Sazuna/UAT_keywords huggingface dataset:
Late-time Hubble Space Telescope Observations of a Hydrogen-poor Superluminous Supernova Reveal the Power-law Decline of a Magnetar Central Engine. The light-curve diversity of hydrogen-poor superluminous supernovae (SLSNe) has kept open the possibility that multiple power sources account for the population. Specifically, pair-instability explosions (PISNe), which produce large masses of 56Ni, have been argued as the origin of some slowly-evolving SLSNe. Here we present detailed observations of SN 2016inl (=PS16fgt), a slowly-evolving SLSN at z = 0.3057, whose unusually red spectrum matches PS1-14bj, an SLSN with an exceptionally long rise time consistent with a PISN. Ground-based and Hubble Space Telescope data, spanning about 800 rest-frame days, reveal a significant light-curve flattening, similar to that seen in SN 2015bn and much slower than the decline rate expected from radioactive decay of 56Co. We therefore conclude that despite its slow evolution, SN 2016inl is inconsistent with a PISN. Instead, the light-curve evolution matches the expected power-law spindown of a magnetar central engine, but with a shallower power law (L ∝ t-2.8) compared to that in SN 2015bn, indicating a possible difference in the γ-ray opacity between the two events. Analytical modeling indicates typical magnetar engine parameters, but one of the highest ejecta masses (≍20 M☉) inferred for an SLSN. Our results indicate that monitoring the late-time light-curve evolution of SLSNe provides a powerful diagnostic of their energy source.

Keywords: Magnetars, Type Ic supernovae, Supernovae, Core-collapse supernovae
A Possible Link between Turbulence and Plasma Heating. Numerical simulations and experimental results have shown that the formation of current sheets in space plasmas can be associated with enhanced vorticity. Also, in simulations the generation of such structures is associated with strong plasma heating. Here, we compare four-point measurements in the terrestrial magnetosheath turbulence from the Magnetospheric Multiscale mission of the flow vorticity and the magnetic field curlometer versus their corresponding one-point proxies PVI(V) and PVI(B) based on the Partial Variance of Increments (PVI) method. We show that the one-point proxies are sufficiently precise in identifying not only the generic features of the current sheets and vortices statistically, but also their appearance in groups associated with plasma heating. The method has been further applied to the region of the turbulent sheath of an interplanetary coronal mass ejection (ICME) observed at L1 by the WIND spacecraft. We observe current sheets and vorticity associated heating in larger groups (blobs), which so far have not been considered in the literature on turbulent data analysis. The blobs represent extended spatial regions of activity with enhanced regional correlations between the occurrence of conditioned currents and vorticity, which at the same time are also correlated with enhanced temperatures. This heating mechanism is substantially different from the plasma heating in the vicinity of the ICME shock, where plasma beta is strongly fluctuating and there is no vorticity. The proposed method describes a new pathway for linking the plasma heating and plasma turbulence, and it is relevant to in situ observations when only single spacecraft measurements are available.

