adsabs/SciX_UAT_keywords huggingface dataset:
Investigating the Impact of Vertically Extended Coronae on X-Ray Reverberation Mapping

Accreting black holes commonly exhibit hard X-ray emission, originating from a region of hot plasma near the central engine referred to as the corona. The origin and geometry of the corona are poorly understood, and models invoking either inflowing or outflowing material (or both) can successfully explain only parts of the observed phenomenology. In particular, recent works indicate that the time-averaged and variability property might originate in different regions of the corona. In this paper we present a model designed to move beyond the lamppost paradigm, with the goal of accounting for the vertical extent of the corona. In particular, we highlight the impact of including self-consistently a second lamppost, mimicking, for example, an extended jet base. We fully include the effect that the second source has on the time-dependent disk ionization, reflection spectrum, and reverberation lags. We also present an application of this new model to NICER observations of the X-ray binary MAXI J1820+070 near its hard-to-soft state transition. We demonstrate that in these observations, a vertically extended corona can capture both spectral and timing properties, while a single-lamppost model can not. In this scenario, the illumination responsible for the time-averaged spectrum originates close to the black hole, while the variability is likely associated with the ballistic jet.

Keywords: accretion; black hole physics; reverberation mapping
TT-HEALpix: A New Data Indexing Strategy for Efficient Cross-match of Large-scale Astronomical Catalogs

Cross-matching is an indispensable operation in the data preparation, analysis, and research processes of multi-band astronomy and time-domain astronomy. Multi-catalog time-series data reconstruction is an important part of time-domain astronomy. In the large-scale distributed reconstruction process, boundary problems have always affected the accuracy of time-series data. To optimize these boundary problems and improve data precision, this paper proposes a new hybrid astronomical data indexing method called Translated Transformation based HEALPix Dual Index (TT-HEALPix). Under the reasonable Healpix division level, by translation transformation, the two indexes before and after the transformation form a unique pseudo-hybrid index strategy, which not only retains the advantages of the hybrid index scheme suitable for large-scale parallel computing, but also compensates for its shortage of high omission at the block boundary position. Based on TT-HEALPix, this paper completes the multi-catalog time-series reconstruction process on the Spark platform and compares it with the HEALPix+HTM hybrid indexing strategy. The experiments demonstrate that TT-HEALPix has significant advantages over the traditional HEALPix+HTM hybrid indexing method in terms of data accuracy and cross-matching efficiency. At level 9 of the Healpix index, TT-HEALPix achieves a 6%–19% improvement in cross-matching efficiency in a distributed environment compared to HEALPix+HTM. In terms of data accuracy, for the AST3-II dataset at level 9, TT-HEALPix has 62.2% accuracy improvement over HEALPix and 45.5% improvement over HEALPix+HTM. In conclusion, the proposed novel indexing strategy, TT-HEALPix, is better suited to the efficiency and accuracy requirements of cross-match.

Keywords: astronomy data analysis; catalogs; public domain software
On the Likely Dynamical Origin of GW191109 and Binary Black Hole Mergers with Negative Effective Spin

With the growing number of binary black hole (BBH) mergers detected by LIGO/Virgo/KAGRA, several systems have become difficult to explain via isolated binary evolution, having components in the pair-instability mass gap, high orbital eccentricities, and/or spin-orbit misalignment. Here we focus on GW191109_010717, a BBH merger with component masses of ${65}_{-11}^{+11}$ and ${47}_{-13}^{+15}$ M ⊙ and an effective spin of $-{0.29}_{-0.31}^{+0.42}$ , which could imply a spin-orbit misalignment of more than π/2 rad for at least one of its components. Besides its component masses being in the pair-instability mass gap, we show that isolated binary evolution is unlikely to reproduce the proposed spin-orbit misalignment of GW191109 with high confidence. On the other hand, we demonstrate that BBHs dynamically assembled in dense star clusters would naturally reproduce the spin-orbit misalignment and masses of GW191109 and the rates of GW191109-like events if at least one of the components were to be a second-generation BH. Finally, we generalize our results to all events with a measured negative effective spin, arguing that GW200225 also has a likely dynamical origin.

