Sazuna/UAT_keywords huggingface dataset:
Could the Neutrino Emission of TXS 0506+056 Come from the Accretion Flow of the Supermassive Black Hole?. High-energy neutrinos from the blazar TXS 0506+056 are usually thought to arise from the relativistic jet pointing to us. However, the composition of jets of active galactic nuclei (AGNs), whether they are baryon dominated or Poynting flux dominated, is largely unknown. In the latter case, no comic rays and neutrinos would be expected from the AGN jets. In this work, we study whether the neutrino emission from TXS 0506+056 could be powered by the accretion flow of the supermassive black hole. Protons could be accelerated by magnetic reconnection or turbulence in the inner accretion flow. To explain the neutrino flare of TXS 0506+056 in the years 2014–2015, a super-Eddington accretion is needed. During the steady state, a sub-Eddington accretion flow could power a steady neutrino emission that may explain the long-term neutrino flux from TXS 0506+056. We consider the neutrino production in both magnetically arrested accretion (MAD) flow and the standard and normal evolution (SANE) regime of accretion. In the MAD scenario, due to a high magnetic field, a large dissipation radius is required to avoid the cooling of protons and secondary pions.

Keywords: Blazars, Neutrino astronomy, Active galactic nuclei, High energy astrophysics
Studying the Radiation of a White Dwarf Star Falling onto a Black Hole. We investigate electromagnetic and gravitational radiation generated during the process of the tidal stripping of a white dwarf star circulating a black hole. We go beyond Chandrasekhar's ideas and not only consider the white dwarf itself as a quantum object, but also describe the dynamics of the produced accretion disk in a quantum way. We model the white dwarf star as a Bose–Fermi droplet and use the quantum hydrodynamic equations to simulate the evolution of the black hole–white dwarf binary system. While going through periastron, the white dwarf loses a small fraction of its mass. The mass falling onto a black hole is a source of powerful electromagnetic and gravitational radiation. Bursts of ultraluminous radiation are flared at each periastron passage. This resembles the recurrent flaring of X-ray sources discovered recently by Irwin et al. Gravitational energy bursts occur mainly through emission at very low frequencies. The accretion disk, formed due to stripping of the white dwarf, starts at some point to contribute continuously to radiation of both electromagnetic and gravitational types.

Keywords: Stellar accretion disks, Hydrodynamical simulations, White dwarf stars, Schwarzschild black holes
Extracting the X-Ray Reverberation Response Functions from the Active Galactic Nucleus Light Curves Using an Autoencoder. We study the X-ray reverberation in active galactic nuclei (AGN) using the variational autoencoder (VAE), which is a machine learning algorithm widely used for signal processing and feature reconstruction. While the X-ray reverberation signatures that contain the information of the accretion disk and the X-ray-emitting corona are commonly analyzed in the Fourier domain, this work aims to extract the reverberation response functions directly from the AGN light curves. The VAE is trained using the simulated light curves that contain the primary X-rays from the lamppost corona, varying its height and the corresponding reflection X-rays from the disk. We use progressively more realistic light-curve models, such as those that include the effects of disk-propagating fluctuations and random noises, to assess the ability of the VAE to reconstruct the response profiles. Interestingly, the VAE can recognize the reverberation patterns on the light curves; hence, the coronal height can be predicted. We then deploy the VAE model on the XMM-Newton data of IRAS 13224–3809 and directly estimate, for the first time, the response functions of this source in various observations. The result reveals the corona changing its height between 3rg and 20rg, which is correlated with the source luminosity and in line with previous literature. Finally, we discuss the advantages and limitations of this method.

