Sazuna/UAT_keywords huggingface dataset:
Properties of Carbon-rich Asymptotic Giant Branch Stars in the LMC and the Milky Way. We present a comparative study of carbon-rich asymptotic giant branch (CAGB) stars in the Large Magellanic Cloud (LMC; 7347 stars) and the Milky Way (7163 stars) using infrared color─magnitude diagrams, spectral energy distributions (SEDs), two-color diagrams, and variability data. Observed SEDs are compared with theoretical models to characterize the central stars and their circumstellar dust envelopes and to estimate distances. For the LMC, a set of best-fitting CAGB models is derived by fitting observed SEDs with radiative transfer models, utilizing the galaxy's well-established distance. For Galactic CAGB stars, where Gaia DR3 parallaxes are uncertain, we estimate distances by fitting observed SEDs with the CAGB models validated against LMC stars and for Mira variables, from the period─magnitude relation calibrated with LMC Miras. A comparison of these approaches demonstrates that the SED-based distances are both reliable and practical for a large sample of Galactic CAGB stars. We find that CAGB stars in both galaxies show broadly similar infrared properties, although the LMC sample lacks stars with extremely thick dust envelopes.

Keywords: Asymptotic giant branch, Carbon stars, Infrared astronomy, Long period variable stars, Radiative transfer, Circumstellar dust
Joint Analysis of Optical, Near-infrared, and Mid-infrared Variability of Four Quasars at Redshift &lt;1. Amid rapid advances in time-domain astronomy, multiwavelength (e.g., optical and infrared) time-domain studies of quasars remain scarce. Here, we present a systematic analysis of four quasars initially selected by their Ks-band variability amplitudes in the VISTA Variables in the Vía Láctea Survey (VVV/VVVX). For these objects, we obtain complementary optical light curves from Pan-STARRS1 and the Zwicky Transient Facility and W1-band light curves from the Wide-field Infrared Survey Explorer. We perform correlation analysis to study the time lags between different bands, which may be directly related to the size of the dust torus. After correcting for infrared flux contamination from the accretion disk and accounting for the redshift effect, we measure the Ks─optical and W1─optical lags for the targets VVV J1834-2925 and VVV J1845-2426. Using typical sublimation temperatures and reverberation time lags, we obtain a graphite-to-silicate grain size ratio of  aCaS∼  0.4. Through spectral energy distribution fitting, we determine the luminosities of these quasars and find that their dust torus sizes follow the established Rdust─LAGN relation reported in previous studies.

Keywords: Quasars, Reverberation mapping, Galaxy accretion disks, Active galactic nuclei, Dust continuum emission, Time domain astronomy, Infrared observatories, Time series analysis
Effects of Magnetic Charge on Orbital Dynamics in Einstein─Bronnikov Regular Black Holes. This work investigates the influence of the magnetic charge parameter qm on the orbital dynamics of test particles in Einstein─Bronnikov (EB) regular black holes. Employing a second post-Newtonian (2PN) approximation, we derive analytical solutions for orbital energy, angular momentum, and quasi-Keplerian motion, focusing on how qm modulates key observables such as orbital periods and periastron advance. Theoretical modeling reveals that qm significantly suppresses periastron advance at the first post-Newtonian order through nonlinear electrodynamics─induced nonlinear electromagnetic repulsion, while inducing a nonlinear contraction of orbital periods at the 2PN order, thereby validating the parameter's order-dependent dynamical effects and distinguishing EB black holes from Reissner─Nordström counterparts. By applying observational data from the S2 star's orbital precession around Sgr A*, we give a preliminary and qualitative constraint for the magnetic charge. This establishes a novel discriminative framework for probing regular black hole geometries against classical gravitational theories through combined orbital dynamics and horizon structure analysis.

