Sazuna/UAT_keywords huggingface dataset:
Shadow Geometry of Kerr Naked Singularities. Direct imaging of supermassive black holes (SMBHs) at event horizon-scale resolutions, as recently done by the Event Horizon Telescope, allows for testing alternative models to SMBHs such as Kerr naked singularities (KNSs). We demonstrate that the KNS shadow can be closed, open, or vanishing, depending on the spins and observational inclination angles. We study the critical parameters where the KNS shadow opens a gap, a distinctive phenomenon that does not happen with the black hole shadow. We show that the KNS shadow can only be closed for dimensionless spin a ≲ 1.18 and vanishing for a ≳ 1.18 for certain ranges of inclination angles. We further analyze the effective angular momentum of photon orbits to demonstrate the fundamental connections between light geodesics and the KNS shadow geometry. We also perform numerical general relativistic ray-tracing calculations, which reproduce the analytical topological change in the KNS shadow, and illustrate other observational features within the shadow due to the lack of an event horizon. By comparing the geometric features of the KNS shadow with black hole shadow observations, the topological change in the shadow of KNSs can be used to test the cosmic censorship hypothesis and KNSs as alternative models to SMBHs.

Keywords: Naked singularities, Kerr black holes, Gravitation, General relativity, Geodesics
Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT. The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of &gt;100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the &gt;300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with "Prompt" and "Delayed" (SGRE) gamma-ray components. We found that "Delayed"-component-associated CMEs have higher initial accelerations and space speeds than "Prompt Only"-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6-0.8 au and their speeds were high enough (≈975 km s-1 and ≈750 km s-1, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of &gt;300 MeV protons.

Keywords: Solar energetic particles, Solar gamma-ray emission, Solar coronal mass ejections
The Demographics, Stellar Populations, and Star Formation Histories of Fast Radio Burst Host Galaxies: Implications for the Progenitors. We present a comprehensive catalog of observations and stellar population properties for 23 highly secure host galaxies of fast radio bursts (FRBs). Our sample comprises 6 repeating FRBs and 17 apparent nonrepeaters. We present 82 new photometric and 8 new spectroscopic observations of these hosts. Using stellar population synthesis modeling and employing nonparametric star formation histories (SFHs), we find that FRB hosts have a median stellar mass of ≈109.9 M ☉, mass-weighted age ≈5.1 Gyr, and ongoing star formation rate ≈1.3 M ☉ yr-1 but span wide ranges in all properties. Classifying the hosts by degree of star formation, we find that 87% (20 of 23 hosts) are star-forming, two are transitioning, and one is quiescent. The majority trace the star-forming main sequence of galaxies, but at least three FRBs in our sample originate in less-active environments (two nonrepeaters and one repeater). Across all modeled properties, we find no statistically significant distinction between the hosts of repeaters and nonrepeaters. However, the hosts of repeating FRBs generally extend to lower stellar masses, and the hosts of nonrepeaters arise in more optically luminous galaxies. While four of the galaxies with the clearest and most prolonged rises in their SFHs all host repeating FRBs, demonstrating heightened star formation activity in the last ≲100 Myr, one nonrepeating host shows this SFH as well. Our results support progenitor models with short delay channels (i.e., magnetars formed via core-collapse supernova) for most FRBs, but the presence of some FRBs in less-active environments suggests a fraction form through more delayed channels.

Keywords: Magnetars, Star formation, Galaxies, Radio transient sources
The Crucial Role of Perpendicular Diffusion in the Longitude Distribution of &gt;10 MeV Solar Energetic Protons. Gradual solar proton events are thought to consist of solar components originating near the Sun and interplanetary components associated with interplanetary shocks, and the role of interplanetary shocks is considered to be crucial in supplying particles to regions that are not magnetically connected to the solar source region. We calculate the ratios of the peak intensities for the four energy channels (13-16, 20-25, 32-40, and 40-64 MeV) and compare the ratios observed by multiple spacecraft at different locations. We often find that the ratio of peak intensities observed at different locations in the same event remains almost constant as the energy varies. In other words, the ratio of peak intensities from the different energy channels remains almost constant as the position of the spacecraft changes. The phenomenon implies that in many gradual events, energetic particles observed at different locations are mainly composed of solar components that undergo perpendicular diffusion in both the vicinity of the Sun and the interplanetary space, and that perpendicular diffusion is the main factor enabling energetic particles to be observed in regions without magnetic connection to the solar source region.

