Sazuna/UAT_keywords huggingface dataset:
A Multiwavelength Study of the 2025 Low State of the Intermediate Polar BG CMi. We present multiwavelength observations of the first recorded low state of the intermediate polar BG CMi. Optical monitoring of the source by members of the American Association of Variable Star Observers reveals a decrease of ∼0.5 mag that lasted ∼50 days in early 2025. During the low state the optical timing properties imply that BG CMi underwent a change in accretion mode, as power at the spin frequency ω dramatically dropped. An XMM-Newton observation revealed a substantial decrease in intrinsic absorption and a slight increase in intrinsic X-ray luminosity, compared to archival Suzaku data. Timing analysis of the X-ray light curves shows that power shifted from the orbital frequency Ω (prominent in Suzaku data) to 2Ω in the low-state XMM-Newton data, along with strengthening of certain orbital sidebands. We suggest that BG CMi transitioned to disk-overflow accretion, where the white dwarf accreted matter via both a disk and a stream, the latter becoming more dominant during the low state due to a decrease in the mass and size of the disk.

Keywords: Accretion, White dwarf stars, DQ Herculis stars, Stellar accretion disks, Cataclysmic variable stars
Detection of a Millisecond Periodicity in BATSE Short Gamma-Ray Bursts. Coherent oscillations at kilohertz frequencies have recently been detected in a small number of gamma-ray bursts (GRBs), suggesting quasiperiodic dynamics in their central engines. A prominent example is GRB 230307A, which exhibited a brief, highly coherent, energy-dependent periodic signal interpreted as the possible spin signature of a nascent millisecond magnetar formed after a compact binary merger. Motivated by these developments, we conducted a comprehensive search for similar signals, accounting for both temporal and spectral dependencies, in 532 short GRBs with time-tagged event data recorded by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma-Ray Observatory. Within this sample, we identify a single statistically significant case: GRB 960616 (BATSE trigger 5502), in which the ∼30 ms main emission episode is coherently modulated at 1100 Hz, with the strongest modulation above 320 keV and a fractional amplitude of ∼47%. Assuming the presence of a coherent periodic modulation, we use data-driven Monte Carlo simulations to place an upper limit of ∼8% on the fraction of the total radiated energy that can be modulated by the quasiperiodic oscillation. This event, exhibiting a periodicity at ∼0.91 ms, further supports the possibility that millisecond periodicities can arise during GRBs in merger-driven scenarios.

Keywords: Time series analysis, Gamma-ray bursts, Period search , High energy astrophysics
Investigating Polarization Signatures from GRB Models. There is still much debate around the inner workings of the gamma-ray-burst (GRB) prompt emission phase, with many questions still left unanswered. Polarization signatures offer a promising new avenue for discriminating between the various GRB prompt emission models. The aim of this study is to estimate the energy- and time-resolved polarization signatures resulting from inverse Compton (IC) scattering for two specific GRB prompt emission models—namely, the backscattering-dominated cork model of M. K. Vyas et al. and a Compton drag model of G. Ghisellini et al. In order to achieve this, we apply an IC polarization Monte Carlo algorithm to those two GRB models, in order to estimate the expected polarization signatures. For the backscattering-dominated cork model, we find polarization signatures below ∼10%, likely below the detection limits of current or near-future X-ray and gamma-ray polarimeters. Our results for the Compton drag model indicate polarization results consistent with those found by D. Lazzati et al. Furthermore, we find some energy and time dependence of the estimated polarization, particularly for the polarization angle.

