adsabs/SciX_UAT_keywords huggingface dataset:
On the Formation and Interaction of Multiple Supermassive Stars in Cosmological Flows

Supermassive primordial stars with masses exceeding ~105 M ⊙ that form in atomically cooled halos are the leading candidates for the origin of high-redshift quasars at z > 6. Recent numerical simulations, however, find that multiple accretion disks can form within a halo, each of which can potentially host a supermassive star. We investigate the formation and evolution of secondary supermassive stars in atomically cooled halos, including strong variations in their accretion histories driven by gravitational interactions between their disks and those surrounding the primary supermassive stars in each halo. We find that all secondary disks produce long-lived supermassive stars under sustained rapid accretion. We also find, however, that the majority of secondary supermassive stars do undergo at least one protracted quiescent accretion phase, during which time they thermally relax and may become powerful sources of ionizing feedback. In many halos, the two satellite disks collide, suggesting that the two stars can come into close proximity. This may induce additional mass exchange between them, leading to a great diversity of possible outcomes. These range from coevolution as main-sequence stars to main sequence-black hole pairs and black hole-black hole mergers. We discuss the likely outcome for these binary interactions based on the evolutionary state of both supermassive stars at the end of our simulations, as well as prospects for their future detection by current and next-generation facilities.

Keywords: supermassive black holes; primordial galaxies; population iii stars
4-OGC: Catalog of Gravitational Waves from Compact Binary Mergers

We present the fourth Open Gravitational-wave Catalog (4-OGC) of binary neutron star (BNS), binary black hole (BBH), and neutron star-black hole (NSBH) mergers. The catalog includes observations from 2015 to 2020 covering the first through third observing runs (O1, O2, O3a, and O3b) of Advanced LIGO and Advanced Virgo. The updated catalog includes seven BBH mergers that were not previously reported with high significance during O3b for a total of 94 observations: 90 BBHs, 2 NSBHs, and 2 BNSs. The most confident new detection, GW200318_191337, has component masses ${49.1}_{-12.0}^{+16.4}{M}_{\odot }$ and ${31.6}_{-11.6}^{+12.0}{M}_{\odot };$ its redshift of ${0.84}_{-0.35}^{+0.4}$ (90% credible interval) may make it the most distant merger so far. We estimate the merger rate of BBH sources, assuming a power-law mass distribution containing an additive Gaussian peak, to be ${16.5}_{-6.2}^{+10.4}({25.0}_{-8.0}^{+12.6})$ Gpc-3 yr-1 at a redshift of z = 0 (0.2). For BNS and NSBH sources, we estimate a merger rate of ${200}_{-148}^{+309}$ Gpc-3 yr-1 and ${19}_{-14}^{+30}$ Gpc-3 yr-1, respectively, assuming the known sources are representative of the total population. We provide reference parameter estimates for each of these sources using an up-to-date model accounting for instrumental calibration uncertainty. The corresponding data release also includes our full set of subthreshold candidates.

Keywords: gravitational waves; gravitational wave astronomy; astrophysical black holes; stellar mass black holes; neutron stars; compact objects
Using SDO/AIA to Understand the Thermal Evolution of Solar Prominence Formation

We investigated the thermal properties of prominence formation using time series analysis of Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) data. Here, we report the first time-lag measurements derived from SDO/AIA observations of a prominence and its cavity on the solar limb, made possible by AIA's different wave bands and high time resolution. With our time-lag analysis, which tracks the thermal evolution using emission formed at different temperatures, we find that the prominence cavity exhibited a mixture of heating and cooling signatures. This is in contrast to prior time-lag studies of multiple active regions that chiefly identified cooling signatures and very few heating signatures, which is consistent with nanoflare heating. We also computed time lags for the same pairs of SDO/AIA channels using output from a one-dimensional hydrodynamic model of prominence material forming through thermal nonequilibrium (TNE). We demonstrate that the SDO/AIA time lags for flux tubes undergoing TNE are predicted to be highly complex, changing with time and location along the flux tube, and are consistent with the observed time-lag signatures in the cavity surrounding the prominence. Therefore, the time-lag analysis is a sensitive indicator of the heating and cooling processes in different coronal regions. The time lags calculated for the simulated prominence flux tube are consistent with the behavior deduced from the AIA data, thus supporting the TNE model of prominence formation. Future investigations of time lags predicted by other models for the prominence mass could be a valuable method for discriminating among competing physical mechanisms.

