adsabs/SciX_UAT_keywords huggingface dataset:
Large-amplitude Bidirectional Anisotropy of Cosmic-Ray Intensity Observed with Worldwide Networks of Ground-based Neutron Monitors and Muon Detectors in 2021 November

We analyze the cosmic-ray variations during a significant Forbush decrease observed with worldwide networks of ground-based neutron monitors and muon detectors during 2021 November 3-5. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first ~2% decrease after the interplanetary shock arrival followed by the second ~5% decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak amplitude of ~5% at 15 GV, which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90°, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically, indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.

Keywords: galactic cosmic rays
X-Ray Polarization Detection of Cassiopeia A with IXPE

We report on a ~5σ detection of polarized 3-6 keV X-ray emission from the supernova remnant Cassiopeia A (Cas A) with the Imaging X-ray Polarimetry Explorer (IXPE). The overall polarization degree of 1.8% ± 0.3% is detected by summing over a large region, assuming circular symmetry for the polarization vectors. The measurements imply an average polarization degree for the synchrotron component of ~2.5%, and close to 5% for the X-ray synchrotron-dominated forward shock region. These numbers are based on an assessment of the thermal and nonthermal radiation contributions, for which we used a detailed spatial-spectral model based on Chandra X-ray data. A pixel-by-pixel search for polarization provides a few tentative detections from discrete regions at the ~ 3σ confidence level. Given the number of pixels, the significance is insufficient to claim a detection for individual pixels, but implies considerable turbulence on scales smaller than the angular resolution. Cas A's X-ray continuum emission is dominated by synchrotron radiation from regions within ≲1017 cm of the forward and reverse shocks. We find that (i) the measured polarization angle corresponds to a radially oriented magnetic field, similar to what has been inferred from radio observations; (ii) the X-ray polarization degree is lower than in the radio band (~5%). Since shock compression should impose a tangential magnetic-field structure, the IXPE results imply that magnetic fields are reoriented within ~1017 cm of the shock. If the magnetic-field alignment is due to locally enhanced acceleration near quasi-parallel shocks, the preferred X-ray polarization angle suggests a size of 3 × 1016 cm for cells with radial magnetic fields.

Keywords: supernova remnants; polarimetry; x-ray astronomy; shocks
Self-similarities and Power Laws in the Time-resolved Spectra of GRB 190114C, GRB 130427A, GRB 160509A, and GRB 160625B

Binary-driven hypernova (BdHN) models have been adopted to explain the observed properties of long gamma-ray bursts (GRBs). Here, we perform a comprehensive data analysis (temporal and spectral analysis, GeV emission, and afterglow) on GRB 130427A, GRB 160509A, and GRB 160625B. We identify three specific episodes characterized by different observational signatures and show that these episodes can be explained and predicted to occur within the framework of the BdHNe I model, as first observed in GRB 190114C and reported in an accompanying paper. Episode 1 includes the "SN-rise" with the characteristic cutoff power-law spectrum; Episode 2 is initiated by the moment of formation of the black hole, coincident with the onset of the GeV emission and the ultrarelativistic prompt emission phase, and is characterized by a cutoff power law and blackbody spectra; Episode 3 is the "cavity," with its characteristic featureless spectrum.

Keywords: gamma-ray bursts
The Youngest Planet to Have a Spin-Orbit Alignment Measurement AU Mic b