Keywords: Gamma-ray bursts, High energy astrophysics
Dependence of Halo Properties on Central-satellite Magnitude Gaps through Weak Lensing Measurements. The magnitude gap between the central and satellite galaxies encodes information about the mass accretion history of a dark matter halo and serves as a useful observational probe for the mass distribution in a halo. In this work, we perform the first weak lensing test of the connections between the magnitude gap and the halo profile. We measure the halo profiles of isolated central galaxies (ICGs) selected primarily from the Sloan Digital Sky Survey Main Galaxy Sample. Halo mass and concentration are inferred by fitting stacked lensing profiles in bins of central luminosity, Lc, and the central-satellite magnitude gap, Lgap. We detect dependence on the magnitude gap in both halo properties. The dependence is the strongest in the ICG luminosity range of 1010.3 &lt; Lc[h−2L⊙] ≤ 1010.7, where halos with smaller gaps have higher masses and lower concentrations. When 1010.7 &lt; Lc[h−2L⊙] ≤ 1011.1, however, no significant gap dependence is detected. In the range of 109.9 &lt; Lc[h−2L⊙] ≤ 1010.3, a disordering of the gap dependence is marginally observable. We compare the observational results with predictions by two light-cone catalogs built from the Illustris TNG300 and the Millennium simulations. The gap dependence in the two mock samples show overall consistency with observations, but neither matches them in all Lc bins to a quantitative level, and the flip in the gap dependence in the lowest luminosity bin is not reproduced in the mocks. We also compare the significance of the gap dependence on halo mass and concentration and find that our measurement prefers the halo-mass dependence over the concentration.

Keywords: Weak gravitational lensing, Galaxy dark matter halos, Galaxy luminosities
A Highly Magnetic Ultramassive White Dwarf with a 23 minute Rotation Period. We present a physical characterization of Tsinghua University-Ma Huateng Telescope for Survey (TMTS) J00063798+3104160 (J0006), a rapidly rotating, ultramassive white dwarf (WD) identified in high-cadence light curves from the TMTS. A coherent 23 minute periodicity is detected in TMTS, Transiting Exoplanet Survey Satellite, and Zwicky Transient Facility photometry. A time series of low-resolution spectra with the Keck-I 10 m telescope reveals broad, shallow hydrogen absorption features indicative of an extreme magnetic field and shows no evidence for radial-velocity variations. Atmospheric modeling yields a magnetic field strength of ∼250 MG, while Gaia astrometry and photometry imply a mass of 1.06 ± 0.01 M⊙. A significant infrared excess is detected in the Wide-field Infrared Survey Explorer W1 band and is well fitted by a 550 K blackbody, likely arising from residual material of a merger. We interpret the 23 minute photometric modulation as the rotation period of an isolated, massive WD formed likely through the merger of a double WD binary. With one of the shortest rotation periods known among candidate merger remnants and with constraints from a deep Einstein Probe X-ray nondetection, J0006 provides a rare and important observational window into the poorly explored intermediate stages of postmerger evolution.

Keywords: Stellar astronomy, White dwarf stars, DA stars, Magnetic variable stars
Unveiling Obscured Accretion in the Local Universe. Heavily obscured active galactic nuclei (AGNs), especially Compton-thick sources with line-of-sight column density (NH,los) &gt; 1024 cm−2, are critical to understanding supermassive black hole growth and the origin of the cosmic X-ray background. However, their observed fraction remains significantly below model predictions, due to strong absorption bias, even in the hard X-ray (i.e., above 10 keV) band. We analyze a sample of 26 nearby (z &lt; 0.1) AGNs from the Swift-BAT 150 month catalog, selected via mid-IR to X-ray diagnostics and observed with NuSTAR and soft X-ray telescopes (XMM-Newton, Chandra, or Swift-XRT). Using self-consistent torus models (MyTorus, Borus02, and UXCLUMPY), we aim to constrain NH,los, the average torus column density, and other geometrical parameters of the obscuring medium. A comparative analysis among the three torus models showed that while estimates of NH,los were generally in agreement, Borus02 tended to classify a slightly larger number of sources as Compton-thick AGNs. Building on this comparison, we benchmark two prediction schemes—a mid-IR/X-ray relation and a multivariate analysis model—against our broadband best-fit NH,los measurements to assess which approach more effectively bridges the gap between predicted and measured obscuration. We find that while the former works effectively in the heavily obscured region (logNH ≳ 23.5 cm−2), the latter provides improved accuracy, particularly for Compton-thin to moderately thick regimes (logNH ≲ 23.5 cm−2).

