Sazuna/UAT_keywords huggingface dataset:
Dynamical Effects of Cosmic Rays on the Medium Surrounding Their Sources. Cosmic rays (CRs) leave their sources mainly along the local magnetic field; in doing so they excite both resonant and nonresonant modes through streaming instabilities. The excitation of these modes leads to enhanced scattering and in turn to a large pressure gradient that causes the formation of bubbles of gas, CRs, and self-generated magnetic fields expanding into the interstellar medium. By means of hybrid particle-in-cell simulations, we show that, by exciting the nonresonant instability, CRs excavate a cavity around their source where the diffusivity is strongly suppressed. This finding invalidates the so far largely adopted flux-tube assumption, under which particles move along magnetic lines even in the nonlinear regime. This phenomenon is general and is expected to occur around any sufficiently powerful CR source in the Galaxy. Our results might provide a physical explanation of the numerous claims of suppressed CR diffusion around Galactic sources such as supernova remnants, pulsar wind nebulae, and stellar clusters.

Keywords: Magnetic fields, Cosmic ray sources, Cosmic rays
A Novel Test of Quasar Orientation. The orientation of the disk of material accreting onto supermassive black holes that power quasars is one of most important quantities that are needed to understand quasars—both individually and in the ensemble average. We present a hypothesis for determining comparatively edge-on orientation in a subset of quasars (both radio loud and radio quiet). If confirmed, this orientation indicator could be applicable to individual quasars without reference to radio or X-ray data and could identify some 10%-20% of quasars as being more edge-on than average, based only on moderate resolution and signal-to-noise spectroscopy covering the C IV λ 1549 Å emission feature. We present a test of said hypothesis using X-ray observations and identify additional data that are needed to confirm this hypothesis and calibrate the metric.

Keywords: Optical observation, Metal line absorbers, Radio quiet quasars, Emission line galaxies, Radio loud quasars, X-ray quasars
Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes. We describe the X-ray pulse profile models we use and how we use them to analyze Neutron Star Interior Composition Explorer (NICER) observations of rotation-powered millisecond pulsars to obtain information about the mass-radius relation of neutron stars and the equation of state of the dense matter in their cores. Here we detail our modeling of the observed profile of PSR J0030+0451 that we analyzed in Miller et al. and Riley et al. and describe a cross-verification of computations of the pulse profiles of a star with R/M 3, in case stars this compact need to be considered in future analyses. We also present our early cross-verification efforts of the parameter estimation procedures used by Miller et al. and Riley et al. by analyzing two distinct synthetic data sets. Both codes yielded credible regions in the mass-radius plane that are statistically consistent with one another, and both gave posterior distributions for model parameter values consistent with the values that were used to generate the data. We also summarize the additional tests of the parameter estimation procedure of Miller et al. that used synthetic pulse profiles and the NICER pulse profile of PSR J0030+0451. We then illustrate how the precision of mass and radius estimates depends on the pulsar's spin rate and the size of its hot spot by analyzing four different synthetic pulse profiles. Finally, we assess possible sources of systematic error in the estimates made using this technique, some of which may warrant further investigation.

Keywords: Neutron stars, X-ray astronomy, Neutron star cores, Pulsars, Nuclear astrophysics, Compact objects, X-ray sources, Diffuse x-ray background, Stellar atmospheres
Spectroscopic Detection of Alfvénic Waves in the Chromosphere of Sunspot Regions. Transverse magnetohydrodynamic waves often called Alfvénic (or kink) waves have been often theoretically put forward to solve the outstanding problems of the solar corona like coronal heating, solar wind acceleration, and chemical abundance enhancement. Here we report the first spectroscopic detection of Alfvénic waves around a sunspot at chromospheric heights. By analyzing the spectra of the Hα line and Ca II 854.2 nm line, we determined line-of-sight velocity and temperature as functions of position and time. As a result, we identified transverse magnetohydrodynamic waves pervading the superpenumbral fibrils. These waves are characterized by the periods of 2.5 to 4.5 minutes, and the propagation direction parallel to the fibrils, the supersonic propagation speeds of 45 to 145 km s-1, and the close association with umbral oscillations and running penumbral waves in sunspots. Our results support the notion that the chromosphere around sunspots abounds with Alfvénic waves excited by the mode conversion of the upward-propagating slow magnetoacoustic waves.

