adsabs/SciX_UAT_keywords huggingface dataset:
Constraining X-Ray Variability of the Blazar 3C 273 Using XMM-Newton Observations over Two Decades

Blazars exhibit relentless variability across diverse spatial and temporal frequencies. The study of long- and short-term variability properties observed in the X-ray band provides insights into the inner workings of the central engine. In this work, we present timing and spectral analyses of the blazar 3C 273 using the X-ray observations from the XMM-Newton telescope covering the period from 2000 to 2020. The methods of timing analyses include estimation of fractional variability, long- and short-term flux distribution, rms-flux relation, and power spectral density analysis. The spectral analysis include estimating a model-independent flux hardness ratio and fitting the observations with multiplicative and additive spectral models such as power law, log-parabola, broken power law, and blackbody. The blackbody represents the thermal emission from the accretion disk, while the other models represent the possible energy distributions of the particles emitting synchrotron radiation in the jet. During the past two decades, the source flux changed by a factor of three, with a considerable fractional variability of 27%. However, the intraday variation was found to be moderate. Flux distributions of the individual observations were consistent with a normal or log-normal distribution, while the overall flux distribution including all observations appears to be rather multimodal and of a complex shape. The spectral analyses indicate that a log-parabola added to a blackbody gives the best fit for most of the observations. The results indicate a complex scenario in which the variability can be attributed to the intricate interaction between the disk/corona system and the jet.

Keywords: active galactic nuclei; flat-spectrum radio quasars; blazars; supermassive black holes; quasars; relativistic jets; non-thermal radiation sources
A Reference Meteor Magnitude for Intercomparable Fluxes

The rate at which meteors pass through Earth's atmosphere has been measured or estimated many times over; existing flux measurements span at least 12 astronomical magnitudes, or roughly five decades in mass. Unfortunately, the common practice of scaling flux to a universal reference magnitude of +6.5 tends to collapse the magnitude or mass dimension. Furthermore, results from different observation networks can appear discrepant due solely to the use of different assumed population indices, and readers cannot resolve this discrepancy without access to magnitude data. We present an alternate choice of reference magnitude that is representative of the observed meteors and minimizes the dependence of flux on population index. We apply this choice to measurements of recent Orionid meteor shower fluxes to illustrate its usefulness for synthesizing independent flux measurements.

Keywords: meteor showers; meteors
High-resolution Study of Planetesimal Formation by Gravitational Collapse of Pebble Clouds

Planetary embryos are built through the collisional growth of 10-100 km-sized objects called planetesimals, a formerly large population of objects, of which asteroids, comets, and Kuiper Belt objects represent the leftovers from planet formation in our solar system. Here, we follow the paradigm that turbulence created overdense pebble clouds, which then collapse under their own self-gravity. We use the multiphysics code GIZMO to model the pebble cloud density as a continuum, with a polytropic equation of state to account for collisional interactions and capturing the phase transition to a quasi-incompressible "solid" object, i.e., a planetesimal in hydrostatic equilibrium. Thus, we study cloud collapse effectively at the resolution of the forming planetesimals, allowing us to derive an initial mass function for planetesimals in relation to the total pebble mass of the collapsing cloud. The redistribution of angular momentum in the collapsing pebble cloud is the main mechanism leading to multiple fragmentation. The angular momentum of the pebble cloud and thus the centrifugal radius increases with distance to the Sun, but the solid size of the forming planetesimals is constant. Therefore we find that with increasing distance to the Sun, the number of forming planetesimals per pebble cloud increases. For all distances, the formation of binaries occurs within higher hierarchical systems. The size distribution is top-heavy and can be described with a Gaussian distribution of planetesimal mass. For the asteroid belt, we can infer a most likely size of 125 km, all stemming from pebble clouds of equivalent size 152 km.