Keywords: Solar energetic particles, Solar storm, Interplanetary physics, Solar particle emission
Post-outburst Evolution of Bona Fide FU Ori-type V2493 Cygnus: A Spectro-photometric Monitoring. We present here the results of 8 yr of our near-simultaneous optical-near-infrared spectro-photometric monitoring of the bona fide FU Ori (FUor)-type candidate V2493 Cygnus (V2493 Cyg) starting from 2013 September to 2021 June. During our optical monitoring period (between 2015 October 16 and 2019 December 30), the V2493 Cyg is slowly dimming with an average dimming rate of ~26.6 ± 5.6 mmag yr-1 in the V band. Our optical photometric colors show a significant reddening of the source post the second outburst pointing toward a gradual expansion of the emitting region post the second outburst. The mid-infrared colors, on the contrary, exhibit a blueing trend, which can be attributed to the brightening of the disk due to the outburst. Our spectroscopic monitoring shows a dramatic variation of the Hα line as it transitioned from absorption feature to the emission feature and back. Such transition can possibly be explained by the variation in the wind structure in combination with accretion. Combining our time evolution spectra of the Ca II infrared triplet lines with the previously published spectra of V2493 Cyg, we find that the accretion region has stabilized compared to the early days of the outburst. The evolution of the O I λ7773 Å line also points toward the stabilization of the circumstellar disk post the second outburst.

Keywords: Early-type stars, Young stellar objects, Eruptive variable stars
A Cross-internal Linear Combination Approach to Probe the Secondary CMB Anisotropies: Kinematic Sunyaev-Zel'dovich Effect and CMB Lensing. We propose a cross-internal linear combination (cross-ILC) approach to measure the small-scale cosmic microwave background (CMB) anisotropies robustly against the contamination from astrophysical signals. In particular, we focus on the mitigation of systematics from cosmic infrared background (CIB) and thermal Sunyaev-Zel'dovich (tSZ) signals in kinematic Sunyaev-Zel'dovich (kSZ) power spectrum and CMB lensing. We show the cross-spectrum measurement between two CMB maps created by nulling the contributions from CIB (CIB-free map) and tSZ (tSZ-free map) to be robust for kSZ, as the approach significantly suppresses the total contribution of CIB and tSZ signals. Similarly, for CMB lensing, we use the approach introduced by Madhavacheril &amp; Hill but with a slight modification by using the tSZ-free and CIB-free maps in the two legs of the quadratic estimator. By cross-correlating the CMB lensing map created using this technique with galaxy surveys, we show that the biases from both CIB and tSZ are negligible. We also compute the impact of unmodeled CIB/tSZ residuals on kSZ and cosmological parameters, finding the kSZ measured using the standard ILC to be significantly biased. The kSZ estimate from the cross-ILC remains less affected by CIB/tSZ, making it crucial for current and upcoming CMB surveys such as the South Pole Telescope (SPT), Simons Observatory (SO), and CMB-S4. With the cross-ILC approach, we find that the total kSZ power spectrum can be measured at very high significance in the coming years: 35σ by SPT, 22σ by SO, and 80σ by CMB-S4. Finally, we forecast constraints on the epoch of reionization using the kSZ power spectrum and find that the duration of reionization, currently unconstrained by Planck, can be constrained to $\sigma ({\rm{\Delta }}{z}_{\mathrm{re}})$ = 1.5 or 0.5 depending on the choice of the prior on the optical depth to reionization. The data products and the associated codes can be downloaded from this link (https://github.com/sriniraghunathan/cross_ilc_methods_paper).

