Sazuna/UAT_keywords huggingface dataset:
Evidence for an Instability-induced Binary Merger in the Double-peaked, Helium-rich Type IIn Supernova 2023zkd. We present ultraviolet to infrared observations of the extraordinary Type IIn supernova 2023zkd (SN 2023zkd). Photometrically, it exhibits persistent and luminous precursor emission spanning ∼4 yr preceding discovery (Mr ≍ −15 mag, 1500 days in the observer frame), followed by a secondary stage of gradual brightening in its final year. Post-discovery, it exhibits two photometric peaks of comparable brightness (Mr ≲ −18.7 mag and Mr ≍ −18.4 mag, respectively) separated by 240 days. Spectroscopically, SN 2023zkd exhibits highly asymmetric and multicomponent Balmer and He I profiles that we attribute to ejecta interaction with fast-moving (1000─2000 km s−1) He-rich polar material and slow-moving (∼400 km s−1) equatorially distributed H-rich material. He II features also appear during the second light curve peak and evolve rapidly. Shock-driven models fit to the multiband photometry suggest that the event is powered by interaction with ∼5─6 M⊙ of CSM, with 2─3 M⊙ associated with each light curve peak, expelled during mass-loss episodes ∼3─4 yr and ∼1─2 yr prior to explosion. The observed precursor emission, combined with the extreme mass-loss rates required to power each light curve peak, favors either super-Eddington accretion onto a black hole or multiple long-lived eruptions from a massive star to luminosities that have not been previously observed. We consider multiple progenitor scenarios for SN 2023zkd, and find that the brightening optical precursor and inferred explosion properties are most consistent with a massive (MZAMS ≥ 30 M⊙) and partially stripped He star undergoing an instability-induced merger with a black hole companion.

Keywords: Circumstellar matter, Photometry, Core-collapse supernovae, Spectroscopy
Multiline Spectropolarimetric Observation of Flare Ribbon Fine Structures with ViSP/DKIST. We present an analysis of flare ribbon fine structure observed during a GOES C2-class flare using high spatial and spectral resolution multiline spectropolarimetric observations from the ViSP instrument at the DKIST. The ViSP recorded full Stokes spectra in three lines: Fe I 6301 Å line pair, Na I D1, and Ca II 8542 Å. To infer the stratification of temperature and line-of-sight (LOS) velocity across the ribbon, we performed non–local thermodynamic equilibrium multiline inversions of ViSP spectra. In the red wing of the Ca II line, we identified multiple compact, roundish, and quasi-equally spaced bright structures, referred to as ribbon blobs, embedded within the flare ribbon. The sizes of these blobs range from 320 to 455 km, and they are spaced roughly ∼1100 km apart. These features exhibit complex spectral profiles with pronounced asymmetries and double peaks near the line core of the Ca II 8542 line. The blob regions were found to be significantly hotter (by ∼1 kK) at  logτ500=‑4  compared to surrounding ribbon areas (∼7 kK). The LOS velocity maps revealed both upflows and downflows at  logτ500=‑4  and  logτ500=‑3 , respectively. We discuss the plausible origins of these fine structures in the chromosphere, which may be related to electron beam heating, plasma draining, or tearing-mode instabilities in the reconnecting current sheet.

Keywords: Spectropolarimetry, Solar chromospheric heating, Solar flares
Inclination Effect on Observational Identification of Outflow Rotation in Magnetohydrodynamics Simulations. We investigate the observational signatures of outflow rotation in protostellar systems using magnetohydrodynamics simulations of protostellar evolution with radiative transfer and synthetic observation. The velocity gradient perpendicular to the outflow axis indicates outflow rotation. The rotation signature is clearly seen in the moment 1 map and a position–velocity (PV) diagram across an outflow lobe made from our model with an inclination angle of i ≳ 85°, as in observational studies of protostellar outflows. Velocity projection with lower inclinations distorts the moment 1 map because the outflow vertical (propagation) velocity contributes more to the line-of-sight velocity, leading to an incorrect outflow axis direction. The PV diagram adopting the incorrect outflow axis shows no clear velocity gradient. These effects may prevent us from identifying outflow rotation. Our analysis implies that rotational signatures can be obscured in ∼2/3 to ∼4/5 of the total outflow population (i &lt; 70°–80°), regardless of the evolutionary stage. Complicated structures in observed outflows make it difficult to determine the outflow axis, which may result in the apparent nondetection of outflow rotation.