Keywords: X-ray astronomy, Black hole physics, Reverberation mapping, Active galactic nuclei
Fast and Efficient Bayesian Method to Search for Strongly Lensed Gravitational Waves. A small fraction of the gravitational-wave (GW) signals from binary black holes observable by ground-based detectors will be strongly lensed by intervening objects such as galaxies and clusters. Strong lensing will produce nearly identical copies of the GW signals separated in time. These lensed signals must be identified against a background of unlensed pairs GW events, some of which may appear similar by accident. This is usually done using fast, but approximate methods that, for example, check for the overlap between the posterior distributions of a subset of binary parameters, or using slow, but accurate joint Bayesian parameter estimation. In this work, we present a modified version of the posterior overlap method dubbed "PO2.0" that is mathematically equivalent to joint parameter estimation while still remaining fast. We achieve a significant gain in efficiency by incorporating informative priors about the binary and lensing populations, selection effects, and all the inferred parameters of the binary. For binary black hole signals lensed by galaxies, our improved method can detect 65% lensed events at a pairwise false alarm probability of ∼2 × 10‑6. Consequently, we have a 13% probability of detecting a strongly lensed event above 2.25σ significance during 18 months of observation by the LIGO-Virgo detectors at their current sensitivity. We also show how we can compute the joint posteriors of the lens and source parameters from a pair of lensed events by reweighting the posteriors of individual events in a computationally inexpensive way.

Keywords: Posterior distribution, Strong gravitational lensing, Bayesian statistics, Gravitational waves
Asymmetric Temperature Variations In Protoplanetary Disks. I. Linear Theory, Corotating Spirals, and Ring Formation. Protoplanetary disks can exhibit asymmetric temperature variations due to phenomena such as shadows cast by the inner disk or localized heating by young planets. We investigate the disk features induced by these asymmetric temperature variations. We find that spirals are initially excited, and then break into two and reconnect to form rings. By carrying out linear analyses, we first study the spiral launching mechanism and find that the effects of azimuthal temperature variations share similarities with effects of external potentials. Specifically, rotating temperature variations launch steady spiral structures at Lindblad resonances, which corotate with the temperature patterns. When the cooling time exceeds the orbital period, these spiral structures are significantly weakened, and a checkerboard pattern may appear. A temperature variation of about 10% can induce spirals with order unity density perturbations, comparable to those generated by a thermal mass planet. We then study ring formation and find it is related to the coupling between azimuthal temperature variations and spirals outside the resonances. Such coupling leads to a radially varying angular momentum flux, which produces anomalous wave-driven accretion and forms dense rings separated by the wavelength of the waves. Finally, we speculate that spirals induced by temperature variations may contribute to disk accretion through nonlinear wave steepening and dissipation. Overall, considering that irradiation determines the temperature structure of protoplanetary disks, the change of irradiation both spatially or/and temporarily may produce observable effects in protoplanetary disks, especially spirals and rings in outer disks beyond tens of au.

Keywords: Hydrodynamics, Protoplanetary disks, Planet formation
A Nonstop Aurora? The Intriguing Radio Emission from the Rapidly Rotating Magnetic Massive Star HR 5907. HR 5907 (HD 142184) stands out among magnetic OB stars for its rapid rotation, exceptionally hard X-ray emission, and strong magnetic field. High-frequency (&gt;5 GHz) radio emission from the star exhibits an approximately flat spectrum that can be attributed to gyrosynchrotron emission from a dense centrifugal magnetosphere. In a survey of radio emission from massive stars at sub-GHz frequencies, we noticed remarkable low-frequency radio emission from this star, characterized by high circular polarization and brightness temperature, which is inconsistent with the gyrosynchrotron model. We present a follow-up low-frequency radio study of this star with the upgraded Giant Metrewave Radio Telescope in search of emission mechanisms that can go undiagnosed at higher frequencies. We detect variable radio emission characterized by varying degrees of circular polarization (15%–45%) throughout the rotation cycle. The broadband spectral fitting also suggests additional emission components at lower frequencies. We show that the observed emission is likely auroral emission via electron cyclotron maser emission (ECME) and identify this star as a main-sequence radio pulse emitter (MRP). For MRPs, ECME is usually observed as short polarized enhancements near the magnetic nulls of the star. The detection of a high degree of circular polarization (&gt;15%) at all times makes HR 5907 unique among MRPs. This is only the second MRP after ρ Oph C (detected polarization fraction: 0%–60%) that exhibits persistent coherent radio emission attributed to the nearly aligned stellar magnetic and rotational axes.

