adsabs/SciX_UAT_keywords huggingface dataset:
Fast Radio Bursts from Interacting Binary Neutron Star Systems

Recent observations of repeating fast radio bursts (FRBs) suggest that some FRBs reside in an environment consistent with that of binary neutron star (BNS) mergers. The bursting rate for repeaters could be very high and the emission site is likely from a magnetosphere. We discuss a hypothesis of producing abundant repeating FRBs in BNS systems. Decades to centuries before a BNS system coalesces, the magnetospheres of the two neutron stars start to interact relentlessly. Abrupt magnetic reconnection accelerates particles, which emit coherent radio waves in bunches via curvature radiation. FRBs are detected as these bright radiation beams point toward Earth. This model predicts quasi-periodicity of the bursts at the rotation periods of the two merging neutron stars (tens of milliseconds and seconds, respectively) as well as the period of orbital motion (of the order of 100 s). The bursting activities are expected to elevate with time as the two neutron stars get closer. The repeating FRB sources should be gravitational-wave (GW) sources for space-borne detectors such as Laser Interferometer Space Antenna (LISA), and eventually could be detected by ground-based detectors when the two neutron stars coalesce.

Keywords: radio transient sources; gravitational waves; interacting binary stars
Synchrotron Gamma-Ray Emission Model of the Giant Outburst of Quasar 3C 279 in 2015 June: Fast Reconnection or Stochastic Acceleration with Electromagnetic Cascade?

We test the synchrotron emission scenario for the very bright gamma-ray flare of blazar 3C 279 observed in 2015 June using time-dependent numerical simulations. A bulk Lorentz factor as high as 100 can bring the synchrotron maximum energy above the GeV energy range. We find two possible solutions for the X-ray to gamma-ray spectrum. One is a prompt electron injection model with a hard power-law index as magnetic reconnection models suggest. Too strong a magnetic field yields too bright a synchrotron X-ray flux due to secondary electron-positron pairs. Even in the prompt electron injection model, the Poynting flux luminosity is at most comparable to the gamma-ray or electron luminosity. Another model is the stochastic acceleration model, which leads to a very unique picture accompanying the electromagnetic cascade and reacceleration of the secondary electron-positron pairs. In this model, the energy budget of the magnetic field is very low compared to gamma-rays and electrons.

Keywords: blazars
A Machine Learning Model to Infer Planet Masses from Gaps Observed in Protoplanetary Disks

Observations of bright protoplanetary disks often show annular gaps in their dust emission. One interpretation of these gaps is disk-planet interaction. If so, fitting models of planetary gaps to observed protoplanetary disk gaps can reveal the presence of hidden planets. However, future surveys are expected to produce an ever-increasing number of protoplanetary disks with gaps. In this case, performing a customized fitting for each target becomes impractical owing to the complexity of disk-planet interaction. To this end, we introduce Disk Planet Neural Network (DPNNet), an efficient model of planetary gaps by exploiting the power of machine learning. We train a deep neural network with a large number of dusty disk-planet hydrodynamic simulations across a range of planet masses, disk temperatures, disk viscosities, disk surface density profiles, particle Stokes numbers, and dust abundances. The network can then be deployed to extract the planet mass for a given gap morphology. In this work, first in a series, we focus on the basic concepts of our machine learning framework. We demonstrate its utility by applying it to the dust gaps observed in the protoplanetary disk around HL Tau at 10, 30, and 80 au. Our network predicts planet masses of 80 M⊕, 63 M⊕, and 70 M⊕, respectively, which are comparable to those from other studies based on specialized simulations. We discuss the key advantages of our DPNNet in its flexibility to incorporate new physics as well as any number of parameters and predictions, in addition to its potential to ultimately replace hydrodynamical simulations for disk observers and modelers.

