Sazuna/UAT_keywords huggingface dataset:
Propagation of a Precessing Jet in the Envelope of Tidal Disruption Events. It is likely that the disk of a tidal disruption event (TDE) is misaligned with respect to the equatorial plane of the spinning supermassive black hole (SMBH), since the initial stellar orbit before disruption most likely has an inclined orbital plane. Such a misaligned disk undergoes Lense─Thirring precession around the SMBH spin axis, leading to a precessing jet if launched in the vicinity of the SMBH and aligned with the disk angular momentum. The bound debris can also build a thick envelope that powers optical emission. In this work, we study the propagation of the precessing jet in the TDE envelope. We adopt a "zero-Bernoulli accretion" (ZEBRA) envelope model. An episodic jet will be observed if the line of sight is just at the envelope pole direction and θLT = θenv, since the jet can freely escape from this low-density rotation funnel, where θLT and θenv are the jet precessing angle and the angle between the envelope polar axis and the SMBH spin axis, respectively. The jet will be choked at other directions. For θLT &lt; θenv, the jets can also break out of the envelope for very small precession angle θLT or if the jet is aligned with SMBH spin. If the jet is choked within the envelope, the radiation produced during the cocoon shock breakout will imprint characteristic signatures on the X-ray emission, such as low-amplitude fluctuation in the light curve.

Keywords: Tidal disruption
The Impact of Space Weather on Earth's Atmospheric Chemistry and Climate: Is N<SUB>2</SUB>O a Solution to the Faint Young Sun Paradox?. Space weather could have a profound impact on Earth's climate. Compared to the present-day Sun, the young Sun would have been more magnetically active and should have experienced more frequent extreme space weather events, in the form of coronal mass ejections and solar energetic particles, which steadily bombarded Earth's upper atmosphere. These particles enhanced atmospheric chemistry, potentially resulting in large amounts of kinetically produced greenhouse gases, such as CO, H2, N2O, and HCN. In this work, to explore whether the Sun─Earth interaction could address the faint young Sun paradox (FYSP), we use a chain of three models: (i) an Earth-like planet surface temperature model, (ii) a radiative-convective model (EOS), and (iii) a thermochemical and photochemical kinetic model. We also apply this modeling pipeline to the present-day Earth atmosphere to assess the potential impact of a prolonged period of intense solar activity. Our main results can be summarized as follows. First, we find that, for an Archean Earth-like atmosphere of 90% N2, 10% CO2, and trace amounts of either CH4 or H2, the surface temperature increase due to space weather-produced greenhouse species is no larger than 0.3 K, which makes this solution to the FYSP unviable. Second, we find that the contribution of nitrogen species (N2O and HCN) to this temperature increase is negligible and that the main greenhouse contributors are instead CO and H2. Third, on present-day conditions, the cumulative effects of a prolonged period of intense solar activity would decrease the surface temperature by ∼3 K.

Keywords: Solar flares, Planetary atmospheres, Solar coronal mass ejections, Solar activity, Star-planet interactions
21 cm Signal from the Thermal Evolution of Lyα during Cosmic Dawn. The Lyα photons couple the spin temperature of neutral hydrogen (H I) to the kinetic temperature during the era of cosmic dawn (CD). During this process, they also exchange energy with the medium, heating and cooling the H I. In addition, we expect X-ray photons to heat the mostly neutral gas during this era. We solve this coupled system (Lyα─H I system along with X-ray heating) for a period of 500 Myr (redshift range 8 &lt; z &lt; 25). Our main results are: (a) Without X-ray heating, the temperature of the gas reaches an equilibrium, which is nearly independent of photon intensity and only weakly dependent on the expansion of the Universe. The main determinant of the quasi-static temperature is the ratio of injected and continuum Lyα photons. (b) While X-ray photons provide an additional source of heating at initial times, for large enough Lyα photon intensity, the system tends to reach the same quasi-static temperature as expected without additional heating. This limit is reached when the density of photons close to the Lyα resonance far exceeds the H I number density. (c) We compute the global H I signal for these scenarios. In the limit of the large density of Lyα photons, the spin temperature of the hyperfine line is fixed. This freezes the global H I signal from the era of CD and the crossover redshift from absorption to emission. This feature depends only on the ratio of injected to continuum Lyα photons, and the global H I signal can help us determine this ratio.