Keywords: Interplanetary turbulence, Solar coronal mass ejections, Plasma physics
Signature of a Massive Rotating Metal-poor Star Imprinted in the Phoenix Stellar Stream. The Phoenix stellar stream has a low intrinsic dispersion in velocity and metallicity that implies the progenitor was probably a low-mass globular cluster. In this work we use Magellan/Magellan Inamori Kyocera Echelle (MIKE) high-dispersion spectroscopy of eight Phoenix stream red giants to confirm this scenario. In particular, we find negligible intrinsic scatter in metallicity ( $\sigma ([\mathrm{Fe}\,{\rm\small{II}}/{\rm{H}}])={0.04}_{-0.03}^{+0.11}$ ) and a large peak-to-peak range in [Na/Fe] and [Al/Fe] abundance ratios, consistent with the light element abundance patterns seen in the most metal-poor globular clusters. However, unlike any other globular cluster, we also find an intrinsic spread in [Sr II/Fe] spanning ~1 dex, while [Ba II/Fe] shows nearly no intrinsic spread ( $\sigma ([\mathrm{Ba}\,{\rm\small{II}}/{\rm{H}}])={0.03}_{-0.02}^{+0.10}$ ). This abundance signature is best interpreted as slow-neutron-capture element production from a massive fast-rotating metal-poor star (15-20 M⊙, vini/vcrit = 0.4, [Fe/H] = -3.8). The low inferred cluster mass suggests the system would have been unable to retain supernovae ejecta, implying that any massive fast-rotating metal-poor star that enriched the interstellar medium must have formed and evolved before the globular cluster formed. Neutron-capture element production from asymptotic giant branch stars or magneto-rotational instabilities in core-collapse supernovae provide poor fits to the observations. We also report one Phoenix stream star to be a lithium-rich giant (A(Li) = 3.1 ± 0.1). At [Fe/H ] = -2.93; it is among the most metal-poor lithium-rich giants known. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Stellar streams
The Nature of HI-absorption-selected Galaxies at z ≈ 4. We report a Karl G. Jansky Very Large Array (JVLA) search for redshifted CO(1-0) or CO(2-1) emission, and a Hubble Space Telescope Wide Field Camera 3 (HST-WFC3) search for rest-frame near-ultraviolet (NUV) stellar emission, from seven HI-selected galaxies associated with high-metallicity ([M/H] ≥ -1.3) damped Lyα absorbers (DLAs) at z ≈ 4. The galaxies were earlier identified by Atacama Large Millimeter/submillimeter Array imaging of their [CII] 158 μm emission. We also used the JVLA to search for CO(2-1) emission from the field of a low-metallicity ([M/H] = -2.47) DLA at z ≈ 4.8. No statistically significant CO emission is detected from any of the galaxies, yielding upper limits of Mmol &lt; (7.4-17.9) × 1010 × (αCO/4.36) M⊙ on their molecular gas mass. We detect rest-frame NUV emission from four of the seven [CII] 158 μm-emitting galaxies, the first detections of the stellar continuum from HI-selected galaxies at z ≳ 4. The HST-WFC3 images yield typical sizes of the stellar continua of ≈2-4 kpc and inferred dust-unobscured star formation rates (SFRs) of ≈5.0-17.5 M⊙ yr-1, consistent with, or slightly lower than, the total SFRs estimated from the far-infrared (FIR) luminosity. We further stacked the CO(2-1) emission signals of six [CII] 158 μm-emitting galaxies in the image plane. Our non-detection of CO(2-1) emission in the stacked image yields the limit Mmol &lt; 4.1 × 1010 × (αCO/4.36) M⊙ on the average molecular gas mass of the six galaxies. Our molecular gas mass estimates and NUV SFR estimates in HI-selected galaxies at z ≈ 4 are consistent with those of main-sequence galaxies with similar [CII] 158 μm and FIR luminosities at similar redshifts. However, the NUV emission in the HI-selected galaxies appears more extended than that in main-sequence galaxies at similar redshifts.

Keywords: High-redshift galaxies, Galaxies
GeV Emission in the Region of the Supernova Remnant G51.26+0.11. The supernova remnant G51.26+0.11 was recently discovered and little is known about its properties and environment. Using data from the Fermi Large Area Telescope we study the GeV emission seen in the direction of G51.26+0.11 to constrain the origin of the gamma-rays and their possible relation to this supernova remnant or to a star-forming region. We also search for emission from molecular gas in the region that could provide dense material for the production of gamma-rays. By modeling the multiwavelength spectrum of G51.26+0.11 from radio to gamma-rays we derive the properties of the particle populations that could produce the emission in several possible scenarios. We rule out the star-forming regions (such as G051.010+00.060) seen nearby as the origin of the GeV emission. The correspondence seen between the gamma-ray and radio morphologies supports a scenario in which G51.26+0.11 is the cause of the gamma-rays. The flat spectral energy distribution observed at GeV energies is best fit by hadronic or inverse Compton emission, while a bremsstrahlung model cannot properly account for the radio fluxes under a simple one-zone scenario. A pulsar wind nebula origin of the high-energy photons cannot be ruled out or confirmed.