Keywords: exoplanet detection methods; protoplanetary disks; exoplanet astronomy; neural networks
The Isotropic Interplanetary Dust Cloud and Near-infrared Extragalactic Background Light Observed with COBE/DIRBE

We report observation of isotropic interplanetary dust (IPD) by analyzing the infrared (IR) maps of the Diffuse Infrared Background Experiment (DIRBE) on board the Cosmic Background Explorer (COBE) spacecraft. To search for the isotropic IPD, we perform new analysis in terms of the solar elongation angle (ɛ), because we expect the zodiacal light (ZL) intensity from the isotropic IPD to decrease as a function of ɛ. We use the DIRBE weekly averaged maps covering 64° ≲ ɛ ≲ 124° and inspect the ɛ dependence of residual intensity after subtracting conventional ZL components. We find the ɛ dependence of the residuals, indicating the presence of the isotropic IPD. However, the mid-IR ɛ dependence is different from that of the isotropic IPD model at ɛ ≳ 90°, where the residual intensity increases as a function of ɛ. To explain the observed ɛ dependence, we assume a spheroidal IPD cloud showing higher density farther away from the Sun. We estimate the intensity of the near-IR extragalactic background light (EBL) by subtracting the spheroidal component, assuming the spectral energy distribution from the residual brightness at 12 μm. The EBL intensity is derived as ${45}_{-8}^{+11}$ , ${21}_{-4}^{+3}$ , and $15\pm 3\,{\mathrm{nWm}}^{-2}\,{\mathrm{sr}}^{-1}$ at 1.25, 2.2, and 3.5 μm, respectively. The EBL is still a few times larger than the integrated light of normal galaxies, suggesting the existence of unaccounted-for extragalactic sources.

Keywords: infrared astronomy; zodiacal cloud; cosmic background radiation; interplanetary dust; observational cosmology; infrared astronomical satellite; galaxy evolution; diffuse radiation; early universe; intergalactic medium; population iii stars; primordial black holes
Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST

We have performed a search over 3440 deg2 of Epoch 1 (2017-2019) of the Very Large Array Sky Survey to identify unobscured quasars in the optical (0.2 < z < 3.2) and obscured active galactic nuclei (AGNs) in the infrared that have brightened dramatically in the radio over the past one to two decades. These sources would have been previously classified as "radio-quiet" quasars based on upper limits from the Faint Images of the Radio Sky at Twenty cm survey (1993-2011), but they are now consistent with "radio-loud" quasars ( ${L}_{3\mathrm{GHz}}={10}^{40\mbox{--}42}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ). A quasi-simultaneous, multiband (∼1-18 GHz) follow-up study of 14 sources with the VLA has revealed compact sources (<0"1 or <1 kpc) with peaked radio spectral shapes. The high-amplitude variability over decadal timescales at 1.5 GHz (100% to >2500%) but roughly steady fluxes over a few months at 3 GHz are inconsistent with extrinsic variability due to propagation effects, thus favoring an intrinsic origin. We conclude that our sources are powerful quasars hosting compact/young jets. This challenges the generally accepted idea that "radio-loudness" is a property of the quasar/AGN population that remains fixed on human timescales. Our study suggests that frequent episodes of short-lived AGN jets that do not necessarily grow to large scales may be common at high redshift. We speculate that intermittent but powerful jets on subgalactic scales could interact with the interstellar medium, possibly driving feedback capable of influencing galaxy evolution.

Keywords: active galaxies; radio sources; galaxy evolution; radio loud quasars; quasars; radio quiet quasars; surveys; radio active galactic nuclei; radio astronomy; radio jets; radio transient sources; extragalactic radio sources
The Inner Solar System Chronology (ISOCHRON) Lunar Sample Return Mission Concept: Revealing Two Billion Years of History

We present the Inner SOlar System CHRONology (ISOCHRON) concept to return samples of the youngest extensive mare basalt for age-dating and geochemical analysis. The young basalt is exposed at a site southwest of Aristarchus Plateau, for which complete remote-sensing data are available for thorough landing site analysis. Data from these samples would revolutionize the ability to assign exposure ages to rocky planetary surfaces based on the samples returned by Apollo and Luna. Their petrology and geochemistry will enable assessment of the most recent voluminous lunar magmatism. Regolith evolution and mixing models such as ballistic sedimentation would be directly testable to provide crucial ground truth that would enhance the science value of current and future remotely sensed data sets. ISOCHRON's science goals support NASA's Artemis program to return to the Moon and its related robotic programs currently in planning.

