adsabs/SciX_UAT_keywords huggingface dataset:
Prospect of Detecting TeV Halos with LHAASO: In the Framework of the Anisotropic Diffusion Model

The particle diffusion coefficients of TeV pulsar halos observed so far are inferred to be significantly smaller than the typical value of the interstellar medium (ISM). The anisotropic diffusion model ascribes the slow diffusion to the cross-field diffusion, assuming sub-Alfvénic turbulence in the ISM around the pulsar if the viewing angle between the observer's line-of-sight (LOS) to the pulsar and the local mean field direction is small. In general, the TeV halo's morphology under this model highly depends on the viewing angle, and an elongated, asymmetric morphology is predicted if the LOS is not approximately aligned with the local mean field direction. While the specific requirement of a small viewing angle is supposedly established only for a small fraction of TeV halos, TeV halos with apparent asymmetric morphology have not been detected. In this paper, we will study the expectation of TeV halos measured by the TeV-PeV gamma-ray detector LHAASO in the framework of anisotropic diffusion model, with a particular focus on the influence of the viewing angle on the detectability. We show that a TeV halo is more detectable with a smaller viewing angle, and this selection effect may explain why the morphologies of all three detected TeV halos so far are consistent with being spherical. We also demonstrate that LHAASO is capable of detecting asymmetric TeV halos after several years of operation with reasonable source parameters. This can serve as a critical test of the anisotropic diffusion model.

Keywords: pulsars; gamma-ray sources; cosmic ray sources; extended radiation sources
Middle Corona Magnetic Field Strength Determined by Spacecraft Radio Faraday Rotation

Faraday rotation (FR) of MESSENGER spacecraft X-band transcoronal radio transmissions were studied to evaluate the mid-coronal magnetic field strength, with the line-of-sight closest solar approach at heliocentric altitudes ranging 1.647-1.817 R⊙. A Community Coordinated Modeling Center (CCMC) CORHEL-MAS 3D coronal field map revealed this region to contain closed magnetic fields. By FR analysis we found a field strength of 118,000 nT at r = 1.647 R⊙, with fall-off to 40,000 nT by r = 1.817 R⊙. These values straddle estimates provided by the CCMC model. The mean value of 79,000 nT at r = 1.732 R⊙ is comparable to the value provided by an established empirical model for average coronal magnetic field strength. FR can be used to evaluate middle coronal magnetic fields, but improved methods to constrain concurrent electron column density will be needed to produce the most accurate results.

Keywords: solar corona; solar magnetic fields
Please Repeat: Strong Lensing of Gravitational Waves as a Probe of Compact Binary and Galaxy Populations

Strong gravitational lensing of gravitational wave sources offers a novel probe of both the lens galaxy and the binary source population. In particular, the strong lensing event rate and the time-delay distribution of multiply imaged gravitational-wave binary coalescence events can be used to constrain the mass distribution of the lenses as well as the intrinsic properties of the source population. We calculate the strong lensing event rate for a range of second- (2G) and third-generation (3G) detectors, including Advanced LIGO/Virgo, A+, Einstein Telescope (ET), and Cosmic Explorer (CE). For 3G detectors, we find that ~0.1% of observed events are expected to be strongly lensed. We predict detections of ~1 lensing pair per year with A+, and ~50 pairs per year with ET/CE. These rates are highly sensitive to the characteristic galaxy velocity dispersion, σ *, implying that observations of the rates will be a sensitive probe of lens properties. We explore using the time-delay distribution between multiply imaged gravitational-wave sources to constrain properties of the lenses. We find that 3G detectors would constrain σ * to ~21% after 5 yr. Finally, we show that the presence or absence of strong lensing within the detected population provides useful insights into the source redshift and mass distribution out to redshifts beyond the peak of the star formation rate, which can be used to constrain formation channels and their relation to the star formation rate and delay-time distributions for these systems.

