Sazuna/UAT_keywords huggingface dataset:
Unraveling the Origins of an Extreme Solar Eruptive Event with Hard X-Ray Imaging Spectroscopy. Hard X-ray (HXR) observations are crucial for understanding the initiation and evolution of solar eruptive events, as they provide a key signature of flare-accelerated electrons and heated plasma. The potential of high-cadence HXR imaging for deciphering the erupting structure, however, has not received adequate attention in an era of extreme ultraviolet (EUV) imaging abundance. An extreme solar eruptive event on 2022 September 5 observed on the solar far side by both Parker Solar Probe and Solar Orbiter provides the opportunity to showcase the power of HXR imaging in the absence of high-cadence EUV imaging. We investigate the evolution of flare energy release through HXR timing, imaging, and spectral analyses using data from the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter. STIX provides the highest cadence imaging of the energy release sites for this far-side event and offers crucial insight into the nature of energy release, timing of flare particle acceleration, and evolution of the acceleration efficiency. We find that this is a two-phase eruptive event, rather than two distinct eruptions, as has been previously suggested. The eruption begins with an initial peak in flare emission on one side of the active region (AR), marking the rise/destabilization of a loop system followed by notable episodes of energy release across the AR and an eruptive phase associated with a very fast coronal mass ejection, type III radio bursts, and solar energetic particles. We demonstrate that high-cadence HXR imaging spectroscopy is indispensable for understanding the formation of powerful, space-weather relevant eruptions.

Keywords: Solar flares, Solar flare spectra, Solar x-ray emission, Eruptive phenomena, Solar coronal mass ejections, Solar x-ray flares, Solar activity
The NANOGrav 15 yr Data Set: Chromatic Gaussian Process Noise Models for Six Pulsars. Pulsar timing arrays (PTAs) are designed to detect low-frequency gravitational waves (GWs). GWs induce achromatic signals in PTA data, meaning that the timing delays do not depend on radio frequency. However, pulse arrival times are also affected by radio-frequency-dependent "chromatic" noise from sources such as dispersion measure (DM) and scattering delay variations. Furthermore, the characterization of GW signals may be influenced by the choice of chromatic noise model for each pulsar. To better understand this effect, we assess if and how different chromatic noise models affect the achromatic noise properties in each pulsar. The models we compare include existing DM models used by the North American Nanohertz Observatory for Gravitational waves (NANOGrav) and noise models used for the European PTA Data Release 2 (EPTA DR2). We perform this comparison using a subsample of six pulsars from the NANOGrav 15 yr data set, selecting the same six pulsars as from the EPTA DR2 six-pulsar data set. We find that the choice of chromatic noise model noticeably affects the achromatic noise properties of several pulsars. This is most dramatic for PSR J1713+0747, where the amplitude of its achromatic red noise lowers from  log10ARN=‑14.1‑0.1+0.1  to  ‑14.7‑0.5+0.3 , and the spectral index broadens from  γRN=2.6‑0.4+0.5  to  γRN=3.5‑0.9+1.2 . We also compare each pulsar's noise properties with those inferred from the EPTA DR2, using the same models. From the discrepancies, we identify potential areas where the noise models could be improved. These results highlight the potential for custom chromatic noise models to improve PTA sensitivity to GWs.

Keywords: Gravitational wave detectors, Pulsar timing method, Millisecond pulsars, Astronomy data analysis, Gravitational wave astronomy, Interstellar medium
GWSkyNet. II. A Refined Machine-learning Pipeline for Real-time Classification of Public Gravitational Wave Alerts. Electromagnetic follow-up observations of gravitational wave events offer critical insights and provide significant scientific gain from this new class of astrophysical transients. Accurate identification of gravitational wave candidates and rapid release of sky localization information are crucial for the success of these electromagnetic follow-up observations. However, searches for gravitational wave candidates in real time suffer from a nonnegligible false alarm rate. By leveraging the sky localization information and other metadata associated with gravitational wave candidates, GWSkyNet, a machine-learning classifier developed by Cabero et al., demonstrated promising accuracy for the identification of the origin of event candidates. We improve the performance of the classifier for LIGO–Virgo–KAGRA's (LVK) fourth observing run by reviewing and updating the architecture and features used as inputs by the algorithm. We also retrain and fine-tune the classifier with data from the third observing run. To improve the prospect of electromagnetic follow-up observations, we incorporate GWSkyNet into LVK's low-latency infrastructure as an automatic pipeline for the evaluation of gravitational wave alerts in real time. We test the readiness of the algorithm on an LVK mock data challenge campaign. The results show that by thresholding on the GWSkyNet score, noise masquerading as astrophysical sources can be rejected efficiently and the majority of true astrophysical signals can be correctly identified.

