Sazuna/UAT_keywords huggingface dataset:
Statistical Study of Small-scale Magnetic Holes in the Upstream Regime of the Martian Bow Shock. Small-scale magnetic holes (SSMHs) are frequently observed in the solar wind at 1 au, as well as the terrestrial current sheet and magnetosheath. These kinetic-size structures play an important role in energy dissipation and particle transportation. Here, we report the existence of SSMHs in the upstream regime of the Martian bow shock and statistically investigate these SSMHs based on 5 yr observations of the Mars Atmosphere and Volatile EvolutioN spacecraft. A total of 549 SSMHs are found, and their durations and sizes obey the lognormal distribution. The median duration is ~0.46 s, and the median size is ~2 ion inertial lengths. We regard an isolated SSMH or a train of SSMHs as a SSMH event. The average occurrence rate of the SSMH events is ~0.6 event per day. The occurrence rate is much larger in the region belonging to the ion foreshock on average, suggesting that the ion foreshock is an important source of SSMHs. The occurrence of the SSMH events tends to be larger when the ion number density and the interplanetary magnetic field (IMF) strength are larger, indicating that the generation of SSMHs might be associated with ions and the IMF strength. Although their generation mechanism is still unclear, the finding of the link between the occurrence rate of the SSMH events and ion number density, as well as the IMF strength, might provide a clue to further reveal the generation mechanism of SSMHs in the solar wind or planetary foreshock.

Keywords: Solar wind, Solar-planetary interactions, Interplanetary magnetic fields
Beyond the Detector Horizon: Forecasting Gravitational-Wave Strong Lensing. When gravitational waves pass near massive astrophysical objects, they can be gravitationally lensed. The lensing can split them into multiple wave fronts, magnify them, or imprint beating patterns on the waves. Here we focus on the multiple images produced by strong lensing. In particular, we investigate strong lensing forecasts, the rate of lensing, and the role of lensing statistics in strong lensing searches. Overall, we find a reasonable rate of lensed detections for double, triple, and quadruple images at the LIGO-Virgo-KAGRA design sensitivity. We also report the rates for A+ and LIGO Voyager and briefly comment on potential improvements due to the inclusion of subthreshold triggers. We find that most galaxy-lensed events originate from redshifts z ~ 1-4 and report the expected distribution of lensing parameters for the observed events. Besides forecasts, we investigate the role of lensing forecasts in strong lensing searches, which explore repeated event pairs. One problem associated with the searches is the rising number of event pairs, which leads to a rapidly increasing false alarm probability. We show how knowledge of the expected galaxy-lensing time delays in our searches allow us to tackle this problem. Once the time delays are included, the false alarm probability increases linearly (similar to nonlensed searches) instead of quadratically with time, significantly improving the search. For galaxy cluster lenses, the improvement is less significant. The main uncertainty associated with these forecasts are the merger-rate density estimates at high redshift, which may be better resolved in the future.

Keywords: Gravitational lensing, Gravitational waves, General relativity
Spectral and Timing Analysis of NuSTAR and Swift/XRT Observations of the X-Ray Transient MAXI J0637-430. We present results for the first observed outburst from the transient X-ray binary source MAXI J0637-430. This study is based on eight observations from the Nuclear Spectroscopic Telescope Array (NuSTAR) and six observations from the Neil Gehrels Swift Observatory X-Ray Telescope (Swift/XRT) collected from 2019 November 19 to 2020 April 26 as the 3-79 keV source flux declined from 8.2 × 10-10 to 1.4 × 10-12 erg cm-2 s-1. We see the source transition from a soft state with a strong disk-blackbody component to a hard state dominated by a power-law or thermal Comptonization component. NuSTAR provides the first reported coverage of MAXI J0637-430 above 10 keV, and these broadband spectra show that a two-component model does not provide an adequate description of the soft-state spectrum. As such, we test whether blackbody emission from the plunging region could explain the excess emission. As an alternative, we test a reflection model that includes a physical Comptonization continuum. Finally, we also test a spectral component based on reflection of a blackbody illumination spectrum, which can be interpreted as a simple approximation to the reflection produced by returning disk radiation due to the bending of light by the strong gravity of the black hole. We discuss the physical implications of each scenario and demonstrate the value of constraining the source distance.

