Sazuna/UAT_keywords huggingface dataset:
Instability of Circumnuclear Gas Supply as an Origin of the "Changing-look" Phenomenon of Supermassive Black Holes. The origin of the "changing-look" (CL) phenomenon in supermassive black holes (SMBHs) remains an open issue. This study aims to shed light on this phenomenon by focusing on a sample that encompasses all known repeating CL active galactic nuclei (AGNs). Through the identification of a characteristic timescale for the CL phenomenon, it was observed that larger SMBHs possess shorter characteristic timescales, while smaller SMBHs exhibit longer timescales. These findings reveal a significant contrast to the traditional AGN variability that has been adequately explained by the AGN's disk instability model. This stark discrepancy highlights a distinct origin of the CL phenomenon, distinguishing it from traditional AGN variability. By properly predicting the characteristic timescale and its dependence on SMBH mass, we propose that the CL phenomenon is likely a result of a variation in accretion rate caused by a sudden change in the supply of circumnuclear gas during the transition between active and passive SMBH fueling stages.

Keywords: Accretion, Bondi accretion, Active galactic nuclei, Time domain astronomy, Spectroscopy, Galaxy evolution
AGEL: Is the Conflict Real? Investigating Galaxy Evolution Models Using Strong Lensing at 0.3 &lt; z &lt; 0.9. Observed evolution of the total mass distribution with redshift is crucial to testing galaxy evolution theories. To measure the total mass distribution, strong gravitational lenses complement the resolved dynamical observations that are currently limited to z ≲ 0.5. Here we present the lens models for a pilot sample of seven galaxy-scale lenses from the ASTRO3D Galaxy Evolution with Lenses (AGEL) survey. The AGEL lenses, modeled using HST/WFC3-F140W images with Gravitational Lens Efficient Explorer (GLEE) software, have deflector redshifts in the range 0.3 &lt; z defl &lt; 0.9. Assuming a power-law density profile with slope γ, we measure the total density profile for the deflector galaxies via lens modeling. We also measure the stellar velocity dispersions (σ obs) for four lenses and obtain σ obs from SDSS-BOSS for the remaining lenses to test our lens models by comparing observed and model-predicted velocity dispersions. For the seven AGEL lenses, we measure an average density profile slope of ‑1.95 ± 0.09 and a γ–z relation that does not evolve with redshift at z &lt; 1. Although our result is consistent with some observations and simulations, it differs from other studies at z &lt; 1 that suggest the γ–z relation evolves with redshift. The apparent conflicts among observations and simulations may be due to a combination of (1) systematics in the lensing and dynamical modeling; (2) challenges in comparing observations with simulations; and (3) assuming a simple power law for the total mass distribution. By providing more lenses at z defl &gt; 0.5, the AGEL survey will provide stronger constraints on whether the mass profiles evolve with redshift as predicted by current theoretical models.

Keywords: Strong gravitational lensing, Galaxy evolution, Galaxy mergers, Dark matter, Early-type galaxies
Applications of Fast Magnetic Reconnection Models to the Atmospheres of the Sun and Protoplanetary Disks. Partially ionized plasmas consist of charged and neutral particles whose mutual collisions modify magnetic reconnection compared with the fully ionized case. The collisions alter the rate and locations of the magnetic dissipation heating and the distribution of energies among the particles accelerated into the nonthermal tail. We examine the collisional regimes for the onset of fast reconnection in two environments: the partially ionized layers of the solar atmosphere, and the protoplanetary disks that are the birthplaces for planets around young stars. In both these environments, magnetic nulls readily develop into resistive current sheets in the regime where the charged and neutral particles are fully coupled by collisions, but the current sheets quickly break down under the ideal tearing instability. The current sheets collapse repeatedly, forming magnetic islands at successively smaller scales, until they enter a collisionally decoupled regime where the magnetic energy is rapidly turned into heat and charged-particle kinetic energy. Small-scale, decoupled fast reconnection in the solar atmosphere may lead to preferential heating and energization of ions and electrons that escape into the corona. In protoplanetary disks such reconnection causes localized heating in the atmospheric layers that produce much of the infrared atomic and molecular line emission observed with the Spitzer and James Webb Space Telescopes.

