Sazuna/UAT_keywords huggingface dataset:
Pair Plasma Cascade in Rotating Black Hole Magnetospheres with a Split Monopole Flux Model. An electron-positron cascade in the magnetospheres of Kerr black holes (BHs) is a fundamental ingredient to fueling the relativistic γ-ray jets seen at the polar regions of galactic supermassive BHs (SMBHs). This leptonic cascade occurs in the spark gap region of a BH magnetosphere where the unscreened electric field parallel to the magnetic field is present; hence, it is affected by the magnetic field structure. A previous study explored the case of a thin accretion disk, representative of active galactic nuclei. Here we explore the case of a quasi-spherical gas distribution, as is expected to be present around the SMBH Sgr A* in the center of our Milky Way galaxy, for example. The properties and efficiency of the leptonic cascade are studied. The findings of our study and the implications for SMBH systems in various spectral and accretion states are discussed. The relationships and scalings derived from varying the mass of the BH and background photon spectra are further used to analyze the leptonic cascade process to power jets seen in astronomical observations. In particular, one finds the efficiency of the cascade in a quasi-spherical gas distribution peaks at the jet axis. Observationally, this should lead to a more prominent jet core, in contrast to the thin disk accretion case, where it peaks around the jet-disk interface. One also finds the spectrum of the background photons plays a key role. The cascade efficiency is maximum for a spectral index of 2, while harder and softer spectra lead to a less efficient cascade.

Keywords: Black hole physics, Jets, Plasma astrophysics, Gamma-rays
Accretion Flow Properties of EXO 1846-031 during Its Multi-peaked Outburst after Long Quiescence. We study the recent outburst of the black hole candidate EXO 1846-031, which went into an outburst in 2019 after almost 34 yr in quiescence. We use archival data from the Swift/XRT, MAXI/GSC, NICER/XTI, and NuSTAR/FPM satellites/instruments to study the evolution of the spectral and temporal properties of the source during the outburst. The low-energy (2-10 keV) X-ray flux of the outburst shows multiple peaks, making it a multipeak outburst. Evolving type-C quasi-periodic oscillations are observed in the NICER data in the hard, hard-intermediate, and soft-intermediate states. We use the physical two-component advective flow (TCAF) model to analyze the combined spectra of multiple satellite instruments. According to the TCAF model, the accreting matter is divided into Keplerian and sub-Keplerian parts, and the variation in the observed spectra in different spectral states arises out of the variable contributions of these two types of accreting matter in the total accretion rate. Studying the evolution of the accretion rates and other properties of the accretion flow obtained from the spectral analysis, we show that the multiple peaks in the outburst flux arise out of the variable supply of accreting matter from the pile-up radius. We determine the probable mass of the black hole to be ${10.4}_{-0.2}^{+0.1}\,{M}_{\odot }$ from the spectral analysis with the TCAF model. We also estimate the viscous timescale of the source in this outburst to be ~8 days from the peak difference of the Keplerian and sub-Keplerian mass-accretion rates.

Keywords: Accretion, Black hole physics, X-ray binary stars, Black holes, X-ray transient sources
Mapping Physical Conditions in Neighboring Hot Cores: NOEMA Studies of W3(H<SUB>2</SUB>O) and W3(OH). The complex chemistry that occurs in star-forming regions can provide insight into the formation of prebiotic molecules at various evolutionary stages of star formation. To study this process, we present millimeter-wave interferometric observations of the neighboring hot cores W3(H2O) and W3(OH) carried out using the NOEMA interferometer. We have analyzed distributions of six molecules that account for most observed lines across both cores and have constructed physical parameter maps for rotational temperature, column density, and velocity field with corresponding uncertainties. We discuss the derived spatial distributions of these parameters in the context of the physical structure of the source. We propose the use of HCOOCH3 as a new temperature tracer in W3(H2O) and W3(OH) in addition to the more commonly used ${\mathrm{CH}}_{3}\mathrm{CN}$ . By analyzing the physically derived parameters for each molecule across both W3(H2O) and W3(OH), the work presented herein further demonstrates the impact of physical environment on hot cores at different evolutionary stages.

