Sazuna/UAT_keywords huggingface dataset:
Kilonova Emission from Black Hole-Neutron Star Mergers. II. Luminosity Function and Implications for Target-of-opportunity Observations of Gravitational-wave Triggers and Blind Searches. We present detailed simulations of the kilonova and gamma-ray burst (GRB) afterglow and kilonova luminosity function from black hole-neutron star (BH-NS) mergers, and discuss the detectability of an electromagnetic (EM) counterpart in connection with gravitational wave (GW) detections, GW-triggered target-of-opportunity observations, and time-domain blind searches. The predicted absolute magnitude of BH-NS kilonovae at 0.5 days after the merger falls in the range [-10, -15.5]. The simulated luminosity function contains potential information on the viewing-angle distribution of the anisotropic kilonova emission. We simulate the GW detection rates, detectable distances, and signal duration for future networks of 2nd/2.5th/3rd generation GW detectors. BH-NSs tend to produce brighter kilonovae and afterglows if the BH has a higher aligned spin, and a less massive NS with a stiffer equation of state. The detectability of kilonovae is especially sensitive to the BH spin. If BHs typically have low spins, the BH-NS EM counterparts are hard to discover. For 2nd generation GW detector networks, a limiting magnitude of mlimit ~ 23-24 mag is required to detect kilonovae even if high BH spin is assumed. Thus, a plausible explanation for the lack of BH-NS-associated kilonova detection during LIGO/Virgo O3 is that either there is no EM counterpart (plunging events) or the current follow-ups are too shallow. These observations still have the chance to detect the on-axis jet afterglow associated with a short GRB or an orphan afterglow. Follow-up observations can detect possible associated short GRB afterglows, from which kilonova signatures may be studied. For time-domain observations, a high-cadence search in redder filters is recommended to detect more BH-NS-associated kilonovae and afterglows.

Keywords: Neutron stars, Gamma-ray bursts, Gravitational waves, Black holes
The Formation and Lifetime of Outflows in a Solar Active Region. Active regions are thought to be one contributor to the slow solar wind. Upflows in EUV coronal spectral lines are routinely observed at their boundaries, and provide the most direct way for upflowing material to escape into the heliosphere. The mechanisms that form and drive these upflows, however, remain to be fully characterized. It is unclear how quickly they form, or how long they exist during their lifetimes. They could be initiated low in the atmosphere during magnetic flux emergence, or as a response to processes occurring high in the corona when the active region is fully developed. On 2019 March 31 a simple bipolar active region (AR 12737) emerged and upflows developed on each side. We used observations from Hinode, SDO, IRIS, and Parker Solar Probe (PSP) to investigate the formation and development of the upflows from the eastern side. We used the spectroscopic data to detect the upflow, and then used the imaging data to try to trace its signature back to earlier in the active region emergence phase. We find that the upflow forms quickly, low down in the atmosphere, and that its initiation appears associated with a small field-opening eruption and the onset of a radio noise storm detected by PSP. We also confirmed that the upflows existed for the vast majority of the time the active region was observed. These results suggest that the contribution to the solar wind occurs even when the region is small, and continues for most of its lifetime.

Keywords: Slow solar wind, Solar physics, Solar active regions, Solar energetic particles
Resolving Complex Inner X-Ray Structure of the Gravitationally Lensed AGN MG B2016+112. We use a Chandra X-ray observation of the gravitationally lensed system MG B2016+112 at z = 3.273 to elucidate the presence of at least two X-ray sources. We find that these sources are consistent with the very long baseline interferometry (VLBI) components measured by Spingola, which are separated by ~200 pc. Their intrinsic 0.5-7 keV source frame luminosities are 1.5 × 1043 and 1.8 × 1044 erg s-1, respectively. Most likely this system contains a dual active galactic nucleus (AGN), but we are possibly detecting an AGN plus a parsec-scale X-ray jet, the latter lying in a region at very high magnification. The quadruply lensed X-ray source is within ±40 pc (1σ) of its VLBI counterpart. Using a gravitational lens as a telescope, and a novel statistical application, we have achieved unprecedented accuracy for measuring metric distances at such large redshifts in X-ray astronomy. This is tens of mas if the source is located close to the caustics, while it is of hundreds of mas if the source is in a region at lower amplification. The present demonstration of this approach has implications for future X-ray investigations of large numbers of lensed systems.

