Sazuna/UAT_keywords huggingface dataset:
Unveiling Sub-pc Supermassive Black Hole Binary Candidates in Active Galactic Nuclei. The elusive supermassive black hole binaries (SMBHBs) are thought to be the penultimate stage of galaxy mergers, preceding a final coalescence phase. SMBHBs are sources of continuous gravitational waves, possibly detectable by pulsar timing arrays; the identification of candidates could help in performing targeted gravitational wave searches. Due to SMBHBs' origin in the innermost parts of active galactic nuclei (AGN), X-rays are a promising tool for unveiling their presence, by means of either double Fe Kα emission lines or periodicity in their light curve. Here we report on a new method for selecting SMBHBs by means of the presence of a periodic signal in their Swift Burst Alert Telescope (BAT) 105 month light curves. Our technique is based on Fisher's exact g-test and takes into account the possible presence of colored noise. Among the 553 AGN selected for our investigation, only the Seyfert 1.5 galaxy Mrk 915 emerges as a candidate SMBHB; from subsequent analysis of its light curve we find a period P0 = 35 ± 2 months, and the null hypothesis is rejected at the 3.7σ confidence level. We also present a detailed analysis of the BAT light curve of the only previously X-ray-selected binary candidate source in the literature, the Seyfert 2 galaxy MCG+11-11-032. We find P0 = 26.3 ± 0.6 months, consistent with the one inferred from previously reported double Fe Kα emission lines.

Keywords: Seyfert galaxies, X-ray active galactic nuclei
Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point. We performed a numerical study for interpreting observations of plasma blobs occurring in the solar corona. Considering all of the previous studies and the presence of magnetic null points together with propagating magnetohydrodynamic waves in the solar corona, we guessed that the interaction of fast magnetoacoustic waves with null points could give rise to blobs under coronal conditions. The outcome of these interactions contributes to coronal jets and flares that directly affects us on Earth. The propagation of magnetoacoustic waves in the vicinity of a magnetic null point contributes to the high current density accumulation at the small scale around the magnetic null point, which has significant magnetic gradients. When nonlinearity becomes dominant, the variation of current density could result in instabilities and thus anomalous resistivity. Moreover, it is demonstrated that plasmoids with eruption events take place in the solar corona without considering the transition region. In our numerical simulation results, it is interesting that plasma blobs manifest themselves in many parameters, including current density, temperature, plasma density, flows, and magnetic fields, simultaneously and consistent with the generation of plasmoids. In this work, it is found that plasmoid instability is the reason for the plasma blobs and tiny blobs are produced by the tearing instability occurring in thin current sheets.

Keywords: The Sun, Magnetohydrodynamics, Solar corona, Magnetohydrodynamical simulations
Measuring the Stellar Population Parameters of the Early-type Galaxy NGC 3923: The Challenging Measurement of the Initial Mass Function. Recent studies of early-type galaxies have suggested that the initial mass function (IMF) slope is bottom-heavy; that is, they contain a larger fraction of low-mass stars than the Milky Way. However, measurements of the IMF remain challenging in unresolved galaxies because features in their observed spectra are sensitive to a number of factors, including the stellar age, metallicity, and elemental abundances, in addition to the IMF. In this paper, we use new high signal-to-noise IMACS (Magellan) spectra to study the elliptical shell galaxy NGC 3923 at optical (3700-6600 Å) and near-infrared (7900-8500 Å) wavelengths, as a function of radius. We have undertaken a number of independent approaches to better understand the uncertainties in our results. (1) We compare two different stellar population model libraries; (2) we undertake spectral index fitting as well as full spectral fitting; (3) we have performed simulations for which we a priori know the input IMF and that closely match our data; (4) we also investigate the effects of including a two-component rather than a single stellar population. We show that our results are sensitive to the assumptions we make and to the methods we use. In addition, we evaluate the accuracy and precision of our results based on simulated mock data. We find some indication (although assumption dependent) for a bottom-heavy IMF in the mass range 0.5-1.0 M⊙, while the IMF in the mass range 0.08-0.5 M⊙ appears to be Milky Way-like and constant. Including near-infrared data in our analysis gives consistent results and improves the precision. * "This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile." following the Las Campanas guidelines (http://www.lco.cl/?page_id=4409).