Keywords: High energy astrophysics, Active galaxies, Active galactic nuclei, X-ray active galactic nuclei
Lensing, Not Luck! Detection Prospects of Strongly Lensed Gravitational Waves. A small fraction of gravitational-wave (GW) signals detected by ground-based observatories will be strongly lensed by intervening galaxies or clusters. This may produce multiple copies of the signals (i.e., lensed images) arriving at different times at the detector. These, if observed, could offer new probes of astrophysics and cosmology. However, identification of lensed image pairs among a large number of unrelated GW events is challenging. Though the number of lensed events increases with improved detector sensitivity, the false alarms increase quadratically faster. While this "lensing or luck" problem would appear to be insurmountable, we show that the expected increase in measurement precision of source parameters will efficiently weed out false alarms. Based on current astrophysical models and anticipated sensitivities, we predict that the first confident detection could occur in the fifth observing run of LIGO, Virgo, and KAGRA. We expect computational costs to be a major hurdle in achieving such a detection, and show that the Posterior Overlap 2.0 method may offer a near-optimal solution to this challenge.

Keywords: Strong gravitational lensing, Bayesian statistics, Gravitational waves
Turbulent Properties of Interplanetary Coronal Mass Ejections Observed by Solar Orbiter in the Inner Heliosphere. We investigate the turbulent properties of 12 interplanetary coronal mass ejections (ICMEs) observed by Solar Orbiter between 0.29 and 1.0 au. We analyze fluctuation power, spectral indices, break scales, and correlations between magnetic and velocity fluctuations (v─b), to quantify differences between ICME substructures (sheath and magnetic ejecta (ME)) and the surrounding solar wind. The ICME sheath is consistently the most turbulent region at all distances. In the solar wind, Alfvénicity influences inertial-range scaling, resulting in either single power laws near f−3/2 or f−5/3, or a coexistence of both, whereas ICME substructures consistently exhibit Kolmogorov-like f−5/3 spectra. Alfvénicity is reduced within ICMEs, in particular in the ejecta, indicating more balanced Alfvénic fluctuations than in the solar wind. Spectral breaks shift to higher frequencies in ICME regions, with average break frequencies of 0.53 ± 0.35 Hz (solar wind), 1.87 ± 1.46 Hz (sheath), and 1.46 ± 1.28 Hz (ME), reflecting differences in underlying microphysical scales. Our findings highlight distinct turbulence regimes in ICMEs compared to the solar wind and support the use of fluctuation power, spectral breaks, and v─b correlations as effective diagnostics for identifying ICME boundaries.

Keywords: Space plasmas, Interplanetary turbulence, The Sun, Solar wind, Solar magnetic fields, Solar coronal mass ejections
Ruling Out Compact Jets as the Dominant Source of Radio Emission in Radio-quiet, High-Eddington-ratio Active Galactic Nuclei. The origin of core radio emission in radio-quiet active galactic nuclei (AGNs) is still actively debated. General-relativistic magnetohydrodynamics simulations often predict the launching of moderately large-scale jets from super-Eddington accretion flows, but this prediction seems at odds with observations indicating most high/super-Eddington AGNs appear radio-quiet. Here, we use the ratio of radio to X-ray luminosities as a multiwavelength diagnostic to probe the origin of radio emission in a sample of 69 radio-quiet, high/super-Eddington AGNs with black hole masses MBH ∼ 105─109 M⊙. With this wide dynamic range in MBH, we adapt existing formalisms for how jetted radio emission and accretion-powered X-ray emission scale with black hole mass into the super-Eddington regime. We find that the radio/X-ray luminosity ratios observed across this MBH range are inconsistent with a jet-dominated model for radio emission. We discuss how our results may instead be consistent with a corona-dominated radio emission origin with a contribution from outflows at higher accretion rates.

Keywords: Radio quiet quasars, Active galactic nuclei, Radio jets, High energy astrophysics
XFit: Global Optimization and Degeneracy Mapping in X-Ray Spectral Modeling. The standard approach to modeling X-ray spectral data relies on local optimization methods, such as the Levenberg─Marquardt algorithm. While effective for simple models and speedy spectral fitting, these local optimizers are prone to becoming trapped in local minima, particularly in high-dimensional or degenerate parameter spaces, and typically require extensive user intervention. In this work, we introduce XFit, a global optimization method for fitting X-ray data, which makes extensive use of the Ferret evolutionary algorithm. XFit enables automated exploration of complex parameter spaces, efficient mapping of confidence intervals, and identification of degenerate solutions that may be overlooked by local methods. We demonstrate the performance of XFit using two representative X-ray sources: the central compact object in Cassiopeia A and the supernova remnant G41.1─0.3. These examples span both low- and high-dimensional models, allowing us to illustrate the advantages of global optimization. In both cases, XFit produces solutions that are consistent with or improve upon those found with traditional methods, while also revealing alternative fits or degenerate solutions within statistically acceptable confidence levels. The automated mapping of parameter space offered by XFit makes it a powerful complement to existing spectral-fitting tools, particularly as models and data quality become increasingly complex. Future work will expand the application of XFit to broader datasets and more physically motivated models.

