adsabs/SciX_UAT_keywords huggingface dataset:
Suppression of the TeV Pair-beam-Plasma Instability by a Tangled Weak Intergalactic Magnetic Field

We study the effect of a tangled sub-fG level intergalactic magnetic field (IGMF) on the electrostatic instability of a blazar-induced pair beam. Sufficiently strong IGMF may significantly deflect the TeV pair beams, which would reduce the flux of secondary cascade emission below the observational limits. A similar flux reduction may result from the electrostatic beam-plasma instability, which operates the best in the absence of IGMF. Considering IGMF with correlation lengths smaller than a kiloparsec, we find that weak magnetic fields increase the transverse momentum of the pair-beam particles, which dramatically reduces the linear growth rate of the electrostatic instability and hence the energy-loss rate of the pair beam. We show that the beam-plasma instability is eliminated as an effective energy-loss agent at a field strength three orders of magnitude below that needed to suppress the secondary cascade emission by magnetic deflection. For intermediate-strength IGMF, we do not know a viable process to explain the observed absence of GeV-scale cascade emission.

Keywords: gamma-rays; particle astrophysics; intergalactic medium; blazars
Full-sky Cosmic Microwave Background Foreground Cleaning Using Machine Learning

In order to extract cosmological information from observations of the millimeter and submillimeter sky, foreground components must first be removed to produce an estimate of the cosmic microwave background (CMB). We developed a machine-learning approach for doing so for full-sky temperature maps of the millimeter and submillimeter sky. We constructed a Bayesian spherical convolutional neural network architecture to produce a model that captures both spectral and morphological aspects of the foregrounds. Additionally, the model outputs a per-pixel error estimate that incorporates both statistical and model uncertainties. The model was then trained using simulations that incorporated knowledge of these foreground components that was available at the time of the launch of the Planck satellite. On simulated maps, the CMB is recovered with a mean absolute difference of <4 μK over the full sky after masking map pixels with a predicted standard error of >50 μK; the angular power spectrum is also accurately recovered. Once validated with the simulations, this model was applied to Planck temperature observations from its 70 GHz through 857 GHz channels to produce a foreground-cleaned CMB map at a HEALPIX map resolution of NSIDE = 512. Furthermore, we demonstrate the utility of the technique for evaluating how well different simulations match observations, particularly in regard to the modeling of thermal dust.

Keywords: cosmic microwave background radiation; observational cosmology; convolutional neural networks
A CO2 Cycle on Ariel? Radiolytic Production and Migration to Low-latitude Cold Traps

CO2 ice is present on the trailing hemisphere of Ariel but is mostly absent from its leading hemisphere. The leading/trailing hemispherical asymmetry in the distribution of CO2 ice is consistent with radiolytic production of CO2, formed by charged particle bombardment of H2O ice and carbonaceous material in Ariel's regolith. This longitudinal distribution of CO2 on Ariel was previously characterized using 13 near-infrared reflectance spectra collected at "low" sub-observer latitudes between 30°S and 30°N. Here we investigated the distribution of CO2 ice on Ariel using 18 new spectra: 2 collected over low sub-observer latitudes, 5 collected at "mid" sub-observer latitudes (31°N-44°N), and 11 collected over "high" sub-observer latitudes (45°N-51°N). Analysis of these data indicates that CO2 ice is primarily concentrated on Ariel's trailing hemisphere. However, CO2 ice band strengths are diminished in the spectra collected over mid and high sub-observer latitudes. This sub-observer latitudinal trend may result from radiolytic production of CO2 molecules at high latitudes and subsequent migration of this constituent to low-latitude cold traps. We detected a subtle feature near 2.13 μm in two spectra collected over high sub-observer latitudes, which might result from a "forbidden" transition mode of CO2 ice that is substantially stronger in well-mixed substrates composed of CO2 and H2O ice, consistent with regolith-mixed CO2 ice grains formed by radiolysis. Additionally, we detected a 2.35 μm feature in some low sub-observer latitude spectra, which might result from CO formed as part of a CO2 radiolytic production cycle.