Keywords: Cosmology, Reionization, Intergalactic medium, H I line emission
Hubble Reveals Complex Multiscale Structure in the Edge-on Protoplanetary Disk IRAS23077+6707. We present high-resolution ( ≲0.″1 ) Hubble Space Telescope/Wide Field Camera 3 imaging of the near edge-on (i ∼ 80°) protoplanetary disk IRAS23077+6707 ("Dracula's Chivito"), obtained across six broadband filters spanning 0.4─1.6 μm. These observations unveil the scattered light from this unusually large disk (∼14″, or ∼4200 au at 300 pc) in remarkable detail, revealing a rich tapestry of substructures, including brightness asymmetries and signatures of dynamical activity. Extended filaments are detected extending ∼10″ from the northern edges of both nebulae, while no comparable southern features are observed. In addition to large-scale asymmetries, the disk exhibits prominent wispy features that extend well above the midplane and are visible in all filters, suggesting a complex, possibly turbulent outer disk atmosphere shaped by infall, dynamical stirring, or gravitational instability. The central dark lane narrows from optical to near-IR wavelengths, and high-resolution millimeter data reveal compact midplane emission. Although our radiative transfer simulations show that the current data cannot yet distinguish between dust settling and no-settling scenarios, they underscore the need for resolved midinfrared observations of this unique system. IRAS23077 thus represents a rare and valuable laboratory for studying the vertical structure, asymmetries, and evolutionary state of protoplanetary disks.

Keywords: Herbig Ae/Be stars, Hubble Space Telescope, Protoplanetary disks, Circumstellar dust, Planet formation
Mode Composition Shapes Magnetic Anisotropy in Solar Wind Turbulence. Turbulence is a ubiquitous process that transfers energy across many spatial and temporal scales, thereby influencing particle transport and heating. Recent progress has improved our understanding of the anisotropy of turbulence with respect to the mean magnetic field; however, its exact form and implications for magnetic topology and energy transfer remain unclear. In this study, we investigate the nature of magnetic anisotropy in compressible magnetohydrodynamic turbulence within low-β solar wind using measurements from the Cluster spacecraft. By decomposing small-amplitude fluctuations into Alfvén and compressible modes, we reveal that magnetic anisotropy is largely mode dependent: Alfvénic fluctuations are broadly distributed in propagation angle, whereas compressible fluctuations are concentrated near the quasi-parallel (slab) direction, a feature closely linked to collisionless damping of compressible modes. For β → 0, compressible modes become dominant within the slab component at smaller scales. These findings advance our understanding of magnetic anisotropy in solar wind turbulence and offer a new perspective on the three-dimensional turbulence cascade, with broad implications for particle transport, acceleration, and magnetic reconnection.

Keywords: Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Plasma astrophysics, Interplanetary physics
Nondetection of FAST and Parkes Follow-up Observation for 27 Parkes-discovered Fast Radio Bursts. To investigate whether apparently nonrepeating fast radio bursts (FRBs) are truly one-off transients, we conducted systematic follow-up observations of 27 out of 81 nonrepeating FRBs identified in the Parkes Transient Database. Using 59.0 hr of data from the Parkes Ultra-Wideband Low receiver and 6.3 hr from the Five-hundred-meter Aperture Spherical Telescope 19-beam receiver, we searched for repeated bursts from these sources. No additional bursts were detected from any of the 27 FRBs. Combining these nondetections with prior archival observations, we derived stringent upper limits on their repetition rates above 1 Jy under two statistical models: Poisson process constraints range from ∼10−3.5 to 10−1.9 hr−1, while Weibull process constraints range from ∼10−3.4 to 10−1.5 hr−1. These limits are approximately an order of magnitude stricter than those reported in previous studies. By applying consistent observational setups and analytical methodologies across all sources, the derived rate limits converge to a narrow, well-defined range. This suggests that these FRBs form a relatively homogeneous population with extremely low intrinsic activity rates.

