Sazuna/UAT_keywords huggingface dataset:
Robustness of Neural Ratio and Posterior Estimators to Distributional Shifts for Population-level Dark Matter Analysis in Strong Gravitational Lensing. We investigate the robustness of neural ratio estimators (NREs) and sequential neural posterior estimators (SNPEs) to distributional shifts in the context of measuring the abundance of dark matter subhalos using strong gravitational lensing data. While these data-driven inference frameworks can be accurate on test data from the same distribution as the training sets, in real applications, it is expected that simulated training data and true observational data will differ in their distributions. We explore the behavior of a trained NRE and trained SNPEs to estimate the population-level parameters of dark matter subhalos from a large sample of images of strongly lensed galaxies with test data presenting distributional shifts within and beyond the bounds of the training distribution in the nuisance parameters (e.g., the background source morphology). While our results show that NREs and SNPEs perform well when tested perfectly in distribution, they exhibit significant biases that often lead to not recovering the ground truth in the 3σ interval when confronted with slight deviations from the examples seen in the training distribution. This indicates the necessity for caution when applying NREs and SNPEs to real astrophysical data, where high-dimensional underlying distributions are not perfectly known.

Keywords: Galaxy dark matter halos, Neural networks, Strong gravitational lensing, Gravitational lensing, Dark matter
The Population of NuSTAR Black Hole X-Ray Binaries. The spin of a black hole (BH) encodes information about its formation and evolution history. Yet the understanding of the distribution of BH spins in X-ray binaries (XBs), of the models used to measure spin, and of their impact on systematic uncertainties remains incomplete. In this work, we expand on previous analyses of the entire NuSTAR archive of accreting BH XBs. Prior work compiled a sample of 245 spectral fits using the relativistic reflection method for NuSTAR observations of 36 BH systems. Here, we aim to probe two aspects: the connection between BH spin and binary system properties, and the relationships between parameters in the spectral fits. We identify moderate negative correlations between spin uncertainty and both BH mass and system inclination, and a moderate positive correlation with distance. We also point out tentative multidimensional degeneracies between inclination, disk density, Fe abundance, ionization, and the presence or absence of absorption features from ionized outflows linked to disk winds. Lastly, we provide a comprehensive view of the observed distribution of BH spins in XBs, in comparison to spins inferred from gravitational waves. We find that the distribution of BH spins in XBs can be described by a beta distribution with α = 5.66 and β = 1.09. This data set is highly complex, and the analysis presented here does not fully explore all potential parameter correlations. We make the full data set available in Zenodo to the community to encourage further exploration.

Keywords: X-ray binary stars, Black holes, High energy astrophysics, High mass x-ray binary stars, Compact objects, Low-mass x-ray binary stars, Astrophysical black holes
Pulsar Cyclic Spectroscopy in the Partial-deconvolution Regime: Benefits and Limitations. We explore possible advantages of cyclic spectroscopy for observations of pulsars in instances where full cyclic deconvolution is not possible. We compute cyclic merits and full-deconvolution regime boundaries for pulsars observed by NANOGrav and discuss which sources stand to benefit the most from using cyclic spectroscopy when observed with the Green Bank Telescope and DSA-2000 in a given frequency range. We compare data products, namely the wavefield, in both full-deconvolution and partial-deconvolution regimes to demonstrate what can be accomplished with incomplete phase retrieval. Additionally, we show how some phase retrieval can still be achieved in the partial-deconvolution regime and how this allows for additional information in scintillation-based data products, like the dynamic wavefield power, compared to what can be found in traditional dynamic spectra. An examination of dynamic wavefield phase as a function of observing frequency reveals more complete phase retrieval is achieved the closer one gets to the full-deconvolution regime, agreeing with the expectations of cyclic merit. While we demonstrate that fragmentary recovery of the secondary wavefield can be accomplished in the partial-deconvolution regime, we advocate for a synergistic approach with phase retrieval methods like the θ−θ transform, although we also provide discussion about shortcomings of this strategy. Finally, we use the combination of modest cyclic merit and lack of discernible results for PSR J1903+0327 to motivate the creation of an updated "cyclic merit 2.0," which relies on scintillation bandwidth instead of observing bandwidth.