Keywords: Star forming regions, H II regions, Interferometry, Astrochemistry
The Peculiar Ejecta Rings in the O-Rich Supernova Remnant Puppis A: Evidence of a Binary Interaction?. Near the center of the Puppis A supernova remnant a series of nested, optically emitting rings of high-velocity ejecta (known as "the Swirl") were identified several decades ago by Winkler et al. To date, no follow-up observations of these rings have been published, and their physical origin has remained a mystery. We present results of integral field spectroscopy of the Swirl using the Wide Field Integral Spectrograph on the 2.3 m telescope at Siding Spring Observatory in Australia. The outermost ring exhibits a nitrogen-rich spectrum blueshifted to 1350 km s-1, with smaller blueshifted rings within the first exhibiting mostly oxygen-rich spectra moving at 1000 and 750 km s-1. The structures are connected by material of intermediate velocity and variable composition, including sulfur-rich material. The Swirl is turbulent and shock-excited, and contains as much as 0.5 M ☉ of metal-rich material. The chemical composition and exclusively blueshifted radial velocities of the Swirl are consistent with progressively deeper nucleosynthetic layers in a massive progenitor star. We suggest the possibility that the Swirl marks a "funnel" carved into the supernova ejecta by a close, massive binary companion at the moment of explosion.

Keywords: Supernova remnants
H I in Molecular Clouds: Irradiation by FUV Plus Cosmic Rays. We extend the analytic theory presented by Sternberg et al. and Bialy &amp; Sternberg for the production of atomic hydrogen (H I) via far-ultraviolet (FUV) photodissociation at the boundaries of dense interstellar molecular (H2) clouds to also include the effects of penetrating (low-energy) cosmic rays (CRs) for the growth of the total H I column densities. We compute the steady-state abundances of the H I and H2 in one-dimensional gas slabs in which the FUV photodissociation rates are reduced by depth-dependent H2 self-shielding and dust absorption and the CR ionization rates are either constant or reduced by transport effects. The solutions for the H I and H2 density profiles and the integrated H I columns depend primarily on the ratios I UV/Rn and ζ/Rn, where I UV is the intensity of the photodissociating FUV field, ζ is the H2 CR ionization rate, n is the hydrogen gas density, and R is the dust surface H2 formation rate coefficient. We present computations for a wide range of FUV field strengths, CR ionization rates, and dust-to-gas ratios. We develop analytic expressions for the growth of the H I column densities. For Galactic giant molecular clouds (GMCs) with multiphased (warm/cold) H I envelopes, the interior CR zones will dominate the production of the H I only if $\zeta \gtrsim 4.5\times {10}^{-16}\times {({M}_{\mathrm{GMC}}/{10}^{6}\ {M}_{\odot })}^{-1/2}$ s-1, where M GMC is the GMC mass, and including attenuation of the CR fluxes. For most Galactic GMCs and conditions, FUV photodissociation dominates over CR ionization for the production of the H I column densities. Furthermore, the CRs do not affect the H I-to-H2 transition points.

Keywords: Interstellar atomic gas, Molecular clouds, Interstellar dust extinction, Neutral hydrogen clouds, Galactic cosmic rays, Giant molecular clouds, Radiative transfer
Structure and Color Gradients of Ultradiffuse Galaxies in Distant Massive Galaxy Clusters. We have measured structural parameters and radial color profiles of 108 ultradiffuse galaxies (UDGs), carefully selected from six distant massive galaxy clusters in the Hubble Frontier Fields (HFF) in a redshift range from 0.308 to 0.545. Our best-fitting GALFIT models show that the HFF UDGs have a median Sérsic index of 1.09, which is close to 0.86 for local UDGs in the Coma cluster. The median axis-ratio value is 0.68 for HFF UDGs and 0.74 for Coma UDGs, respectively. The structural similarity between HFF and Coma UDGs suggests that they are the same kind of galaxies seen at different times, and that the structures of UDGs do not change at least for several billion years. By checking the distribution of HFF UDGs in the rest-frame UVJ and UVI diagrams, we find a large fraction of them are star forming. Furthermore, a majority of HFF UDGs show small U - V color gradients within the 1 ∗ R e,SMA region, and the fluctuation of the median radial color profile of HFF UDGs is smaller than 0.1 mag, which is compatible to Coma UDGs. Our results indicate that cluster UDGs may fade or quench in a self-similar way, irrespective of the radial distance, in less than ~4 Gyr.