Keywords: Radio loud quasars, X-ray active galactic nuclei, Gravitational lensing, Astrometry
Measuring the Magnetic Origins of Solar Flares, Coronal Mass Ejections, and Space Weather. We take a broad look at the problem of identifying the magnetic solar causes of space weather. With the lackluster performance of extrapolations based upon magnetic field measurements in the photosphere, we identify a region in the near-UV (NUV) part of the spectrum as optimal for studying the development of magnetic free energy over active regions. Using data from SORCE, the Hubble Space Telescope, and SKYLAB, along with 1D computations of the NUV spectrum and numerical experiments based on the MURaM radiation-magnetohydrodynamic and HanleRT radiative transfer codes, we address multiple challenges. These challenges are best met through a combination of NUV lines of bright Mg II, and lines of Fe II and Fe I (mostly within the 4s-4p transition array) which form in the chromosphere up to 2 × 104 K. Both Hanle and Zeeman effects can in principle be used to derive vector magnetic fields. However, for any given spectral line the τ = 1 surfaces are generally geometrically corrugated owing to fine structure such as fibrils and spicules. By using multiple spectral lines spanning different optical depths, magnetic fields across nearly horizontal surfaces can be inferred in regions of low plasma β, from which free energies, magnetic topology, and other quantities can be derived. Based upon the recently reported successful sub-orbital space measurements of magnetic fields with the CLASP2 instrument, we argue that a modest space-borne telescope will be able to make significant advances in the attempts to predict solar eruptions. Difficulties associated with blended lines are shown to be minor in an Appendix.

Keywords: Magnetohydrodynamics, Spectropolarimetry, Solar flares, Space weather, The Sun, Active sun, Solar coronal mass ejections, Solar corona, Solar transition region, Solar chromosphere
White Dwarf Subsystems in Core-Collapsed Globular Clusters. Numerical and observational evidence suggests that massive white dwarfs dominate the innermost regions of core-collapsed globular clusters by both number and total mass. Using NGC 6397 as a test case, we constrain the features of white dwarf populations in core-collapsed clusters, both at present day and throughout their lifetimes. The dynamics of these white dwarf subsystems have a number of astrophysical implications. We demonstrate that the collapse of globular cluster cores is ultimately halted by the dynamical burning of white dwarf binaries. We predict that core-collapsed clusters in the local universe yield a white dwarf merger rate of ${ \mathcal O }(10)\,{{\rm{Gpc}}}^{-3}\,{{\rm{yr}}}^{-1}$ , roughly 0.1%-1% of the observed Type Ia supernova rate. We show that prior to merger, inspiraling white dwarf binaries will be observable as gravitational-wave sources at millihertz and decihertz frequencies. Over 90% of these mergers have a total mass greater than the Chandrasekhar limit. We argue that the merger/collision remnants, if not destroyed completely in an explosive transient, may be observed in core-collapsed clusters either as young neutron stars/pulsars/magnetars (in the event of accretion-induced collapse) or as young massive white dwarfs offset from the standard white dwarf cooling sequence. Finally, we show that collisions between white dwarfs and main-sequence stars, which may be detectable as bright transients, occur at a rate of ${ \mathcal O }(100)\,{{\rm{Gpc}}}^{-3}\,{{\rm{yr}}}^{-1}$ in the local universe. We find that these collisions lead to depletion of blue straggler stars and main-sequence star binaries in the centers of core-collapsed clusters.

Keywords: Globular star clusters, White dwarf stars, Stellar dynamics, Gravitational wave astronomy, Type Ia supernovae
Hydrodynamics of Small Transient Brightenings in the Solar Corona. Small scale transients occur in the solar corona at much higher frequencies than flares and play a significant role in coronal dynamics. Here we study three well-identified transients discovered by Hi-C and also detected by the EUV channels of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. We use 0D enthalpy-based hydrodynamical simulations and produce synthetic light curves to compare with AIA observations. We have modeled these transients as loops of ~1.0 Mm length depositing energies ~1023 erg in ~50 s. The simulated synthetic light curves show reasonable agreement with the observed light curves. During the initial phase, conduction flux from the corona dominates over the radiation, like impulsive flaring events. Our results further show that the time-integrated net enthalpy flux is positive, hence into the corona. The fact that we can model the observed light curves of these transients reasonably well by using the same physics as those for nanoflares, microflares, and large flares, suggests that these transients may have a common origin.