Keywords: lunar geochronology; lunar petrology; lunar craters; planetary science; planetary probes
Herschel 158 μm [{C} {II}}] Observations of "CO-dark" Gas in the Perseus Giant Molecular Cloud

We present observations of velocity-resolved [C II] 158 μm emission from both a dense and a more diffuse photodissociation region (PDR) in the Perseus giant molecular cloud using the Heterodyne Instrument for the Far-Infrared on board the Herschel Space Telescope. We detect [C II] emission from 80% of the total positions, with a 95% detection rate from the dense boundary region. The integrated intensity of the [C II] emission remains relatively constant across each boundary, despite the observed range in optical extinction between 1 and 10 mag. This flat profile indicates a constant heating and cooling rate within both regions observed. The integrated intensity of [C II] emission is reasonably well correlated with the neutral hydrogen (H I) column density, as well as the total gas column density. This, in addition to the 80' (7 pc) extent of the [C II] emission from the cloud center, suggests that the H I envelope plays a dominant role in explaining the [C II] emission emanating from Perseus. We compare the [C II] and 12CO integrated intensities with predictions from a 1D, two-sided slab PDR model and show that a simple core + envelope, equilibrium model without an additional "CO-dark" H2 component can reproduce observations well. Additional observations are needed to disentangle how much of the [C II] emission is associated with the "CO-dark" H2 gas, as well as constrain spatial variations of the dust-to-gas ratio across Perseus.

Keywords: giant molecular clouds; interstellar clouds; molecular gas; diffuse molecular clouds; dark interstellar clouds; photodissociation regions; astronomy data modeling; astronomy data analysis; far infrared astronomy
A Mean Density of 112 M⊙ pc-3 for Central Molecular Zone Clumps—Evidences for Shear-enabled Pressure Equilibrium in the Galactic Center

We carry out a systematic study of the density structure of gas in the Central Molecular Zone (CMZ) in the Galactic center by extracting clumps from the APEX Telescope Large Area Survey of the Galaxy survey at 870 μm. We find that the clumps follow a scaling of m = ρ0r3, which corresponds to a characteristic density of ${n}_{{{\rm{H}}}_{2}}=1.6\times {10}^{3}\,{\mathrm{cm}}^{-3}$ (ρ0 = 112 M⊙ pc-3) with a variation of ≈0.5 dex, where we assumed a gas-to-dust mass ratio of 100. This characteristic density can be interpreted as the result of thermal pressure equilibrium between the molecular gas and the warm ambient interstellar medium. Such an equilibrium can plausibly be established since shear has approximately the same strength as self-gravity. Our findings may explain the fact that star formation in the CMZ is highly inefficient compared to the rest of the Milky Way disk. We also identify a population of clumps whose densities are two orders of magnitudes higher in the vicinity of the Sgr B2 region, which we propose are produced by collisions between the clumps of lower densities. For these collisions to occur, processes such as compressive tides probably have created the appropriate condition by assembling the clumps together.

Keywords: galactic center; gravitational collapse; star formation; interstellar medium; tidal interaction
OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt

We investigate different conditions, including the orbital and size-frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor-target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s-1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion.

Keywords: trans-neptunian objects; collisional processes; kuiper belt; planetesimals
Recurring Outbursts of P/2019 LM4 (Palomar)

We present a preliminary analysis of comet P/2019 LM4 (Palomar) as observed by the Zwicky Transient Facility (ZTF) survey in 2019 and 2020. We find that the discovery of the comet in 2019 and the recovery in 2020 is largely attributed to two separate outbursts that are ≳2 and ≳3.9 mag in strength. The two outbursts occurred between the end of April and early May in 2019, and between 2020 May 8.31 and 9.52 UTC.