Keywords: uranian satellites; planetary surfaces; surface composition; surface processes; surface ices
CHIME/FRB Discovery of 25 Repeating Fast Radio Burst Sources

We present the discovery of 25 new repeating fast radio burst (FRB) sources found among CHIME/FRB events detected between 2019 September 30 and 2021 May 1. The sources were found using a new clustering algorithm that looks for multiple events colocated on the sky having similar dispersion measures (DMs). The new repeaters have DMs ranging from ~220 to ~1700 pc cm-3, and include sources having exhibited as few as two bursts to as many as twelve. We report a statistically significant difference in both the DM and extragalactic DM (eDM) distributions between repeating and apparently nonrepeating sources, with repeaters having a lower mean DM and eDM, and we discuss the implications. We find no clear bimodality between the repetition rates of repeaters and upper limits on repetition from apparently nonrepeating sources after correcting for sensitivity and exposure effects, although some active repeating sources stand out as anomalous. We measure the repeater fraction over time and find that it tends to an equilibrium of ${2.6}_{-2.6}^{+2.9}$ % over our total time-on-sky thus far. We also report on 14 more sources, which are promising repeating FRB candidates and which merit follow-up observations for confirmation.

Keywords: radio transient sources; high energy astrophysics
Does the Streaming Instability Exist within the Terminal Velocity Approximation?

Terminal velocity approximation is appropriate to study the dynamics of a gas-dust mixture with solids tightly coupled to the gas. This work reconsiders its compatibility with physical processes giving rise to the resonant streaming instability in the low-dust-density limit. It is shown that the linearized equations that have been commonly used to study the streaming instability within the terminal velocity approximation actually exceed the accuracy of this approximation. For that reason, the corresponding dispersion equation recovers the long-wavelength branch of the resonant streaming instability caused by the stationary azimuthal drift of the dust. However, the latter must remain beyond the terminal velocity approximation by its physical definition. The refined equations for gas-dust dynamics in the terminal velocity approximation does not lead to the resonant streaming instability. The work additionally elucidates the physical processes responsible for the instability.

Keywords: protoplanetary disks
Simulations Show that Vortex Flows Could Heat the Chromosphere in Solar Plage

The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low-resolution data is grossly underestimated. In full-resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating.

Keywords: magnetohydrodynamics; plages; solar chromospheric heating
Modeling the Multiwavelength Evolution of the V960 Mon System

We study the evolution of the FU Ori object V960 Mon since its outburst, using available multiwavelength photometric time series over 8 yr, complemented by several epochs of moderate-dispersion spectrophotometry. We find that the source fading can be well-described by a decrease in the temperature of the inner disk, which results from a combination of decreasing accretion rate and increasing inner disk radius. We model the system with a disk atmosphere model that produces the observed variations in multiband photometry (this paper) and high-resolution spectral lines (a companion paper).

Keywords: fu orionis stars; young stellar objects; infrared sources; stellar accretion disks; optical bursts
Lags in Desorption of Lunar Volatiles

Monte Carlo simulations of gas motion inside a granular medium are presented in order to understand the interaction of lunar gases with regolith and improve models for surface-boundary exospheres, a common type of planetary atmosphere. Results demonstrate that current models underestimate the lifetime of weakly bonded adsorbates (e.g., argon) on the surface by not considering the effect of Knudsen diffusion, and suggest that thermal desorption of adsorbates should be modeled as a second-or-higher-order process with respect to adsorbate coverage. An additional discrepancy between present models and outgassing from a realistic porous boundary is found for surface-adsorbate systems containing a distribution of activation energies (e.g., water). In that case, the mobility of adsorbates between desorption events (i.e., surface diffusion), not considered in global models of the exosphere, controls their surface residence time via transitions between sites of low and high binding energy. Without mobility the equatorial surface retains more water over a lunar day because sites of low binding energy are not repopulated by motion along the grain surface when depleted. The effects of Knudsen and surface diffusion apply to other volatile species and help us partly understand why measurements of lunar exosphere constituents appear to indicate stronger bonding of gas with the lunar surface than measured in some laboratory experiments.

