Sazuna/UAT_keywords huggingface dataset:
Classification of Radio Backgrounds at Cosmic Dawn and 21 cm Signal Confirmation Using Neural Networks. Several ongoing and upcoming radio telescopes aim to detect either the global 21 cm signal or the 21 cm power spectrum. The extragalactic radio background, as detected by ARCADE-2 and LWA-1, suggests a strong radio background from cosmic dawn, which can significantly alter the cosmological 21 cm signal, enhancing both the global signal amplitude and the 21 cm power spectrum. In this paper, we employ an artificial neural network (ANN) to check if there is a radio excess over the cosmic microwave background in mock data, and if present, we classify its type into one of two categories, a background from high-redshift radio galaxies or a uniform exotic background from the early Universe. Based on clean data (without observational noise), the ANN can predict the type of background radiation with 96% accuracy for the power spectrum and 90% for the global signal. Although observational noise reduces the accuracy, the results remain quite useful. We also apply ANNs to map the relation between the 21 cm power spectrum and the global signal. By predicting the global signal using the 21 cm power spectrum, an ANN can estimate the global signal range consistent with an observed power spectrum from SKA-like experiments. Conversely, we show that an ANN can predict the 21 cm power spectrum over a wide range of redshifts and wavenumbers given the global signal over the same redshifts. Such trained networks can potentially serve as valuable tools for cross-confirmation of the 21 cm signal.

Keywords: Cosmology, Early universe, H I line emission
Hunt for the mHz Variability in TESS and XMM-Newton Observations of Nova-like Cataclysmic Variables. We analysed the flickering of selected nova-like cataclysmic variables observed by the TESS satellite and XMM-Newton. We searched for break frequencies (fb) in the corresponding power density spectra (PDSs), and for any long-term evolution. We find a new optical fb in three nova-like systems, and confirm that the value of this frequency is clustered around 1 mHz. V504 Cen and V751 Cyg show possible X-ray counterparts of fb that had previously only been seen in MV Lyr. This points toward the very central disk for source localization. We investigated a previously proposed correlation between white dwarf mass and fb, but thanks to the new measurements, we do not confirm its existence. V3885 Sgr and V1193 Ori show flaring activity in the long-term light curve during which TESS observations were made. The corresponding PDSs show changes in shape and the disappearance of fb. TT Ari and SGRt 062340.2−265715 exhibit smooth changes in the long-term optical light curve, and the corresponding TESS observations show variable fb during these changes. fb is higher at lower brightness levels, which so far has been observed only in MV Lyr.

Keywords: Stellar accretion disks, White dwarf stars, Cataclysmic variable stars
Episodic Feedback in Triple Active Galactic Nucleus Candidate SDSS J0849+1114 Revealed by Extended Ionized Gas. Galaxy mergers funnel gas toward the nuclei, igniting starbursts and active galactic nuclei (AGNs). The AGN feedback can reshape the host galaxy and regulate both star formation and supermassive black hole accretion. Using Very Large Telescope/MUSE integral-field spectroscopy, we conduct a spatially resolved study of the triple-AGN candidate SDSS J0849+1114. Extended ionized gas structures (&gt;10 kpc from nucleus A) primarily associated with tidal tails are detected. Meanwhile, two distinct ionized gas outflows are revealed. One extends over &gt;5 kpc around nuclei A with a kinetic power of  Ėout,A=3.0×1042ergs−1 , which might be driven by the radio jet. The other outflow extends ∼5.9 kpc around nucleus C, with a kinetic power of  Ėout,C  = 2.0 × 1040 erg s−1. High [O III]/Hα and [N II]/Hα ratios in the tidal gas require that nucleus A radiated at a high accretion rate with LA,bol ∼ 0.1─0.5 LEdd,A at least ∼3─×104 yr ago, 20─100 times brighter than today. Combined with multiwavelength constraints, we find evidence for episodic AGN feedback that expelled circumnuclear gas and rapidly quenched accretion. This triple AGN candidate demonstrates how AGN feedback can self-regulate black hole growth and impact hosts during mergers.