Keywords: Low surface brightness galaxies
First Constraints on Helium <SUP>+</SUP>He<SUP>3</SUP> Evolution in z = 3-4 Using the 8.67 GHz Hyperfine Transition. We present the first constraints on the cross-correlation power spectrum of the He II (+He3) signal strength using the redshifted 8.67 GHz hyperfine transition between z = 2.9 and 4.1 and with interferometric data obtained from the public archive of the Australia Telescope Compact Array (ATCA). 210 hr of observations of the primary calibrator source B1934-638 were extracted from data obtained with the telescope from 2014-2021, and coherently combined in a power spectrum pipeline to measure the He II power across a range of spatial scales, and at three redshifts that span the period of helium reionization. Our best limit places the fluctuation of the brightness temperature to be less than 557 μK on spatial scales of 30' at z = 2.91, and less than 755 μK on scales of 30' at z = 4.14 (2σ noise limited). We measure a temperature of 489 μK at z = 2.91. ATCA's few antennas and persistent remaining radio frequency interference in the data prevent deeper integrations improving the results. This work is a proof of principle to demonstrate how this type of experiment can be undertaken to reach the 0.01-1 μK level expected for the helium signal at z ~ 4.

Keywords: Cosmology, Reionization, Astronomical instrumentation, Radio interferometers
Rapid Optical Flares in the Blazar OJ 287 on Intraday Timescales with TESS. We have analyzed the optical light curves of the blazar OJ 287 obtained with the Transiting Exoplanet Survey Satellite over about 80 days from 2021 October 13 to December 31, with an unprecedented sampling of 2 minutes. Although significant variability has been found during the entire period, we have detected two exceptional flares with flux nearly doubling and then nearly tripling over 2 days in the middle of 2021 November. We went through the light-curve analysis using the excess variance, generalized Lomb-Scargle periodogram, and continuous autoregressive moving average methods and estimated the flux halving/doubling timescales. The most probable shortest variability timescale was found to be 0.38 days in the rising phase of the first flare. We briefly discuss some emission models for the variability in radio-loud active galactic nuclei that could be capable of producing such fast flares.

Keywords: Blazars, Jets, Active galactic nuclei, BL Lacertae objects
Magnetogenesis in a Collisionless Plasma: From Weibel Instability to Turbulent Dynamo. We report on a first-principles numerical and theoretical study of plasma dynamo in a fully kinetic framework. By applying an external mechanical force to an initially unmagnetized plasma, we develop a self-consistent treatment of the generation of "seed" magnetic fields, the formation of turbulence, and the inductive amplification of fields by the fluctuation dynamo. Driven large-scale motions in an unmagnetized, weakly collisional plasma are subject to strong phase mixing, which leads to the development of thermal pressure anisotropy. This anisotropy triggers the Weibel instability, which produces filamentary "seed" magnetic fields on plasma-kinetic scales. The plasma is thereby magnetized, enabling efficient stretching and folding of the fields by the plasma motions and the development of Larmor-scale kinetic instabilities such as the firehose and mirror. The scattering of particles off the associated microscale magnetic fluctuations provides an effective viscosity, regulating the field morphology and turbulence. During this process, the seed field is further amplified by the fluctuation dynamo until energy equipartition with the turbulent flow is reached. By demonstrating that equipartition magnetic fields can be generated from an initially unmagnetized plasma through large-scale turbulent flows, this work has important implications for the origin and amplification of magnetic fields in the intracluster and intergalactic mediums.

Keywords: Plasma astrophysics, Intergalactic medium, Cosmic magnetic fields theory, Intracluster medium, Extragalactic magnetic fields
Modeling the High-energy Ionizing Output from Simple Stellar and X-Ray Binary Populations. We present a methodology for modeling the joint ionizing impact due to a "simple X-ray population" (SXP) and its corresponding simple stellar population (SSP), where "simple" refers to a single age and metallicity population. We construct composite spectral energy distributions (SEDs) including contributions from ultraluminous X-ray sources and stars, with physically meaningful and consistent consideration of the relative contributions of each component as a function of instantaneous burst age and stellar metallicity. These composite SEDs are used as input for photoionization modeling with Cloudy, from which we produce a grid for the time- and metallicity-dependent nebular emission from these composite populations. We make the results from the photoionization simulations publicly available. We find that the addition of the SXP prolongs the high-energy ionizing output from the population-and correspondingly increases the intensity of nebular lines such as He II λ1640,4686, [Ne V] λ3426,14.3 μm, and [O IV] 25.9 μm by factors of at least two relative to models without an SXP spectral component. This effect is most pronounced for instantaneous bursts of star formation on timescales &gt;10 Myr and at low metallicities (~0.1 Z ⊙), due to the imposed time- and metallicity-dependent behavior of the SXP relative to the SSP. We propose nebular emission line diagnostics accessible with JWST suitable for inferring the presence of a composite SXP + SSP, and we discuss how the ionization signatures compare to models for sources such as intermediate-mass black holes.