Keywords: Galaxy stellar content, Galaxy abundances, Elliptical galaxies, Initial mass function
Recurrent Solar Energetic Particle Flux Enhancements Observed near Earth and Mars. The period 2016 August 1 to November 15 was characterized by the presence of corotating interaction regions (CIRs) and a few weak coronal mass ejections (CMEs) in the heliosphere. In this study we show recurrent energetic electron and proton enhancements observed near Earth (1 au) and Mars (1.43-1.38 au) during this period. The observations near Earth use data from instruments on board the Advanced Composition Explorer, the Solar and Heliospheric Observatory, and Solar Dynamics Observatory and those near Mars are from the Solar Energetic Particle, Solar Wind Ion Analyzer, and Magnetometer instruments on board the Mars Atmosphere and Volatile EvolutioN (MAVEN). During this period, the energetic electron fluxes observed near Earth and Mars showed prominent periodic enhancements over four solar rotations, with major periodicities of ∼27 days and ∼13 days. Periodic radar blackouts/weakenings of radar signals at Mars were observed by the Mars Advanced Radar for Subsurface and Ionosphere Sounding/Mars Express, and are associated with these solar energetic electron enhancements. During this period, a weak CME and a high-speed stream (HSS)-related interplanetary shock could have interacted with the CIR and enhance energetic proton fluxes near 1.43-1.38 au, causing ∼27 days periodicity in proton fluxes to be significantly diminished at 1.43-1.38 au. These events also have an unexpected impact on the Martian topside ionosphere, such as topside ionospheric depletion and compression observed by the Langmuir Probe and Waves and Neutral Gas and Ion Mass Spectrometer on board MAVEN. These observations are unique not only because of the recurring nature of electron enhancements seen at two vantage points, but also because they reveal the unexpected impact of the weak CME and interplanetary shock on the Martian ionosphere, which provides new insights into the impact of CME-HSS interactions on the Martian plasma environment.

Keywords: Earth ionosphere, Solar energetic particles, Mars, Solar system terrestrial planets, Solar coronal mass ejections, Corotating streams, Solar particle emission
Effects of Supernova Redshift Uncertainties on the Determination of Cosmological Parameters. Redshifts used in current cosmological supernova samples are measured using two primary techniques, one based on well-measured host galaxy spectral lines and the other based on supernova-dominated spectra. Here, we construct an updated Pantheon catalog with revised redshifts, redshift sources, and estimated uncertainties for the entire sample to investigate whether these two techniques yield consistent results. The best-fit cosmological parameters using these two measurement techniques disagree, with a supernova-only sample producing Ωm 3.2σ higher and H0 2.5σ lower than a hostz-only sample, and we explore several possible sources of bias that could result from using the lower-precision supernova-dominated redshifts. In a pilot study, we show that using a host redshift-only subsample will generically produce lower Ωm and matter density Ωmh2 and slightly higher H0 than previous analysis which, for the Pantheon data set, could result in supernova and cosmic microwave background measurements agreeing on Ωmh2 despite tension in H0. To obtain rigorous results, though, the Pantheon catalog should be improved by obtaining host spectra for supernovae that have faded, and future surveys should be designed to use host galaxy redshifts rather than lower-precision methods.

Keywords: Cosmology, Cosmological parameters, Standard candles, Astronomy data analysis, Type Ia supernovae
In Search of an Interface between Warm and Hot Gas within the Local Bubble. We have examined UV spectra recorded by the Space Telescope Imaging Spectrograph on the Hubble Space Telescope for three stars, HD32309, 41 Ari, and η Tel, that are located well inside the boundary of the Local Hot Bubble in our search for absorption features of Si IV, C IV, and N V that could reveal the presence of an interface between the local warm (T ∼ 7000 K), neutral medium, and a more distant hot (T ∼ 106 K) interstellar medium. In all cases, we failed to detect such ions. Our most meaningful upper limit is that for log N(C IV) $\lt $ 11.86 toward HD32309, which is below the expectation for a sight line that penetrates either a conductive/evaporative interface or a turbulent mixing layer. We offer conjectures on the reasons for these negative results in terms of either a suppression of a conductive layer caused by the shielding of the local cloud by other clouds, which may make it more difficult for us to sense discrete absorption features from gases at intermediate temperatures, or by the presence of a tangential magnetic field at most locations on the surface of the local cloud.

