adsabs/SciX_UAT_keywords huggingface dataset:
A Very Large Array Study of Newly Discovered Southern Latitude Nonthermal Filaments in the Galactic Center: Radio Continuum Total-intensity and Spectral Index Properties

The nonthermal filament (NTF) radio structures clustered within a few hundred parsecs of the Galactic center (GC) are apparently unique to this region of the Galaxy. Recent radio images of the GC using MeerKAT at 1 GHz have revealed a multitude of faint, previously unknown NTF bundles (NTFBs), some of which are comprised of as many as 10 or more individual filaments. In this work we present Very Large Array observations at the C- and X-bands (4-12 GHz) at arcsecond-scale resolutions of three of these newly discovered NTFBs, all located at southern Galactic latitudes. These observations allow us to compare their total-intensity properties with those of the larger NTF population. We find that these targets generally possess properties similar to what is observed in the larger NTF population. However, the larger NTF population generally has steeper spectral indices than what we observe for our chosen targets. The results presented here based on the total-intensity properties of these structures indicate that the NTFs are likely a result of synchrotron emission from relativistic electrons that have been generated either by a nearby compact source or by extended magnetic field structures in which the magnetic field line reconnection has accelerated the electrons. In either scenario, once the relativistic electrons are produced and injected locally into the field they diffuse along the magnetic field lines, producing the filaments.

Keywords: galactic center; radio astronomy; spectral index; non-thermal radiation sources; galactic cosmic rays
Negative Magnetic Diffusivity β Replacing the α Effect in the Helical Dynamo

In the Sun, the converting process of a poloidal magnetic field (Bpol) from a toroidal field (Btor) is essential to sustaining the solar magnetic fields. However, the converting process, dominated by α and β effects, is not yet clearly understood. Conventional theories expect that the α effect should be quenched as the magnetic field grows. Also, plasma kinetic energy is thought to diffuse magnetic energy (positive β effect). Then, Bpol is supposed to decay resulting in the dissipation of Btor, followed by the diminishing dynamo process. But the solar magnetic field evolves periodically, as is observed. To solve this inconsistency between the theory and real nature, we first need to check if the α and β effects indeed evolve as the conventional theories expect. However, these effects are theoretically or conceptually inferred quantities, and their exact expressions are not yet known. So, instead of their incomplete formulas, we used more practical representations composed of large-scale magnetic helicity ${\overline{H}}_{M}\,(\equiv \overline{{\boldsymbol{A}}}\cdot \overline{{\boldsymbol{B}}})$ and energy ${\overline{E}}_{M}\,(\equiv {\overline{B}}^{2}/2)$ . We verified that the α effect quenches as the conventional theory expects. However, we also found that the β effect can be negative. This negative β apparently looks inconsistent with the conventional conclusion, but it can be a promising substitution for the decaying α effect. We discuss their physical bases and mechanisms using a field structure model supported by an analytic method. The model shows that the interaction between the poloidal velocity component (Upol) and nonlocally transferred magnetic field (B · ∇ U) induces a current density jind along with the magnetic field. Their combined structure yields magnetic helicity to the system, which is the α effect. However, Upol can also interact with the locally transferred magnetic field, i.e., Upol × (- U · ∇ B) inducing a current density jdiff. This current density can produce additional magnetic helicity (negative β effect) to the system. Simultaneously, the toroidal component Utor with - U · ∇ B leads to the usual positive β effect, which diffuses the magnetic field. Finally, using the negative β effect, we show how the plasma motion is suppressed in a helically forced dynamo system where Lorentz force (J × B) apparently looks negligible.

Keywords: solar dynamo; magnetohydrodynamics; solar magnetic fields; plasma astrophysics
Abundance of LIGO/Virgo Black Holes from Microlensing Observations of Quasars with Reverberation Mapping Size Estimates

Assuming a population of black holes (BHs) with masses in the range inferred by LIGO/Virgo from BH mergers, we use quasar microlensing observations to estimate their abundances. We consider a mixed population of stars and BHs and the presence of a smooth dark matter component. We adopt reverberation mapping estimates of the quasar size. According to a Bayesian analysis of the measured microlensing magnifications, a population of BHs with masses ~30M ⊙ constitutes less than 0.4% of the total matter at the 68% confidence level (less than 0.9% at the 90% confidence level). We have explored the whole mass range of LIGO/Virgo BHs, finding that this upper limit ranges from 0.5% to 0.4% at the 68% confidence level (from 1.1% to 0.9% at the 90% confidence level) when the BH masses change from 10 to 60M ⊙. We estimate a 16% contribution from the stars, in agreement with previous studies based on a single-mass population that do not explicitly consider the presence of BHs. These results are consistent with the estimates of BH abundances from the statistics of LIGO/Virgo mergers, and rule out primordial BHs (or any other types of compact object) in this mass range constituting a significant fraction of the dark matter.