Keywords: Hydrodynamical simulations, Solar coronal transients, Solar flares, Solar coronal loops, Solar coronal heating, Solar corona, Solar transition region
Signatures of Recent Cosmic-Ray Acceleration in the High-latitude Gamma-Ray Sky. Cosmic-ray (CR) sources temporarily enhance the relativistic particle density in their vicinity over the background distribution accumulated from the Galaxy-wide past injection activity and propagation. If individual sources are close enough to the solar system, their localized enhancements may present as features in the measured spectra of the CRs and in the associated secondary electromagnetic emissions. Large-scale loop-like structures visible in the radio sky are possible signatures of such nearby CR sources. If so, these loops may also have counterparts in the high-latitude γ-ray sky. Using ~10 yr of data from the Fermi Large Area Telescope, applying Bayesian analysis including Gaussian Processes, we search for extended enhanced emission associated with putative nearby CR sources in the energy range from 1 GeV to 1 TeV for the sky region ∣b∣ &gt; 30°. We carefully control the systematic uncertainty due to imperfect knowledge of the interstellar gas distribution. Radio Loop IV is identified for the first time as a γ-ray emitter, and we also find significant emission from Loop I. Strong evidence is found for asymmetric features about the Galactic l = 0° meridian that may be associated with parts of the so-called "Fermi Bubbles," and some evidence is also found for γ-ray emission from other radio loops. Implications for the CRs producing the features and possible locations of the sources of the emissions are discussed.

Keywords: High-energy cosmic radiation, Galaxy structure, Galactic cosmic rays, Interstellar medium, Cosmic ray sources, Gamma-ray astronomy
Tides in the High-eccentricity Migration of Hot Jupiters: Triggering Diffusive Growth by Nonlinear Mode Interactions. High-eccentricity migration is a possible formation channel for hot Jupiters. However, in order for it to be consistent with the observed population of planets, tides must circularize the orbits in an efficient manner. A potential mechanism for such rapid circularization is the diffusive growth of the tidally driven planetary f-mode. Such growth occurs if the f-mode phase at pericenter varies chaotically from one pericenter passage to the next. Previous studies focused on the variation of the orbital period due to tidal back-reaction on the orbit as the source of chaos. Here we show that nonlinear mode interactions can also be an important source. Specifically, we show that nonlinear interactions between a parent f-mode and daughter f-/p-modes induce an energy-dependent shift in the oscillation frequency of the parent. This frequency shift varies randomly from orbit to orbit because the parents' energy varies. As a result, the parents' phase at pericenter varies randomly, which we find can trigger it to grow diffusively. We show that the phase shift induced by nonlinear mode interactions in fact dominates the shift induced by tidal back-reaction and lowers the one-kick energy threshold for diffusive growth by about a factor of 5 compared to the prediction from the linear theory. For a given pericenter distance, this reduces the semimajor axis needed to trigger diffusive growth from ≳2 au to ≃1 au. Nonlinear interactions could thus enhance the formation rate of hot Jupiters through the high-eccentricity migration channel and potentially mitigate the discrepancy between the observed and predicted occurrence rates for close-in gas giants as compared to those farther from the star.