Keywords: Computational astronomy, High energy astrophysics, Astronomy data analysis, Stellar remnants, Supernovae
Statistical Analysis of Multiband Plateaus in Gamma-Ray Burst Afterglows. Plateau features are frequently observed in the afterglows of gamma-ray bursts (GRBs), yet their physical origins remain under debate. In this work, we compile a sample of 124 GRBs with known redshifts and simultaneous X-ray and optical afterglow observations. We categorize them into four subsets based on the existence of plateaus and the bands in which they appear. Namely, Dataset 1: plateaus are detected simultaneously in both X-ray and optical bands (75 bursts); Dataset 2: plateaus are only in X-rays (15 bursts); Dataset 3: plateaus appear only in the optical band (17 bursts); Dataset 4: no plateaus in either band (17 bursts). We employ these datasets to test the applicability of the energy-injection model by examining whether the temporal decay index α and the spectral index β of GRB afterglows simultaneously satisfy the closure relations in X-ray and optical bands. We find that 47 bursts of Dataset 1 simultaneously obey the closure relations in both bands under the conditions of the electron spectral index p &gt; 2 and the injection parameter q ∈ (0, 0.5), and 69 of the dataset for p &gt; 1 and q ∈ (0, 0.8), providing strong support for the energy-injection interpretation. However, for Datasets 2 and 3, although α and β of the plateaus mostly satisfy the closure relations, those in the other band show significant deviations, which implies that bursts with a single-band plateau are inconsistent with the interpretation of energy injection. Furthermore, we also compare the isotropic X-ray energy of plateaus with the rotational energy budget of millisecond magnetars.

Keywords: Shocks, Gamma-ray bursts
Probing Dust Composition in Distant Galaxies with JWST Mid-IR Spectroscopy of Quasars with Foreground 2175 Å Absorbers. I. Methodology. Interstellar dust plays a crucial role in gas cooling and molecule formation, influencing galaxy evolution. However, the composition and structure of dust in distant galaxies are still poorly understood. We have started a JWST Mid-Infrared Instrument (MIRI) medium-resolution spectrograph (MRS) program investigating the dust features in gas-rich and dusty galaxies at redshifts z &lt; 1.2, with strong 2175 Å bumps detected in absorption along the lines of sight to distant background quasars. Here, we describe our program strategy, and present MIRI MRS observations of IR dust features at z = 0.5─1.2 in five quasar spectra that form the first part of our full sample. We identify artifacts in MIRI MRS data that affect the background in IFU cubes, and propose methods to reduce their effects. We pay special attention to modeling the quasar mid-IR continuum, which shows significant variation depending on active galactic nucleus morphology, redshift, and black hole mass. Dust in foreground galaxies produces significant absorption from the 10 μm silicate feature in all five quasar spectra. Compared with the average 10 μm silicate feature in the diffuse interstellar medium (ISM) of the Milky Way, we find differences in the absorption peak position, width of the features, and asymmetry of the profiles. A detailed study of these silicate features is presented in our next paper. In two quasar spectra, we tentatively detect weak IR features near 3.0 and 3.4 μm. Their strengths are comparable to those seen in the Milky Way ISM, but follow-up observations are required in order to confirm these detections.

