Sazuna/UAT_keywords huggingface dataset:
Time Profile Study of Type III Solar Radio Bursts Using Parker Solar Probe. Solar type III radio bursts are crucial indicators of energetic electron activity in the solar corona and interplanetary space. Our assessment of 43 interplanetary type III bursts, recorded by the FIELDS instrument on board the Parker Solar Probe during Encounters 05 to 11, has led to significant and complex findings. We have analyzed time profile features across a frequency range of 19–0.5 MHz, revealing dependencies on frequency and providing insights into duration, burst speeds, bandwidths, and drift rates. This novel analysis has unveiled a spectral index of ‑0.63 ± 0.04 for rise, ‑0.69 ± 0.03 for decay time, and ‑0.68 ± 0.03 for the total duration. We have determined the average electron beam velocities for front, middle, and back as 0.15c, 0.13c, and 0.08c, respectively. Our findings show that faster electron beams generate emissions with shorter duration. The average ratio of the front-to-back velocity is 1.87, and the ratio of front-to-middle velocity is 1.23. We have also discovered a strong relationship between burst duration with rise, peak, and decay times, particularly pronounced with decay time (correlation coefficient = 0.95). This indicates that the entire temporal profile, including rise, peak, and decay phases, collectively contributes to event duration and is not solely influenced by external factors like plasma conditions or electron beam dynamics but also by internal burst processes. These complex findings shed light on the physical mechanisms governing burst dynamics, revealing intricate interactions between electron beam characteristics and observed temporal and spectral traits of type III solar radio bursts.

Keywords: Solar energetic particles, Solar radio emission, Solar corona
A High-resolution Imaging Survey of Massive Young Stellar Objects in the Magellanic Clouds. Constraints on the binary fraction of massive young stellar objects (mYSOs) are important for binary and massive star formation theory. Here, we present speckle imaging of 34 mYSOs located in the Large Magellanic Cloud (1/2 Z ⊙) and Small Magellanic Cloud (∼1/5 Z ⊙), probing projected separations in the 2000 to 20,000 au (at angular scales of 0.″02─0.″2) range, for stars above 8 M ⊙. We find two wide binaries in the Large Magellanic Cloud (from a sample of 23 targets), but none in a sample of 11 in the Small Magellanic Cloud, leading us to adopt a wide binary fraction of 9% ± 5% and &lt;5%, respectively. We rule out a wide binary fraction greater than 35% in the Large Magellanic Cloud and 38% in the Small Magellanic Cloud at the 99% confidence level. This is in contrast to the wide binary fraction of mYSOs in the Milky Way (presumed to be 1 Z ⊙), which within the physical parameter space probed by this study is ∼15%─60% from the literature. We argue that while selection effects could be responsible for the lower binary fraction observed, it is more likely that there are underlying physical mechanisms responsible for the observed properties. This indicates that metallicity and environmental effects may influence the formation of wide binaries among massive stars. Future larger, more statistically significant samples of high-mass systems in low-metallicity environments for comparison to the Milky Way, are essential to confirm or repudiate our claim.

Keywords: Binary stars, Massive stars, Small Magellanic Cloud, Large Magellanic Cloud, Young stellar objects, Star formation, Wide binary stars, Visual binary stars
Closing the Net on Transient Sources of Ultrahigh-energy Cosmic Rays. The arrival directions of ultrahigh-energy cosmic rays (UHECRs) observed above 4 × 1019 eV provide evidence of localized excesses that are key to identifying their sources. We leverage the 3D matter distribution from optical and infrared surveys as a density model of UHECR sources, which are considered to be transient. Agreement of the sky model with UHECR data imposes constraints on both the emission rate per unit matter and the time spread induced by encountered turbulent magnetic fields. Based on radio measurements of cosmic magnetism, we identify the Local Sheet as the magnetized structure responsible for the kiloyear duration of UHECR bursts for an observer on Earth and find that the turbulence amplitude must be within 0.5–20 nG for a coherence length of 10 kpc. At the same time, the burst-rate density must be above 50 Gpc‑3 yr‑1 for Local Sheet galaxies to reproduce the UHECR excesses and below 5000 Gpc‑3 yr‑1 (30,000 Gpc‑3 yr‑1) for the Milky Way (Local Group galaxies) not to outshine other galaxies. For the transient emissions of protons and nuclei to match the energy spectra of UHECRs, the kinetic energy of the outflows responsible for UHECR acceleration must be below 4 × 1054 erg and above 5 × 1050 erg (2 × 1049 erg) if we consider the Milky Way (or not). The only stellar-sized transients that satisfy both Hillas' and our criteria are long-duration gamma-ray bursts.