Keywords: Exoplanet migration, Hot Jupiters, Hydrodynamics, Exoplanets, Exoplanet tides
Pair Cascades at the Edge of the Broad-line Region Shaping the Gamma-Ray Spectrum of 3C 279. The blazar 3C 279 emits a flux of gamma rays that is variable on timescales as short as the light-crossing time across the event horizon of its central black hole. It is commonly reported that the spectral energy distribution (SED) does not show signs of pair attenuation due to interactions of the gamma rays with ambient ultraviolet photons, concluding that the gamma rays must originate from substructures in the jet outside of the broad-line region (BLR). We address the spectral signature imprinted by atomic emission lines on the gamma-ray spectrum produced by an inverse-Compton pair cascade in the photon field of the BLR. We determine with high precision the gamma-ray SED of 3C 279 using Fermi Large Area Telescope data from MJD 58129-58150 and simulate the pair cascade spectrum for three different injection terms. Satisfactory fits to the observational data are obtained. The obtained SED shows features imprinted by pair production on atomic emission line photons due to optically thick radiation transport, but lacking further exponential attenuation expected if the emission region would lie buried deep within the BLR. The SED of 3C 279 is consistent with an inverse-Compton pair cascade spectrum without exponential external pair absorption. Our findings support the view that the gamma-ray emission in 3C 279 originates from the edge of the BLR.

Keywords: Supermassive black holes, Quasars, Gamma-ray sources, Blazars, Active galaxies, Flat-spectrum radio quasars, Relativistic jets, Active galactic nuclei, Non-thermal radiation sources, Radiative processes, Gamma-rays
A Flexible Gaussian Process Reconstruction Method and the Mass Function of the Coalescing Binary Black Hole Systems. We develop a new method based on Gaussian processes to reconstruct the mass distribution of binary black holes (BBHs). Instead of prespecifying the formalisms of mass distribution, we introduce a more flexible and nonparametric model with which the distribution can be mainly determined by the observed data. We first test our method with simulated data and find that it can well recover the injected distribution. Then, we apply this method to analyze the data of BBHs' observations from LIGO-Virgo Gravitational-Wave Transient Catalog 2. By reconstructing the chirp mass distribution, we find that there is a peak or a platform located at 20-30 M⊙ rather than a single-power-law-like decrease from low mass to high mass. Moreover, one or two peaks in the chirp mass range of ${ \mathcal M }\lt 20\,{M}_{\odot }$ may be favored by the data. Assuming a mass-independent mass ratio distribution of p(q) ∝ q1.4, we further obtain a distribution of primary mass and find that there is a feature located in the range of (30, 40) M⊙, which can be related to BROKEN POWER LAW and POWER LAW &amp; PLUS PEAK distributions described in Collaboration et al. Besides, the merger rate of BBHs is estimated to be ${ \mathcal R }={26.29}_{-8.96}^{+14.21}\,{\mathrm{Gpc}}^{-3}\,{\mathrm{yr}}^{-1}$ , supposing that there is no redshift evolution.

Keywords: Gravitational wave astronomy, Astrophysical black holes, Gaussian Processes regression
Supermassive Star Formation in Magnetized Atomic-cooling Gas Clouds: Enhanced Accretion, Intermittent Fragmentation, and Continuous Mergers. The origin of supermassive black holes (with ≳109 M⊙) in the early universe (redshift z ~ 7) remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We focus on the magnetic effects on star formation that occurs in an atomic-cooling gas cloud. Using a set of three-dimensional magnetohydrodynamic simulations, we investigate the star formation process in the magnetized atomic-cooling gas cloud with different initial magnetic field strengths. Our simulations show that the primordial magnetic seed field can be quickly amplified during the early accretion phase after the first protostar formation. The strong magnetic field efficiently extracts angular momentum from accreting gas and increases the accretion rate, which results in the high fragmentation rate in the gravitationally unstable disk region. On the other hand, the coalescence rate of fragments is also enhanced by the angular momentum transfer due to the magnetic effects. Almost all the fragments coalesce to the primary star, so the mass growth rate of the massive star increases due to the magnetic effects. We conclude that the magnetic effects support the direct collapse scenario of supermassive star formation.