Keywords: Interacting galaxies, Galaxy winds, Interstellar medium
Polarized Signatures of Variable Worlds: Modeling Heterogeneous Habitable Earth- and Early Mars-like (Exo)planets. Determining the habitability of terrestrial exoplanets is a complex problem that represents the next major step for the astrophysical community. The majority of current models treat these planets as homogeneous or contain heterogeneity that is constant in time. In reality, habitable exoplanets are expected to contain atmospheric and surface heterogeneities similar to Earth, with diurnal rotation, seasonal changes, and weather patterns resulting in complex, time-dependent signatures. Due to its ability to measure light as a vector, polarimetry provides an important tool that will enhance the characterizations of heterogeneous worlds. Here we model the visible to near-infrared linear spectropolarimetric signatures, as functions of wavelength and planetary phase angle, of various heterogeneous Earth scenarios as well as the first signals of an early wet and potentially habitable Mars. The contributions from the different atmospheric and surface properties result in asymmetric phase curves and variable spectra, with the polarization appearing to be more sensitive than flux to heterogeneities such as patchy clouds and continents moving into and out of view. Our models provide important predictions of expected polarized and unpolarized signatures of heterogeneous exoplanets that will help guide the designs and observing plans of future polarimeters, including those proposed for the upcoming Habitable Worlds Observatory.

Keywords: Spectropolarimetry, Exoplanets, Planetary atmospheres, Radiative transfer, Polarimetry, Habitable planets
Can Repeating and Nonrepeating Fast Radio Bursts Be Drawn from the Same Population?. Do all fast radio burst (FRB) sources repeat? We present evidence that FRB sources follow a Zipf-like distribution, in which the number density of sources is approximately inversely proportional to their burst rate above a fixed energy threshold—even though both the burst rate and number density span many orders of magnitude individually. We introduce a model-independent framework that predicts the distribution of observed fluences and distances, and the repetition rates of an FRB population based on an assumed burst rate distribution per source. Using parameters derived directly from observations, this framework simultaneously explains several key features of the FRB population: (i) the observed ratio of repeaters to apparent nonrepeaters; (ii) the much lower ratio of apparent nonrepeaters to the total number of soft gamma repeater (SGR) sources within the observable Universe; and (iii) the slightly smaller average distances of known repeaters compared to nonrepeaters. We further explore how survey parameters, such as radio sensitivity and observation time, influence these statistics. Notably, we find that the fraction of repeaters rises only mildly with improved sensitivity or longer exposure. This weak dependence could be misinterpreted as evidence that not all FRBs repeat. Overall, our results support the idea that a single population—likely magnetars—can account for the full observed diversity of FRB activity, from very inactive FRB sources like SGR 1935+2154 to the most active repeaters.

Keywords: Magnetars, Radio transient sources
The Hot Inner AU of V883 Ori. The V883 Ori system is a rapidly accreting young stellar object that has been used as a laboratory for studying the molecular inventory of young circumstellar disks with high luminosity. We simultaneously fit high-resolution spectroscopy and medium-resolution spectrophotometry of the system to constrain the physical conditions in the inner au. Using our thin viscous accretion disk model, we find  Ṁ=10−3.9±0.2M⊙  yr−1, Rinner = 5.86 ± 1 R⊙, i = 38 .° 2 ± 3°, and AV = 20.8 ± 0.7 mag, resulting in an accretion luminosity of 458 L⊙ and maximum disk temperature of 7045 K. The optical portion of the spectral energy distribution greatly exceeds the flux level expected for a highly extincted accretion disk. We propose that the excess emission arises from a contribution due to scattering of the accretion disk spectrum off nearby envelope material that is viewed along a line of sight with less extinction. Additionally, we use photometric observations spanning 137 years to demonstrate that the source has accreted at least 18 MJup of disk material to date. Finally, we discuss the importance of considering both the viscous heating from the midplane and the consequent irradiation effects on the outer disk when modeling the temperature structure to reproduce millimeter-wavelength observations.