Keywords: the moon; exosphere; lunar surface; surface processes; land-atmosphere interactions
Verification of Astrometrically Accelerating Stars from Hipparcos and Gaia. I. Methodology and Application to HIP 44842

A large number of candidate binary stars with apparent acceleration on the sky has emerged from analysis of astrometric data collected by the Hipparcos, Tycho-2, and Gaia space missions. Although the apparent acceleration can serve as a relatively reliable indicator of binarity, it provides scarce information about the orbital and physical parameters of the components. With an emphasis on the search for stellar-mass black holes and neutron stars hidden in binary systems, we start a broader effort to characterize the most promising candidates using follow-up ground-based observations. Accurate quantification of orbital and physical parameters of systems with dim or invisible companions requires combination of Hipparcos, Gaia, and precision spectroscopic measurements. In this paper, we review the necessary steps in this implementation and describe the improved Hipparcos–Gaia sample of long-term astrometric accelerations, which includes correction of sky-correlated systematic errors using the vector spherical decomposition method. As an example, we study one Hipparcos star with a large acceleration, HIP 44842, where the companion is revealed to be a normal main-sequence star.

Keywords: gaia; stellar mass black holes; proper motions; spectroscopic binary stars; astrometry; astrometric binary stars
GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc

We report the discovery of the transiting planet GJ 238 b, with a radius of 0.566 ± 0.014 R ⊕ (1.064 ± 0.026 times the radius of Mars) and an orbital period of 1.74 days. The transit signal was detected by the TESS mission and designated TOI-486.01. The star's position close to the southern ecliptic pole allows for almost continuous observations by TESS when it is observing the southern sky. The host star is an M2.5 dwarf with V = 11.57 ± 0.02 mag, K = 7.030 ± 0.023 mag, a distance of 15.2156 ± 0.0030 pc, a mass of M ☉, a radius of R ☉, and an effective temperature of 3485 ± 140 K. We validate the planet candidate by ruling out or rendering highly unlikely each of the false positive scenarios, based on archival data and ground-based follow-up observations. Validation was facilitated by the host star's small size and high proper motion of 892.633 ± 0.025 mas yr–1.

Keywords: exoplanets; exoplanet detection methods; transit photometry
WARP: The Data Reduction Pipeline for the WINERED Spectrograph

We present a data reduction pipeline written in Python for data obtained with the near-infrared cross-dispersed echelle spectrograph, WINERED, which yields a 0.91–1.35 μm spectrum with the resolving power of ${R}_{\max }\equiv \lambda /{\rm{\Delta }}\lambda ={\rm{28,000}}$ or 70,000 depending on the observing mode. The pipeline was developed to efficiently extract the spectrum from the raw data with high quality. It comprises two modes: the calibration and the science mode. The calibration mode automatically produces the flat-fielding image, bad pixel map, echellogram distortion map and the dispersion solution from the set of the calibration data. Using calibration images and parameters, the science data of astronomical objects can be reduced automatically using the science mode. The science mode is also used for the real-time quick look at the data during observations. An example of the spectra reduced with WARP is presented. The effect of the highly inclined slit image on the spectral resolution is discussed.