Keywords: cosmology; dark matter; primordial black holes; astrophysical black holes; gravitational lensing
No Peaks without Valleys: The Stable Mass Transfer Channel for Gravitational-wave Sources in Light of the Neutron Star-Black Hole Mass Gap

Gravitational-wave (GW) detections are starting to reveal features in the mass distribution of double compact objects. The lower end of the black hole (BH) mass distribution is especially interesting as few formation channels contribute here and because it is more robust against variations in the cosmic star formation than the high-mass end. In this work we explore the stable mass transfer channel for the formation of GW sources with a focus on the low-mass end of the mass distribution. We conduct an extensive exploration of the uncertain physical processes that impact this channel. We note that, for fiducial assumptions, this channel reproduces the peak at ~9 M ☉ in the GW-observed binary BH mass distribution remarkably well and predicts a cutoff mass that coincides with the upper edge of the purported neutron star-black hole (NS-BH) mass gap. The peak and cutoff mass are a consequence of the unique properties of this channel; namely (1) the requirement of stability during the mass transfer phases, and (2) the complex way in which the final compact object masses scale with the initial mass. We provide an analytical expression for the cutoff in the primary component mass and show that this adequately matches our numerical results. Our results imply that selection effects resulting from the formation channel alone can provide an explanation for the purported NS-BH mass gap in GW detections. This provides an alternative to the commonly adopted view that the gap emerges during BH formation.

Keywords: stellar mass black holes; supernova remnants; gravitational wave sources; gravitational waves; interacting binary stars
Follow-up Survey for the Binary Black Hole Merger GW200224_222234 Using Subaru/HSC and GTC/OSIRIS

The LIGO/Virgo detected a gravitational wave (GW) event, named GW200224_222234 (also known as S200224ca) and classified as a binary-black hole coalescence, on 2020 February 24. Given its relatively small localization skymap (71 deg2 for a 90% credible region; revised to 50 deg2 in GWTC-3), we performed target-of-opportunity observations using the Subaru/Hyper Suprime-Cam (HSC) in the r2 and z bands. Observations were conducted on 2020 February 25 and 28 and March 23, with the first epoch beginning 12.3 hr after the GW detection. The survey covered the highest-probability sky area of 56.6 deg2, corresponding to a 91% probability. This was the first deep follow-up (m r ≳ 24, m z ≳ 23) for a binary-black hole merger covering >90% of the localization. By performing image subtraction and candidate screening including light-curve fitting with transient templates and examples, we found 22 off-nucleus transients that were not ruled out as the counterparts of GW200224_222234 with our Subaru/HSC data alone. We also performed GTC/OSIRIS spectroscopy of the probable host galaxies for five candidates; two are likely to be located within the 3D skymap, whereas the others are not. In conclusion, 19 transients remain as possible optical counterparts of GW200224_222234; but we could not identify a unique promising counterpart. If there are no counterparts in the remaining candidates, the upper limits of the optical luminosity are $\nu {L}_{\nu }\lt {5.2}_{-1.9}^{+2.4}\times {10}^{41}$ erg s-1 and $\nu {L}_{\nu }\lt {1.8}_{-0.6}^{+0.8}\times {10}^{42}$ erg s-1 in the r2 and z bands, respectively, at ~12 hr after GW detection. We also discuss improvements in the strategies of optical follow-ups for future GW events.

