Sazuna/UAT_keywords huggingface dataset:
An In Situ Interplanetary "U-burst": Observation and Results. We report and examine the observation of an unusual and rare in situ electron observation associated with a solar type III radio burst on 1996 December 24. This radio event was accompanied by high-energy electrons, measured by the Solid State Telescope on board the Wind spacecraft. The type III radio emission started at ≈13:10 UTC and was associated with a C2.1 GOES-class flare whose maximum was at 13:11 UTC and hosted by the active region NOAA 8007/8004, located on the west limb at N05° W74°/N06° W85°. During this event, the observation of an electron energy distribution likely to be associated with the radio emission was registered. The electrons arrive at the spacecraft predominantly from the antisolar direction, suggesting that their general motion is sunward along a closed magnetic field line. Leblanc et al. propose a model in which energetic electrons are injected into a coronal flux tube at one of its footpoints, releasing standard type-III emission. As the magnetic field then directs them back toward the magnetic-conjugate footpoint of the first, the electrons release subsequent emission whose radio profile is a quasi-time reversal of the standard. We have constructed a cylindrical flux rope facsimile of this scenario that reproduces the U-burst profiles. We also report observational features indicating a secondary electron energy distribution and propose a scenario that explains this feature.

Keywords: Solar coronal mass ejections
A White Dwarf with Transiting Circumstellar Material Far outside the Roche Limit. We report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative of circumstellar planetary debris. Using Zwicky Transient Facility DR2 photometry of ZTF J013906.17+524536.89 and follow-up observations from the Las Cumbres Observatory, we identify multiple transit events that recur every ≍107.2 days, much longer than the 4.5-4.9 hr orbital periods observed in WD 1145+017, the only other white dwarf known with transiting planetary debris. The transits vary in both depth and duration, lasting 15-25 days and reaching 20%-45% dips in flux. Optical spectra reveal strong Balmer lines, identifying the white dwarf as a DA with ${T}_{\mathrm{eff}}=10,530\pm 140\,{\rm{K}}$ and $\mathrm{log}(g)=7.86\pm 0.06$ . A Ca II K absorption feature is present in all spectra both in and out of transit. Spectra obtained during one night at roughly 15% transit depth show increased Ca II K absorption with a model atmospheric fit suggesting [Ca/H] = -4.6 ± 0.3, whereas spectra taken on three nights out of transit have [Ca/H] of -5.5, -5.3, and -4.9 with similar uncertainties. While the Ca II K line strength varies by only 2σ, we consider a predominantly interstellar origin for Ca absorption unlikely. We suggest a larger column density of circumstellar metallic gas along the line of site or increased accretion of material onto the white dwarf's surface are responsible for the Ca absorption, but further spectroscopic studies are required. In addition, high-speed time series photometry out of transit reveals variability with periods of 900 and 1030 s, consistent with ZZ Ceti pulsations.

Keywords: Eclipses, Transits, Stellar pulsations, Tidal disruption, White dwarf stars, Roche limit, Planetesimals, Circumstellar dust, Debris disks, Circumstellar gas
Nonresonant Instability of Kinetic Alfvén Waves with κ-electrons. A nonresonant instability of kinetic Alfvén waves (KAWs) is studied in a three-component plasma system consisting of background cold ions, an ion beam, and hot electrons with a κ-distribution. The nonresonant KAW instability is produced by the combined sources of ion beam and velocity shear. It is found that the wave excitation by velocity shear alone will give rise to purely growing KAWs, whereas the ion beam velocity alone as a source cannot excite the waves for the considered plasma parameters. It is also observed that the combined sources of ion beam and velocity shear can excite the KAWs in nonresonant instability with finite wave frequency (the mode is not a purely growing mode). Also note that κ-electrons restrict the wave propagation very close to 90°, whereas the Maxwellian electrons permit the wave to propagate a few degrees away from 90°. It is inferred that the presence of κ-electrons shrinks the wave-unstable region of a KAW's nonresonant instability. The coupling between KAWs and ion-acoustic waves occurs at a lower value of βI for Maxwellian electrons as compared to κ-electrons.