Keywords: Protostars, Stellar jets, Low mass stars, Magnetohydrodynamical simulations
Modeling the Impacts of Galaxy Intrinsic Alignments on Weak Lensing Peak Statistics. Weak gravitational lensing (WL) peak statistics capture cosmic nonlinear structures and can provide additional cosmological information complementary to cosmic shear two-point correlation analyses. They have been applied to different WL surveys successfully. To further facilitate their high-precision applications, it is very timely to investigate the impacts of different systematics on WL peak statistics and how to mitigate them. Concerning the influence of galaxy intrinsic alignments (IAs), in this paper, we develop a theoretical model for WL high peaks taking into account the IA effects. It is an extension of our previous halo-based model. The IA corrections mainly include the modification of the lensing profile of clusters of galaxies due to the alignments of satellite galaxies and the additional shape noise correlations. We validate our model using simulations with the semi-analytical galaxy formation. We consider the cases where the satellite galaxies are on average radially aligned toward the centers of their host clusters but with different dispersions σθ. We show that our model works well for σθ &gt; 45°. If the IA corrections are not included in the model, for the Euclid/CSST─like source galaxy distribution and the survey area of ∼1000 deg2, the IA-induced bias on S8 can reach ∼8σ even for σθ = 75°. With our model, not only can the bias be well mitigated, but we can also constrain the satellite IA to the level of σ(σθ) ∼ ±24° simultaneously from WL high peak analyses alone using data from such a survey.

Keywords: Weak gravitational lensing
A Radio Flaring, Chromospherically Inactive K Dwarf. We report on an unusual radio source (J180526−292953), initially identified as a steep spectrum, polarized point source toward the Galactic bulge and found to coincide with the nearby K dwarf HD 317101A. We conducted a multiwavelength radio study utilizing new GMRT observations and archival data from ASKAP, MeerKAT, and the Very Large Array. At 1.5 GHz, HD 317101A exhibits highly polarized coherent emission with variable activity lasting several hours with an apparent period of 3.7 days, which is consistent with electron cyclotron maser (ECM) emission. The behavior at 3 GHz is distinctive, with a short burst lasting tens of seconds to minutes, a flat spectrum, and no detected polarization, possibly suggesting gyro-synchrotron emission. High-resolution optical spectroscopy from CHIRON/SMARTS confirms HD 317101A as a mature, chromospherically inactive K7V star, while Gaia astrometry, combined with speckle imaging from Zorro/Gemini-S, indicates the presence of a close-in M5.5V companion. We evaluated three possible origins for the combined radio behavior: chromospheric activity, auroral emission (possibly from a star─planet interaction), or an ultralong-period transient. The bulk of the evidence favors an auroral origin, but the dominant stellar source of the ECM emission remains uncertain. Future very-long baseline interferometry observations, long-term TESS monitoring, high-resolution spectroscopy, and further radio characterization will be key to distinguishing between various scenarios.

Keywords: Radio continuum emission, Star-planet interactions, Late-type dwarf stars, Stellar magnetic fields
On the Width and Profiles of Cosmic Filaments. We investigated the widths and profiles of cosmic filaments using the IllustrisTNG simulations. Filaments were identified with DisPerSE, using galaxy samples in simulations as input. Since the width of an individual filament can vary significantly along its spine, we divided each filament into segments with lengths between 1.5 and 2.5 h‑1 Mpc and measure their properties. The typical width of these filament segments increases gradually from approximately 0.3 Mpc at redshift z = 2 to about 1.0–1.5 Mpc at z = 0. We find that the segment width correlates nearly linearly with the linear halo mass density, consistent with previous studies. A similar linear relation is observed between the segment width and the linear stellar mass density, providing a potential estimator for filament width. Furthermore, the density profiles of filaments with different widths exhibit self-similarity and can be described by a unified formula akin to the isothermal β model. For segments with a given width, the rescaled density profiles show only mild evolution from z = 2 to z = 0. Within the filament width, the gas temperature decreases slowly from the center to the boundary, with thicker filaments generally containing hotter gas than thinner ones. These trends in filament width, density, and thermal profiles are consistently observed across the TNG50, TNG100, and TNG300 simulations, and align well with results from earlier studies. We briefly discuss the potential implications and applications of our findings.

