Sazuna/UAT_keywords huggingface dataset:
Neutrino Counterparts of Fast Radio Bursts. The discovery of a luminous radio burst, FRB 200428, with properties similar to those of fast radio bursts (FRBs), in coincidence with an X-ray flare from the Galactic magnetar SGR 1935+2154, supports magnetar models for cosmological FRBs. The burst's X-ray to radio fluence ratio, as well as the X-ray spectral shape and peak energy, are consistent with FRB 200428 being the result of an ultra-relativistic shock (powered, e.g., by an ejected plasmoid) propagating into a magnetized baryon-rich external medium; the shock simultaneously generates X-ray/gamma-rays via thermal synchrotron emission from electrons heated behind the shock, and coherent radio emission via the synchrotron maser mechanism. Here, we point out that a unique consequence of this baryon-loaded shock scenario is the generation of a coincident burst of high-energy neutrinos, generated by photohadronic interaction of relativistic ions—heated or accelerated at the shock—with thermal synchrotron photons. We estimate the properties of these neutrino burst FRB counterparts and find that a fraction ∼10-8-10-5 of the flare energy (or ∼10-4-10-1 of the radio isotropic energy) is channeled into production of neutrinos with typical energies ∼TeV-PeV. We conclude by discussing prospects for detecting this signal with IceCube and future high-energy neutrino detectors.

Keywords: Shocks, Cosmological neutrinos, Magnetars, Gamma-rays, Radio transient sources
FIRST J1419+3940 as the First Observed Radio Flare from a Neutron Star Merger. During their violent merger, two neutron stars can shed a few percent of their mass. As this ejecta expands, it collides with the surrounding interstellar gas, producing a slowly fading radio flare that lasts for years. Radio flares uniquely probe the neutron star merger populations as many events from past decades could still be detectable. Nonetheless, no radio flare observation has been reported to date. Here we show that the radio transient FIRST J1419+3940, first observed in 1993 and still detectable, could have originated from a neutron star merger. We carry out numerical simulations of neutron star merger ejecta to demonstrate that the observed radio light curve is well reproduced by a merger model with astrophysically expected parameters. We examine the observed radio data, as well as the host galaxy, to find clues that could differentiate the transient's neutron star merger origin from the alternative explanation—the afterglow of an off-axis long gamma-ray burst. Near-future observations could find further evidence for the FIRST J1419+3940 radio transient's origin. We show that existing radio surveys likely already recorded multiple radio flares, informing us of the origin and properties of neutron star mergers and their role in the nucleosynthesis of the heaviest elements in the universe.

Keywords: Neutron stars, Extragalactic radio sources, Gravitational wave sources
Detection of Pb II in the Ultraviolet Spectra of Three Metal-poor Stars. We report the first detection of the Pb II line at 2203.534 Šin three metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We perform a standard abundance analysis assuming local thermodynamic equilibrium (LTE) to derive lead (Pb, Z = 82) abundances. The Pb II line yields a higher abundance than Pb I lines by +0.36 ± 0.34 dex and +0.49 ± 0.28 dex in the stars HD 94028 and HD 196944, where Pb I lines had been detected previously. The Pb II line is likely formed in LTE, and these offsets affirm previous calculations showing that Pb I lines commonly used as abundance indicators underestimate the Pb abundance in LTE. Pb is enhanced in the s-process-enriched stars HD 94028 ([Pb/Fe] = +0.95 ± 0.14) and HD 196944 ([Pb/Fe] = +2.28 ± 0.23), and we show that 208Pb is the dominant Pb isotope in these two stars. The $\mathrm{log}\varepsilon $ (Pb/Eu) ratio in the r-process-enhanced star HD 222925 is 0.76 ± 0.14, which matches the solar system r-process ratio and indicates that the solar system r-process residuals for Pb are, in aggregate, correct. The Th/Pb chronometer in HD 222925 yields an age of 8.2 ± 5.8 Gyr, and we highlight the potential of the Th/Pb chronometer as a relatively model-insensitive age indicator in r-process-enhanced stars. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555. These observations are associated with programs GO-14161, GO-14765, and GO-15657. This Letter includes data taken at The McDonald Observatory of The University of Texas at Austin.