Keywords: Interstellar medium, Pulsar timing method, Pulsars, Millisecond pulsars
Exploring the Accretion Disk/Corona Connection in NGC 6814: Insights from UV and X-Ray Spectral-timing Studies. We conducted a comprehensive spectral and timing analysis of NGC 6814 using AstroSat's 2019 and XMM-Newton's 2021 observations. A cross-correlation analysis revealed a significant correlation between far-UV (1541 Å)/X-ray and UVW1 (2910 Å)/X-ray variations, with delays of ∼15 ks and 30 ks, respectively. We constructed four broadband spectral energy distributions (SEDs) after applying aperture correction (for the Ultra-Violet Imaging Telescope filter), subtracting host galaxy and emission-line contributions from UV flux, and using mean X-ray spectra alongside selected UV data points. First, we fitted the SEDs with the KYNSED model, assuming various combinations of inclination θ, color correction factors fcol, and black hole spins. Best-fit models were achieved for θ = 70° (consistent with past estimates for this source) and for spin ≤0.5, while fcol is not constrained. KYNSED provided a satisfactory fit to all SEDs in the case when the corona is powered by the accretion process, with ∼10%–20% of the accretion power transferred to the corona,  ṁ/ṁEdd∼0.1 , a corona radius of ∼6–10rg, and a height of ∼7.5–35rg. Model time lags computed using the SED best-fit results are aligned well with the observed time lags. Although some of the model parameters are not constrained, the important result of our work is that both the broadband X-ray/UV spectra and the X-ray/UV time lags in NGC 6814 are consistent with the hypothesis of X-ray illumination of the disk in a lamp-post geometry framework. Within this model framework, we do not need to assume an outer or inner truncated disk.

Keywords: Seyfert galaxies, Active galactic nuclei, Time series analysis, Spectroscopy
Powerful Nuclear Outflows and Circumgalactic Medium Shocks Driven by the Most Luminous Known Obscured Quasar in the Universe. We report integral field spectroscopy observations with the Near-Infrared Spectrograph on board the James Webb Space Telescope, targeting the 60 kpc environment surrounding the most luminous obscured quasar known at z = 4.6. We detect ionized gas filaments on 40 kpc scales connecting a network of merging galaxies, likely to form a cluster. We find regions of low ionization consistent with large-scale shock excitation surrounding the central dust-obscured quasar, out to distances nearly 8 times the effective stellar radius of the quasar host galaxy. In the nuclear region, we find an ionized outflow driven by the quasar with velocities reaching 13,000 km s−1, one of the fastest discovered to date, with an outflow rate of 2000 M⊙ yr−1 and a kinetic luminosity of 6 × 1046 erg s−1, resulting in a coupling efficiency between the bolometric luminosity of the quasar and the outflow of 5%. The kinetic luminosity of the outflow is sufficient to power the turbulent motion of the gas on galactic and circumgalactic scales, and is likely the primary driver of the radiative shocks on interstellar medium and circumgalactic medium scales. This provides compelling evidence supporting long-standing theoretical predictions that powerful quasar outflows are a main driver in regulating the heating and accretion rate of gas onto massive central cluster galaxies.

Keywords: Supermassive black holes, High-redshift galaxy clusters, Quasars, Circumgalactic medium, Shocks
New Determination of the <SUP>14</SUP>C(n, γ)<SUP>15</SUP>C Reaction Rate and Its Astrophysical Implications. We present a novel experiment to investigate the spectroscopic factor (SF) of the 15C ground state for the first time using single-neutron removal transfer reactions on 15C. Two consistent SFs were derived from the (p, d) and (d, t) reactions, which were subsequently used to deduce the 14C(n, γ)15C reaction cross section and the corresponding stellar reaction rate. A typical cross section of 3.89 ± 0.76 μb is determined at  Ec.m.  = 23.3 keV. At the temperature range of 0.01–4 GK, our new reaction rate is 2.4–3.7 times higher than that of the first direct measurement and 20%–25% lower than that of the most recent direct measurement. Moreover, it is interesting that we can associate a long-standing nuclear structure issue, i.e., the so-called "quenching" effect, with this astrophysically relevant reaction. Finally, motivated by astrophysical interests of this reaction decades ago, implications of our new rate for several astrophysical problems are evaluated using state-of-the-art theoretical models. Our calculations demonstrate that the abundances of 14N and 15N can be enhanced in the inner regions of asymptotic giant branch stars, though with minimal impact on the chemical compositions of the interstellar medium. In the inhomogeneous Big Bang nucleosynthesis, the updated reaction rate can lead to a ∼20% variation in the final yields of 15N in neutron-rich regions. For the r-process in the core-collapse supernovae, a slight difference of ∼0.2% in the final abundances of heavy elements with A &gt; 90 can be found by using our new rate.