Keywords: Space plasmas, Solar wind
A Quake Quenching the Vela Pulsar. The remarkable null pulse coincident with the 2016 glitch in Vela rotation indicates a dynamical event involving the crust and the magnetosphere of the neutron star. We propose that a crustal quake associated with the glitch strongly disturbed the Vela magnetosphere and thus interrupted its radio emission. We present the first global numerical simulations of a neutron starquake. Our code resolves the elasto-dynamics of the entire crust and follows the evolution of Alfvén waves excited in the magnetosphere. We observe Rayleigh surface waves propagating away from the epicenter of the quake, around the circumference of the crust—an instance of the so-called whispering gallery modes. The Rayleigh waves set the initial spatial scale of the magnetospheric disturbance. Once launched, the Aflvén waves bounce in the closed magnetosphere, become de-phased, and generate strong electric currents, capable of igniting electric discharge. Most likely, the discharge floods the magnetosphere with electron-positron plasma, quenching the radio emission. We find that the observed ∼0.2 s disturbance is consistent with the damping time of the crustal waves if the crust is magnetically coupled to the superconducting core of the neutron star. The quake is expected to produce a weak X-ray burst of short duration.

Keywords: Magnetic fields, Plasma astrophysics, Pulsars
Global 21 cm Signal Extraction from Foreground and Instrumental Effects. II. Efficient and Self-consistent Technique for Constraining Nonlinear Signal Models. We present the completion of a data analysis pipeline that self-consistently separates global 21 cm signals from large systematics using a pattern recognition technique. This pipeline will be used for both ground and space-based hydrogen cosmology instruments. In the first paper of this series, we obtain optimal basis vectors from signal and foreground training sets to linearly fit both components with the minimal number of terms that best extracts the signal given its overlap with the foreground. In this second paper, we utilize the spectral constraints derived in the first paper to calculate the full posterior probability distribution of any signal parameter space of choice. The spectral fit provides the starting point for a Markov Chain Monte Carlo (MCMC) engine that samples the signal without traversing the foreground parameter space. At each MCMC step, we marginalize over the weights of all linear foreground modes and suppress those with unimportant variations by applying priors gleaned from the training set. This method drastically reduces the number of MCMC parameters, augmenting the efficiency of exploration, circumvents the need for selecting a minimal number of foreground modes, and allows the complexity of the foreground model to be greatly increased to simultaneously describe many observed spectra without requiring extra MCMC parameters. Using two nonlinear signal models, one based on the Experiment to Detect the Global Epoch-of-Reionization Signature (EDGES) observations and the other on phenomenological frequencies and temperatures of theoretically expected extrema, we demonstrate the success of this methodology by recovering the input parameters from multiple randomly simulated signals at low radio frequencies (10-200 MHz), while rigorously accounting for realistically modeled beam-weighted foregrounds.

Keywords: Reionization, Astrostatistics techniques, Computational methods
Global 21 cm Signal Extraction from Foreground and Instrumental Effects. III. Utilizing Drift-scan Time Dependence and Full Stokes Measurements. When using valid foreground and signal models, the uncertainties on extracted signals in global 21 cm signal experiments depend principally on the overlap between signal and foreground models. In this paper, we investigate two strategies for decreasing this overlap: (I) utilizing time dependence by fitting multiple drift-scan spectra simultaneously, and (II) measuring all four Stokes parameters instead of only the total power, Stokes I. Although measuring polarization requires different instruments than are used in most existing experiments, all existing experiments can utilize drift-scan measurements merely by averaging their data differently. In order to evaluate the increase in constraining power from using these two techniques, we define a method for connecting root-mean-square (rms) uncertainties to probabilistic confidence levels. Employing simulations, we find that fitting only one total power spectrum leads to rms uncertainties at the few K level, while fitting multiple time-binned, drift-scan spectra yields uncertainties at the ≲10 mK level. This significant improvement only appears if the spectra are modeled with one set of basis vectors instead of using multiple sets of basis vectors that independently model each spectrum. Assuming that they are simulated accurately, measuring all four Stokes parameters also leads to lower uncertainties. These two strategies can be employed simultaneously, and fitting multiple time bins of all four Stokes parameters yields the most precise measurements of the 21 cm signal, approaching the noise level in the data.

