Sazuna/UAT_keywords huggingface dataset:
Successive Coronal Mass Ejections Associated with Weak Solar Energetic Particle Events. The scenario of twin coronal mass ejections (CMEs), i.e., a fast and wide primary CME (priCME) preceded by preceding CMEs (preCMEs), has been found to be favorable to a more efficient particle acceleration in large solar energetic particle (SEP) events. Here we study 19 events during 2007-2014 associated with twin-CME eruptions but without large SEP observations at the L1 point. We combine remote-sensing and in situ observations from multiple spacecraft to investigate the role of magnetic connectivity in SEP detection and the CME information in three-dimensional (3D) space. We study one-on-one correlations of the priCME 3D speed, flare intensity, suprathermal backgrounds, and height of CME-CME interaction with the SEP intensity. Among these, the priCME speed is found to correlate with the SEP peak intensity at the highest level. We use the projection correlation method to analyze the correlations between combinations of these multiple independent factors and the SEP peak intensity. We find that the only combination of two or more parameters that has a higher correlation with the SEP peak intensity than the CME speed is the CME speed combined with the propagation direction. This further supports the dominant role of the priCME in controlling the SEP enhancements and emphasizes the consideration of the latitudinal effect. Overall, the magnetic connectivity in longitude as well as latitude and the relatively lower priCME speed may explain the existence of the twin-CME SEP-poor events. The role of the barrier effect of preCME(s) is discussed for an event on 2013 October 28.

Keywords: Solar energetic particles, Solar coronal mass ejections
Presolar Grain Isotopic Ratios as Constraints to Nuclear and Stellar Parameters of Asymptotic Giant Branch Star Nucleosynthesis. Recent models for evolved low-mass stars (with M ≲ 3 M⊙), undergoing the asymptotic giant branch (AGB) phase assume that magnetic flux-tube buoyancy drives the formation of 13C reservoirs in He-rich layers. We illustrate their crucial properties, showing how the low abundance of 13C generated below the convective envelope hampers the formation of primary 14N and the ensuing synthesis of intermediate-mass nuclei, like 19F and 22Ne. In the mentioned models, their production is therefore of a purely secondary nature. Shortage of primary 22Ne has also important effects in reducing the neutron density. Another property concerns AGB winds, which are likely to preserve C-rich subcomponents, isolated by magnetic tension, even when the envelope composition is O-rich. Conditions for the formation of C-rich compounds are therefore found in stages earlier than previously envisaged. These issues, together with the uncertainties related to several nuclear physics quantities, are discussed in the light of the isotopic admixtures of s-process elements in presolar SiC grains of stellar origin, which provide important and precise constraints to the otherwise uncertain parameters. By comparing nucleosynthesis results with measured SiC data, it is argued that such a detailed series of constraints indicates the need for new measurements of weak-interaction rates in ionized plasmas, as well as of neutron-capture cross sections, especially near the N = 50 and N = 82 neutron magic numbers. Nonetheless, the peculiarity of our models allows us to achieve fits to the presolar grain data of a quality so far never obtained in previously published attempts.

Keywords: Nuclear reaction cross sections, Asymptotic giant branch stars, Nuclear astrophysics, Circumstellar grains, Stellar nucleosynthesis, S-process
Resolved Nuclear Kinematics Link the Formation and Growth of Nuclear Star Clusters with the Evolution of Their Early- and Late-type Hosts. We present parsec-scale kinematics of 11 nearby galactic nuclei, derived from adaptive-optics assisted integral-field spectroscopy at (near-infrared) CO band-head wavelengths. We focus our analysis on the balance between ordered rotation and random motions, which can provide insights into the dominant formation mechanism of nuclear star clusters (NSCs). We divide our target sample into late- and early-type galaxies, and discuss the nuclear kinematics of the two subsamples, aiming at probing any link between NSC formation and host galaxy evolution. The results suggest that the dominant formation mechanism of NSCs is indeed affected by the different evolutionary paths of their hosts across the Hubble sequence. More specifically, nuclear regions in late-type galaxies are on average more rotation dominated, and the formation of nuclear stellar structures is potentially linked to the presence of gas funneled to the center. Early-type galaxies, in contrast, tend to display slowly rotating NSCs with lower ellipticity. However, some exceptions suggest that in specific cases, early-type hosts can form NSCs in a way similar to spirals.