Keywords: Nucleosynthesis, R-process, Asymptotic giant branch stars, Nuclear astrophysics, Big Bang nucleosynthesis, Nuclear physics
Assessing the Role of Intrinsic Variability in Black Hole Parameter Inference Using Multiepoch EHT Data. Event Horizon Telescope (EHT) observations of M87* provide a means of constraining the parameters of both the black hole and its surrounding plasma. However, the intrinsic variability of the emitting material introduces major sources of uncertainty, which complicates parameter inference. The precise nature of this variability remains uncertain, and previous studies have largely relied on general relativistic magnetohydrodynamic simulations to estimate its effects. Here, we fit a semianalytic, dual-cone model of the emitting plasma to multiple years of EHT observations to empirically assess the impact of intrinsic variability and improved array coverage on key measurements, including the black hole mass-to-distance ratio, spin, and viewing inclination. Despite substantial differences in the images of the two epochs, we find that the inferred mass-to-distance ratio remains stable and mutually consistent. The black hole spin is unconstrained for both observations, despite the improved baseline coverage in 2018. We show that intrinsic variability can contribute significantly to the inference error and that the inferred position angle and inclination of the black hole spin axis are discrepant between the two years. Our findings highlight both the promise and challenges of multiepoch EHT observations: while they can refine parameter constraints, they also reveal the limitations of simple parametric models in capturing the full source complexity. Our analysis—the first to fit semianalytic emission models to 2018 EHT observations—underscores the importance of quantifying data contributions from intrinsic variability in future high-resolution imaging studies of black hole environments and the role of repeated observations in quantifying these uncertainties.

Keywords: Black hole physics, Supermassive black holes, Kerr black holes, Very long baseline interferometry, Classical black holes, Radio astronomy
The Intracluster Light of Abell 3667: Unveiling an Optical Bridge in LSST Precursor Data. Intracluster light (ICL), the diffuse glow of stars stripped from galaxies during a cluster's formation, is an established tracer of a cluster's dynamical history. The upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) is set to revolutionize studies of ICL by imaging the entire southern sky down to a limiting surface brightness μ ≳ 30 mag arcsec–2 by year 10. In this Letter, we create a precursor LSST data set (reaching the equivalent of year 8 depth) using Dark Energy Camera observations of Abell 3667 (A3667) and study its ICL. We have discovered a low surface brightness (μ ≳ 26 mag arcsec–2) optical bridge extending over ∼400 kpc, which connects the two brightest galaxies (BCG1 and BCG2) in the cluster; the color and surface brightness of the bridge is consistent with formation via a major merger. The inner regions of BCG1 (r &lt; 200 kpc) and BCG2 (r &lt; 50 kpc) are consistent with formation via gradual stripping of satellite galaxies, but BCG2's outer profile appears disrupted by a recent merger. We hypothesize that the bridge is a relic of a recent first pass between the two brightest galaxies and is composed of stars being stripped from BCG2. Future studies of ICL with LSST will discover new features such as the bridge in local clusters while enabling detailed studies of the stellar populations of these features with its six photometric bands.

Keywords: Galaxy clusters, Abell clusters, Galaxy mergers, Ground-based astronomy
Solar Disk Gamma-Ray Emission via Synthetic Magnetic Field from Photosphere to Low Corona. Gamma-ray emission in the GeV─TeV range from the solar disk is likely to arise from collisions of galactic cosmic rays (GCRs) with solar atmospheric plasma. In a previous study, we demonstrated that closed turbulent magnetic arcades trap GCRs efficiently, leading to a gamma-ray flux consistent with the Fermi-HAWC observations (from ∼0.1 GeV to ∼1 TeV). Here, we model a synthetic magnetic field with a static, laminar structure of open field lines in the chromosphere, increasingly braided near the solar surface, with a scale height of ∼10−2 R⊙. The height-dependent increase in magnetic field line braiding is modulated by an exponential scalar function, mimicking the bending of the photo- and chromospheric magnetic field revealed by polarimetric observations and reproduced by MHD simulations. Employing 3D test-particle numerical simulations, we investigate how distorted magnetic field lines affect the gamma-ray production by injecting GeV─TeV protons into both magnetically laminar and braided regions. We find that with the chosen spatial resolution, this synthetic magnetic field can account for the &gt;10 GeV gamma-ray spectrum observed by Fermi/HAWC. A rebrightening between approximately 30 and 100 GeV (following a ∼30 GeV spectral dip) suggests an enhanced confinement within the photo-/chromospheric layer by stronger braiding.