Keywords: black holes; gravitational waves; surveys
Hidden Companions to Intermediate-mass Stars. XIII. Discovery of a 0.80 M ⊙, 4.3 au Companion to HIP 7298

Proper motion changes between astrometric surveys provide a hint for unresolved companions and near-infrared interferometry is arguably the most efficient way to reveal or constrain their nature. Here we report on the VLTI/GRAVITY. detection of a companion to the nearby star HIP 7298 with a K band flux ratio of 11.9% at a projected separation ρ = 57.1 mas ↔ 4.3 au. Through isochrone fitting we find that the primary is a 1 Gyr old M A = 1.56M ⊙ star while the newly discovered secondary is a M B = 0.80M ⊙ K dwarf. The stars will most likely avoid common envelope evolution and will become a system similar to Gliese 86 in about 1.5 Gyr. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: a stars; multiple stars; optical interferometry
Spectropolarimetric Analysis of FRB 181112 at Microsecond Resolution: Implications for Fast Radio Burst Emission Mechanism

We have developed a new coherent dedispersion mode to study the emission of fast radio bursts (FRBs) that trigger the voltage capture capability of the Australian SKA Pathfinder (ASKAP) interferometer. In principle the mode can probe emission timescales down to 3 ns with full polarimetric information preserved. Enabled by the new capability, here we present a spectropolarimetric analysis of FRB 181112 detected by ASKAP, localized to a galaxy at redshift 0.47. At microsecond time resolution the burst is resolved into four narrow pulses with a rise time of just 15 μs for the brightest. The pulses have a diversity of morphology, but do not show evidence for temporal broadening by turbulent plasma along the line of sight, nor is there any evidence for periodicity in their arrival times. The pulses are highly polarized (up to 95%), with the polarization position angle varying both between and within pulses. The pulses have apparent rotation measures that vary by 15± 2 rad {m}-2 and apparent dispersion measures that vary by 0.041± 0.004 pc {cm}-3 . Conversion between linear and circular polarization is observed across the brightest pulse. We conclude that the FRB 181112 pulses are most consistent with being a direct manifestation of the emission process or the result of propagation through a relativistic plasma close to the source. This demonstrates that our method, which facilitates high-time-resolution polarimetric observations of FRBs, can be used to study not only burst emission processes, but also a diversity of propagation effects present on the gigaparsec paths they traverse.

Keywords: radio transient sources; radio interferometry; astronomical instrumentation; polarimetry
Exploring Martian Magnetic Fields with a Helicopter

The era of helicopter-based surveys on Mars has already begun, creating opportunities for future aerial science investigations with a range of instruments. We argue that magnetometer-based studies can make use of aerial technology to answer some of the key questions regarding early Mars evolution. As such, we discuss mission concepts for a helicopter equipped with a magnetometer on Mars, measurements it would provide, and survey designs that could be implemented. For a range of scenarios, we build magnetization models and test how well structures can be resolved using a range of different inversion approaches. With this work, we provide modeling ground work and recommendations to plan the future of aerial Mars exploration.

Keywords: mars; solar system terrestrial planets; planetary magnetospheres; planetary science; planetary interior; planetary structure
Effects of Spatial Discretization in Lyα Line Radiation Transfer Simulations

We describe the addition of Lyα resonant line transfer to our dust continuum radiation transfer code SKIRT, verifying our implementation with published results for spherical problems and using some self-designed three-dimensional setups. We specifically test spatial discretization through various grid types, including hierarchical octree grids and unstructured Voronoi tessellations. We then use a radiation transfer postprocessing model for one of the spiral galaxies produced by the Auriga cosmological zoom simulations to investigate the effect of spatial discretization on the synthetic observations. We find that the calculated Lyα line profiles exhibit an extraordinarily strong dependence on the type and resolution of the spatial grid, rendering the results untrustworthy at best. We attribute this effect to the large gradients in the hydrogen density distribution over small distances, which remain significantly underresolved in the input model. We therefore argue that further research is needed to determine the required spatial resolution of a hydrodynamical simulation snapshot to enable meaningful Lyα line transfer postprocessing.