Keywords: Radio bursts, Astronomy databases, Radio transient sources
Little Red Dots as Late-stage Quasi-stars. We argue that the "Little Red Dots" (LRDs) discovered with the James Webb Space Telescope are quasi-stars in their late stages of evolution. Quasi-stars are hypothetical objects predicted to form following the core collapse of supermassive stars and consist of black holes (BHs) accreting from massive envelopes at a super-Eddington rate. We show that models of late-stage quasi-stars, with BH masses exceeding ∼10% of the total, predict thermal and radiative properties that are insensitive to both BH and envelope mass and spectrally resemble LRDs. Specifically, we show that they are likely to exhibit reddish colors, a strong Balmer break, and possess conditions favorable to the production of Balmer lines that are broadened by electron scattering. Their huge electron column densities suppress any X-rays. Late-stage quasi-stars, with BH masses ≳106 M⊙, should dominate the overall quasi-star population. Their short predicted lifetimes (tens of Myr), coupled with the high observed comoving density of LRDs, suggest that most or all supermassive BHs go through a quasi-star/LRD phase during their formation and growth.

Keywords: Accretion, Supermassive black holes, Quasars, Active galactic nuclei, High-redshift galaxies
XRISM Observations of Accretion Disk Corona in Cyg X-2. We present the high-resolution X-ray spectrum of the Z-source Cygnus X-2, obtained with the X-Ray Imaging and Spectroscopy Mission (XRISM). The observations have enabled a precise characterization of the Fe─K emission lines from the accretion disk corona (ADC) and a possible detection of an ultrafast outflow. The ADC component has at least two distinct regions. The Fe─K emission lines are remarkably broad, with a velocity dispersion of  σv=2300−700+900  km s−1. This can be larger than what was observed in previous Chandra observations (1120 ± 870 km s−1) and recent XRISM observations of the similar Z-source GX 340+0 (360─800 km s−1). Furthermore, we marginally detect a blueshifted absorption feature, which we identify as either Fe XXVI or Fe XXV, with outflow velocities of −0.29c or −0.26c, respectively. The mass loss rate is  Ṁ∼10−8M⊙yr−1 . Our findings suggest that the ADC in Cyg X-2 has a kinematically active environment with a high degree of turbulence and kinetic energy.

Keywords: Accretion, Neutron stars, X-ray binary stars, High energy astrophysics, Low-mass x-ray binary stars
Revealing Limitation in the Standard Cosmological Model: A Redshift-dependent Hubble Constant from Fast Radio Bursts. A major issue in contemporary cosmology is the persistent discrepancy, known as the Hubble tension, between the Hubble constant (H0) estimates from local measurements and those inferred from early-Universe observations under the standard Lambda cold dark matter (ΛCDM) paradigm. Recent advances have identified fast radio bursts (FRBs), a class of extragalactic phenomena observable at considerable redshifts, as a promising observational tool for probing late-time cosmology. In this study, we incorporate two complementary methodologies, machine learning algorithms and Bayesian analysis, on a set of localized FRBs to rigorously test the consistency of the ΛCDM model at late cosmic epochs. Our results reveal a statistically significant redshift-dependent variation of H0 when using separate priors on baryon density parameters Ωb or Ωbh2, indicating contradiction to the core postulate of ΛCDM. However, when the priors are combined, this redshift dependence disappears, yielding a consistent estimate of H0. We further validate that the redshift dependency of H0 can be removed within the more flexible framework of the w0waCDM model even without combining the priors. These findings highlight that the redshift evolution of H0 is not merely an artifact of the standard model but an indication of a deeper inadequacy in the ΛCDM model, supporting the need for a more flexible cosmological framework.

Keywords: Cosmology, Cosmological models, Neural networks, Cosmological parameters, Hubble constant, Radio transient sources
Modeling Reflection Spectra of Super-Eddington X-Ray Sources. Relativistic reflection is a common feature in the X-ray observations of accreting compact objects. We present reflux, a new X-ray reflection model for spectral analysis of super-Eddington sources. We develop two relativistic reflection frameworks for super-Eddington accretion: a slim-disk model that self-consistently accounts for disk thickening and self-shadowing and an optically thick wind model that treats reflection off a funnel-shaped outflow. The slim-disk model offers a geometry where the inner disk thickness is proportional to radius, becoming thicker as the mass accretion rate increases. The wind model measures the opening angle of the funnel, the wind speed, and wind acceleration radius. The slim-disk profile reduces the brightness of the blue horn in the Fe K emission line for a fixed emissivity and significantly changes the intensity profile for a lamppost geometry. The wind model shows a blueshifted iron line due to high-velocity outflows. Both models assume a spherically symmetric spacetime. We apply the wind model to the XMM-Newton spectrum of the tidal disruption event Swift J1644+57, where the Fe K profile is expected to be shaped by scattering in an outflowing funnel. We constrain the opening angle of the funnel and find a high velocity of the wind.