Keywords: gravitational wave astronomy; gravitational lensing
Exploring Gamma-Ray Burst Diversity: Clustering Analysis of the Emission Characteristics of Fermi- and BATSE-detected Gamma-Ray Bursts

Gamma-ray bursts (GRBs), often attributed to massive star collapse or binary compact object mergers, exhibit diverse emission characteristics hinting at multiple GRB classes based on various factors like progenitors, radiation mechanisms, and central engines. This study employs unsupervised clustering using the nested Gaussian mixture model algorithm to analyze data from Fermi and BATSE, identifying four classes (A–D) based on duration, spectral peak, and spectral index of time-integrated spectra of GRBs. Class proportions are approximately 70%, 10%, 3%, and 17%, respectively, with A and B comprising mostly long GRBs, C mainly short GRBs, and D encompassing both types. The classes are further assessed based on spectral index α, indicating distinct radiation mechanisms: α > ‑0.67 for photospheric emission, α ≤ ‑1.5 for fast-cooling synchrotron, and ‑1.5 < α ≤ ‑0.67 for slow-cooling synchrotron. Classes B and C align with photospheric emission, while A and D predominantly exhibit synchrotron radiation. Short GRBs are predominantly photospheric emission, whereas long GRBs tend to favor synchrotron emission. Overall, 63% of the total bursts exhibit α profiles indicative of synchrotron emission, with the remaining 37% associated with photospheric emission. Considering the limited data of kilonova and supernova associated with GRBs, classes are examined for progenitor origins, suggesting a hybrid nature for A and D, and collapsar and merger origins for B and C, respectively. This clustering analysis results in four GRB classes, which, upon investigation, reveal the diverse and complex nature of GRBs in terms of their radiation, duration, and progenitor.

Keywords: gamma-ray bursts; multivariate analysis; catalogs; clustering
A Spectroscopic Characterization of a Blazar Candidate Excluded by Automated Morphology Classification

Blazars are radio-loud Active Galactic Nuclei (AGNs) with their jets pointing at us at a very small angle. J064334.60–331430.29 (hereafter J0643–3314) was selected as a blazar candidate by its colors and compactness in archival radio images. In Xie et al. 2024, we introduce an algorithm to recognize likely blazars using the morphology observed in the 3 GHz Very Large Array Sky Survey. According to our algorithm, J0643–3314 is unlikely a blazar based on the two-sided jet seen in VLASS. To validate the result of our algorithm, we investigate this source further. From the extended two-sided jet lobes, the upturn radio spectrum, and the broad emission lines in the follow-up spectrum, we robustly conclude that J0643–3314 is not a blazar. We spectroscopically confirm it as a radio-loud AGN at z = 0.3, with a projected jet size of 100.4 kpc. We estimate its bolometric luminosity to be ∼6×1044 erg s‑1, black hole mass of ∼2×108 M ⊙, and Eddington ratio of ∼0.02 from Hβ and Hα broad emission lines.

Keywords: blazars; active galactic nuclei
The Nature of γ-Ray Emission from HESS J1912+101

Since the discovery of HESS J1912+101 at teraelectronvolt energies, its nature has been extensively studied. Due to the absence of X-ray and radio counterparts, whether its γ-ray emission is produced by relativistic electrons or ions is still a matter of debate. We reanalyze its megaelectronvolt to gigaelectronvolt γ-ray emission using 14 yr of Pass 8 data of the Fermi-LAT, and find that the gigaelectronvolt γ-ray emission is more extended than the teraelectronvolt shell detected by H. E. S. S. and flux above 10 GeV from the northern half is much higher than that from the southern half, where there is evident interaction between shocks and molecular clouds. As a consequence, the gigaelectronvolt spectrum of the northern half (with an index of 2.19 ± 0.12) is much harder than that in the south (with an index of 2.72 ± 0.08), and the overall gigaelectronvolt spectrum shows a concave shape, which is distinct from most γ-ray supernova remnants (SNRs). In combination with the teraelectronvolt spectrum, the overall γ-ray spectrum can be fitted with a broken power-law model for trapped ions and a low energy component due to escaping ions. The diffusion coefficient for escaping ions however needs to be proportional to the energy, implying that the low energy component may also be attributed to ions accelerated via recent shock-cloud interactions. A hadronic origin for the γ-ray emission is therefore favored and the overall emission properties are consistent with ion acceleration by SNR shocks. On the other hand, it is still undeniable that stellar cluster or PWN may have some contribution in some parts of this extended source.

