adsabs/SciX_UAT_keywords huggingface dataset:
On the Stabilization of a Twisted Magnetic Flux Tube

The linear magnetohydrodynamic stability of a shielding magnetic flux rope with a surface current under coronal solar conditions is analyzed in the framework of an energy principle. The equation describing the potential energy change induced by disturbances of the equilibrium was derived. It has been shown that the surface reverse current shielding the azimuthal component of the magnetic field lines outside a flux rope stabilizes the development of kink- and flute-type instabilities in the long-wavelength limit independently of the cross-sectional radial profile of current density. Kink modes are the most unstable ones as their generation requires less energy than other modes. Based on the obtained dispersion relation for kink oscillations, we proposed a new expression for the determination of magnetic field components of the twisted loop.

Keywords: magnetohydrodynamics; space plasmas
Multimessenger Picture of J1048+7143

We draw a multimessenger picture of J1048+7143, a flat-spectrum radio quasar known to show quasiperiodic oscillations in the γ-ray regime. We generate the adaptively binned Fermi Large Area Telescope light curve of this source above 168 MeV to find three major γ-ray flares of the source, such that each of the three flares consists of two sharp subflares. Based on radio interferometric imaging data taken with the Very Large Array, we find that the kiloparsec-scale jet is directed west, while our analysis of 8.6 GHz very long baseline interferometry data, mostly taken with the Very Long Baseline Array, revealed signatures of two parsec-scale jets, one pointing east, one pointing south. We suggest that the misalignment of the kiloparsec- and parsec-scale jets is a revealing signature of jet precession. We also analyze the 5 GHz total flux density curve of J1048+7143 taken with the Nanshan (Ur) and RATAN-600 single-dish radio telescopes and find two complete radio flares, lagging slightly behind the γ-ray flares. We model the timing of γ-ray flares as a signature of the spin-orbit precession in a supermassive black hole binary, and find that the binary could merge in the next ~60-80 yr. We show that both pulsar timing arrays and the planned Laser Interferometer Space Antenna lack sensitivity and frequency coverage to detect the hypothetical supermassive black hole binary in J1048+7143. We argue that the identification of sources similar to J1048+7143 plays a key role in revealing periodic high-energy sources in the distant universe. *Released xxxx 2022.

Keywords: high energy astrophysics; active galactic nuclei; radio active galactic nuclei; gamma-ray astronomy
Binary Interaction Can Yield a Diversity of Circumstellar Media around Type II Supernova Progenitors

Recent observations of supernovae (SNe) have indicated that a fraction of massive stars possess dense circumstellar medium (CSM) at the moment of their core collapses. They suggest the presence of additional activities of the SN progenitor driving the enhancement of the mass-loss rate, and some physical processes attributing to a single star's activities have been considered. In this study, we carry out binary evolutionary simulations of massive stars by MESA and investigate effects on the subsequent CSM formation through hydrodynamical simulations by PLUTO. We show that the mass transfer rate in a binary can increase at the beginning of the Roche lobe overflow, and this enhancement would be associated with the structure of the CSM before the explosion. We also illustrate that, depending on the orbital period of the binary, the density structure of the CSM can have a diverse distribution, including shell-like and cliff-like structures. These characteristic structures appear within the length scale of ∼1017 cm and could be traced by long-term observations of SNe, if the slow velocity of the CSM is assumed (∼10 km s‑1). Our results highlight the importance of binary interaction in the aspect of reproducing the diversity of the CSM configuration.

Keywords: massive stars; binary stars; circumstellar matter; core-collapse supernovae; stellar mass loss
A Formally Motivated Retrieval Framework Applied to the High-resolution Transmission Spectrum of HD 189733 b

Ground-based high-resolution spectra provide a powerful tool for characterizing exoplanet atmospheres. However, they are greatly hampered by the dominating telluric and stellar lines, which need to be removed prior to any analysis. Such removal techniques ("preparing pipelines") deform the spectrum; hence, a key point is to account for this process in the forward models used in retrievals. We develop a formal derivation on how to prepare froward models for retrievals, in the case where the telluric and instrumental deformations can be represented as a matrix multiplied element-wise with the data. We also introduce the notion of a "bias pipeline metric," which can be used to compare the bias potential of preparing pipelines. We use the resulting framework to retrieve simulated observations of 1D and 3D exoplanet atmospheres and to reanalyze high-resolution ( ${ \mathcal R }\approx {\rm{80,400}}$ ) near-infrared (0.96–1.71 μm) CARMENES transit data of HD 189733 b. We compare these results with those obtained from a cross-correlation function analysis. With our fiducial retrieval, we find a blueshift of the absorption features of $-{5.51}_{-0.53}^{+0.66}$ km s‑1. In addition, we retrieve a H2O log10(VMR) of $-{2.39}_{-0.16}^{+0.12}$ and a temperature of ${660}_{-11}^{+6}$ K. We are also able to put upper limits for the abundances of CH4, CO, H2S, HCN, and NH3, consistent with a subsolar-metallicity atmosphere enriched in H2O. We retrieve a broadened line shape, consistent with rotation- and wind-induced line broadening. Finally, we find a lower limit for the pressure of an opaque cloud consistent with a clear atmosphere, and we find no evidence for hazes.