Keywords: Gravitation, Orbits, General relativity
Evidence for Gravitational Lensing in FRB 20190320B: A Potential Lens Mass of ∼420 Solar Masses. Due to their millisecond-duration pulses and high flux, fast radio bursts (FRBs) are ideal probes for detecting low-mass gravitational lensing signals, as their distinctive characteristics make them highly sensitive to subtle time delays and lensing effects. We search for lensing events using the high-time-resolution (2.56 μs) channelized raw voltage (baseband) data of 58 FRBs consisting of at least two components publicly released by the Canadian Hydrogen Intensity Mapping Experiment/FRB Collaboration, which allows the microstructures of FRBs to be better resolved compared to the intensity data. We apply different algorithms to examine these FRBs and identify a lensing candidate, FRB 20190320B, with a delay of ∼1.24 ms and an intensity ratio of ∼1.16 between the two pulses. Although some methods show a significance exceeding 5σ, we conservatively regard this event as a candidate due to the potential limitations of these methods. Assuming it is indeed a lensed signal, we estimate its redshifted lens mass to be ∼424 M⊙, which ranks among the lowest mass estimates reported for candidate lensed FRBs.

Keywords: Radio transient sources
Cosmological Implications of the Extended Uncertainty Principle: Energy Conditions, Stability, and Late-time Acceleration. We study the cosmological consequences of the extended uncertainty principle (EUP) by deriving modified Friedmann equations through thermodynamic arguments. The evolution of the effective equation of state induced by EUP corrections is analyzed and characterized using the Chevallier─Polarski─Linder parameterization. We then examine the fulfillment of classical energy conditions, including the null, weak, strong, and dominant conditions. The dynamical and thermodynamic stability of the model is investigated, showing that the EUP cosmology admits a late-time de Sitter attractor. Finally, we evaluate the effective speed of sound associated with the model and discuss implications for perturbative stability. Our findings indicate that EUP-induced corrections can produce a consistent late-time acceleration without requiring a cosmological constant.

Keywords: Cosmological models, Dark energy, Cosmological parameters
Revisiting γ-ray Orbital Modulation in the Redback Millisecond Pulsar PSR J2039−5617. PSR J2039−5617 is a redback millisecond pulsar binary system consisting of a compact star with a mass of 1.1─1.6 M⊙ and a low-mass companion of 0.15─0.22 M⊙. For this binary, we performed a timing analysis using 16 yr of data from the Fermi Large Area Telescope, covering the period from 2008 August to 2024 October. Our analysis detected an orbital modulation with a period of 0.2279781 days at a significance level of ∼4σ, which is in good agreement with previous findings. However, unlike previous reports, we identified a transition in the orbital modulation around 2021 August, after which the orbital signal disappeared. We speculate that the system may be undergoing a transition from a rotation-powered to an accretion-powered state at this epoch. Additionally, we conducted the phase-resolved and spectral analyses, and in the phase-resolved results, we observed an anticorrelation between its γ-ray and X-ray emissions, which is consistent with the predictions of high-energy radiation models for such systems. We provide some predictive discussions based on the results of γ-ray data analysis, and future Fermi-LAT observations will determine whether these predictions hold true.

Keywords: Gamma-ray sources, Periodic variable stars, Pulsars, Millisecond pulsars
Fully Self-consistent Nova Explosion Models Reproducing Light Curves of KT Eri, V339 Del, V597 Pup, and SMC NOVA 2016-10a. The rising phase toward the optical maximum of a classical nova is one of the last frontiers of nova study. Constructing free─free emission model light curves based on our fully self-consistent nova explosion models, we present several theoretical light curves of classical novae and compare them with the four novae having the observed rising phase toward the optical maximum. Our 1.25 M⊙ white dwarf (WD) models show excellent agreements with the light curves of KT Eri, V339 Del, and V597 Pup, while our 1.35 M⊙ WD models are consistent with the light curves of SMC NOVA 2016-10a. These agreements indicate that the light curves toward the optical maximum of these novae are dominated by free─free emission, rather than by photospheric emission. Our results justify the previously obtained WD masses and distance moduli for these novae and show that the postmaximum evolution can be well approximated with the evolution sequences of steady-state envelope solutions.

