Sazuna/UAT_keywords huggingface dataset:
Twin Stars and the Stiffness of the Nuclear Equation of State: Ruling Out Strong Phase Transitions below 1.7 n<SUB>0</SUB> with the New NICER Radius Measurements. We explore the connection between the stiffness of a hadronic equation of state (EoS) with a sharp phase transition to quark matter to its tidal deformability. For this we employ a hadronic relativistic mean field model with a parameterized effective nucleon mass to vary the stiffness in conjunction with a constant speed of sound EoS for quark matter. We compute multiple scenarios with phase transitions according to the four possible cases of a hybrid star EoS with a stable second branch. We demonstrate how the effective nucleon mass can be constrained by using gravitational-wave data. We find that certain values of the effective nucleon mass are incompatible with GW170817 and a phase transition simultaneously. By using the recent NICER measurements of J0030+0451 we constrain our results further and find that strong phase transitions with a visible jump in the mass-radius relation are ruled out at 1σ at densities below 1.7 times saturation density.

Keywords: Neutron stars, Compact objects
Constraining Black Hole Populations in Globular Clusters Using Microlensing: Application to Omega Centauri. We estimate the rate of gravitational microlensing events of cluster stars due to black holes (BHs) in the globular cluster NGC 5139 (ωCen). Theory and observations both indicate that ωCen may contain thousands of BHs, but their mass spectrum and exact distribution are not well constrained. In this Letter we show that one may observe microlensing events on a timescale of years in ωCen, and such an event sample can be used to infer the BH distribution. Direct detection of BHs will, in the near future, play a major role in distinguishing binary BH merger channels. Here we explore how gravitational microlensing can be used to put constraints on BH populations in globular clusters.

Keywords: Globular star clusters, Black holes, Gravitational microlensing
Examining a Peak-luminosity/Decline-rate Relationship for Tidal Disruption Events. We compare the luminosity, radius, and temperature evolution of the UV/optical blackbodies for 21 well-observed tidal disruption events (TDEs), 8 of which were discovered by the All-Sky Automated Survey for Supernovae. We find that the blackbody radii generally increase prior to peak and slowly decline at late times. The blackbody temperature evolution is generally flat, with a few objects showing small-scale variations. The bolometric UV/optical luminosities generally evolve smoothly and flatten out at late times. Finally, we find an apparent correlation between the peak luminosity and the decline rate of TDEs. This relationship is strongest when comparing the peak luminosity to its decline over 40 days. A linear fit yields ${\mathrm{log}}_{10}({L}_{\mathrm{peak}})$ = $({44.1}_{-0.1}^{+0.1})$ + $({1.6}_{-0.2}^{+0.4})({\rm{\Delta }}{L}_{40}+0.5)$ in cgs, where ${\rm{\Delta }}{L}_{40}={\mathrm{log}}_{10}({L}_{40}/{L}_{\mathrm{peak}})$.

Keywords: Black hole physics, Tidal disruption, Supermassive black holes, Transient sources
Solar-type Stars Observed by LAMOST and Kepler. Obtaining measurements of chromospheric and photometric activity of stars with near-solar fundamental parameters and rotation periods is important for a better understanding of solar-stellar connection. We select a sample of 2603 stars with near-solar fundamental parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST)-Kepler field and use LAMOST spectra to measure their chromospheric activity and Kepler light curves to measure their photospheric activity (I.e., the amplitude of the photometric variability). While the rotation periods of 1556 of these stars could not be measured due to the low amplitude of the photometric variability and highly irregular temporal profile of light curves, 254 stars were further identified as having near-solar rotation periods. We show that stars with near-solar rotation periods have chromospheric activities that are systematically higher than stars with undetected rotation periods. Furthermore, while the solar level of photospheric and chromospheric activity appears to be typical for stars with undetected rotation periods, the Sun appears to be less active than most stars with near-solar rotation periods (both in terms of photospheric and chromospheric activity).

Keywords: Stellar photometry, Stellar activity, Solar activity, Stellar rotation, Stellar spectral lines
Counterstreaming Strahls and Heat Flux Dropouts as Possible Signatures of Local Particle Acceleration in the Solar Wind. Suprathermal electrons with energies of ∼70 eV and above are observed at 1 au as dispersionless halo electrons and magnetic field-aligned beams of strahls. For a long time, it has been thought that both populations originate only from the solar corona, and that the only active process impacting their properties in the solar wind is scattering. This view has consequently impacted the interpretation of typical patterns of pitch-angle distributions (PADs) of suprathermal electrons. Meanwhile, recent observational studies supported by numerical simulations have shown that there is an unaccounted population of electrons accelerated to suprathermal energies at reconnecting current sheets (RCSs) and 3D dynamical plasmoids (or 2D magnetic islands (MIs)) directly in the heliosphere. We present multispacecraft observations of counterstreaming strahls and heat flux dropouts in PADs within a region filled with plasmoids and RCSs unaffected by interplanetary shocks, comparing observed PAD features with those predicted by particle-in-cell simulations. We show typical PAD patterns determined by local acceleration of thermal-core electrons up to hundreds of electron volts. Resulting PAD views depend on properties and topology of particular RCSs, MIs, and plasma/magnetic field parameters. Our study suggests that solar wind-borne suprathermal electrons coexist with those of solar origin. Therefore, some of heat flux dropout and bidirectional strahl events can be explained by local dynamical processes involving magnetic reconnection. Possible implications of the results for the interpretation of the actively debated decrease in the strahl/halo relative density with heliocentric distance and puzzling features of suprathermal electrons observed at crossings of the heliospheric current sheet and cometary comas are also discussed.

