Sazuna/UAT_keywords huggingface dataset:
A Machine Learning Model to Infer Planet Masses from Gaps Observed in Protoplanetary Disks. Observations of bright protoplanetary disks often show annular gaps in their dust emission. One interpretation of these gaps is disk-planet interaction. If so, fitting models of planetary gaps to observed protoplanetary disk gaps can reveal the presence of hidden planets. However, future surveys are expected to produce an ever-increasing number of protoplanetary disks with gaps. In this case, performing a customized fitting for each target becomes impractical owing to the complexity of disk-planet interaction. To this end, we introduce Disk Planet Neural Network (DPNNet), an efficient model of planetary gaps by exploiting the power of machine learning. We train a deep neural network with a large number of dusty disk-planet hydrodynamic simulations across a range of planet masses, disk temperatures, disk viscosities, disk surface density profiles, particle Stokes numbers, and dust abundances. The network can then be deployed to extract the planet mass for a given gap morphology. In this work, first in a series, we focus on the basic concepts of our machine learning framework. We demonstrate its utility by applying it to the dust gaps observed in the protoplanetary disk around HL Tau at 10, 30, and 80 au. Our network predicts planet masses of 80 M⊕, 63 M⊕, and 70 M⊕, respectively, which are comparable to those from other studies based on specialized simulations. We discuss the key advantages of our DPNNet in its flexibility to incorporate new physics as well as any number of parameters and predictions, in addition to its potential to ultimately replace hydrodynamical simulations for disk observers and modelers.

Keywords: Exoplanet astronomy, Exoplanet detection methods, Protoplanetary disks, Neural networks
The Demagnetization of the Venusian Ionosphere under Nearly Flow-aligned Interplanetary Magnetic Fields. Previous studies suggested that the interplanetary magnetic field (IMF) has a significant influence on the Venusian-induced magnetosphere. We present observations by Venus Express under a nearly flow-aligned IMF condition to investigate the demagnetization of the Venusian ionosphere. Our results show that the magnetic barrier becomes weak and narrow, and the ionosphere can be demagnetized under the IMF with the dominating flow-aligned component while the solar wind dynamic pressure remains almost unchanged. The demagnetization of the Venusian ionosphere implies that the total pressure of the magnetic barrier above the ionopause decreases. The magnetic field lines upstream from Venus drape differently under the nearly flow-aligned IMF condition. And thus the upstream solar wind flow is affected by the outward magnetic tension, which leads to the decrease of the dynamic pressure that directly acts on the magnetic barrier.

Keywords: Earth ionosphere, Solar wind, Solar-planetary interactions, Venus, Interplanetary magnetic fields
The Effects of Oscillations and Collisions of Emerging Bipolar Regions on the Triggering of Solar Flares. The ability to predict the occurrence of solar flares in advance is important to humankind due to the potential damage they can cause to Earth's environment and infrastructure. It has been shown in Kusano et al. that a small-scale bipolar region (BR), with its flux reversed relative to the potential component of the overlying field, appearing near the polarity inversion line (PIL) is sufficient to effectively trigger a solar flare. In this study we perform further 3D magnetohydrodynamic simulations to study the effect that the motion of these small-scale BRs has on the effectiveness of flare triggering. The effect of two small-scale BRs colliding is also simulated. The results indicate that the strength of the triggered flare is dependent on how much of the overlying field is disrupted by the BR. Simulations of linear oscillations of the BR showed that oscillations along the PIL increase the flare strength while oscillations across the PIL detract from the flare strength. The flare strength is affected more by larger amplitude oscillations but is relatively insensitive to the frequency of oscillations. In the most extreme case the peak kinetic energy of the flare increased more than threefold compared to a non-oscillating BR. Simulations of torsional oscillations of the BR showed a very small effect on the flare strength. Finally, simulations of colliding BRs showed the generation of much stronger flares as the flares triggered by each individual BR coalesce. These results show that significantly stronger flares can result from motion of the BR along the PIL of a sheared field or from the presence of multiple BRs in the same region.

