Sazuna/UAT_keywords huggingface dataset:
Evaluating Star─Planet Interactions with Zeeman Doppler Imaging: Case Study in YZ Ceti. The recent detections of radio emission from the nearby exoplanet host, YZ Ceti, suggest that the star is possibly interacting with its rocky innermost planet. These radio emissions are characterized by strong circular polarization, and appear to repeat within consistent orbital phase windows dictated by the orbital position of YZ Ceti b. If confirmed, this interaction would provide a first means to concretely assess the magnetic field of a close-in rocky exoplanet. This kind of magnetic star─planet interaction (SPI) should depend on both the exoplanetary orbit and the geometry of the stellar magnetic field. In this article, we report measurements of the large-scale magnetic field topology of the star YZ Ceti for the first time, and interpret the cumulative radio data sets in that context to evaluate the plausibility of magnetic SPIs. We find evidence both against and in support of the SPI hypothesis, but crucially that the measured magnetic field does not rule out SPI scenarios. However, clear evaluation of these possibilities requires more accurate assessments of the magnetic field evolution across time. We additionally suggest that YZ Ceti may be exhibiting planet-induced flaring, potentially triggered by exoplanet crossings of the Alfvén surface as the planet's orbit approaches the stellar magnetic equator, and YZ Ceti b experiences dramatic shifts in the ambient field, its polarity, and connectivity to the host star.

Keywords: Magnetospheric radio emissions, Star-planet interactions, Spectropolarimetry, Exoplanet systems
Constraining the Properties of a GRB Accreting Magnetar with R/I Evolutionary Effects Using Swift/XRT Data. A newly born millisecond magnetar has been proposed as one possible central engine of some long gamma-ray bursts (LGRBs) with X-ray plateau emission. In this work, we used a universal correlation between the initial spin period (P0) and the surface magnetic field (Bp) of the newborn magnetar based on an LGRB sample in L. Lan et al. (2025) to explore the propeller properties of accreting magnetars with R/I evolutionary effects. We found that the Bp─P0 relation is approximately consistent with  Bp∝Peq7/6 . Here Peq is the equilibrium spin period in the magnetic propeller model, where the electromagnetic dipole radiation and the propeller mechanism jointly modulate the spin evolution of a newborn magnetar. The Bp─P0 relation indicates that P0 constrained by X-ray plateau data may not be the true initial spin period of a newborn magnetar but had reached an equilibrium spin period via fallback accretion in the propeller model. The magnetar accretion rate in our LGRBs is in the range of  Ṁ∼10−5to10−2M⊙s−1  by incorporating R/I evolutionary effects and using the transition relation between gravitational mass Mg and baryonic mass Mb in different equations of state and X-ray radiation efficiencies. Such accretion rates ensure that the accreting magnetars in our sample survive until reaching the equilibrium spin period, and the accretion rate is one order of magnitude lower compared to the statistical results in G. Stratta et al. (2018) and W. L. Lin et al. (2020), which used the constant R/I/Mg scenario. The fallback rate of progenitor envelope materials onto the magnetar accretion disk for our LGRBs is compatible with the theoretical mass fallback rate of some low-metallicity progenitors. We suggested that adopting a constant R/I/Mg scenario for modeling the propeller regime in accreting magnetars results in a higher mass accretion rate, which may impair our understanding of the physical nature of an accreting magnetar and its surroundings, and that the low-metallicity progenitors can provide enough material to satisfy the accretion requirements of the newborn accreting magnetar in LGRBs.

Keywords: Magnetars, Gamma-ray bursts
Fluid and Kinetic Properties of the Near-Sun Heliospheric Current Sheet. The heliospheric current sheet (HCS) is an important large-scale structure of the heliosphere, and, for the first time, the Parker Solar Probe (PSP) mission enables us to study its properties statistically, close to the Sun. We visually identify the 39 HCS crossings measured by PSP below 50 R⊙ during encounters 6─21, and investigate the occurrence and properties of magnetic reconnection, the behavior of the spectral properties of the turbulent energy cascade, and the occurrence of kinetic instabilities at the HCS. We find that 82% of the HCS crossings present signatures of reconnection jets, showing that the HCS is continuously reconnecting close to the Sun. The proportion of inward and outward jets depends on heliocentric distance, and the main HCS reconnection X-line has a higher probability of being located close to the Alfvén surface. We also observe a radial asymmetry in jet acceleration, where inward jets do not reach the local Alfvén speed, contrary to outward jets. We find that turbulence levels are enhanced in the ion kinetic range, consistent with the triggering of an inverse cascade by magnetic reconnection. Finally, we highlight the ubiquity of magnetic hole trains in the high-β environment of the HCS, showing that the mirror mode instability plays a key role in regulating the ion temperature anisotropy in HCS reconnection. Our findings shed new light on the properties of magnetic reconnection in the high-β plasma environment of the HCS, its interplay with the turbulent cascade, and the role of the mirror mode instability.