Keywords: Accretion, Black hole physics, Low-mass x-ray binary stars
No Detectable Kilonova Counterpart is Expected for O3 Neutron Star-Black Hole Candidates. We analyze the tidal disruption probability of potential neutron star-black hole (NSBH) merger gravitational-wave (GW) events, including GW190426_152155, GW190814, GW200105_162426, and GW200115_042309, detected during the third observing run of the LIGO/Virgo Collaboration and the detectability of kilonova emission in connection with these events. The posterior distributions of GW190814 and GW200105_162426 show that they must be plunging events, and hence no kilonova signal is expected from these events. With the stiffest NS equation of state allowed by the constraint of GW170817 taken into account, the probability that GW190426_152155 and GW200115_042309 can make tidal disruption is ~24% and ~3%, respectively. However, the predicted kilonova brightness is too faint to be detected for present follow-up search campaigns, which explains the lack of electromagnetic (EM) counterpart detection after triggers of these GW events. Based on the best-constrained population synthesis simulation results, we find that disrupted events account for only ≲20% of cosmological NSBH mergers, since most of the primary BHs could have low spins. The associated kilonovae for those disrupted events will still be difficult for LSST to discover after GW triggers in the future because of their low brightness and larger distances. For future GW-triggered multimessenger observations, potential short-duration gamma-ray bursts and afterglows are more probable EM counterparts of NSBH GW events.

Keywords: Neutron stars, Gravitational waves, Black holes
Panspermia in a Milky Way-like Galaxy. We study the process of panspermia in Milky Way-like galaxies by modeling the probability of successful travel of organic compounds between stars harboring potentially habitable planets. To this end, we apply the modified habitability recipe of Gobat &amp; Hong to a model galaxy from the McMaster Unbiased Galaxy Simulations suite of zoom-in cosmological simulations. We find that, unlike habitability, which only occupies a narrow dynamic range over the entire galaxy, the panspermia probability can vary by orders of magnitude between the inner (R, b &amp;equals; 1-4 kpc) and outer disk. However, only a small fraction of star particles have very large values for the panspermia probability and, consequently, the fraction of star particles where the panspermia process is more effective than prebiotic evolution is much lower than from naïve expectations based on the ratio between the panspermia probability and natural habitability.

Keywords: Galaxy stellar content, Interstellar dust extinction, Astrobiology, Exoplanet formation, Habitable planets, Milky Way Galaxy
New Limits on the Lorentz/CPT Symmetry Through 50 Gravitational-wave Events. Lorentz invariance plays a fundamental role in modern physics. However, tiny violations of the Lorentz invariance may arise in some candidate quantum gravity theories. Prominent signatures of the gravitational Lorentz invariance violation (gLIV) include anisotropy, dispersion, and birefringence in the dispersion relation of gravitational waves (GWs). Using a total of 50 GW events in the GW transient catalogs GWTC-1 and GWTC-2, we perform an analysis on the anisotropic birefringence phenomenon. The use of multiple events allows us to completely break the degeneracy among gLIV coefficients and globally constrain the coefficient space. Compared to previous results at mass dimensions 5 and 6 for the Lorentz-violating operators, we tighten the global limits of 34 coefficients by factors ranging from 2 to 7.

Keywords: General relativity, Gravitational waves, Compact binary stars
Uncovering Intense Ancient Solar Activity from Naked-eye Observations of Egg-like Sunspots. Ancient sunspot records written in classical Chinese provide important information regarding ancient solar activity. The Chinese recorded 14 observations of sunspots that resembled an egg (hereafter, egg record; the word egg is used to represent approximate sunspot sizes) before 1000 CE. However, the egg records in classical Chinese were too short to provide sufficient sunspot details. This study was conducted to decode egg records from 1769 and 1917 through telescopic sunspot observations. The results of our decoding show that egg-like sunspots were generally used by observers in East Asia to represent a very large sunspot group with an approximately elliptical outline. An egg record generally served as a marker of intense solar activity. Three egg records (in 1278, 1769, and 1917) were observed to be close to the solar maxima, with the time difference being smaller than 1 yr. Some egg records could thus be used to identify the solar maxima. The mean time difference between 10 egg records and the nearest solar maxima is 2 yr. Therefore, egg records can provide necessary information for uncovering additional intense solar activity from ancient times.