Keywords: Solar magnetic reconnection, Solar energetic particles, Solar wind, Interplanetary particle acceleration, Interplanetary magnetic fields
ALMA Observations of Massive Clouds in the Central Molecular Zone: Jeans Fragmentation and Cluster Formation. We report Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 continuum observations of 2000 au resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy. To study gas fragmentation, we use the dendrogram method to identify cores as traced by the dust continuum emission. The four clouds exhibit different fragmentation states at the observed resolution despite having similar masses at the cloud scale (∼1-5 pc). Assuming a constant dust temperature of 20 K, we construct core mass functions of the clouds and find a slightly top-heavy shape as compared to the canonical initial mass function, but we note several significant uncertainties that may affect this result. The characteristic spatial separation between the cores as identified by the minimum spanning tree method, ∼104 au, and the characteristic core mass, 1-7 ${M}_{\odot }$, are consistent with predictions of thermal Jeans fragmentation. The three clouds showing fragmentation may be forming OB associations (stellar mass ∼103 ${M}_{\odot }$). None of the four clouds under investigation seem to be currently able to form massive star clusters like the Arches and the Quintuplet (≳104 ${M}_{\odot }$), but they may form such clusters by further gas accretion onto the cores.

Keywords: Galactic center, Star formation, Molecular clouds
Milky Way Satellites Shining Bright in Gravitational Waves. The population of Milky Way satellite galaxies is of great interest for cosmology, fundamental physics, and astrophysics. They represent the faint end of the galaxy luminosity function, are the most dark-matter-dominated objects in the local universe, and contain the oldest and most metal-poor stellar populations. Recent surveys have revealed around 60 satellites, but this could represent less than half of the total. Characterization of these systems remains a challenge due to their low luminosity. We consider the gravitational-wave observatory LISA as a potential tool for studying these satellites through observations of their short-period double white dwarf populations. LISA will observe the entire sky without selection effects due to dust extinction, complementing optical surveys, and could potentially discover massive satellites hidden behind the disk of the Galaxy.

Keywords: Gravitational wave astronomy, White dwarf stars, Dwarf galaxies, Magellanic Clouds
Probing the Magnetic Field in the GW170817 Outflow Using H.E.S.S. Observations. The detection of the first electromagnetic counterpart to the binary neutron star (BNS) merger remnant GW170817 established the connection between short γ-ray bursts and BNS mergers. It also confirmed the forging of heavy elements in the ejecta (a so-called kilonova) via the r-process nucleosynthesis. The appearance of nonthermal radio and X-ray emission, as well as the brightening, which lasted more than 100 days, were somewhat unexpected. Current theoretical models attempt to explain this temporal behavior as either originating from a relativistic off-axis jet or a kilonova-like outflow. In either scenario, there is some ambiguity regarding how much energy is transported in the nonthermal electrons versus the magnetic field of the emission region. Combining the Very Large Array (radio) and Chandra (X-ray) measurements with observations in the GeV-TeV domain can help break this ambiguity, almost independently of the assumed origin of the emission. Here we report for the first time on deep H.E.S.S. observations of GW170817/GRB 170817A between 124 and 272 days after the BNS merger with the full H.E.S.S. array of telescopes, as well as on an updated analysis of the prompt (&lt;5 days) observations with the upgraded H.E.S.S. phase-I telescopes. We discuss implications of the H.E.S.S. measurement for the magnetic field in the context of different source scenarios.

Keywords: Ejecta, Gamma-ray bursts, Stellar mergers, Gamma-ray astronomy, Gamma-ray transient sources
Simulations Show that Vortex Flows Could Heat the Chromosphere in Solar Plage. The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low-resolution data is grossly underestimated. In full-resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating.

