Sazuna/UAT_keywords huggingface dataset:
Analysis of Short-term Solar Activity Variability and Estimating the Timings of the Next Enhanced Bursts. We present a novel hybrid forecasting strategy combining numerical, statistical, and machine learning─based forecasting to detect the occurrence of the next enhanced solar activity bursts. These enhanced bursts are called "space weather seasons," which occur on intermediate timescales (6─18 months). Monthly smoothed sunspot number (SSN) data from 1878 to 2025 are analyzed using Gaussian fitting techniques to identify burst events and their properties such as amplitude and duration. The SSN data are divided into training, test, and forecast, which shows hindcast and forecast. Each hemisphere is modeled via a seasonal autoregressive integrated moving average approach, refined with an asymmetric Gaussian override to capture rapid burst rise and gradual decay, and burst amplitudes and duration are predicted using a random forest regression model. This hybrid approach successfully hindcasts burst timing in between 2024 November and 2025 May, with a peak SSN of ∼70 around 2025 March for the Northern Hemisphere. The next burst in the Northern Hemisphere is forecast to be in 2025 December with a slightly lower SSN of 60. By contrast, the Southern Hemisphere shows relatively complicated behavior, where the bursts show multiple amplitudes starting approximately in 2024 October and ending in 2025 October. The main burst shows an amplitude of 130 SSN. The next burst in the Southern Hemisphere is forecast to occur approximately in 2025 December. Combining SSN properties in both hemispheres, we find that the total SSN is mainly influenced by a stronger cycle in the Southern Hemisphere.

Keywords: Random Forests, Space weather, Solar active regions, Sunspot cycle
Low-latitude Sunspot Group Tilt Angles in 15─24 Activity Cycles. An analysis of the tilt angles of the active regions in 15─24 activity cycles was performed. We used data from measurements of magnetic fields in the sunspot umbra in the period 1918─2019 at the Mount Wilson Observatory, as well as the tilt angles of active regions in "white" light at the Kodaikanal and Mount Wilson observatories in activity cycles 15─21. The mean tilt angles of active regions  γ̄  and the slope μ from latitude θ in the activity cycles are considered. Low-latitude bipoles are the most important in predicting the strength of solar cycles. In this work, we selected the cutoff latitude θcut at which the highest correlation is observed with the strength of the next activity cycle for active regions with latitude θ &lt; θcut. It was found that for magnetic field measurement data, the highest correlation of the parameters  γ̄  and μ with the strength of the next solar activity cycle is characteristic of bipoles in the equatorial zone with θ &lt; θcut ≍ 14 .° 2. For "white" light observation data, θcut ≍ 8 .° 5 for Mount Wilson Observatory and θcut ≍ 9 .° 4 for Kodaikanal Observatory.

Keywords: Solar cycle, Solar active regions, Sunspot cycle, Bipolar sunspot groups
Estimation of Effective Viscosity to Quantify Collisional Behavior in Collisionless Plasma. While dissipation in collisional plasma is defined in terms of viscosity and resistivity, the exact functional form of dissipation, i.e., the so-called dissipation function in nearly collisionless plasma, is unknown. Nevertheless, previous studies have suggested that there exists viscous-like energy conversion in collisionless plasma with scaling characteristics analogous to collisional plasma, and in particular that the average dissipation is proportional to the square of the rate of strain as in hydrodynamics. In this study, using 2.5D kinetic particle-in-cell (PIC) simulation of collisionless plasma turbulence, we provide an estimate of effective viscosity at each scale, obtained via a scale-filtering approach. We then compare the turbulent dynamics of the PIC simulation with that from MHD and two-fluid simulations in which the viscosity is equal to the effective viscosity estimate obtained from the PIC simulation. We find that the global behavior in these MHD and two-fluid simulations has a striking similarity to that in their kinetic/PIC counterpart. In addition, we explore the scale dependence of the effective viscosity and discuss implications of this approach for space plasmas.