Keywords: spectroscopy; near infrared astronomy; astronomy data reduction
Quasi-elastodynamic Processes Involved in the Interaction between Solar Wind and Magnetosphere

The interaction between the solar wind and the magnetosphere is one of the most important research subjects in the fields of astrophysics and space physics. For more than half a century, based on the pressure balance assumption between the solar wind and the magnetosphere and considering other important factors, such as the interplanetary magnetic field and magnetic reconnection process, the dynamic processes at the magnetopause have been extensively analyzed. However, the responses of magnetopause to the solar wind dynamic pressure variations are still complicated to understand. Here, we show that the interaction between the solar wind and the magnetosphere can be regarded as a quasi-elastodynamic process. The driving frequency of the solar wind is determined as a crucial reason for the phase difference between solar wind dynamic pressure variations and magnetopause standoff distance. The low-pass filter effect and oscillation properties of the magnetopause can also be well explained by the forced damped vibrations. Moreover, the quasi-elastodynamic processes predict deformations at the magnetopause, which resemble the magnetopause surface wave. Finally, a three-dimensional time-dependent magnetopause model is constructed and verified by observation. Based on 12,242 magnetopause crossing events, it is found that the new model reveals ~9.7% better prediction accuracy than the widely used time-independent model. These results can also shed light on our understanding of the solar-wind-magnetopause interaction for other planets.

Keywords: solar wind; solar-planetary interactions; planetary magnetospheres; theoretical models
Shock Heating of Incident Thermal and Superthermal Populations of Different Ion Species

Using ion tracing in a model shock front we study heating of thermal (Maxwellian) and superthermal (Vasyliunas-Siscoe) populations of protons, singly charged helium, and alpha particles. It is found that heating of thermal and superthermal populations is different, mainly because of substantially higher ion reflection in the superthermal populations. Accordingly, the temperature increase of initially superthermal populations is substantially higher than that of the thermal ions. Heating per mass decreases with the increase of the mass-to-charge ratio because of the reduced effect of the cross-shock potential and, accordingly, weaker ion reflection. The findings are supported by two-dimensional hybrid simulations.

Keywords: shocks; interplanetary shocks; planetary bow shocks; heliosphere
Observation of the Tailward Electron Flows Commonly Detected at the Flow Boundary of the Earthward Ion Bursty Bulk Flows in the Magnetotail

Using measurements of the Magnetospheric Multiscale mission in the magnetotail from -24 to -15RE, we identified 40 ion Bursty Bulk Flow events (BBFs) and investigated the electron behaviors during these BBFs. The ion flows peaked near the center of the plasma sheet and had a sharp flow boundary. The electron-flow profile is distinct from the ion flows of the BBFs. Inside the BBFs, the strongest Earthward electron flows are observed in the ion flow boundary, away from the current sheet center. Farther away from the peak of the Earthward electron flows, the tailward electron flows are observed in the edges of the ion flows, are mainly field-aligned with low energy, and are stronger than the Earthward flows. It seems that the tailward low-energy electrons are energized at some places tailward of the spacecraft and then ejected Earthward, consistent with the magnetic reconnection scenario in the magnetotail. We suggest this has implications for our understanding of astrophysical jets.

Keywords: space plasmas; interplanetary particle acceleration; solar magnetic reconnection
M17 MIR: A Massive Star Is Forming via Episodic Mass Accretion

We analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 data for the outbursting massive protostar M17 MIR. The ALMA CO J = 2–1 data reveal a collimated and bipolar north–south outflow from M17 MIR. The blueshifted outflow exhibits four CO knots (N1 to N4) along the outflow axis, while the redshifted outflow appears as a single knot (S1). The extremely high velocity (EHV) emissions of N1 and S1 are jetlike and contain subknots along the outflow axis. Assuming the nearest EHV subknots trace the ejecta from the accretion outbursts in the past decades, a tangential ejection velocity of ∼421 km s‑1 is derived for M17 MIR. Assuming the same velocity, the dynamical times of the multiple ejecta, traced by the four blueshifted CO knots, range from 20 to 364 yr. The four blueshifted CO knots imply four clustered accretion outbursts with a duration of tens of years in the past few hundred years. The intervals between the four clustered accretion outbursts are also about tens of years. These properties of the four clustered accretion outbursts are in line with the disk gravitational instability and fragmentation model. The episodic accretion history of M17 MIR traced by episodic outflow suggests that a massive star can form from a lower-mass protostar via frequent episodic accretion events triggered by disk gravitational instability and fragmentation. The first detection of the knotty outflow from an outbursting massive protostar suggests that mass ejections accompanied with accretion events could serve as an effective diagnostic tool for the episodic accretion histories of massive protostars.