Keywords: Interstellar line absorption, Warm neutral medium, Hot ionized medium
Modeling the Transport of Nonthermal Particles in Flares Using Fokker-Planck Kinetic Theory. We describe a new approach for modeling the transport of high-energy particles accelerated during flares from the acceleration region in the solar corona until their eventual thermalization in the flare footpoint. Our technique numerically solves the Fokker-Planck equation and includes forces corresponding to Coulomb collisions in a flux loop with nonuniform ionization, synchrotron emission reaction, magnetic mirroring, and a return current electric field. Our solution to the Fokker-Planck equation includes second-order pitch angle and momentum diffusion. It is applicable to particles of arbitrary mass and charge. By tracking the collisions, we predict the bremsstrahlung produced as these particles interact with the ambient stellar atmosphere. This can be compared directly with observations and used to constrain the accelerated particle energy distribution. We have named our numerical code FP and distributed it for general use. We demonstrate its effectiveness in several test cases.

Keywords: Solar flares, Solar flare spectra, Computational methods, Non-thermal radiation sources, Stellar flares, Solar magnetic fields, Solar x-ray flares
The Velocity Dispersion Function for Quiescent Galaxies in Nine Strong-lensing Clusters. We measure the central stellar velocity dispersion function for quiescent galaxies in a set of nine northern clusters in the redshift range 0.18 &lt; z &lt; 0.29 and with strong lensing arcs in Hubble Space Telescope images. The velocity dispersion function links galaxies directly to their dark matter halos. From dense SDSS and MMT/Hectospec spectroscopy, we identify 222-463 spectroscopic members in each cluster. We derive physical properties of cluster members including redshift, ${D}_{n}4000$ , and central stellar velocity dispersion and we include a table of these measurements for 3419 cluster members. We construct the velocity dispersion functions for quiescent galaxies with ${D}_{n}4000$ &gt; 1.5 and within R200. The cluster velocity dispersion functions all show excesses at σ ≳ 250 km s-1 compared to the field velocity dispersion function. The velocity dispersion function slope at large velocity dispersion (σ &gt; 160 km s-1) is steeper for more massive clusters, consistent with the trend observed for cluster luminosity functions. The spatial distribution of galaxies with large velocity dispersion at radii larger than R200 further underscores the probable major role of dry mergers in the growth of massive cluster galaxies during cluster assembly.

Keywords: Galaxy clusters, Luminosity function, Galaxy mass distribution, Redshift surveys, Early-type galaxies
Two Complete Spectral Transitions of Swift J0243.6+6124 Observed by Insight-HXMT. We performed the broadband (1-100 keV) spectral analysis of the first Galactic Be ultraluminous X-ray pulsar (BeULX) Swift J0243.6+6124 observed by Insight-HXMT during the 2017-2018 outburst. The results show spectral transitions at two typical luminosities, roughly consistently with those reported previously via pure timing analysis. We find that the spectrum evolves and becomes softer and has higher cutoff energies until the luminosity reaches L1 (∼1.5 × 1038 erg s-1). Afterwards the spectrum becomes harder with lower cutoff energies until the luminosity increases to L2 (∼4.4 × 1038 erg s-1), around which the second spectral transition occurs. Beyond L2, the spectrum softens again and has larger cutoff energies. Similar behaviors were observed previously in other high-mass X-ray binary systems (HMXBs), especially for the second transition at higher luminosities, which is believed to have a correlation with the magnetic field of the harbored neutron star. Accordingly, we speculate that Swift J0243.6+6124 owns a neutron star with magnetic field strength &gt;1013 G. The spectral transition at around L1 of Swift J0243.6+6124 is first observed thoroughly for any HMXB outburst characterized by strong evolution of the thermal component: the temperature of the blackbody drops sharply accompanied by a sudden increase of the blackbody radius. These spectral transitions can in principle be understood in a general scenario of balancing the emission patterns between the pencil and the fan beams at the magnetic pole, for which the extreme brightness of Swift J0243.6+6124 may provide an almost unique lab to probe the details.