Keywords: Large-scale structure of the universe, Cosmic ray astronomy, Transient sources, Magnetic fields, Ultra-high-energy cosmic radiation
Why Are (Almost) All the Protostellar Outflows Aligned in Serpens Main?. We present deep 1.4–4.8 μm JWST-NIRCam imaging of the Serpens Main star-forming region and identify 20 candidate protostellar outflows, most with bipolar structure and identified driving sources. The outflow position angles (PAs) are strongly correlated, and they are aligned within ±24° of the major axis of the Serpens filament. These orientations are further aligned with the angular momentum vectors of the two disk shadows in this region. We estimate that the probability of this number of young stars being coaligned if sampled from a uniform PA distribution is 10‑4. This in turn suggests that the aligned protostars, which seem to be at similar evolutionary stages based on their outflow dynamics, formed at similar times with a similar spin inherited from a local cloud filament. Further, there is tentative evidence for a systematic change in average PA between the northwestern and southeastern cluster, as well as increased scatter in the PAs of the southeastern protostars. SOFIA-HAWC+ archival dust polarization observations of Serpens Main at 154 and 214 μm are perpendicular to the dominant jet orientation in the northwestern region in particular. We measure and locate shock knots and edges for all of the outflows and provide an identifying catalog. We suggest that Serpens main is a cluster that formed from an isolated filament and due to its youth retains its primordial outflow alignment.

Keywords: Stellar-interstellar interactions, Interstellar filaments, Stellar jets, Star forming regions, Interstellar magnetic fields, Circumstellar matter, Protostars
Flaring Stars in a Nontargeted Millimeter-wave Survey with SPT-3G. We present a flare star catalog from 4 yr of nontargeted millimeter-wave survey data from the South Pole Telescope (SPT). The data were taken with the SPT-3G camera and cover a 1500 deg2 region of the sky from 20h40m0s to 3h20m0s in right ascension and from ‑42° to ‑70° in declination. This region was observed on a nearly daily cadence from 2019 to 2022 and chosen to avoid the plane of the galaxy. A short-duration transient search of this survey yields 111 flaring events from 66 stars, increasing the number of both flaring events and detected flare stars by an order of magnitude from the previous SPT-3G data release. We provide cross-matching to Gaia DR3, as well as matches to X-ray point sources found in the second ROSAT all-sky survey. We have detected flaring stars across the main sequence, from early-type A stars to M dwarfs, as well as a large population of evolved stars. These stars are mostly nearby, spanning 10–1000 pc in distance. Most of the flare spectral indices are constant or gently rising as a function of frequency at 95/150/220 GHz. The timescale of these events can range from minutes to hours, and the peak ν L  ν  luminosities range from 1027 to 1031 erg s‑1 in the SPT-3G frequency bands.

Keywords: Millimeter astronomy, Transient sources, Flare stars, Stellar flares, Transient detection
The Zwicky Transient Facility Bright Transient Survey. III. BTSbot: Automated Identification and Follow-up of Bright Transients with Deep Learning. The Bright Transient Survey (BTS) aims to obtain a classification spectrum for all bright (m peak ≤ 18.5 mag) extragalactic transients found in the Zwicky Transient Facility (ZTF) public survey. BTS critically relies on visual inspection ("scanning") to select targets for spectroscopic follow-up, which, while effective, has required a significant time investment over the past ∼5 yr of ZTF operations. We present BTSbot, a multimodal convolutional neural network, which provides a bright transient score to individual ZTF detections using their image data and 25 extracted features. BTSbot is able to eliminate the need for daily human scanning by automatically identifying and requesting spectroscopic follow-up observations of new bright transient candidates. BTSbot recovers all bright transients in our test split and performs on par with scanners in terms of identification speed (on average, ∼1 hr quicker than scanners). We also find that BTSbot is not significantly impacted by any data shift by comparing performance across a concealed test split and a sample of very recent BTS candidates. BTSbot has been integrated into Fritz and Kowalski, ZTF's first-party marshal and alert broker, and now sends automatic spectroscopic follow-up requests for the new transients it identifies. Between 2023 December and 2024 May, BTSbot selected 609 sources in real time, 96% of which were real extragalactic transients. With BTSbot and other automation tools, the BTS workflow has produced the first fully automatic end-to-end discovery and classification of a transient, representing a significant reduction in the human time needed to scan.