Keywords: Solar cycle, Sunspots
A 99 minute Double-lined White Dwarf Binary from SDSS-V. We report the discovery of SDSS J133725.26+395237.7 (hereafter SDSS J1337+3952), a double-lined white dwarf (WD+WD) binary identified in early data from the fifth-generation Sloan Digital Sky Survey (SDSS-V). The double-lined nature of the system enables us to fully determine its orbital and stellar parameters with follow-up Gemini spectroscopy and Swift UVOT ultraviolet fluxes. The system is nearby (d = 113 pc), and consists of a 0.51 M☉ primary and a 0.32 M☉ secondary. SDSS J1337+3952 is a powerful source of gravitational waves in the millihertz regime, and will be detectable by future space-based interferometers. Due to this gravitational wave emission, the binary orbit will shrink down to the point of interaction in ≍220 Myr. The inferred stellar masses indicate that SDSS J1337+3952 will likely not explode as a Type Ia supernova (SN Ia). Instead, the system will probably merge and evolve into a rapidly rotating helium star and could produce an underluminous thermonuclear supernova along the way. The continuing search for similar systems in SDSS-V will grow the statistical sample of double-degenerate binaries across parameter space, constraining models of binary evolution and SNe Ia.

Keywords: White dwarf stars, Gravitational wave sources, Spectroscopic binary stars, Detached binary stars, DA stars
Resolving the Fastest Ejecta from Binary Neutron Star Mergers: Implications for Electromagnetic Counterparts. We examine the effect of spatial resolution on initial mass ejection in grid-based hydrodynamic simulations of binary neutron star mergers. The subset of the dynamical ejecta with velocities greater than ~0.6c can generate an ultraviolet precursor to the kilonova on approximately hour timescales and contribute to a years long nonthermal afterglow. Previous work has found differing amounts of this fast ejecta, by one to two orders of magnitude, when using particle-based or grid-based hydrodynamic methods. Here, we carry out a numerical experiment that models the merger as an axisymmetric collision in a corotating frame, accounting for Newtonian self-gravity, inertial forces, and gravitational wave losses. The lower computational cost allows us to reach spatial resolutions as high as 4 m, or ~3 × 10-4 of the stellar radius. We find that fast ejecta production converges to within 10% for a cell size of 20 m. This suggests that fast ejecta quantities found in existing grid-based merger simulations are unlikely to increase to the level needed to match particle-based results upon further resolution increases. The resulting neutron-powered precursors are in principle detectable out to distances ≲200 Mpc with upcoming facilities.We also find that head-on collisions at the freefall speed, relevant for eccentric mergers, yield fast and slow ejecta quantities of order 10-2 M⊙, with a kilonova signature distinct from that of quasi-circular mergers.

Keywords: Neutron stars, Hydrodynamics, Transient sources, Nuclear astrophysics, Gravitational waves, Shocks
Split Invariant Curves in Rotating Bar Potentials. Invariant curves are generally closed curves in Poincaré's surface of section. Here we study an interesting dynamical phenomenon, first discovered by Binney et al. in a rotating Kepler potential, where an invariant curve of the surface of section can split into two disconnected line segments under certain conditions, which is distinctively different from the islands of resonant orbits. We first demonstrate the existence of split invariant curves in the Freeman bar model, where all orbits can be described analytically. We find that the split phenomenon occurs when orbits are nearly tangent to the minor/major axis of the bar potential. Moreover, the split phenomenon seems "necessary" to avoid invariant curves intersecting with each other. Such a phenomenon appears only in rotating potentials, and we demonstrate its universal existence in other general rotating bar potentials. It also implies that actions are no longer proportional to the area bounded by an invariant curve if the split occurs, but they can still be computed by other means.