Keywords: Space plasmas, Collisional processes
Searching for Continuous Gravitational Waves in the Parkes Pulsar Timing Array Data Release 3. We present results from an all-sky search for continuous gravitational waves from individual supermassive binary black holes using the third data release of the Parkes Pulsar Timing Array (PPTA). Even though we recover a common-spectrum stochastic process, potentially induced by a nanohertz gravitational-wave background, we find no evidence of continuous waves. Therefore, we place upper limits on the gravitational-wave strain amplitude: in the most sensitive frequency range around 10 nHz, we obtain a sky-averaged 95% credibility upper limit of ≍ 7 × 10−15. Our search is sensitive to supermassive binary black holes with a chirp mass of ≥109M⊙ up to a luminosity distance of 50 Mpc for our least sensitive sky direction and 200 Mpc for the most sensitive direction. This work provides at least 4 times better sensitivity in the 1─200 nHz frequency band than our last search based on the PPTA's first data release. We expect that PPTA will continue to play a key role in detecting continuous gravitational waves in the exciting era of nanohertz gravitational-wave astronomy.

Keywords: Supermassive black holes, Gravitational waves, Millisecond pulsars
The Response of Warm Absorbers to the Variations in the Ionizing Continuum in the Active Galaxy NGC 4051. We present a time-resolved X-ray spectral analysis of the warm absorbers in the Seyfert galaxy NGC 4051, which has an active galactic nucleus (AGN), using observations from the Neutron Star Interior Composition Explorer (NICER). Despite NICER's moderate spectral resolution, its high-cadence monitoring allows us to probe the response of the ionized outflows, also known as warm absorbers, on timescales of ∼5500 s. We detect two distinct components of ionized absorbers in this source. The variability in the ionization parameter of the low-ionization warm absorber component, which tracks changes in the ionizing flux with no measurable time lag. This rapid response implies photoionization equilibrium and places a lower limit on the electron density of ≳9 × 106 cm−3 based on the most abundant ionic species, O VII. The absorber is located within ∼0.02 pc of the central source, consistent with an origin in the inner regions of the active nucleus. In contrast, the high-ionization absorber remains consistently under-ionized relative to equilibrium predictions. This suggests that it may be the collisional plasma, which was also detected in this source in the previous studies. These results demonstrate that time-resolved spectroscopy, even with moderate-resolution instruments, can provide valuable constraints on the density and location of warm absorbers in AGN. As a potential candidate source of AGN feedback, the study of these ionized outflows is crucial in understanding AGN─host galaxy interactions.

Keywords: Active galactic nuclei, X-ray active galactic nuclei, Quasars, Galaxy nuclei
Electron Acceleration in Thinning Nonreconnecting Current Sheets in a Quasi-parallel Shock. We study electron energization in turbulence-generated current sheets in the shock transition region by means of fully kinetic collisionless plasma simulations and theory. Using parameters in the Earth's bow shock, we perform a two-dimensional particle-in-cell simulation of a quasi-parallel shock. In shock turbulence, many current sheets are produced, including those exhibiting magnetic reconnection and those that are not reconnecting. The electron temperature is enhanced in nonreconnecting current sheets as well as in reconnecting current sheets and magnetic islands. Performing electron trajectory tracing analysis, we find that energetic electrons are produced in nonreconnecting thinning current sheets. The motional electric field during the thinning process of a current sheet energizes both magnetized and unmagnetized electrons. We analytically show that the energization rate for unmagnetized electrons is slightly less than that of adiabatic energization for magnetized electrons, but unmagnetized electrons can be effectively trapped in magnetic field structures formed in thinning current sheets and continue to be energized. These nonreconnecting current sheets produce energetic electrons whose energies are comparable to the energetic electrons produced in magnetic islands, and they can reach the injection energy for diffusive shock acceleration, which is an acceleration mechanism for producing cosmic rays. The number of electrons that are energized in nonreconnecting current sheets is about a quarter of that in reconnection regions. The energization mechanism can be applicable to various space and astrophysical environments, including planetary bow shocks and supernova remnant shocks.