Keywords: Space plasmas, Solar wind, Interplanetary magnetic fields, Heliosphere
Bell Instability and Cosmic-Ray Acceleration in Active Galactic Nuclei Ultrafast Outflow Shocks. We investigate magnetic field amplification driven by the nonresonant hybrid (NRH, or Bell) instability and its impact on cosmic-ray (CR) acceleration at the reverse shocks of ultrafast outflows (UFOs) from active galactic nuclei. Previous kinetic studies by particle-in-cell simulations have demonstrated that when the maximum CR energy is near the injection scale, the NRH instability efficiently amplifies the magnetic field up to the saturation level. However, the efficiency of the NRH instability decreases as the maximum energy increases, since the CR current is carried by escaping CRs near the maximum energy. We employ a one-dimensional MHD-CR framework solving telegraph-type diffusion─convection equations to trace the coupled evolution of CRs, magnetic fields, and shock dynamics under realistic parameters. We find a distinct transition with magnetic field strength. For weak background fields (B0 ≲ 10−4 G), the NRH instability efficiently amplifies upstream turbulence, driving a self-regulated state where  Emax  becomes independent of the initial strength of the magnetic turbulence. In contrast, for stronger background fields (B0 ≳ 10−3 G), the escaping CR current is too weak to drive the NRH instability, and magnetic turbulence further decays through parametric instabilities, potentially reducing the acceleration efficiency. We give a physical interpretation for the transition and discuss conditions for PeV to EeV acceleration at UFO reverse shocks.

Keywords: Magnetohydrodynamics, Plasma astrophysics, Active galactic nuclei, Shocks, Particle astrophysics, Magnetohydrodynamical simulations
Revisiting the 150 MHz Radio Luminosity Function of Star-forming Galaxies with LOFAR Deep Fields through a Refined Statistical Framework. We present a comprehensive analysis of the 150 MHz radio luminosity function (LF) of star-forming galaxies (SFGs) using deep observations from the LOFAR Two-metre Sky Survey in the ELAIS-N1, Boötes, and Lockman Hole fields. Our sample comprises ∼56,000 SFGs over 0 &lt; z &lt; 5.7. We first analyze the deepest field (ELAIS-N1), then jointly model all three fields while accounting for their distinct flux limits and selection functions. Using adaptive kernel density estimation (KDE), we reconstruct the LF continuously across redshift and luminosity without binning or parametric assumptions. The KDE results reveal clear signatures of joint luminosity and density evolution (LADE). Motivated by this, we construct and fit three parametric models—pure luminosity evolution (PLE) and two LADE variants—using a full maximum-likelihood method that includes completeness corrections and constraints from the local radio LF and Euclidean-normalized source counts (SCs). Model selection using Akaike and Bayesian information criteria strongly favors LADE over PLE. For ELAIS-N1, the more flexible LADE model (Model C) provides the best fit, while for the combined fields, the simpler Model B balances fit quality and complexity more effectively. Both LADE models reproduce the observed LFs and SCs across luminosity and flux density ranges, whereas PLE underperforms. We also identify a mild excess at the bright end of the LF, likely due to residual active galactic nucleus contamination. This study demonstrates that combining KDE with parametric modeling offers a robust framework for quantifying the evolving radio LF of SFGs, paving the way for future work with next-generation surveys like the Square Kilometre Array.