Keywords: Galaxy formation, Late-type galaxies, Galaxy nuclei, Galaxy kinematics, Galaxy evolution, Early-type galaxies
Ultra-wideband, Multiepoch Radio Study of the First Discovered "Main-sequence Radio Pulse Emitter" CU Vir. The presence of a large-scale surface magnetic field in early-type stars leads to several unique electromagnetic phenomena producing radiation over X-ray to radio bands. Among them, the rarest type of emission is electron cyclotron maser emission (ECME) observed as periodic, circularly polarized radio pulses. The phenomenon was first discovered in the hot magnetic star CU Vir. Past observations of this star led to the consensus that the star produces only right circularly polarized ECME, suggesting that only one magnetic hemisphere takes part in the phenomenon. Here we present the first ultra-wideband (0.4-4 GHz) study of this star using the upgraded Giant Metrewave Radio telescope and the Karl G. Jansky Very Large Array, which led to the surprising discovery of ECME of both circular polarizations up to around 1.5 GHz. The GHz observations also allowed us to infer that the upper ECME cutoff frequency is at ≳5 GHz. The sub-GHz observation led to the unexpected observation of more than two pairs of ECME pulses per rotation cycle. In addition, we report the discovery of a "giant pulse" and transient enhancements, which are potentially the first observational evidence of "centrifugal breakout" of plasma from the innermost part of the stellar magnetosphere. The stark contrast between the star's behavior at GHz and sub-GHz frequencies could either be due to propagation effects, a manifestation of varying magnetic field topology as a function of height, or a signature of an additional "ECME engine."

Keywords: Magnetic stars, B stars, Magnetospheric radio emissions, Astrophysical masers, Transient detection, Radio astronomy
Hydrodynamic Model of Hα Emission from Accretion Shocks of a Proto-giant Planet and Circumplanetary Disk. Recent observations have detected excess Hα emission from young stellar systems with an age of several Myr such as PDS 70. One-dimensional radiation-hydrodynamic models of shock-heated flows that we developed previously demonstrate that planetary accretion flows of &gt;a few ten km s-1 can produce Hα emission. It is, however, a challenge to understand the accretion process of proto-giant planets from observations of such shock-originated emission because of a huge gap in scale between the circumplanetary disk (CPD) and the microscopic accretion shock. To overcome the scale gap problem, we combine two-dimensional, high-spatial-resolution global hydrodynamic simulations and the one-dimensional local radiation-hydrodynamic model of the shock-heated flow. From such combined simulations for the protoplanet-CPD system, we find that the Hα emission is mainly produced in localized areas on the protoplanetary surface. The accretion shocks above the CPD produce much weaker Hα emission (approximately one to two orders of magnitude smaller in luminosity). Nevertheless, the accretion shocks above the CPD significantly affect the accretion process onto the protoplanet. The accretion occurs at a quasi-steady rate if averaged on a 10 day timescale, but its rate shows variability on shorter timescales. The disk surface accretion layers including the CPD shocks largely fluctuate, which results in the time-variable accretion rate and Hα luminosity of the protoplanet. We also model the spectral emission profile of the Hα line and find that the line profile is less time-variable despite the large variability in luminosity. High-spectral-resolution spectroscopic observation and monitoring will be key to revealing the property of the accretion process.