Keywords: Space plasmas, Protoplanetary disks, Solar magnetic reconnection, Plasma astrophysics
Does Metallicity Affect the Protoplanetary Disk Fraction? Answers from the Outer Milky Way. The role of metallicity in shaping protoplanetary disk evolution remains poorly comprehended. This study analyzes the disk fraction of 10 young (0.9–2.1 Myr) and low-metallicity (0.34–0.83 Z ⊙) clusters located in the outer Milky Way with Galactocentric distances between 10 and 13 kpc. Using JHK data obtained from UKIDSS, the calculated disk fraction values for low-mass stars (0.2–2 M ⊙) ranged from 42% to 7%. To enhance the statistical reliability of our analysis, eight additional low-metallicity clusters are sourced from previous studies with metallicity range 0.25–0.85 Z ⊙ along with our sample, resulting in a total of 18 regions with low metallicity. We find that low-metallicity clusters exhibit on average a 2.6 ± 0.2 times lower disk fraction compared to solar-metallicity clusters in all the age bins we have. Within the age range we can probe, our study does not find evidence of faster disk decay in subsolar-metallicity regions compared to solar-metallicity regions. Furthermore, we observe a positive correlation between cluster disk fraction and metallicity for two different age groups of 0.3–1.4 and 1.4–2.5 Myr. We emphasize that both cluster age and metallicity significantly affect the fraction of stars with evidence of inner disks.

Keywords: Star formation, Metallicity, Protoplanetary disks, Pre-main sequence
Tidal Disruption Event AT2020ocn: Early Time X-Ray Flares Caused by a Possible Disk Alignment Process. A tidal disruption event (TDE) may occur when a star is torn apart by the tidal force of a black hole (BH). Eventually, an accretion disk is thought to form out of stellar debris falling back toward the BH. If the star's orbital angular momentum vector prior to disruption is not aligned with the BH spin angular momentum vector, the disk will be tilted with respect to the BH equatorial plane. The disk will eventually be drawn into the BH equatorial plane due to a combination of the Bardeen─Petterson effect and internal torques. Here, we analyze the X-ray and UV observations of the TDE AT2020ocn obtained by Swift, XMM-Newton, and Neutron star Interior Composition ExploreR. The X-ray light curve shows strong flares during the first ≍100 days, while, over the same period, the UV emission decays gradually. We find that the X-ray flares can be explained by a model that also explains the spectral evolution. This model includes a slim disk viewed under a variable inclination plus an inverse-Comptonization component processing the slim disk emission. A scenario where the ongoing Lense─Thirring precession during the disk alignment process is responsible for the observed inclination variations is consistent with the data. In later observations, we find that the X-ray spectrum of AT2020ocn becomes harder, while the mass accretion rate remains at super-Eddington levels, suggesting the formation of a corona in line with accretion onto other compact objects. We constrain the BH mass to be  (7−3+13)×105  M ⊙ at the 1σ (68%) confidence level.

Keywords: X-ray astronomy, Tidal disruption, Accretion
VLBA Astrometry of the Galactic Double Neutron Stars PSR J0509+3801 and PSR J1930–1852: A Preliminary Transverse Velocity Distribution of Double Neutron Stars and its Implications. The mergers of double neutron star (DNS) systems are believed to drive the majority of short γ-ray bursts (SGRBs), while also serving as production sites of heavy r-process elements. Despite being key to (i) confirming the nature of the extragalactic SGRBs, (ii) addressing the poorly understood r-process enrichment in the ultrafaint dwarf galaxies (UFDGs), and (iii) probing the formation process of DNS systems, the space velocity distribution of DNSs is still poorly constrained, due to the small number of DNSs with well-determined astrometry. In this work, we determine new proper motions and parallaxes of two Galactic DNSs, PSR J0509+3801 and PSR J1930‑1852, using the Very Long Baseline Array, and we estimate the transverse velocities v ⊥ of all 11 isolated Galactic DNSs having proper-motion measurements in a consistent manner. Our correlation analysis reveals that the DNS v ⊥ is tentatively correlated with three parameters: spin period, orbital eccentricity, and companion mass. With the preliminary v ⊥ distribution, we obtain the following findings. First, the refined v ⊥ distribution is confirmed to agree with the observed displacements of the localized SGRBs from their host galaxy birth sites. Second, we estimate that around 11% and 25% of DNSs remain gravitationally bound to UFDGs with escape velocities of 15 and 25 km s‑1, respectively. Hence, the retained DNSs might indeed be responsible for the r-process enrichment confirmed so far in a few UFDGs. Finally, we discuss how a future ensemble of astrometrically determined DNSs may probe the multimodality of the v ⊥ distribution.

