Sazuna/UAT_keywords huggingface dataset:
MeerKAT Observations of the Reversing Drifting Subpulses in PSR J1750-3503. We present an analysis of the subpulse drift in PSR J1750-3503, which is characterized by abrupt transitions of drift direction. As the pulsar does not exhibit other mode changes or clear nulling, it is an ideal candidate system for studying the phenomenon of drift direction change. For ~80% of the time, the subpulses are characterized by positive drift-from early to later longitudes-while the drift direction is negative in the other ~20%. The subpulse separation for single pulses with positive drift, P 2 = (18.8 ± 0.1)°, is higher than for single pulses with negative drift, P 2 = (17.5 ± 0.2)°. When the drift is stable, the measured repetition time of the drift pattern is P 3 obs = (43.5 ± 0.4)P, where P is the pulsar period. We show that the observed data can be reproduced by a carousel models with subpulse rotation around the magnetic axis using a purely dipolar configuration of the surface magnetic field. The observed drift characteristics can be modeled assuming that the actual repetition time P 3 &lt; 2P, such that we observe its aliased value. A small variation in P 3, of the order of 6% (or less assuming higher alias orders), is enough to reproduce the characteristic drift direction changes we observe.

Keywords: Radio pulsars
The Discovery of a Rotating Radio Transient J1918-0449 with Intriguing Emission Properties with the Five-hundred-meter Aperture Spherical Radio Telescope. In this study, we report on a detailed single-pulse analysis of the radio emission from a rotating radio transient (RRAT) J1918-0449, which is discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The sensitive observations were carried out on 2021 April 30 using the FAST with a central frequency of 1250 MHz and a short time resolution of 49.152 μs, which forms a reliable basis to probe single-pulse emission properties in detail. The source was successively observed for around 2 hr. A total of 83 dispersed bursts with significance above 6σ are detected over 1.8 hr. The source's dispersion measure (DM) and rotational period are determined to be 116.1 ± 0.4 pc cm-3 and 2479.21 ± 0.03 ms, respectively. The share of registered pulses from the total number of observed periods is 3.12%. No underlying emission is detected in the averaged off-pulse profile. For bursts with fluence larger than 10 Jy ms, the pulse energy follows a power-law distribution with an index of -3.1 ± 0.4, suggesting the existence of bright pulse emission. We find that the distribution of time between subsequent pulses is consistent with a stationary Poisson process and find no evidence of clustering over the 1.8 hr observations, giving a mean burst rate of one burst every 66 s. Close inspection of the detected bright pulses reveals that 21 pulses exhibit well-defined quasiperiodicities. The subpulse drifting is present in nonsuccessive rotations with periodicity of 2.51 ± 0.06 periods. Finally, possible physical mechanisms are discussed.

Keywords: Radio pulsars
Probing Dynamics and Thermal Properties Inside Molecular Tori with CO Rovibrational Absorption Lines. A recent hydrodynamic model, the radiation-driven fountain model (Wada et al. 2016), presented a dynamical picture that active galactic nuclei (AGNs) tori sustain their geometrical thickness by gas circulation around AGNs, and previous papers have confirmed that this picture is consistent with multiwavelength observations of nearby Seyfert galaxies. Recent near-infrared observations implied that CO rovibrational absorption lines (ΔJ = ± 1, v = 0 - 1, λ ~ 4.7 μm) could probe the physical properties of the inside tori. However, the origin of the CO absorption lines has been under debate. In this paper, we investigate the origin of the absorption lines and conditions for detecting them by performing line radiative transfer calculations based on the radiation-driven fountain model. We find that CO rovibrational absorption lines are detected at inclination angles θ obs = 50°-80°. At the inclination angle θ obs = 77°, we observe multi-velocity components: inflow (v LOS = 30 km s-1), systemic (v LOS = 0 km s-1), and outflows (v LOS = -75, - 95, and -105 km s-1). The inflow and outflow components (v LOS = 30 and -95 km s-1) are collisionally excited at the excitation temperatures of 186 and 380 K up to J = 12 and 4, respectively. The inflow and outflow components originate from the accreting gas on the equatorial plane at 1.5 pc from the AGN center and the outflowing gas driven by AGN radiation pressure at 1.0 pc, respectively. These results suggest that CO rovibrational absorption lines can provide us with the velocities and kinetic temperatures of the inflow and outflow in the inner few parsec region of AGN tori, and the observations can probe the gas circulation inside the tori.

