Sazuna/UAT_keywords huggingface dataset:
Relativistic Shear Boundary Layer and the Gamma-Ray Emission of GW170817. We present an analysis of the radiation characteristics of kinetic shear boundary layers created by relativistic plasma jets. Using a model of electromagnetic field data based on particle-in-cell simulations of an electron-ion plasma, we solve the motion of individual test electrons and compute their instantaneous radiated power and peak frequency. By analyzing a large number of test electrons in this manner, we find two distinct electron populations present around the shear boundary layer. The most highly radiative electrons execute looping motion due to crossed electric and magnetic fields as they are accelerated along the bulk flow of the jet, and eventually cross the shear boundary interface at steep angles. Electrons that never cross the shear boundary interface radiate much less energy as a group. Summing over all of the highly radiative electrons, we compute the distribution of the total radiated energy as a function of the angle relative to the bulk flow. This result has important potential implications for the observed radiation output of short gamma-ray bursts viewed at large angles from the jet axis, such as the neutron star merger event GW170817/GRB 170817A.

Keywords: Gamma-ray bursts, Plasma astrophysics, Relativistic jets
A Geometric Origin for Quasi-periodic Oscillations in Black Hole X-Ray Binaries. We expand the relativistic precession model to include nonequatorial and eccentric trajectories and apply it to quasi-periodic oscillations (QPOs) in black hole X-ray binaries (BHXRBs) and associate their frequencies with the fundamental frequencies of the general case of nonequatorial (with Carter's constant, $Q\ne 0$ ) and eccentric ( $e\ne 0$ ) particle trajectories, around a Kerr black hole. We study cases with either two or three simultaneous QPOs and extract the parameters {e, rp, a, Q}, where rp is the periastron distance of the orbit, and a is the spin of the black hole. We find that the orbits with $\left[Q=0-4\right]$ should have e ≲ 0.5 and rp ∼ 2-20 for the observed range of QPO frequencies, where a ∈ [0, 1], and that the spherical trajectories {e = 0, $Q\ne 0$ } with Q = 2-4 should have rs ∼ 3-20. We find nonequatorial eccentric solutions for both M82 X-1 and GROJ 1655-40. We see that these trajectories, when taken together, span a torus region and give rise to a strong QPO signal. For two simultaneous QPO cases, we found equatorial eccentric orbit solutions for XTEJ 1550-564, 4U 1630-47, and GRS 1915+105, and spherical orbit solutions for BHXRBs M82 X-1 and XTEJ 1550-564. We also show that the eccentric orbit solution fits the Psaltis-Belloni-Klis correlation observed in BHXRB GROJ 1655-40. Our analysis of the fluid flow in the relativistic disk edge suggests that instabilities cause QPOs to originate in the torus region. We also present some useful formulae for trajectories and frequencies of spherical and equatorial eccentric orbits.

Keywords: Accretion, X-ray binary stars, Kerr black holes, Stellar mass black holes, General relativity, Geodesics, Astrophysical black holes
Detailed Characterization of Heartbeat Stars and Their Tidally Excited Oscillations. Heartbeat stars are a class of eccentric binary stars with short-period orbits and characteristic "heartbeat" signals in their light curves at periastron, caused primarily by tidal distortion. In many heartbeat stars, tidally excited oscillations can be observed throughout the orbit, with frequencies at exact integer multiples of the orbital frequency. Here, we characterize the tidally excited oscillations in the heartbeat stars KIC 6117415, KIC 11494130, and KIC 5790807. Using Kepler light curves and radial-velocity measurements, we first model the heartbeat stars using the binary modeling software ELLC, including gravity darkening, limb darkening, Doppler boosting, and reflection. We then conduct a frequency analysis to determine the amplitudes and frequencies of the tidally excited oscillations. Finally, we apply tidal theories to stellar structure models of each system to determine whether chance resonances can be responsible for the observed tidally excited oscillations, or whether a resonance-locking process is at work. We find that resonance locking is likely occurring in KIC 11494130, but not in KIC 6117415 or KIC 5790807.