Keywords: high resolution spectroscopy; extrasolar gaseous giant planets; near infrared astronomy; astronomy data analysis
An Extensive Hubble Space Telescope Study of the Offset and Host Light Distributions of Type I Superluminous Supernovae

We present an extensive Hubble Space Telescope rest-frame UV imaging study of the locations of Type I superluminous supernovae (SLSNe) within their host galaxies. The sample includes 65 SLSNe with detected host galaxies in the redshift range z ≈ 0.05–2. Using precise astrometric matching with SN images, we determine the distributions of the physical and host-normalized offsets relative to the host centers, as well as the fractional flux distribution relative to the underlying UV light distributions. We find that the host-normalized offsets of SLSNe roughly track an exponential disk profile, but exhibit an overabundance of sources with large offsets of 1.5–4 times their hosts' half-light radii. The SLSNe normalized offsets are systematically larger than those of long gamma-ray bursts (LGRBs), and even Type Ib/c and Type II SNe. Furthermore, we find from a Monte Carlo procedure that about ${37}_{-8}^{+6} \% $ of SLSNe occur in the dimmest regions of their host galaxies, with a median fractional flux value of 0.16, in stark contrast to LGRBs and Type Ib/c and Type II SNe. We do not detect any significant trends in the locations of SLSNe as a function of redshift, or as a function of explosion and magnetar engine parameters inferred from modeling of their optical light curves. The significant difference in SLSN locations compared to LGRBs (and normal core-collapse SNe) suggests that at least some of their progenitors follow a different evolutionary path. We speculate that SLSNe arise from massive runaway stars from disrupted binary systems, with velocities of ∼102 km s‑1.

Keywords: stellar populations; supernovae
Simulations of Precessing Jets and the Formation of X-shaped Radio Galaxies

Jet precession is sometimes invoked to explain asymmetries in radio galaxy (RG) jets and "X/S/Z-shaped" RGs, caused by the presence of a binary black hole companion to the source active galactic nucleus or by accretion instabilities. We present a series of simulations of RG jet precession to examine how these sources would evolve over time, including a passive distribution of cosmic-ray electrons so we can model radio synchrotron emissions and create synthetic radio maps of the sources. We find that a single source viewed from different angles can result in differing RG morphological classifications, confusing physical implications of these classifications. Additionally, the jet trajectories can become unstable due to their own self-interactions and lead to "reorientation events" that may look like the effects of external dynamics such as shocks, winds, or cold fronts in the medium. Finally, something akin to an "Odd Radio Circle" may be observed in the case of viewing the radio remnant of such a precessing source from a line of sight near the precession axis.

Keywords: astronomical simulations; magnetohydrodynamical simulations; galaxy jets; jets; radio jets; radio galaxies; extragalactic radio sources
Verification of the Standard Theory of Plasma Emission with Particle-in-cell Simulations

The standard theory of plasma emission is based on kinetic couplings between a single beam of energetic electrons and unmagnetized thermal plasmas, involving multistep nonlinear wave-particle and wave-wave interactions. The theory has not yet been completely verified with fully kinetic electromagnetic particle-in-cell (PIC) simulations. Earlier studies, greatly limited by available computational resources, are controversial regarding whether the fundamental emission can be generated according to the standard theory. To resolve the controversy, we conducted PIC simulations with a large domain of simulations and a large number of macroparticles, among the largest ones of similar studies. We found significant fundamental emission if the relative beam density is small enough (say, ≤0.01), in line with an earlier study with a much smaller domain; the relative intensity (normalized by the total initial beam energy) of all modes, except the mode associated with the beam-electromagnetic Weibel instability, decreases with the increasing relative density of the beam. We also found a significant transverse magnetic component associated with the superluminal Langmuir turbulence, which has been mistakenly regarded as evidence of the F emission in the earlier study. Further investigations are required to reveal their origin.