Keywords: Gravitational wave astronomy, Gravitational waves, Gravitational wave sources
Lyα Imaging around the Hyperluminous Dust-obscured Quasar W2246─0526 at z = 4.6. Hot dust-obscured galaxies (hot DOGs) are a population of hyperluminous, heavily obscured quasars discovered by the Wide-field Infrared Survey Explorer all-sky survey at high redshift. Observations suggested the growth of these galaxies may be driven by mergers. Previous environmental studies have statistically shown hot DOGs may reside in dense regions. Here we use the Very Large Telescope narrowband and broadband imaging to search for Lyα emitters (LAEs) in the  6.'8×6.'8  field of the hot DOG W2246−0526 at z = 4.6. W2246−0526 is the most distant hot DOG. We find that there is an overdensity of LAEs in the W2246−0526 field compared with the blank fields. This is direct evidence that this most distant hot DOG is in an overdense environment on the Mpc scale, and the result relates to the merger origin of hot DOGs.

Keywords: Galaxy formation, High-redshift galaxy clusters, Active galaxies, Active galactic nuclei, Galaxy evolution
Evaluating the Geoeffectiveness of Interplanetary Coronal Mass Ejections: Insights from a Support Vector Machine Approach with SHAP Value Analysis. In this study, we compiled a data set of 510 interplanetary coronal mass ejections (ICME) events from 1996–2023 and trained a radial basis function support vector machine (RBF-SVM) model to investigate the geoeffectiveness of ICMEs and its dependence on the solar wind conditions observed at 1 au. The model demonstrates high performance in classifying geomagnetic storm intensities at specific Disturbance Storm Time thresholds and evaluating the geoeffectiveness of ICMEs. The model's output was assessed using precision, recall, F1 score, and true skill statistics (TSS), complemented by stratified k-folds cross-validation for robustness. At the ‑50 nT threshold, the model achieves precisions of 0.84 and 0.93, recalls of 0.94 and 0.82, and corresponding F1 scores of 0.89 and 0.87 for the categories separated by this threshold, respectively. Overall accuracy is noted at 0.88, with a TSS of 0.76. Despite challenges at the ‑100 nT threshold due to data set imbalance and limited samples, the model maintains an overall accuracy of 0.87, with a TSS of 0.69, demonstrating the model's ability to effectively handle imbalanced data. Physical insights were gained through model explanation with a SHapley Additive exPlanations (SHAP) value analysis, pinpointing the role of the southward magnetic field component in triggering geomagnetic storms, as well as the critical impact of shock-ICME combinations in intensifying these storms. The effective application of an SVM model with SHAP value analysis offers a way to understand and predict the geoeffectiveness of ICMEs. It also underscores the capability of a relatively simple machine learning model in predicting space weather and revealing the underlying physical mechanisms.

Keywords: Geomagnetic fields, Support vector machine, Solar coronal mass ejections
The Instability Mechanism of Compact Multiplanet Systems. To improve our understanding of orbital instabilities in compact planetary systems, we compare suites of N-body simulations against numerical integrations of simplified dynamical models. We show that, surprisingly, dynamical models that account for small sets of resonant interactions between the planets can accurately recover N-body instability times. This points toward a simple physical picture in which a handful of three-body resonances, generated by interactions between nearby two-body mean motion resonances, overlap and drive chaotic diffusion, leading to instability. Motivated by this, we show that instability times are well described by a power law relating instability time to planet separations, measured in units of fractional semimajor axis difference divided by the planet-to-star mass ratio to the 1/4 power, rather than the frequently adopted 1/3 power implied by measuring separations in units of mutual Hill radii. For idealized systems, the parameters of this power-law relationship depend only on the ratio of the planets' orbital eccentricities to the orbit-crossing value, and we report an empirical fit to enable quick instability time predictions. This relationship predicts that observed systems comprised of three or more sub-Neptune-mass planets must be spaced with period ratios  P≳1.35  and that tightly spaced systems ( P≲1.5 ) must possess very low eccentricities (e ≲ 0.05) to be stable for more than 109 orbits.