Keywords: Gravitational lensing, Cosmic microwave background radiation, Sunyaev-Zeldovich effect
Star Formation in Self-gravitating Disks in Active Galactic Nuclei. III. Efficient Production of Iron and Infrared Spectral Energy Distributions. Strong iron lines are a common feature of the optical spectra of active galactic nuclei (AGNs) and quasars from z ~ 6-7 to the local universe, and [Fe/Mg] ratios do not show cosmic evolution. During active episodes, accretion disks surrounding supermassive black holes (SMBHs) inevitably form stars in the self-gravitating part, and these stars accrete with high accretion rates. In this paper, we investigate the population evolution of accretion-modified stars (AMSs) to produce iron and magnesium in AGNs. The AMSs, as a new type of star, are allowed to have any metallicity but without significant loss from stellar winds, since the winds are choked by the dense medium of the disks and return to the core stars. Mass functions of the AMS population show a pile-up or cutoff pile-up shape in top-heavy or top-dominant forms if the stellar winds are strong, consistent with the narrow range of supernovae (SNe) explosions driven by the known pair-instability. This provides an efficient way to produce metals. Meanwhile, SN explosions support an inflated disk as a dusty torus. Furthermore, the evolving top-heavy initial mass functions lead to bright luminosity in infrared bands in dusty regions. This contributes a new component in infrared bands, which is independent of the emissions from the central part of accretion disks, appearing as a long-term trending of the NIR continuum compared to optical variations. Moreover, the model can be further tested through reverberation mapping of emission lines, including LIGO/LISA detections of gravitational waves and signatures from spatially resolved observations of GRAVITY+/VLTI.

Keywords: Supermassive black holes, Galaxy accretion disks, Active galactic nuclei
Efficiency of Magnetohydrodynamic Wave Generation in Weakly Ionized Atmospheres. The generation of Alfvén and slow magnetoacoustic waves in weakly ionized atmospheres by excitation of the charges-only component of the two-fluid (charge and neutral) plasma is shown to be more or less efficient depending on the energy fraction initially allocated to the three stationary flow differential modes, which characterize the inter-species drift. This is explained via detailed analysis of the full 10-dimensional spectral description of two-fluid linear magnetohydrodynamics. Excitation via the velocity of the charges only is found to be very inefficient, in accord with previous results, while excitation via the magnetic field perturbation alone is highly efficient. All 10 eigenvalues and eigenvectors are presented analytically in the high collision frequency regime.

Keywords: Magnetohydrodynamics, Solar photosphere, Quiet sun, Plasma astrophysics, Solar physics, Alfven waves, Solar oscillations
MFPIM: A Deep Learning Model Based on Multimodal Fusion Technology for Pulsar Identification. With the development of radio telescope technology, the quantity and types of acquired pulsar candidate data have increased dramatically. However, it is difficult to accurately identify pulsar candidates. Therefore, we propose to use multimodal fusion technology, called the multimodal fusion-based pulsar identification model (MFPIM), to build a deep learning model to improve the efficiency and accuracy of pulsar candidate identification. MFPIM treats each diagnostic plot of pulsar candidates as a modality and uses multiple convolutional neural networks to extract effective features from the diagnostic plots. After fusing the features, the commonality of different modalities in high-dimensional space is obtained to ensure that the model can take full advantage of the complementarity between diagnostic plots and thus identify pulsar candidates, achieved better classification performance than other current supervised learning algorithms. In addition, a channel attention mechanism is used in the model to enable it to learn the importance of different channel features so that the model focuses more on the channel information in the input data that is more meaningful for classification, reducing the model size while extracting pulsar diagnostic map features more accurately. We conducted experiments on the Five-hundred-meter Aperture Spherical radio Telescope (FAST) data set, and the results show that MFPIM can effectively identify the pulsars in the FAST data set with an identification accuracy of over 98%. To further verify the robustness of the model, we applied the MFPIM to the High Time Resolution Universe data set using transfer learning, with the test accuracy and F1 score reaching over 99%.