Keywords: Supernovae, Convolutional neural networks, Sky surveys, Time domain astronomy
The Ultraviolet Luminosity Function at 0.6 &lt; z &lt; 1 from UVCANDELS. UVCANDELS is a Hubble Space Telescope Cycle-26 Treasury Program awarded 164 orbits of primary ultraviolet (UV) F275W imaging and coordinated parallel optical F435W imaging in four CANDELS fields—GOODS-N, GOODS-S, EGS, and COSMOS—covering a total area of ∼426 arcmin2. This is ∼2.7 times larger than the area covered by previous deep-field space UV data combined, reaching a depth of about 27 and 28 ABmag (5σ in 0."2 apertures) for F275W and F435W, respectively. Along with new photometric catalogs, we present an analysis of the rest-frame UV luminosity function (LF), relying on our UV-optimized aperture photometry method, yielding a factor of 1.5 increase over H-isophot aperture photometry in the signal-to-noise ratios of galaxies in our F275W imaging. Using well-tested photometric redshift measurements, we identify 5810 galaxies at redshifts 0.6 &lt; z &lt; 1, down to an absolute magnitude of M UV = ‑14.2. In order to minimize the effect of uncertainties in estimating the completeness function, especially at the faint end, we restrict our analysis to sources above 30% completeness, which provides a final sample of 4726 galaxies at ‑21.5 &lt; M UV &lt; ‑15.5. We performed a maximum likelihood estimate to derive the best-fit parameters of the UV LF. We report a best-fit faint-end slope of  α=‑1.359‑0.041+0.041  at z ∼ 0.8. Creating subsamples at z ∼ 0.7 and z ∼ 0.9, we observe a possible evolution of α with redshift. The unobscured UV luminosity density at M UV &lt; ‑10 is derived as  ρUV=1.339‑0.030+0.027(×1026ergs‑1Hz‑1Mpc‑3)  using our best-fit LF parameters. The new F275W and F435 photometric catalogs from UVCANDELS have been made publicly available on the Barbara A. Mikulski Archive for Space Telescopes.

Keywords: Luminosity function, High-redshift galaxies, Galaxy evolution, Galaxies
Concurrent Particle Acceleration and Pitch-angle Anisotropy Driven by Magnetic Reconnection: Ion-electron Plasmas. Particle acceleration and pitch-angle anisotropy resulting from magnetic reconnection are investigated in highly magnetized ion-electron plasmas. By means of fully kinetic particle-in-cell simulations, we demonstrate that magnetic reconnection generates anisotropic particle distributions  fs∣cosα∣,ɛ , characterized by broken power laws in the particle energy spectrum f  s (ɛ) ∝ ɛ ‑p  and pitch angle  &lt;sin2α&gt;∝ɛm . The characteristics of these distributions are determined by the relative strengths of the magnetic field's guide and reconnecting components (B  g /B 0) and the plasma magnetization (σ 0). Below the injection break energy ɛ 0, ion and electron energy spectra are extremely hard (p &lt; ≲ 1) for any B  g /B 0 and σ 0 ≳ 1, while above ɛ 0 the spectral index steepens (p &gt; ≳ 2), displaying high sensitivity to both B  g /B 0 and σ 0. The pitch angle displays power-law ranges with negative slopes (m &lt;) below and positive slopes (m &gt;) above  ɛminα , steepening with increasing B  g /B 0 and σ 0. The ratio B  g /B 0 regulates the redistribution of magnetic energy between ions (ΔE  i ) and electrons (ΔE  e ), with ΔE  i  ≫ ΔE  e  for B  g /B 0 ≪ 1, ΔE  i  ∼ ΔE  e  for B  g /B 0 ∼ 1, and ΔE  i  ≪ ΔE  e  for B  g /B 0 ≫ 1, with ΔE  i /ΔE  e  approaching unity when σ 0 ≫ 1. The anisotropic distribution of accelerated particles results in an optically thin synchrotron power spectrum F  ν (ν) ∝ ν (2‑2p+m)/(4+m) and a linear polarization degree Πlin = (p + 1)/(p + 7/3 + m/3) for a uniform magnetic field. Pitch-angle anisotropy also induces temperature anisotropy and eases synchrotron cooling, along with producing beamed radiation aligned with the magnetic field, which is potentially responsible for rapid frequency-dependent variability.