Keywords: Magnetohydrodynamics, Solar chromospheric heating, Plages
The Persistent Radio Jet Coupled to Hard X-Rays in the Soft State of Cyg X-1. We study long-term radio/X-ray correlations in Cyg X-1. We find the persistent existence of a compact radio jet in its soft state. This represents a new phenomenon in black hole binaries, in addition to compact jets in the hard state and episodic ejections of ballistic blobs in the intermediate state. While the radio emission in the hard state is strongly correlated with both the soft and hard X-rays, the radio flux in the soft state is not directly correlated with the flux of the dominant disk blackbody in soft X-rays, but instead it is lagged by about 100 days. We interpret the lag as occurring in the process of advection of the magnetic flux from the donor through the accretion disk. On the other hand, the soft-state radio flux is very tightly correlated with the hard X-ray, 15-50 keV, flux without a measurable lag and at the same rms. This implies that the X-ray-emitting disk corona and the soft-state jet are powered by the same process, probably magnetically.

Keywords: X-ray binary stars, Stellar jets, Non-thermal radiation sources, X-ray sources, Magnetic fields, Radio sources
The Heliospheric Current Sheet and Plasma Sheet during Parker Solar Probe's First Orbit. We present heliospheric current sheet (HCS) and plasma sheet (HPS) observations during Parker Solar Probe's (PSP) first orbit around the Sun. We focus on the eight intervals that display a true sector boundary (TSB; based on suprathermal electron pitch angle distributions) with one or several associated current sheets. The analysis shows that (1) the main density enhancements in the vicinity of the TSB and HCS are typically associated with electron strahl dropouts, implying magnetic disconnection from the Sun, (2) the density enhancements are just about twice that in the surrounding regions, suggesting mixing of plasmas from each side of the HCS, (3) the velocity changes at the main boundaries are either correlated or anticorrelated with magnetic field changes, consistent with magnetic reconnection, (4) there often exists a layer of disconnected magnetic field just outside the high-density regions, in agreement with a reconnected topology, (5) while a few cases consist of short-lived density and velocity changes, compatible with short-duration reconnection exhausts, most events are much longer and show the presence of flux ropes interleaved with higher-β regions. These findings are consistent with the transient release of density blobs and flux ropes through sequential magnetic reconnection at the tip of the helmet streamer. The data also demonstrate that, at least during PSP's first orbit, the only structure that may be defined as the HPS is the density structure that results from magnetic reconnection, and its byproducts, likely released near the tip of the helmet streamer.

Keywords: Slow solar wind, Space plasmas, Solar coronal transients, Solar magnetic reconnection, Heliosphere, Plasma jets, Solar coronal streamers
Independent Core Rotation in Massive Filaments in Orion. We present high-angular-resolution Atacama Large Millimeter/submillimeter Array images of N2H+ (1-0) that have been combined with those from the Nobeyama telescope toward the Orion Molecular Cloud (OMC)-2 and OMC-3 filamentary regions. The filaments (with typical widths of ∼0.1 pc) and dense cores are resolved. The measured 2D velocity gradients of cores are between 1.3 and 16.7 km s-1 pc-1, corresponding to a specific angular momentum (J/M) between 0.0012 and 0.016 pc km s-1. With respect to the core size R, the specific angular momentum follows a power law J/M ∝ R1.52±0.14. The ratio (β) between the rotational energy and gravitational energy ranges from 0.00041 to 0.094, indicating insignificant support from rotation against gravitational collapse. We further focus on the alignment between the cores' rotational axes, which is defined to be perpendicular to the direction of the velocity gradient (θG), and the direction of elongation of filaments (θf) in this massive star-forming region. The distribution of the angle between θf and θG was found to be random, I.e., the cores' rotational axes have no discernible correlation with the elongation of their hosting filament. This implies that, in terms of angular momentum, the cores have evolved to be dynamically independent from their natal filaments.

Keywords: Interstellar molecules, Interstellar dynamics, Interstellar filaments, Interstellar clouds, Interstellar medium
Chromospheric Bubbles in Solar Flares. We analyze a grid of radiative hydrodynamic simulations of solar flares to study the energy balance and response of the atmosphere to nonthermal electron beam heating. The appearance of chromospheric bubbles is one of the most notable features that we find in the simulations. These pockets of chromospheric plasma get trapped between the transition region and the lower atmosphere as it is superheated by the particle beam. The chromospheric bubbles are seen in the synthetic spectra, appearing as an additional component to Balmer line profiles with high Doppler velocities as high as 200 km s-1. Their signatures are also visible in the wings of Ca II 8542 Å line profiles. These bubbles of chromospheric plasma are driven upward by a wave front that is induced by the shock of energy deposition, and require a specific heating rate and atmospheric location to manifest.

