Modeling. The phenomenon of pulsar nulling, observed as the temporary inactivity of a pulsar, remains poorly understood both observationally and theoretically. Most observational studies that quantify nulling employ a variant of Ritchings algorithm, which can suffer significant biases for pulsars where the emission is weak. Using a more robust mixture model method, we study pulsar nulling in a sample of 22 recently discovered pulsars, for which we publish the nulling fractions for the first time. These data clearly demonstrate biases of the former approach and show how an otherwise nonnulling pulsar can be classified as having significant nulls. We show that the population-wide studies that find a positive correlation of nulling with pulsar period/characteristic age can similarly be biased because of the bias in estimating the nulling fraction. We use our probabilistic approach to find the evidence for periodicity in the nulls in a subset of three pulsars in our sample. In addition, we also provide improved timing parameters for 17 of the 22 pulsars that had no prior follow-up.

Keywords: Neutron stars, Radio astronomy, Radio pulsars
Hubble Space Telescope Proper Motion Measurements of Supernova Remnant N132D: Center of Expansion and Age. We present proper motion measurements of the oxygen-rich ejecta of the LMC supernova remnant N132D using two epochs of Hubble Space Telescope Advanced Camera for Surveys data spanning 16 years. The proper motions of 120 individual knots of oxygen-rich gas were measured and used to calculate a center of expansion (CoE) of α = 5h25m01.ˢ71 and δ = -69°38'41.″64 (J2000) with a 1σ uncertainty of 2.″90. This new CoE measurement is 9.″2 and 10.″8 from two previous CoE estimates based on the geometry of the optically emitting ejecta. We also derive an explosion age of 2770 ± 500 yr, which is consistent with recent age estimates of ≈2500 yr made from 3D ejecta reconstructions. We verified our estimates of the CoE and age using a new automated procedure that detected and tracked the proper motions of 137 knots, with 73 knots that overlap with the visually identified knots. We find that the proper motions of the ejecta are still ballistic, despite the remnant's age, and are consistent with the notion that the ejecta are expanding into an interstellar medium cavity. Evidence for explosion asymmetry from the parent supernova is also observed. Using the visually measured proper motion measurements and corresponding CoE and age, we compare N132D to other supernova remnants with proper motion ejecta studies.

Keywords: Supernova remnants, Interstellar medium
Comparing Be Star Inclination Angles Determined from Hα Fitting and Gravitational Darkening. Using a sample of 92 Galactic Be stars, we compare inclination angles (the angle between a star's rotation axis and the line of sight) determined from Hα emission-line profile fitting to those determined by the spectroscopic signature of gravitational darkening. We find good agreement: 70% of the sample (64 out of 92 stars) is consistent with zero difference between the two methods using 1σ errors, and there is a strong linear correlation coefficient between the two methods of r = +0.63 ± 0.05. There is some evidence that the Hα profile fitting method overestimates the inclination angle for i ≲ 25°, perhaps due to the neglect of incoherent electron scattering on the Hα line widths, while the gravitational darkening method underestimates the inclination angle for i ≳ 70°, perhaps due to the neglect of disk radiative transfer effects on the optical spectrum. Overall, it is demonstrated that a single Hα spectrum of modest resolution and SNR can be used to extract a useful estimate for the inclination angle of an individual Be star. This allows equatorial rotation velocities for individual Be stars to be derived from $v\sin i$ measurements and will allow Be stars to be used to search for correlated spin axes in young, open clusters if unbiased (with respect to inclination) samples of Be stars are used.

Keywords: Early-type stars, Fundamental parameters of stars, Star formation, Circumstellar disks, Stellar rotation, Open star clusters, Be stars
Evidence of First Stars-enriched Gas in High-redshift Absorbers. The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] &lt; -2) stars, characterized by high abundances of carbon over iron ([C/Fe] &gt; +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ~ 3-4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars.

Keywords: Metallicity, Chemical abundances, Quasar absorption line spectroscopy
The Surprising Evolution of the Shadow on the TW Hya Disk. We report new total-intensity visible-light high-contrast imaging of the TW Hya disk taken with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. This represents the first published images of the disk with STIS since 2016, when a moving shadow on the disk surface was reported. We continue to see the shadow moving in a counterclockwise fashion, but in these new images the shadow has evolved into two separate shadows, implying a change in behavior for the occulting structure. Based on radiative-transfer models of optically thick disk structures casting shadows, we infer that a plausible explanation for the change is that there are now two misaligned components of the inner disk. The first of these disks is located between 5 and 6 au with an inclination of 5.5° and position angle (PA) of 170°, and the second between 6 and 7 au with an inclination of 7° and PA of 50°. Finally, we speculate on the implications of the new shadow structure and determine that additional observations are needed to disentangle the nature of TW Hya's inner-disk architecture. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs #16228 and #13573.

Keywords: Hubble Space Telescope, Coronagraphic imaging, Protoplanetary disks, Circumstellar disks, Exoplanet formation
Space Weather in the Saturn-Titan System. New evidence based on Cassini magnetic field and plasma data has revealed that the discovery of Titan outside Saturn's magnetosphere during the T96 flyby on 2013 December 1 was the result of the impact of two consecutive interplanetary coronal mass ejections (ICMEs) that left the Sun in 2013 early November and interacted with the moon and the planet. We study the dynamic evolution of Saturn's magnetopause and bow shock, which evidences a magnetospheric compression from late November 28 to December 4 (at least), under prevailing solar wind dynamic pressures of 0.16-0.3 nPa. During this interval, transient disturbances associated with the two ICMEs are observed, allowing for the identification of their magnetic structures. By analyzing the magnetic field direction, and the pressure balance in Titan's induced magnetosphere, we show that Cassini finds Saturn's moon embedded in the second ICME after being swept by its interplanetary shock and amid a shower of solar energetic particles that may have caused dramatic changes in the moon's lower ionosphere. Analyzing a list of Saturn's bow shock crossings during 2004-2016, we find that the magnetospheric compression needed for Titan to be in the supersonic solar wind can be generally associated with the presence of an ICME or a corotating interaction region. This leads to the conclusion that Titan would rarely face the pristine solar wind, but would rather interact with transient solar structures under extreme space weather conditions.

Keywords: Saturn, Space weather, Titan, Solar coronal mass ejection shocks, Solar coronal mass ejections, Planetary magnetospheres