Keywords: Nucleosynthesis, Stellar abundances, R-process, Ultraviolet astronomy, S-process
Exclusion of Cosmic Rays from Molecular Clouds by Self-generated Electric Fields. It was recently discovered that in some regions of the Galaxy, the cosmic-ray (CR) abundance is several orders of magnitude higher than previously thought. Additionally, there is evidence that in molecular cloud envelopes, the CR ionization may be dominated by electrons. We show that for regions with high, electron-dominated ionization, the penetration of CR electrons into molecular clouds is modulated by the electric field that develops as a result of the charge they deposit. We evaluate the significance of this novel mechanism of self-modulation and show that the CR penetration can be reduced by a factor of a few to a few hundred in high-ionization environments, such as those found near the Galactic center.

Keywords: Galactic cosmic rays, Interstellar medium, Interstellar plasma
On the Origin of GW190521-like Events from Repeated Black Hole Mergers in Star Clusters. LIGO and Virgo have reported the detection of GW190521, from the merger of a binary black hole (BBH) with a total mass around 150 M⊙. While current stellar models limit the mass of any black hole (BH) remnant to about 40-50 M⊙, more massive BHs can be produced dynamically through repeated mergers in the core of a dense star cluster. The process is limited by the recoil kick (due to anisotropic emission of gravitational radiation) imparted to merger remnants, which can escape the parent cluster, thereby terminating growth. We study the role of the host cluster metallicity and escape speed in the buildup of massive BHs through repeated mergers. Almost independent of host metallicity, we find that a BBH of about 150 M⊙ could be formed dynamically in any star cluster with escape speed ≳200 km s-1, as found in galactic nuclear star clusters as well as the most massive globular clusters and super star clusters. Using an inspiral-only waveform, we compute the detection probability for different primary masses (≥60 M⊙) as a function of secondary mass and find that the detection probability increases with secondary mass and decreases for larger primary mass and redshift. Future additional detections of massive BBH mergers will be of fundamental importance for understanding the growth of massive BHs through dynamics and the formation of intermediate-mass BHs.

Keywords: Globular star clusters, Intermediate-mass black holes, Black hole physics, Gravitational wave detectors, Black holes, Superclusters, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves, Open star clusters, Astrophysical black holes, Star clusters
Monte-Carlo Neutrino Transport in Neutron Star Merger Simulations. Gravitational waves and electromagnetic signals from merging neutron star binaries provide valuable information about the the properties of dense matter, the formation of heavy elements, and high-energy astrophysics. To fully leverage observations of these systems, we need numerical simulations that provide reliable predictions for the properties of the matter unbound in these mergers. An important limitation of current simulations is the use of approximate methods for neutrino transport that do not converge to a solution of the transport equations as numerical resolution increases, and thus have errors that are impossible to quantify. Here, we report on a first simulation of a binary neutron star merger that uses Monte-Carlo techniques to directly solve the transport equations in low-density regions. In high-density regions, we use approximations inspired by implicit Monte-Carlo to greatly reduce the cost of simulations, while only introducing errors quantifiable through more expensive convergence studies. We simulate an unequal mass neutron star binary merger up to 5 ms past merger, and report on the properties of the matter and neutrino outflows. Finally, we compare our results to the output of our best approximate "M1" transport scheme, demonstrating that an M1 scheme that carefully approximates the neutrino energy spectrum only leads to ∼10% uncertainty in the composition and velocity of the ejecta, and ∼20% uncertainty in the νe and ${\bar{\nu }}_{e}$ luminosities and energies. The most significant disagreement found between M1 and Monte-Carlo results is a factor of ∼2 difference in the luminosity of heavy-lepton neutrinos.