Keywords: Convolutional neural networks, Radio pulsars, Pulsars
Comparative Analysis of TRGBs (CATs) from Unsupervised, Multi-halo-field Measurements: Contrast is Key. The tip of the red giant branch (TRGB) is an apparent discontinuity of the luminosity function (LF) due to the end of the red giant evolutionary phase and is used to measure distances in the local universe. In practice, tip localization via edge detection response (EDR) relies on several methods applied on a case-by-case basis. It is hard to evaluate how individual choices affect a distance estimation using only a single host field while also avoiding confirmation bias. To devise a standardized approach, we compare unsupervised, algorithmic analyses of the TRGB in multiple halo fields per galaxy. We first optimize methods for the lowest field-to-field dispersion, including spatial filtering, smoothing, and weighting of LF, color band selection, and tip selection based on the number of likely RGB stars and the ratio of stars below versus above the tip (R). We find R, which we call the tip contrast, to be the most important indicator of the quality of EDR measurements; higher R selection can decrease field-to-field dispersion. Further, since R is found to correlate with the age or metallicity of the stellar population based on theoretical modeling, it might result in a displacement of the detected tip magnitude. We find a tip-contrast relation with a slope of -0.023 ± 0.0046 mag/ratio, an ~5σ result that can be used to correct these variations in the detections. When using TRGB to establish a distance ladder, consistent TRGB standardization using tip-contrast relation across rungs is vital to make robust cosmological measurements.

Keywords: Stellar distance, Standard candles, Distance indicators
IXPE and XMM-Newton Observations of the Soft Gamma Repeater SGR 1806-20. Recent observations with the Imaging X-ray Polarimetry Explorer (IXPE) of two anomalous X-ray pulsars provided evidence that X-ray emission from magnetar sources is strongly polarized. Here we report on the joint IXPE and XMM-Newton observations of the soft γ-repeater SGR 1806-20. The spectral and timing properties of SGR 1806-20 derived from XMM-Newton data are in broad agreement with previous measurements; however, we found the source at an all-time low persistent flux level. No significant polarization was measured apart from the 4-5 keV energy range, where a probable detection with PD = 31.6% ± 10.5% and $\mathrm{PA}=-17\buildrel{\circ}\over{.} {6}_{-15\buildrel{\circ}\over{.} 0}^{+15\buildrel{\circ}\over{.} 5}$ was obtained. The resulting polarization signal, together with the upper limits we derive at lower and higher energies (2-4 and 5-8 keV, respectively), is compatible with a picture in which thermal radiation from the condensed star surface is reprocessed by resonant Compton scattering in the magnetosphere, similar to what was proposed for the bright magnetar 4U 0142+61.

Keywords: Neutron stars, Magnetars, Polarimetry, X-ray sources
Improving Distances to Binary Millisecond Pulsars with Gaia. Pulsar distances are notoriously difficult to measure, and play an important role in many fundamental physics experiments, such as pulsar timing arrays. Here, we perform a cross-match between International PTA pulsars (IPTA) and Gaia's Data Release 2 (DR2) and Data Release 3 (DR3). We then combine the IPTA pulsar's parallax with its binary companion's parallax, found in Gaia, to improve the distance measurement to the binary. We find seven cross-matched IPTA pulsars in Gaia DR2, and when using Gaia DR3 we find six IPTA pulsar cross-matches but with seven Gaia objects. Moving from Gaia DR2 to Gaia DR3, we find that the Gaia parallaxes for the successfully cross-matched pulsars improved by 53%, and pulsar distances improved by 29%. Finally, we find that binary companions with a &lt;3.0σ detection are unreliable associations, setting a high bar for successful cross-matches.

