adsabs/SciX_UAT_keywords huggingface dataset:
Confirming the Calibration of ALMA Using Planck Observations

We test the accuracy of ALMA flux density calibration by comparing ALMA flux density measurements of extragalactic sources to measurements made by the Planck mission; Planck is absolutely calibrated to subpercent precision using the dipole signal induced by the satellite's orbit around the solar system barycenter. Planck observations ended before ALMA began systematic observations, however, and many of the sources are variable, so we employ measurements by the Atacama Cosmology Telescope (ACT) to bridge the two epochs. We compare ACT observations at 93 and ~145 GHz to Planck measurements at 100 and 143 GHz and to ALMA measurements made at 91.5 and 103.5 GHz in Band 3. For both comparisons, flux density measurements were corrected to account for the small differences in frequency using the best available spectral index for each source. We find the ALMA flux density scale (based on observations of Uranus) is consistent with Planck. All methods used to make the comparison are consistent with ALMA flux densities in Band 3 averaging 0.99 times those measured by Planck. One specific test gives ALMA/Planck = 0.996 ± 0.024. We also test the absolute calibration of both ACT at 93 and ~145 GHz and the South Pole Telescope (SPT) at 97.43, 152.9, and 215.8 GHz, again with reference to Planck measurements at 100, 143, and 217 GHz, as well as the internal consistency of measurements of compact sources made by all three instruments.

Keywords: flux calibration; radio observatories; astronomical instrumentation
Multiple Moist Climate Equilibrium States on Arid Rocky M-dwarf Planets: A Last-saturation Tracer Analysis

Terrestrial-type exoplanets orbiting nearby red dwarf stars (M dwarfs) are the first potentially habitable exoplanets suitable for atmospheric characterization in the near future. Understanding the stability of water in cold-trap regions on such planets is critical because it directly impacts transmission spectroscopy observations, the global energy budget, and long-term surface water evolution. Here we diagnose the humidity distribution in idealized general circulation model simulations of terrestrial-type exoplanets. We use the "tracer of last saturation" technique to study the saturation statistics of air parcels. We find that on synchronously rotating planets the water vapor abundance in the nightside upper troposphere depends weakly on planetary rotation, while more water vapor builds up in the nightside lower troposphere on fast-rotating planets. We then discuss how last-saturation statistics can elucidate the multiple moist climate equilibrium states on synchronously and asynchronously rotating arid planets. We show that the multiple moist climate states arise from the cold-trapping competition between the substellar upper atmosphere and cold surface regions. We find that fast synchronously rotating planets tend to trap surface water on the nightside as a result of their weak atmospheric and strong surface cold traps compared to the slow-rotating case. These results elucidate the nature of the water cycle on arid rocky exoplanets and will aid interpretation of atmospheric observations in the future.

Keywords: astrobiology; computational methods; atmospheric circulation; extrasolar rocky planets; water vapor; exoplanet atmospheres
Galactic Positrons from Thermonuclear Supernovae

Type Ia supernovae (SNe Ia) may originate from a wide variety of explosion scenarios and progenitor channels. They exhibit a factor of ≈10 difference in brightness and thus a differentiation in the mass of 56Ni → 56Co → 56Fe. We present a study on the fate of positrons within SNe Ia in order to evaluate their escape fractions and energy spectra. Our detailed Monte Carlo transport simulations for positrons and γ-rays include both β + decay of 56Co and pair production. We simulate a wide variety of explosion scenarios, including the explosion of white dwarfs (WDs) close to the Chandrasekhar mass (M Ch), He-triggered explosions of sub-M Ch WDs, and dynamical mergers of two WDs. For each model, we study the influence of the size and morphology of the progenitor magnetic field between 1 and 1013 G. Population synthesis based on the observed brightness distribution of SNe Ia was used to estimate the overall contributions to Galactic positrons due to escape from SNe Ia. We find that this is dominated by SNe Ia of normal brightness, where variations in the distribution of emitted positrons are small. We estimate a total SNe Ia contribution to Galactic positrons of <2% and, depending on the magnetic field morphology, <6-20% for M Ch and sub-M Ch, respectively.