Keywords: Magnetospheric radio emissions, Massive stars, Stellar magnetic fields, Non-thermal radiation sources, Radio interferometry
Multifrequency Models of Black Hole Photon Rings from Low-luminosity Accretion Disks. Images of black holes encode both astrophysical and gravitational properties. Detecting highly lensed features in images can differentiate between these two effects. We present an accretion disk emission model coupled to the Adaptive Analytical Ray Tracing (AART) code that allows a fast parameter space exploration of black hole photon ring images produced from synchrotron emission from 10 to 670 GHz. As an application, we systematically study several disk models and compute their total flux density, average radii, and optical depth. The model parameters are chosen around fiducial values calibrated to general relativistic magnetohydrodynamic (GRMHD) simulations and observations of M87*. For the parameter space studied, we characterize the transition between optically thin and thick regimes and the frequency at which the first photon ring is observable. Our results highlight the need for careful definitions of photon ring radius in the image domain, as in certain models the highly lensed photon ring is dimmer than the direct emission at certain angles. We find that at low frequencies the ring radii are set by the electron temperature, while at higher frequencies the magnetic field strength plays a more significant role, demonstrating how multifrequency analysis can also be used to infer plasma parameters. Lastly, we show how our implementation can qualitatively reproduce multifrequency black hole images from GRMHD simulations when adding time variability to our disk model through Gaussian random fields. This approach provides a new method for simulating observations from the Event Horizon Telescope and the proposed Black Hole Explorer space mission.

Keywords: Accretion, Supermassive black holes, Magnetohydrodynamics, Black hole physics, Black holes, Very long baseline interferometry, Photon sphere, Radiative transfer, Event horizons
Evidence for Jet/Outflow Shocks Heating the Environment around the Class I Protostellar Source Elias 29: FAUST XXI. We have observed the late Class I protostellar source Elias 29 at a spatial resolution of 70 au with the Atacama Large Millimeter/submillimeter Array as part of the FAUST Large Program. We focus on the line emission of SO, while that of 34SO, C18O, CS, SiO, H13CO+, and DCO+ are used supplementarily. The spatial distribution of the SO rotational temperature (Trot(SO)) is evaluated by using the intensity ratio of its two rotational excitation lines. Besides in the vicinity of the protostar, two hot spots are found at a distance of 500 au from the protostar; Trot(SO) locally rises to 53  K at the interaction point of the outflow and the southern ridge, and 72  K within the southeastern outflow probably due to a jet-driven bow shock. However, the SiO emission is not detected at these hot spots. It is likely that active gas accretion through the disk-like structure and onto the protostar still continues even at this evolved protostellar stage, at least sporadically, considering the outflow/jet activities and the possible infall motion previously reported. Interestingly, Trot(SO) is as high as 20–30 K even within the quiescent part of the southern ridge apart from the protostar by 500–1000 au without clear kinematic indication of current outflow/jet interactions. Such a warm condition is also supported by the low deuterium fractionation ratio of HCO+ estimated by using the H13CO+ and DCO+ lines. The B-type star HD147889 ∼0.5 pc away from Elias 29, previously suggested as a heating source for this region, is likely responsible for the warm condition of Elias 29.