Keywords: Active solar corona, Solar flares, Magnetohydrodynamical simulations
Stabilization of Magnetic Reconnection in the Relativistic Current Sheet. Recently, magnetic reconnection, where a relativistically hot plasma is confined by a strong magnetic field, has received great attention in relation to astrophysical objects (e.g., a pulsar magnetosphere and magnetar). However, reconnection with a relativistic high-speed drift current in the plasma sheet has not been investigated yet. Thus, from both theoretical and computational points of view, we studied the growth rate of relativistic reconnection for the high-speed drift current in a relativistically hot plasma sheet. Consequently, we argue that, contrary to the conventional understanding of the fast energy dissipation by the relativistic reconnection, the growth of magnetic reconnection is suppressed.

Keywords: Plasma astrophysics, High energy astrophysics, Plasma physics
Prospective Annual Detection Rate of High-energy Gamma-Ray Bursts with LHAASO-WCDA. Gamma-ray bursts (GRBs) are considered one of the most violent, explosive events in the universe and serve as high-redshift probes for cosmological study due to their high-energy observations. Such observations, particularly in the GeV regime, have already proven fruitful for deriving useful scientific results, such as the determination of extragalactic background light (EBL) and the stringent constraint on the Lorentz invariance violation effect. Owing to the advantages of a very large effective area, a low threshold energy, a wide field of view, and high duty cycle, the upcoming Large High Altitude Air Shower Observatory-Water Cerenkov Detector Array (LHAASO-WCDA) will have potential sensitivity for discovering GRBs in the 100 GeV energy region. In this work, a sample of GRBs has been generated and examined based on existing observations reported by the Large Area Telescope on board the Fermi satellite. The Fermi spectra are extrapolated to high energy by taking into account the absorption due to the pair production processes occurring between γ rays and EBL. With an assumption that an ultrahigh-energy component accounts for 10% of the total luminosity, it is found that LHAASO-WCDA has a GRB detection rate of ∼one GRB per year.

Keywords: Gamma-ray bursts
Far-infrared Photometric Redshifts: A New Approach to a Highly Uncertain Enterprise. This paper presents a new approach to deriving far-infrared (FIR) photometric redshifts for galaxies based on their reprocessed emission from dust at rest-frame FIR through millimeter wavelengths. FIR photometric redshifts ("FIR-z") have been used over the past decade to derive redshift constraints for highly obscured galaxies that lack photometry at other wavelengths like the optical/near-IR. Most literature FIR-z fits are performed through ${\chi }^{2}$ minimization to a single galaxy's FIR template spectral energy distribution (SED). The use of a single galaxy template, or modest set of templates, can lead to an artificially low uncertainty estimate on FIR-z's because real galaxies display a wide range in intrinsic dust SEDs. I use the observed distribution of galaxy SEDs (for well-constrained samples across $0\lt z\lt 5$ ) to motivate a new FIR through millimeter photometric redshift technique called MMpz. The MMpz algorithm asserts that galaxies are most likely drawn from the empirically observed relationship between rest-frame peak wavelength, ${\lambda }_{\mathrm{peak}}$ , and total IR luminosity, L ${}_{\mathrm{IR}}$ ; the derived photometric redshift accounts for the measurement uncertainties and intrinsic variation in SEDs at the inferred L ${}_{\mathrm{IR}}$ , as well as heating from the cosmic microwave background at $z\gtrsim 5$ . The MMpz algorithm has a precision of ${\sigma }_{{\rm{\Delta }}z/(1+z)}\approx 0.3\mbox{--}0.4$ , similar to single-template fits, while providing a more accurate estimate of the FIR-z uncertainty with reduced chi-squared of order ${ \mathcal O }({\chi }_{\nu }^{2})=1$ , compared to alternative FIR photometric redshift techniques (with ${ \mathcal O }({\chi }_{\nu }^{2})\approx 10\mbox{--}{10}^{3}$ ).