Keywords: Annual parallax, Very long baseline interferometry, Proper motions, Radio pulsars
Big Bang Nucleosynthesis with f(R) Gravity Scalarons and Astrophysical Consequences. f(R) gravity is one of the serious alternatives of general relativity with a large range of astronomical consequences. In this work, we study Big Bang nucleosynthesis (BBN) in f(R) gravity theory. We consider a modification to gravity due to the existence of primordial black holes (PBHs) in the radiation era that introduce additional degrees of freedom known as scalarons. We calculate the light element abundances by using the BBN code PArthENoPE. It is found that for a range of scalaron mass (2.2 ‑ 3.5) × 104 eV, the abundance of lithium is lowered by 3‑4 times the value predicted by general relativistic BBN, which is a level desired to address the cosmological lithium problem. For the above scalaron mass range, the helium abundance is within the observed bound. However, the deuterium abundance is found to be increased by 3‑6 times the observed primordial abundance. It calls for a high efficiency of stellar formation and evolution processes for the destruction of primordial deuterium, which is suggested as possible in scalaron gravity. A novel relation between scalaron mass and black hole mass has been used to show that the above scalaron mass range corresponds to PBHs of subplanetary mass (∼1019 g) serving as one of the potential candidates of nonbaryonic dark matter. We infer Big Bang equivalence of power-law f(R) gravity with PBHs that are detectable with upcoming gravitational wave detectors.

Keywords: Cosmology, Big Bang nucleosynthesis, Gravitation, Dark energy
Spectrum and Polarization of the Galactic Center Radio Transient ASKAP J173608.2–321635 from THOR-GC and VLITE. The radio transient ASKAP J173608.2–321635, at the position (ℓ, b) = (356.°0872, ‑0.°0390), was serendipitously observed by The H I/OH/Recombination line survey of the Galactic center at three epochs in 2020 March, 2020 April, and 2021 February. The source was detected only on 2020 April 11 with a flux density of 20.6 ± 1.1 mJy at 1.23 GHz and in-band spectral index of α = ‑3.1 ± 0.2. The commensal Very Large Array Low-band Ionsophere and Transient Experiment simultaneously detected the source at 339 MHz with a flux density of 122.6 ± 20.4 mJy, indicating a spectral break below 1 GHz. The rotation measure (RM) in 2020 April was 63.9 ± 0.3 rad m‑2, which almost triples the range of the variable RM observed by Wang et al. to ∼130 rad m‑2. The polarization angle, corrected for Faraday rotation, was 97° ± 6°. The 1.23 GHz linear polarization was 76.7% ± 3.9% with wavelength-dependent depolarization, indicating a Faraday depth dispersion of  σϕ=4.8‑0.7+0.5radm‑2 . We find an upper limit to the circular polarization of ∣V∣/I &lt; 10.1%. Interpretation of the data in terms of diffractive scattering of radio waves by a plasma near the source indicates an electron density and a line-of-sight magnetic field strength within a factor of 3 of n  e  ∼ 2 cm‑3 and B ∥ ∼ 2 × 105 μ G. Combined with causality limits to the size of the source, these parameters are consistent with the low-frequency spectral break resulting from synchrotron self-absorption, not free–free absorption. A possible interpretation of the source is a highly supersonic neutron star interacting with a changing environment.