Keywords: High energy astrophysics, Plasma physics, Non-thermal radiation sources, Magnetic fields, Particle astrophysics
Local Transition of Electron Pitch Angle Distribution within Flux Pileup Region behind Dipolarization Front. Dipolarization fronts (DFs), earthward-propagating magnetic transients with a strong magnetic field, are important regions favorable for energetic electron acceleration in the magnetotail. The DF-driven electron acceleration usually generates coherent pitch angle distributions (PADs) inside flux pileup regions (FPRs), i.e., strong magnetic field regions behind the DFs, such as pancake, butterfly, and cigar distributions, which dominate at different tail regions and often occur separately. Here we present unique observations of electron PAD evolution inside the FPR, showing that electron PAD underwent local transition from cigar distribution, to butterfly distribution, then toward pancake distribution, forming a U-shaped distribution. During the local transition, electron perpendicular flux (relative to the local magnetic field) is anticorrelated with magnetic field strength, contrary to traditional expectation. The unexpected feature of the electron U-shaped distribution is associated with multiple physical processes at different scales, including local expansion of flux tubes and pitch angle variation near the neutral sheet. These atypical observations can advance our current understanding of electron acceleration and transport in the magnetosphere.

Keywords: Space plasmas
STELLA Lightcurves of Energetic Pair-instability Supernovae in the Context of SN2018ibb. SN2018ibb is a recently observed hydrogen-poor superluminous supernova that appears to be powered by the decay of 30 M ⊙ of radioactive nickel. This supernova has been suggested to show hybrid signatures of a pair-instability supernova and an interacting supernova. In a previous paper, we found that rotating, metal-enriched pair-instability supernova progenitors appeared to check both of these boxes. In this paper, we model the lightcurves of the pair-instability supernovae using STELLA. We find that the STELLA models can explain the overall shape of the bolometric lightcurve of SN2018ibb, though not specific morphological features such as the luminosity peak or the bump at roughly 300 days after the peak. We also estimate the contribution from interaction and find that with relatively low wind velocities, the circumstellar medium originating from the stellar winds is consistent with the evidence for interaction in the spectra. The observed values of the photosphere velocity in the 100 days after peak luminosity are similar to the STELLA models, but the deceleration is lower. This leads to the biggest inconsistency, which is the blackbody temperature of SN2018ibb being much hotter than any of the STELLA models. We note that this high temperature (and the flat velocity) may be difficult to reconcile with the long rise time of SN2018ibb, but nevertheless conclude that if it is accurate, this discrepancy represents a challenge for SN2018ibb being a robust PISN candidate. This result is noteworthy given the lack of other scenarios for this supernova.

Keywords: Supernovae
Laboratory Transition-rate Measurement of the Coronal Intercombination Line of Ar XV by Time-resolved Laser Spectroscopy. The extreme-ultraviolet emission line (424 Å) of the intercombination 1s 22s 2 1 S 0–1s 22s2p 3 P 1 transition of Ar XV can potentially characterize the electron temperature of astrophysical plasma. Various theoretical studies have investigated the intercombination transition rate, which is essential for the plasma diagnostics; however, experimental difficulties have prevented its measurement. We present here measurement of the lifetime of the 3 P 1 excited state of Ar XV, providing the experimental value of the intercombination transition rate. Employing time-resolved plasma-assisted laser spectroscopy, a method we recently demonstrated, enables us to measure this submicrosecond lifetime. The experimental result exhibits a 25%–43% higher transition rate than theoretical predictions.

Keywords: Experimental data, Atomic physics, Laboratory astrophysics, Experimental techniques, Transition probabilities
A Brown Dwarf Orbiting around the Planetary-nebula Central Binary KV Vel. KV Vel is a noneclipsing short-period (P = 0.3571 days) close binary containing a very hot subdwarf primary (77,000 K) and a cool low-mass secondary star (3400 K) that is located at the center of the planetary nebula DS 1. The changes in the orbital period of the close binary were analyzed based on 262 new times of light maximum together with those compiled from the literature. It is discovered that the O ‑ C curve shows a small-amplitude (0.ͩ0034) cyclic period variation with a period of 29.55 yr. The explanation by the solar-type magnetic activity cycles of the cool component is ruled out because the required energies are much larger than the total radiant energy of this component in a whole cycle. Therefore, the cyclic variation was plausibly explained as the light-travel time effect via the presence of a tertiary component, which is supported by the periodic changes of the O ‑ C curve and the rather symmetric and stable light curves obtained by the Transiting Exoplanet Survey Satellite. The mass of the tertiary companion is determined to be  M3sini'=0.060(±0.007)  M ⊙. If the third body is coplanar with the central binary (i.e.,  i'=62.°5 ), the mass of the tertiary component is computed as M 3 ∼ 0.068 M ⊙, and thus it would be below the stable hydrogen-burning limit and is a brown dwarf. The orbital separation is shorter than 9.35 au. KV Vel together with its surrounding planetary nebula and the brown-dwarf companion may be formed through the common-envelope evolution after the primary filled its Roche lobe during the early asymptotic giant branch stage.