Keywords: Millimeter astronomy, Astronomical techniques, Submillimeter astronomy
Testing ΛCDM with Dwarf Galaxy Morphology. The leading tensions to the collisionless cold dark matter (CDM) paradigm are the "small-scale controversies," discrepancies between observations at the dwarf-galactic scale, and their simulational counterparts. In this work we consider methods to infer 3D morphological information on Local Group dwarf spheroidals and test the fitness of CDM+hydrodynamics simulations to the observed galaxy shapes. We find that the subpopulation of dwarf galaxies with mass-to-light ratio $\gtrsim 100{M}_{\odot }/{L}_{\odot }$ reflects an oblate morphology. This is discrepant with the dwarf galaxies with mass-to-light ratios $\lesssim 100{M}_{\odot }/{L}_{\odot }$ , which reflect prolate morphologies, as well as simulations of CDM-sourced bright isolated galaxies that are explicitly prolate. Although more simulations and data are called for if evidence of oblate pressure-supported stellar distributions persists in observed galaxies while being absent from simulations, we argue that an underlying oblate non-CDM dark matter halo may be required and present this as motivation for future studies.

Keywords: Galaxy dark matter halos, Dark matter distribution, Hydrodynamical simulations, Dwarf galaxies, Dwarf spheroidal galaxies
A Cosmography Approach to Dark Energy Cosmologies: New Constraints Using the Hubble Diagrams of Supernovae, Quasars, and Gamma-Ray Bursts. In the context of a cosmography approach to using the data of the Hubble diagram for supernovae, quasars, and gamma-ray bursts, we study dark energy (DE) parameterizations and the concordance cold dark matter (ΛCDM) universe. Using different combinations of data samples including (i) supernovae (Pantheon), (ii) Pantheon + quasars. and (iii) Pantheon + quasars + gamma-ray bursts, and applying the minimization of χ2 function of the distance modulus of data samples in the context of the Markov Chain Monte Carlo method, we obtain constrained values of cosmographic parameters in a model-independent cosmography scenario. We then investigate our analysis, for different concordance ΛCDM cosmology, wCDM, Chevallier-Polarski-Linder, and Pade parameterizations. Comparing the numerical values of the cosmographic parameters obtained for DE scenarios with those of the model-independent method, we show that the concordance ΛCDM model has serious issues when we involve quasar and gamma-ray burst data in our analysis. While high-redshift quasars and gamma-ray bursts can falsify the concordance model, our results using a cosmography approach indicate that the other DE parameterizations are still consistent with these observations.

Keywords: Cosmology, Cosmological constant, Dark energy, Cosmological parameters
Multi-frequency General Relativistic Radiation-hydrodynamics with M<SUB>1</SUB> Closure. We report on recent upgrades to our general relativistic radiation-magnetohydrodynamics code, Cosmos++, which expands the two-moment, M1, radiation treatment from gray to multi-frequency transport, including Doppler and gravitational frequency shifts. The solver accommodates either photon (Bose-Einstein) or neutrino (Fermi-Dirac) statistical distribution functions with absorption, emission, and elastic scattering processes. An implicit scheme is implemented to simultaneously solve the primitive inversion problem together with the radiation-matter coupling source terms, providing stability over a broad range of opacities and optical depths where the interaction terms can be stiff. We discuss our formulations and numerical methods, and validate our methods against a wide variety of test problems spanning optically thin to thick regimes in flat, weakly curved, and strongly curved spacetimes.

Keywords: Astrophysical fluid dynamics, Computational methods, Radiative magnetohydrodynamics
Awakening of Two Gamma-Ray High-redshift, Flat-spectrum Radio Quasars in the Southern Hemisphere. High-redshift blazars are valuable tools to study the early universe. So far, only a handful of γ-ray blazars have been found at redshifts above 3. Gamma-ray signals are detected in the direction of PMN J2219-2719 (z = 3.63) and PMN J2321-0827 (z = 3.16) by analyzing the 10 yr Fermi-LAT Pass 8 data. PMN J2219-2719 is not distinguished from the background in the global analysis. During the 5 month epoch, the TS value is 47.8 and the flux is more than 10 times that of the 10 yr averaged flux. In addition, the angular distance between the γ-ray position and the radio position of PMN J2219-2719 is only 0°04. Moreover, the long timescale γ-ray and infrared light curves are very similar, which supports the association between the γ-ray source and PMN J2219-2719. The global analysis of PMN J2321-0827 suggest a new γ-ray source; during the flare phase, the TS value is 61.4 and the γ-ray flux increased significantly. The association probability suggests that PMN J2321-0827 may be the counterpart of the new γ-ray source. In the future, the number of high-redshift γ-ray sources will increase by combining Fermi-LAT and the upcoming Large Synoptic Survey Telescope.