Keywords: Supernova remnants, Interplanetary particle acceleration, Planetary bow shocks, Solar magnetic reconnection
New TeV-emitting BL Lac Candidates from the eROSITA X-Ray Survey. TeV-emitting BL Lac─type blazars represent the extreme end of the blazar population. They are characterized by relatively weak jets and radiatively inefficient accretion disks. Particles accelerated in these jets experience fewer radiative losses, allowing them to reach energies beyond the TeV scale and produce TeV gamma-ray emission. The study of TeV blazars is constrained by the limited number of known sources in this category. Currently, only 56 high-synchrotron-peaked BL Lacs have been detected at energies above 0.1 TeV. Searches for TeV emission from BL Lacs typically target sources with bright X-ray emission and a synchrotron peak at or above 1 keV. The recently released eRASS1 catalog by the eROSITA collaboration, which covers half of the sky, represents the deepest X-ray survey in the soft X-ray band to date. Utilizing the eROSITA survey, combined with infrared data from the Wide-field Infrared Survey Explorer and archival radio observations, we have identified 121 TeV-emitting blazar candidates. Our search introduces selection criteria based on the radio to infrared that remove quasar-like objects that have similar infrared spectra and X-ray fluxes as TeV-emitting BL Lacs. In our search, we find 23 objects that had not been detected in the ROSAT X-ray survey and 11 that have not been previously associated with blazars. The candidates resulting from our search are suitable for follow-up observations with currently operating imaging atmospheric Cherenkov telescopes, as well as future facilities like the CTAO Observatory.

Keywords: BL Lacertae objects, Blazars, Relativistic jets, Gamma-ray telescopes, X-ray surveys, Infrared sources
Long-term Simultaneous 2.25/8.60 GHz Monitoring of the Newly Discovered Repeating FRB 20240114A. We report on the simultaneous monitoring of the repeating fast radio burst (FRB) 20240114A at 2.25 and 8.60 GHz, conducted 66 times between 2024 January 29 and 2025 February 15 with the Shanghai Tianma Radio Telescope. In about 180 hr of observation, we detected 155 bursts at 2.25 GHz above a fluence threshold of 0.72 Jy ms but none at 8.60 GHz above a fluence threshold of 0.27 Jy ms. FRB 20240114A exhibited frequency-dependent activity, as evidenced by the nondetections in 14.3 hr of observations at 2.25 GHz prior to 2024 February 24, despite its reported activity below 2 GHz. In contrast to its low-activity state reported below 1.4 GHz between 2024 June and December, FRB 20240114A exhibited high activity at 2.25 GHz in 2024 July with a mean burst rate of  1.72−0.16+0.18hr−1 , followed by a low-activity state. We also detected a short-term reactivation at 2.25 GHz around 2025 January 20, about 2 weeks after renewed activity was reported below 1.4 GHz by other telescopes. The median burst width at 2.25 GHz is 3 ms, which is narrower than that at lower frequencies. The waiting time distribution peaks at 1019 s, and bursts arrive on hourly timescales consistent with a Poisson process. The isotropic-equivalent energy of the bursts spans 1037─1039 erg. The distribution of burst energy above the completeness threshold (7.5 × 1037 erg) follows a power-law relation with an index of γ = −1.20 ± 0.03 ± 0.02. Finally, we find that FRB 20240114A is at least 2 orders of magnitude less active at 8.60 GHz than at 2.25 GHz, and we constrain the broadband spectra of the detected bursts.

Keywords: Radio bursts, Radio transient sources
A High-precision Dynamical Model of Callisto: Incorporating Rotation Effects within Multilayer Internal Structure Models. China is planning to launch the "Tianwen-4" mission around the year 2030, with its aim being the exploration of Jupiter and its moon, Callisto. Within the realm of deep space exploration, the accuracy of ephemerides is of great importance. Current ephemerides employ a simplified rotation model for Callisto, which this study addresses by proposing a novel dynamical model. This model enhances the existing orbital dynamics by integrating Callisto's rotational motions influenced by gravitational torques from the Sun, Jupiter, and other Galilean moons within an inertial frame, capturing the intricate coupling between Callisto's orbital and rotational dynamics. The study establishes a full dynamical model by deriving analytical expressions for this coupling and developing an adjustment model for data fitting using precise orbit determination methods. Furthermore, the influence of tidal effects on Callisto's motion is investigated, considering its multilayered internal structure. Results demonstrate that the difference between the newly established full model and the model in current ephemerides is on the order of tens of meters. When calculating the impact of different internal structures of Callisto on its orbit, the influence of three-layered and two-layered structures is on the order of meters, suggesting that the development of a high-precision dynamical model requires additional constraints on the internal structure of Callisto. This research provides a novel alternative for a new generation of precise numerical ephemerides for Callisto. Additionally, these findings provide a testing platform for the data from the "Tianwen-4" mission.