Keywords: asteroids; small solar system bodies; kuiper belt; planet formation; planetesimals; protoplanetary disks
Shocks in Radiatively Driven Time-dependent, Relativistic Jets around Black Holes

We study time-dependent relativistic jets under the influence of the radiation field of the accretion disk. The accretion disk consists of an inner compact corona and an outer sub-Keplerian disk. The thermodynamics of the fluid is governed by a relativistic equation of state (EOS) for multispecies fluid that enables us to study the effect of composition on jet dynamics. Jets originate from the vicinity of the central black hole, where the effect of gravity is significant and traverses large distances where only special relativistic treatment is sufficient. So we have modified the flat metric to include the effect of gravity. In this modified relativistic framework we have developed a new total variation diminishing routine along with a multispecies EOS for the purpose. We show that the acceleration of jets crucially depends on flow composition. All the results presented are transonic in nature; starting from very low injection velocities, the jets can achieve high Lorentz factors. For sub-Eddington luminosities, lepton-dominated jets can be accelerated to Lorentz factors >50. The change in radiation field due to variation in the accretion disk dynamics will be propagated to the jet in a finite amount of time. Hence, any change in radiation field due to a change in disk configuration will affect the lower part of the jet before it affects the outer part. This can drive shock transition in the jet flow. Depending on the disk oscillation frequency, amplitude, and jet parameters, these shocks can collide with each other and may trigger shock cascades.

Keywords: hydrodynamics; computational methods; relativistic jets; black hole physics
Gaia EDR3 Proper Motions of Milky Way Dwarfs. I. 3D Motions and Orbits

Based on Gaia Early Data Release 3 (EDR3), we estimate the proper motions of 46 dwarf galaxies of the Milky Way (MW). The uncertainties in proper motions, determined by combining both statistical and systematic errors, are smaller by a factor of 2.5 when compared with Gaia Data Release 2. We have derived orbits in four MW potential models that are consistent with the MW rotation curve, with total mass ranging from 2.8 × 1011 M⊙ to 15 × 1011 M⊙. Although the type of orbit (ellipse or hyperbola) are very dependent on the potential model, the pericenter values are firmly determined, largely independent of the adopted MW mass model. By analyzing the orbital phases, we found that the dwarf galaxies are highly concentrated close to their pericenter, rather than to their apocenter as expected from Kepler's law. This may challenge the fact that most dwarf galaxies are MW satellites, or alternatively indicates an unexpectedly large number of undiscovered dwarf galaxies lying very close to their apocenters. Between half and two-thirds of the satellites have orbital poles that indicate them to orbit along the vast polar structure, with the vast majority of these co-orbiting in a common direction also shared by the Magellanic Clouds, which is indicative of a real structure of dwarf galaxies.

Keywords: dwarf galaxies; galaxy kinematics; galaxy dynamics
Is a Recently Discovered H I Cloud near M94 a Starless Dark Matter Halo?

Observations with the Five-hundred-meter Aperture Spherical Telescope have revealed the presence of a marginally resolved source of 21 cm emission from a location $\sim 50^{\prime} $ from the M94 galaxy, without a stellar counterpart down to the surface brightness limit of the DESI Imaging Legacy Survey (~29.15 mag arcsec-2 in the g band). The system (hereafter Cloud-9) has round column density isocontours and a line width consistent with thermal broadening from gas at T ~ 2 × 104 K. These properties are unlike those of previously detected dark H I clouds and similar to the expected properties of REionization-Limited-H I Clouds (RELHICs), namely, starless dark matter (DM) halos filled with gas in hydrostatic equilibrium and in thermal equilibrium with the cosmic ultraviolet background. At the distance of M94, d ~ 4.7 Mpc, we find that Cloud-9 is consistent with being a RELHIC inhabiting a Navarro-Frenk-White (NFW) DM halo of mass M 200 ~ 5 × 109 M ⊙ and concentration c NFW ~ 13. Although the agreement between the model and observations is good, Cloud-9 appears to be slightly, but systematically, more extended than expected for ΛCDM RELHICs. This may imply either that Cloud-9 is much closer than implied by its recessional velocity, v CL9 ~ 300 km s-1, or that its halo density profile is flatter than NFW, with a DM mass deficit greater than a factor of 10 at radii r ≲ 1 kpc. Further observations may aid in constraining these scenarios better and help elucidate whether Cloud-9 is the first ever observed RELHIC, a cornerstone prediction of the ΛCDM model on the smallest scales.