Keywords: Cosmology, Reionization, Astronomy data analysis
The Molecular Interstellar Medium in the Super Star Clusters of the Starburst NGC 253. We present submillimeter spectra of the (proto-)super star cluster (SSC) candidates in the starbursting center of the nearby galaxy NGC 253 identified by Leroy et al. The 2.5 pc resolution of our Atacama Large Millimeter/submillimeter Array cycle 3 observations approaches the size of the SSCs and allows for the study of physical and chemical properties of the molecular gas in these sources. In the 14 SSC sources and in the frequency ranges 342.0-345.8 GHz and 353.9-357.7 GHz, we detect 55 lines belonging to 19 different chemical species. The SSCs differ significantly in chemical complexity, with the richest clusters showing 19 species and the least complex showing four species. We detect HCN isotopologues and isomers (H13CN, HC15N, H15NC), abundant HC3N, SO and S18O, SO2, and H2CS. The gas ratios CO/HCN, CO/HCO+ are low, ∼1-10, implying high dense gas fractions in the SSCs. Line ratio analyses suggests chemistry consistent with photon-dominated regions and mechanical heating. None of the SSCs near the galaxy center show line ratios that imply an X-ray-dominated region, suggesting that heating by any (still unknown) active galactic nucleus does not play a major role. The gas temperatures are high in most sources, with an average rotational temperature of ∼130 K in SO2. The widespread existence of vibrationally excited HCN and HC3N transitions implies strong infrared radiation fields, potentially trapped by a greenhouse effect due to high continuum opacities.

Keywords: Starburst galaxies, Dense interstellar clouds, Astrochemistry, Star formation, Interstellar medium, Star clusters
Blazars at the Cosmic Dawn. The uncharted territory of the high-redshift (z ≳ 3) universe holds the key to understanding the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, that is, blazars, we have carried out a multiwavelength study of a large sample of radio-loud quasars beyond z = 3. Our sample consists of nine γ-ray-detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3-10 keV photon index ≤1.75), including 15 with Nuclear Spectroscopic Telescope Array (NuSTAR) observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint γ-ray emitters with steep spectra. The high-redshift blazars host massive black holes ( $\langle \mathrm{log}\,{M}_{\mathrm{BH},M\odot }\rangle \gt 9$ ) and luminous accretion disks ( $\langle {L}_{\mathrm{disk}}\rangle \gt {10}^{46}$ erg s-1). Their broadband spectral energy distributions are found to be dominated by high-energy radiation, indicating their jets are among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other z &gt; 3 blazars, indicating faster moving jets. We conclude that the presented list of high-redshift blazars may act as a reservoir for follow-up observations, such as with NuSTAR, to understand the evolution of relativistic jets at the dawn of the universe.

Keywords: Blazars, Active galactic nuclei, High-redshift galaxies, Radiative processes
A Search for Lensed Gamma-Ray Bursts in 11 yr of Observations by Fermi GBM. Macrolensing of gamma-ray bursts (GRBs) is expected to manifest as a GRB recurring with the same light curve and spectrum as a previous one, but with a different flux and a slightly offset position. Identifying such lensed GRBs may give important information about the lenses, the cosmology, and the GRBs themselves. Here we present a search for lensed GRBs among ∼2700 GRBs observed by the Fermi Gamma-ray Burst Monitor during 11 yr of operations. To identify lensed GRBs, we perform initial cuts on position, time-averaged spectral properties, and relative duration. We then use the cross-correlation function to assess the similarity of light curves, and finally we analyze the time-resolved spectra of the most promising candidates. We find no convincing lens candidates. The most similar pairs are single-pulsed GRBs with relatively few time bins for the spectral analysis. This is best explained by similarities within the GRB population rather than lensing. However, the null result does not rule out the presence of macrolensed GRBs in the sample. In particular, we find that observational uncertainties and Poisson fluctuations can lead to significant differences within a pair of lensed GRBs.

Keywords: Strong gravitational lensing, Gamma-ray bursts
Sun-Heliosphere Observation-based Ionization Rates Model. The solar wind (SW) and the extreme ultraviolet (EUV) radiation modulate fluxes of interstellar and heliospheric particles inside the heliosphere both in time and in space. Understanding this modulation is necessary to correctly interpret measurements of particles of interstellar origin inside the heliosphere. We present a revision of heliospheric ionization rates and provide the Sun-Heliosphere Observation-based Ionization Rates model based on the currently available data. We calculate the total ionization rates using revised SW and solar EUV data. We study the in-ecliptic variation of the SW parameters, the latitudinal structure of the SW speed and density, and the reconstruction of the photoionization rates. The revision most affects the SW out of the ecliptic plane during solar maximum and the estimation of the photoionization rates, the latter due to a change of the reference data. The revised polar SW is slower and denser during the solar maximum of solar cycle (SC) 24. The current estimated total ionization rates are higher than the previous ones for H, O, and Ne, and lower for He. The changes for the in-ecliptic total ionization rates are less than 10% for H and He, up to 20% for O, and up to 35% for Ne. Additionally, the changes are not constant in time and vary as a function of time and latitude.