Keywords: Cosmology, Intergalactic medium, Cosmic web, Large-scale structure of the universe
Mass-gap Black Holes in Coalescing Neutron Star–Black Hole Binaries. The existence of a mass gap of 3–5 M⊙ between the heaviest neutron stars (NSs) and the lightest black holes (BHs), inferred from the BH mass distribution in low-mass X-ray binaries (LMXBs), has been suggested for decades. The gravitational-wave (GW) source GW230529 is most likely a neutron star–black hole (NSBH) merger, with the BH mass falling within this gap. This detection strongly challenges the existence of the gap and has implications for the NSBH population, including a revised BH mass distribution and an updated local merger rate. In this study, we employ POSYDON, a binary population synthesis code that integrates detailed single- and binary-star models, to investigate coalescing NSBH binaries, focusing on the BH mass distribution of the intrinsic NSBH merger population. For typical population models, we find that better matching the observed BH mass distribution requires the use of common-envelope (CE) efficiencies exceeding unity, a rather uncomfortable choice since most energy sources are already included. Alternatively, we find that a two-stage CE prescription calibrated to 1D hydrodynamic simulations has a similar effect. Moreover, motivated by a possible explanation for the firm presence of the mass gap in the LMXB sample, we examine models where the NS birth mass is limited to ≲2 M⊙ and find excellent agreement with GW observations. Additionally, we present observable distributions of NSBH merger properties, finding good agreement with the measured properties of observed systems and a predicted fraction of NSBH mergers with potential electromagnetic counterparts that ranges from 1% all the way up to 32%.

Keywords: Neutron stars, Gravitational waves, Black holes
Precise Asteroseismic Ages for the Helmi Streams. The Helmi streams are remnants of a dwarf galaxy that was accreted by the Milky Way and whose stars now form a distinct kinematic and chemical substructure in the Galactic halo. Precisely age-dating these typically faint stars of extragalactic origin has been notoriously difficult due to the limitations of using only spectroscopic data, interferometry, or coarse asteroseismic measurements. Using observations from NASA's Transiting Exoplanet Survey Satellite, we report detailed asteroseismic modeling results for two of the brightest red giants within the Helmi streams, HD 175305 and HD 128279. By modeling the individual oscillation mode frequencies and the spectroscopic properties of both stars, we determine their fundamental properties including mass, radius, and age (τ). We report τ = 11.16 ± 0.91 Gyr for HD 175305 and τ = 12.52 ± 1.05 Gyr for HD 128279, consistent with previously inferred star formation histories for the Helmi streams and the differential chemical abundances between the two stars. With precise ages for individual stream members, our results reinforce the hypothesis that the Helmi streams' progenitor must have existed at least 12 Gyr ago. Our results also highlight that the ages of metal-poor, α-enhanced red giants can be severely underestimated when inferred using global asteroseismic parameters instead of individual mode frequencies.

Keywords: Stellar streams, Milky Way formation, Milky Way stellar halo, Stellar oscillations, Asteroseismology
X-Ray Reflection Signatures of Supermassive Black Hole Binaries. We investigate the presence of supermassive black hole (SMBH) binary signatures and the feasibility of identifying them through X-ray reflection spectra. The X-ray emitting region is modeled as a set of two mini-disks bound to the individual SMBHs separated by 100 GM/c2 and the spectra calculated as a function of the mass, mass ratio, and total accretion rate of the binary. The X-ray reflection features are strongly influenced by the accretion-inversion phenomenon expected in SMBH binaries, which results in a wide range of ionization conditions in the two mini-disks. These are imprinted in the resulting composite spectra and the double-peaked and time-variable relativistic Fe Kα line profiles. To test whether these features can be used as evidence for the presence of an SMBH binary, we fit mock 100 ks observations with a single active galactic nucleus (AGN) model. For a 109 M⊙ binary targeted by pulsar timing arrays (PTAs), at z = 0.1, the single AGN model clearly fails to fit the data, while at z = 1, the fit is acceptable but unable to converge on the SMBH spin. For a 106 M⊙ binary, a progenitor of a Laser Interferometer Space Antenna (LISA) source, spectral fitting is only possible at z = 0.1, with the outcomes similar to the PTA binary at z = 1. We also find that PTA binaries can be expected to show a distinct X-ray spectral variability in multiepoch observations, whereas for LISA precursors, orbital averaging results in the loss of spectral variability signatures.