Keywords: cosmology; reionization; dark matter
Insights into Neutron Star Equation of State by Machine Learning

Due to its powerful capability and high efficiency in big data analysis, machine learning has been applied in various fields. We construct a neural network platform to constrain the behaviors of the equation of state of nuclear matter with respect to the properties of nuclear matter at saturation density and the properties of neutron stars. It is found that the neural network is able to give reasonable predictions of parameter space and provide new hints into the constraints of hadron interactions. As a specific example, we take the relativistic mean field approximation in a widely accepted Walecka-type model to illustrate the feasibility and efficiency of the platform. The results show that the neural network can indeed estimate the parameters of the model at a certain precision such that both the properties of nuclear matter around saturation density and global properties of neutron stars can be saturated. The optimization of the present modularly designed neural network and extension to other effective models is straightforward.

Keywords: neural networks
FEASTS: IGM Cooling Triggered by Tidal Interactions through the Diffuse H I Phase around NGC 4631

We use the single-dish radio telescope Five-hundred meter Aperture Spherical Telescope (FAST) to map the H I in the tidally interacting NGC 4631 group with a resolution of 3.'24 (7 kpc), reaching a 5σ column density limit of 1017.9 cm-2 assuming a line width of 20 km s-1. Taking the existing interferometric H I image from the Hydrogen Accretion in LOcal GAlaxieS project of Westerbork Synthesis Radio Telescope as a reference, we are able to identify and characterize a significant excess of large-scale, low-density, and diffuse H I in the group. This diffuse H I extends more than 120 kpc across, and accounts for more than one-fourth of the total H I detected by FAST in and around the galaxy NGC 4631. In the region of the tidal tails, the diffuse H I has a typical column density above 1019.5 cm-2, and is highly turbulent with a velocity dispersion of around 50 km s-1. It increases in column density with the dense H I, and tends to be associated with the kinematically hotter part of the dense H I. Through simple modeling, we find that the majority of the diffuse H I in the tail region is likely to induce cooling out of the hot intragalactic medium (IGM) instead of evaporating or being radiatively ionized. Given these relations of gas in different phases, the diffuse H I may represent a condensing phase of the IGM. Ongoing and past active tidal interactions may have produced the wide-spreading H I distribution, and triggered the gas accretion to NGC 4631 through the phase of the diffuse H I.

Keywords: intergalactic medium; neutral hydrogen clouds; galaxy accretion; galaxy evolution
The Dragonfly Edge-on Galaxies Survey: Shaping the Outer disk of NGC 4565 via Accretion

We present deep g- and r-band imaging of the well-known edge-on galaxy NGC 4565 (the "Needle Galaxy"), observed as part of the Dragonfly Edge-on Galaxies Survey. The 3σ local surface brightness contrast limit on 10″ scales is 28.616 ± 0.005 mag arcsec-2 for the r-band image and 28.936 ± 0.005 mag arcsec-2 for the g-band image. We trace the galaxy's starlight in narrow slice profiles spanning over 90 kpc along the major axis (with bin sizes ranging from 1.7 × 0.5 to 1.7 × 7.8 kpc) to surface brightnesses below 29 mag arcsec-2. We confirm the previously observed asymmetric disk truncation in NGC 4565. In addition, the sharp northwest truncation turns over to a shallower component that coincides with a fan-like feature seen to wrap around the northwest disk limb. We propose that the fan may be a tidal ribbon and qualitatively replicate the fan with simple simulations, although alternative explanations of the fan and the disk's asymmetry are shown to be possible. In any case, we conclude that there is strong evidence for accretion-based outer disk growth in NGC 4565.