Keywords: Luminosity function, Star formation, Galaxy evolution, Radio continuum emission
Deep X-Ray Observation of NGC 3221: Everything Everywhere All at Once. We present a comprehensive analysis of 475 ks (438 ks unpublished and 37 ks archival) XMM-Newton/EPIC-pn observations of a nearby, highly inclined, star-forming, luminous infrared galaxy NGC 3221 through spatial, temporal, and spectral information. We confirm the presence of a low-luminosity (presumably Compton-thick) active galactic nucleus (AGN). The 0.4─12 keV luminosity and the hardness ratio of the six ultraluminous X-ray sources previously identified in Chandra data exhibit diverse variability on day scales. The collective emission from unresolved sources exhibits a different day-scale variability. We have also discovered two new predominantly soft (&lt;1 keV) sources. One of these has an enigmatic spectral shape featuring a soft component, which we interpret as a superbubble in NGC 3221, and a variable hard component from a compact object, unresolved from the superbubble. We do not confidently detect any X-ray emission from SN 1961L. The hot gas in the interstellar medium (ISM, out to ±6 kpc from the disk plane) and that in the extraplanar region (6─12 kpc) both require two thermal phases at ∼0.15 keV and ∼0.55 keV. The ∼0.55 keV component is fainter in the ISM than the ∼0.15 keV component, but the emission from the latter falls off more steeply with disk height than the emission from the former. This makes the extraplanar region hotter and less dense than the ISM. The proximity of NGC 3221 and the occurrence of the underluminous AGN offer a unique observing opportunity to study the hot diffuse medium along with nuclear and diskwide point sources.

Keywords: X-ray astronomy, Starburst galaxies, AGN host galaxies, X-ray binary stars, High energy astrophysics, Interstellar plasma, Ultraluminous x-ray sources, Active galactic nuclei, Interstellar medium, Hot ionized medium, Superbubbles, Luminous infrared galaxies
Fast Magnetoacoustic Wave Behavior within Gravitationally Stratified, Magnetically Inhomogeneous Media. The nature of MHD waves within inhomogeneous media is fundamental to understanding and interpreting wave behavior in the solar atmosphere. We investigate fast magnetoacoustic wave behavior within gravitationally stratified, magnetically inhomogeneous media, by studying a magnetic environment containing a simple 2D X-type magnetic null point. The addition of gravitational stratification fundamentally changes the nature of the system, including breaking the symmetry. There are two main governing effects: the stratified density profile acts in combination with the inhomogeneous magnetic field, creating a large gradient in the Alfvén speed and hence a system replete with refraction. The system is investigated using both numerical simulations and a semianalytical WKB solution (via Charpit's method and a fourth-order Runge─Kutta solver) and we find strong agreement between both. The results show a fundamental difference between the stratification-free and stratified cases, including the formation of caustic surfaces and cusps, and we contextualize these results in the theoretical understanding of fast magnetoacoustic waves.

Keywords: Magnetohydrodynamics, Solar coronal waves, Magnetohydrodynamical simulations
JWST Observations of SN 2023ixf. I. Completing the Early Multiwavelength Picture with Plateau-phase Spectroscopy. We present and analyze panchromatic (0.35─14 μm) spectroscopy of the Type II supernova 2023ixf, including near- and mid-infrared spectra obtained 33.6 days after explosion during the plateau phase, with the James Webb Space Telescope (JWST). This is the first in a series of papers examining the evolution of SN 2023ixf with JWST during the initial 1000 days after explosion and monitoring the formation and growth of molecules and dust in ejecta and the surrounding environment. The JWST infrared spectra are overwhelmingly dominated by H lines, whose profiles reveal ejecta structures, including flat tops, blue notches, and red shoulders, unseen in the optical spectra. We characterize the nature of these structures, concluding that they likely result from a combination of ejecta geometry, viewing angle, and opacity effects. We find no evidence for the formation of dust precursor molecules such as carbon monoxide (CO), nor do we observe an infrared excess attributable to dust. These observations imply that the detections of molecules and dust in SN 2023ixf at later epochs arise either from freshly synthesized material within the ejecta or circumstellar material at radii not yet heated by the supernova at this epoch.