Keywords: supernova remnants; molecular clouds; high energy astrophysics
High-precision Transition Energy Measurements of Neon-like Fe XVII Ions

We improve by a factor of 4–20 the energy accuracy of the strongest soft X-ray transitions of Fe XVII ions by resonantly exciting them in an electron beam ion trap with a monochromatic beam at the P04 beamline of the PETRA III synchrotron facility. By simultaneously tracking instantaneous photon-energy fluctuations with a high-resolution photoelectron spectrometer, we minimize systematic uncertainties down to 10–15 meV, or velocity equivalent ±∼5 km s‑1 in their rest energies, substantially improving our knowledge of this key astrophysical ion. Our large-scale configuration-interaction computations include more than 4 million relativistic configurations and agree with the experiment at a level without precedent for a 10-electron system. Thereby, theoretical uncertainties for interelectronic correlations become far smaller than those of quantum electrodynamics (QED) corrections. The present QED benchmark strengthens our trust in future calculations of many other complex atomic ions of interest to astrophysics, plasma physics, and the development of optical clocks with highly charged ions.

Keywords: atomic data benchmarking; laboratory astrophysics; line positions; atomic spectroscopy; experimental data; theoretical techniques; space plasmas
Material around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation

A stellar occultation of Gaia DR3 2646598228351156352 by the Centaur (2060) Chiron was observed from the South African Astronomical Observatory on 2018 November 28 UT. Here we present a positive detection of material surrounding Chiron from the 74-inch telescope for this event. Additionally, a global atmosphere is ruled out at the tens of microbars level for several possible atmospheric compositions. There are multiple 3σ drops in the 74-inch light curve: three during immersion and two during emersion. Occulting material is located between 242 and 270 km from the center of the nucleus in the sky plane. Assuming the ring-plane orientation proposed for Chiron from the 2011 occultation, the flux drops are located at 352, 344, and 316 km (immersion) and 357 and 364 km (emersion) from the center, with normal optical depths of 0.26, 0.36, and 0.22 (immersion) and 0.26 and 0.18 (emersion) and equivalent widths between 0.7 and 1.3 km. This detection is similar to the previously proposed two-ring system and is located within the error bars of that ring-pole plane; however, the normal optical depths are less than half of the previous values, and three features are detected on immersion. These results suggest that the properties of the surrounding material have evolved between the 2011, 2018, and 2022 observations.

Keywords: centaur group; stellar occultation; planetary rings; small solar system bodies
Convective Overshooting in the Envelopes of A-type Stars Using the k-ω Model

Mixing between convective zones is quite uncertain in the envelopes of A-type stars. To study the mixing in A-type envelopes, we use a new convection model, the k-ω model, in the MESA stellar evolution code. Using the k-ω model, we find that the overshooting regions of the He II and H/He I convection zones are integrated with each other. There is material exchange between the He II and H/He I convection zones through overshooting, in agreement with recent numerical simulations.We obtain the overshooting distance of about 3.5Hp below the base of the H/He I convection zone in a 2.3 M⊙ star. There are two overshooting regions beyond the He II convection zone in the same stellar model. We obtain that the overshooting distance of the upper one is about 3.9Hp and about 2.0Hp for the lower one. We find that the turbulent diffusion effect is particularly strong in the convective envelopes of A-type stars. In addition, we find that the typical size of the convective rolling cells is restricted by the actual thickness of the convective zones, because the thickness of the convection zones are usually smaller than or approximately equal to the local pressure scale height. Through comparisons with the results of the k-ω model, we find that a suitable value of fov is about 0.45 for the H/He I convective overshooting region. It is about 0.27 for the upper He II convective overshooting region and about 0.25 for the lower one.

Keywords: stellar convection envelopes; a stars; stellar evolution
Fitting Thermal Evolution Models to the Chronological Record of Erg Chech 002 and Modeling the Ejection Conditions of the Meteorite