Keywords: Gamma-ray astronomy, Gamma-rays
Extreme Variability and Episodic Lifetime of Quasars. We constrain the average episodic quasar lifetime (as in steady-state accretion) using two statistics of quasars that are recently turned off (i.e., dimmed by a large factor): (1) the fraction of turned-off quasars in a statistical sample photometrically observed over an extended period (e.g., Δt = 20 yr) and (2) the fraction of massive galaxies that show "orphan" broad Mg II emission, argued to be short-lived echoes of recently turned-off quasars. The two statistics constrain the average episodic quasar lifetime to be hundreds to thousands of years. Much longer (or shorter) episodic lifetimes are strongly disfavored by these observations. This average episodic lifetime is broadly consistent with the infall timescale (viscous time) in the standard accretion-disk model for quasars, suggesting that quasar episodes are governed by accretion-disk physics rather than by the gas supply on much larger scales. Compared with the cumulative quasar lifetime of ~106-108 yr constrained from quasar clustering and massive black hole demographics, our results suggest that there are ~103-105 episodes of quasar accretion during the assembly history of the supermassive black hole. Such short episodes should be clustered over intervals of ~104 yr to account for the sizes of ionized narrow-line regions in quasars. Our statistical argument also dictates that there will always be a small fraction of extreme variability quasars caught in "state transitions" over multiyear observing windows, despite the much longer episodic lifetime. These transitions could occur in a rather abrupt fashion during non-steady accretion.

Keywords: Surveys, Active galactic nuclei, Quasars
Preventing Anomalous Torques in Circumbinary Accretion Simulations. Numerical experiments are the primary method of studying the evolution of circumbinary disks due to the strong nonlinearities involved. Many circumbinary simulations also require the use of numerical mass sinks: source terms that prevent gas from unphysically accumulating around the simulated point masses by removing gas at a given rate. However, special care must be taken when drawing physical conclusions from such simulations to ensure that results are not biased by numerical artifacts. We demonstrate how improved sink methods reduce some of these biases, using simulations of aspect ratio 0.1 accretion disks around binaries with mass ratios between 0.1 and 1. We show that sink terms that do not reduce the angular momentum of gas relative to the accreting object (1) reduce the dependence on the sink rate of quantities such as the torque on the binary, distribution of accretion between binary components, and evolution of the binary semimajor axis; (2) reduce the degree to which the sink rate affects the structure of the accretion disks around each binary component; (3) alter the variability of accretion onto the binary, regularizing it in time. We also investigate other potential sources of systematic error, such as gravitational softening and simplifications to the viscous stress tensor. Because of the strong dependence of binary orbital evolution on both the torque and the distribution of mass between binary components, the sink method influences the orbital evolution of the binary at all mass ratios, with mass ratios below ~0.3 most affected.

Keywords: Accretion, Black holes, Computational methods, Active galactic nuclei, Circumstellar disks, Astrophysical fluid dynamics
Bridging the Gap between Protoplanetary and Debris Disks: Separate Evolution of Millimeter and Micrometer-sized Dust. The connection between the nature of a protoplanetary disk and that of a debris disk is not well understood. Dust evolution, planet formation, and disk dissipation likely play a role in the processes involved. We aim to reconcile both manifestations of dusty circumstellar disks through a study of optically thin Class III disks and how they correlate to younger and older disks. In this work, we collect literature and Atacama Large Millimeter/submillimeter Array archival millimeter fluxes for 85 disks (8%) of all Class III disks across nearby star-forming regions. We derive millimeter-dust masses Mdust and compare these with Class II and debris disk samples in the context of excess infrared luminosity, accretion rate, and age. The mean Mdust of Class III disks is 0.29 ± 0.19 M⊕. We propose a new evolutionary scenario wherein radial drift is very efficient for nonstructured disks during the Class II phase resulting in a rapid Mdust decrease. In addition, we find possible evidence for long infrared protoplanetary disk timescales, ~8 Myr, consistent with overall slow disk evolution. In structured disks, the presence of dust traps allows for the formation of planetesimal belts at large radii, such as those observed in debris disks. We propose therefore that the planetesimal belts in debris disks are the result of dust traps in structured disks, whereas protoplanetary disks without dust traps decrease in dust mass through radial drift and are therefore undetectable as debris disks after the gas dissipation. These results provide a hypothesis for a novel view of disk evolution.