Keywords: Accretion, Neutron stars, X-ray astronomy, X-ray binary stars, Stellar accretion disks, Magnetic fields, Binary pulsars
Small Electron Events Observed by Parker Solar Probe/IS⊙IS during Encounter 2. The current understanding of the characteristics of solar and inner heliospheric electron events is inferred almost entirely from observations made by spacecraft located at 1 astronomical unit (au). Previous observations within 1 au of the Sun, by the Helios spacecraft at ∼0.3-1 au, indicate the presence of electron events that are not detected at 1 au or may have merged during transport from the Sun. Parker Solar Probe's close proximity to the Sun at perihelion provides an opportunity to make the closest measurements yet of energetic electron events. We present an overview of measurements of electrons with energies between ∼17 keV and ∼1 MeV made by the Parker Solar Probe Integrated Science Investigation of the Sun (IS⊙IS) instrument suite during Encounter 2 (2019 March 31-April 10 with perihelion of ∼0.17 au), including several small electron events. We examine these events in the context of the electromagnetic and solar wind environment measured by the FIELDS and SWEAP instruments on Parker Solar Probe. We find most of these electron enhancements to be associated with type III radio emissions that reach the local plasma frequency and one enhancement that appears to be primarily associated with abrupt changes in the local magnetic field. Together, these associations suggest that these are indeed the first measurements of energetic electron events within 0.2 au.

Keywords: Solar flares, Solar energetic particles, Radio bursts, Solar physics, Solar particle emission
SUMER Measurement of the Fe X 3p<SUP>4</SUP>3d <SUP>4</SUP>D<SUB>5/2,7/2</SUB> Energy Difference. Recent studies have shown that magnetic fields in the solar corona are strong enough to significantly mix the two 3p43d 4D5/2,7/2 levels in Cl-like Fe X. This mixing gives rise to a magnetically induced transition (MIT) component in the bright Fe X 257.3 Å line, commonly observed by current instrumentation, that can be used for coronal magnetic field diagnostics. This line, commonly observed by the still operational EIS spectrometer on board the Hinode satellite since 2007, opens a new window into the coronal magnetic field. However, the strength of this MIT transition depends on the square of the energy difference ΔE of the two ${}^{4}{{\rm{D}}}_{5/\mathrm{2,7}/2}$ levels, so that an accurate determination of ΔE is of critical importance to accurately measure coronal magnetic field strengths. In the present work we present a new measurement of ΔE obtained determining the separation of the two component of the Fe X doublet close to 1603.3 Å from deep-exposure spectra of a quiescent streamer at the solar limb taken with the SUMER instrument on board SoHO. Our measurement of ΔE = 2.29 ± 0.50 cm-1 agrees with, and improves upon, an earlier measurements by Judge et al. by decreasing its uncertainty from 80% to approximately 20%, improving the attainable accuracy of magnetic field strength measurements obtainable with the Fe X 257.26 Å line.

Keywords: Solar magnetic fields
The Halo Spin Transition As a Probe of Dark Energy. We present numerical evidence supporting the claim that the mass-dependent transitions of the halo spin orientations from the intermediate to the minor principal directions of the local tidal fields can in principle be useful discriminators of dark energy models. We first define a spin transition zone as the mass range of the halos, ${\rm{\Delta }}{m}_{{\rm{t}}}$ , for which the intrinsic spin alignments with the minor tidal principal directions become as strong as that with the intermediate principal directions. Then, utilizing the halo samples from the DEUS simulations performed separately for the WMAP7 ΛCDM, phantom dark energy, and quintessence models, we investigate if and how the three different dark energy models differ in ${\rm{\Delta }}{m}_{{\rm{t}}}$ . It is shown that the differences in ${\rm{\Delta }}{m}_{{\rm{t}}}$ among the three dark energy models are significant enough to discriminate the models from one another and robust against the variations of the smoothing scale of the tidal field and redshift. Noting that a narrower spin transition zone is more powerful as a probe of dark energy, we also show that the spin transition zones become narrower at higher redshifts in the filamentary environments and, for the case of the tidal fields, smoothed on smaller scales. Our result is consistent with the scenario that ${\rm{\Delta }}{m}_{{\rm{t}}}$ is mainly determined by how fast the nonlinear evolution of the tidal field proceeds, which in turn sensitively depends on the background cosmology.