Keywords: Interstellar dust, Silicate grains, High-redshift galaxies, Quasar absorption line spectroscopy
The Mass Distribution of Clumpy Accretion onto the Nearby Young Star TW Hya. The proliferation of high time resolution and decades-long monitoring of classical T Tauri stars provides a vast opportunity to test the variability of star─disk connections. However, most monitoring surveys use single broadband filters, which makes the conversion of photometric variability into accretion rate difficult. In this study, we analyze accretion bursts onto the nearby young star TW Hya over short (hours, days) and long (months, years) timescales by calibrating Transiting Exoplanet Survey Satellite (TESS) and All-Sky Automated Survey for Supernovae (ASAS-SN) g-band photometry to accretion rates with simultaneous spectroscopy. The high-cadence TESS light curve shows bursts of accretion in clumps with masses from a sensitivity limit of ∼10−13 M⊙ up to 3 × 10−11 M⊙. The average burst duration of 1.8 days is longer than a simple estimate of the thermal response timescale, supporting the interpretation that the photometric variability probes the instantaneous accretion rate. The reset timescale of 1.2─2 days derived from the structure function and previously reported quasi-periods of 3.5─4 days are consistent with bursts that may be related to the different rotation between the stellar magnetosphere and inner disk or with azimuthal asymmetries in the inner disk. The near-daily ASAS-SN light curve across 8 yr reveals some seasonal changes in brightness with a standard deviation of ∼0.13 mag, about half of the scatter seen on short timescales. This study demonstrates the importance of coordinating contemporaneous multiepoch spectroscopy with time domain surveys to interpret light curves of young stars.

Keywords: Accretion, Time series analysis, Classical T Tauri stars
A Comprehensive Study of the Relations between the Properties of Planetary Systems and the Chemical Compositions of Their Host Stars. The giant planet─metallicity correlation revealed that planetary formation depends on the stellar properties. There is growing evidence that it is also valid for smaller hot planets, but it is not clear whether elements other than iron also influence the properties of planetary systems. To investigate this, we determined the abundances of 13 chemical elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Cu) for a sample of 561 Kepler exoplanet-hosting stars using high-resolution Keck/High Resolution Echelle Spectrometer (HIRES) spectra. We find that stars in systems having only large or hot planets are enriched in some elements relative to those having only small or warm planets, respectively, with this signature being related to the underlying stellar metallicity. This Kepler sample is composed of stars belonging to the Galactic low- and high-α sequences, corresponding to the chemical thin and thick disks. Our results reveal that stars enhanced in α-elements may facilitate the formation of large planets in metal-poor environments although the iron abundance is still a limiting factor. We also investigated chemical abundances as a function of elemental condensation temperatures and found that there is a diversity of slopes regardless of the exoplanetary systems hosted by the star. We confirmed that the Sun is depleted in refractory elements relative to the solar twins in our sample, all of which host a diversity of exoplanets, suggesting that this depletion is caused by processes not related to planet formation.

Keywords: Stellar abundances, Exoplanet formation, Stellar properties, Exoplanet systems
ALMAGAL. VII. Cataloging Hierarchical Continuum Structure from Cores to Clumps across the Galactic Disk. Investigating the multiscale fragmentation of dense clumps into compact cores is essential for understanding the processes that govern the initial distribution of mass in stellar clusters and how high-mass stars (&gt;8 M⊙) form. We present a catalog of the hierarchical continuum structure from 904 clumps observed in the ALMAGAL program, a high-resolution (0 .″ 15─0 .″ 8) 1.38 mm Atacama Large Millimeter/submillimeter Array large program targeting dense clumps capable of high-mass star formation throughout the Galactic disk. We use astrodendro, a dendrogram-based algorithm, on a uniform linear resolution (2000 au) version of the data to extract 5160 continuum structures with effective radii spanning 800─42000 au and estimated masses between 0.05─670 M⊙. With our large sample, we statistically examine differences in clump properties for regions with varying levels of hierarchical complexity. We find that clumps exhibiting the richest hierarchical morphology have distributions with higher dust temperatures, surface densities, luminosity-to-mass (L/M) ratios, and most massive core masses, indicating that these regions tend to be at later evolutionary stages. We find a positive correlation between the mass of cores from the ALMAGAL core catalog and the surface density of their surrounding structures identified in this work. However, this correlation is weaker for cores in more evolved clumps, where lower-mass cores can be found at higher local surface densities. This could indicate that some cores accrete mass less efficiently from the intraclump reservoir than others, despite the total available mass increasing over time, a scenario that is congruent with a clump-fed core accretion model.

Keywords: Star formation, Milky Way Galaxy, Interstellar medium