Keywords: quiescent solar prominence; quiet solar corona; solar coronal heating; solar extreme ultraviolet emission; solar filaments; solar physics
Monte Carlo Simulations on Possible Collimation Effects of Outflows to Fan Beam Emission of Ultraluminous Accreting X-Ray Pulsars

Pulsating ultraluminous X-ray sources (PULXs) are accreting pulsars with apparent X-ray luminosity exceeding 1039 erg s-1. We perform Monte Carlo simulations to investigate whether a high collimation effect (or strong beaming effect) is dominant in the presence of accretion outflows, for the fan beam emission of the accretion column of the neutron stars in PULXs. We show that the three nearby PULXs (RX J0209.6-7427, Swift J0243.6+6124, and SMC X-3), namely, the Three Musketeers here, have their main pulsed emission not strongly collimated even if strong outflows exist. This conclusion can be extended to the current sample of extragalactic PULXs, if accretion outflows are commonly produced from them. This means that the observed high luminosity of PULXs is indeed intrinsic, which can be used to infer the existence of very strong surface magnetic fields of ~1013-14 G, possibly multipole fields. However, if strong outflows are launched from the accretion disks in PULXs as a consequence of disk spherization by radiation pressure, regular dipole magnetic fields of ~1012 G may be required, comparable to that of the Three Musketeers, which have experienced large luminosity changes from well below their Eddington limit (2 × 1038 erg s-1 for an NS) to super-Eddington and whose maximum luminosity fills the luminosity gap between Galactic pulsars and extragalactic PULXs.

Keywords: ultraluminous x-ray sources; binary pulsars; accretion
Discovery of High-velocity Hα Emission in the Direction of the Fermi Bubble

Wisconsin H-Alpha Mapper observations reveal high-velocity Hα and [N II]λ6584 emission lines in the same direction and velocity as ultraviolet absorption-line features that have been previously associated with the biconical gamma-ray lobes known as the Fermi Bubbles. We measure an extinction-corrected intensity of ${I}_{{\rm{H}}\alpha }={0.84}_{-0.09}^{+0.10}\,\mathrm{Rayleigh}$ for emission with line center vLSR = -221 ± 3 km s-1, corresponding to an emission measure of $\mathrm{EM}={2.00}_{-0.63}^{+0.64}\,{\mathrm{cm}}^{-6}\,\mathrm{pc}$ . This emission arises at the same velocity as Hubble Space Telescope/Cosmic Origins Spectrograph observations of ultraviolet absorption features detected in the PDS 456 quasar sight line that passes through the northern bubble near l = 10°4, b = +11°2. We estimate the total column density of ionized gas in this velocity component to be $N({{\rm{H}}}^{+})=\left(3.28\pm 0.33\right)\times {10}^{18}\,{\mathrm{cm}}^{-2}$ . The comparison of ionized gas emission and absorption yields an estimate for the characteristic density of ne,c = 1.8 ± 0.6 cm-3 and a characteristic length of Lc = 0.56 ± 0.21 pc assuming 30% solar metallicity. For a temperature of ${T}_{e}={8500}_{-2600}^{+2700}\,{\rm{K}}$ —consistent with the measured line widths and [N II]/Hα line ratio—the gas has a thermal pressure of $p/k={{\rm{32,000}}}_{-14,000}^{+15,000}\,{\mathrm{cm}}^{-3}\,{\rm{K}}$ . Assuming the gas is ∼6.5 kpc distant, the derived density and pressure appear to be anomalously high for gas ∼1.3 kpc above the Galactic midplane. The large thermal pressure is comparable to both a hot halo or Fermi Bubble model, but suggest that the Hα arises in an overpressurized zone.