Keywords: Hydrodynamical simulations, Exoplanets, Radiative transfer simulations, Extrasolar gaseous giant planets, Planet formation
Resolving the Formation of Cold H I Filaments in the High-velocity Cloud Complex C. The physical properties of galactic halo gas have a profound impact on the life cycle of galaxies. As gas travels through a galactic halo, it undergoes dynamical interactions, influencing its impact on star formation and the chemical evolution of the galactic disk. In the Milky Way halo, considerable effort has been made to understand the spatial distribution of neutral gas, which is mostly in the form of large complexes. However, the internal variations of their physical properties remain unclear. In this study, we investigate the thermal and dynamical state of the neutral gas in high-velocity clouds. High-resolution observations (1'1) of the 21 cm line emission in the EN field of the DHIGLS H I survey are used to analyze the physical properties of the bright concentration CIB located at an edge of a large HVC complex, complex C. We use the Gaussian decomposition code ROHSA to model the multiphase content of CIB and perform a power spectrum analysis to analyze its multiscale structure. The physical properties of some 200 structures extracted using dendrograms are examined. Each phase exhibits different thermal and turbulent properties. We identify two distinct regions, one of which has a prominent protrusion extending from the edge of complex C that exhibits an ongoing phase transition from warm diffuse gas to cold dense gas and filaments. The scale at which the warm gas becomes unstable and undergoes thermal condensation is about 15 pc, corresponding to a cooling time of about 1.5 Myr. Our study characterizes the statistical properties of turbulence in the fluid of an HVC for the first time. We find that a transition from subsonic to transonic turbulence is associated with the thermal condensation, going from large to small scales. A large-scale perspective of complex C suggests that hydrodynamic instabilities are involved in creating the structured concentration CIB and the phase transition therein. However, the details of the dynamical and thermal processes remain unclear and will require further investigation through both observations and numerical simulations.

Keywords: High-velocity clouds, Neutral hydrogen clouds, Interstellar medium
Rotating Motion of the Outflow of IRAS 16293-2422 A1 at Its Origin Point Near the Protostar. The Class 0 protostar IRAS 16293-2422 Source A is known to be a binary system (A1 and A2) or even a multiple system that processes a complex outflow structure. We have observed this source in the C34S, SO, and OCS lines at 3.1 mm with the Atacama Large Millimeter/submillimeter Array. A substructure of this source is traced by our high angular-resolution observation (0"12; 20 au) of the continuum emission. The northwest-southeast (NW-SE) outflow on a 2″ scale is detected in the SO (JN = 22-11) line. Based on the morphology of the SO distribution, this bipolar outflow structure seems to originate from the protostar A1 and its circumstellar disk, or the circummultiple structure of Source A. The rotation motion of the NW-SE outflow is detected in the SO and OCS emissions. We evaluate the specific angular momentum of the outflowing gas to be (8.6-14.3) × 10-4 km s-1 pc. If the driving source of this outflow is the protostar A1 and its circumstellar disk, it can be a potential mechanism to extract the specific angular momentum of the disk structure. These results can be a hint for the outflow launching mechanism in this source. Furthermore, they provide us with an important clue to resolve the complicated structure of IRAS 16293-2422 Source A.

Keywords: Protostars, Stellar jets, Low mass stars, Interstellar medium
Characterizing Magnetic Connectivity of Solar Flare Electron Sources to STEREO Spacecraft Using ADAPT-WSA Modeling. Onsets and intensity profiles of six energetic (E &gt; 30 keV) electron events common to STEREO A and B (STA and STB) spacecraft were analyzed by Klassen et al. with the STEREO Solar Electron and Proton Telescopes when the spacecraft were separated by &lt;70° in solar longitude. All six events were characterized by earlier onsets and higher peak intensities for the spacecraft with magnetic footpoints at the solar longitudes of larger source separations. The 2.5 Rs footpoint locations, based on Parker spiral (PS) calculations with spacecraft solar wind (SW) speeds Vsw, are compared with 5 Rs footpoint locations calculated by selected realizations of ADAPT-WSA (Air Force Data Assimilative Photospheric flux Transport-Wang-Sheeley-Arge) solar wind (SW) forecast model runs for each spacecraft. ADAPT-WSA footpoint locations support the Klassen et al. results of azimuthally nonuniform injections from two shock-associated events and confirm locations for the flare source event on 2014 July 17. Substantial footpoint differences of the two methods diminish the disparity of the flare event of 2014 May 2 but exacerbate the case of two flare electron events on 2014 August 1. As limited test cases for a comparison of ADAPT-WSA and PS methods at slightly different source surfaces, the Carrington longitude differences range from several to ~30°. We review the importance and limitations of methods for determining the solar magnetic footpoints for solar energetic particle studies.