Keywords: Solar atmosphere, Magnetohydrodynamics, Sunspots, Alfven waves, Solar chromosphere
Discovery of Carbon Monoxide in Distant Comet C/2017 K2 (PANSTARRS). Optical observations of the Oort cloud comet C/2017 K2 (PANSTARRS) show that its activity began at large heliocentric distances (up to 35 au), which cannot be explained by either the sublimation or the crystallization of water ice. Supervolatile sublimation, most likely of carbon monoxide (CO), has been proposed as a plausible driver of the observed mass loss. Here, we present the detection of the J = 2-1 rotational transition in outgassed CO from C/2017 K2 when at heliocentric distance rH = 6.72 au, using the James Clerk Maxwell Telescope. The CO line is blueshifted by 0.20 ± 0.03 km s-1 with an area and width of 8.3 ± 2.3 mK km s-1 and 0.28 ± 0.08 km s-1, respectively. The CO production rate is QCO = (1.6 ± 0.5) × 1027 s-1. These are the first observations of a gaseous species in C/2017 K2 and provide observational confirmation of the role of supervolatile sublimation in this comet.

Keywords: Small Solar System bodies
Black Hole Leftovers: The Remnant Population from Binary Black Hole Mergers. The inspiral and merger of two black holes produces a remnant black hole with mass and spin determined by the properties of its parent black holes. Using the inferred population properties of component black holes from the first two and a half observing runs of Advanced LIGO and Virgo, we calculate the population properties of the leftover remnant black holes. By integrating their rate of formation over the age of the universe, we estimate the number density of remnant black holes today. Using simple prescriptions for the cosmic star formation rate and black hole inspiral delay times, we determine the number density of this leftover black hole population to be ${660}_{-240}^{+440}\,{\mathrm{Mpc}}^{-3}$ , corresponding to ∼60,000 black hole remnants per Milky Way-equivalent galaxy. The mass spectrum of these remnants starts at ∼10 M⊙ and can be approximated by a decreasing exponential with characteristic length ∼15 M⊙, the final spin distribution is sharply peaked at χf ∼ 0.7, and the kick velocities range from tens to thousands of kilometers per second. These kick velocities suggest that globular clusters and nuclear star clusters may retain up to ${3}_{-2}^{+3} \%$ and ${46}_{-15}^{+17} \%$ of their remnant black holes, respectively, while young star clusters would only retain a few tenths of a percent. The estimates in this work assume that none of the remnants participate in subsequent hierarchical mergers. If hierarchical mergers occur, the overall number density would drop accordingly and the remnant mass distribution shape would evolve over time. This population of leftover black holes is an inescapable result from gravitational-wave observations of binary black hole mergers.

Keywords: Gravitational waves, Black holes
Thermonuclear Explosions and Accretion-induced Collapses of White Dwarfs in Active Galactic Nucleus Accretion Disks. White dwarfs (WDs) embedded in the gaseous disks of active galactic nuclei (AGNs) can rapidly accrete materials from these disks and grow in mass to reach, or even exceed, the Chandrasekhar limit. Binary WD (BWD) mergers are also believed to occur in AGN accretion disks. We study observational signatures from these events. We suggest that mass-accreting WDs and BWD mergers in AGN disks can lead to thermonuclear explosions that drive an ejecta shock breakout from the disk surface and power a slow-rising, relatively dim Type Ia supernova (SN). It is possible that such SNe Ia may be outshone by the emission of the AGN disk around a supermassive black hole (BH) with a mass of MSMBH ≳ 108 M⊙. In addition, accretion-induced collapses (AICs) of WDs in AGN disks may sometimes occur, which may form highly magnetized millisecond neutron stars (NSs). The subsequent spindown process of this nascent magnetar can deposit its rotational energy into the disk materials, resulting in a magnetar-driven shock breakout and a luminous magnetar-powered transient. We show that such an AIC event could power a rapidly evolving and luminous transient for a magnetic field of B ∼ 1015 G. The rising time and peak luminosity of the transient, powered by a magnetar with B ∼ 1014 G, are predicted to have similar properties to those of superluminous SNe. AIC events taking place in the inner parts of disks around relatively less massive supermassive BHs (MSMBH ≲ 108 M⊙) are more likely to power transients that are much brighter than the AGN disk emission, and hence easily identified.