Keywords: Celestial mechanics, Planetary dynamics, Exoplanets, Orbital resonances
The Differences in the Origination and Properties of the Near-Earth Solar Wind between Solar Cycles 23 and 24. The dependence of the sources and properties of the near-Earth solar wind on solar cycle activity is an important issue in solar and space physics. We use the improved "two-step" mapping procedure that takes into account the initial acceleration processes to trace the near-Earth solar winds back to their source regions from 1999–2020, covering solar cycles (SCs) 23 and 24. Then, the solar wind is categorized into coronal hole (CH), active region (AR), and quiet Sun (QS) solar wind based on the source region type. We find that the proportions of CH and AR (QS) wind during SC 23 are higher (lower) than those during SC 24. During solar maximum and declining phases, the magnetic field strength, speed, helium abundance (A He), and charge states of all three types of solar wind during SC 23 are generally higher than those during SC 24. During solar minimum, these parameters of solar wind are generally lower during SC 23 than those during SC 24. There is a significant decrease in the charge states of all three types of solar wind during the solar minimum of SC 23. The present statistical results demonstrate that the sources and properties of the solar wind are both influenced by solar cycle amplitude. The temperatures of AR, QS, and CH regions exhibit significant differences at low altitudes, whereas they are almost uniform at high altitudes.

Keywords: Solar cycle, Solar abundances, Solar wind, Solar activity
GRMHD Simulations of Accretion Structures with Different Angular Momentum Profiles. In this article, we explore the dynamics of accretion structures encircling spherically symmetric black holes, comparing three accretion disk models with distinct angular momentum profiles: (i) the geometrically thin Keplerian disk, (ii) the Fishbone–Moncrief torus; and (iii) the Polish Doughnut. Employing general relativistic magnetohydrodynamics simulations with the High Accuracy Relativistic Magnetohydrodynamics code, we investigate these three models, considering the magnetic field's influence on the accretion disk angular momentum redistribution. We show that the magnetic field is a key factor in accretion disk structures, especially in regions with lower mass density. Our investigation verifies the well-established fact that the presence of a magnetic field significantly influences the accretion rate and its temporal variability.

Keywords: Black hole physics, General relativity, Magnetohydrodynamical simulations
Lyα Emission Line Profiles of Extreme [O III]- emitting Galaxies at z ≳ 2: Implications for Lyα Visibility in the Reionization Era. JWST observations have recently begun delivering the first samples of Lyα velocity profile measurements at z &gt; 6, opening a new window into the reionization process. Interpretation of z ≳ 6 line profiles is currently stunted by limitations in our knowledge of the intrinsic Lyα profile (before encountering the intergalactic medium (IGM)) of the galaxies that are common at z ≳ 6. To overcome this shortcoming, we have obtained resolved (R ∼ 3900) Lyα spectroscopy of 42 galaxies at z = 2.1–3.4 with similar properties as are seen at z &gt; 6. We quantify a variety of Lyα profile statistics as a function of [O III]+Hβ equivalent width (EW). Our spectra reveal a new population of z ≃ 2–3 galaxies with large [O III]+Hβ EWs (&gt;1200 Å) and a large fraction of Lyα flux emerging near the systemic redshift (peak velocity ≃0 km s‑1). These spectra indicate that low-density neutral hydrogen channels are able to form in a subset of low-mass galaxies (≲1 × 108 M ⊙) that experience a burst of star formation (sSFR &gt; 100 Gyr‑1). Other extreme [O III] emitters show weaker Lyα that is shifted to higher velocities (≃240 km s‑1) with little emission near the line center. We investigate the impact the IGM is likely to have on these intrinsic line profiles in the reionization era, finding that the centrally peaked Lyα emitters should be strongly attenuated at z ≳ 5. We show that these line profiles are particularly sensitive to the impact of resonant scattering from infalling IGM and can be strongly attenuated even when the IGM is highly ionized at z ≃ 5. We compare these expectations against a new database of z ≳ 6.5 galaxies with robust velocity profiles measured with JWST/NIRSpec.