Keywords: Cosmological models, Large-scale structure of the universe
Identifying the 3FHL Catalog. IV. Swift Observations of Unassociated Fermi-LAT 3FHL Sources. The Fermi Large Area Telescope (Fermi-LAT) 3FHL catalog is the latest catalog of &gt;10 GeV sources and will remain an important resource for the high-energy community for the foreseeable future. Therefore, it is crucial that this catalog is made complete by providing associations for most sources. In this paper, we present the results of the X-ray analysis of 38 3FHL sources. We found a single bright X-ray source in 20 fields, two sources each in two fields, and none for the remaining 16. The analysis of the properties of the 22 3FHL fields with X-ray sources led us to believe that most (∼19/22) are of extragalactic origin. A machine-learning algorithm was used to determine the source type and we find that 15 potential blazars are likely BL Lacertae objects (BL Lac objects). This is consistent with the fact that BL Lac objects are by far the most numerous population detected above &gt;10 GeV in the 3FHL.

Keywords: X-ray identification, Blazars, Gamma-ray astronomy, Active galactic nuclei
Short-term Variability of Evolved Massive Stars with TESS. II. A New Class of Cool, Pulsating Supergiants. Massive stars briefly pass through the yellow supergiant (YSG) phase as they evolve redward across the H-R diagram and expand into red supergiants (RSGs). Higher-mass stars pass through the YSG phase again as they evolve blueward after experiencing significant RSG mass loss. These post-RSG objects offer us a tantalizing glimpse into which stars end their lives as RSGs and why. One telltale sign of a post-RSG object may be an instability to pulsations, depending on the star's interior structure. Here we report the discovery of five YSGs with pulsation periods faster than 1 day, found in a sample of 76 cool supergiants observed by the Transiting Exoplanet Survey Satellite at a two-minute cadence. These pulsating YSGs are concentrated in an H-R diagram region not previously associated with pulsations; we conclude that this is a genuine new class of pulsating star, fast yellow pulsating supergiants (FYPSs). For each FYPS, we extract frequencies via iterative prewhitening and conduct a time-frequency analysis. One FYPS has an extracted frequency that is split into a triplet, and the amplitude of that peak is modulated on the same timescale as the frequency spacing of the triplet; neither rotation nor binary effects are likely culprits. We discuss the evolutionary status of FYPS and conclude that they are candidate post-RSGs. All stars in our sample also show the same stochastic low-frequency variability found in hot OB stars and attributed to internal gravity waves. Finally, we find four α Cygni variables in our sample, of which three are newly discovered.

Keywords: Evolved stars, Stellar pulsations, Red supergiant stars, Light curves, Massive stars, Multi-periodic pulsation, Lomb-Scargle periodogram, Yellow hypergiant stars, Stellar astronomy, Wavelet analysis, Supergiant stars, Asteroseismology
Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus. Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 days orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of spectra with high signal-to-noise ratio and high resolution obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component. We detect a weak peak in the co-added residuals that has the properties expected for a faint pre-white dwarf. We use the dependence of the peak height and width on assumed secondary velocity semiamplitude to derive the semiamplitude, which yields masses of M1/M⊙ = 3.7 ± 1.4 and M2/M⊙ = 0.31 ± 0.10 (assuming orbital inclination equals the spin inclination of Regulus). We estimate the temperature of the pre-white dwarf Teff = (20 ± 4) kK through tests with differing temperature model spectra, and we find the radius R2/R⊙ = 0.061 ± 0.011 from the component temperatures and the flux ratio associated with the amplitude of the signal in the cross-correlation residuals.

Keywords: White dwarf stars, B stars, Binary stars