Keywords: Neutron stars, White dwarf stars, Active galactic nuclei, Radiative transfer, Supernovae
Continued Radio Observations of GW170817 3.5 yr Post-merger. We present new radio observations of the binary neutron star merger GW170817 carried out with the Karl G. Jansky Very large Array (VLA) more than 3 yr after the merger. Our combined data set is derived by coadding more than ≈32 hr of VLA time on-source, and as such provides the deepest combined observation (rms sensitivity ≈0.99 μJy) of the GW170817 field obtained to date at 3 GHz. We find no evidence for a late-time radio rebrightening at a mean epoch of t ≈ 1200 days since merger, in contrast to a ≈2.1σ excess observed at X-ray wavelengths at the same mean epoch. Our measurements agree with expectations from the post-peak decay of the radio afterglow of the GW170817 structured jet. Using these results, we constrain the parameter space of models that predict a late-time radio rebrightening possibly arising from the high-velocity tail of the GW170817 kilonova ejecta, which would dominate the radio and X-ray emission years after the merger (once the structured jet afterglow fades below detection level). Our results point to a steep energy-speed distribution of the kilonova ejecta (with energy-velocity power-law index α ≳ 5). We suggest possible implications of our radio analysis, when combined with the recent tentative evidence for a late-time rebrightening in the X-rays, and highlight the need for continued radio-to-X-ray monitoring to test different scenarios.

Keywords: Radio continuum emission, X-ray transient sources, Radio transient sources
Orbital Evolution of Equal-mass Eccentric Binaries due to a Gas Disk: Eccentric Inspirals and Circular Outspirals. We solve the equations of two-dimensional hydrodynamics describing a circumbinary disk accreting onto an eccentric, equal-mass binary. We compute the time rate of change of the binary semimajor axis a and eccentricity e over a continuous range of eccentricities spanning e = 0 to e = 0.9. We find that binaries with initial eccentricities e0 ≲ 0.1 tend to e = 0, where the binary semimajor axis expands. All others are attracted to e ≈ 0.4, where the binary semimajor axis decays. The e ≈ 0.4 attractor is caused by a rapid change in the disk response from a nearly origin-symmetric state to a precessing asymmetric state. The state change causes the time rates of change $\dot{a}$ and $\dot{e}$ to steeply change sign at the same critical eccentricity resulting in an attracting solution where $\dot{a}=\dot{e}=0$ . This does not, however, result in a stalled, eccentric binary. The finite transition time between disk states causes the binary eccentricity to evolve beyond the attracting eccentricity in both directions resulting in oscillating orbital parameters and a drift of the semimajor axis. For the chosen disk parameters, binaries with e0 ≳ 0.1 evolve toward and then oscillate around e ≈ 0.4 where they shrink in semimajor axis. Because unequal mass binaries grow toward equal mass through preferential accretion, our results are applicable to a wide range of initial binary mass ratios. Hence, these findings merit further investigations of this disk transition; understanding its dependence on disk parameters is vital for determining the fate of binaries undergoing orbital evolution with a circumbinary disk.

Keywords: Stellar accretion disks, Binary stars, Gravitational waves, Hydrodynamics
The Abundance of Lead in Four Metal-poor Stars. Cowan et al. review how roughly half the elements heavier than iron found in the Sun are produced by rapid neutron capture and half by slow neutron capture, the r- and s-processes. In the Sun, their relative contribution to individual elemental abundances is well understood, except for the lightest and heaviest elements beyond iron. Their contributions are especially uncertain for the heaviest nonradioactive element, lead (Pb, Z = 82). This is constrained by deriving lead abundances in metal-poor stars. For in the most metal-poor halo stars, strontium and heavier elements are found in the solar r-process proportion; s-process elements appear only at metallicities above one-thirtieth solar. In unevolved metal-poor stars of roughly solar heavy-element content, only two UV Pb lines are detectable. Four such stars have high-resolution spectra of the strongest line, Pb ii at 2203.53 Å. Roederer et al. analyzed this line in one star, deriving a lead-to-iron abundance ratio 10 times solar. This and its blueshifted profile suggested strong s-process production. This work analyzes the UV spectra of all four stars. Calculations including a predicted Fe i line blueward of the Pb ii line, and assuming the lead abundance scales with r-process abundances, match all four profiles extremely well. A scaled s-process contribution might improve the match to the much lower lead abundance found in the unevolved star analyzed previously, but its s-process excess is modest. An Fe ii line blends the other lead line, Pb i at 2833.05 Å, which constrains the lead abundance only in the coolest star.