Keywords: interstellar line emission; interstellar scattering; radiative transfer simulations; hydrodynamical simulations; computational methods; publicly available software
In the Trenches of the Solar-Stellar Connection. I. Ultraviolet and X-Ray Flux-Flux Correlations across the Activity Cycles of the Sun and Alpha Centauri AB

This study focuses on high-energy proxies of stellar magnetic activity over long-term starspot cycles of three low-activity Sun-like stars: α Centauri A (HD 128620: G2 V), α Cen B (HD 128621: K1 V), and the Sun itself. Data sets include: daily solar ultraviolet irradiance spectra and X-ray fluxes from the Solar Radiation and Climate Experiment, during recent sunspot Cycles 23 and 24; Interface Region Imaging Spectrograph long-slit stigmatic imaging of solar Mg II h (2803 Å) and k (2796 Å) in quiet and active regions; and Hubble Space Telescope Imaging Spectrograph ultraviolet, and Chandra X-ray, campaigns on α Cen AB. Established stellar "flux-flux" relations, for example X-rays (T ∼ 1 MK) versus Mg II (T ∼ 8000 K), showed increasing power-law slopes with increasing formation temperature, but these give way on the Sun to bent power laws, and surprising inversions in the activity hierarchy: Si III is more "active" (steeper power laws) than N V, despite the latter's four times higher formation temperature. The Sun's flux-flux behavior, nevertheless, remarkably parallels its low-activity solar twin α Cen A. In contrast, the cooler, somewhat more active, K dwarf companion displays correlations more in line with the previous stellar paradigm. The new flux-flux relations offer a way to vet numerical spectral simulations and proxy-based irradiance models, and extrapolate solar global activity indices into regimes below or above the grasp of contemporary records, or to exoplanet hosts at the low end of the Sun-like activity ladder.

Keywords: solar cycle; active sun; quiet sun; solar ultraviolet emission; solar x-ray emission; solar analogs; stellar physics; time domain astronomy; stellar activity; stellar chromospheres; stellar coronae; stellar spectral lines
X-Rays in Cepheids: Identifying Low-mass Companions of Intermediate-mass Stars

X-ray observations have been made of a sample of 20 classical Cepheids, including two new observations (Polaris and l Car) reported here. The occurrence of X-ray flux around the pulsation cycle is discussed. Three Cepheids are detected (δ Cep, β Dor, and Polaris). X-rays have also been detected from the low-mass F, G, and K companions of four Cepheids (V473 Lyr, R Cru, V659 Cen, and W Sgr) and one hot companion (S Mus). Upper limits on the X-ray flux of the remaining Cepheids provide an estimate that 28% have low-mass companions. This fraction of low-mass companions in intermediate-mass Cepheids is significantly lower than expected from random pairing with the field initial mass function (IMF). Combining the companion fraction from X-rays with that from ultraviolet observations results in a binary/multiple fraction of 57% ± 12% for Cepheids with ratios q > 0.1 and separations a >1 au. This is a lower limit since M stars are not included. X-ray observations detect less massive companions than other existing studies of intermediate-mass stars. Our measured occurrence rate of unresolved, low-mass companions to Cepheids suggests that intermediate-period binaries derive from a combination of disk and core fragmentation and accretion. This yields a hybrid mass ratio distribution that is skewed toward small values compared to a uniform distribution but is still top-heavy compared to random pairings drawn from the IMF. *Based on observations obtained with the Chandra X-ray Observatory.

Keywords: cepheid variable stars
Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter WASP-76b

Recent observations of the ultra-hot Jupiter WASP-76b have revealed a diversity of atmospheric species. Here we present new high-resolution transit spectroscopy of WASP-76b with GRACES at the Gemini North Observatory, serving as a baseline for the Large and Long Program "Exploring the Diversity of Exoplanet Atmospheres at High Spectral Resolution" (Exoplanets with Gemini Spectroscopy, or ExoGemS for short). With a broad spectral range of 400-1050 nm, these observations allow us to search for a suite of atomic species. We recover absorption features due to neutral sodium (Na I), and report a new detection of the ionized calcium (Ca II) triplet at ~850 nm in the atmosphere of WASP-76b, complementing a previous detection of the Ca II H and K lines. The triplet has line depths of 0.295% ± 0.034% at ~849.2 nm, 0.574% ± 0.041% at ~854.2 nm, and 0.454% ± 0.024% at ~866.2 nm, corresponding to effective radii close to (but within) the planet's Roche radius. These measured line depths are significantly larger than those predicted by model LTE and NLTE spectra obtained on the basis of a pressure-temperature profile computed assuming radiative equilibrium. The discrepancy suggests that the layers probed by our observations are either significantly hotter than predicted by radiative equilibrium and/or in a hydrodynamic state. Our results shed light on the exotic atmosphere of this ultra-hot world, and will inform future analyses from the ExoGemS survey.