Keywords: High resolution spectroscopy, FU Orionis stars, Light curves, Young stellar objects, Protoplanetary disks, Near infrared astronomy
SN 2023ixf in M101: Physical Parameters from Bolometric Light Curve Modeling. We present new photometric observations of the core-collapse supernova SN 2023ixf occurred in M101, taken with the RC 80 and BRC80 robotic telescopes in Hungary. The initial nickel mass from the late-phase bolometric light curve extending up to 400 days after explosion, is inferred as MNi = 0.046 ± 0.007 M⊙. The comparison of the bolometric light curve with models from hydrodynamical simulations as well as semi-analytic radiative diffusion codes reveals a relatively low-mass ejecta of Mej ≲ 9 M⊙, contrary to SN 2017eaw, another H-rich core-collapse event, which had Mej ≳ 15 M⊙.

Keywords: Type II supernovae, Late stellar evolution, Core-collapse supernovae, Radiative processes
Temporal Evolution of Quasiperiodic Oscillations in an Accreting Black Hole Swift J1727.8-1613: Coevolution of the Disk─Corona during the State Transition. Low-frequency quasiperiodic oscillations (QPOs) are commonly observed in black hole X-ray binaries, and their frequency has been found to correlate with various spectral properties. In this work, we present a detailed timing analysis of Swift J1727.8-1613, revealing a novel two-branch correlation between the QPO frequency and the observed disk emission, which differs from previous findings of a single correlation. Specifically, at QPO frequencies below 3 Hz, the QPO frequency is negatively correlated with the observed disk emission. This negative relation transitions to a positive one, as the QPO frequency exceeds approximately 3 Hz. The correlation between QPO frequency and Compton flux exhibits an opposite trend, with a positive correlation at lower frequencies and a negative correlation at higher ones. We interpret these behaviors as signatures of an evolving disk─corona geometry, within the framework of a Lense─Thirring precessing hot flow. Additionally, we find that during the flare state, the QPO fractional rms remains nearly constant above 15 keV, but increases with energy below this threshold. The slope of the rms─energy relation increases as the energy spectrum softens.

Keywords: Accretion, Black hole physics, Low-mass x-ray binary stars, X-ray astronomy
Simulations of Flare Chemistry in Brown Dwarf Companions to Active M Dwarfs. Brown dwarfs that are short-period (&lt;10 days) companions to actively flaring M dwarfs may provide a context to directly observe flare-driven photochemistry and structural changes in an extrasolar planet-like atmosphere. To assess the viability of directly observing flare impacts in the atmosphere of a brown dwarf, we perform self-consistent temperature─chemistry modeling of the atmospheric response to individual energetic superflares. We modified the existing open-source VULCAN chemical─kinetics and HELIOS radiative-transfer codes for this purpose. Similar to previous studies of flare impacts on hydrogen-dominated atmospheres, we find flares are capable of orders-of-magnitude changes in the mixing abundances of many chemical species, including important opacity sources like CH4 and CO2. However, due to the fast chemical timescales resulting from high temperatures and densities in brown dwarf atmospheres, these changes last for a short period of time, generally less than a day, and are only plausibly observable via high-resolution emission spectroscopy. We find that the most observable, short-term spectral changes in hot (Teff ∼ 2000 K), high-gravity ( logg∼5 ), cloudless brown dwarfs are the photolysis of H2O and an enhancement of CO2, which can result in part-per-thousands spectral changes in the hours after a flare.

Keywords: Brown dwarfs, Upper atmosphere, Planetary atmospheres, L dwarfs, Stellar flares, Atmospheric composition, Star-planet interactions, Atmospheric variability
Environment of SDSS Quasars at z = 0.4─1.0 Explored by Subaru HSC. The relationship between quasars and their galaxy environment is important for understanding the evolution of galaxies and supermassive black holes, but it is not fully understood. We perform a wide and deep exploration of the environment of quasars at 0.4 &lt; z &lt; 1.0 using the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. We investigate the environment of the 1912 spectroscopically selected quasars from the Sloan Digital Sky Survey (SDSS), using photometrically selected galaxies from the HSC-SSP data, over an area of 505 deg2. The quasar environment is compared to the environment of matched galaxies with similar stellar mass and redshift. We employ the k-nearest neighbor method to define the local galaxy number density for both the quasars and the matched galaxies at a scale of a few hundred kpc. As a result, we find that the number density of galaxies around SDSS quasars is lower than that of the matched galaxies by ∼11%─20%. We also investigate possible correlations between the local galaxy number densities and the quasar properties such as black hole mass (MBH) and Eddington ratio (REdd). We find that the number density is weakly correlated with MBH and only marginally with REdd. The apparent correlation with MBH is likely driven by their common dependence on redshift rather than a direct physical connection, while the marginal trend with REdd is statistically insignificant. These results suggest that the quasar activity is not triggered by the high number density of surrounding galaxies at the scale of a few hundred kpc.