Keywords: Astrochemistry, Stellar winds, Star formation, Low mass stars, Protostars
MUSEQuBES: The Kinematics of O VI-bearing Gas in and around Low-redshift Galaxies. We present a detailed study of the kinematics of O VI-bearing gas around 60 low-mass (median   = 8.9) galaxies at low redshift (0.1 &lt; z &lt; 0.7) using background quasars (median impact parameter ≍115 kpc) as part of the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). We find that the majority of the O VI absorbers detected within the virial radius have line-of-sight velocities smaller than the escape velocities and are thus consistent with being gravitationally bound, irrespective of the halo mass. However, the fraction of such absorbers declines at larger impact parameters. The Doppler b parameter and the velocity width (∆v90) of the O VI absorbers exhibit large scatter inside the virial radius of the host galaxies, but the scatter declines sharply at impact parameter D ≳ 2Rvir. For high-mass galaxies (  &gt; 9), O VI absorption displays a larger kinematic spread, quantified by the pixel-velocity two-point correlation function (TPCF). However, the difference becomes marginal when the pixel velocities are scaled by the galaxies' circular velocities. We do not find any significant difference between the TPCF of isolated and group galaxies when the stellar mass is controlled for. A significant fraction of groups (4/6) with four or more member galaxies do not show any detectable O VI absorption, likely due to the passive nature of the nearest galaxies.

Keywords: Galaxy evolution, Circumgalactic medium
High Lithium Abundance Connection with the Chromospheric Helium in Red Giants: Spectroscopic and Asteroseismic Analyses. We present a study of correlations between high Li abundances and strong chromospheric He I λ10830 absorption-line strengths in Kepler field giant stars. Our sample includes 84 giants with detectable solar-like oscillations in their light curves, and their Li abundances come from the literature or are measured here using LAMOST medium-resolution spectra. Evolutionary phases are determined through asteroseismic analysis, with mixed-mode period spacing (ΔP) used to infer the time evolution of red clump (RC) giants. Near-IR observations of the He I λ10830 line were obtained with the high-resolution Habitable-zone Planet Finder spectrograph on the Hobby–Eberly Telescope. We find high Li abundances and strong He I lines exclusively among RC giants, with their absence in red giant branch stars suggesting a shared origin linked to the He flash. Additionally, a steady decline in He I strength with decreasing Li abundance among RC giants indicates a correlation between these properties. Older, Li-normal RC giants are He weak, while most younger, super-Li-rich giants are He strong, suggesting temporal evolution of both phenomena. We hypothesize that the core He flash and subsequent subflashes may enhance Li abundances in RC giant photospheres and trigger heightened chromospheric activity, leading to stronger He I λ10830 lines in younger RCs. Over time, following He flash, chromospheric activity diminishes, resulting in weaker He I lines in older, Li-normal RCs.

Keywords: Red giant clump, Stellar abundances, Stellar chromospheres, Helium burning, Stellar oscillations
Fractality of Magnetic Helicity Distribution in the Solar Corona. We find a universal power-law scaling of magnetic helicity distribution in the solar corona. Magnetic helicity is a dynamical invariant for ideal magnetohydrodynamics (MHD) and characterizes complex magnetic field structure by measuring the degree of knottiness of its field lines. We treat turbulent solar magnetic field as a superposition of random waves and develop a statistical topology method regarding the randomly tangled field lines. Based on the statistical behavior of the field lines, we consider their topology-specified structure and theoretically derive power laws for the distribution of magnetic flux and helicity. We find a power law of ‑7/4 to the magnetic helicity distribution when the field line topology is equivalent to handle and ‑5/4 when the field line topology is local open curve. We verify the universality of this new magnetic helicity fractality by observation to a number of 185 sunspots in newly emerging active regions during the 23rd and 24th solar cycle. This new distribution law reveals the fractal structure of the solar magnetic field.