Keywords: Close binary stars, Stellar evolutionary models, Stellar oscillations, Asteroseismology, Time series analysis
Spatially Resolved C III] λ1909 Emission in Haro 11. The C III] 1909 (hereafter C III]) line is the strongest ultraviolet emission line after Lyα and is therefore of interest to high-redshift studies of star-forming (SF) galaxies near the epoch of reionization. It is thought that C III] emission is strongest in galaxies with subsolar metallicity and low mass; however, spectral observations of numerous such galaxies at high and low redshift produce inconclusive or even contradictory results. We present the first-ever C III] imaging, obtained with HST/STIS for the low-redshift SF galaxy Haro 11. Cluster parameters like stellar mass, dust fraction and attenuation, and ionization parameter, obtained through spectral energy distribution fitting, show no correlation with the C III] equivalent width (EW), which may be due to a combination of the limitation of the models and the age homogeneity of the cluster population. Comparing the ratio of C III] emission line flux from individual clusters to that of Hα, [O III], and [O II], we find that the clusters with the highest EW(C III]) can be reconciled only with Cloudy models with an extremely high C/O ratio of ≥1.4(C/O)⊙ for an ionizing population of single stars, binary stars, or a mixture of binary stars and active galactic nuclei. Given the pointlike nature of strong C III], the integrated total strength of EW(C III]) becomes dependent on the morphology of the galaxy, which would explain the large scatter in EW(C III]) strengths observed in galaxies with otherwise similar SF properties and of similarly low metallicity and stellar mass.

Keywords: Starburst galaxies, Photoionization, Interstellar medium
Hints for Icy Pebble Migration Feeding an Oxygen-rich Chemistry in the Inner Planet-forming Region of Disks. We present a synergic study of protoplanetary disks to investigate links between inner-disk gas molecules and the large-scale migration of solid pebbles. The sample includes 63 disks where two types of measurements are available: (1) spatially resolved disk images revealing the radial distribution of disk pebbles (millimeter to centimeter dust grains), from millimeter observations with the Atacama Large Millimeter/Submillimeter Array or the Submillimeter Array, and (2) infrared molecular emission spectra as observed with Spitzer. The line flux ratios of H2O with HCN, C2H2, and CO2 all anticorrelate with the dust disk radius Rdust, expanding previous results found by Najita et al. for HCN/H2O and the dust disk mass. By normalization with the dependence on accretion luminosity common to all molecules, only the H2O luminosity maintains a detectable anticorrelation with disk radius, suggesting that the strongest underlying relation is between H2O and Rdust. If Rdust is set by large-scale pebble drift, and if molecular luminosities trace the elemental budgets of inner-disk warm gas, these results can be naturally explained with scenarios where the inner disk chemistry is fed by sublimation of oxygen-rich icy pebbles migrating inward from the outer disk. Anticorrelations are also detected between all molecular luminosities and the infrared index n13-30, which is sensitive to the presence and size of an inner-disk dust cavity. Overall, these relations suggest a physical interconnection between dust and gas evolution, both locally and across disk scales. We discuss fundamental predictions to test this interpretation and study the interplay between pebble drift, inner disk depletion, and the chemistry of planet-forming material.

Keywords: Molecular gas, Millimeter astronomy, Molecular spectroscopy, Planetary system formation, Infrared astronomy, Pre-main sequence stars, Protoplanetary disks, Circumstellar disks
A 3D Parametric Martian Bow Shock Model with the Effects of Mach Number, Dynamic Pressure, and the Interplanetary Magnetic Field. Using global MHD simulations, we construct a 3D parametric Martian bow shock model that employs a generalized conic section function defined by seven parameters. Effects of the solar wind dynamic pressure (Pd), the magnetosonic Mach number (MMS), and the intensity and the orientation of the interplanetary magnetic field (IMF) on the seven parameters are examined based on 250 simulation cases. These 250 cases have a Pd range of 0.36-9.0 nPa (the solar wind number density varying from 3.5 to 12 cm-3 and the solar wind speed varying from 250 to 670 km s-1), an MMS range of 2.8-7.9, and an IMF strength range from zero to 10 nT. The results from our parametric model show several things. (1) The size of the Martian bow shock is dominated by Pd. When Pd increases, the bow shock moves closer to Mars, and the flaring of the bow shock decreases. (2) The MMS has a similar effect on the bow shock as Pd but with different coefficients. (3) The effects of IMF components on the bow shock position are associated with the draping and pileup of the IMF around the Martian ionosphere; hence, we find that both the subsolar standoff distance and the flaring angle of the bow shock increase with the field strength of the IMF components that are perpendicular to the solar wind flow direction (BY and BZ in the MSO coordinate system). The parallel IMF component (BX) has little effect on the subsolar standoff distance but affects the flaring angle. (4) The cross section of the bow shock is elongated in the direction perpendicular to the IMF on the Y-Z plane, and the elongation degree is enhanced with increasing intensities of BY and BZ. The north-south (dawn-dusk) asymmetry is controlled by the cone angle when the IMF is on the X-Z (X-Y) plane. These results show a good agreement with the previous empirical and theoretical models. The current parametric model is obtained under solar maximum conditions with the strongest Martian crustal magnetic field located at the subsolar point. In fact, the bow shock shape can also be affected by both the solar extreme ultraviolet radiation and the orientation of crustal magnetic anomalies to the Sun, which should be considered in future models.