Keywords: Fast novae, Stellar mass loss, Classical novae
The Detection Prospects of the Polarizations in the Plateau Phase of the Gamma-Ray Burst Afterglow by eXTP. Approximately 20%─50% of the gamma-ray burst (GRB) X-ray afterglows exhibit shallow decay features. Two popular energy-injection models have been proposed to interpret such observational phenomena, the relativistic wind bubble (RWB) model with a Poynting-flux injection and the structured ejecta (SE) model with a dynamical energy injection. Polarization predictions of the two models have been investigated and can be used as a test of the two models. However, the impacts of the parameters on the model predictions were not studied, and the comparisons with the detection ability of the forthcoming mission, enhanced X-ray Timing and Polarimetry (eXTP), has not been discussed. We considered the above issues and found that influences of the model parameters on the predicted polarizations of the two models are very limited. To perform a feasible polarization detection during the plateau phase, a priority target-of-opportunity (ToO) response is required. The detection probability of the GRB plateau phase is about 1/3 for one pointing under a priority ToO. The polarization detection probability would depend on the ratio between the Poynting-flux injection to the dynamical energy injection, which is unclear currently. The predicted flux density and polarization degree (PD) of the RWB model could be well above the threshold flux and minimal detectable PD of the Polarimetry Focusing Array (PFA) on board eXTP, while the predicted PDs of the SE model would be difficult to be detected by eXTP/PFA. Therefore, a detection of a significant polarization signal during the GRB plateau phase would prefer the RWB model, and the injected energy would be in the form of the Poynting flux, while a no detection of the polarized signal would indicate a dynamical energy injection of the SE model.

Keywords: Starlight polarization, Gamma-ray bursts
The Feasibility of Using Fe XXIII Metastable Transitions as a Density Diagnostic for Low-mass X-Ray Binary Disk Winds. Low-mass X-ray binaries (LMXBs) occasionally show signs of outflowing material from the accretion disk. Studying these outflows can inform the understanding of the geometry of the systems, as well as the dynamics and energetics of accretion. One key variable for determining the location of these disk winds is the density of the outflowing material. In this paper we explore a density diagnostic based upon the absorption of ionizing photons by density-sensitive metastable states of Fe XXIII. This can yield a blueshifted complex of absorption features in the region of 6.61─6.64 keV. We use the photoionization code PION to test how varying the ionizing spectrum affects the detectability and interpretation of these features. We base these ionizing spectral energy distributions on GX 13+1 to represent a bright thermally dominated spectrum, 4U 1735−44 to represent a harder, fainter LMXB spectrum, and MAXI J1820+070 to represent a black hole (BH) LMXB spectrum completely dominated by Comptonized emission. For each of these, we find that the regime where Fe XXIII can be used as a density diagnostic is with an ionization parameter  log(ξ/ergcms−1)∼2─3  and an outflow density  log(nH/cm−3)≳14 . The typical range of ionization parameters for LMXBs indicates that this technique is more feasibly achieved with BH LMXBs than their neutron star counterparts.

Keywords: Low-mass x-ray binary stars, Accretion
Supernova Ia Remnants with M-dwarf Surviving Companions. We study the possibility that Type Ia supernovae might be produced by binary systems where the companion of the exploding white dwarf is an M-dwarf star. Such a companion would appear as a runaway star, retaining its pre-explosion orbital velocity along with a kick imparted by the supernova ejecta. It might be rapidly rotating, from being tidally locked with the white dwarf prior to explosion in a very close binary. For this study, we perform a series of multidimensional hydrodynamic simulations to investigate the interaction between M-dwarf companions and SN ejecta, followed by post-impact stellar evolution modeling using the MESA code. Our initial models in the 3D simulations had high spin angular momenta, and the effects of magnetic braking have been included. They very significantly reduce the final rotation. A surviving companion candidate, MV-G272, has recently been discovered in the supernova remnant G272.2-3.2, which is an 8.9σ proper motion outlier, although it is slowly rotating. Our results show that the properties of this companion (luminosity, effective temperature, and surface gravity) can be reproduced by our post-impact M-dwarf models. The slow rotation, which is a common characteristic of several proposed hypervelocity SN companions, can be explained by magnetic braking during the post-impact evolution, thus supporting the possibility that the MV-G272 star is the surviving companion of the Type Ia supernova now found as supernova remnant G272.2-3.2.