Keywords: comets; short period comets
Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No Evidence for Temporal Variation of the Spin-Orbit Angle

We present 12 new transit light curves and 16 new out-of-transit radial-velocity measurements for the XO-3 system. By modeling our newly collected measurements together with archival photometric and Doppler velocimetric data, we confirmed the unusual configuration of the XO-3 system, which contains a massive planet ( ${M}_{{\rm{P}}}={11.92}_{-0.63}^{+0.59}\,\,{\text{}}{M}_{{\rm{J}}}$ ) on a relatively eccentric ( $e={0.2853}_{-0.0026}^{+0.0027}$ ) and short-period (3.19152 ± 0.00145 day) orbit around a massive star ( ${M}_{* }={1.219}_{-0.095}^{+0.090}{M}_{\odot }$ ). Furthermore, we find no strong evidence for a temporal change of either $V\sin {i}_{* }$ (and by extension, the stellar spin vector of XO-3), or the transit profile (and thus orbital angular momentum vector of XO-3b). We conclude that the discrepancy in previous Rossiter-McLaughlin measurements (70.0° ± 15.0°; Hébrard et al. 2008; 37.3° ± 3.7°; Winn et al. 2009; 37.3° ± 3.0°; Hirano et al. 2011) may have stemmed from systematic noise sources.

Keywords: exoplanets
Spectroscopic and Photometric Monitoring of a Poorly Known Highly Luminous OH/IR Star: IRAS 18278+0931

We present the time-dependent properties of a poorly known OH/IR star, IRAS 18278+0931 (hereafter IRAS 18+09), toward the Ophiuchus constellation. We have carried out long-term optical/near-infrared photometric and spectroscopic observations to study the object. From optical R- and I-band light curves, the period of IRAS 18+09 is estimated to be 575 ± 30 days and the variability amplitudes range from ΔR ∼ 4.0 mag to ΔI ∼ 3.5 mag. From the standard period-luminosity relations, the distance (D) to the object, 4.0 ± 1.3 kpc, is estimated. Applying this distance in the radiative transfer model, the spectral energy distribution is constructed from multiwavelength photometric and IRAS-LRS spectral data, which provide the luminosity, optical depth, and gas mass-loss rate of the object to be 9600 ± 500 L⊙, 9.1 ± 0.6 at 0.55 μm, and 1.0 × 10-6 M⊙ yr-1, respectively. The current mass of the object is inferred to be in the range 1.0-1.5 M⊙ assuming solar metallicity. Notably, the temporal variation of atomic and molecular features (e.g., TiO, Na I, Ca I, CO, H2O) over the pulsation cycle of the OH/IR star illustrates the sensitivity of the spectral features to the dynamical atmosphere as observed in pulsating AGB stars.

Keywords: oh/ir stars; long period variable stars; spectroscopy; asymptotic giant branch stars; late-type stars; observational astronomy; evolved stars; period determination; near infrared astronomy; stellar astronomy
Toward an Optimal Reconstruction of the Shear Field with PDF-folding

Weak lensing provides a direct way of mapping the density distribution in the Universe. To reconstruct the density field from the shear catalog, an important step is to build the shear field from the shear catalog, which can be quite nontrivial due to the inhomogeneity of the background galaxy distribution and the shape noise. We propose the PDF-folding method as a statistically optimal way of reconstructing the shear field. It is an extention of the PDF-SYM method, which was previously designed for optimizing the stacked shear signal as well as the shear-shear correlation for the Fourier_Quad shear estimators. PDF-folding does not require smoothing kernels as in traditional methods, therefore it suffers less information loss on small scales and avoids possible biases due to the spatial variation in the shear on the scale of the kernel. We show with analytic reasoning as well as numerical examples that the new method can reach the optimal signal-to-noise ratio on the reconstructed shear map under general observing conditions, i.e., with inhomogeneous background densities or masks. We also show the performance of the new method on real data around foreground galaxy clusters.