Keywords: Sky surveys, Galactic radio sources, Interstellar magnetic fields, Radio bursts, Radio transient sources
Performance of SK-Gd's Upgraded Real-time Supernova Monitoring System. Among multimessenger observations of the next Galactic core-collapse supernova, Super-Kamiokande (SK) plays a critical role in detecting the emitted supernova neutrinos, determining the direction to the supernova (SN), and notifying the astronomical community of these observations in advance of the optical signal. In 2022, SK has increased the gadolinium dissolved in its water target (SK-Gd) and has achieved a Gd concentration of 0.033%, resulting in enhanced neutron detection capability, which in turn enables more accurate determination of the supernova direction. Accordingly, SK-Gd's real-time supernova monitoring system has been upgraded. SK_SN Notice, a warning system that works together with this monitoring system, was released on 2021 December 13, and is available through GCN Notices. When the monitoring system detects an SN-like burst of events, SK_SN Notice will automatically distribute an alarm with the reconstructed direction to the supernova candidate within a few minutes. In this paper, we present a systematic study of SK-Gd's response to a simulated Galactic SN. Assuming a supernova situated at 10 kpc, neutrino fluxes from six supernova models are used to characterize SK-Gd's pointing accuracy using the same tools as the online monitoring system. The pointing accuracy is found to vary from 3° to 7° depending on the models. However, if the supernova is closer than 10 kpc, SK_SN Notice can issue an alarm with three-degree accuracy, which will benefit follow-up observations by optical telescopes with large fields of view.

Keywords: Particle astrophysics, Supernova neutrinos, Core-collapse supernovae
Open Star Clusters and Their Asymmetrical Tidal Tails. Stars that evaporate from their star cluster by the energy equipartition process end up in either a leading or a trailing tidal tail. In Newtonian gravitation and for open star clusters in the solar vicinity, the tidal threshold, or práh, for escape is symmetrical, such that the leading and trailing tails are equally populated. The data from six independent teams that applied the convergent point method to map out the tidal tails of four open clusters (the Hyades, Praesepe, Coma Berenices, and COIN-Gaia 13) using Gaia DR2 and DR3 are here applied to test for the expected symmetry. All tidal tails contain more stars in the leading tail. The combined confidence amounts to an 8σ falsification of the práh symmetry. The same test using Milgromian dynamics leads to consistency with the data. More effort needs to be exerted on this matter, but the data indicate with high confidence that the tidal práh of an open star cluster is asymmetrical, with the corresponding confidence that Newtonian gravitation is falsified. Open star clusters depopulate more rapidly in Milgromian than in Newtonian dynamics, and the COIN-Gaia 13 cluster is here found to be nearly completely dissolved. In view of these results, the wide-binary star test and the finding of a Keplerian Galactic rotation curve are briefly discussed.

Keywords: Gravitation, Newtonian gravitation, Tidal tails, Open star clusters, Modified Newtonian dynamics, Star clusters
The Coherent Magnetic Field of the Milky Way. We present a suite of models of the coherent magnetic field of the Galaxy based on new divergence-free parametric functions describing the global structure of the field. The model parameters are fit to the latest full-sky Faraday rotation measures (RMs) of extragalactic sources and polarized synchrotron intensity (PI) maps from the Wilkinson Microwave Anisotropy Probe and Planck. We employ multiple models for the density of thermal and cosmic-ray electrons in the Galaxy, needed to predict the sky maps of RMs and PI for a given Galactic magnetic field (GMF) model. The robustness of the inferred properties of the GMF is gauged by studying many combinations of parametric field models and electron density models. We determine the pitch angle of the local magnetic field (11° ± 1°), explore the evidence for a grand-design spiral coherent magnetic field (inconclusive), determine the strength of the toroidal and poloidal magnetic halo fields below and above the disk (magnitudes the same for both hemispheres within ≈10%), set constraints on the half-height of the cosmic-ray diffusion volume (≥2.9 kpc), investigate the compatibility of RM- and PI-derived magnetic field strengths (compatible under certain assumptions), and check if the toroidal halo field could be created by the shear of the poloidal halo field due to the differential rotation of the Galaxy (possibly). A set of eight models is identified to help quantify the present uncertainties in the coherent GMF spanning different functional forms, data products, and auxiliary input. We present the corresponding sky maps of rates for axion–photon conversion in the Galaxy and deflections of ultrahigh-energy cosmic rays.