We report measurements of the sky-projected spin-orbit angle for AU Mic b, a Neptune-size planet orbiting a very young (~20 Myr) nearby pre-main-sequence M-dwarf star, which also hosts a bright, edge-on, debris disk. The planet was recently discovered from preliminary analysis of radial-velocity observations and confirmed to be transiting its host star from photometric data from the NASA's TESS mission. We obtained radial-velocity measurements of AU Mic over the course of two partially observable transits and one full transit of planet b from high-resolution spectroscopic observations made with the MINERVA-Australis telescope array. Only a marginal detection of the Rossiter-McLaughlin effect signal was obtained from the radial velocities, in part due to AU Mic being an extremely active star and the lack of full transit coverage plus sufficient out-of-transit baseline. As such, a precise determination of the obliquity for AU Mic b is not possible in this study and we find a sky-projected spin-orbit angle of $\lambda ={47}_{-54}^{{+26}^{\circ}} $ . This result is consistent with both the planet's orbit being aligned or highly misaligned with the spin axis of its host star. Our measurement independently agrees with, but is far less precise than observations carried out on other instruments around the same time that measure a low-obliquity orbit for the planet. AU Mic is the youngest exoplanetary system for which the projected spin-orbit angle has been measured, making it a key data point in the study of the formation and migration of exoplanets-particularly given that the system is also host to a bright debris disk.

Keywords: exoplanets; hot neptunes; exoplanet astronomy; radial velocity; exoplanet detection methods; dynamical evolution
Alpha-to-proton Temperature Ratio Distributions Using Parker Solar Probe Measurements

The distributions of the temperature excess of alphas to protons (ɛ) were studied using Parker Solar Probe measurements for Encounters 2 through 14. The distributions were mapped based on heliographic distance, Coulomb number, plasma β, and Alfvén Mach number (M A ). The importance of collisional effects in the thermalization of solar wind is observed for a wide range of Coulomb numbers. The distributions correlate better with N β and NM A than just N. Furthermore, evidence was found for a narrow region immediately above the Alfvén surface (1 < M A < 2) where ɛ has values much higher than the mass ratio.

Keywords: solar energetic particles; solar wind; space weather
OH Emission Among Mira Variables in Color-Magnitude and Period-Magnitude Diagrams

Infrared absolute-magnitude versus color diagrams have been derived for long-period Mira variables with and without OH-maser emission through the use of Gaia DR3 parallaxes and two samples of stars drawn from the literature. The OH-emitting Miras are mostly consistent with (J - K s ) > 1.4, an average absolute K s magnitude of around -7.6, and pulsation periods greater than 316 days.

Keywords: stellar mass loss; pulsating variable stars; mira variable stars; me stars
Dimming the Lights: 2D Simulations of Deflagrations of Hybrid C/O/Ne White Dwarfs Using FLASH

The dimmest and most numerous outlier of the Type Ia supernova population, the Type Iax event, is increasingly being found in the results of observational campaigns. There is currently no single accepted model to describe these events. This 2D study explores the viability of modeling Type Iax events as a hybrid C/O/Ne white dwarf progenitor undergoing a deflagration using the multiphysics software FLASH. This hybrid was created using the stellar evolution code MESA, and its C-depleted core and mixed structure have demonstrated lower yields than traditional C/O progenitors in previous deflagration-to-detonation studies. To generate a sample, 30 "realizations" of this simulation were performed, the only difference being the shape of the initial match head used to start the deflagration. Consistent with earlier work, these realizations produce the familiar hot dense bound remnant surrounded by sparse ejecta. Our results indicate that the majority of the star remains unburned (~70%) and bound (>90%). Our realizations produce total ejecta yields on the order of 10-2-10-1 M ☉, ejected 56Ni yields on the order of 10-4-10-2 M ☉, and ejecta kinetic energies on the order of 1048-1049 erg. Compared to yields inferred from recent observations of the dimmest Type Iax events-SN 2007qd, SN 2008ha, SN 2010ae, SN 2019gsc, SN 2019muj, SN 2020kyg, and SN 2021fcg-our simulation produces comparable 56Ni yields but too-small total yields and kinetic energies. Reignition of the remnant is also seen in some realizations.