Keywords: Mars, Solar wind, Planetary bow shocks, Interplanetary magnetic fields
Propagation Effects in Quiet Sun Observations at Meter Wavelengths. Quiet Sun meterwave emission arises from thermal bremsstrahlung in the MK corona, and can potentially be a rich source of coronal diagnostics. On its way to the observer, it gets modified substantially due to propagation effects—primarily refraction and scattering—through the magnetized and turbulent coronal medium, leading to the redistribution of the intensity in the image plane. By comparing the full-disk meterwave solar maps during a quiet solar period and the modeled thermal bremsstrahlung emission, we characterize these propagation effects. The solar radio maps between 100 MHz and 240 MHz come from the Murchison Widefield Array. The FORWARD package is used to simulate thermal bremsstrahlung images using the self-consistent Magnetohydrodynamic Algorithm outside a Sphere coronal model. The FORWARD model does not include propagation effects. The differences between the observed and modeled maps are interpreted to arise due to scattering and refraction. There is a good general correspondence between the predicted and observed brightness distributions, though significant differences are also observed. We find clear evidence for the presence of significant propagation effects, including anisotropic scattering. The observed radio size of the Sun is 25-30% larger in area. The emission peak corresponding to the only visible active region shifts by 8-11ʹ and its size increases by 35-40%. Our simple models suggest that the fraction of scattered flux density is always larger than a few tens of percent, and varies significantly between different regions. We estimate density inhomogeneities to be in the range 1-10%.

Keywords: Solar coronal radio emission, The Sun, Solar active regions, Quiet solar corona, Solar coronal holes
Scaling and Anisotropy of Solar Wind Turbulence at Kinetic Scales during the MMS Turbulence Campaign. We employ data from the 2019 Magnetospheric Multiscale (MMS) Solar Wind Turbulence Campaign to evaluate scaling and anisotropy of second-order magnetic field structure functions and scale-dependent kurtosis from a single data interval. Prior results have been based either on the Taylor approximation, which conflates time and space dependence, or on averaging many data sets, which introduces sample-to-sample variation of plasma parameters. The present results overcome these systematic effects. We find that for length scales between 57 and 201 km the fluctuations are anisotropic with a preferred orientation of 60°-70° to the magnetic field direction. The peak kurtosis also lies in this angular range. This confirms anisotropy of the spectrum and suggests that coherent structures such as current sheets are oriented nearly perpendicular to the magnetic field direction. Both the anisotropy and the kurtosis decrease approaching the ion inertial length, here ≈91 km.

Keywords: Interplanetary turbulence, Space plasmas, Interplanetary magnetic fields, Plasma astrophysics
Search for High-redshift Blazars with Fermi/LAT. High-z blazars (z ≥ 2.5) are the most powerful class of persistent γ-ray sources in the universe. These objects possess the highest jet powers and luminosities and have black hole masses often in excess of 109 solar masses. In addition, high-z blazars are important cosmological probes and serve as test objects for blazar evolution models. Due to their large distance, their high-energy emission typically peaks below the GeV range, which makes them difficult to study with Fermi/Large Area Telescope (LAT). Therefore, only the very brightest objects are detectable and, to date, only a small number of high-z blazars have been detected with Fermi/LAT. In this work, we studied the monthly binned long-term γ-ray emission of a sample of 176 radio and optically detected blazars that have not been reported as known γ-ray sources in the 3FGL catalog. To account for false-positive detections, we calculated monthly Fermi/LAT light curves for a large sample of blank sky positions and derived the number of random fluctuations that we expect at various test statistic (TS) levels. For a given blazar, a detection of TS &gt; 9 in at least one month is expected ∼15% of the time. Although this rate is too high to secure detection of an individual source, half of our sample shows such single-month γ-ray activity, indicating a population of high-energy blazars at distances of up to z = 5.2. Multiple TS &gt; 9 monthly detections are unlikely to happen by chance, and we have detected several individual new sources in this way, including the most distant γ-ray blazar, BZQ J1430+4204 (z = 4.72). Finally, two new γ-ray blazars at redshifts of z = 3.63 and z = 3.11 are unambiguously detected via very significant (TS &gt; 25) flares in individual monthly time bins.