Keywords: X-ray astronomy, Supermassive black holes, High energy astrophysics, Gravitational wave sources
On the Origin of the Short-lived Cocoon in 3C 84: Powered by Tidal Disruption Events?. We evaluated the jet power and the density of ambient matter in 3C 84 by using the momentum balance along the jet axis and the transonic condition for the cocoons observed at two different scales (approximately 1 and 6 pc). For the inner cocoon, we precisely determined the ratio of jet power to ambient density Lj/na to be (0.3–0.7) × 1043 erg s‑1 cm3. Similarly, for the outer cocoon, we found that this value is more than an order of magnitude larger at (0.9–3.7) × 1044 erg s‑1 cm3. This indicates that the outer cocoon is formed by a powerful jet that propagates through an ambient density of 20–300 cm‑3 with a jet power of 1045‑46.5 erg s‑1. On the other hand, the inner cocoon is formed by a weaker jet with a power of 1043‑44 erg s‑1, propagating through a relatively low-density environment of 6–20 cm‑3. These results suggest that (1) with respect to the difference in na, it appears to support the hypothesis that the inner cocoon, recently formed about 10 yr ago, is expanding in the low-density environment created by the jet emitted about 25–50 yr ago; (2) to achieve the short-lived and high Lj that generated the outer cocoon, a large mass-accretion rate is required over a short period to activate the jet. These may imply an extreme accretion event driven by the tidal disruption events of massive stars and/or the disk instability.

Keywords: Tidal disruption, Radio galaxies, Active galactic nuclei, Relativistic jets
Peaky Finders: Characterizing Double-peaked Type IIb Supernovae in Large-scale Live-stream Photometric Surveys. We present the first photometric population study of double-peaked Type IIb supernovae (SNe IIb). SNe IIb are produced from the core collapse of massive stars whose outermost hydrogen layer has been partially stripped prior to explosion. These double-peaked light curves, consisting of a shock-cooling emission (SCE) peak followed by the main nickel-powered peak, contain more crucial information about the progenitor system than the typical single-peaked light curves. We compiled and analyzed a sample of 14 spectroscopically confirmed SNe IIb—including previously unpublished and reclassified—with publicly available photometric observations, discovered between 2018 and 2022, from the Zwicky Transient Facility and Asteroid Terrestrial-impact Last Alert System surveys. We developed and fit a piecewise linear model, referred to as the "lightning bolt" model, to describe the early-time behavior of these objects to measure population statistics. Notably, we find the SCE peak lasts, on average, fewer than 5 days above half-maximum light, with a mean rise time of 2.07 ± 1.0 and 1.1 ± 0.8 mag day−1 in the g and r bands, respectively. These SCE rise rates are over 10× faster than—and last only a third the duration of—the rise to the Ni-powered peak. These rise times are comparable to those of fast blue optical transient events, and we discuss the implications in the text. Finally, we present a proof-of-concept alert filter, using the ANTARES broker, to demonstrate how to translate these population statistics into simple and effective filters to find potential double-peaked SNe IIb in large-scale survey alert streams, like the imminent Vera C. Rubin Observatory Legacy Survey of Space and Time.