Keywords: type ia supernovae; supernova remnants; white dwarf stars; hydrodynamical simulations
The IAG Solar Flux Atlas: Telluric Correction with a Semiempirical Model

Observations of the Sun as a star have been key to guiding models of stellar atmospheres and additionally provide useful insights on the effects of granulation and stellar activity on radial velocity measurements. Most high-resolution solar atlases contain telluric lines that span the optical and limit the spectral regions useful for analysis. We present here a telluric-corrected solar atlas covering 0.5-1.0 μm derived from solar spectra taken with a Fourier transform spectrograph at the Institut für Astrophysik, Göttingen. This atlas is the highest-resolution spectrum with a wavelength calibration precise to ±10 m s-1 across this 500 nm spectral window. We find that the atlas matches to within 3% of the telluric-corrected Kitt Peak atlas in regions containing telluric absorption weaker than 50% in transmission. The telluric component of the spectral data is fit with a semiempirical model composed of Lorentz profiles initialized to the High-resolution Transmission Molecular Absorption Database (HITRAN) parameters for each absorption feature. Comparisons between the best-fit telluric parameters describing the Lorentz profile for each absorption feature and the original HITRAN values in general show excellent agreement considering the effects atmospheric pressure and temperature have on our final parameters. However, we identify a small subset of absorption features with larger offsets relative to the cataloged line parameters. We make our final solar atlas available online. We additionally make available the telluric spectra extracted from the data that, given the high resolution of the spectrum, would be useful for studying the time evolution of telluric line shapes and their impact on Doppler measurements.

Keywords: astronomy data analysis; earth atmosphere; computational methods; radial velocity; atmospheric effects; the sun
Statistics of Low Frequency Cutoffs for Type III Radio Bursts Observed by Parker Solar Probe during Its Encounters 1-5

The low frequency cutoffs flo and the observed plasma frequency fp of 176 type III radio bursts are investigated in this paper. These events are observed by the Parker Solar Probe when it is in the encounter phase from the first to the fifth orbit. The result shows that the distribution of cutoffs flo is widely spread between 200 kHz and 1.6 MHz. While the plasma frequency fp at the spacecraft is between 50 and 250 kHz, which is almost all smaller than flo. The result also shows that the maximum probability distribution of flo (∼680 kHz) is remarkably higher than that observed by Ulysses and Wind (∼100 kHz) in previous research. Three possible reasons, i.e., solar activity intensity, event electing criteria, and radiation attenuation effect, are also preliminarily discussed.

Keywords: interplanetary physics; solar radio emission
A Note on the Construction of Explicit Symplectic Integrators for Schwarzschild Spacetimes

In recent publications, the construction of explicit symplectic integrators for Schwarzschild- and Kerr-type spacetimes is based on splitting and composition methods for numerical integrations of Hamiltonians or time-transformed Hamiltonians associated with these spacetimes. Such splittings are not unique but have various options. A Hamiltonian describing the motion of charged particles around the Schwarzschild black hole with an external magnetic field can be separated into three, four, and five explicitly integrable parts. It is shown through numerical tests of regular and chaotic orbits that the three-part splitting method is the best of the three Hamiltonian splitting methods in accuracy. In the three-part splitting, optimized fourth-order partitioned Runge-Kutta and Runge-Kutta-Nyström explicit symplectic integrators exhibit the best accuracies. In fact, they are several orders of magnitude better than the fourth-order Yoshida algorithms for appropriate time steps. The first two algorithms have a small additional computational cost compared with the latter ones. Optimized sixth-order partitioned Runge-Kutta and Runge-Kutta-Nyström explicit symplectic integrators have no dramatic advantages over the optimized fourth-order ones in accuracy during long-term integrations due to roundoff errors. The idea of finding the integrators with the best performance is also suitable for Hamiltonians or time-transformed Hamiltonians of other curved spacetimes including Kerr-type spacetimes. When the numbers of explicitly integrable splitting sub-Hamiltonians are as small as possible, such splitting Hamiltonian methods would bring better accuracies. In this case, the optimized fourth-order partitioned Runge-Kutta and Runge-Kutta-Nyström methods are worth recommending.