Keywords: Stellar populations, Population II stars, Galactic archaeology
A Recently Quenched Isolated Dwarf Galaxy Outside of the Local Group Environment. We report the serendipitous identification of a low-mass (M* ∼ 2 × 106 M⊙), isolated, likely quenched dwarf galaxy in the "foreground" of the COSMOS-CANDELS field. From deep Hubble Space Telescope (HST) imaging we infer a surface brightness fluctuation distance for COSMOS-dw1 of DSBF = 22 ± 3 Mpc, which is consistent with its radial velocity of cz = 1222 ± 64 km s-1 via Keck/LRIS. At this distance, the galaxy is 1.4 Mpc in projection from its nearest massive neighbor. We do not detect significant Hα emission (EW(Hα)= - 0.4 ± 0.5 Å), suggesting that COSMOS-dw1 is likely quenched. Very little is currently known about isolated quenched galaxies in this mass regime. Such galaxies are thought to be rare, as there is no obvious mechanism to permanently stop star formation in them; to date there are only four examples of well-studied quenched field dwarfs, only two of which appear to have quenched in isolation. COSMOS-dw1 is the first example outside of the immediate vicinity of the Local Group. COSMOS-dw1 has a relatively weak Dn4000 break and the HST data show a clump of blue stars indicating that star formation ceased only recently. We speculate that COSMOS-dw1 was quenched due to internal feedback, which was able to temporarily suspend star formation. In this scenario the expectation is that quenched isolated galaxies with masses M* = 106-107 M⊙ generally have luminosity-weighted ages ≲1 Gyr.

Keywords: Galaxy evolution, Galaxy quenching, Dwarf galaxies, Quenched galaxies
Seeding Supermassive Black Holes with Self-interacting Dark Matter: A Unified Scenario with Baryons. Observations show that supermassive black holes (SMBHs) with a mass of ∼109 M☉ exist when the universe is just 6% of its current age. We propose a scenario where a self-interacting dark matter halo experiences gravothermal instability and its central region collapses into a seed black hole. The presence of baryons in protogalaxies could significantly accelerate the gravothermal evolution of the halo and shorten collapse timescales. The central halo could dissipate its angular momentum remnant via viscosity induced by the self-interactions. The host halo must be on high tails of density fluctuations, implying that high-z SMBHs are expected to be rare in this scenario. We further derive conditions for triggering general relativistic instability of the collapsed region. Our results indicate that self-interacting dark matter can provide a unified explanation for diverse dark matter distributions in galaxies today and the origin of SMBHs at redshifts z ∼ 6-7.

Keywords: Supermassive black holes, Dark matter
A Dynamical Measurement of the Disk Mass in Elias 227. Recent multi-wavelength Atacama Large Millimeter/submillimeter Array (ALMA) observations of the protoplanetary disk orbiting around Elias 227 revealed a two-armed spiral structure. The observed morphology, together with the young age of the star and the disk-to-star mass ratio estimated from dust-continuum emission, make this system a perfect laboratory to investigate the role of self-gravity in the early phases of star formation. This is particularly interesting if we consider that gravitational instabilities could be a fundamental first step for the formation of planetesimals and planets. In this Letter, we model the rotation curve obtained by CO data of Elias 227 with a theoretical rotation curve, including both the disk self-gravity and the star contribution to the gravitational potential. We compare this model with a purely Keplerian one and with a simple power-law function. We find that (especially for the 13CO isotopologue) the rotation curve is better described by considering not only the star, but also the disk self-gravity. We are thus able to obtain for the first time a dynamical estimate of the disk mass of 0.08 0.04 M and the star mass of 0.46 0.03 M (in the more general case), the latter being comparable with previous estimates. From these values, we derive that the disk is 17 of the star mass, meaning that it could be prone to gravitational instabilities. This result would strongly support the hypothesis that the two spiral arms are generated by gravitational instabilities.

Keywords: Gravitational instability, Protoplanetary disks
Nonequilibrium Ionization Plasma during a Large Solar Limb Flare Observed by Hinode/EIS. This study on plasma heating considers the time-dependent ionization process during a large solar flare on 2017 September 10, observed by Hinode/EUV Imaging Spectrometer (EIS). The observed Fe XXIV/Fe XXIII ratios increase downstream of the reconnection outflow, and they are consistent with the time-dependent ionization effect at a constant electron temperature Te 25 MK. Moreover, this study also shows that the nonthermal velocity, which can be related to the turbulent velocity, reduces significantly along the downstream of the reconnection outflow, even when considering the time-dependent ionization process.