Keywords: type ia supernovae; supernovae; galaxy chemical evolution
The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings-Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 1014, and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200-1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10-3 (≈3σ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10-5 to 1.9 × 10-4 (≈3.5σ-4σ). Assuming a fiducial f -2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is ${2.4}_{-0.6}^{+0.7}\times {10}^{-15}$ (median + 90% credible interval) at a reference frequency of 1 yr-1. The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings-Downs correlations points to the gravitational-wave origin of this signal.

Keywords: gravitational waves; gravitational wave astronomy; millisecond pulsars; radio pulsars; supermassive black holes
Deterministic Aspect of the γ-Ray Variability in Blazars

Linear time series analysis, mainly the Fourier transform-based methods, has been quite successful in extracting information contained in the ever-modulating light curves of active galactic nuclei, and thereby contribute in characterizing the general features of supermassive black hole systems. In particular, the statistical properties of γ-ray variability of blazars are found to be fairly represented by flicker noise in the temporal frequency domain. However, these conventional methods have not been able to fully encapsulate the richness and the complexity displayed in the light curves of the sources. In this work, to complement our previous study on a similar topic, we perform nonlinear time series analysis of the decade-long Fermi/LAT observations of 20 γ-ray bright blazars. The study is motivated to address one of the most relevant queries: whether the dominant dynamical processes leading to the observed γ-ray variability are of deterministic or stochastic nature. For the purpose, we perform recurrence quantification analysis of the blazars and directly measure the quantities, which suggest that the dynamical processes in blazars could be a combination of deterministic and stochastic processes, while some of the source light curves revealed significant deterministic content. The result, with possible implication of strong disk-jet connection in blazars, could prove to be significantly useful in constructing models that can explain the rich and complex multiwavelength observational features in active galactic nuclei. In addition, we estimate the dynamical timescales, so-called trapping timescales, in the order of a few weeks.

Keywords: time series analysis; time domain astronomy; blazars; relativistic jets; gamma-ray transient sources; high energy astrophysics; active galactic nuclei; supermassive black holes
The 107 GHz Methanol Transition Is a Dasar in G0.253+0.016

We present observations of population anti-inversion in the 31 - 40 A + transition of CH3OH (methanol) at 107.013831 GHz toward the Galactic center cloud G0.253+0.016 ("The Brick"). Anti-inversion of molecular level populations can result in absorption lines against the cosmic microwave background (CMB) in a phenomenon known as a "dasar." We model the physical conditions under which the 107 GHz methanol transition dases and determine that dasing occurs at densities below 106 cm-3 and column densities between 1013 and 1016 cm-2. We also find that for this transition, dasing does not strongly depend on the gas kinetic temperature. We evaluate the potential of this tool for future deep galaxy surveys. We note that other works have already reported absorption in this transition (e.g., in NGC 253), but we provide the first definitive evidence that it is absorption against the CMB rather than against undetected continuum sources.

Keywords: astrophysical masers; galactic center; molecular clouds
Microlensing Optical Depth and Event Rate toward the Large Magellanic Cloud Based on 20 yr of OGLE Observations