Keywords: Type II supernovae, James Webb Space Telescope, Supernovae, Core-collapse supernovae
X-Ray Observations of Old Nearby Supernovae—Constraints on Compact Object Populations and Late Interaction. The properties of the population of compact objects created in core-collapse supernovae (SNe) are uncertain. X-ray observations years to decades after the explosions offer a way to gain insight into this, as hard X-ray emission from the central regions will emerge as the ejecta absorption decreases. Here, we analyze and place upper limits on late-time X-ray emission in 242 nearby SNe, using 607 observations from Chandra, XMM-Newton, Swift, and NuSTAR. We use absorption models based on 3D simulations of neutrino-driven explosions to account for absorption of emission from the compact objects by the asymmetric ejecta. We detect X-ray emission from 12 SNe, including 4 for the first time (SN 1982R, SN 1984J, SN 1992bu, and SN 2003gk), and several of the others at later epochs than before. The X-ray spectra of these SNe are consistent with interaction with the circumstellar medium (CSM), with the possible exception of SN 1979C, which shows an additional hard component, as also noted in previous studies at earlier epochs. This emission may be due to a pulsar wind nebula. Using the upper limits in the full sample, we also perform a population synthesis to constrain the fraction of SNe that produce pulsars and the properties of the pulsars themselves. We find that pulsar populations with mean initial spin periods ≳100 ms are favored. Finally, we note that the high luminosities of several of the SNe with CSM interaction imply interactions with dense shells.

Keywords: X-ray astronomy, Ejecta, Core-collapse supernovae, Pulsars, Compact objects, Pulsar wind nebulae
Igniting Galaxy Formation in the Postreionization Universe. It is widely believed that the ultraviolet background produced during the epoch of reionization conspires against the formation of low-mass galaxies. Indeed, this mechanism is often invoked as part of the solution to the so-called "missing satellites problem." In this paper we employ FIREbox, a large-volume cosmological simulation based on the Feedback In Realistic Environments physics model, to characterize the mechanisms governing galaxy ignition in the postreionization era. By carefully matching recently ignited halos (with stellar ages below 100 Myr at the time of selection) to halos that failed to form any stars, we conclude that the presence of cold dense gas and halo concentration helps incite the process of galaxy formation. Concretely, we find that 100% of recently ignited halos experience cold dense gas enhancements relative to their matched failed counterparts. Likewise, approximately 83% display enhancements in both cold dense gas and Navarro─Frenk─White concentration (cNFW), while the remaining ∼17% exhibit enhanced cold dense gas content and suppressed cNFW values. Lastly, our simulation suggests that galaxy ignition can occur as late as z = 2, potentially allowing us to observationally catch this process "in the act" in the foreseeable future.

Keywords: Galaxy dark matter halos, Dwarf galaxies, Star formation, Galaxies
Breaking Down the CosmoGEMS: Toward Modeling and Understanding Globular Cluster Stellar Streams in a Fully Cosmological Context. Next-generation surveys are expected to uncover thousands of globular cluster (GC) stellar streams, motivating the need for a theoretical framework that produces realistic GC streams in a fully cosmological, Milky Way─like environment. We present CosmoGEMS, a star-by-star cosmological GC stream framework that self-consistently links small-scale cluster physics with large-scale Galactic dynamics. The initial phase-space positions of stream stars are informed by post-processed GC populations within the FIRE cosmological simulation. Escaped stars are orbit-integrated from their time of escape to the present day in a time-evolving Galactic potential extracted from the same simulation using a basis function expansion. We explore two example streams on different orbits. One forms a long, thin stream with a velocity dispersion consistent with Milky Way GC streams. However, it exhibits a clump and orbital-phase-dependent misalignments due to the evolving potential. The other stream develops both a thin component and a diffuse, shell-like structure, similar to features observed in streams like Jhelum. These results highlight the power of fully cosmological models in producing realistic stream morphologies and kinematics. Unlike idealized simulations, our models naturally incorporate time-dependent changes in the progenitor's orbit, including orbital plane evolution, which significantly affects stream structure. This challenges common assumptions in stream-finding algorithms and interpretation. CosmoGEMS provides a key step toward connecting future stellar stream observations with the physics of GC evolution and hierarchical galaxy formation in a cosmological context.