Keywords: Solar flares
Discovery of a Radio Halo (and Relic) in a M<SUB>500</SUB>&lt;2×10<SUP>14</SUP> M<SUB>☉</SUB> Cluster. Radio halos are diffuse synchrotron sources observed in dynamically unrelaxed galaxy clusters. Current observations and models suggest that halos trace turbulent regions in the intracluster medium where mildly relativistic particles are reaccelerated during cluster mergers. Due to the higher luminosities and detection rates with increasing cluster mass, radio halos have been mainly observed in massive systems (M500 ≳ 4 × 1014 M☉). Here, we report the discovery of a radio halo with a largest linear scale of ≃ 750 kpc in PSZ2G145.92-12.53 (z = 0.03) using LOw Frequency ARray (LOFAR) observations at 120-168 MHz. With a mass of M500 = (1.9 ± 0.2)×1014 M☉ and a radio power at 150MHz of P150 = (3.5 ± 0.7)×1023 W Hz-1, this is the least powerful radio halo in the least massive cluster discovered to date. Additionally, we discover a radio relic with a mildly convex morphology at 1.7 Mpc from the cluster center. Our results demonstrate that LOFAR has the potential to detect radio halos even in low-mass clusters, where the expectation to form them is very low (∼5%) based on turbulent reacceleration models. Together with the observation of large samples of clusters, this opens the possibility to constrain the low end of the powermass relation of radio halos.

Keywords: Galaxy clusters, Extragalactic radio sources, Extended radiation sources, Intracluster medium, Non-thermal radiation sources, Radio interferometry, Radio astronomy
The Time Delay Distribution and Formation Metallicity of LIGO-Virgos Binary Black Holes. We derive the first constraints on the time delay distribution of binary black hole (BBH) mergers using the LIGO-Virgo Gravitational-Wave Transient Catalog. Assuming that the progenitor formation rate follows the star formation rate (SFR), the data favor that 43100 of mergers have delay times &lt;4.5 Gyr (90 credibility). Adopting a model for the metallicity evolution, we derive joint constraints for the metallicity-dependence of the BBH formation efficiency and the distribution of time delays between formation and merger. Short time delays are favored regardless of the assumed metallicity dependence, although the preference for short delays weakens as we consider stricter low-metallicity thresholds for BBH formation. For a p() 1 time delay distribution and a progenitor formation rate that follows the SFR without metallicity dependence, we find that min &lt; 2.2 Gyr, whereas considering only the low-metallicity Z &lt; 0.3 Z SFR, min &lt; 3.0 Gyr (90 credibility). Alternatively, if we assume long time delays, the progenitor formation rate must peak at higher redshifts than the SFR. For example, for a p() 1 time delay distribution with min 4 Gyr, the inferred progenitor rate peaks at z &gt; 3.9 (90 credibility). Finally, we explore whether the inferred formation rate and time delay distribution vary with BBH mass.

Keywords: Cosmological evolution, Bayesian statistics, Stellar mass black holes, Gravitational wave astronomy, Gravitational waves, Astrophysical black holes
Effect of H<SUB>2</SUB>S on the Near-infrared Spectrum of Irradiation Residue and Applications to the Kuiper Belt Object (486958) Arrokoth. On 2019 January 1, the New Horizons spacecraft flew by (486958) Arrokoth, a small body in the Kuiper Belt that is the most distant object ever visited by a spacecraft. A strong unidentified absorption band was observed in the spectrum of Arrokoth at 1.8 m. We report here experimental evidence suggesting that the near-infrared spectrum of Arrokoth is indicative of sulfur-rich, tholin-like organic residue. The spectra of organic residues produced by irradiating ice mixtures with H2S CH3OH:NH3:H2S:H2O (3:3:3:1) and without H2S CH3OH:NH3:H2O (3:3:1) were measured to study the effect of H2S. The with H2S sulfur-rich laboratory-synthesized organic residue displays an absorption band at 1.8 m that is absent in the spectrum of without H2S sample. This feature matches the Arrokoth spectrum better than any other expected material. This suggests the past presence of H2S ice on the surface of Arrokoth and a role for Kuiper Belt objects as a key S reservoir in the early solar system.

Keywords: Small Solar System bodies, Kuiper belt, Laboratory astrophysics, Solar system, Astrochemistry, Trans-Neptunian objects