Keywords: Solar cycle, Charge exchange ionization, Photoionization, Heliosphere, Solar wind, Interstellar medium, Ionization, Solar activity
Spitzer + VLTI-GRAVITY Measure the Lens Mass of a Nearby Microlensing Event. We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555 (Kojima-1). We measure the microlens parallax vector ${{\boldsymbol{\pi }}}_{{\rm{E}}}$ using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this ${{\boldsymbol{\pi }}}_{{\rm{E}}}$ determination with the angular Einstein radius ${\theta }_{{\rm{E}}}$ measured by VLTI-GRAVITY observations, we find that the lens is a star with mass ${M}_{{\rm{L}}}=0.495\pm 0.063\,{M}_{\odot }$ at a distance DL = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lens-source proper motion is ${\mu }_{\mathrm{rel},\mathrm{hel}}=26.55\pm 0.36\,\mathrm{mas}\,{\mathrm{yr}}^{-1}$ , so with currently available adaptive-optics instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite-parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

Keywords: Gravitational microlensing, Stellar distance, Satellite microlensing parallax, Stellar masses
70 Years of Chromospheric Solar Activity and Dynamics. From 1915 to 1985 the monitoring program of the Mount Wilson Observatory, one of the Observatories of the Carnegie Institution of Washington, has taken over 35,000 daily images (spectroheliograms) of the Sun in the chromospheric resonance line of Ca II K. This important database constitutes a unique resource for a variety of retrospective analyses of the state of solar magnetism on multidecadal timescales. These observations may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability for current dynamo models. We describe here a procedure to calibrate and rescale these images so that homogeneous Carrington synoptic maps can be derived for the whole period covered by these observations. Temporal variations in full-disk chromospheric activity clearly show the signature of the 11 yr solar cycle, but no evidence is found for a statistically significant north/south hemispheric asymmetry. Using a feature-tracking technique we were also able to obtain the average solar rotation profile. We find no indication of any detectable periodicity in the temporal behavior of the orthogonalized rotation rate coefficients, suggesting the global chromospheric dynamics has not changed during the 70 years investigated in this work. We found also no significant evidence in our analysis for a hemispheric asymmetry in rotation rates.

Keywords: Solar activity
Detailed Model of the Growth of Fluffy Dust Aggregates in a Protoplanetary Disk: Effects of Nebular Conditions. The coagulation of dust aggregates plays an important role in the formation of planets and is of key importance to the evolution of protoplanetary disks (PPDs). The characteristics of dust, such as the diversity of particle size, porosity, charge, and the manner in which dust couples to turbulent gas, affect the collision outcome and the rate of dust growth. Here we present a numerical model of the evolution of the dust population within a PPD which incorporates all of these effects. The probability that any two particles collide depends on the particle charge, cross-sectional area, and their relative velocity. The actual collision outcome is determined by a detailed collision model that takes into account the aggregate morphology, trajectory, orientation, and electrostatic forces acting between charged grains. Our model is applicable to the epoch of time during which hit-and-stick is the primary collision outcome, the duration of which varies greatly depending on the environment. The data obtained in this research reveal the characteristics of dust populations in different environments at the end of the hit-and-stick growth, which establishes the foundation for the onset of the next growth stage where bouncing, mass transfer, and fragmentation become important. For a given level of turbulence, neutral and weakly charged particles collide more frequently and grow faster than highly charged particles. In general, the epoch of hit-and-stick growth is much shorter in high turbulence than it is in regions with low turbulence or highly charged grains. In addition, highly charged particles grow to a larger size before reaching the bouncing barrier, especially in environments with low turbulence, and exhibit "runaway" growth, in which a few large particles grow quickly by accreting smaller particles while the rest of the population grows very slowly. In general, highly charged aggregates have a more compact structure and are comprised of larger monomers than neutral/weakly charged aggregates. The differences in the particle structure/composition not only affect the threshold velocities for bouncing and fragmentation, but also change the scattering and absorption opacity of dust, influencing the appearance of PPDs.

Keywords: Space plasmas, Circumstellar dust, Protoplanetary disks
Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis. We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( $\geqslant $ 20 M⊙) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Keywords: Stellar abundances, Chemically peculiar stars, Dwarf galaxies, Chemical abundances