Keywords: Starburst galaxies, Photoionization, Stellar populations, Emission line galaxies, Ultraluminous x-ray sources
Constraints on Neutron Star Structure from the Clocked X-Ray Burster 1RXS J180408.9-342058. Type I X-ray bursts are rapid-brightening transient phenomena on the surfaces of accreting neutron stars (NSs). Some X-ray bursts, called clocked bursters, exhibit regular behavior with similar light-curve profiles in their burst sequences. The periodic nature of clocked bursters has the advantage of constraining X-ray binary parameters and physics inside the NS. In the present study, we compute numerical models, based on different equations of state and NS masses, which are compared with the observations of a recently identified clocked burster, 1RXS J180408.9-342058. We find that the relation between the accretion rate and the recurrence time is highly sensitive to the NS mass and radius. We determine, in particular, that 1RXS J180408.9-342058 appears to possess a mass less than 1.7M ⊙ and favors a stiffer nuclear equation of state (with an NS radius ≳12.7 km). Consequently, the observations of this new clocked burster may provide additional constraints for probing the structure of NSs.

Keywords: Neutron stars, Low-mass x-ray binary stars, X-ray bursts
Coevolution and Nuclear Structure in the Dwarf Galaxy POX 52 Studied by Multiwavelength Data from Radio to X-Ray. The nearby dwarf galaxy POX 52 at z = 0.021 hosts an active galactic nucleus (AGN) with a black hole (BH) mass of M BH ~ 105-6 M ☉ and an Eddington ratio of ~0.1-1. This object provides the rare opportunity to study both AGN and host-galaxy properties in a low-mass highly accreting system. To do so, we collected its multiwavelength data from X-ray to radio. First, we construct a spectral energy distribution, and by fitting it with AGN and host-galaxy components, we constrain AGN-disk and dust-torus components. Then, while considering the AGN-disk emission, we decompose optical Hubble Space Telescope images. As a result, it is found that a classical bulge component is probably present, and its mass (M bulge) is consistent with an expected value from a local relation. Lastly, we analyze new quasi-simultaneous X-ray (0.2-30 keV) data obtained by the Nuclear Spectroscopic Telescope Array and XMM-Newton. The X-ray spectrum can be reproduced by multicolor blackbody, warm and hot coronae, and disk and torus reflection components. Based on this, the spin is estimated to be a spin = 0.998-0.814, which could suggest that most of the current BH mass was achieved by prolonged mass accretion. Given the presence of the bulge, POX 52 would have undergone a galaxy merger, while the M BH-M bulge relation and the inferred prolonged accretion could suggest that AGN feedback occurred. Regarding the AGN structure, the spectral slope of the hot corona, its relative strength to the bolometric emission, and the torus structure are found to be consistent with Eddington-ratio dependencies found for nearby AGNs.

Keywords: AGN host galaxies, Intermediate-mass black holes, Active galactic nuclei, X-ray active galactic nuclei, Galaxy evolution, Astrophysical black holes
Suprathermal Population Associated with Stream Interaction Regions Observed by STEREO-A: New Insights. Stream interaction regions (SIRs) are often thought to be responsible for the generation of suprathermal population in the interplanetary medium. Even though the source is the same, wide variations in the spectral indices of suprathermal populations are observed at 1 au during SIRs. This poses a significant uncertainty in understanding the generation of suprathermal ion populations by SIRs and indicates an interplay of multiple source mechanisms. By analyzing variations in suprathermal 4He, O, and Fe for 20 SIR events recorded by STEREO-A during 2007-2014, we find that the spectral indices of these elements vary in the range of 2.06-4.08, 1.85-4.56, and 2.11-4.04 for 19 events. However, in one special case, all three suprathermal elements show nearly identical (~1.5) spectral indices. We describe possible mechanisms that might cause significant variations in the spectral indices of suprathermal particles. More importantly, we show the possible role of merging and/or contraction of small-scale magnetic islands near 1 au in producing nearly identical spectral indices for three different elements with different first ionization potentials and mass-to-charge ratios. The occurrence of these magnetic islands near 1 au also supports the minimal modulation in the spectral indices of these particles. We also suggest that a possible solar flare may have played a role in generating these magnetic islands near the heliospheric current sheet.