Keywords: Reionization, Observational cosmology, High-redshift galaxies, Galaxies
The K <SUB> s </SUB>-band Luminosity Function of the Rich Cluster VC04 in the Vela Supercluster. To learn more about the properties of the Vela Supercluster (VSCL), located behind the Milky Way at cz ∼ 18,000 km s‑1, we determine the K  s -band luminosity function (LF) of VC04, the richest known galaxy cluster in the VSCL, and two other VSCL clusters (VC02 and VC08). The galaxy sample is based on NIR observations that are complete to an extinction-corrected absolute magnitude of  MKso&lt;‑21.ͫ5  (∼2.ͫ5 below  MK* ), within the clustercentric radius of r  c  &lt; 1.5 Mpc (∼70% of the Abell radius). For VC04, we obtained 90 new spectroscopic redshifts of galaxies, observed with the 11 m Southern African Large Telescope. We found the Schechter parameters of the VC04 LF to be M* = ‑24.ͫ41 ± 0.44, α = ‑1.10 ± 0.20, and ϕ* = 8.84 ± 0.20. Both the redshift data and the LF confirm VC04 to be a rich but not yet fully relaxed cluster. We independently determined the LF of VC04 on membership defined by the red-sequence method and demonstrated that this method can be used in the absence of high spectroscopic coverage over a cluster. This allowed us to determine the LFs of VC02 and VC08. We also derived the LFs of the Coma, Norma, and Virgo clusters to similar depth and extent as the VSCL clusters. We found that the Schechter parameters of VC04 are within 1σ uncertainties of these local clusters, as well as VC02 and VC08. We do not find significant differences between the LFs in the different cluster environments probed in this work down to  MK*+2.ͫ5 .

Keywords: Galaxy clusters, Galaxy spectroscopy, Luminosity function, Near infrared astronomy
The Dzhanibekov Effect as a Possible Source of Magnetar Activity. Magnetars, which are neutron stars with strong magnetic fields, exhibit occasional bursting activities. The shape of a magnetar is not perfectly spherical due to the Lorentz force exerted by its strong magnetic fields and is described as a triaxial body. We study the unstable free precession in a triaxial magnetar; one of the principal axes undergoes an upside-down flip. This flip is known as the Dzhanibekov effect. We find that during the flip, the Euler force can suddenly disturb the force balance on the surface layer of the magnetar, potentially leading to plastic flow of the layer. This, in turn, may trigger different forms of magnetar activity, such as the emission of the bursts and/or of gravitational waves.

Keywords: Neutron stars, Magnetars, X-ray transient sources, X-ray bursts
RRAT J1913+1330: An Extremely Variable and Puzzling Pulsar. Rotating radio transients (RRATs) are neutron stars that emit sporadic radio bursts. We detected 1955 single pulses from RRAT J1913+1330 using the 19 beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope. These pulses were detected in 19 distinct clusters, with 49.4% of them occurring with a waiting time of one rotation period. The energy distribution of these individual pulses exhibited a wide range, spanning 3 orders of magnitude, reminiscent of repeating fast radio bursts (FRBs). Furthermore, we observed abrupt variations in pulse profile, width, peak flux, and fluence between adjacent sequential pulses. These findings suggest that this RRAT could be interpreted as a pulsar with extreme pulse-to-pulse modulation. The presence of sequential pulse trains during active phases, along with significant pulse variations in profile, fluence, flux, and width, should be intrinsic to a subset of RRATs. Our results indicate that J1913+1330 represents a peculiar source that shares certain properties with populations of nulling pulsars, giant pulses, and FRBs from different perspectives. The dramatic pulse-to-pulse variation observed in J1913+1330 could be attributed to unstable pair creation above the polar cap region and the variation of the site where streaming pairs emit coherently. Exploring a larger sample of RRATs exhibiting similar properties to J1913+1330 has the potential to significantly advance our understanding of pulsars, RRATs, and FRBs.