Keywords: Orbits, Galaxy dynamics, Barred spiral galaxies
Merging Criteria for Planetesimal Collisions. In the standard scenario of planet formation, terrestrial planets, ice giants, and cores of gas giants are formed by the accumulation of planetesimals. However, there are few N-body simulation studies of planetesimal accretion that correctly take into account the merging condition of planetesimals. In order to investigate a realistic accretion process of planetesimals, it is necessary to clarify the merging criteria of planetesimals at collision. We perform numerical collision experiments using smoothed particle hydrodynamics and obtain the merging criteria as a function of planetesimal mass and impact parameters for undifferentiated rocky and icy planetesimals and differentiated icy planetesimals. We vary the total mass of colliding planetesimals, their mass ratios, and the impact angle and obtain the critical impact velocity as the merging criteria distinguishing merging from hit-and-run collision. We find that the critical impact velocity normalized by the two-body surface escape velocity decreases with increasing impact angle. The critical impact velocity does not depend on the total mass, while it has a weak positive dependence on the mass ratio. These results barely depend on the composition and internal structure of the planetesimals.

Keywords: Solar system, Exoplanets, Solar system planets
Signature of a Heliotail Organized by the Solar Magnetic Field and the Role of Nonideal Processes in Modeled IBEX ENA Maps: A Comparison of the BU and Moscow MHD Models. Energetic neutral atom (ENA) models typically require post-processing routines to convert the distributions of plasma and H atoms into ENA maps. Here we investigate how two kinetic-MHD models of the heliosphere (the BU and Moscow models) manifest in modeled ENA maps using the same prescription and how they compare with Interstellar Boundary Explorer (IBEX) observations. Both MHD models treat the solar wind as a single-ion plasma for protons, which include thermal solar wind ions, pick-up ions (PUIs), and electrons. Our ENA prescription partitions the plasma into three distinct ion populations (thermal solar wind, PUIs transmitted and ones energized at the termination shock) and models the populations with Maxwellian distributions. Both kinetic-MHD heliospheric models produce a heliotail with heliosheath plasma that is organized by the solar magnetic field into two distinct north and south columns that become lobes of high mass flux flowing down the heliotail; however, in the BU model, the ISM flows between the two lobes at distances in the heliotail larger than 300 au. While our prescription produces similar ENA maps for the two different plasma and H atom solutions at the IBEX-Hi energy range (0.5-6 keV), the modeled ENA maps require a scaling factor of ~2 to be in agreement with the data. This problem is present in other ENA models with the Maxwellian approximation of multiple ion species and indicates that either a higher neutral density or some acceleration of PUIs in the heliosheath is required.

Keywords: Heliopause, Slow solar wind, Magnetohydrodynamics, Heliosphere, Fast solar wind, Termination shock, Solar wind, Solar system, Interstellar medium, Heliosheath, Magnetohydrodynamical simulations
Photometric Variability of the Pre-main-sequence Stars toward the Sh 2-190 Region. We present the results from our time-series imaging data taken with the 1.3 m Devasthal fast optical telescope and 0.81 m Tenagara telescope in V, Rc, and Ic bands covering an area of ~18'4 × 18'4 toward the star-forming region Sh 2-190. This photometric data helped us to explore the nature of the variability of pre-main-sequence (PMS) stars. We have identified 85 PMS variables, i.e., 37 Class II and 48 Class III sources. Forty-five of the PMS variables show periodicity in their light curves. We show that the stars with thicker disks and envelopes rotate slower and exhibit larger photometric variations compared to their diskless counterparts. This result suggests that rotation of the PMS stars is regulated by the presence of circumstellar disks. We also found that the periods of the stars show a decreasing trend with increasing mass in the range of ~0.5-2.5 M⊙. Our result indicates that most of the variability in Class II sources is ascribed to the presence of a thick disk, while the presence of cool spots on the stellar surface causes the brightness variation in Class III sources. X-ray activities in the PMS stars were found to be at the saturation level reported for the main-sequence stars. The younger counterparts of the PMS variables show less X-ray activity, hinting at a less significant role of a stellar disk in X-ray generation.