Keywords: solar corona; solar activity; radio bursts; solar coronal radio emission; plasma astrophysics
Signatures of r-process Enrichment in Supernovae from Collapsars

Despite recent progress, the astrophysical channels responsible for rapid neutron capture (r-process) nucleosynthesis remain an unsettled question. Observations of the kilonova following the gravitational-wave-detected neutron star merger GW170817 established mergers as one site of the r-process, but additional sources may be needed to fully explain r-process enrichment in the universe. One intriguing possibility is that rapidly rotating massive stars undergoing core collapse launch r-process-rich outflows off the accretion disks formed from their infalling matter. In this scenario, r-process winds are one component of the supernova (SN) ejecta produced by "collapsar" explosions. We present the first systematic study of the effects of r-process enrichment on the emission from collapsar-generated SNe. We semianalytically model r-process SN emission from explosion out to late times and determine its distinguishing features. The ease with which r-process SNe can be identified depends on how effectively wind material mixes into the initially r-process-free outer layers of the ejecta. In many cases, enrichment produces a near-infrared (NIR) excess that can be detected within ~75 days of explosion. We also discuss optimal targets and observing strategies for testing the r-process collapsar theory, and find that frequent monitoring of optical and NIR emission from high-velocity SNe in the first few months after explosion offers a reasonable chance of success while respecting finite observing resources. Such early identification of r-process collapsar candidates also lays the foundation for nebular-phase spectroscopic follow-up in the NIR and mid-infrared, for example, with the James Webb Space Telescope.

Keywords: core-collapse supernovae; r-process
The Relationship between IGM Lyα Opacity and Galaxy Density near the End of Reionization

Observed scatter in the Lyα opacity of quasar sightlines at z < 6 has motivated measurements of the correlation between Lyα opacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyα troughs at z ~ 5.7 with a deficit of Lyα emitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward the z = 6.02 quasar SDSS J1306+0356 and the z = 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10 h -1 Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyα troughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyα opacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyα opacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent.

Keywords: intergalactic medium; reionization; high-redshift galaxies; lyman-alpha galaxies
Binary Black Hole Mergers from Young Massive and Open Clusters: Comparison to GWTC-2 Gravitational Wave Data

Several astrophysical scenarios have been proposed to explain the origin of the population of binary black hole (BBH) mergers detected in gravitational waves by the LIGO/Virgo Collaboration. Among them, BBH mergers assembled dynamically in young massive and open clusters have been shown to produce merger rate densities consistent with LIGO/Virgo estimated rates. We use the results of a suite of direct, high-precision N-body evolutionary models of young massive and open clusters and build the population of BBH mergers, by accounting for both a cosmologically motivated model for the formation of young massive and open clusters and the detection probability of LIGO/Virgo. We show that our models produce dynamically paired BBH mergers that are well consistent with the observed masses, mass ratios, effective spin parameters, and final spins of the second Gravitational Wave Transient Catalog (GWTC-2).

Keywords: astrophysical black holes; black holes; stellar mass black holes; gravitational wave astronomy; gravitational wave detectors; gravitational wave sources; gravitational waves; kerr black holes; rotating black holes
Plumelets: Dynamic Filamentary Structures in Solar Coronal Plumes

Solar coronal plumes long seemed to possess a simple geometry supporting spatially coherent, stable outflow without significant fine structure. Recent high-resolution observations have challenged this picture by revealing numerous transient, small-scale, collimated outflows ("jetlets") at the base of plumes. The dynamic filamentary structure of solar plumes above these outflows, and its relationship with the overall plume structure, have remained largely unexplored. We analyzed the statistics of continuously observed fine structure inside a single representative bright plume within a mid-latitude coronal hole during 2016 July 2-3. By applying advanced edge-enhancement and spatiotemporal analysis techniques to extended series of high-resolution images from the Solar Dynamics Observatory's Atmospheric Imaging Assembly, we determined that the plume was composed of numerous time-evolving filamentary substructures, referred to as "plumelets" in this paper, that accounted for most of the plume emission. The number of simultaneously identifiable plumelets was positively correlated with plume brightness, peaked in the fully formed plume, and remained saturated thereafter. The plumelets had transverse widths of 10 Mm and intermittently supported upwardly propagating periodic disturbances with phase speeds of 190-260 km s-1 and longitudinal wavelengths of 55-65 Mm. The characteristic frequency (≈ 3.3 mHz) is commensurate with that of solar p-modes. Oscillations in neighboring plumelets are uncorrelated, indicating that the waves could be driven by p-mode flows at spatial scales smaller than the plumelet separation. Multiple independent sources of outflow within a single coronal plume should impart significant fine structure to the solar wind that may be detectable by Parker Solar Probe and Solar Orbiter.