Keywords: gravitational wave sources; black holes
An Analysis of Glacial and Fluvial Morphologies within Impact Craters in the Equatorial Region in Arabia Terra, Mars

Arabia Terra is an ancient and large terrain which is located north of the Martian equator. Due to its ancient nature, it is heavily cratered, and these craters hold evidence of geologic processes during Mars' history. During periods of high obliquity (>35°) it has been suggested that polar ice migration can occur at the lower latitudes. By investigating the impact craters within a localized area in the equatorial region of Arabia Terra, it can be determined how far this migration once occurred. This study aimed to investigate craters ≥1 km in diameter within the 0°N-10°N, 340°E-350°E area of Arabia Terra and determine the frequency of glacial and fluvial morphologies within this region. We divided the search area into two sections, 0°N-5°N, 340°E-350°E and 5°N-10°N, 340°E-350°E, to help identify any latitudinal variations between the glacial and fluvial morphologies.

Keywords: mars; craters; glaciers
The Collisional Evolution of the Primordial Kuiper Belt, Its Destabilized Population, and the Trojan Asteroids

The tumultuous early era of outer solar system evolution culminated when Neptune migrated across the primordial Kuiper Belt (PKB) and triggered a dynamical instability among the giant planets. This event led to the ejection of ∼99.9% of the PKB (here called the destabilized population), heavy bombardment of the giant planet satellites, and the capture of Jupiter's Trojans. While this scenario has been widely tested using dynamical models, there have been fewer investigations into how the PKB, its destabilized population, and the Trojans experienced collisional evolution. Here we examined this issue for all three populations with the code Boulder. Our constraints included the size–frequency distributions (SFDs) of the Trojan asteroids and craters on the giant planet satellites. Using this combination, we solved for the unknown disruption law affecting bodies in these populations. The weakest ones, from an impact energy per mass perspective, were diameter D ∼ 20 m. Overall, collisional evolution produces a power-law-like shape for multikilometer Trojans and a wavy-shaped SFD in the PKB and destabilized populations. The latter can explain (i) the shapes of the ancient and younger crater SFDs observed on the giant planet satellites, (ii) the shapes of the Jupiter family and long-period comet SFDs, which experienced different degrees of collision evolution, and (iii) the present-day impact frequency of superbolides on Jupiter and smaller projectiles on Saturn's rings. Our model results also indicate that many observed comets, the majority which are D < 10 km, are likely to be gravitational aggregates formed by large-scale collision events.

Keywords: kuiper belt; trans-neptunian objects; collisional processes; jupiter trojans; comet origins; jovian satellites; saturnian satellites; uranian satellites; long period comets; short period comets; dynamical evolution; plutonian satellites
Two-sided Loop Solar Jet Driven by the Eruption of a Small Filament in a Big Filament Channel

Similar to the cases of anemone jets, two-sided loop solar jets can also be produced by either flux emergence from the solar interior or small-scale filament eruptions. Using high-quality data from the Solar Dynamics Observatory, we have analyzed a two-sided loop solar jet triggered by the eruption of a small filament. The jet occurred in a pre-existing big filament channel. The detailed processes involved in the eruption of the small filament, the interaction between the erupted filament and the big filament channel, and the launch of the two-sided loop jet are presented. The observations further revealed notable asymmetry between the two branches of the jet spire: the northeastern branch is narrow and short, while the southern branch is wide and long and accompanied by discernible untwisting motions. We explored the unique appearance of the jet by employing the method of local potential field extrapolation to calculate the coronal magnetic field configuration around the jet. The photospheric magnetic flux below the small filament underwent cancellation for approximately 7 hr before the filament eruption, and the negative flux near the southern footpoint of the filament decreased by about 56% during this interval. Therefore, we propose that the primary photospheric driver of the filament eruption and the associated two-sided loop jet in this event is flux cancellation rather than flux emergence.