Keywords: Kuiper belt, Young stellar objects, Pre-main sequence stars, Protoplanetary disks, Submillimeter astronomy
The Impact of Black Hole Formation on Population-averaged Supernova Yields. The landscape of black hole (BH) formation-in which massive stars explode as core-collapse supernovae (CCSN) and which implode into BHs-profoundly affects the initial-mass-function (IMF)-averaged nucleosynthetic yields of a stellar population. Building on the work of Sukhbold et al., we compute IMF-averaged yields at solar metallicity for a wide range of assumptions, including neutrino-driven engine models with extensive BH formation, models with a simple mass threshold for BH formation, and a model in which all stars from 8 to 120 M⊙ explode. For plausible choices, the overall yields of α-elements span a factor of 3, but changes in relative yields are more subtle, typically 0.05-0.2 dex. To constrain the overall level of BH formation, ratios of C and N to O or Mg are promising diagnostics. To distinguish complex, theoretically motivated landscapes from simple mass thresholds, abundance ratios involving Mn or Ni are promising because of their sensitivity to the core structure of the CCSN progenitors. We confirm previous findings of a substantial (factor 2.5-4) discrepancy between predicted O/Mg yield ratios and observationally inferred values, implying that models either overproduce O or underproduce Mg. No landscape choice achieves across-the-board agreement with observed abundance ratios; the discrepancies offer empirical clues to aspects of massive star evolution or explosion physics still missing from the models. We find qualitatively similar results using the massive star yields of Limongi &amp; Chieffi. We provide tables of IMF-integrated yields for several landscape scenarios, and more flexible user-designed models can be implemented through the publicly available Versatile Integrator for Chemical Evolution (VICE; https://pypi.org/project/vice/).

Keywords: Abundance ratios, Nucleosynthesis, Core-collapse supernovae, Stellar abundances, Stellar mass black holes, Stellar nucleosynthesis
Numerical Modeling and Physical Interplay of Stochastic Turbulent Acceleration for Nonthermal Emission Processes. Particle acceleration is a ubiquitous phenomenon in astrophysical and space plasma. Diffusive shock acceleration (DSA) and stochastic turbulent acceleration (STA) are known to be the possible mechanisms for producing very highly energetic particles, particularly in weakly magnetized regions. An interplay of different acceleration processes along with various radiation losses is typically observed in astrophysical sources. While DSA is a systematic acceleration process that energizes particles in the vicinity of shocks, STA is a random energizing process, where the interaction between cosmic ray particles and electromagnetic fluctuations results in particle acceleration. This process is usually interpreted as a biased random walk in energy space, modeled through a Fokker-Planck equation. In the present work, we describe a novel Eulerian algorithm, adopted to incorporate turbulent acceleration in the presence of DSA and radiative processes like synchrotron and inverse Compton emission. The developed framework extends the hybrid Eulerian-Lagrangian module in a full-fledged relativistic Magneto-hydrodynamic (RMHD) code PLUTO. From our validation tests and case studies, we showcase the competing and complementary nature of both acceleration processes. Axisymmetric simulations of an RMHD jet with this extended hybrid framework clearly demonstrate that emission due to shocks is localized, while that due to turbulent acceleration originates in the backflow and is more diffuse, particularly in the high-energy X-ray band.