Measurements of the microlensing optical depth and event rate toward the Large Magellanic Cloud (LMC) can be used to probe the distribution and mass function of compact objects in the direction toward that galaxy—in the Milky Way disk, the Milky Way dark matter halo, and the LMC itself. The previous measurements, based on small statistical samples of events, found that the optical depth is an order of magnitude smaller than that expected from the entire dark matter halo in the form of compact objects. However, these previous studies were not sensitive to long-duration events with Einstein timescales longer than 2.5–3 yr, which are expected from massive (10–100 M ⊙) and intermediate-mass (102–105 M ⊙) black holes. Such events would have been missed by the previous studies and would not have been taken into account in calculations of the optical depth. Here, we present the analysis of nearly 20 yr long photometric monitoring of 78.7 million stars in the LMC by the Optical Gravitational Lensing Experiment (OGLE) from 2001 through 2020. We describe the observing setup, the construction of the 20 yr OGLE data set, the methods used for searching for microlensing events in the light-curve data, and the calculation of the event detection efficiency. In total, we find 16 microlensing events (13 using an automated pipeline and three with manual searches), all of which have timescales shorter than 1 yr. We use a sample of 13 events to measure the microlensing optical depth toward the LMC τ = (0.121 ± 0.037) × 10‑7 and the event rate Γ = (0.74 ± 0.25) × 10‑7 yr‑1 star‑1. These numbers are consistent with lensing by stars in the Milky Way disk and the LMC itself, and they demonstrate that massive and intermediate-mass black holes cannot comprise a significant fraction of the dark matter.

Keywords: gravitational microlensing; dark matter; milky way dark matter halo; large magellanic cloud; primordial black holes; intermediate-mass black holes
Observations of the Quiet Sun during the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM: Sub-A-class Microflares outside Active Regions

Solar flares, with energies ranging over several orders of magnitude, result from impulsive release of energy due to magnetic reconnection in the corona. Barring a handful, almost all microflares observed in X-rays are associated with the solar active regions. Here we present, for the first time, a comprehensive analysis of a large sample of quiet-Sun microflares observed in soft X-rays by the Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission during the 2019-2020 solar minimum. A total of 98 microflares having peak flux below GOES A-level were observed by the XSM during observations spanning 76 days. By using the derived plasma temperature and emission measure of these events obtained by fitting the XSM spectra along with volume estimates from concurrent imaging observations in EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly, we estimated their thermal energies to be ranging from 3 × 1026 to 6 × 1027 erg. We present the frequency distribution of the quiet-Sun microflares with energy and discuss the implications of these observations of small-scale magnetic reconnection events outside active regions on coronal heating.

Keywords: quiet sun; solar x-ray flares
Spectral Line Asymmetries of Hot Fe Lines in Multiloop Models

Extreme ultraviolet emission line profiles often show asymmetries, in the form of wing enhancements, during solar flares. Various explanations, ranging from magnetic disturbances to non-Maxwellian electron distributions to plasma turbulence have been proposed to explain these features. Plasma dynamics in a single loop can also satisfactorily explain line asymmetry. However, the presence of sub-resolution structures, confirmed by increasingly high-resolution observations, and observational difficulties in isolating a monolithic loop from nearby loops, necessitate detailed modeling efforts to investigate the effect of superposed dynamics on some line asymmetries. In the present work, we design multiloop models, representative of three possible loop configurations, to study how the resultant Fe XXIII spectral line profiles differ in each case and examine the differences between these multiloop models and the single loop model. We also briefly explore the role of a constant time delay in heating successive sub-loops on the spectral line shape. We find that for a multiloop model with sub-loops of the same length, heating time delay is an important factor that alters the line profile shape from the single loop case. Whereas, multiloop models with sub-loops of varied lengths predict significantly different line profiles, such as asymmetric lines for longer durations and with large blueshifts, without the necessity of introducing time delays.

Keywords: solar flare spectra; solar flares
Multiwavelength and Neutrino Emission from Blazar PKS 1502 + 106