Keywords: Globular star clusters, Hydrodynamical simulations, Stellar streams
Project AMIGA: The Inner Circumgalactic Medium of Andromeda from Thick Disk to Halo. The inner circumgalactic medium (CGM) of galaxies, where disk and halo processes intersect, remains poorly characterized despite its critical role in regulating galaxy evolution. We present results from Project AMIGA Insider, mapping Andromeda's (M31) inner CGM within 0.25 Rvir (∼75 kpc) using 11 QSO sightlines, bringing our total sample to 54 sightlines from the disk to 2Rvir. We detect a clear transition between M31's thick disk and CGM at R ≲ 30 kpc, where low/intermediate ions show thick-disk corotating components with higher column densities than the CGM ones, while high ions exhibit similar column densities in both the CGM and thick disk. Beyond this region, all ion column densities decrease with impact parameter, with steeper gradients for low ions than high ions. The inner CGM (R ≲ 100 kpc) shows more complex gas phases and multicomponent absorption compared to the predominantly single-component outer CGM. We find no significant azimuthal dependence for any observed ions, suggesting M31's CGM is shaped by radial processes (e.g., cooling flows, precipitation) rather than disk-aligned outflows. We estimate the total metal mass in M31's cool (Si II, Si III, Si IV) CGM within Rvir to be (1.9 ± 0. 3stat ± 0. 7sys) × 107 M⊙, leading to a cool gas mass of  ≍6×109(Z/0.3Z⊙)−1  M⊙. The warmer O VI gas may contain at least 10 times more metal and gas mass. Compared to the COS-Halos L*galaxies, M31's cool CGM shows lower Si column densities at R ≲ 0.4 R200 and overall lower cool CGM masses, likely reflecting differences in galaxy mass and environment. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

Keywords: Local Group, Andromeda Galaxy, Galaxy disks, Circumgalactic medium
Minijets and Broken Stationarity in a Blazar: Novel Insights into the Origin of γ-Ray Variability in CTA 102. High-energy blazar light curves, in X-rays and beyond, have historically preferred a log-normal flux distribution, signifying multiplicative processes either in the jet itself or due to connection(s) with accretion. Here we present 18 yr archival Fermi Large Area Telescope light curves (0.1─100 GeV) of the flat spectrum radio quasar CTA 102 from 2008 August to 2025 November, which underwent a huge flare in 2017, with a ∼ factor of 100 jump in γ-ray flux, along with similar flaring in X-rays. Our statistical analyses confirm that neither the pre- nor the postflare total GeV light curves follow a strictly log-normal distribution. Instead, we observe a statistically significant reduction in skewness from the pre- to the postflare light curves, which implies the blazar transitioned from an energetic state with frequent flaring to a more plateaued state with occasional flaring. We further find that this state transition can be explained through magnetic relaxation, where many reconnection events caused the 2017 flare, after which the magnetic field was ordered and its energy reached a minimum. To explain this further, we use a Monte Carlo simulation of a modified minijets-in-a-jet model where GeV flares are produced only when a maximum number of minijets move toward the broad line region and toward the line of sight, in the context of an external Compton model. The flux distributions (both observed and simulated) could be fit by a modified log-normal power-law distribution, implying our minijets model can reproduce the GeV flares in CTA 102 as well as their flux distributions.

Keywords: Flat-spectrum radio quasars
SIGNALS of Giant H II Regions: A Spatially Resolved Analysis of NGC 604. Observing giant H II regions at fine spatial scales uncovers detailed structures and reveals variations in ionization, abundance, and dynamical properties of ionized gas and the effect of stellar feedback. Using emission-line data of M33 observed with SITELLE as part of the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey (SIGNALS), we present maps of the principal optical emission-line ratios for NGC 604, the most luminous H II region in M33. The excitation maps align well with the Hα morphology and are clearly related to the location of the central stellar cluster and secondary stellar groups. The maps of ionization-sensitive line ratios show substantial variations across the face of NGC 604. We demonstrate that these variations are unlikely to be due to chemical inhomogeneities but are primarily caused by changes in ionization, which in turn affect the observed line ratios. We present the Hα kinematics of the region and connect it to the excitation structure, showing how the dynamic motions influence the spatial distribution of ionized gas. We note two distinct sources identified in these excitation maps: a known supernova remnant and a previously unknown planetary nebula. Such parsec-scale features contribute only a small percentage to the overall light and would remain undetected without the use of high-resolution spatial data. Throughout the paper, we make comparisons to and raise concerns about single-aperture and long-slit spectroscopic measurements of giant H II regions, highlighting the limitations and potential inaccuracies of such methods.

Keywords: Photoionization, H II regions, Interstellar medium, Spectroscopy