Keywords: Radio pulsars, Radio transient sources
Apparently Ultralong Period Radio Signals from Self-lensed Pulsar–Black Hole Binaries. Pulsar–black hole (BH) close binary systems, which have not been found yet, are unique laboratories for testing theories of gravity and understanding the formation channels of gravitational-wave sources. We study the self-gravitational lensing effect in a pulsar–BH system on the pulsar's emission. Because this effect occurs once per orbital period for almost edge-on binaries, we find that it could generate apparently ultralong period (minutes to hours) radio signals when the intrinsic pulsar signal is too weak to detect. Each of such lensed signals, or "pulse," is composed of a number of amplified intrinsic pulsar pulses. We estimate that a radio telescope with a sensitivity of 10 mJy could detect a few systems that emit such signals in our Galaxy. The model is applied to three recently found puzzling long-period radio sources: GLEAM-X J1627, PSR J0901-4046, and GPM J1839-10. To explain their observed signal durations and periods, the masses of their lensing components are estimated as ∼104 M ⊙, ∼4 M ⊙, and 103‑6 M ⊙, respectively, with their binary coalescence times ranging from a few tens to thousands of years. However, the implied merger rates (as high as ∼103‑4 Myr‑1 per galaxy) and the large period decay rates (&gt;10‑8 s s‑1) tend to disfavor this self-lensing scenario for these three sources. Despite this, our work still provides observational characteristics for self-lensed pulsar–BH binaries, which could help the detection of related sources in the future. Finally, for a binary containing a millisecond pulsar and a stellar-mass BH, the Shapiro delay effect would cause a ≥10% variation of the profile width for the subpulses in such lensed signals.

Keywords: Gravitational microlensing, Compact binary stars, Astrophysical black holes, Radio pulsars
In-field Phasing at the Upgraded GMRT. In time-domain radio astronomy with arrays, voltages from individual antennas are added together with proper delay and fringe correction to form the beam in real time. In order to achieve the correct phased addition of antenna voltages, one has to also correct for the ionospheric and instrumental gains. Conventionally this is done using observations of a calibrator source located near to the target field. This scheme is suboptimal since it does not correct for the variation of the gains with time and position in the sky. Further, since the ionospheric phase variation is typically most rapid at the longest baselines, the most distant antennas are often excluded while forming the beam. We present here a different methodology ("in-field phasing"), in which the gains are obtained in real-time using a model of the intensity distribution in the target field, which overcomes all of these drawbacks. We present observations with the upgraded Giant Metrewave Radio Telescope (uGMRT) which demonstrates that in-field phasing does lead to a significant improvement in sensitivity. We also show, using observations of the millisecond pulsar J1120‑3618 that this in turn leads to a significant improvement of measurements of the Dispersion Measure and Time of Arrival. Finally, we present test observations of the GMRT discovered eclipsing black widow pulsar J1544+4937 showing that in-field phasing leads to improvement in the measurement of the cut-off frequency of the eclipse.

Keywords: Eclipsing binary stars, Calibration, Astronomical techniques, Pulsar timing method
5–25 μm Galaxy Number Counts from Deep JWST Data. Galaxy number counts probe the evolution of galaxies over cosmic time and serve as a valuable comparison point to theoretical models of galaxy formation. We present new galaxy number counts in eight photometric bands between 5 and 25 μm from the Systematic Mid-infrared Instrument Legacy Extragalactic Survey and the JWST Advanced Deep Extragalactic Survey deep MIRI parallel, extending to unprecedented depth. By combining our new MIRI counts with existing data from Spitzer and AKARI, we achieve counts across 3–5 orders of magnitude in flux in all MIRI bands. Our counts diverge from predictions from recent semianalytical models of galaxy formation, likely due to their treatment of mid-IR aromatic features. Finally, we integrate our combined JWST‑Spitzer counts at 8 and 24 μm to measure the cosmic infrared background (CIB) light at these wavelengths; our measured CIB fluxes are consistent with those from previous mid-IR surveys but larger than predicted by models based on TeV blazar data.

Keywords: Galaxy counts
Evidence of Gradients of Density and Magnetic Field in the Remnant of Tycho's Supernova. By using surface brightness maps of Tycho's supernova remnant (SNR) in radio and X-rays, along with the properties of thermal and synchrotron emission, we have derived the postshock density and magnetic field (MF) strength distributions over the projection of this remnant. Our analysis reveals a density gradient oriented toward the northwest, while the MF strength gradient aligns with the Galactic plane, pointing eastward. Additionally, utilizing this MF map, we have derived the spatial distributions of the cutoff frequency and maximum energy of electrons in Tycho's SNR. We further comment on the implications of these findings for interpreting the gamma-ray emission from Tycho's SNR.

Keywords: Supernova remnants, Interstellar magnetic fields, Interstellar medium