Keywords: Galaxy magnetic fields, Milky Way magnetic fields, Cosmic ray astronomy, Milky Way Galaxy physics, Cosmic rays
The Early Ultraviolet Light Curves of Type II Supernovae and the Radii of Their Progenitor Stars. We present a sample of 34 normal Type II supernovae (SNe II) detected with the Zwicky Transient Facility, with multiband UV light curves starting at t ≤ 4 days after explosion, and X-ray observations. We characterize the early UV-optical color, provide empirical host-extinction corrections, and show that the t &gt; 2 day UV-optical colors and the blackbody evolution of the sample are consistent with shock cooling (SC) regardless of the presence of "flash ionization" features. We present a framework for fitting SC models that can reproduce the parameters of a set of multigroup simulations up to 20% in radius and velocity. Observations of 15 SNe II are well fit by models with breakout radii &lt;1014 cm. Eighteen SNe are typically more luminous, with observations at t ≥ 1 day that are better fit by a model with a large &gt;1014 cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest that these large-breakout events are explosions of stars with an inflated envelope or with confined circumstellar material (CSM). Using the X-ray data, we derive constraints on the extended (∼1015 cm) CSM density independent of spectral modeling and find that most SN II progenitors lose  Ṁ&lt;10‑4M⊙yr‑1  up to a few years before explosion. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the  66‑22+11%  of red supergiants (RSGs) explode as SNe II with breakout radii consistent with the observed distribution of RSGs, with a tail extending to large radii, likely due to the presence of CSM.

Keywords: Core-collapse supernovae, Type II supernovae, Plasma astrophysics, Transient sources, Ultraviolet astronomy, Shocks, Ultraviolet transient sources
Free-floating Planets, Survivor Planets, Captured Planets, and Binary Planets from Stellar Flybys. In star clusters, close stellar encounters can strongly impact the architecture of a planetary system or even destroy it. We present a systematic study of the effects of stellar flybys on two-planet systems. When such a system experiences flybys, one or both planets can be ejected, forming free-floating planets (FFPs), captured planets (CPs) around the flyby star, and free-floating binary planets (BPs); the remaining single-surviving planets (SSPs) can have their orbital radii and eccentricities greatly changed. Through numerical experiments, we calculate the formation fractions (or branching ratios) of FFPs, SSPs, CPs, and BPs as a function of the pericenter distance of the flyby, and use them to derive analytical expressions for the formation rates of FFPs, SSPs, CPs and BPs in general cluster environments. We find that the production rates of FFPs and SSPs are similar (for the initial planet semimajor axis ratio a 1/a 2 = 0.6–0.8), while the rate for CPs is a few times smaller. The formation fraction of BPs depends strongly on a 1/a 2 and on the planet masses. For Jupiter-mass planets, the formation fraction of BPs is always less than 1% (for a 1/a 2 = 0.8) and typically much smaller (≲0.2% for a 1/a 2 ≲ 0.7). The fraction remains less than 1% when considering 4M J planets. Overall, when averaging over all flybys, the production rate of BPs is less than 0.1% of that of FFPs. We also derive the velocity distribution of FFPs produced by stellar flybys, and the orbital parameter distributions of SSPs, CPs, and BPs. These results can be used in future studies of exotic planets (including FFPs) and planetary systems.

Keywords: Free floating planets, Extrasolar gaseous giant planets, Planetary dynamics, Star clusters
Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun. We present an event observed by Parker Solar Probe (PSP) at ∼0.2 au on 2022 March 2 in which imaging and in situ measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout coronal mass ejection (CME) including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and in situ helicity and principal variance signatures consistently show the presence of flux ropes internal to the CME. In both the sheath and the CME interval, the distributions are more isotropic, the spectra are softer, and the abundance ratios of Fe/O and He/H are lower than those in the isolated flux tube, and yet elevated relative to typical plasma and solar energetic particle abundances. These signatures in the sheath and the CME indicate that both flare populations and those from the plasma are accelerated to form the observed energetic particle enhancements. In contrast, the isolated flux tube shows large streaming, hard spectra, and large Fe/O and He/H ratios, indicating flare sources. Energetic particle fluxes are most enhanced within the CME interval from suprathermal through energetic particle energies (∼keV to &gt;10 MeV), indicating particle acceleration, as well as confinement local to the closed magnetic structure. The flux-rope morphology of the CME helps to enable local modulation and trapping of energetic particles, in particular along helicity channels and other plasma boundaries. Thus, the CME acts to build up energetic particle populations, allowing them to be fed into subsequent higher-energy particle acceleration throughout the inner heliosphere where a compression or shock forms on the CME front.

Keywords: Solar energetic particles, Solar magnetic fields, Solar flares, Solar coronal mass ejections