Keywords: Distance measure, Gaia, Binary pulsars, Millisecond pulsars
The Fine-scale Structure of Polar Coronal Holes. Coronal holes are thought to be composed of relatively broad columnar structures known as plumes. Here, we demonstrate that the plumes (and interplumes) in polar coronal holes are composed of fine-scale filamentary structure, with average scales of 2″-10″. The fine structure is the off-limb analog of the previously found "plumelets" of Uritsky et al. The off-limb observations enable an examination of the fine structure without the influence of the underlying atmosphere along the line of sight. Hence, we show that the fine-scale structure is present at least until the edge of the field of view of the Solar Dynamics Observatory. The fine structure is found to have spatial distribution that follows a k -1 power law perpendicular to the inferred magnetic field direction. For a small sample of the fine structure, the cross-sectional profiles are measured as a function of height. In some cases, the measurements indicate that the fine structure expands super-radially, consistent with existing models of polar field expansion and the expansion of the plumes. We discuss the implications of the presence of the fine structure with respect to understanding wave propagation in the coronal holes and their contribution to powering the solar wind.

Keywords: Solar coronal holes, The Sun, Solar coronal plumes, Solar corona
Lithium in Turnoff Stars in the Globular Cluster M5: A Quest for Primordial Lithium. The light element lithium is formed by nucleosynthesis during the Big Bang. Its abundance can help to define the parameters of the early Universe. To find this primordial value, it is necessary to determine Li abundances in the oldest stars because it is readily destroyed by nuclear reactions in stellar interiors. We have made high-resolution (~45,000) spectroscopic observations of five identical unevolved turnoff stars in the 13 Gyr old globular cluster M5. In our analysis we find a range in Li abundance of a factor of 2; the spread is 5 times the individual error. The comparison of these results with those for turnoff stars from five other globular clusters reveals a similarly large range in Li. Lithium in M5 and the other clusters all have stars above the field star Li plateau, but none are as high as the predictions for primordial Li. The maximum values for Li are the same in all six clusters. Multiple generations of stars are found in many globular clusters; those later generations are expected to have formed from Li-depleted gas. Such second- and later-generation stars would have no Li. However, only one of the six clusters has a few unevolved stars with upper limits on the Li abundance.

Keywords: Stellar astronomy, Stellar abundances, Stellar interiors, Stellar atmospheres
Unpacking Merger Jets: A Bayesian Analysis of GW170817, GW190425 and Electromagnetic Observations of Short Gamma-Ray Bursts. We present a novel fully Bayesian analysis to constrain short gamma-ray burst (sGRB) jet structures associated with cocoon, wide-angle, and simple top-hat jet models, as well as the binary neutron star (BNS) merger rate. These constraints are made given the distance and inclination information from GW170817, observed flux of GRB 170817A, observed rate of sGRBs detected by Swift, and the neutron star merger rate inferred from LIGO's first and second observing runs. A separate analysis is conducted where a fitted sGRB luminosity function is included to provide further constraints. The jet structure models are further constrained using the observation of GW190425, and we find that the assumption that it produced a GRB 170817-like sGRB which went undetected due to the jet geometry is consistent with previous observations. We find and quantify evidence for low-luminosity and wide-angle jet structuring in the sGRB population, independently from afterglow observations, with log Bayes factors of 0.45-0.55 for such models when compared to a classical top-hat jet. Slight evidence is found for a Gaussian jet structure model over all others when the fitted luminosity function is provided, producing log Bayes factors of 0.25-0.9 ± 0.05 when compared to the other models. However, without considering GW190425 or the fitted luminosity function, the evidence favors a cocoon-like model with log Bayes factors of 0.14 ± 0.05 over the Gaussian jet structure. We provide new constraints to the BNS merger rates of 1-1300 Gpc-3 yr-1 or 2-680 Gpc-3 yr-1 when a fitted luminosity function is assumed.

Keywords: Gamma-ray bursts, Gravitational waves