Keywords: Infrared astronomy, Radiative transfer simulations, Active galactic nuclei
Radio Spectra of Luminous, Heavily Obscured WISE-NVSS Selected Quasars. We present radio spectra spanning 0.1-10 GHz for the sample of heavily obscured luminous quasars with extremely red mid-infrared-optical colors and compact radio emission. The spectra are constructed from targeted 10 GHz observations and archival radio survey data that together yield 6-11 flux-density measurements for each object. Our primary result is that most (62%) of the sample have peaked or curved radio spectra and many (37%) could be classified as Gigahertz-Peaked Spectrum (GPS) sources. This indicates compact emission regions likely arising from recently triggered radio jets. Assuming synchrotron self-absorption (SSA) generates the peaks, we infer compact source sizes (3-100 pc) with strong magnetic fields (6-100 mG) and young ages (30-104 yr). Conversely, free-free absorption (FFA) could also create peaks due to the high column densities associated with the deeply embedded nature of the sample. However, we find no correlations between the existence or frequency of the peaks and any parameters of the MIR emission. The high-frequency spectral indices are steep (α ≈ -1) and correlate, weakly, with the ratio of MIR photon energy density to magnetic energy density, suggesting that the spectral steepening could arise from inverse Compton scattering off the intense MIR photon field. This study provides a foundation for combining multifrequency and mixed-resolution radio survey data for understanding the impact of young radio jets on the ISM and star-formation rates of their host galaxies. faGithub

Keywords: Supermassive black holes, Radio jets, Radio continuum emission, Radio loud quasars, Spectral energy distribution, Galaxy evolution, Radio active galactic nuclei
Measuring Star Formation and Black Hole Accretion Rates in Tandem Using Mid-infrared Spectra of Local Infrared Luminous Galaxies. We present the results of a stacking analysis performed on Spitzer/Infrared Spectrograph high-resolution mid-infrared (mid-IR) spectra of luminous infrared galaxies (LIRGs) in the Great Observatories All-Sky LIRG Survey. By binning in relation to mid-IR active galactic nucleus (AGN) fraction and stacking spectra, we detect bright emission lines [Ne II] and [Ne III], which trace star formation, and fainter emission lines [Ne V] and [O IV], which trace AGN activity, throughout the sample. We find that the [Ne II] luminosity is fairly constant across all AGN fraction bins, while the [O IV] and [Ne V] luminosities increase by over an order of magnitude. Our measured average line ratios, [Ne V]/[Ne II] and [O IV]/[Ne II], at low AGN fraction are similar to H II galaxies, while the line ratios at high AGN fraction are similar to LINERs and Seyferts. We decompose the [O IV] luminosity into star formation and AGN components by fitting the [O IV] luminosity as a function of the [Ne II] luminosity and the mid-IR AGN fraction. The [O IV] luminosity in LIRGs is dominated by star formation for mid-IR AGN fractions ≲0.3. With the corrected [O IV] luminosity, we calculate black hole accretion rates (BHARs) ranging from 10-5 M ⊙ yr-1 at low AGN fractions to 0.2 M ⊙ yr-1 at the highest AGN fractions. We find that using the [O IV] luminosity, without correcting for star formation, can lead to overestimation of the BHAR by up to a factor of 30 in starburst-dominated LIRGs. Finally, we show that the BHAR/star formation rate ratio increases by more than three orders of magnitude as a function of mid-IR AGN fraction in LIRGs.

Keywords: Supermassive black holes, Star formation, Galaxy evolution, Ultraluminous infrared galaxies, Luminous infrared galaxies
Metallicity Properties of the Galactic Bulge Stars Near and Far: Expectations from the Auriga Simulation. Using the high-resolution Milky Way-like model from Auriga simulation we study the chemical properties of the Galactic bulge, focusing on the metallicity difference between stars on the near side (in front of the Galactic center) and the far side (behind the Galactic center). In general, along certain sight lines the near side is more metal-rich than the far side, consistent with the negative vertical metallicity gradient of the disk, since the far side is located higher above the disk plane than the near side. However, at the region l &lt; 0° and ∣b∣ ≤ 6°, the near side is even more metal-poor than the far side, and their difference changes with the Galactic longitude. This is mainly due to the fact that stars near the minor axis of the bar are more metal-poor than that around the major axis. Since the bar is tilted, in the negative longitude region, the near side is mainly populated by stars close to the minor-axis region rather than the far side resulting in such a metallicity difference. We extract stars in the X-shape structure by identifying the overdensities in the near and far sides. Their metallicity properties are consistent with the results of the whole Galactic bulge. The boxy/peanut-shaped bulge can naturally explain the metallicity difference of the double red clump stars in the observation. There is no need to involve a classical bulge component with different stellar populations.