Keywords: Solar atmosphere, Solar flares, Solar coronal loops, Solar spectral irradiance, Solar flare spectra, Solar transition region, Radiative transfer simulations, Solar chromospheric heating, Solar chromosphere
Is GRB 110715A the Progenitor of FRB 171209?. The physical origin of fast radio bursts (FRBs) is unknown. Young magnetars born from gamma-ray bursts (GRBs) have been suggested as a possible central engine of FRBs. We test such a hypothesis by systematically searching for GRB-FRB spatial associations from 110 FRBs and 1440 GRBs. We find that one FRB event discovered by the Parkes telescope, FRB 171209, is spatially coincident with a historical long-duration GRB 110715A at z = 0.82. The afterglow of GRB 110715A is consistent with being powered by a millisecond magnetar. The extragalactic dispersion measure of FRB 171209 is in excess of that contributed by the intergalactic medium, which can be interpreted as being contributed by a young supernova remnant associated with the GRB. Overall, the significance of the association is (2.28-2.55)σ. If the association is indeed physical, our result suggests that the magnetars associated with long GRBs can be the progenitors of at least some FRBs.

Keywords: Gamma-ray sources, Magnetars, Radio transient sources
Standing Kink Waves in Sigmoid Solar Coronal Loops: Implications for Coronal Seismology. Using full three-dimensional magnetohydrodynamic numerical simulations, we study the effects of magnetic field sigmoidity or helicity on the properties of the fundamental kink oscillation of solar coronal loops. Our model consists of a single denser coronal loop, embedded in a plasma with dipolar force-free magnetic field with a constant α-parameter. For the loop with no sigmoidity, we find that the numerically determined oscillation period of the fundamental kink mode matches the theoretical period calculated using WKB theory. In contrast, with increasing sigmoidity of the loop, the actual period is increasingly smaller than the one estimated by WKB theory. Translated through coronal seismology, increasing sigmoidity results in magnetic field estimates that are increasingly shifting toward higher values, and even surpassing the average value for the highest α value considered. Nevertheless, the estimated range of the coronal magnetic field value lies within the minimal/maximal limits, proving the robustness coronal seismology. We propose that the discrepancy in the estimations of the absolute value of the force-free magnetic field could be exploited seismologically to determine the free energy of coronal loops, if averages of the internal magnetic field and density can be reliably estimated by other methods.

Keywords: Solar coronal seismology, Magnetohydrodynamics, Magnetohydrodynamical simulations
Multiphase Gas and the Fractal Nature of Radiative Turbulent Mixing Layers. A common situation in galactic and intergalactic gas involves cold dense gas in motion relative to hot diffuse gas. Kelvin-Helmholtz instability creates a turbulent mixing layer and populates the intermediate-temperature phase, which often cools rapidly. The energy lost to cooling is balanced by the advection of hot high enthalpy gas into the mixing layer, resulting in growth and acceleration of the cold phase. This process may play a major role in determining the interstellar medium and circumgalactic medium phase structure, and accelerating cold gas in galactic winds and cosmic filaments. Cooling in these mixing layers occurs in a thin corrugated sheet, which we argue has an area with fractal dimension D = 5/2 and a thickness that adjusts to match the hot phase mixing time to the cooling time. These cooling sheet properties form the basis of a new model for how the cooling rate and hot gas inflow velocity depend on the size L, cooling time of the mixed phase ${t}_{\mathrm{cool}}$, relative velocity ${V}_{\mathrm{rel}}$, and density contrast ${\rho }_{\mathrm{cold}}/{\rho }_{\mathrm{hot}}$ of the system. Entrainment is expected to be enhanced in environments with short ${t}_{\mathrm{cool}}$, large ${V}_{\mathrm{rel}}$, and large ${\rho }_{\mathrm{cold}}/{\rho }_{\mathrm{hot}}$. Using a large suite of three-dimensional hydrodynamic simulations, we demonstrate that this fractal cooling layer model accurately captures the energetics and evolution of turbulent interfaces and can therefore be used as a foundation for understanding multiphase mixing with strong radiative cooling.

Keywords: Galactic winds, Galaxy formation, Star formation, Galaxy evolution, Interstellar medium, Circumgalactic medium, Intracluster medium, Astrophysical fluid dynamics
Data-driven Detection of Multimessenger Transients. The primary challenge in the study of explosive astrophysical transients is their detection and characterization using multiple messengers. For this purpose, we have developed a new data-driven discovery framework, based on deep learning. We demonstrate its use for searches involving neutrinos, optical supernovae, and gamma-rays. We show that we can match or substantially improve upon the performance of state-of-the-art techniques, while significantly minimizing the dependence on modeling and on instrument characterization. Particularly, our approach is intended for near- and real-time analyses, which are essential for effective follow-up of detections. Our algorithm is designed to combine a range of instruments and types of input data, representing different messengers, physical regimes, and temporal scales. The methodology is optimized for agnostic searches of unexpected phenomena, and has the potential to substantially enhance their discovery prospects.

Keywords: Gamma-ray bursts, Neural networks, Neutrino astronomy, Transient detection, Gamma-ray transient sources, Time series analysis