In 2019 July, the IceCube experiment detected a high-energy neutrino from the direction of the powerful blazar PKS 1502+106. We perform multiwavelength and multimessenger modeling of this source, using a fully selfconsistent one-zone model that includes the contribution of external radiation fields typical of flat-spectrum radio quasars. We identify three different activity states of the blazar: one quiescent state and two flaring states with hard and soft gamma-ray spectra. We find two hadronic models that can describe the multiwavelength emission during all three states: a leptohadronic model with a contribution from photohadronic processes to X-rays and gamma-rays, and a proton synchrotron model, where the emission from keV to 10 GeV comes from proton synchrotron radiation. Both models predict a substantial neutrino flux that is correlated with the gamma-ray and soft X-ray fluxes. Our results are compatible with the detection of a neutrino during the quiescent state, based on event rate statistics. We conclude that the soft X-ray spectra observed during bright flares strongly suggest a hadronic contribution, which can be interpreted as additional evidence for cosmic-ray acceleration in the source independently of neutrino observations. We find that more arguments can be made in favor of the leptohadronic model vis-a-vis the proton synchrotron scenario, such as a lower energetic demand during the quiescent state. However, the same leptohadronic model would be disfavored for flaring states of PKS 1502+106 if no IceCube events were found from the direction of the source before 2010, which would require an archival search.

Keywords: blazars; cosmological neutrinos; astronomy data modeling; gamma-ray sources; ultra-high-energy cosmic radiation; high-luminosity active galactic nuclei; astronomical simulations
Ages of "Singles" versus "Multis": Predictions for Dynamical Sculpting over Gyr in the Kepler Sample

The sample of host stars with multiple transiting planets has illuminated the orbital architectures of exoplanetary systems. These architectures may be shaped mostly by formation conditions, be continually sculpted by ongoing dynamical processes, or both. As more studies have placed planet occurrence within a galactic context, evidence has emerged for variable planet multiplicity over time. In this manuscript, we investigate the use of transit multiplicity as a tool to constrain longer-timescale (>1 Gyr) dynamical sculpting. First, with a suite of injection-and-recovery tests, we quantify sensitivity to sculpting laws across different regimes. We employ a forward modeling framework in which we generate synthetic planetary systems, according to a prescribed sculpting speed and timescale, around the FGK dwarfs studied by the Kepler Mission. Some sculpting scenarios are hypothetically detectable in the Kepler sample, while others can be disfavored from Kepler transit statistics alone. Second, we apply our analysis to reverse engineer the sculpting laws consistent with the true yield from Kepler. We confirm the present-day fraction of host stars containing dynamically cool "systems with tightly packed inner planets" is 4%–13%. A variety of Gyr-timescale sculpting laws successfully predict the transit multiplicity of the Kepler sample, but none of these laws succeed in also producing a detectable trend with transit multiplicity and stellar age. An improvement to measured stellar age precision may help uncover such a sculpting law, but nevertheless reflects limitations in transit multiplicity as an observable. Therefore, other phenomena, apart from Gyr-timescale dynamical sculpting, may be required to explain the Kepler yield.

Keywords: exoplanet dynamics; planetary system evolution
Formation and Reconnection of Electron Scale Current Layers in the Turbulent Outflows of a Primary Reconnection Site

We simulate with 3D particle in cell, the spontaneous formation of turbulent outflows in an initially laminar 3D reconnecting current layer. We observe the formation of many secondary current layers and reconnection sites in the outflow. The approach we follow is to study each individual feature within the turbulent outflow. To identify all clusters of current in the outflow we use a clustering technique widely used in unsupervised machine learning: density-based spatial clustering of applications with noise. Once the clusters are identified we measure their size and compute reconnection indicators to establish which are undergoing reconnection. With this analysis we establish that the size of the current clusters reaches all the way from its initial system scale down to subelectron skin depth scale. We observe that the smaller current clusters are more prone to reconnecting and to releasing energy. We then find the process of reconnection of the smaller current cluster to be of the recently observed electron-only type that leaves the ions essentially unaffected.