Keywords: Hydrodynamical simulations, White dwarf stars, Type Ia supernovae, Companion stars
The Effect of Intrinsic Alignments on Weak-lensing Statistics in Hydrodynamical Simulations. The next generation of weak-gravitational-lensing surveys has the potential to place stringent constraints on cosmological parameters. However, their analysis is limited by systematics such as the intrinsic alignments of galaxies, which alter weak-lensing convergence and can lead to biases in cosmological parameter estimations. For the first time, in this work, we investigate the impact of intrinsic alignments on non-Gaussian statistics of the weak-lensing field using galaxy shapes derived from the IllustrisTNG hydrodynamical simulation. We create two catalogs of ray-traced convergence maps: one that includes the measured intrinsic shape of each galaxy and another where all galaxies are randomly rotated to eliminate intrinsic alignments. We compare a range of weak-lensing statistics between the two catalogs, including the shear─shear correlation function, the map-level angular power spectrum, one-point, peak count, and minimum distribution functions, and Minkowski functionals. For each statistic, we assess the level of statistical distinguishability between catalogs for a set of future survey angular areas. Our results reveal strong small-scale correlation in the alignment of galaxies and statistically significant boosts in weak-lensing convergence in both positive and negative directions for high-significance peaks and minima, respectively. We note that our analysis is at a fixed number density of  ∼5arcmin−2 , drawn from a single realization of initial conditions, and does not include observational uncertainties or supersample covariance contributions. Weak-lensing analyses utilizing non-Gaussian statistics must account for intrinsic alignments to avoid significantly compromised cosmological inferences.

Keywords: Weak gravitational lensing, Hydrodynamical simulations, Large-scale structure of the universe
The AURORA Survey: Ionizing Photon Production Efficiency with Minimal Nebular Dust Attenuation Systematics. We present ionizing photon production efficiencies (ξion) for 63 z = 1.5─6.9 star-forming galaxies using precise nebular dust attenuation corrections from the JWST Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey. A subset of objects within AURORA have individually determined nebular dust attenuation curves, which vary significantly in shape and normalization, resulting in reduced systematic uncertainty when constraining the total attenuation of Hα luminosity, and thus the intrinsic ionizing output within our sample. We find evidence for positive correlations between ξion and redshift, equivalent width of [O III] λ5007, and O32 = [O III] λ5007/[O II] λλ3726, 3729, and negative correlations between ξion and stellar attenuation, UV luminosity (LUV), stellar mass, and direct-method metallicity. We test alternate dust prescriptions within this sample, and find that the total attenuation is lower when using the commonly assumed Galactic extinction curve or when assuming that stellar attenuation is equal to nebular attenuation. We also find that assuming either of these alternate dust prescriptions can change the slope of the relationships between ξion and galaxy property, notably inducing a flat trend between ξion and LUV within AURORA. While the novel nebular dust curves derived from AURORA spectroscopy reveal obscured ionizing photon production within star-forming galaxies at these redshifts, a more complete understanding of stellar attenuation is required to fully reduce the dust systematics on ξion for inclusion in reionization models.

Keywords: Interstellar dust, Galaxy evolution, Reionization, High-redshift galaxies, Near infrared astronomy
Probing a Cosmogenic Origin of Astrophysical Neutrinos and Cosmic Rays Using Gamma-Ray Observations of TXS 0506+056. In 2017 September, a high-energy neutrino event detected by the IceCube Neutrino Observatory (IceCube-170922A) was associated, at the 3σ level, with a gamma-ray flare from the blazar TXS 0506+056. Cosmic rays that are accelerated in astrophysical sources can escape from their jets and interact with background radiation fields. Interactions with the extragalactic background light can produce pions and hence neutrinos, while interactions with the cosmic microwave background predominantly drive inverse Compton scattering, contributing to electromagnetic cascades in intergalactic space. The resulting secondary gamma-ray emission can be detected with high-energy gamma-ray telescopes. Here, we report on a new search for such cosmogenic cascade emission from the blazar TXS 0506+056, using a combined data set from the Fermi Large Area Telescope and VERITAS. We compare the gamma-ray spectrum and neutrino observations with the predictions of cosmic-ray-induced cascades in intergalactic space. The observed gamma-ray spectrum is modeled as a combination of the primary spectrum and the cascade spectrum. We apply a Monte Carlo simulation with a ∆χ2-based likelihood analysis to jointly determine the best-fit parameters of a proton emission spectrum describing the data and derive constraints on the proton escape luminosity. Assuming an LP primary photon spectrum, we find consistency with a proton injection spectral index of αp ≃ 2.0 and a cutoff energy of Ep,max ≃ 1.3 × 1016 eV and constrain the isotropic proton escape luminosity to 1 × 1044 erg s−1 ≲ Lp,esc ≲ 3 × 1045 erg s−1 at the 90% confidence level.