Keywords: exoplanet atmospheres; transmission spectroscopy; hot jupiters; high resolution spectroscopy; optical astronomy; exoplanet atmospheric composition; exoplanet atmospheric variability; transits
Bridging the Bondi and Event Horizon Scales: 3D GRMHD Simulations Reveal X-shaped Radio Galaxy Morphology

X-shaped radio galaxies (XRGs) produce misaligned X-shaped jet pairs and make up ≲10% of radio galaxies. XRGs are thought to emerge in galaxies featuring a binary supermassive black hole (SMBH), SMBH merger, or large-scale ambient medium asymmetry. We demonstrate that XRG morphology can naturally form without such special, preexisting conditions. Our 3D general-relativistic magnetohydrodynamic (GRMHD) simulation for the first time follows magnetized rotating gas from outside the SMBH sphere of influence of radius R B to the SMBH of gravitational radius R g at the largest scale separation, R B/R g = 103, to date. Initially, our axisymmetric system of constant-density hot gas contains a weak vertical magnetic field and rotates in the equatorial plane of a rapidly spinning SMBH. We seed the gas with small-scale 2% level pressure perturbations. Infalling gas forms an accretion disk, and the SMBH launches relativistically magnetized collimated jets reaching well outside R B. Under the pressure of the infalling gas, the jets intermittently turn on and off, erratically wobble, and inflate pairs of cavities in different directions, resembling an X-shaped jet morphology. Synthetic X-ray images reveal multiple pairs of jet-powered shocks and cavities. Large-scale magnetic flux accumulates on the SMBH, becomes dynamically important, and leads to a magnetically arrested disk state. The SMBH accretes at 2% of the Bondi rate ( $\dot{M}\simeq 2.4\times {10}^{-3}{M}_{\odot }\,{\mathrm{yr}}^{-1}$ for M87*) and launches twin jets at η = 150% efficiency. These jets are powerful enough (P jets ≃ 2 × 1044 erg s-1) to escape along the SMBH spin axis and end the short-lived intermittent jet state, whose transient nature can account for the rarity of XRGs.

Keywords: high energy astrophysics; active galactic nuclei; black hole physics; jets; magnetohydrodynamical simulations; general relativity
Gemini Near Infrared Spectrograph-Distant Quasar Survey: Augmented Spectroscopic Catalog and a Prescription for Correcting UV-based Quasar Redshifts

Quasars at z ≳ 1 most often have redshifts measured from rest-frame ultraviolet emission lines. One of the most common such lines, C IV λ1549, shows blueshifts up to ≈5000 km s-1 and in rare cases even higher. This blueshifting results in highly uncertain redshifts when compared to redshift determinations from rest-frame optical emission lines, e.g., from the narrow [O III] λ5007 feature. We present spectroscopic measurements for 260 sources at 1.55 ≲ z ≲ 3.50 having -28.0 ≲ M i ≲ - 30.0 mag from the Gemini Near Infrared Spectrograph-Distant Quasar Survey (GNIRS-DQS) catalog, augmenting the previous iteration, which contained 226 of the 260 sources whose measurements are improved upon in this work. We obtain reliable systemic redshifts based on [O III] λ5007 for a subset of 121 sources, which we use to calibrate prescriptions for correcting UV-based redshifts. These prescriptions are based on a regression analysis involving C IV full-width-at-half-maximum intensity and equivalent width, along with the UV continuum luminosity at a rest-frame wavelength of 1350 Å. Applying these corrections can improve the accuracy and the precision in the C IV-based redshift by up to ~850 km s-1 and ~150 km s-1, respectively, which correspond to ~8.5 and ~1.5 Mpc in comoving distance at z = 2.5. Our prescriptions also improve the accuracy of the best available multifeature redshift determination algorithm by ~100 km s-1, indicating that the spectroscopic properties of the C IV emission line can provide robust redshift estimates for high-redshift quasars. We discuss the prospects of our prescriptions for cosmological and quasar studies utilizing upcoming large spectroscopic surveys.

Keywords: quasars; surveys; active galactic nuclei