Keywords: solar activity; solar filament eruptions; solar magnetic fields
Properties of Electron-scale Magnetic Reconnection at a Quasi-perpendicular Shock

Recent spacecraft observations have shown that magnetic reconnection occurs commonly in turbulent environments at shocks. At quasi-perpendicular shocks, magnetic field lines are bent by the back-streaming reflected ions, which form a current sheet in the foot region, and then electron-scale reconnection occurs when the current sheet is fragmented at the shock front. Here we study magnetic reconnection at a quasi-perpendicular shock by using a two-dimensional particle-in-cell simulation. Collective properties of the reconnection sites from the shock transition to the downstream region are analyzed by adopting a statistical approach to the simulation data. Reconnecting current sheets are found to be densely distributed near the shock front, with a reconnection electric field larger than those in the downstream region. By tracing a reconnection site from its formation until it is convected downstream, we show the reconnection proceeds intermittently after an active stage near the shock front. Our tracing further shows that, in addition to being originated from the shock front, reconnection in the downstream region can also occur locally, driven by turbulent flows therein. The results help us better understand the evolution of electron-scale reconnection at a perpendicular shock.

Keywords: space plasmas; plasma physics; solar magnetic reconnection; planetary bow shocks
Dynamics of Plasma Turbulence at Earth's Bow Shock and through the Magnetosheath

Earth's magnetosheath can be treated as a natural laboratory to study turbulence development in confined space. The present study focuses on the characteristics of turbulent cascade downstream of the bow shock, where properties of turbulence are known to differ from those in the upstream solar wind. Characteristics of the turbulent spectrum are considered in two distinct points of the magnetosheath for two case studies. The analysis is based on high-resolution measurements of plasma parameters by the Spektr-R spacecraft and magnetic field data by the Themis/Arthemis mission. The measurements are performed for two distinct cases: in the dayside magnetosheath behind the quasi-perpendicular bow shock and in the nightside flank of the magnetosheath behind the quasi-parallel bow shock. The study focuses on the scales at which kinetic effects in plasma become significant and the turbulent spectrum is known to break. The analysis reveals that modification of the fluctuation spectrum at the bow shock is controlled by the distance of the measurement point from the bow shock's nose. Also, performed statistical results suggest the influence of the large-scale parameters of the upstream solar wind and the type of the bow shock on the turbulent spectrum's modification in the downstream region.

Keywords: solar-terrestrial interactions; magnetohydrodynamics; interplanetary turbulence; solar wind
Testing General Relativity with the Stellar-mass Black Hole in LMC X-1 Using the Continuum-fitting Method

The iron-line and continuum-fitting methods are currently the two leading techniques for measuring black-hole spins with electromagnetic radiation. They can be naturally extended for probing the spacetime geometry around black holes and testing general relativity in the strong field regime. In the past couple of years, there has been significant work to use the iron-line method to test the nature of black holes. Here we use the continuum-fitting method and we show its capability of constraining the spacetime geometry around black holes by analyzing 17 Rossi X-ray Timing Explorer data of the X-ray binary LMC X-1.

Keywords: x-ray astronomy; astrophysical black holes; kerr metric
Optimizing Numerical Simulations of Colliding Galaxies. I. Fitness Functions and Optimization Algorithms

Gravitational n-body models can be used to simulate the dynamical evolution of colliding galaxies. Given observational data in the form of images of the galaxies, we seek to estimate the true values of various dynamical parameters through the careful application of optimization methods. However, optimizing these models can be quite difficult due to (1) their expensive run-time, (2) the dimensionality and complexity of the parameter space which must be explored, (3) the presence of morphological symmetries which introduce many false extrema into the fitness landscape, and (4) the fact that the majority of orbital trajectories produce systems with little to no tidal features. To combat these issues, we have developed novel "two-factor" fitness functions for image similarity quantification and an adaptive genetic algorithm with crossover and mutation operators designed to handle parameter correlation. We test these methods by fitting to a synthetic target image.