Keywords: Active galaxies, Active galactic nuclei, Quasars, Galaxy environments
Synthetic Ca II 8542 Å Stokes Profile Associated with Chromospheric Magnetic Reconnection in a Simulated Active Region. Magnetic reconnection is an important driving mechanism of many chromospheric phenomena, e.g., UV bursts and chromospheric jets. Information about magnetic fields is indispensable for analyzing chromospheric magnetic reconnection, which is mainly encoded in polarization signals. The purpose of this work is to predict possible Stokes features related to chromospheric reconnection events, from realistic two-dimensional magnetohydrodynamic simulation and Stokes profile synthesis. An emerging magnetic flux sheet is imposed at the bottom boundary of a well-relaxed unipolar atmosphere that spans from the upper convection zone to the corona. The reconnection region is heated to ∼7 kK and the outflow velocity reaches up to ∼35 km s−1. Through Stokes profile synthesis, several Stokes features related to reconnections and plasmoids are reproduced. We found sign reversal features on circular polarization and amplitude reduction features on linear polarization at reconnection sites. Also, we report strong linear and circular polarization signals corresponding to huge (∼300 km) and tiny (∼40 km) plasmoids, respectively. We conclude that both linear and circular polarization signals may reveal the distinctive physical mechanisms in reconnections and enhance our understanding of magnetic reconnection in observations.

Keywords: Magnetohydrodynamics, Spectropolarimetry, Solar magnetic reconnection, Solar activity, Solar chromosphere, Magnetic fields
Highly Ionized Gas in the Zone of Avoidance: Using the CIViL<SUP>⋆</SUP> Survey to Pinpoint Physical Conditions of Gaseous Halos. This paper investigates the physical conditions of the circumgalactic medium of L⋆ galaxies through explorations of observed ion tracer gas kinematics and comparisons of observations to different ionization models. For this analysis, we utilize C IV observations from the CIViL⋆ survey (∼0.14 ≤ zgal ≤ 0.25) and directly compare them to observations of matched lines of sight from the Cosmic Origins Spectrograph-Halos survey. We find that the kinematic parameters for C IV and O VI are likely (&gt;95%) drawn from the same parent distribution, suggesting that these two ions are kinematically coincident and potentially originate under the same physical conditions. We find that the measured C IV/O VI and N V/O VI ratios are inconsistent with single-phase equilibrium models. For 70% of the objects in our sample, regions allowed by the column density ratios in the density-temperature space do not overlap, creating a "zone of avoidance." We also investigate the origins of C IV, N V, and O VI by exploring a cooling flow model under collisional ionization. We find that both N V and O VI are consistent with the predictions of the model, but the column densities of C IV are ∼2.5 times higher than the predictions. As C IV has a lower ionization energy than N V and O VI, it is possible that C IV has contributions from both the warm/hot and cool photoionized phase.

Keywords: Galaxy evolution, Quasar absorption line spectroscopy, Circumgalactic medium
Optical Spectroscopy Reveals Hidden Neutron-capture Elemental Abundance Differences among APOGEE-identified Chemical Doppelgängers. Grouping stars by chemical similarity has the potential to reveal the Milky Way's evolutionary history. The APOGEE stellar spectroscopic survey has the resolution and sensitivity for this task. However, APOGEE lacks access to strong lines of neutron-capture elements (Z &gt; 28), which have nucleosynthetic origins that are distinct from those of the lighter elements. We assess whether APOGEE abundances are sufficient for selecting chemically similar disk stars by identifying 25 pairs of chemical "doppelgängers" in APOGEE DR17 and following them up with the Tull spectrograph, an optical, R ∼ 60,000 echelle on the McDonald Observatory 2.7 m telescope. Line-by-line differential analyses of pairs' optical spectra reveal neutron-capture (Y, Zr, Ba, La, Ce, Nd, and Eu) elemental abundance differences of ∆[X/Fe] ∼ 0.020 ± 0.015 to 0.380 ± 0.15 dex (4%─140%), and up to 0.05 dex (12%) on average, a factor of 1─2 times higher than intracluster pairs. This is despite the pairs sharing nearly identical APOGEE-reported abundances and [C/N] ratios, a tracer of giant-star age. This work illustrates that even when APOGEE abundances derived from spectra with a signal-to-noise ratio &gt; 300 are available, optically measured neutron-capture element abundances contain critical information about composition similarity. These results hold implications for the chemical dimensionality of the disk, mixing within the interstellar medium, and chemical tagging with the neutron-capture elements. *This paper includes data taken with the Harlan J. Smith 2.7 m telescope at The McDonald Observatory of The University of Texas at Austin.