Keywords: galactic center; interstellar medium; galactic winds; warm ionized medium; interstellar absorption; interstellar emissions
Machine-learning Inferences of the Interior Structure of Rocky Exoplanets from Bulk Observational Constraints

Characterizing the interiors of rocky exoplanets is important to understand planetary populations and further investigate planetary habitability. New observable constraints and inference techniques have been explored for this purpose. In this work, we design and train mixture density networks (MDNs) to predict the interior properties of rocky exoplanets with large compositional diversity. In addition to measurements of mass and radius, bulk refractory elemental abundance ratios and the static Love number k 2 are used to constrain the interior of rocky exoplanets. It is found that the MDNs are able to infer the interior properties of rocky exoplanets from the available measurements of exoplanets. Compared with powerful inversion methods based on Bayesian inference, the trained MDNs provide a more rapid characterization of planetary interiors for each individual planet. The MDN model offers a convenient and practical tool for probabilistic inferences of planetary interiors.

Keywords: extrasolar rocky planets; planetary interior; neural networks; computational methods
Modeling Stellar Surface Features on a Subgiant Star with an M-dwarf Companion

Understanding magnetic activity on the surface of stars other than the Sun is important for exoplanet analyses to properly characterize an exoplanet's atmosphere and to further characterize stellar activity on a wide range of stars. Modeling stellar surface features of a variety of spectral types and rotation rates is key to understanding the magnetic activity of these stars. Using data from Kepler, we use the starspot modeling program STarSPot (STSP) to measure the position and size of spots for KOI-340, which is an eclipsing binary consisting of a subgiant star (T eff = 5593 ± 27 K, R ⋆ = 1.98 ± 0.05 R ⊙) with an M-dwarf companion (M ⋆ = 0.214 ± 0.006 M ⊙). STSP uses a novel technique to measure the spot positions and radii by using the transiting secondary to study and model individual active regions on the stellar surface using high-precision photometry. We find that the average size of spot features on KOI-340's primary is ~10% the radius of the star, i.e., two times larger than the mean size of solar-maximum sunspots. The spots on KOI-340 are present at every longitude and show possible signs of differential rotation. The minimum fractional spotted area of KOI-340's primary is ${2}_{-2}^{+12}{\rm{ \% }}$ , while the spotted area of the Sun is at most 0.2%. One transit of KOI-340 shows a signal in the transit consistent with a plage; this plage occurs right before a dark spot, indicating that the plage and spot might be colocated on the surface of the star.

Keywords: stellar activity; starspots; plages; stellar physics; eclipsing binary stars
Swift Observations of Mrk 421 in Selected Epochs. III. Extreme X-Ray Timing/Spectral Properties and Multiwavelength Lognormality during 2015 December-2018 April

We present the results from the timing and spectral study of Mrk 421 based mainly on the Swift data in the X-ray energy range obtained during the time interval 2015 December-2018 April. The most extreme X-ray flaring activity on long-term, daily, and intraday timescales was observed during the 2 month period that started in 2017 December, when the 0.3-10 keV flux exceeded a level of 5 × 10-9 erg cm-2 s-1, recorded only twice previously. While the TeV-band and X-ray variabilities were mostly correlated, the source often varied in a complex manner in the MeV-GeV and radio-UV energy ranges, indicating that the multifrequency emission of Mrk 421 could not always be generated in a single zone. The longer-term flares at X-rays and γ-rays showed a lognormal character, possibly indicating a variability imprint of the accretion disk onto the jet. A vast majority of the 0.3-10 keV spectra were consistent with the log-parabolic model, showing relatively low spectral curvature and correlations between the different spectral parameters, predicted in the case of the first- and second-order Fermi processes. The position of the synchrotron spectral energy distribution peak showed an extreme variability on diverse timescales between the energies Ep < 0.1 and >15 keV, with 15% of the spectra peaking at the hard X-ray, and was related to the peak height as Sp∝ Epα with α ∼ 0.6, which is expected for the transition from Kraichnan-type turbulence into the "hard sphere" one. The 0.3-300 GeV spectra showed features of the hadronic contribution, jet-star interaction, and upscatter in the Klein-Nishina regime in different time intervals.