Keywords: weak gravitational lensing; gravitational lensing shear
Modeling of Thermal Emission from ULX Pulsar Swift J0243.6+6124 with General Relativistic Radiation MHD Simulations

We perform general relativistic radiation magnetohydrodynamics simulations of super-Eddington accretion flows around a neutron star with a dipole magnetic field for modeling the Galactic ultraluminous X-ray source exhibiting X-ray pulsations, Swift J0243.6+6124. Our simulations show the accretion columns near the magnetic poles, the accretion disk outside the magnetosphere, and the outflows from the disk. It is revealed that the effectively optically thick outflows, consistent with the observed thermal emission at ~107 K, are generated if the mass accretion rate is much higher than the Eddington rate ${\dot{M}}_{\mathrm{Edd}}$ and the magnetospheric radius is smaller than the spherization radius. In order to explain the blackbody radius (~100-500 km) without contradicting the reported spin period (9.8 s) and spin-up rate ( $\dot{P}=-2.22\times {10}^{-8}\,{\rm{s}}\,{{\rm{s}}}^{-1}$ ), a mass accretion rate of $(200\mbox{--}1200){\dot{M}}_{\mathrm{Edd}}$ is required. Since the thermal emission was detected in two observations with $\dot{P}$ of -2.22 × 10-8 s s-1 and -1.75 × 10-8 s s-1 but not in another with $\dot{P}=-6.8\times {10}^{-9}\,{\rm{s}}\,{{\rm{s}}}^{-1}$ , the surface magnetic field strength of the neutron star in Swift J0243.6+6124 is estimated to be between 3 × 1011 G and 4 × 1012 G. From this restricted range of magnetic field strength, the accretion rate would be $(200\mbox{--}500){\dot{M}}_{\mathrm{Edd}}$ when the thermal emission appears and $(60\mbox{--}100){\dot{M}}_{\mathrm{Edd}}$ when it is not detected. Our results support the hypothesis that the super-Eddington phase in the 2017-2018 giant outburst of Swift J0243.6+6124 is powered by highly super-Eddington accretion flows onto a magnetized neutron star.

Keywords: neutron stars; radiative magnetohydrodynamics; general relativity; x-ray sources; accretion; high energy astrophysics
Hurricane Genesis is Favorable on Terrestrial Exoplanets Orbiting Late-type M Dwarf Stars

Hurricanes are one of the most extreme storm systems that occur on Earth, characterized by strong rainfall and fast winds. The terrestrial exoplanets that will be characterized with future infrared space telescopes orbit M dwarf stars. As a result, the best observable terrestrial exoplanets have vastly different climates from Earth, with a large dayside-to-nightside irradiation contrast and relatively slow rotation. Hurricanes may affect future observations of terrestrial exoplanets because they enhance the vertical transport of water vapor and could influence ocean heat transport. In this work, we explore how the environment of terrestrial exoplanets orbiting M dwarf stars affects the favorability of hurricane genesis (formation). To do so, we apply metrics developed to understand hurricane genesis on Earth to three-dimensional climate models of ocean-covered exoplanets orbiting M dwarf stars. We find that hurricane genesis is most favorable on intermediate-rotating tidally locked terrestrial exoplanets with rotation periods of ∼8-10 days. As a result, hurricane genesis is most favorable for terrestrial exoplanets in the habitable zones of late-type M dwarf stars. The peak in the favorability of hurricane genesis at intermediate rotation occurs because sufficient spin is required for hurricane genesis, but the vertical wind shear on fast-rotating terrestrial exoplanets disrupts hurricane genesis. We find that hurricane genesis is less favorable on slowly rotating terrestrial exoplanets, which agrees with previous work. Future work using simulations that resolve hurricane genesis and evolution can test our expectations for how the environment affects the favorability of hurricane genesis on tidally locked terrestrial exoplanets.

Keywords: exoplanet atmospheres; atmospheric circulation; extrasolar rocky planets; habitable planets