Keywords: Surveys, S-process, Chemical abundances, Galaxy chemical evolution
The Optical to X-Ray Luminosity and Spectrum of Supernova Wind Breakouts. Observations indicate that an optically thick circumstellar medium (CSM) at radii of 1014─1015 cm around Type II core-collapse supernova (SN) progenitors is common (and may be present in other types of massive star explosions). The breakout of the SN radiation-mediated shock (RMS) through such a CSM leads to the formation of a collisionless shock (CLS). We analyze the evolution of the shock structure and associated radiation field during and after the RMS─CLS transition for nonrelativistic shock breakout velocities (vbo = 109 v9 cm s−1 &lt; 0.1c) through a hydrogen-rich CSM "wind" density profile, ρ ∝ r−2, with breakout radius Rbo = 1014 R14 cm, much larger than the progenitor radius. An analytic description of the key properties of the emitted optical to X-ray radiation is provided, supported by numeric radiation hydrodynamics calculations self-consistently describing the time-dependent spatial distribution of the plasma and radiation, governed by bremsstrahlung emission/absorption and inelastic Compton scattering. The characteristic energy of the photons carrying most of the luminosity,  ≍1043R14v92 erg s−1, shifts from UV to X-rays, reaching 1 keV as the shock reaches ≍3 Rbo, in ≍3 R14/v9 days. The X-ray signal is not suppressed by propagation through the upstream wind, and its absence may suggest that the dense CSM does not extend much beyond Rbo. Our results provide the basis for a quantitative calculation of the high-energy γ-ray and neutrino emission that is expected from particles accelerated at the CLS, and will allow using data from upcoming surveys that will systematically detect large numbers of young SNe, particularly ULTRASAT, to infer the preexplosion mass-loss history of the SN progenitor population.

Keywords: High energy astrophysics, Late stellar evolution, Stellar mass loss, X-ray transient sources, Time domain astronomy, Shocks, Supernovae, Ultraviolet transient sources
Electronic Spectroscopy of C<SUB>60</SUB><SUP>+</SUP> and Its Analogs C<SUB>60</SUB>H<SUB>2</SUB>O<SUP>+</SUP>, C<SUB>60</SUB>H<SUP>+</SUP>, C<SUB>60</SUB>D<SUP>+</SUP>, and C<SUB>60</SUB>Mg<SUP>+</SUP>. The fullerenes C60 and C70 have been detected in various interstellar environments, and the cation  C60+  has been identified as a carrier of at least four of the diffuse interstellar bands (DIBs). Based on the presence of fullerenes in space, it is plausible that certain fullerene analogs are abundant in interstellar environments as well. In this context, we present the first electronic laboratory spectra of the analogs C60H2O+, C60H+, C60D+, and C60Mg+. Furthermore, the electronic  C60+  spectrum is remeasured and assignments of the observed transitions are proposed. In the spectrum of C60H2O+, several distinct absorption features could be detected between 10,300 and 10,800 cm−1, whereas the analogs C60H+, C60D+, and C60Mg+ show a broad absorption in the visible region between 17,000 and 25,000 cm−1. None of the detected absorption features in these analogs of  C60+  could be assigned to DIBs.

Keywords: Interstellar molecules, Electronic spectroscopy, Diffuse interstellar bands, Fullerenes