Keywords: active galactic nuclei; x-ray active galactic nuclei; galaxy jets; extragalactic astronomy
Multiwavelength Photometry Derived from Monochromatic Kepler Data

The Kepler mission has provided a wealth of data, revealing new insights in time-domain astronomy. However, Kepler's single bandpass has limited studies to a single wavelength. In this work we build a data-driven, pixel-level model for the pixel response function (PRF) of Kepler targets, modeling the image data from the spacecraft. Our model is sufficiently flexible to capture known detector effects, such as nonlinearity, intrapixel sensitivity variations, and focus change. In theory, the shape of the Kepler PRF should also be weakly wavelength-dependent, due to optical chromatic aberration and a wavelength-dependent detector response functions. We are able to identify these predicted changes in shape of the PRF using the residuals between Kepler data and our model. In this work, we show that these PRF changes correspond to wavelength variability in Kepler targets using a small sample of eclipsing binaries. Using our model, we demonstrate that pixel-level light curves of eclipsing binaries show variable eclipse depths, ellipsoidal modulation, and limb darkening. These changes at the pixel level are consistent with multiwavelength photometry. Our work suggests that each pixel in the Kepler data of a single target has a different effective wavelength, ranging from ≈550 to 750 nm. In this proof of concept, we demonstrate our model, and discuss possible uses for the wavelength-dependent PRF of Kepler. These uses include characterizing variable systems, and vetting exoplanet discoveries at the pixel level. The chromatic PRF of Kepler is due to weak wavelength dependence in the optical systems and detector of the telescope, and similar chromatic PRFs are expected in other similar telescopes, notably the NASA TESS telescope.

Keywords: time series analysis; multi-color photometry; astronomical instrumentation
Habitability of Martian Noachian Hydrothermal Systems as Constrained by a Terrestrial Analog on the Colorado Plateau

Volcanic features and impact craters are ubiquitous features on Mars, and hydrothermal systems associated with the production of these features should have been abundant in Mars's early history. These hydrothermal systems represent potentially habitable environments and are therefore a high priority for continued investigations of the Martian crust. Here we present a Mars analog study where basaltic magma intruded water-bearing sediments to produce a high-temperature (as high as ~700°C) hydrothermal system, which we use to constrain the potential habitability of similar systems on Mars via mineralogy and geochemistry including S, C, and O isotopic systematics. Our analog site suggests evidence for a habitable environment once the system cooled below 120°C and the potential presence of microbial activity based on the combination of dolomite and C-isotopic systems in the same sample. These findings highlight the importance of future missions to investigate the interface of sediments with magmas and/or late-stage impact melts where microbial life may have taken hold when temperature conditions allowed.

Keywords: mars
A Narrow Uniform Core with a Wide Structured Wing: Modeling the TeV and Multiwavelength Afterglows of GRB 221009A

The TeV afterglow of the BOAT GRB 221009A was interpreted as arising from a narrow jet, while the radio-to-X-ray afterglows were interpreted as arising from a wide structured jet. However, there is no model explaining the TeV and lower-energy multiwavelength afterglows simultaneously. We here investigate a two-component jet model, including a narrow uniform core with a wide structured wing, to explain both the multiwavelength afterglows that last up to 100 days. We find that to explain the early TeV afterglow with the inverse-Compton process, we need a circumburst density higher than ≳0.1 cm‑3, while the radio afterglow and the H.E.S.S. upper limit combine to constrain the density to be lower at larger radii. Thus, a decreasing density profile with radius is favored. Considering that the rising TeV light curve during the afterglow onset favors a constant-density medium, we invoke a stratified density profile, including a constant-density profile at small radii and a wind density profile at large radii. We find that the two-component jet model with such a stratified density profile can explain the TeV, X-ray, and optical afterglows of GRB 221009A, although the radio fluxes exceed the observed ones by a factor of 2 at later epochs. The discrepancy in the radio afterglow could be resolved by invoking some nonstandard assumption about the microphysics of afterglow shocks. The total kinetic energy of the two components in our model is ≲1052 erg, significantly smaller than that in the single structured jet models.