Keywords: Solar magnetic fields, Solar physics, Magnetic fields, Solar corona
Comparison of Global H I and Hα Line Profiles in MaNGA Galaxy Pairs with FAST. We present case studies comparing the global H I and Hα emission line profiles of six galaxy pairs. The six pairs are selected to have different nuclear activities, with two hosting an active galactic nucleus, and in different merging stages—two of each from the premerging, merging, and postmerging stages. We observe their global H I spectra with the Five-hundred-meter Aperture Spherical radio Telescope, achieving a noise level of ~0.5 mJy. Five out of the six pair systems have secure detections of H I emissions (signal-to-noise ratio &gt; 10). The H I fraction and star formation efficiency of the six pairs do not deviate from isolated galaxies. For the H I line profiles, common unique asymmetry is observed, indicating disturbances of the atomic gas from the galaxy interaction. The global Hα spectra of the merger systems are constructed from the optical integral field spectroscopic observations by integrating the flux in corresponding line-of-sight velocity bins. The Hα spectra tend to show multiple components in the premerger phase and single-component line profiles in the postmerger systems, while all H I spectra show single-component line profiles regardless of merger stages. The H I and Hα spectra show offsets in the central velocities, which appear to decrease from &gt;100 km s‑1 in the premerger pair to &lt;10 km s‑1 in the postmergers. This trend is consistent with the scenario that, despite the significantly different distributions and kinematics of the atomic and ionized gases, the merging process may contribute to the mixing and eventually align various gas contents.

Keywords: AGN host galaxies, Galaxy interactions, Interstellar line emission, H I line emission
LEIA Discovery of the Longest-lasting and Most Energetic Stellar X-Ray Flare Ever Detected. The Lobster Eye Imager for Astronomy (LEIA) detected a new X-ray transient on 2022 November 7, identified as a superflare event occurring on a nearby K-type giant star HD 251108. The flux increase was also detected in follow-up observations at X-ray, UV, and optical wavelengths. The flare lasted for about 40 days in soft X-ray observations, reaching a peak luminosity of ∼1.1 × 1034 erg s‑1 in 0.5–4.0 keV, which is roughly 60 times the quiescent luminosity. Optical brightening was observed for only one night. The X-ray light curve is well described by a double fast rise and exponential decay model, attributed to the cooling process of a loop arcade structure formed subsequent to the initial large loop with a half-length of ∼1.9 × 1012 cm. Time-resolved X-ray spectra were fitted by a four-temperature apec model (with three components being the quiescent background), showing significant evolution of plasma temperature and emission measure over time. The estimated energy released in the LEIA band is ∼3 × 1039 erg, suggesting that this is likely the most energetic X-ray stellar flare with the longest duration detected to date.

Keywords: X-ray transient sources, Stellar flares, Stellar activity
ALMA 0.1 pc View of Molecular Clouds Associated with High-mass Protostellar Systems in the Small Magellanic Cloud: Are Low-metallicity Clouds Filamentary or Not?. Filamentary molecular clouds are an essential intermediate stage in the star formation process. To test whether these structures are universal throughout cosmic star formation history, it is crucial to study low-metallicity environments within the Local Group. We present an analysis of Atacama Large Millimeter/submillimeter Array (ALMA) archival data at the spatial resolution of ~0.1 pc for 17 massive young stellar objects (YSOs) in the Small Magellanic Cloud (SMC; Z ~ 0.2 Z⊙). This sample represents approximately 30% of the YSOs confirmed by Spitzer spectroscopy. Early ALMA studies of the SMC have shown that the CO emission line traces an H2 number density of ≳104 cm‑3, an order of magnitude higher than in typical Galactic environments. Using the CO(J = 3–2) data, we investigate the spatial and velocity distribution of molecular clouds. Our analysis shows that about 60% of the clouds have steep radial profiles from the spine of the elongated structures, while the remaining clouds have a smooth distribution and are characterized by lower brightness temperatures. We categorize the former as filaments and the latter as nonfilaments. Some of the filamentary clouds are associated with YSOs with outflows and exhibit higher temperatures, likely reflecting their formation conditions, suggesting that these clouds are younger than the nonfilamentary ones. This indicates that even if filaments form during star formation, their steep structures may become less prominent and transition to a lower-temperature state. Such transitions in structure and temperature have not been reported in metal-rich regions, highlighting a key behavior for characterizing the evolution of the interstellar medium and star formation in low-metallicity environments.

Keywords: Local Group, Interstellar filaments, Small Magellanic Cloud, Molecular clouds, Star formation, Interstellar medium, Protostars