Keywords: Blazars, Gamma-ray astronomy, High-redshift galaxies
Magnetohydrodynamic Simulation of Magnetic Null-point Reconnections and Coronal Dimmings during the X2.1 Flare in NOAA AR 11283. The magnetohydrodynamics of active region NOAA 11283 is simulated using an initial non-force-free magnetic field extrapolated from its photospheric vector magnetogram. We focus on the magnetic reconnections at a magnetic null point that participated in the X2.1 flare on 2011 September 6 around 22:21 UT (SOL2011-09-06T22:21X2.1) followed by the appearance of circular flare ribbons and coronal dimmings. The initial magnetic field from extrapolation displays a three-dimensional (3D) null topology overlying a sheared arcade. Prior to the flare, magnetic loops rise due to the initial Lorentz force, and reconnect at the 3D null, leading to expansion and loss of confined plasma that produce the observed pre-flare coronal dimmings. Further, the simulated dynamics documents the transfer of twist from the arcade to the overlying loops through reconnections, developing a flux rope. The nonparallel field lines comprising the rope and lower-lying arcades form an X-type geometry. Importantly, the simultaneous reconnections at the 3D null and the X-type geometry can explain the observed circular and parallel flare ribbons. Reconnections at the 3D null transform closed inner spine field lines into open field lines of the outer spine. The footpoints of these open field lines correspond to a ring-shaped coronal dimming region, tracing the dome. Further, the flux rope bifurcates because of these reconnections, which also results in the generation of open magnetic field lines. The plasma loss along the open field lines can potentially explain the observed coronal dimming.

Keywords: Solar magnetic fields, Magnetohydrodynamical simulations
Tracing Dark Matter Halos with Satellite Kinematics and the Central Stellar Velocity Dispersion of Galaxies. It has been suggested that the central stellar velocity dispersion of galaxies can trace dark matter halo mass directly. We test this hypothesis using a complete spectroscopic sample of isolated galaxies surrounded by faint satellite galaxies from the Sloan Digital Sky Survey Data Release 12. We apply a friends-of-friends algorithm with projected linking length ${\rm{\Delta }}D\lt 100\,\,\mathrm{kpc}$ and radial velocity linking length ${\rm{\Delta }}V\lt 1000$ km s-1 to construct our sample. Our sample includes 2807 isolated galaxies with 3417 satellite galaxies at $0.01\lt z\lt 0.14$ . We divide the sample into two groups based on the primary galaxy color: red and blue primary galaxies separated at ${\left(g-r\right)}_{0}=0.85$ . The central stellar velocity dispersions of the primary galaxies are proportional to the luminosities and stellar masses of the same galaxies. Stacking the sample based on the central velocity dispersion of the primary galaxies, we derive the velocity dispersions of their satellite galaxies, which trace the dark matter halo mass of the primary galaxies. The system velocity dispersion of the satellite galaxies shows a remarkably tight correlation with the central velocity dispersion of the primary galaxies for both red and blue samples. In particular, the slope of the relation is identical to 1 for red primary systems. This tight relation suggests that the central stellar velocity dispersion of galaxies is indeed an efficient and robust tracer for dark matter halo mass. We provide empirical relations between the central stellar velocity dispersion and the dark matter halo mass.