Keywords: interplanetary turbulence; solar magnetic reconnection
The Chandra Source Catalog Normal Galaxy Sample

We present the extensive and well-characterized Chandra X-ray Galaxy Catalog (CGC) of 8547 galaxy candidates in the redshift range z ~ 0.04-0.7, optical luminosity 1010-1011 Lr ⊙, and X-ray luminosity (0.5-7 keV) L X = 2 × 1040-2 × 1043 erg s-1. We estimate a ~5% false-match fraction and contamination by quasi-stellar objects (QSOs). The CGC was extracted from the Chandra Source Catalog version 2 (CSC2) by cross-correlating with optical and IR all-sky survey data, including the Sloan Digital Sky Survey, Pan-STARRS, DESI Legacy, and Wide-field Infrared Survey Explorer (WISE). Our selection makes use of two main criteria that we have tested on the subsample with optical spectroscopical identification. (1) A joint selection based on X-ray luminosity (L X) and X-ray-to-optical flux ratio (F XO), which recovers 63% of the spectroscopically classified galaxies with a small contamination fraction (7%), which is a significant improvement over methods using L X or F XO alone (<50% recovery). (2) A joint W1-W2 (W12) WISE color and L X selection that proves effective in excluding QSOs and improves our selection by recovering 72% of the spectroscopically classified galaxies and reducing the contamination fraction (4%). Of the CGC, 24% was selected by means of optical spectroscopy; 30% on the basis of L X, F XO, and W12; and 46% by using either the L X-F XO or the L X-W12 selection criteria. We have individually examined the data for galaxies with z < 0.1, which may include more than one CSC2 X-ray source, leading to the exclusion of 110 local galaxies. Our catalog also includes near-IR and UV data and galaxy morphological types.

Keywords: galaxies
The Measurement of Dynamic Tidal Contribution to Apsidal Motion in Heartbeat Star KIC 4544587

Apsidal motion is a gradual shift in the position of periastron. The impact of dynamic tides on apsidal motion has long been debated, because the contribution could not be quantified due to the lack of high-quality observations. KIC 4544587 with tidally excited oscillations has been observed by Kepler high-precision photometric data based on long-time-baseline and short-cadence schema. In this paper, we compute the rate of apsidal motion that arises from the dynamic tides as 19.05 ± 1.70 mrad yr-1 via tracking the orbital phase shifts of tidally excited oscillations. We also calculate the procession rate of the orbit due to the Newtonian and general relativistic contribution as 21.49 ± 2.8 and 2.4 ± 0.06 mrad yr-1, respectively. The sum of these three factors is in excellent agreement with the total observational rate of apsidal motion 42.97 ± 0.18 mrad yr-1 measured by eclipse timing variations. The tidal effect accounts for about 44% of the overall observed apsidal motion and is comparable to that of the Newtonian term. Dynamic tides have a significant contribution to the apsidal motion. The analysis method mentioned in this paper presents an alternative approach to measuring the contribution of the dynamic tides quantitatively.

Keywords: apsidal motion; asteroseismology; binary stars; tidal interaction
The Impact-driven Atmospheric Loss of Super-Earths around Different Spectral Types of Host Stars

A planet's mass loss is important for the its formation and evolution. The radius valley (RV) is believed to be triggered by evaporation-induced mass loss. As an alternative mechanism for RV, the mass loss of post-impact planets is thoroughly investigated in this work. The impact energy is converted to the planet's internal energy, enhancing its core energy and accelerating mass loss and orbital migration. As the host star changes from K type to F type, the planet's mass loss and orbital migration increase. When the initial gas-to-core-mass ratio is small, the migration efficiency for planets around K-type stars will increase, which helps to suppress mass loss and retain the planet's mass and radius within a specific range. On the contrary, planets around more massive F-type stars experience more substantial mass loss, potentially leading to complete mass loss, and migrate to orbits with longer periods. Our calculation shows that planets around different spectral types of host stars give rise to an RV ranging from 1.3 to 2.0 R ⊕, consistent with the observed range of 1.3–2.6 R ⊕. Despite the presence of uncertain parameters, the planetesimal impact can promote the RV establishment for planets around host stars of different spectral types.

Keywords: exoplanets; exoplanet evolution; exoplanet formation; exoplanet atmospheres; exoplanet migration; super earths