Keywords: Plasma astrophysics, Computational methods, Non-thermal radiation sources, Shocks, Magnetohydrodynamical simulations
Scaling of Small-scale Dynamo Properties in the Rayleigh-Taylor Instability. We derive scaling relations based on freefall and isotropy assumptions for the kinematic small-scale dynamo growth rate and amplification factor over the course of the mixing, saturation, and decay phases of the Rayleigh-Taylor instability (RTI) in a fully ionized plasma. The scaling relations are tested using sets of three-dimensional, visco-resistive MHD simulations of the RTI. They are found to hold in the saturation phase, but exhibit discrepancies during the mixing and decay phases, suggesting a need to relax either the freefall or isotropy assumptions. Application of the scaling relations allows for quantitative prediction of the net amplification of magnetic energy in the kinematic dynamo phase and therefore a determination of whether the magnetic energy either remains sub-equipartition at all velocity scales or reaches equipartition with at least some scales of the turbulent kinetic energy in laboratory and astrophysical scenarios. As an example, we consider the dynamo in RTI-unstable regions of the outer envelope of a binary neutron star merger, and predict that the kinematic regime of the small-scale dynamo ends on the timescale of nanoseconds and then reaches saturation on a timescale of microseconds, which are both fast compared to the millisecond relaxation time of the post-merger.

Keywords: Neutron stars, Magnetohydrodynamics, Astrophysical fluid dynamics, Astrophysical magnetism, Plasma astrophysics, Magnetars, Magnetic fields, Magnetohydrodynamical simulations
Prediction of Soft Proton Intensities in the Near-Earth Space Using Machine Learning. The spatial distribution of energetic protons contributes to the understanding of magnetospheric dynamics. Based upon 17 yr of the Cluster/RAPID observations, we have derived machine-learning-based models to predict the proton intensities at energies from 28 to 962 keV in the 3D terrestrial magnetosphere at radial distances between 6 and 22 RE. We used the satellite location and indices for solar, solar wind, and geomagnetic activity as predictors. The results demonstrate that the neural network (multi-layer perceptron regressor) outperforms baseline models based on the k-nearest neighbors and historical binning on average by ~80% and ~33%, respectively. The average correlation between the observed and predicted data is about 56%, which is reasonable in light of the complex dynamics of fast-moving energetic protons in the magnetosphere. In addition to a quantitative analysis of the prediction results, we also investigate parameter importance in our model. The most decisive parameters for predicting proton intensities are related to the location-Z geocentric solar ecliptic direction-and the radial distance. Among the activity indices, the solar wind dynamic pressure is the most important. The results have a direct practical application, for instance, for assessing the contamination particle background in the X-ray telescopes for X-ray astronomy orbiting above the radiation belts. To foster reproducible research and to enable the community to build upon our work we publish our complete code, the data, and the weights of trained models. Further description can be found in the GitHub project at https://github.com/Tanveer81/deep_horizon.

Keywords: Space plasmas, Astronomy data modeling, X-ray detectors, Astronomy data analysis, X-ray telescopes, X-ray observatories
Probing the Nucleosynthetic Contribution of Low-metallicity, Low-mass Star Companions of CEMP Stars. The observed abundance diversities among CEMP stars can shed light on the formation and evolution of elements in the early Galaxy. In this work, we present results obtained from a detailed abundance analysis of a sample of seven extrinsic carbon stars. The analysis is based on high-resolution spectra obtained with HCT/HESP (R~60,000) and SUBARU/HDS (R~50,000). We present, for the first time, the elemental abundance results for the objects BD-19 132, BD-19 290, HE 1304-2111, HE 1354-2257, and BD+19 3109. Abundances of a few elements are available in the literature for HE 1157-0518 and HD 202851; we present an update on the abundances of these elements along with new abundance estimates for several other elements. Our analysis confirms the object HD 202851 to be a CH star. While BD-19 132, HE 1354-2257, and BD+19 3109 are found to be CEMP-s stars, the objects BD-19 290, HE 1157-0518, and HE 1304-2111 are found to belong to CEMP-r/s group. The observed abundance patterns of the three CEMP-r/s stars are well reproduced with the i-process model predictions. While the objects BD+19 3109 and HD 202851 are confirmed binaries, the binary status of the remaining objects is not known. Analysis based on different elemental abundance ratios confirms low-mass former AGB companions for all the objects. Kinematic analysis shows that BD-19 290, HE 1157-0518, HE 1354-2257, and BD+19 3109 belong to the Galactic halo, whereas BD-19 132, HE 1304-2111, and HD 202851 are members of Galactic thin disk. * Based on data collected using HCT/HESP and SUBARU/HDS.

Keywords: Population II stars