Keywords: Gamma-ray astronomy, Neutrino astronomy, Blazars, Cosmic rays
Exploring the Nature of the Gamma-Ray Dimming in the Blazar PMN J1326-5256 since 2022 August. This study focuses on the blazar PMN J1326-5256, which experienced a drop in gamma-ray flux in 2022 August and has stayed low ever since. Based on multiwavelength observations, we analyzed the broadband spectral energy distributions (SEDs) before and after this transition. As a first step, we reproduced the broadband SEDs by the traditional one-zone leptonic model. While this model is capable of reproducing the observed data, it requires an approximately tenfold reduction in the external photon field after 2022 August compared to before, which may not be physically plausible. By contrast, the two-zone model offers a more plausible explanation: the decline in gamma-ray flux may result from the disappearance or suppression of the emission region near the central engine, allowing the far emission region to dominate the observed emission. The dynamical variation in PMN J1326-5256 is similar to that seen in PKS 1510-089, indicating a comparable jet restructuring. These findings offer valuable insights into the complex emission mechanisms and jet morphology of blazars.

Keywords: Blazars
Numerical Test of the PBA Periodogram and Period Analysis of FRB 20190520B. The periodicity of repeating fast radio bursts (FRBs) is crucial for understanding their origins and usually requires appropriate methods to identify. In a recent paper, we developed the Phase-folding probability Binomial Analysis (PBA) periodogram and found a candidate period of 4.605 days for FRB 20121102A. As a follow-up, thorough tests of the PBA method are first performed using numerically generated data in this paper. The tests are done for observations of 20 hr with different observation windows. PBA shows its different effects in identifying the periodicity of bursts compared with the Lomb─Scargle periodogram and χ2 test. The PBA method is particularly sensitive for bursty sources with high burst rates (R ≥ 2 hr−1), narrow active phase widths (∆P ≤ 0.2), and a high percentage of bursts that show periodicity (pb ≥ 0.8). We then apply PBA to analyze the periodicity of bursts from FRB 20190520B, aiming toward periods ranging from 1 day to 1024 days. For bursts with fluences higher than 0.5 Jy ms, a period of  381.14−0.29+1.25  days with an active phase width of 0.1 is identified. For bursts with fluences lower than 0.5 Jy ms, no periodicity is detected.

Keywords: Radio bursts, Time series analysis, Radio transient sources
Chandra and HST Observations of Radio-selected (Wandering) Massive Black Hole Candidates in Dwarf Galaxies. We present Chandra X-ray Observatory and Hubble Space Telescope (HST) follow-up observations of 12 dwarf galaxies from A. E. Reines et al. that are potential hosts of radio-selected active galactic nuclei (AGNs), eight of which are nonnuclear and possible "wandering" black holes (BHs). Our multiwavelength analysis indicates a heterogeneous sample with five radio sources detected at both X-ray and optical wavelengths within the positional uncertainties and nondetections for the remaining objects. Of the radio objects detected in the X-ray and optical, three have multiwavelength evidence for hosting nuclear massive BHs and one object is consistent with an extreme compact starburst. Only one of the off-nuclear radio sources has a significant optical counterpart and we present Palomar spectroscopy that identifies this object as a background AGN. We cannot definitively determine if the seven remaining off-nuclear radio sources are wandering massive BHs in the target dwarf galaxies or background AGNs, although the three sources with the largest offsets have compact radio cores detected with the Very Long Baseline Array and are consistent with expectations for background AGNs. Our HST sensitivity limits also allow for wandering massive BHs in the target dwarf galaxies that are hosted by stellar clusters with masses ≲ 106 M⊙.

Keywords: X-ray astronomy, Dwarf galaxies, Active galactic nuclei, Optical astronomy