Keywords: disk galaxies; galaxy evolution; spiral galaxies
Pre-common-envelope Mass Loss from Coalescing Binary Systems

Binary systems undergoing unstable Roche Lobe overflow spill gas into their circumbinary environment as their orbits decay toward coalescence. In this paper, we use a suite of hydrodynamic models of coalescing binaries involving an extended donor and a more compact accretor. We focus on the period of unstable Roche Lobe overflow that ends as the accretor plunges within the envelope of the donor at the onset of a common envelope phase. During this stage, mass is removed from the donor and flung into the circumbinary environment. Across a wide range of binary mass ratios, we find that the mass expelled as the separation decreases from the Roche limit to the donor's original radius is of the order of 25% of the accretor's mass. We study the kinematics of this ejecta and its dependencies on binary properties and find that it assembles into a toroidal circumbinary distribution. These circumbinary tori have approximately constant specific angular momenta due to momentum transport by spiral shocks launched from the orbiting binary. We show that an analytic model with these torus properties captures many of the main features of the azimuthally averaged profiles of our hydrodynamic simulations. Our results, in particular the simple relationship between accretor mass and expelled mass and its spatial distribution, may be useful for interpreting stellar coalescence transients like luminous red novae and initializing hydrodynamic simulations of the subsequent common envelope phase.

Keywords: common envelope evolution; interacting binary stars; hydrodynamical simulations
Elemental Abundances of Prominence Material inside ICMEs

A small number of interplanetary coronal mass ejections (ICMEs) have been identified that contain measurable contributions from prominence plasma. In situ measurements from during these events are marked by the presence of unusually low-charge states of C, O, and Fe, representing ionization equilibrium formation temperatures of ∼104-105 K, consistent with prominence material observed at the Sun. We present a thorough analysis of the elemental abundances of a wide variety of heavy ions, measured by Advanced Composition Explorer/SWICS, in prominence material observed in the solar wind. We find that prominence material observed in situ tends to be more enriched in heavy ions than the surrounding ICME plasma and the fast and slow solar wind. We also find that the material is on average moderately enhanced in low first ionization potential elements compared to photospheric abundances, with values that lie between fast and slow solar wind. In rare instances, where in situ prominence material is observed to have clear, persistent, low-charge states over longer periods of time, it exhibits elemental abundances that are photospheric in nature. However, in most prominence events we see indications that the associated material contains a mixture of prominence and adjacent ICME plasma. The anomalous behavior of the elemental and ionic composition in ICMEs with and without prominence material can be used to study physical processes that occur during CME initiation and release.

Keywords: heliosphere; solar wind; solar coronal mass ejections; solar prominences; solar filaments
Understanding the Lunar Nearside-Farside Dichotomy via In Situ Trace Element Measurements: The Scientific Framework of a Prospective Landed Mission

Trace elements, distinguished by their low abundances (parts per million by weight (ppmw)), track local, regional, and planetary-scale processes in samples sourced from throughout the solar system. Such analyses of lunar samples have provided insights on its surface rocks and interpretations of its deep interior. However, returned samples, sourced from the lunar nearside, cannot be used to address processes responsible for the morphological dichotomy between the lunar nearside and farside. The hemispherical dichotomy points to distinct evolutionary histories of these two domains, rendering our understanding of lunar history incomplete. We outline the scientific justification for a landed, in situ investigation of lunar farside lithologies, focusing on chemical analyses that will constrain the Moon's bi-hemispherical chemical evolution. Newly developed and heritage spaceflight instruments, capable of measuring low element abundances (limits of detection <10 ppmw ± 20%), can be deployed on the lunar farside and provide constraints on (1) the temperature and pressure of mare basalt crystallization, (2) depth-dependent mineralogical and compositional changes in the lunar mantle, (3) the chronology of major geologic events, and (4) abundances and distributions of refractory and heat-producing elements of the lunar farside mantle. The science return and logistical challenges of targeting four specific landing sites on the lunar farside are identified: Moscoviense, Apollo, Von Kármán, and Leibnitz craters. These sites maximize impact melt basin lithologies and later mare magmatism, and they minimize terrain hazards.