The history of accretion and differentiation processes in the planetesimals is provided by various groups of meteorites. Sampling different parent body layers, they reveal the circumstances of the metal-silicate segregation and the internal structures of the protoplanets. The ungrouped achondrite Erg Chech 002 (EC 002) added to the suite of samples from primitive igneous crusts. Here we present models that utilize thermochronological data for EC 002 and fit the accretion time and size of its parent body to these data. The U-corrected Pb-Pb pyroxene, Pb-Pb phosphate, and Ar-Ar ages used imply a best-fit planetesimal with a radius of 20-30 km that formed at 0.1 Ma after calcium-aluminum-rich inclusions. Its interior melted early and differentiated by 0.5 Ma, allowing core and mantle formation with a transient lower mantle magma ocean and a melt fraction of <25% at the meteorite layering depth. EC 002 formed from this melt at a depth of 0.8 km in a partially differentiated region covered by an undifferentiated crust. By simulating collisions with impactors of different sizes and velocities, we analyzed the minimum ejection conditions of EC 002 from its original parent body and the surface composition of the impact site. The magma ocean region distinct from the layering depth of EC 002 implies that it was not involved in the EC 002 genesis. Our models estimate closure temperatures for the Al-Mg ages as 1030-1200 K. A fast parent body cooling attributes the late Ar-Ar age to a local reheating by another, late impact.

Keywords: planetary interior; planetesimals; asteroids; meteorites; achondrites; cosmochronology; accretion; impact phenomena
The Effects of Waves on the Meridional Thermal Structure of Jupiter's Stratosphere

A thermal oscillation in Jupiter's equatorial stratosphere, thought to have ∼4 Earth year period, was first discovered in 7.8 μm imaging observations from the 1980s and 1990s. Such imaging observations were sensitive to the 10-20 hPa pressure region in the atmosphere. More recent 7.8 μm long-slit high-spectroscopic observations from 2012 to 2017 taken using the Texas Echelon cross-dispersed Echelle Spectrograph (TEXES), mounted on the NASA Infrared Telescope Facility (IRTF), have vertically resolved this phenomenon's structure, and show that it spans a range of pressure from 2 to 20 hPa. The TEXES instrument was mounted on the Gemini North telescope in March 2017, improving the diffraction-limited spatial resolution by a factor of ∼2.5 compared with that offered by the IRTF. This Gemini spatial scale sensitivity study was performed in support of the longer-termed Jupiter monitoring being performed at the IRTF. We find that the spatial resolution afforded by the smaller 3 m IRTF is sufficient to spatially resolve the 3D structure of Jupiter's equatorial stratospheric oscillation by comparing the thermal retrievals of IRTF and Gemini observations. We then performed numerical simulations in a general circulation model to investigate how the structure of Jupiter's stratosphere responds to changes in the latitudinal extent of wave forcing in the troposphere. We find our simulations produce a lower limit in meridional wave forcing of ±7° (planetocentric coordinates) centered about the equator. This likely remains constant over time to produce off-equatorial thermal oscillations at ±13°, consistent with observations spanning nearly four decades.

Keywords: jupiter; stratosphere; infrared observatories
On Innermost Stable Spherical Orbits near a Rotating Black Hole: A Numerical Study of the Particle Motion near the Plunging Region

According to general relativity, astrophysical black holes are described by a small number of parameters. Apart from the mass of the black hole (M), among the most interesting characteristics is the spin (a), which determines the degree of rotation, i.e., the angular momentum of the black hole. The latter is observationally constrained by the spectral and timing properties of the radiation signal emerging from an accretion disk of matter orbiting near the event horizon. In the case of the planar (standard, equatorial) accretion disk, this is the location of the innermost stable circular orbit that determines the observable radiation characteristics and allows us to measure the spin. In this paper, we discuss a more general case of the innermost stable spherical orbits (ISSOs) extending above and below the equatorial plane. To this end, we study the nonequatorial geodesic motion of particles following inclined, spherical, relativistically precessing trajectories with the aim of exploring the boundary between the regions of stable (energetically bound) and escaping (energetically unbound) motion. The concept of the radius of the ISSO should play a role in determining the inner rim of a tilted or geometrically thick accretion flow. We demonstrate that the region of inclined bound orbits has a complicated structure due to enhanced precession near the inner rim. We also explore the fate of particles launched below the radius of the marginally bound spherical orbit: these may either plunge into the event horizon or escape to radial infinity.