Keywords: Neutron stars, Computational astronomy, R-process, Gravitational wave sources, Computational methods
Toward a Direct Measure of the Galactic Acceleration. High-precision spectrographs can enable not only the discovery of exoplanets, but can also provide a fundamental measurement in Galactic dynamics. Over about 10 year baselines, the expected change in the line-of-sight velocity due to the Galaxy's gravitational field for stars at ∼kiloparsec scale distances above the Galactic midplane is ∼few tens of cm s-1, and may be detectable by the current generation of high-precision spectrographs. Here, we provide theoretical expectations for this measurement based on both static models of the Milky Way and isolated Milky Way simulations, as well from controlled dynamical simulations of the Milky Way interacting with dwarf galaxies. We simulate a population synthesis model to analyze the contribution of planets and binaries to the Galactic acceleration signal. We find that while low-mass, long-period planetary companions are a contaminant to the Galactic acceleration signal, their contribution is very small. Our analysis of ∼10 years of data from the Lick-Carnegie Exoplanet Survey HIRES/Keck precision radial-velocity (RV) survey shows that slopes of the RV curves of standard RV stars agree with expectations of the local Galactic acceleration near the Sun within the errors, and that the error in the slope scales inversely as the square root of the number of observations. Thus, we demonstrate that a survey of stars with low intrinsic stellar jitter at kiloparsec distances above the Galactic midplane for realistic sample sizes can enable a direct determination of the dark matter density.

Keywords: Exoplanets, Dark matter density, Exoplanet astronomy, Dark matter, Milky Way Galaxy
Gravitational-wave Merger Forecasting: Scenarios for the Early Detection and Localization of Compact-binary Mergers with Ground-based Observatories. We present the prospects for the early (pre-merger) detection and localization of compact-binary coalescences using gravitational waves over the next 10 yr. Early warning can enable the direct observation of the prompt and early electromagnetic emission of a neutron star merger. We examine the capabilities of the ground-based detectors at their "Design" sensitivity (2021-2022), the planned "A+" upgrade (2024-2026), and the envisioned "Voyager" concept (late 2020s). We find that for a fiducial rate of binary neutron star mergers of 1000 Gpc-3 yr-1, the Design, A+, and Voyager era networks can provide 18, 54, and 195 s of warning for one source per year of observing, respectively, with a sky localization area &lt;100 deg2 at a 90% credible level. At the same rate, the A+ and Voyager era networks will be able to provide 9 and 43 s of warning, respectively, for a source with &lt;10 deg2 localization area. We compare the idealized search sensitivity to that achieved by the PyCBC Live search tuned for pre-merger detection. The gravitational-wave community will be prepared to produce pre-merger alerts. Our results motivate the operation of observatories with wide fields of view, automation, and the capability for fast slewing to observe simultaneously with the gravitational-wave network.

Keywords: Gravitational wave astronomy
First Solar Energetic Particles Measured on the Lunar Far-side. On 2019 May 6 the Lunar Lander Neutron &amp; Dosimetry (LND) Experiment on board the Chang'E-4 lander on the far-side of the Moon detected its first solar energetic particle (SEP) event with proton energies up to 21 MeV. Combined proton energy spectra are studied based on the LND, SOHO/EPHIN, and ACE/EPAM measurements, which show that LND could provide a complementary data set from a special location on the Moon, contributing to our existing observations and understanding of space environment. We applied velocity dispersion analysis to the impulsive electron event and weak proton enhancement and show that electrons are released only 22 minutes after the flare onset and ∼15 minutes after the type II radio burst, while protons are released more than one hour after the electron release. The beam-like in situ electrons and clear velocity dispersion indicate a good magnetic connection between the source and Earth. This is remarkable because stereoscopic remote-sensing observations from Earth and STEREO-A suggest that the SEPs are associated with an active region nearly 113° away from the magnetic footpoint of Earth. This suggests that these SEPs did not propagate along the nominal Parker spiral normally assumed for ballistic mapping and that the release and propagation mechanism of electrons and protons are likely to differ significantly for this event.