Keywords: Population III stars, Primordial magnetic fields, Star formation, Protostars, Magnetic fields, Magnetohydrodynamical simulations
Magnetic Properties of Star-forming Dense Cores. Magnetic and energetic properties are presented for 17 dense cores within a few hundred parsecs of the Sun. Their plane-of-sky field strengths Bpos are estimated from the dispersion of polarization directions, following Davis, Chandrasekhar, and Fermi (DCF). Their ratio of mass to magnetic critical mass is $0.5\lesssim M/{M}_{B}\lesssim 3$ , indicating nearly critical field strengths. The field strength Bpos is correlated with column density N as ${B}_{\mathrm{pos}}\propto {N}^{p}$ , where $p=1.05\pm 0.08$ , and with density n as ${B}_{\mathrm{pos}}\propto \ {n}^{q}$ , where $q=0.66\pm 0.05$ . These magnetic properties are consistent with those derived from Zeeman studies, with less scatter. Relations between virial mass MV, magnetic critical mass MB, and Alfvén amplitude ${\sigma }_{B}/B$ match the observed range of M/MB for cores observed to be nearly virial, $0.5\lesssim M/{M}_{V}\lesssim 2$ , with moderate Alfvén amplitudes, $0.1\lesssim {\sigma }_{B}/B\lesssim 0.4$ . The B - N and B - n correlations in the DCF and Zeeman samples can be explained when such bound, Alfvénic, and nearly critical cores have central concentration and spheroidal shape. For these properties, $B\propto N$ because M/MB is nearly constant compared to the range of N, and $B\propto {n}^{2/3}$ because M1/3 is nearly constant compared to the range of n2/3. The observed core fields that follow $B\propto {n}^{2/3}$ need not be much weaker than gravity, in contrast to core fields that follow $B\propto {n}^{2/3}$ owing to spherical contraction at constant mass. Instead, the nearly critical values of M/MB suggest that the observed core fields are nearly as strong as possible, among values that allow gravitational contraction.

Keywords: Interstellar magnetic fields, Star forming regions, Star formation
Illuminating Black Hole Subsystems in Young Star Clusters. There is increasing evidence that globular clusters retain sizeable black hole populations at present day. This is supported by dynamical simulations of cluster evolution, which have unveiled the spatial distribution and mass spectrum of black holes in clusters across cosmic age. However, black hole populations of young, high metallicity clusters remain unconstrained. Black holes hosted by these clusters mass segregate early in their evolutionary history, forming central subsystems of hundreds to thousands of black holes. We argue that after supernova feedback has subsided (≳50 Myr), the host cluster can accumulate gas from its dense surroundings, from which the black hole subsystem accretes at highly enhanced rates. The collective accretion luminosity can be substantial and provides a novel observational constraint for young massive clusters. We test this hypothesis by performing 3D hydrodynamic simulations where we embed discretized potentials, representing our black holes, within the potential of a massive cluster. This system moves supersonically with respect to a gaseous medium from which it accretes. We study the accretion of this black hole subsystem for different subsystem populations and determine the integrated accretion luminosity of the black hole subsystem. We apply our results to the young massive clusters of the Antennae Galaxies and find that a typical subsystem accretion luminosity should be in excess of ≈ 1040 erg s-1. We argue that no strong candidates of this luminous signal have been observed and constrain the subsystem population of a typical cluster in the Antennae Galaxies to ≲ 10-2 × 102 10 M⊙ black holes, given that feedback does not significantly impede accretion and that the gas remains optically thin.

Keywords: Bondi accretion, Black holes, X-ray sources, Star clusters
TauREx 3: A Fast, Dynamic, and Extendable Framework for Retrievals. TauREx 3 is the next generation of the TauREx exoplanet atmospheric retrieval framework for Windows, Mac, and Linux. It is a complete rewrite with a full Python stack that makes it easy-to-use, high-performance, dynamic, and flexible. The new main TauREx program is built with modularity in mind, allowing the user to augment its functionalities with custom code and efficiently perform retrievals on custom parameters. We achieve this result by dynamic determination of fitting parameters, whereby TauREx 3 can detect new parameters for retrieval from user code through a simple interface. TauREx 3 can act as a library with a simple import taurex command, providing a rich set of classes and functions related to atmospheric modeling. A 10× speedup in forward model computations is achieved as compared to the previous version with a sixfold reduction in retrieval times while maintaining robust results. TauREx 3 is intended as a standalone, all-in-one package for retrievals while the TauREx 3 Python library can build or augment a user's custom data pipeline easily.

Keywords: Open source software, Bayesian statistics, Astronomy software, Planetary atmospheres, Radiative transfer, Planetary science, Exoplanet atmospheres