Keywords: gamma-ray bursts; gamma-ray astronomy; high energy astrophysics
Toward Robust Detections of Nanohertz Gravitational Waves

The recent observation of a common red-noise process in pulsar timing arrays (PTAs) suggests that the detection of nanohertz gravitational waves might be around the corner. However, in order to confidently attribute this red process to gravitational waves, one must observe the Hellings-Downs curve-the telltale angular correlation function associated with a gravitational-wave background. This effort is complicated by the complex modeling of pulsar noise. Without proper care, misspecified noise models can lead to false-positive detections. Background estimation using "quasi-resampling" methods such as sky scrambles and phase shifts, which use the data to characterize the noise, are therefore important tools for assessing significance. We investigate the ability of current PTA experiments to estimate their background with "quasi-independent" scrambles-characterized by a statistical "match" below the fiducial value: ∣M∣ < 0.1. We show that sky scrambling is affected by "saturation" after ${ \mathcal O }(10)$ quasi-independent realizations; subsequent scrambles are no longer quasi-independent. We show that phase scrambling saturates after ${ \mathcal O }(100)$ quasi-independent realizations. With so few independent scrambles, it is difficult to make reliable statements about the ≳5σ tail of the null distribution of the detection statistic. We sketch out various methods by which one may increase the number of independent scrambles. We also consider an alternative approach, wherein one reframes the background estimation problem so that the significance is calculated using statistically dependent scrambles. The resulting p-value is in principle well defined, but may be susceptible to failure if assumptions about the data are incorrect.

Keywords: astronomy data analysis; millisecond pulsars; gravitational waves
Do Current X-Ray Observations Capture Most of the Black-hole Accretion at High Redshifts?

The cosmic black hole accretion density (BHAD) is critical for our understanding of the formation and evolution of supermassive black holes (BHs). However, at high redshifts (z > 3), X-ray observations report BHADs significantly (~10 times) lower than those predicted by cosmological simulations. It is therefore paramount to constrain the high-z BHAD using independent methods other than direct X-ray detections. The recently established relation between star formation rate and BH accretion rate among bulge-dominated galaxies provides such a chance, as it enables an estimate of the BHAD from the star formation histories (SFHs) of lower-redshift objects. Using the CANDELS Lyα Emission At Reionization (CLEAR) survey, we model the SFHs for a sample of 108 bulge-dominated galaxies at z = 0.7-1.5, and further estimate the BHAD contributed by their high-z progenitors. The predicted BHAD at z ≈ 4-5 is consistent with the simulation-predicted values, but higher than the X-ray measurements (by ≈3-10 times at z = 4-5). Our result suggests that the current X-ray surveys could be missing many heavily obscured Compton-thick active galactic nuclei (AGNs) at high redshifts. However, this BHAD estimation assumes that the high-z progenitors of our z = 0.7-1.5 sample remain bulge-dominated where star formation is correlated with BH cold-gas accretion. Alternatively, our prediction could signify a stark decline in the fraction of bulges in high-z galaxies (with an associated drop in BH accretion). JWST and Origins will resolve the discrepancy between our predicted BHAD and the X-ray results by constraining Compton-thick AGN and bulge evolution at high redshifts.

Keywords: supermassive black holes; active galactic nuclei; x-ray active galactic nuclei; star formation; high-redshift galaxies; agn host galaxies; galaxy evolution
Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-poor K Dwarf

Using radial-velocity measurements from four instruments, we report the mass and density of a 2.043 ±0.069 R ⊕ sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence K2 campaign 17 photometry and conduct a joint radial-velocity-transit fit to constrain the eccentricity at 0.41 ± 0.05. The addition of a transit observation by Spitzer also allows us to refine the orbital ephemeris in anticipation of further follow-up. Our mass determination, 6.26 ${}_{-0.70}^{+0.69}$ M ⊕ , in combination with the updated radius measurements, gives Wolf 503 b a bulk density of $\rho ={2.92}_{-0.44}^{+0.50}$ g cm-3. Using interior composition models, we find this density is consistent with an Earth-like core with either a substantial H2O mass fraction (45 ${}_{-16}^{+19}$ %) or a modest H/He envelope (0.5% ± 0.3%). The low H/He mass fraction, along with the old age of Wolf 503 (11 ± 2 Gyr), makes this sub-Neptune an opportune subject for testing theories of XUV-driven mass loss while the brightness of its host (J = 8.3 mag) makes it an attractive target for transmission spectroscopy.

Keywords: exoplanet astronomy; radial velocity; transit photometry; extrasolar gaseous planets; ephemerides; k dwarf stars