Keywords: Astronomy data modeling, Bayesian statistics, Core-collapse supernovae, Transient sources, Time domain astronomy, Supernovae
Detection of Transitions between Dwarf Nova Outbursts, Standstills, and IW And–type Cycles. IW And–type objects represent a rare and intriguing subclass of cataclysmic variables that challenge the classical disk instability model. Due to their long timescales, often lasting several months, observed samples are scarce, leaving the physics of state transitions poorly understood. Here, we report the discovery of ASASSN-V J175721.00+152502.1 as a new IW And–type system based on both ground-based and space-based survey data. For the first time, we measure its orbital period and negative superhump (NSH) period as 0.25619(81) days and 0.24107(33) days, respectively. We present detailed observational evidence for transitions between IW And–type cycles, classical standstills, and normal dwarf nova outbursts. Notably, the transition from the IW And–type cycle to a classical standstill is presented in detail for the first time, together with a decrease in the NSH period, which provides evidence for accretion disk expansion. We evaluate theoretical models that could explain the observed light variations and rule out simple scenarios such as mass-transfer bursts or superoutbursts. Although the tilted-disk thermal instability model is the most plausible, it does not fully account for the detailed behavior. We propose that a combination of factors, such as thermal-viscous instabilities, fluctuations in the mass-transfer rate, changes in the disk radius, tilted disk precession, and tidal dissipation involving the secondary star, is likely needed to explain the full range of observed phenomena.

Keywords: Z Camelopardalis stars, Cataclysmic variable stars, Binary stars, Dwarf novae
Where Is the Supervirial Gas? III. Insights from X-Ray Shadow Observations and a Revised Model for the Soft Diffuse X-Ray Background. Shadow observations provide a powerful tool to separate foreground components of the soft diffuse X-ray background (SDXB) from the background components. Such observations have now established that the "local" foreground is made of the solar wind charge exchange and the Local Bubble, and the background emission is from the extended circumgalactic medium (CGM) of the Milky Way and from the unresolved extragalactic sources. New data and careful analyses of the SDXB led to two new discoveries in recent years: (1) excess emission near 0.5 keV that is identified as the N VII emission line, and (2) excess emission near 0.8−1.0 keV that is identified with an additional, supervirial temperature hot thermal component of the CGM. The goal of this paper is to use Suzaku shadow observations along six sightlines to determine whether either of these components is from the "local" sources. We eliminate the ambiguity regarding the origin of N VII emission, ruling out the local origin. We confirm that the Milky Way CGM contains nitrogen-rich plasma, with a supersolar average (N/O) of 2.6 ± 0.5, and suggest that nitrogen-enhanced plasma is widespread throughout the CGM. We find supersolar Ne abundance in two sightlines, also from the CGM. Similarly, we rule out the local origin of the hot thermal component and confirm that it is present beyond the shadowing clouds. Furthermore, we provide a revised model of the SDXB, which is crucial for extragalactic astronomy.

Keywords: X-ray astronomy, Diffuse x-ray background, Spiral galaxies, Circumgalactic medium
Weak X-Ray Bursts on Slowly Accreting Neutron Stars. Nearly all observed thermonuclear X-ray bursts are thought to be triggered by the thermally unstable triple-alpha process. Unlike in accreting white dwarfs, the ≳108 K envelope temperature forces hydrogen burning to proceed via the β-limited, thermally stable hot CNO cycle. Recent observations of weak X-ray bursts from SAX J1808.4─3658 occurring within 1─3 days of the onset of an accretion outburst have raised the question that these bursts were triggered by thermally unstable hydrogen ignition, analogously to classical novae. Using the stellar evolution code MESA, we explore the unstable ignition of hydrogen on slowly accreting neutron stars. For solar metallicities, the burning is insufficiently vigorous to launch convection and the burst rise is on the envelope thermal timescale, with the hydrogen being consumed over hours. For elevated metallicities (Z ≳ 0.06), however, the initial proton captures onto CNO nuclei heat the envelope enough to drive convection and produce a sharp peak in the luminosity. This peak can match that of the SAX J1808.4─3658 burst for sufficient enrichment. Following this peak, the hydrogen burning stabilizes at a rate set solely by the ignition depth and CNO abundance in the accreted matter. This quasi-steady-state burning produces an extended tail of elevated emission that lasts until the hydrogen is exhausted. Observations of the tail's luminosity and duration measure the hydrogen and metallicity abundance of the accreted material, while the distance-independent ratio of peak-to-tail luminosities would suggest the presence of significant metallicity gradients prior to convection.

Keywords: Neutron stars, Carbon-nitrogen cycle, Hydrogen burning, X-ray transient sources, Astrophysical explosive burning, X-ray bursts