Keywords: solar coronal holes; solar activity; solar coronal transients; solar coronal waves; solar magnetic reconnection; solar wind; plasma jets; solar coronal plumes; solar extreme ultraviolet emission; direct imaging; astronomy data analysis; solar oscillations
Detection of a Radio Bubble around the Ultraluminous X-Ray Source Holmberg IX X-1

We present C- and X-band radio observations of the famous utraluminous X-ray source (ULX) Holmberg IX X-1, previously discovered to be associated with an optical emission line nebula several hundred parsecs in extent. Our recent infrared study of the ULX suggested that a jet could be responsible for the infrared excess detected at the ULX position. The new radio observations, performed using the Karl G. Jansky Very Large Array (VLA) in B-configuration, reveal the presence of a radio counterpart to the nebula with a spectral slope of -0.56 similar to other ULXs. Importantly, we find no evidence for an unresolved radio source associated with the ULX itself, and we set an upper limit on any 5 GHz radio core emission of 6.6 μJy (4.1 × 1032 erg s-1). This is 20 times fainter than what we expect if the bubble is energized by a jet. If a jet exists its core component is unlikely to be responsible for the infrared excess unless it is variable. Strong winds which are expected in super-Eddington sources could also play an important role in inflating the radio bubble. We discuss possible interpretations of the radio/optical bubble and we prefer the jet+winds-blown bubble scenario similar to the microquasar SS 433.

Keywords: x-ray binary stars; emission nebulae; black holes; radio jets; supernova remnants
The Late Afterglow of GW170817/GRB 170817A: A Large Viewing Angle and the Shift of the Hubble Constant to a Value More Consistent with the Local Measurements

The multimessenger data of neutron star merger events are promising for constraining the Hubble constant. So far, GW170817 is still the unique gravitational wave event with multiwavelength electromagnetic counterparts. In particular, its radio and X-ray emission have been measured in the past ~3-5 yr. In this work, we fit the long-lasting X-ray, optical, and radio afterglow light curves of GW170817/GRB 170817A, including the forward shock radiation from both the decelerating relativistic gamma-ray burst outflow and the subrelativistic kilonova outflow (though whether the second component contributes significantly is still uncertain), and find out a relatively large viewing angle (~0.5 rad). Such a viewing angle has been taken as a prior in the gravitational wave data analysis, and the degeneracy between the viewing angle and the luminosity distance is broken. Finally, we have a Hubble constant ${H}_{0}={72.57}_{-4.17}^{+4.09}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{Mpc}}^{-1}$ , which is more consistent with that obtained by other local measurements. If rather similar values are inferred from multimessenger data of future neutron star merger events, it will provide critical support to the existence of the Hubble tension.

Keywords: hubble constant; gravitational wave astronomy; gamma-ray bursts
Variation of Magnetic Flux Ropes through Major Solar Flares

It remains unclear how solar flares are triggered and in what conditions they can be eruptive with coronal mass ejections. Magnetic flux ropes (MFRs) has been suggested as the central magnetic structure of solar eruptions, and their ideal instabilities, including the kink instability (KI) and torus instability (TI), are important candidates for triggering mechanisms. Here, using magnetic field extrapolations from observed photospheric magnetograms, we systematically studied the variation of coronal magnetic fields, focusing on MFRs, through major flares including 29 eruptive and 16 confined events. We found that nearly 90% of events possess MFRs before flares, and 70% have MFRs even after flares. We calculated the controlling parameters of KI and TI, including the MFR's maximum twist number and the decay index of its strapping field. Using the KI and TI thresholds empirically derived solely from the pre-flare MFRs, two distinctly different regimes are shown in the variation of the MFR controlling parameters through flares. For the events with both parameters below their thresholds before flares, we found no systematic change of the parameters after the flares, in either the eruptive or confined events. In contrast, for the events with any of the two parameters exceeding their threshold before flares (most of them are eruptive), there is systematic decrease in the parameters to below their thresholds after flares. These results provide a strong constraint for the values of the instability thresholds and also stress the necessity of exploring other eruption mechanisms in addition to the ideal instabilities.

Keywords: solar coronal mass ejections; solar flares; solar active regions
Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg

We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011-2016), which offers insight into the short and long-term evolution of surface features on RSGs. Using a spectrum of AZ Cyg obtained with SpeX on the NASA InfraRed Telescope Facility (IRTF) and synthetic spectra calculated from spherical MARCS, spherical PHOENIX, and SAtlas model atmospheres, we derive Teff is between 3972 K and 4000 K and $\mathrm{log}\,g$ between -0.50 and 0.00, depending on the stellar model used. Using fits to the squared visibility and GAIA parallaxes, we measure its average radius $R={911}_{-50}^{+57}\,{R}_{\odot }$ . Reconstructions of the stellar surface using our model-independent imaging codes SQUEEZE and OITOOLS.jl show a complex surface with small bright features that appear to vary on a timescale of less than one year and larger features that persist for more than one year. The 1D power spectra of these images suggest a characteristic size of 0.52-0.69 R⋆ for the larger, long lived features. This is close to the values of 0.51-0.53 R⋆ that are derived from 3D RHD models of stellar surfaces. We conclude that interferometric imaging of this star is in line with predictions of 3D RHD models but that short-term imaging is needed to more stringently test predictions of convection in RSGs.

Keywords: optical interferometry; red supergiant stars; stellar surfaces; stellar properties; evolved stars