Keywords: Solar active region magnetic fields, Solar energetic particles, Space weather, Solar coronal mass ejection shocks, Lunar surface, Solar active regions, Solar physics, Solar instruments, Interplanetary physics
Formation of Population II Star Clusters in the Aftermath of a Pair Instability Supernova. Population II (Pop II) stars formed a few hundred million years after the Big Bang were key drivers of cosmic reionization and building blocks of high-redshift galaxies. How and when these stars formed is a subject of ongoing research. We conduct cosmological radiation hydrodynamical simulations to investigate the formation of Pop II star clusters in dark matter halos forming at z = 10-25 in the aftermath of a pair instability supernova (PISN). Our simulations model the formation of Population III and Pop II stars in a self-consistent manner along with their radiative, chemical, and SN feedback in halos of 5 × 105-7 × 107 M⊙. We find that a PISN evacuates the gas from halos ≤3 × 106 M⊙ and thereafter shuts off in situ star formation for at least 30 Myr. Pop II stellar clusters of 923 M⊙ and 6800 M⊙ form in halos of 3.8 × 107 M⊙ and 9 × 107 M⊙, respectively. The mode of star formation is highly episodic and mainly regulated by Pop II SN feedback. The average star formation rates are 10-5-10-4 M⊙ yr-1, and the star formation efficiency is less than 1%.

Keywords: Cosmology, Population III stars, Star forming regions, Star formation, Population II stars, High-redshift galaxies, Supernovae
On the Rate of Crustal Failures in Young Magnetars. The activity of magnetars is powered by their intense and dynamic magnetic fields and has been proposed as the trigger to extragalactic fast radio bursts. Here we estimate the frequency of crustal failures in young magnetars, by computing the magnetic stresses in detailed magnetothermal simulations including Hall drift and ohmic dissipation. The initial internal topology at birth is poorly known but is likely to be much more complex than a dipole. Thus, we explore a wide range of initial configurations, finding that the expected rate of crustal failures varies by orders of magnitude depending on the initial magnetic configuration. Our results show that this rate scales with the crustal magnetic energy, rather than with the often used surface value of the dipolar component related to the spin-down torque. The estimated frequency of crustal failures for a given dipolar component can vary by orders of magnitude for different initial conditions, depending on how much magnetic energy is distributed in the crustal nondipolar components, likely dominant in newborn magnetars. The quantitative reliability of the expected event rate could be improved by a better treatment of the magnetic evolution in the core and the elastic/plastic crustal response, not included here. Regardless of that, our results are useful inputs in modeling the outburst rate of young Galactic magnetars, and their relation with the fast radio bursts in our and other galaxies.

Keywords: Neutron stars, Magnetars, Magnetic fields, Radio transient sources
A Tale of Two Transition Disks: ALMA Long-baseline Observations of ISO-Oph 2 Reveal Two Closely Packed Nonaxisymmetric Rings and a ∼2 au Cavity. ISO-Oph 2 is a wide-separation (240 au) binary system where the primary star harbors a massive (Mdust ∼ 40 M⊕) ring-like disk with a dust cavity ∼50 au in radius and the secondary hosts a much lighter (Mdust ∼ 0.8 M⊕) disk. As part of the high-resolution follow-up of the "Ophiuchus Disk Survey Employing ALMA" (ODISEA) project, we present 1.3 mm continuum and 12CO molecular line observations of the system at 0"02 (3 au) resolution. We resolve the disk around the primary into two nonaxisymmetric rings and find that the disk around the secondary is only ∼7 au across and also has a dust cavity (r ∼ 2.2 au). Based on the infrared flux ratio of the system and the M0 spectral type of the primary, we estimate the mass of the companion to be close to the brown-dwarf limit. Hence, we conclude that the ISO-Oph 2 system contains the largest and smallest cavities, the smallest measured disk size, and the resolved cavity around the lowest-mass object (M⋆ ∼ 0.08 M⊙) in Ophiuchus. From the 12CO data, we find a bridge of gas connecting both disks. While the morphology of the rings around the primary might be due to an unseen disturber within the cavity, we speculate that the bridge might indicate an alternative scenario in which the secondary has recently flown by the primary star causing the azimuthal asymmetries in its disk. The ISO-Oph 2 system is therefore a remarkable laboratory to study disk evolution, planet formation, and companion-disk interactions.