Keywords: black hole physics; computational astronomy; computational methods; celestial mechanics
Milli-Hertz Gravitational-wave Background Produced by Quasiperiodic Eruptions

Extreme-mass-ratio inspirals (EMRIs) are important targets for future space-borne gravitational-wave (GW) detectors, such as the Laser Interferometer Space Antenna (LISA). Recent works suggest that EMRIs may reside in a population of newly discovered X-ray transients called "quasiperiodic eruptions" (QPEs). Here, we follow this scenario and investigate whether LISA could in the future detect the QPEs. We consider two specific models, in which the QPEs are made of either stellar-mass objects moving on circular orbits around massive black holes (MBHs) or white dwarfs (WDs) on eccentric orbits around MBHs. We find that in either case the five QPEs detected so far are too weak to be resolvable by LISA. However, if QPEs are made of eccentric WD-MBH binaries, they radiate GWs over a wide range of frequencies. The broad spectra overlap to form a background that peaks in the milli-Hertz band and has a signal-to-noise ratio of 9-17 even in the most pessimistic scenario. The presence of this GW background in the LISA band could impact future searches for seed black holes at high redshift as well as stellar-mass binary black holes in the local universe.

Keywords: gravitational waves; intermediate-mass black holes; white dwarf stars; x-ray transient sources
A Spectral-timing Study of the Inner Flow Geometry in MAXI J1535-571 with Insight-HXMT and NICER

We have performed a spectral-timing analysis of the black hole X-ray binary MAXI J1535-571 during its 2017 outburst, with the aim of exploring the evolution of the inner accretion flow geometry. X-ray reverberation lags are observed in the hard-intermediate state (HIMS) and soft-intermediate state of the outburst. During the HIMS, the characteristic frequency of the reverberation lags ν 0 (the frequency at which the soft lag turns to zero in lag-frequency spectra) increases when the spectrum softens. This reflects a reduction of the spatial distance between the corona and accretion disk, when assuming the measured time lags are associated with the light travel time. We also find a strong correlation between ν 0 and the type-C quasi-periodic oscillation (QPO) centroid frequency ν QPO, which can be well explained by the Lense-Thirring precession model under a truncated disk geometry. Despite the degeneracy in the spectral modeling, our results suggest that the accretion disk is largely truncated in the low hard state, and moves inward as the spectrum softens. Combine the spectral modeling results with the ν 0 - ν QPO evolution, we are inclined to believe that this source probably has a truncated disk geometry in the hard state.

Keywords: accretion; x-ray binary stars; black hole physics
THEMIS: A Parameter Estimation Framework for the Event Horizon Telescope

The Event Horizon Telescope (EHT) provides the unprecedented ability to directly resolve the structure and dynamics of black hole emission regions on scales smaller than their horizons. This has the potential to critically probe the mechanisms by which black holes accrete and launch outflows, and the structure of supermassive black hole spacetimes. However, accessing this information is a formidable analysis challenge for two reasons. First, the EHT natively produces a variety of data types that encode information about the image structure in nontrivial ways; these are subject to a variety of systematic effects associated with very long baseline interferometry and are supplemented by a wide variety of auxiliary data on the primary EHT targets from decades of other observations. Second, models of the emission regions and their interaction with the black hole are complex, highly uncertain, and computationally expensive to construct. As a result, the scientific utilization of EHT observations requires a flexible, extensible, and powerful analysis framework. We present such a framework, THEMIS, which defines a set of interfaces between models, data, and sampling algorithms that facilitates future development. We describe the design and currently existing components of THEMIS, how THEMIS has been validated thus far, and present additional analyses made possible by THEMIS that illustrate its capabilities. Importantly, we demonstrate that THEMIS is able to reproduce prior EHT analyses, extend these, and do so in a computationally efficient manner that can efficiently exploit modern high-performance computing facilities. THEMIS has already been used extensively in the scientific analysis and interpretation of the first EHT observations of M87.