Keywords: Galactic cosmic rays, Solar atmosphere, Solar gamma-ray emission, Solar magnetic fields
Magnetic Webs in Stellar Radiative Zones. Rotational evolution of stellar radiative zones is an old puzzle. We argue that angular momentum transport by turbulent processes induced by differential rotation is insufficient, and propose that a key role is played by "magnetic webs." We define magnetic webs as stable magnetic configurations that enforce corotation of their coupled mass shells, and discuss their resistance to differential torques that occur in stars. Magnetic webs are naturally expected in parts of radiative zones that were formerly convective, retaining memory of extinguished dynamos. For instance, red giants with moderate masses M ≳ 1.3M⊙ likely contain a magnetic web deposited on the main sequence during the retreat of the central convective zone. The web couples the helium core to the hydrogen envelope of the evolving red giant and thus reduces spin-up of the contracting core. The magnetic field and the resulting slower rotation of the core are both consistent with asteroseismic observations, as we illustrate with a stellar evolution model with mass 1.6M⊙. Evolved massive stars host more complicated patterns of convective zones that may leave behind many webs, transporting angular momentum toward the surface. Efficient web formation likely results in most massive stars dying with magnetized and slowly rotating cores.

Keywords: Stellar interiors, Magnetohydrodynamics, Stellar magnetic fields, Stellar physics, Stellar rotation, Astrophysical fluid dynamics
Bifurcated Evolutionary Pathways in Multiplanet Systems Driven by Misaligned Protoplanetary Disks. Stellar obliquities, or spin–orbit angles, prevalent in exoplanet systems, can impose important constraints on their formation and evolution histories. Recent studies suggest that primordial misalignments between protoplanetary disks and stellar spin axes may significantly contribute to these obliquities, such as those frequently observed in systems hosting hot Jupiters. In this study, we demonstrate that misaligned protoplanetary disks combined with stellar oblateness drive complex dynamical evolution in planetary systems during their disk dispersal stages. Specifically, we identify bifurcated evolutionary pathways in multiplanet systems: systems with low star–disk misalignment angles (ψ⋆0) undergo smooth, adiabatic transport, producing nearly coplanar, low-obliquity configurations. In contrast, systems with high misalignment angles typically experience abrupt separatrix crossings in phase space, leading to large-amplitude libration of mutual planetary inclinations and then triggering chaotic eccentricity excitation. This libration and eccentricity excitation process can propagate outward in compact multiplanet systems, forming an excitation chain that can destabilize the entire system. The separatrix crossing arises from the dynamical bifurcation-induced effect, which occurs during disk dissipation when  ψ⋆0≳44.°6  (for one-planet systems). Our framework predicts that surviving typical compact multiplanet systems originating from misaligned disks evolve toward coplanar, low-obliquity configurations, consistent with observations of Kepler multiplanet systems. These results advance our understanding of planetary dynamics in misaligned disks and their evolutionary outcomes.