Keywords: Solar energetic particles, Solar flares
Leveraging the ALMA Atacama Compact Array for Cometary Science: An Interferometric Survey of Comet C/2015 ER61 (PanSTARRS) and Evidence for a Distributed Source of Carbon Monosulfide. We report the first survey of molecular emission from cometary volatiles using standalone Atacama Compact Array (ACA) observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2015 ER61 (PanSTARRS) carried out on UT 2017 April 11 and 15, shortly after its April 4 outburst. These measurements of HCN, CS, CH3OH, H2CO, and HNC (along with continuum emission from dust) probed the inner coma of C/2015 ER61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for each molecule and a stringent upper limit for CO. HCN is consistent with direct nucleus release in C/2015 ER61, whereas CS, H2CO, HNC, and potentially CH3OH are associated with distributed sources in the coma. Adopting a Haser model, parent scale lengths determined for H2CO (Lp ~ 2200 km) and HNC (Lp ~ 3300 km) are consistent with previous work in comets, whereas significant extended source production (Lp ~ 2000 km) is indicated for CS, suggesting production from an unknown parent in the coma. The continuum presents a point-source distribution with a flux density implying an excessively large nucleus, inconsistent with other estimates of the nucleus size. It is best explained by the thermal emission of slowly moving outburst ejectas, with total mass 5-8 × 1010 kg. These results demonstrate the power of the ACA for revealing the abundances, spatial distributions, and locations of molecular production for volatiles in moderately bright comets such as C/2015 ER61.

Keywords: High resolution spectroscopy, Comae, Molecular spectroscopy, Comets, Radio interferometry, Radio astronomy
Macro Magnetic Holes Caused by Ripples in Heliospheric Current Sheet from Coordinated Imaging and Parker Solar Probe Observations. Macro magnetic holes (MMHs), which are significant magnetic field decreases in the solar wind lasting tens of minutes, were found during the first four orbits of the Parker Solar Probe (PSP). We performed a detailed analysis of the 2020 January 30 event and found the possible cause of the MMH using coordinated remote sensing observations from STEREO A and PSP in situ measurements. The results indicate that an MMH represents a brief encounter with the rippled heliospheric current sheet (HCS). Out of the data from the first four orbits of PSP, we identified 17 MMHs and carried out a statistical analysis. Basic characteristics of MMHs include (1) MMHs usually last tens of minutes; (2) the magnetic field strength inside the events is much lower than that in the ambient solar wind; (3) enhanced plasma density, radial velocity, and plasma β are usually found inside the MMHs; and (4) the radial magnetic field has the same polarity before and after an MMH. Based on potential field-source surface and magnetohydrodynamics models, for each of the events we roughly estimate the radial size and the lower limit of the vertical size (i.e., the separation distance between PSP and the HCS), which are 2 R⊙ and 10 R⊙ on average, respectively. These results suggest that MMHs are a frequent phenomenon that may shed light on the dynamics of the HCS and the origins and evolutions of the solar wind structures in the heliosphere.

Keywords: Solar wind, Solar magnetic fields, Heliosphere
Prompt Emission of High-energy Nonthermal Photons from a Radiation-dominated Relativistic Magnetic Reconnection. In astrophysics, relativistic magnetic reconnection, where particles can accelerate in a region of a strong electric field and weak magnetic field, is a key physical process for the explanation of high-energy photon synchrotron emission above 160 MeV, the limit given by the balance between the accelerating electric force and the radiation reaction force. However, the reconnection dynamics-more importantly, the particle acceleration and photon emission dynamics-in this radiation-dominated, relativistic regime have not been self-consistently investigated yet. In this paper, through theoretical derivation of the modified relativistic tearing instability (RTI) and kinetic particle-in-cell simulations, we find that, because of the radiation reaction, the compression of the reconnecting current sheet is significantly enhanced, leading to an increase in the RTI growth rate in the short-wavelength range. As a result, during reconnection, the current sheet is fragmented into a chain of many more magnetic null points separated by much smaller plasmoids, which eventually gives rise to significant improvement of particle acceleration efficiency and shortening of photon emission duration. In the simulations, prompt emission at duration ωpeΔT ≃ 233 (reduced by a factor of 3) of high-energy nonthermal photons with a hard power law of index 2.11 for photon energies &lt;100 MeV and index 1.39 for those &gt;100 MeV is observed. These characteristics are consistent with the observed emission properties of short gamma-ray bursts, particularly of GRB 090510, supporting the radiation-dominated reconnection scenario.