Keywords: astrophysical black holes; general relativity; geodesics; accretion; kerr black holes
Signature of Supersonic Turbulence in Galaxy Clusters Revealed by AGN-driven Hα Filaments

The hot intracluster medium (ICM) is thought to be quiescent with low observed velocity dispersions. Surface brightness fluctuations of the ICM also suggest that its turbulence is subsonic with a Kolmogorov scaling relation, indicating that the viscosity is suppressed and the kinetic energy cascades to small scales unscathed. However, recent observations of the cold gas filaments in galaxy clusters find that the scaling relations are steeper than that of the hot plasma, signaling kinetic energy losses and the presence of supersonic flows. In this work we use high-resolution simulations to explore the turbulent velocity structure of the cold filaments at the cores of galaxy clusters. Our results indicate that supersonic turbulent structures can be "frozen" in the cold gas that cools and fragments out of a fast, ~107 K outflow driven by the central active galactic nucleus (AGN), when the radiative cooling time is shorter than the dynamical sound-crossing time. After the cold gas formation, however, the slope of the velocity structure function (VSF) flattens significantly over short, ~10 Myr timescales. The lack of flattened VSF in observations of Hα filaments indicates that the Hα-emitting phase is short-lived for the cold gas in galaxy clusters. On the other hand, the ubiquity of supersonic turbulence revealed by observed filaments strongly suggests that supersonic outflows are an integral part of AGN-ICM interaction, and that AGN activity plays a crucial role at driving turbulence in galaxy clusters.

Keywords: galaxy winds; filamentary nebulae; galaxy clusters; intracluster medium
Early Planet Formation in Embedded Disks (eDisk). XIII. Aligned Disks with Nonsettled Dust around the Newly Resolved Class 0 Protobinary R CrA IRAS 32

Young protostellar binary systems, with expected ages less than ∼105 yr, are little modified since birth, providing key clues to binary formation and evolution. We present a first look at the young, Class 0 binary protostellar system R CrA IRAS 32 from the Early Planet Formation in Embedded Disks ALMA large program, which observed the system in the 1.3 mm continuum emission, 12CO (2‑1), 13CO (2‑1), C18O (2‑1), SO (65‑54), and nine other molecular lines that trace disks, envelopes, shocks, and outflows. With a continuum resolution of ∼0.″03 (∼5 au, at a distance of 150 pc), we characterize the newly discovered binary system with a separation of 207 au, their circumstellar disks, and a circumbinary disklike structure. The circumstellar disk radii are 26.9 ± 0.3 and 22.8 ± 0.3 au for sources A and B, respectively, and their circumstellar disk dust masses are estimated as 22.5 ± 1.1 M ⊕ and 12.4 ± 0.6 M ⊕, respectively. The circumstellar disks and the circumbinary structure have well-aligned position angles and inclinations, indicating formation in a smooth, ordered process such as disk fragmentation. In addition, the circumstellar disks have a near/far-side asymmetry in the continuum emission, suggesting that the dust has yet to settle into a thin layer near the midplane. Spectral analysis of CO isotopologues reveals outflows that originate from both of the sources and possibly from the circumbinary disklike structure. Furthermore, we detect Keplerian rotation in the 13CO isotopologues toward both circumstellar disks and likely Keplerian rotation in the circumbinary structure; the latter suggests that it is probably a circumbinary disk.

Keywords: protoplanetary disks; close binary stars
Transport of Interstellar Neutral Helium throughout the Heliosphere

A number of physical processes accompanying the solar wind interaction with the local interstellar medium (LISM) are governed by charge exchange between ions and neutral atoms of interstellar origin. A new, 3D, MHD-plasma/kinetic-neutral model is developed that self-consistently includes both neutral hydrogen and helium atoms, and their feedback on the plasma, through charge exchange and photoionization. Focusing on the transport of interstellar neutral helium, quantitative estimates are provided for bulk properties, deflection angles, and velocity distribution functions (VDFs) along the upwind direction. It is shown that the average deflection of secondary He atoms born in the outer heliosheath (OHS) from their original direction in the LISM is ~12° in front of the heliopause, and occurs in the directions parallel to the plane formed by the velocity and magnetic field vectors in the unperturbed LISM. While these properties are consistent with Interstellar Boundary Explorer observations of the "warm breeze," we show that charge exchange in the OHS leads to remarkable deviations of their VDF from the Maxwellian distribution. He atom filtration in the OHS results in a significant temperature anisotropy and VDF asymmetries, even for the primary helium atoms that experience no charge exchange at all. This is an entirely kinetic phenomenon that shows that primary He atoms observed at 1 au have distributions substantially different from those in the LISM.

Keywords: interstellar medium; interstellar atomic gas; interstellar plasma; astrosphere interstellar medium interactions; charge exchange ionization; heliopause; heliosphere