Keywords: X-ray astronomy, Neutron stars, Accretion, Ultraluminous x-ray sources, Astrophysical black holes
The Gas-phase Nitridation Processes of Fullerene Cations in the Interstellar Medium. The chemical evolution of fullerene molecules is an important and interesting topic in astrochemistry. In this work, the coevolution processes occurring in fullerene cations ([C60]+ and [C58/56]+) in response to ultraviolet radiation and N atom bombardment are first investigated in the gas phase. A series of nitridated fullerene cations (e.g., [C60N(1−5)]+ and [C56/58N]+) are observed. An N atom loss channel and no CN-unit loss channel are identified during their photodissociation processes. Through quantum chemistry electronic structure calculations, the structures of the nitridated fullerene cations ([C60N]+) and bonding energies for their formation pathways are obtained. The exothermic energy is relatively high; consequently, the nitridation states and forms of interstellar fullerenes may be complex and stable. Importantly, we infer that the photodissociation of nitridated fullerene species is not involved in the top-down chemical evolution routes of buckminsterfullerene (C60) in the interstellar medium. Moreover, the IR spectra of functionalized (i.e., nitridated, oxygenated, sulfurated, hydrogenated, and deuterated) fullerene cations are discussed in light of astronomical observations.

Keywords: Interstellar molecules, Laboratory astrophysics, Astrochemistry, Interstellar medium, Diffuse molecular clouds
Role of Magnetic Reconnection in Blazar Variability Using Numerical Simulation. Fast γ-ray variability in blazars remains a central puzzle in high-energy astrophysics, challenging standard shock acceleration models. Blazars, a subclass of active galactic nuclei with jets pointed close to our line of sight, offer a unique view into jet dynamics. Blazar γ-ray light curves exhibit rapid, high-amplitude flares that point to promising alternative dissipation mechanisms such as magnetic reconnection. This study uses three-dimensional relativistic magnetohydrodynamic (RMHD) and resistive relativistic magnetohydrodynamic (ResRMHD) simulations with the PLUTO code to explore magnetic reconnection in turbulent, magnetized plasma columns. Focusing on current-driven kink instabilities, we identify the formation of current sheets due to magnetic reconnection, leading to plasmoid formation. We develop a novel technique combining hierarchical structure analysis and reconnection diagnostics to identify reconnecting current sheets. A statistical analysis of their geometry and orientation reveals a smaller subset that aligns closely with the jet axis, consistent with the jet-in-jet model. These structures can generate relativistically moving plasmoids with significant Doppler boosting, offering a plausible mechanism for the fast flares superimposed on slowly varying blazar light curves. These findings provide new insights into the plasma dynamics of relativistic jets and strengthen the case for magnetic reconnection as a key mechanism in blazar γ-ray variability.

Keywords: Relativistic jets, Active galactic nuclei, High energy astrophysics, Magnetohydrodynamical simulations
KIC 5623923: A Faint Eclipsing Binary Consisting of δ Scuti Pulsations. In this paper, we present a detailed analysis of the light variation of KIC 5623923 using high-precision time-series data from the Kepler mission. The analysis reveals this target is an eclipsing binary system with δ Scuti-type pulsations from the primary component, rather than from the secondary as previously reported. The frequency analysis of three short-cadence data reveals 41 significant frequencies, including the orbital frequency (forb = 0.827198 day−1) due to orbital motion from the binary system and the pulsational frequencies. Most of the pulsational signal lies in the frequency range of 20─32 day−1, with amplitude between 0.3 and 8.8 mmag, in which seven peaks are identified as "independent" modes. The strongest one (f3 = 28.499399 day−1) likely corresponds to a high-order radial mode. In other peaks (f7, f10, and f18), several pairs of multiplet structures centered on them are found. The fitting of spectral energy distribution using the collected photometry measurement of multiple bands reveals the effective temperatures of the primary and secondary components as  8348−225+230  K and  4753−229+237  K, respectively, which place the primary star in the classical pulsating instability zone. The characteristic light-curve morphology and short orbital period are consistent with a tidally locked system. Based on the characteristics of amplitude spectra of pulsating stars in close binaries, the analysis of the multiplet structures reveals that three independent frequencies (i.e., f7, f10, and f18) correspond to nonradial modes with l = 2, while the associated sidelobes are produced by the orbital motion. We highlight the potential of this method in future studies of pulsating binary stars.