Keywords: computational astronomy; computational methods
Uncertainties on Asteroid Albedos Determined by Thermal Modeling

We present an analysis of the accuracy of geometric albedos determined for asteroids through the modeling of observed thermal infrared radiation. We show that albedo uncertainty is dominated by the uncertainty on the measured HV absolute magnitude, and that any analysis using albedos in a statistical application will also be dominated by this source of uncertainty. For all but the small fraction of asteroids with a large amount of characterization data, improved knowledge of the HV magnitude will be fundamentally limited by incomplete phase-curve coverage, incomplete light-curve knowledge, and the necessary conversion from the observed band to the V band. Switching the absolute magnitude standard to a different band such a $r^{\prime} $ would mitigate the uncertainty due to band conversion for many surveys, but this only represents a small component of the total uncertainty. Therefore, techniques making use of these albedos must ensure that their uncertainties are properly accounted for.

Keywords: asteroids; photometry
Causes and Consequences of Magnetic Complexity Changes within Interplanetary Coronal Mass Ejections: A Statistical Study

We present the first statistical analysis of complexity changes affecting the magnetic structure of interplanetary coronal mass ejections (ICMEs), with the aim of answering the questions: How frequently do ICMEs undergo magnetic complexity changes during propagation? What are the causes of such changes? Do the in situ properties of ICMEs differ depending on whether they exhibit complexity changes? We consider multispacecraft observations of 31 ICMEs by MESSENGER, Venus Express, ACE, and STEREO between 2008 and 2014 while radially aligned. By analyzing their magnetic properties at the inner and outer spacecraft, we identify complexity changes that manifest as fundamental alterations or significant reorientations of the ICME. Plasma and suprathermal electron data at 1 au, and simulations of the solar wind enable us to reconstruct the propagation scenario for each event, and to identify critical factors controlling their evolution. Results show that ~65% of ICMEs change their complexity between Mercury and 1 au and that interaction with multiple large-scale solar wind structures is the driver of these changes. Furthermore, 71% of ICMEs observed at large radial (>0.4 au) but small longitudinal (<15°) separations exhibit complexity changes, indicating that propagation over large distances strongly affects ICMEs. Results also suggest that ICMEs may be magnetically coherent over angular scales of at least 15°, supporting earlier theoretical and observational estimates. This work presents statistical evidence that magnetic complexity changes are consequences of ICME interactions with large-scale solar wind structures, rather than intrinsic to ICME evolution, and that such changes are only partly identifiable from in situ measurements at 1 au.

Keywords: solar coronal mass ejections; solar wind; corotating streams; interplanetary magnetic fields
Square Root Compression and Noise Effects in Digitally Transformed Images

We report on a particular example of noise and data representation interacting to introduce systematic error into scientific measurements. Many instruments collect integer digitized values and apply nonlinear coding, in particular square root coding, to compress the data for transfer or downlink; this can introduce surprising systematic errors when they are decoded for analysis. Square root coding and subsequent decoding typically introduces a variable ±1 count value-dependent systematic bias in the data after reconstitution. This is significant when large numbers of measurements (e.g., image pixels) are averaged together. Using direct modeling of the probability distribution of particular coded values in the presence of instrument noise, one may apply Bayes' theorem to construct a decoding table that reduces this error source to a very small fraction of a digitizer step; in our example, systematic error from square root coding is reduced by a factor of 20 from 0.23 to 0.012 count rms. The method is suitable both for new experiments such as the upcoming PUNCH mission, and also for post facto application to existing data sets-even if the instrument noise properties are only loosely known. Further, the method does not depend on the specifics of the coding formula, and may be applied to other forms of nonlinear coding or representation of data values.