Keywords: Ephemerides, Natural satellite dynamics, Celestial mechanics, Astrometry, Galilean satellites, Jovian satellites
Rotational Spectroscopy and Tentative Interstellar Detection of 3-hydroxypropanal (HOCH<SUB>2</SUB>CH<SUB>2</SUB>CHO) in the G+0.693-0.027 Molecular Cloud. We synthesized the astrochemically relevant molecule 3-hydroxypropanal (HOCH2CH2CHO) and subsequently measured and analyzed its rotational spectrum in several frequency regions ranging from 130 to 485 GHz. We analyzed the ground vibrational state as well as the two perturbed lowest-lying vibrationally excited states. With the resulting rotational parameters, we searched for this molecule in the Sagittarius B2(N) and NGC 6334I hot cores, the IRAS 16293-2422B hot corino, and the G+0.693-0.027 and TMC-1 molecular clouds. Rotational emission of 3-hydroxypropanal was tentatively detected toward G+0.693-0.027, and a column density of (8.6 ±1.4) × 1012 cm−2 was determined. However, this molecule was not detected in the other sources that were investigated. The chemical implications of this tentative discovery are analyzed, and several potential chemical formation pathways of this species are discussed.

Keywords: Rotational spectroscopy, Interstellar molecules, Astrochemistry
Monte Carlo Simulations of Polarized Radiative Transfer in Neutron Star Atmospheres. Soft X-ray emission from neutron stars affords powerful diagnostic tools for uncovering their surface and interior properties, as well as their geometric configurations. In the atmospheres of neutron stars, the presence of magnetic fields alters the photon-electron scattering cross sections, resulting in nontrivial angular dependence of intensity and polarization of the emergent signals. This paper presents recent developments of our Monte Carlo simulation, MAGTHOMSCATT, which tracks the complex electric field vector for each photon during its transport. Our analysis encompasses the anisotropy and polarization characteristics of X-ray emission for field strengths ranging from nonmagnetic to extremely magnetized regimes that are germane to magnetars. In the very low field domain, we reproduced the numerical solution to the radiative transfer equation for nonmagnetic Thomson scattering, and provided analytical fits for the angular dependence of the intensity and the polarization degree. These fits can be useful for studies of millisecond pulsars and magnetic white dwarfs. By implementing a refined injection protocol, we show that, in the magnetar regime, the simulated intensity and polarization pulse profiles of emission from extended surface regions becomes invariant with respect to the ratio of photon (ω) and electron cyclotron (ωB) frequencies once ω/ωB ≲ 0.01. This circumvents the need for simulations pertinent to really high magnetic field strengths, which are inherently slower. Our approach will be employed elsewhere to model observational data to constrain neutron star geometric parameters and properties of emitting hot spots on their surfaces.

Keywords: Neutron stars, Magnetars, Magnetic fields, Radiative transfer
Machine Learning Identification of Gravitationally Microlensed Gamma-Ray Bursts. Gravitational microlensing of gamma-ray bursts (GRBs) provides a unique opportunity to probe compact dark matter and small-scale structures in the Universe. However, identifying such microlensed GRBs within large data sets is a significant challenge. In this study, we develop a machine learning (ML) approach to distinguish lensed GRBs from their nonlensed counterparts, using simulated light curves. A comprehensive data set is generated, comprising labeled light curves for both categories. Features are extracted using the Cesium package, capturing critical temporal properties of the light curves. Multiple ML models are trained on the extracted features, with Random Forest achieving the best performance, delivering an accuracy of 86% and an F1 score of 0.86 (0.87) for the nonlensed (lensed) class. This approach successfully demonstrates the potential of ML for identifying gravitational lensing in GRBs, paving the way for future observational applications.

Keywords: Gamma-ray bursts, Support vector machine, Gravitational lensing, Gravitational microlensing, Random Forests
Natal Kick by Early-asymmetrical Pairs of Jets to the Neutron Star of Supernova Remnant S147. We analyze the bipolar morphology of the jet-shaped core-collapse supernova remnant (CCSNR) S147 and its neutron star (NS) kick velocity, and suggest that two pairs of unequal, opposite jets contributed to the NS kick velocity. This kick by early asymmetrical pairs (kick-BEAP) of jets mechanism operates within the framework of the jittering jets explosion mechanism (JJEM). We examine the prominent pair of large ears and, based on their flat structure rather than the more common conical structure of ears, conclude that two pairs of jets close in angle inflated the two opposite ears. We connect two opposite X-ray bright zones by an additional axis to create the full point-symmetric morphology of CCSNR S147. We propose that the two unequal jets that formed the X-ray bright zones imparted the first kick-BEAP, while the two pairs of jets that formed the ears imparted the second kick-BEAP. The two kick velocities are of about equal magnitude of ≃450 km s−1, which implies very energetic jets. Such jets can excite gravitational waves that present detectors can detect from the Galaxy and the Magellanic Clouds. We use the morphology we identify to estimate the CCSNR age at 23,000 yr. Our results strengthen the JJEM.