Keywords: Interplanetary shocks, Solar flares, Solar energetic particles, Solar wind, Corotating streams
Sharp Decay of the Internal Plateau in Gamma-Ray Bursts: The Effect of a Cocoon's Thermal Photons on the Jet Emission. Sub-TeV or TeV γ-rays have been convincingly detected in the afterglows of some gamma-ray bursts (GRBs). The relativistic jet associated with GRBs may be surrounded by a cocoon and thus the thermal photons of the cocoon pervading the emission region of the jet can be upscattered to the very-high-energy regime (e.g., sub-TeV/TeV) by the electrons in the jet. In this scenario, the electrons in the jet cool down and thus the jet emission in the low-energy regime, e.g., the X-ray or optical, may be suppressed. In this paper, we study the effect of the cocoon's thermal photons on the jet emission in the low-energy regime. We find that the jet emission in the low-energy regime is significantly suppressed when the emission region of the jet is just encircled by a hot cocoon. Correspondingly, there is a sharp decay in the light curves of the jet emission in the low-energy regime, which can be understood to signify strong TeV emission in GRBs. Since the radius of the cocoon expands with the observer time t obs, the suppression of the jet emission in the low-energy regime may be relieved and thus the light curves of the jet emission would return to those of emission without a cocoon-external inverse-Compton cooling effect. For a long-lasting jet with power $\propto {(1+{t}_{\mathrm{obs}}/{t}_{c})}^{\alpha }$ , an internal plateau followed by a sharp decay may generally appear.

Keywords: Gamma-ray bursts
ÆSOPUS 2.0: Low-temperature Opacities with Solid Grains. In this study we compute the equation of state and Rosseland mean opacity from temperatures of T ≃ 30,000 K down to T ≃ 400 K, pushing the capabilities of the ÆSOPUS code into the regime where solid grains can form. The GGchem code is used to solve the chemistry for temperatures less than ≃3000 K. Atoms, molecules, and dust grains in thermodynamic equilibrium are all included in the equation of state. To incorporate monochromatic atomic and molecular cross sections, an optimized opacity sampling technique is used. The Mie theory is employed to calculate the opacity of 43 grain species. Tables of Rosseland mean opacities for scaled-solar compositions are provided. Based on our computing resources, opacities for other chemical patterns, as well as various grain sizes, porosities, and shapes, can be easily computed upon user request to the corresponding author.

Keywords: Stellar atmospheric opacity, Carbonaceous grains, Silicate grains, Astrochemistry
Particle Clustering in Turbulence: Prediction of Spatial and Statistical Properties with Deep Learning. We investigate the utility of deep learning for modeling the clustering of particles that are aerodynamically coupled to turbulent fluids. Using a Lagrangian particle module within the Athena++ hydrodynamics code, we simulate the dynamics of particles in the Epstein drag regime within a periodic domain of isotropic forced hydrodynamic turbulence. This setup is an idealized model relevant to the collisional growth of micron- to millimeter-sized dust particles in early-stage planet formation. The simulation data are used to train a U-Net deep-learning model to predict gridded three-dimensional representations of the particle density and velocity fields, given as input the corresponding fluid fields. The trained model qualitatively captures the filamentary structure of clustered particles in a highly nonlinear regime. We assess model fidelity by calculating metrics of the density field (the radial distribution function) and of the velocity field (the relative velocity and the relative radial velocity between particles). Although trained only on the spatial fields, the model predicts these statistical quantities with errors that are typically &lt;10%. Our results suggest that, given appropriately expanded training data, deep learning could complement direct numerical simulations in predicting particle clustering within turbulent flows.

Keywords: Hydrodynamical simulations, Protoplanetary disks, Planet formation, Neural networks