Keywords: Short period variable stars, Stellar oscillations, Eclipsing binary stars, Delta Scuti variable stars
Microwave Bright Points with Multiple Periodic Oscillations in the Solar Polar Coronal Hole during Solar Cycle Minimum. During solar cycle minimum, polar coronal holes show a prominent radio brightening cap. The analysis of polar microwave enhanced radiation in polar coronal holes is helpful for understanding the magnetic field characteristics and the origin of the solar wind. Using the Koshix synthesis method on Nobeyama Radioheliograph data, we identified microwave bright points (BPs) superposed on the microwave brightening cap of the northern polar coronal hole. These microwave BPs manifested intermittently at fixed locations, with their radiation intensities displaying multiperiodic oscillations (20 s, 50 s, and 2.5 minutes). Multiwavelength analysis revealed that nearly all BPs were adjacent to or coincide with 171 Å open structures, indicating a strong correlation between microwave BPs and solar wind, propagating along the open field lines. At lower layers, BPs were associated with bright ribbons in the chromosphere and local enhanced magnetic structures in photosphere. The 20 s lifetime of microwave BP enhancement corresponds to their shortest oscillation period, which, in the temporal characteristics of Alfvén waves, implies a localized heating or a small-scale magnetic reconnection process modulated by Alfvén waves at the root of open magnetic field lines. The microwave 2.5 minute and 171 Å 5 minute oscillations likely stem from chromospheric and photospheric oscillation leakage/propagation, respectively. And longer-period (12 minute) oscillations in 171 Å open structures may link to large-scale coronal hole evolution. The multiperiod oscillatory processes in the polar coronal hole imply complex plasma dynamics inside, which contributes to our understanding of the origin and propagation of solar wind along the open structures in the coronal hole.

Keywords: Magnetohydrodynamics, Solar wind, Solar radio emission, Solar oscillations, Solar coronal holes
A Jovian Decametric Emission Event Observed Locally by Juno and Remotely by Wind and STEREO-A at 1 au. Juno in situ observations provide insightful data on plasma, electric, and magnetic fields associated with Jovian decametric (DAM) emission, while remote-sensing observations offer broader spatial and temporal coverage. Combining both perspectives may help us understand the dynamic processes of DAM radiation. In this work, we present an Io-related DAM emission continued intermittently for at least 2 hr, observed by Juno in situ and remotely by Wind and STEREO-A. The Io-DAM emission evolved from three discrete narrow arcs to one mixed broad arc within 11 minutes in remote-sensing dynamic spectra. The source remained near a lead angle of 6° from the main Alfvén wing spot during the observation. Juno/JADE detected peaks in electron energy flux and an upward loss-cone distribution. Using a set of resonance circles, we estimate a maximum growth rate γ/ωc of 6.4 × 10−4, corresponding to electron energies of 0.2─10 keV and emission angles of 77°─88°. Meanwhile, we infer the properties of the source region of the event from the remote-sensing observations at 1 au. The inferred results on electron energy, emission angle, and source locations are consistent with the Juno in situ observations, suggesting the consistent properties of this Io-DAM event over 2 hr observational intervals. This consistency also reinforces the reliability of the remote sensing inversion method. Our work contributes to the establishment of long-term stereoscopic remote monitoring, addressing limitations in local observational coverage and enhancing our understanding of the dynamic processes of DAM emission.

Keywords: Magnetospheric radio emissions, Jupiter, Remote sensing, Planetary science, Radio observatories, Planetary magnetospheres, Jovian satellites, Solar system astronomy