Keywords: Quasars, Gamma-ray sources, Galaxy jets, Non-thermal radiation sources, High-redshift galaxies
Comparative Spectral Analysis of the Superluminous Supernova 2019neq. We present a spectroscopic analysis of the recently discovered fast-evolving Type I superluminous supernova (SLSN-I) SN 2019neq (at redshift z = 0.1059). We compare it to the well-studied slowly evolving SLSN-I SN 2010kd (z = 0.101). Our main goal is to search for spectroscopic differences between the two groups of SLSNe-I. Differences in the spectra may reveal different ejecta compositions and explosion mechanisms. Our investigation concentrates on optical spectra observed with the 10 m Hobby-Eberly Telescope Low Resolution Spectrograph-2 at McDonald Observatory during the photospheric phase. We apply the SYN++ code to model the spectra of SN 2019neq taken at -4 days, +5 days, and +29 days from maximum light. We examine the chemical evolution and ejecta composition of the SLSN by identifying the elements and ionization states in its spectra. We find that a spectral model consisting of O III, Co III, and Si IV gives a SYN++ fit that is comparable to the typical SLSN-I spectral model consisting of O II, and conclude that the true identification of those lines, at least in the case of SN 2019neq, is ambiguous. Based on modeling the entire optical spectrum, we classify SN 2019neq as a fast-evolving SLSN-I having a photospheric velocity gradient of $\dot{v}\sim 375$ km s-1 day-1, which is among the highest velocity gradients observed for an SLSN-I. Inferring the velocity gradient from the proposed Fe II λ5169 feature alone would result in $\dot{v}\sim 100$ km s-1 day-1, which is still within the observed range of fast-evolving SLSNe-I. In addition, we derive the number density of relevant ionization states for a variety of identified elements at the epoch of the three observations. Finally, we give constraints on the lower limit of the ejecta mass and find that both SLSNe have an ejecta mass at least one order of magnitude higher than normal SNe Ia, while the fast-evolving SN 2019neq has an ejecta mass a factor of two lower than the slowly evolving SN 2010kd. These mass estimates suggest the existence of a possible correlation between the evolution timescale and the ejected mass of SLSNe-I.

Keywords: Ejecta, Core-collapse supernovae, Chemical abundances, Astrochemistry, Atomic spectroscopy, Supernovae
Kinetic Simulations of the Jovian Energetic Ion Circulation around Ganymede. The temporal and spatial variability of the radiation environment around Ganymede has a direct impact on the moon's exosphere, which links Jupiter's magnetosphere with the satellite's icy surface. The dynamics of the entry and circulation inside Ganymede's magnetosphere of the Jovian energetic ions, as well as the morphology of their precipitation on the moon's surface, determine the variability of the sputtered-water release. For this reason, the so-called planetary space weather conditions around Ganymede can also have a long-term impact on the weathering history of the moon's surface. In this work, we simulate the Jovian energetic ion precipitation to Ganymede's surface for different relative configurations between the moon's magnetic field and Jupiter's plasma sheet using a single-particle Monte Carlo model driven by the electromagnetic fields from a global MHD model. In particular, we study three science cases characterized by conditions similar to those encountered during the NASA Galileo G2, G8, and G28 flybys of Ganymede (i.e., when the moon was above, inside, and below the center of Jupiter's plasma sheet). We discuss the differences between the various surface precipitation patterns and the implications in the water sputtering rate. The results of this preliminary analysis are relevant to ESA's JUICE mission and in particular to the planning and optimization of future observation strategies for studying Ganymede's environment.