Keywords: Variable stars, Pre-main sequence
The Poissonian Origin of Power Laws in Solar Flare Waiting Time Distributions. In this study we aim for a deeper understanding of the power-law slope, α, of waiting time distributions. Statistically independent events with linear behavior can be characterized by binomial, Gaussian, exponential, or Poissonian size distribution functions. In contrast, physical processes with nonlinear behavior exhibit spatiotemporal coherence (or memory) and "fat tails" in their size distributions that fit power-law-like functions, as a consequence of the time variability of the mean event rate, as demonstrated by means of Bayesian block decomposition in the work of Wheatland et al. In this study we conduct numerical simulations of waiting time distributions N(τ) in a large parameter space for various (polynomial, sinusoidal, Gaussian) event rate functions λ(t), parameterized with an exponent p that expresses the degree of the polynomial function λ(t) ∝ tp. We derive an analytical exact solution of the waiting time distribution function in terms of the incomplete gamma function, which is similar to a Pareto type II function and has a power-law slope of α = 2 + 1/p, in the asymptotic limit of large waiting times. Numerically simulated random distributions reproduce this theoretical prediction accurately. Numerical simulations in the nonlinear regime (p ≥ 2) predict power-law slopes in the range of 2.0 ≤ α ≤ 2.5. The self-organized criticality model yields a prediction of α = 2. Observations of solar flares and coronal mass ejections (over at least a half solar cycle) are found in the range of αobs ≈ 2.1-2.4. Deviations from strict power-law functions are expected due to the variability of the flare event rate λ(t), and deviations from theoretically predicted slope values α occur due to the Poissonian weighting bias of power-law fits.

Keywords: Astrostatistics distributions, Solar flares, Solar x-ray flares
Interstellar Objects Follow the Collapse of Molecular Clouds. Interstellar objects (ISOs), the parent population of 1I/'Oumuamua and 2I/Borisov, are abundant in the interstellar medium of the Milky Way. This means that the interstellar medium, including molecular-cloud regions, has three components: gas, dust, and ISOs. From observational constraints of the field density of ISOs drifting in the solar neighborhood, we infer that a typical molecular cloud of 10 pc diameter contains some 1018 ISOs. At typical sizes ranging from hundreds of meters to tens of kilometers, ISOs are entirely decoupled from the gas dynamics in these molecular clouds. Here we address the question of whether ISOs can follow the collapse of molecular clouds. We perform low-resolution simulations of the collapse of molecular clouds containing initially static ISO populations toward the point where stars form. In this proof-of-principle study, we find that the interstellar objects definitely follow the collapse of the gas-and many become bound to the new-forming numerical approximations to future stars (sinks). At minimum, 40% of all sinks have one or more ISO test particles gravitationally bound to them for the initial ISO distributions tested here. This value corresponds to at least 1010 actual ISOs being bound after three initial freefall times. Thus, ISOs are a relevant component of star formation. We find that more massive sinks bind disproportionately large fractions of the initial ISO population, implying competitive capture of ISOs. Sinks can also be solitary, as their ISOs can become unbound again-particularly if sinks are ejected from the system. Emerging planetary systems will thus develop in remarkably varied environments, ranging from solitary to richly populated with bound ISOs.

Keywords: Collapsing clouds, Molecular clouds, Interstellar objects
Dust Rings as a Footprint of Planet Formation in a Protoplanetary Disk. Relatively large dust grains (referred to as pebbles) accumulate at the outer edge of the gap induced by a planet in a protoplanetary disk, and a ring structure with a high dust-to-gas ratio can be formed. Such a ring has been thought to be located immediately outside the planetary orbit. We examined the evolution of the dust ring formed by a migrating planet, by performing two-fluid (gas and dust) hydrodynamic simulations. We found that the initial dust ring does not follow the migrating planet and remains at the initial location of the planet in cases with a low viscosity of α ~ 10-4. The initial ring is gradually deformed by viscous diffusion, and a new ring is formed in the vicinity of the migrating planet, which develops from the trapping of the dust grains leaking from the initial ring. During this phase, two rings coexist outside the planetary orbit. This phase can continue over ~1 Myr for a planet migrating from 100 au. After the initial ring disappears, only the later ring remains. This change in the ring morphology can provide clues as to when and where the planet was formed, and is the footprint of the planet. We also carried out simulations with a planet growing in mass. These simulations show more complex asymmetric structures in the dust rings. The observed asymmetric structures in the protoplanetary disks may be related to a migrating and growing planet.

Keywords: Exoplanet migration, Protoplanetary disks, Circumstellar disks, Planetary migration, Exoplanet formation, Planet formation