Keywords: Close binary stars, Brown dwarfs, Subdwarf stars
Reconstruction of the Dark Energy Scalar Field Potential by Gaussian Process. Dark energy is believed to be responsible for the acceleration of the Universe. In this paper, we reconstruct the dark energy scalar field potential V(ϕ) using the Hubble parameter H(z) through Gaussian process analysis. Our goal is to investigate dark energy using various H(z) data sets and priors. We find that the selection of the prior and the H(z) data set significantly affects the reconstructed V(ϕ). We compare two models, Power Law and Free Field, to the reconstructed V(ϕ) by computing the reduced chi-square. The results suggest that the models are generally in agreement with the reconstructed potential within a 3σ confidence interval, except in the case of Observational H(z) data with the Planck 18 prior. Additionally, we simulate H(z) data to measure the effect of increasing the number of data points on the accuracy of reconstructed V(ϕ). We find that doubling the number of H(z) data points can improve the accuracy rate of reconstructed V(ϕ) by 5%–30%.

Keywords: Astronomy data analysis, Dark energy
Origin of the Twice-90° Rotations of the Polarization Angle in GRB 170114A and GRB 160821A. The observed abrupt twice-90° rotations of the polarization angle (PA) in the prompt phase of gamma-ray bursts (GRBs) are difficult to understand within the current one-emitting-shell models. Here, we apply a model with multiple emitting shells to solve this new challenging problem. Two configurations of large-scale ordered magnetic fields in the shells are considered: toroidal and aligned. Together with the light curves and the spectral peak energy evolutions, the twice-90° PA rotations in GRB 170114A and GRB 160821A could be well interpreted with the multishell aligned magnetic field configuration (MFC). Our numerical calculations also show that the multiple shells with the toroidal MFC could not explain the observed twice-90° PA rotations. An aligned MFC in the GRB outflow usually indicates the preference of a magnetar central engine, while a toroidal field configuration is typically related to a central black hole. Therefore, the magnetar central engines for the two GRBs are favored.

Keywords: Starlight polarization, Gamma-ray bursts, Magnetic fields
A Cyclic Spectroscopy Scintillation Study of PSR B1937+21. I. Demonstration of Improved Scintillometry. We use cyclic spectroscopy to perform high-frequency resolution analyses of multihour baseband Arecibo observations of the millisecond pulsar PSR B1937+21. This technique allows for the examination of scintillation features in far greater detail than is otherwise possible under most pulsar timing array observing setups. We measure scintillation bandwidths and timescales in each of eight subbands across a 200 MHz observing band in each observation. Through these measurements we obtain intra-epoch estimates of the frequency scalings for scintillation bandwidth and timescale. Thanks to our high-frequency resolution and the narrow scintles of this pulsar, we resolve scintillation arcs in the secondary spectra due to the increased Nyquist limit, which would not have been resolved at the same observing frequency with a traditional filterbank spectrum using NANOGrav's current time and frequency resolutions, and the frequency-dependent evolution of scintillation arc features within individual observations. We observe the dimming of prominent arc features at higher frequencies, possibly due to a combination of decreasing flux density and the frequency dependence of the plasma refractive index of the interstellar medium. We also find agreement with arc curvature frequency dependence predicted by Stinebring et al. in some epochs. Thanks to the frequency-resolution improvement provided by cyclic spectroscopy, these results show strong promise for future such analyses with millisecond pulsars, particularly for pulsar timing arrays, where such techniques can allow for detailed studies of the interstellar medium in highly scattered pulsars without sacrificing the timing resolution that is crucial to their gravitational-wave detection efforts.

Keywords: Millisecond pulsars, Pulsars, Interstellar plasma, Interstellar medium, Intercloud medium, Radio pulsars