Keywords: Neutron stars, Core-collapse supernovae, Stellar jets, Massive stars, Supernova remnants
Stacking PANCAKEZ: Spectroscopic Analysis with NIRSpec Stacks in the Epoch of Reionization. Weak Interstellar Medium Absorption and Implications for Ionizing Photon Escape at z ∼ 7. We present a spectral stacking analysis of galaxies at z ≥ 6 observed with the James Webb Space Telescope (JWST). We curate a sample of 64 galaxies spanning redshifts zspec = 6.0─9.4, which have NIRSpec medium-resolution data. The stacks achieve sufficient signal-to-noise ratios to measure equivalent widths (EWs) and velocity centroids (vcen) of low-ionization species (LIS) absorption features, transmitted Lyα emission, and nebular emission lines. Overall, we find our sample has weaker LIS absorption lines (EW(LIS) ≍ 1 Å), smaller vcen,LIS ≍ ─20 ± 50 km s−1, and significantly suppressed Lyα (EW(Lyα) ≍ 5 Å), compared to similar studies undertaken at lower redshift. The weaker LIS absorption may suggest a lower covering fraction of H I and larger escape fraction of ionizing photons from our sample. Additionally, the smaller blueshifted vcen,LIS indicates less prevalent or weaker outflows in z &gt; 6 galaxies. Stacking our subsample of Lyα emitters (LAEs), we find high EW(Hβ) ≍ 170 ± 4 Å and a detection of nebular C IV emission suggesting higher ξion in LAEs at z &gt; 6. This work showcases the enormous potential for stacked JWST spectra revealing properties of galaxies and their diffuse interstellar medium in the epoch of reionization.

Keywords: High-redshift galaxies, Galaxies
Scintillation Properties of PSR B1133+16 Measured with Very Long Baseline Interferometry. The scintillation of pulsars reveals the small-scale structure of the interstellar medium. A powerful technique for characterizing the scintillating structures (screens) combines analysis of scintillation arcs and very long baseline interferometry (VLBI). We present the results of a VLBI analysis of the scintillation arcs of PSR B1133+16 from simultaneous observations with Arecibo, Very Large Array, Jodrell Bank, Effelsberg, and Westerbork. Three arcs appear in the dataset, all of which appear consistent with being the result of very anisotropic scattering screens. We are able to measure their orientations on the sky, down to uncertainties of 5° for the two stronger screens, and measure distances of 140 ± 30, 180 ± 20, and 250 ± 30 pc, consistent with, but substantially more precise than what was inferred previously from annual modulation patterns in the scintillation. Compared with the differential dust extinction with distance in this direction, the two nearer screens appear associated with the wall of the Local Bubble.

Keywords: Very long baseline interferometry, Pulsars, Interstellar scintillation
Driven Collisionless Reconnection of Force-free Flux Tubes: From Onset to Coalescence. We investigate the onset of driven collisionless reconnection and plasmoid formation in a magnetically dominated pair plasma, using 2D particle-in-cell simulations. Two force-free flux tubes of radius R are initially pushed together with a prescribed velocity, forming a current sheet whose width shrinks until reconnection sets in. Even in our largest simulation with R ≍ 1600 plasma skin depths, the sheet thickness at reconnection onset is comparable to the skin depth. Plasmoid chains develop when the sheet length-to-width aspect ratio A ≳ 30. In the strongly magnetized limit, the onset of reconnection occurs in roughly 2─6 light-crossing times, depending on the imposed driving timescale, which controls the duration of the thinning phase. In the subsequent nonlinear merging phase, the evolution becomes effectively independent of the initially imposed velocity, leading to magnetic-energy dissipation consistent with a normalized reconnection rate ∼0.1. Our results have important implications for explosive release of magnetic energy in magnetospheres of astrophysical compact objects and their surroundings.

Keywords: Plasma astrophysics, High energy astrophysics