Keywords: galactic center; submillimeter astronomy; astronomy data analysis; very long baseline interferometry; astrophysical black holes
Interstellar Complex Organic Molecules in SiO-traced Massive Outflows

The interstellar medium contains dust and gas, in which molecules can proliferate at high densities and in cold conditions. Interstellar complex organic molecules (iCOMs) are C-bearing species that contain at least six atoms. As they are detected in young stellar objects, iCOMs are expected to inhabit early stages of star formation evolution. In this study, we try to determine which iCOMs are present in the outflow component of massive protostars. To do this, we analyzed the morphological extension of blue- and redshifted iCOM emission in a sample of 11 massive protostars employing mapping observations at 1 mm within a ~1 GHz bandwidth for both the IRAM-30 m and APEX telescopes. We modeled the iCOM emission of the central pointing spectra of our objects using the XCLASS local thermal equilibrium radiative transfer code. We detected the presence of several iCOMs such as CH3OH, 13CH3OH, CH3OCHO, C2H5C15N, and (c-C3H2)CH2. In G034.41+0.24, G327.29-0.58, G328.81+0.63, G333.13-0.43, G340.97-1.02, G351.45+0.66, and G351.77-0.54, the iCOM lines show a faint broad-line profile. Due to the offset peak positions of the blue- and redshifted emission, covering from ~0.1 to 0.5 pc, these wings are possibly related to movements external to the compact core, such as large-scale low-velocity outflows. We have also established a correlation between the parent iCOM molecule CH3OH and the shock tracer SiO, reinforcing the hypothesis that shock environments provide the conditions to boost the formation of iCOMs via gas-phase reactions.

Keywords: star forming regions; massive stars; interstellar molecules
The GFCAT: A Catalog of Ultraviolet Variables Observed by GALEX with Subminute Resolution

We have performed the first systematic search of the full Galaxy Evolution Explorer (GALEX) data archive for astrophysical variability on timescales of seconds to minutes by rebinning data across the whole mission to 30 s time resolution. The result is the GALEX Flare Catalog (GFCAT), which describes 1426 ultraviolet variable sources, including stellar flares, eclipsing binaries, δ Scuti and RR Lyrae variables, and active galactic nuclei. Many of these sources have never previously been identified as variable. We have also assembled a table of observations of ultraviolet flares and accompanying statistics and measurements, including energies, and of candidate eclipsing stars. This effort was enabled by a significantly enhanced version of the gPhoton software for analyzing time-domain GALEX data; this "gPhoton2" package is available to support follow-on efforts.

Keywords: ultraviolet astronomy; time domain astronomy; flare stars; eclipsing binary stars; rr lyrae variable stars; delta scuti variable stars; catalogs; active galactic nuclei; space telescopes; astronomy software
Aurora Sightings Observed in Chinese History Caused by CIRs or Great-storm CMEs

Auroras observed at middle and low geographic latitudes are related to external inputs and varying geomagnetic fields. This work aims to exclude corotating interaction region (CIR) storms and identify strong coronal mass ejection (CME) storms according to historical auroral records when the geomagnetic field varies substantially. An existing catalog of the aurora records in Chinese history reported by Zeng & Jin from 193 B.C. to 1911 A.D. is used. Archaeomagnetic field models are adopted to estimate the variation of the dipole field. According to the empirical relation between the equatorward boundary of the auroral oval, Dst index, and geomagnetic field intensity, the auroras caused by CIRs can be excluded, and those caused by strong CMEs are identified. After 1500 A.D., China's magnetic latitude decreased substantially due to the pole shift. This shift provides a better opportunity to investigate the existence of great-level storms. These great-storm CMEs occurred in both solar maximum and minimum. The space weather modeling framework is used to calculate the cusp area and the downward ion flux through the cusp for varied geomagnetic field and solar wind. For the present solar wind condition and tilt angle <15°, stronger geomagnetic field tends to generate a larger cusp area and higher ion flux through the cusp. For the weaker solar wind in the Maunder minimum, the ion flux is lower, but the cusp area is similar to that at present.

Keywords: solar coronal mass ejections; geomagnetic fields