Keywords: Gamma-ray bursts, High energy astrophysics, Plasma astrophysics, Non-thermal radiation sources, Magnetic fields
Updated Transfer Coefficients for Magnetized Plasmas. Accurate radiative transfer coefficients (emissivities, absorptivities, and rotativities) are needed for modeling radiation from relativistically hot, magnetized plasmas such as those found in Event Horizon Telescope sources. Here we review, update, and correct earlier work on radiative transfer coefficients. We also describe an improved method for numerically evaluating rotativities and provide convenient fitting formulae for the relativistic κ distribution of electron energies.

Keywords: Plasma astrophysics, Radiative transfer, Radiative processes, Polarimetry, Relativistic disks
Blazar OJ 287 after First VHE Activity: Tracking the Reemergence of the HBL-like Component in 2020. We report the reemergence of a new broadband emission through a detailed and systematic study of the multiwavelength spectral and temporal behavior of OJ 287 after its first-ever reported very high energy activity in 2017 to date, which includes the second-highest X-ray flux of the source. The source shows high optical to X-ray flux variations, accompanied mainly by strong spectral changes. The optical to X-ray flux variations are correlated and simultaneous except for two durations when they are anticorrelated. The flux variations, however, are anticorrelated with the X-ray spectral state while correlated with optical-UV (ultraviolet). Weekly binned Fermi-LAT data around the duration of the highest X-ray activity show a few detections with a log-parabola model but none with a power law, yet the extracted LAT spectral energy distribution of the high-activity duration for both the models is similar and shows a hardening above 1 GeV. Further, near-infrared data indicate strong spectral change, resembling a thermal component. Overall, the combined optical to gamma-ray broadband spectrum establishes the observed variations to a new high-energy-peaked broadband emission component, similar to the one seen during the highest reported X-ray flux state of the source in 2017. The observed activities indicate some peculiar features that seem to be characteristic of this emission component, while its appearance a few years around the claimed ~12 yr optical outbursts strongly indicates a connection between the two.

Keywords: Supermassive black holes, BL Lacertae objects, High energy astrophysics, Blazars, Active galaxies, Relativistic jets, Non-thermal radiation sources, X-ray active galactic nuclei
Post-explosion Evolution of Core-collapse Supernovae. We investigate the post-explosion phase in core-collapse supernovae with 2D hydrodynamical simulations and a simple neutrino treatment. The latter allows us to perform 46 simulations and follow the evolution of the 32 explosion models during several seconds. We present a broad study based on three progenitors (11.2, 15, and 27 M⊙), different neutrino heating efficiencies, and various rotation rates. We show that the first seconds after shock revival determine the final explosion energy, remnant mass, and properties of ejected matter. Our results suggest that a continued mass accretion increases the explosion energy even at late times. We link the late-time mass accretion to initial conditions such as rotation strength and shock deformation at explosion time. Only some of our simulations develop a neutrino-driven wind (NDW) that survives for several seconds. This indicates that NDWs are not a standard feature expected after every successful explosion. Even if our neutrino treatment is simple, we estimate the nucleosynthesis of the exploding models for the 15 M⊙ progenitor after correcting the neutrino energies and luminosities to get a more realistic electron fraction.

Keywords: Supernovae, Explosive nucleosynthesis, Supernova dynamics, Core-collapse supernovae