Keywords: astronomy data reduction; measurement error model; coronagraphic imaging; direct imaging
SuperBIT Superpressure Flight Instrument Overview and Performance: Near-diffraction-limited Astronomical Imaging from the Stratosphere

SuperBIT was a 0.5 m near-UV to near-infrared wide-field telescope that launched on a NASA superpressure balloon into the stratosphere from New Zealand for a 45-night flight. SuperBIT acquired multiband images of galaxy clusters to study the properties of dark matter using weak gravitational lensing. We provide an overview of the instrument and its various subsystems. We then present the instrument performance from the flight, including the telescope and image stabilization system, the optical system, the power system, and the thermal system. SuperBIT successfully met the instrument's technical requirements, achieving a telescope pointing stability of 0.″34 ± 0.″10, a focal plane image stability of 0.″055 ± 0.″027, and a point-spread function FWHM of ∼0.″35 over 5-minute exposures throughout the 45-night flight. The telescope achieved a near-diffraction-limited point-spread function in all three science bands (u, b, and g). SuperBIT served as a pathfinder to the GigaBIT observatory, which will be a 1.34 m near-UV to near-infrared balloon-borne telescope.

Keywords: high altitude balloons; galaxy clusters; space telescopes; gravitational lensing; weak gravitational lensing; astronomical instrumentation
The Evolution of the Cold Gas Fraction in Nearby Clusters' Ram-pressure-stripped Galaxies

Cluster galaxies are affected by the surrounding environment, which influences, in particular, their gas, stellar content, and morphology. In particular, the ram pressure exerted by the intracluster medium promotes the formation of multiphase tails of stripped gas detectable both at optical wavelengths and in the submillimeter and radio regimes, tracing the cold molecular and atomic gas components, respectively. In this work we analyze a sample of 16 galaxies belonging to clusters at redshift ~0.05 showing evidence of an asymmetric H I morphology (based on MeerKAT observations) with and without a star-forming tail. To this sample we add three galaxies with evidence of a star-forming tail and no H I detection. Here we present the galaxies' H2 gas content from APEX observations of the CO (2-1) emission. We find that in most galaxies with a star-forming tail the H2 global content is enhanced with respect to undisturbed field galaxies with similar stellar masses, suggesting an evolutionary path driven by the ram pressure stripping. As galaxies enter into the clusters, their H I is displaced but also partially converted into H2, so that they are H2 enriched when they pass close to the pericenter, that is, when they also develop the star-forming tails that are well visible in UV or B broad bands and in Hα emission. An inspection of the phase-space diagram for our sample suggests an anticorrelation between the H I and H2 gas phases as galaxies fall into the cluster potential. This peculiar behavior is a key signature of the ram pressure stripping in action.

Keywords: disk galaxies; galaxy clusters; galaxy evolution; late-type galaxies; spiral galaxies; galaxy environments; galaxy tails
Astrophysics Milestones for Pulsar Timing Array Gravitational-wave Detection

The NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its 12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of ${A}_{\mathrm{yr}}={1.92}_{-0.55}^{+0.75}\times {10}^{-15}$ . However, evidence for the quadrupolar Hellings & Downs interpulsar correlations, which are characteristic of gravitational-wave signals, was not yet significant. We emulate and extend the NANOGrav data set, injecting a wide range of stochastic gravitational-wave background (GWB) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones. (I) Given the amplitude measured in the 12.5 yr analysis and assuming this signal is a GWB, we expect to accumulate robust evidence of an interpulsar-correlated GWB signal with 15-17 yr of data, i.e., an additional 2-5 yr from the 12.5 yr data set. (II) At the initial detection, we expect a fractional uncertainty of 40% on the power-law strain spectrum slope, which is sufficient to distinguish a GWB of supermassive black hole binary origin from some models predicting more exotic origins. (III) Similarly, the measured GWB amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive black hole binaries. In addition, power-law models are distinguishable from those having low-frequency spectral turnovers once 20 yr of data are reached. Even though our study is based on the NANOGrav data, we also derive relations that allow for a generalization to other pulsar timing array data sets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.

Keywords: gravitational waves; gravitational wave astronomy; millisecond pulsars; pulsar timing method; astronomical simulations