Keywords: Space weather, Solar system, Planetary magnetospheres, Galilean satellites, Jovian satellites
Statistical Analysis of the Relation between Coronal Mass Ejections and Solar Energetic Particles. To improve the forecasting capability of impactful solar energetic particle (SEP) events, the relation between coronal mass ejections (CMEs) and SEP events needs to be better understood. Here we present a statistical study of SEP occurrences and timescales with respect to the CME source locations and speeds, considering all 257 fast (vCME ≥ 900 km s-1) and wide (angular width ≥60°) CMEs that occurred between 2006 December and 2017 October. We associate them with SEP events at energies above 10 MeV. Examination of the source region of each CME reveals that CMEs more often accompany a SEP event if they originate from the longitude of E20-W100 relative to the observer. However, an SEP event could still be absent if the CME is &lt;2000 km s-1. For the associated CME-SEP pairs, we compute three timescales for each of the SEP events, namely the timescale of the onset (TO), the rise time (TR), and the duration (TD). They are correlated with the longitude of the CME source region relative to the footpoint of the Parker spiral (ΔΦ) and vCME. The TO tends to be short for $| {\rm{\Delta }}{\rm{\Phi }}| \ \lt $ 60°. This trend is weaker for TR and TD. The SEP timescales are only weakly correlated with vCME. Positive correlations of both TR and TD with vCME are seen in poorly connected (large $| {\rm{\Delta }}{\rm{\Phi }}| $ ) events. Additionally, TO appears to be negatively correlated with vCME for events with small $| {\rm{\Delta }}{\rm{\Phi }}| $ .

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Space weather, Solar coronal mass ejections
Simulation of the Interplanetary B<SUB>z</SUB> Using a Data-driven Heliospheric Solar Wind Model. Aimed to be ready for the transition from research to operation, we have developed a solar wind model by coupling a data-driven empirical coronal model with a magnetohydrodynamics heliospheric model. We performed a data-driven simulation of the solar wind for a two-year period during the declining and minimum phases of solar cycle 23. Comparisons with OMNI and Ulysses spacecraft data show that the model can reproduce the large-scale variations of the solar wind plasma parameters. The evolution of geocentric solar magnetospheric (GSM) Bx and Bz components are also reasonably duplicated by the model in terms of polarity and strength. Apparent signatures of the Russell-McPherron (R-M) effect are found from both observed data and simulated results, indicating that during the investigated interval the R-M effect is the dominant mechanism that controls the large-scale evolution of the north-south component of the interplanetary magnetic field in the GSM frame. The results demonstrate that the established model can provide valuable space weather information about the solar wind.

Keywords: Space weather, Solar wind, Interplanetary magnetic fields, Magnetohydrodynamical simulations
On the Approximation of the Black Hole Shadow with a Simple Polar Curve. A black hole embedded within a bright, optically thin emitting region imprints a nearly circular "shadow" on its image, corresponding to the observer's line of sight into the black hole. The shadow boundary depends on the black hole's mass and spin, providing an observable signature of both properties via high-resolution images. However, standard expressions for the shadow boundary are most naturally parametrized by Boyer-Lindquist radii rather than by image coordinates. We explore simple, approximate parameterizations for the shadow boundary using ellipses and a family of curves known as limaçons. We demonstrate that these curves provide excellent and efficient approximations for all black hole spins and inclinations. In particular, we show that the two parameters of the limaçon naturally account for the three primary shadow deformations resulting from mass and spin: size, displacement, and asymmetry. These curves are convenient for parametric model fitting directly to interferometric data, they reveal the degeneracies expected when estimating black hole properties from images with practical measurement limitations, and they provide a natural framework for parametric tests of the Kerr metric using black hole images.

Keywords: Black hole physics
A New Spin on an Old Black Hole: NuSTAR Spectroscopy of EXO 1846-031. The black hole candidate EXO 1846-031 underwent an outburst in 2019, after at least 25 yr in quiescence. We observed the system using NuSTAR on 2019 August 3. The 3-79 keV spectrum shows strong relativistic reflection features. Our baseline model gives a nearly maximal black hole spin value of $a={0.997}_{-0.002}^{+0.001}$ (1σ statistical errors). This high value nominally excludes the possibility of the central engine harboring a neutron star. Using several models, we test the robustness of our measurement to assumptions about the density of the accretion disk, the nature of the corona, the choice of disk continuum model, and the addition of reflection from the outer regions of the accretion disk. All tested models agree on a very high black hole spin value and a high value for the inclination of the inner accretion disk of $\theta \approx 73^\circ $ . We discuss the implications of this spin measurement in the population of stellar mass black holes with known spins, including LIGO and Virgo events.

Keywords: Accretion, Black hole physics, X-ray binary stars, Stellar accretion disks, Low-mass x-ray binary stars