Keywords: Exoplanet dynamics, Celestial mechanics, Planetary-disk interactions, Star-planet interactions
The Effect of Stellar Magnetic Activity on Measurements of Morning and Evening Asymmetry of Planetary Terminator. Differences in the ingress and egress shapes of transit light curves can indicate morning–evening temperature contrasts on transiting planets. Here, we pinpoint an alternative mechanism that can introduce asymmetries in transit light curves, potentially affecting the accurate determination of morning–evening differences. Small-scale magnetic field concentrations on the surfaces of the host star affect the visibility of stellar limb regions, making them brighter relative to the nonmagnetic case. A difference in magnetization between the star's western and eastern limbs can thus create an asymmetry in limb brightness and, consequently, an asymmetry between transit ingress and egress. We model the limb darkening and stellar limb asymmetry in solar-like stars using the 3D radiative magnetohydrodynamics (MHD) code Max-Planck-Institute für Sonnensystemforshung (MPS)/University of Chicago Radiative MHD (MURaM) to simulate magnetized stellar atmospheres and the MPS-ATLAS code to synthesize spectra using a ray-by-ray approach. Our results show that ingress–egress depth differences can reach up to 600 ppm for a 10,000 ppm transit at 0.6 μm, depending on the magnetization of the stellar limbs, significantly interfering with planetary signals. Observations of the Sun show that such concentrations are often not accompanied by spots and do not manifest in photometric variability, indicating that even photometrically quiet stars can produce such asymmetries. However, planetary and stellar asymmetries exhibit distinct wavelength dependencies, which we propose to leverage for disentangling them.

Keywords: Transmission spectroscopy, Exoplanet atmospheres, Stellar activity
CAPERS-LRD-z9: A Gas-enshrouded Little Red Dot Hosting a Broad-line Active Galactic Nucleus at z = 9.288. We present CAPERS-LRD-z9, a little red dot (LRD) that we confirm to be a z = 9.288 broad-line active galactic nucleus (BLAGN). First identified as a high-redshift LRD candidate from PRIMER NIRCam photometry, follow-up NIRSpec/PRISM spectroscopy of CAPERS-LRD-z9 from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS) has revealed a broad 3500 km s‑1 full width at half-maximum Hβ emission line and narrow [O III] λλ4959, 5007 lines, indicative of a BLAGN. Based on the broad Hβ line, we compute a canonical black hole mass of  log(MBH/M⊙)=7.58±0.15 , although full consideration of systematic uncertainties yields a conservative range of  6.65&lt;log(MBH/M⊙)&lt;8.50 . These observations suggest that either a massive black hole seed or a lighter stellar remnant seed undergoing periods of super-Eddington accretion is necessary to grow such a massive black hole in ≲500 Myr of cosmic time. CAPERS-LRD-z9 exhibits a strong Balmer break, consistent with a central AGN surrounded by dense (∼1010 cm‑3) neutral gas. We model CAPERS-LRD-z9 using Cloudy to fit the emission redward of the Balmer break with a dense-gas-enshrouded AGN and bagpipes to fit the rest-ultraviolet emission as a host-galaxy stellar population. This upper limit on the stellar mass of the host galaxy (&lt;109 M⊙) implies that the black hole to stellar mass ratio may be extremely large, possibly &gt;5% (although systematic uncertainties on the black hole mass prevent strong conclusions). However, the shape of the UV continuum differs from typical high-redshift star-forming galaxies, indicating that this UV emission may also be of AGN origin; hence, the true stellar mass of the host may be still lower.

Keywords: AGN host galaxies, Supermassive black holes, James Webb Space Telescope, Active galactic nuclei
The Kick Velocity Distribution of Isolated Neutron Stars. Neutron stars (NSs) are thought to receive natal kicks at their formation in supernovae. In order to investigate the magnitude of these kicks, we analyze the proper motions and distance estimates—through either parallax or dispersion measures—of young isolated pulsars and infer their three-dimensional velocities relative to their local standard of rest. We find that the velocities based on parallax distances of pulsars younger than 10 Myr follow a lognormal distribution with μ = 5.60 ± 0.12 and σ = 0.68 ± 0.10, peaking at ∼150–200 km s‑1, which we adopt as our fiducial kick distribution. Using a previously established method that infers kick magnitudes through the eccentricity of Galactic trajectories, we also estimate the kick velocities of older pulsars, which we find to be consistent with our fiducial kick distribution. A lognormal fit to all pulsars with ages below 40 Myr yields a more constraining (but possibly more prone to systematic errors) fit with μ = 5.67 ± 0.10 and σ = 0.59 ± 0.08, respectively. Moreover, (1) we resolve the tension between our results and the Maxwellian distribution found by Hobbs et al., which has a ∼50% higher median velocity, by showing that their analysis is missing a Jacobian needed to correct for its logarithmic histogram bin sizes, and (2) we argue that the bimodality found by others is not statistically significant and that previous results are consistent with our inferred kick distribution, effectively reconciling the literature on observed NS kicks.

Keywords: Neutron stars, Pulsars