Keywords: earth-moon system; mantle
The Infrared Spectrum of Protonated C70

With the detection of C60, C70, and ${{\rm{C}}}_{60}^{+}$ in the interstellar medium, fullerenes are currently the largest molecules identified in space. The relatively high proton affinities of C60 and C70 support the hypothesis that protonated fullerenes may also be abundant in the interstellar matter. Here, we present the first experimental vibrational spectrum of C70H+, recorded in the gas phase. The attachment of a proton to C70 causes a drastic symmetry lowering, which results in a rich vibrational spectrum. As compared to C60, where all C-atoms are equivalent due to the icosahedral symmetry, C70 belongs to the D5h point group and has five nonequivalent C-atoms, which are available as protonation sites. Combined analysis of the experimental spectrum and spectra computed at the density functional theory level enables us to evaluate the protonation isomers being formed. We compare the IR spectra of C60H+ and C70H+ to IR emission spectra from planetary nebulae, which suggests that a mixture of these fullerene analogs could contribute to their IR emission.

Keywords: molecular spectroscopy; laboratory astrophysics; interstellar medium
Quasar Accretion Disk Sizes from Continuum Reverberation Mapping in the DES Standard-star Fields

Measurements of the physical properties of accretion disks in active galactic nuclei are important for better understanding the growth and evolution of supermassive black holes. We present the accretion disk sizes of 22 quasars from continuum reverberation mapping with data from the Dark Energy Survey (DES) standard-star fields and the supernova C fields. We construct continuum light curves with the griz photometry that span five seasons of DES observations. These data sample the time variability of the quasars with a cadence as short as 1 day, which corresponds to a rest-frame cadence that is a factor of a few higher than most previous work. We derive time lags between bands with both JAVELIN and the interpolated cross-correlation function method and fit for accretion disk sizes using the JAVELIN thin-disk model. These new measurements include disks around black holes with masses as small as ∼107 M⊙, which have equivalent sizes at 2500 Å as small as ∼0.1 lt-day in the rest frame. We find that most objects have accretion disk sizes consistent with the prediction of the standard thin-disk model when we take disk variability into account. We have also simulated the expected yield of accretion disk measurements under various observational scenarios for the Large Synoptic Survey Telescope Deep Drilling Fields. We find that the number of disk measurements would increase significantly if the default cadence is changed from 3 days to 2 days or 1 day.

Keywords: quasars; supermassive black holes; accretion; active galactic nuclei; reverberation mapping
High-sensitivity Beamformed Observations of the Crab Pulsar's Radio Emission

We analyzed four epochs of beamformed European VLBI Network data of the Crab Pulsar at 1658.49 MHz. With the high sensitivity resulting from resolving out the Crab Nebula, we are able to detect even the faint high-frequency components in the folded profile. We also detect a total of 65,951 giant pulses, which we use to investigate the rates, fluence, phase, and arrival time distributions. We find that for the main pulse component, our giant pulses represent about 80% of the total flux. This suggests we have a nearly complete giant pulse energy distribution, although it is not obvious how the observed distribution could be extended to cover the remaining 20% of the flux without invoking large numbers of faint bursts for every rotation. Looking at the difference in arrival time between subsequent bursts in single rotations, we confirm that the likelihood of finding giant pulses close to each other is increased beyond that expected for randomly occurring bursts-some giant pulses consist of causally related microbursts, with typical separations of ~30 μs-but also find evidence that at separations ≳100 μs the likelihood of finding another giant pulse is suppressed. In addition, our high sensitivity enabled us to detect weak echo features in the brightest pulses (at ~0.4% of the peak giant pulse flux), which are delayed by up to ~300 μs.

Keywords: pulsars; radio bursts; very long baseline interferometry