Keywords: Galaxy dark matter halos, Late-type galaxies, Galaxy dynamics, Galaxy kinematics, Early-type galaxies
Existence of the Metal-rich Stellar Halo and High-velocity Thick Disk in the Galaxy. Based on the second Gaia data release (DR2), combined with the LAMOST and APOGEE spectroscopic surveys, we study the kinematics and metallicity distribution of the high-velocity stars that have a relative speed of at least 220 $\mathrm{km}\ {{\rm{s}}}^{-1}$ with respect to the local standard of rest in the Galaxy. The rotational velocity distribution of the high-velocity stars with [Fe/H] $\gt \ -1.0$ dex can be well described by a two-Gaussian model, with peaks at ${V}_{\phi }\sim +164.2\pm 0.7$ and ${V}_{\phi }\sim +3.0\pm 0.3$ $\mathrm{km}\ {{\rm{s}}}^{-1}$ , associated with the thick disk and halo, respectively. This implies that there should exist a high-velocity thick disk (HVTD) and a metal-rich stellar halo (MRSH) in the Galaxy. The HVTD stars have the same position as the halo in the Toomre diagram but show the same rotational velocity and metallicity as the canonical thick disk. The MRSH stars have basically the same rotational velocity, orbital eccentricity, and position in the Lindblad and Toomre diagram as the canonical halo stars, but they are more metal-rich. Furthermore, the metallicity distribution function of our sample stars are well fitted by a four-Gaussian model, associated with the outer halo, inner halo, MRSH, and HVTD, respectively. Chemical and kinematic properties and age imply that the MRSH and HVTD stars may form in situ.

Keywords: Galaxy stellar disks, Galaxy structure, Galaxy stellar halos, Galaxy abundances, Galaxy kinematics
A Non-equipartition Shock Wave Traveling in a Dense Circumstellar Environment around SN 2020oi. We report the discovery and panchromatic follow-up observations of the young Type Ic supernova (SN Ic) SN 2020oi in M100, a grand-design spiral galaxy at a mere distance of 14 Mpc. We followed up with observations at radio, X-ray, and optical wavelengths from only a few days to several months after explosion. The optical behavior of the supernova is similar to those of other normal SNe Ic. The event was not detected in the X-ray band but our radio observations revealed a bright mJy source ( ${L}_{\nu }\approx 1.2\times {10}^{27}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{Hz}}^{-1}$ ). Given the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio data set we obtained. The radio-emitting electrons initially experience a phase of inverse Compton cooling, which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of ɛe/ɛB ≳ 200, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shock wave driven by the SN ejecta into the circumstellar matter (CSM) is moving at $\sim 3\times {10}^{4}\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . Assuming a constant mass loss from the stellar progenitor, we find that the mass-loss rate is $\dot{M}\approx 1.4\times {10}^{-4}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ for an assumed wind velocity of $1000\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard r-2.

Keywords: Type Ic supernovae, Optical observation, Core-collapse supernovae, Transient sources, X-ray transient sources, Radio observatories, Supernovae, Radio transient sources
Orbital Migration of Interacting Stellar Mass Black Holes in Disks around Supermassive Black Holes. II. Spins and Incoming Objects. The masses, rates, and spins of merging stellar mass binary black holes (BBHs) detected by aLIGO and Virgo provide challenges to traditional BBH formation and merger scenarios. An active galactic nucleus (AGN) disk provides a promising additional merger channel because of the powerful influence of the gas that drives orbital evolution, makes encounters dissipative, and leads to migration. Previous work showed that stellar mass black holes (sBHs) in an AGN disk migrate to regions of the disk, known as migration traps, where positive and negative gas torques cancel out, leading to frequent BBH formation. Here we build on that work by simulating the evolution of additional sBHs that enter the inner disk by either migration or inclination reduction. We also examine whether the BBHs formed in our models have retrograde or prograde orbits around their centers of mass with respect to the disk, determining the orientation of the spin of the merged BBHs relative to the disk. Orbiters entering the inner disk form BBHs with sBHs on resonant orbits near the migration trap. When these sBHs reach ≳80 M⊙, they form BBHs with sBHs in the migration trap, which reach ∼1000 M⊙ over 10 Myr. We find 68% of the BBHs in our simulation orbit in the retrograde direction, which implies that BBHs in our merger channel will have small dimensionless aligned spins, χeff. Overall, our models produce BBHs that resemble both the majority of BBH mergers detected thus far (0.66-120 Gpc-3 yr-1) and two recent unusual detections, GW190412 (∼0.3 Gpc-3 yr-1) and GW190521 (∼0.1 Gpc-3 yr-1).

Keywords: Black hole physics, Intermediate-mass black holes, Supermassive black holes, Active galactic nuclei, LIGO