Keywords: Submillimeter astronomy, Protoplanetary disks
Neutron Star Mergers as the Main Source of r-process: Natal Kicks and Inside-out Evolution to the Rescue. Binary neutron star mergers (BNSMs) are currently the most promising source of r-process thanks to the detection of GW170817. The estimated occurring frequency and the amount of mass ejected per merger indicate that BNSMs by themselves can account for all the r-process enrichment in the Galaxy. However, the decreasing trend of [Eu/Fe] versus [Fe/H] of disk stars for [Fe/H] ≳ -1 in the solar neighborhood is inconsistent with the flat trend expected from BNSMs with a standard delay time distribution (DTD) ∝ t-1. This has led to the suggestion that either additional sources or modification to the DTD of BNSMs is required to match the observations. We investigate the effects of natal kicks received during the birth of neutron star binaries on the chemical evolution of r-process element Eu in the Milky Way by combining the results from the galactic dynamics code GALPY with a one-zone Galactic chemical evolution model OMEGA. We show that when key inputs from simulations of the inside-out disk evolution are combined with natal kicks, BNSMs can naturally reproduce the observed decreasing trend of [Eu/Fe] with [Fe/H] in the solar neighborhood without the need for modification to the DTD or additional r-process sources.

Keywords: Neutron stars, Galaxy chemical evolution, R-process, Solar neighborhood, Milky Way Galaxy physics, Compact objects
On Making Magnetic-flux-rope Ω Loops for Solar Bipolar Magnetic Regions of All Sizes by Convection Cells. We propose that the flux-rope Ω loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the Ω-loop's size from initially horizontal magnetic field ingested through the cell's bottom. This idea is based on (1) observed characteristics of BMRs of all spans (∼1000 to ∼200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-sized convection cell from horizontal field placed at cell bottom, and (3) a well-known convection-zone simulation. From the observations and simulations, we (1) infer that the strength of the field ingested by the biggest convection cells (giant cells) to make the biggest BMR Ω loops is ∼103 G, (2) plausibly explain why the span and flux of the biggest observed BMRs are ∼200,000 km and ∼1022 Mx, (3) suggest how giant cells might also make "failed-BMR" Ω loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR Ω loops of their size, (4) suggest why sunspots observed in a sunspot cycle's declining phase tend to violate the hemispheric helicity rule, and (5) support a previously proposed amended Babcock scenario for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR Ω loop avoids having ∼105 G field in the initial flux rope at the bottom of the convection zone, it is an appealing alternative to the present magnetic-buoyancy-based standard scenario and warrants testing by high-enough-resolution giant-cell magnetoconvection simulations.

Keywords: Solar cycle, Solar magnetic flux emergence, Solar convective zone, Solar dynamo, Solar magnetic fields
Constraints from Gravitational-wave Detections of Binary Black Hole Mergers on the <SUP>12</SUP>C(α, γ)<SUP>16</SUP>O Rate. Gravitational-wave detections are starting to allow us to probe the physical processes in the evolution of very massive stars through the imprints they leave on their final remnants. Stellar evolution theory predicts the existence of a gap in the black hole mass distribution at high mass due to the effects of pair instability. Previously, we showed that the location of the gap is robust against model uncertainties, but it does depend sensitively on the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ rate. This rate is of great astrophysical significance and governs the production of oxygen at the expense of carbon. We use the open-source MESA stellar evolution code to evolve massive helium stars to probe the location of the mass gap. We find that the maximum black hole mass below the gap varies between $40\,{M}_{\odot }$ and $90\,{M}_{\odot }$ , depending on the strength of the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ reaction rate. With the first 10 gravitational-wave detections of black holes, we constrain the astrophysical S-factor for ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ , at $300\,\mathrm{keV}$ , to ${S}_{300}\gt 175\,\,{\rm{keV}}\,{\rm{b}}$ at 68% confidence. With ${ \mathcal O }(50)$ detected binary black hole mergers, we expect to constrain the S-factor to within ±10-30 ${\rm{keV}}\,{\rm{b}}$ . We also highlight a role for independent constraints from electromagnetic transient surveys. The unambiguous detection of pulsational pair-instability supernovae would imply that ${S}_{300}\gt 79\,{\rm{keV}}\,{\rm{b}}$ . Degeneracies with other model uncertainties need to be investigated further, but probing nuclear stellar astrophysics poses a promising science case for the future gravitational-wave detectors.

Keywords: Core-collapse supernovae, Late stellar evolution, Massive stars, Stellar mass black holes, Nuclear astrophysics, Supernovae, Astrophysical black holes, Stellar evolution