Keywords: star formation; stellar accretion; stellar jets
Characteristics of Multi-scale Current Sheets in the Solar Wind at 1 au Associated with Magnetic Reconnection and the Case for a Heliospheric Current Sheet Avalanche

Wind spacecraft measurements are analyzed to obtain a current sheet (CS) normal width d cs distribution of 3374 confirmed magnetic reconnection exhausts in the ecliptic plane of the solar wind at 1 au. The d cs distribution displays a nearly exponential decay from a peak at d cs = 25 d i to a median at d cs = 85 d i and a 95th percentile at d cs = 905 d i with a maximum exhaust width at d cs = 8077 d i . A magnetic field θ-rotation angle distribution increases linearly from a relatively few high-shear events toward a broad peak at 35° < θ < 65°. The azimuthal ϕ angles of the CS normal directions of 430 thick d cs ≥ 500 d i exhausts are consistent with a dominant Parker-spiral magnetic field and a CS normal along the ortho-Parker direction. The CS normal orientations of 370 kinetic-scale d cs < 25 d i exhausts are isotropic in contrast, and likely associated with Alfvénic solar wind turbulence. We propose that the alignment of exhaust normal directions from narrow d cs ~ 15-25 d i widths to well beyond d cs ~ 500 d i with an ortho-Parker azimuthal direction of a large-scale heliospheric current sheet (HCS) is a consequence of CS bifurcation and turbulence within the HCS exhaust that may trigger reconnection of the adjacent pair of bifurcated CSs. The proposed HCS-avalanche scenario suggests that the underlying large-scale parent HCS closer to the Sun evolves with heliocentric distance to fracture into many, more or less aligned, secondary CSs due to reconnection. A few wide exhaust-associated HCS-like CSs could represent a population of HCSs that failed to reconnect as frequently between the Sun and 1 au as other HCSs.

Keywords: solar magnetic reconnection; solar wind; heliosphere; interplanetary turbulence
Repeated State Change of Variable Gamma-Ray Pulsar PSR J2021+4026

PSR J2021+4026 is a radio-quiet gamma-ray pulsar and the first pulsar that shows state change of the gamma-ray emission and spindown rate. The state change of PSR J2021+4026 was first observed at 2011 October, at which the pulsar changes the state from high gamma-ray flux/low spindown rate state to low gamma-ray flux/high spindown rate state. In 2014 December, PSR J2021+4026 recovered the state before the 2011 state change over a timescale of a few months. We report that the long-term evolution of the gamma-ray flux and timing behavior suggests that PSR J2021+4026 changed the state near 2018 February 1 and entered a new low gamma-ray flux/high spindown rate state. At the 2018 state change, the averaged flux dropped from (1.29 ± 0.01) × 10-6 cts cm-2 s-1 to (1.12 ± 0.01) × 10-6 cts cm-2 s-1, which is behavior similar to that of the 2011 event. The spindown rate has increased by ∼3% in the new state since the 2018 state change. The shapes of pulse profile and spectrum in GeV bands also changed at the 2018 event, and they are consistent with behavior at the 2011 state change. Our results probably suggest that PSR J2021+4026 is switching between different states with a timescale of several years, like some radio pulsars (e.g., PSR B1828-11). PSR J2021+4026 will provide a unique opportunity to study the mechanism of the state switching.

Keywords: gamma-ray astronomy; rotation powered pulsars; observational astronomy; magnetic fields