Keywords: Galactic bulge
New Theoretical Period-Luminosity-Metallicity Relations for RR Lyrae in the Rubin-LSST Filters. The revolutionary power of future Rubin-LSST observations will allow us to significantly improve the physics of pulsating stars, including RR Lyrae. In this context, an updated theoretical scenario predicting all the relevant pulsation observables in the corresponding photometric filters is mandatory. The bolometric light curves are based on a recently computed extensive set of nonlinear convective pulsation models for RR Lyrae stars, covering a broad range of metal content, and have been transformed into the Vera C. Rubin Observatory Legacy Survey of Space and Time (Rubin-LSST) photometric system. Predicted Rubin-LSST mean magnitudes and pulsation amplitudes have been adopted to build the Bailey diagrams (luminosity amplitude versus period) and the color-color diagrams in these bands. The current findings indicate that the g LSST-r LSST and r LSST-i LSST colors obey to a well-defined linear relation with the metal content. Moreover, the period-luminosity relations display in the reddest filters (r LSST, i LSST, z LSST, y LSST) a significant dependence on the assumed metal abundance. In particular, more metal-rich RR Lyrae are predicted to be fainter at a fixed period. Metal-dependent period-Wesenheit relations for different combinations of optical and near-infrared filters are also provided. These represent powerful tools to infer individual distances independently of reddening uncertainties, once the metal abundance is known and no relevant deviations from the adopted extinction law occur. Finally, we also derived new linear and quadratic absolute magnitude metallicity relations (g LSST versus [Fe/H]) and the metallicity coefficient is consistent with previous findings concerning the B and the V band.

Keywords: RR Lyrae variable stars
Single-pulse Variability in Gamma-Ray Pulsars. The Fermi Large Area Telescope receives ≪1 photon per rotation from any γ-ray pulsar. However, out of the billions of monitored rotations of the bright pulsars Vela (PSR J0835-4510) and Geminga (PSR J0633+1746), a few thousand have ≥2 pulsed photons. These rare pairs encode information about the variability of pulse amplitude and shape. We have cataloged such pairs and find the observed number to be in good agreement with simple Poisson statistics, limiting any amplitude variations to &lt;19% (Vela) and &lt;22% (Geminga) at 2σ confidence. Using an array of basis functions to model pulse-shape variability, the observed pulse phase distribution of the pairs limits the scale of pulse-shape variations of Vela to &lt;13%, while for Geminga we find a hint of ~20% single-pulse-shape variability most associated with the pulse peaks. If variations last longer than a single rotation, more pairs can be collected, and we have calculated upper limits on amplitude and shape variations for assumed coherence times up to 100 rotations, finding limits of ~1% (amplitude) and ~3% (shape) for both pulsars. Because a large volume of the pulsar magnetosphere contributes to γ-ray pulse production, we conclude that the magnetospheres of these two energetic pulsars are stable over one rotation and very stable on longer timescales. All other γ-ray pulsars are too faint for similar analyses. These results provide useful constraints on rapidly improving simulations of pulsar magnetospheres, which have revealed a variety of large-scale instabilities in the thin equatorial current sheets where the bulk of GeV γ-ray emission is thought to originate.

Keywords: Gamma-ray sources, Gamma-ray astronomy, Pulsar timing method, Pulsars
How Do We Optimally Sample Model Grids of Exoplanet Spectra?. The construction and implementation of atmospheric model grids is a popular tool in exoplanet characterization. These typically vary a number of parameters linearly, containing one model for every combination of parameter values. Here we investigate alternative methods of sampling parameters, including random sampling and Latin hypercube (LH) sampling, and how these compare to linearly sampled grids. We use a random forest to analyze the performance of these grids for two different models, as well as investigate the information content of the particular model grid from Goyal et al. (2019). We also use nested sampling to implement mock atmospheric retrievals on simulated James Webb Space Telescope transmission spectra by interpolating on linearly sampled model grids. Our results show that random or LH sampling outperforms linear sampling in parameter predictability for our higher-dimensional models, requiring fewer models in the grid, and thus allowing for more computationally intensive forward models to be used. We also found that using a traditional retrieval with interpolation on a linear grid can produce biased posterior distributions, especially for parameters with nonlinear effects on the spectrum. In particular, we advise caution when performing linear interpolation on the C/O ratio, cloud properties, and metallicity. Finally, we found that the information content analysis of the grid from Goyal et al. (2019) was able to highlight key areas of the spectra where the presence or absence of certain molecules can be detected, providing good indicators for parameters such as temperature and C/O ratio.

Keywords: Exoplanet atmospheres, Exoplanets
Heliospheric Compression Due to Recent Nearby Supernova Explosions. The widespread detection of 60Fe in geological and lunar archives provides compelling evidence for recent nearby supernova explosions within ~100 pc at 3 and 7 Myr ago. The blasts from these explosions had a profound effect on the heliosphere. We perform new calculations to study the compression of the heliosphere due to a supernova blast. Assuming a steady but non-isotropic solar wind, we explore a range of properties appropriate for supernova distances inspired by recent 60Fe data, and for a 20 pc supernova proposed to account for mass extinctions at the end-Devonian period. We examine the locations of the termination shock decelerating the solar wind and the heliopause that marks the boundary between the solar wind and supernova material. Pressure balance scaling holds, consistent with studies of other astrospheres. Solar wind anisotropy does not have an appreciable effect on shock geometry. We find that supernova explosions at 50 pc (95 pc) lead to heliopause locations at 16 au (23 au) when the forward shock arrives. Thus, the outer solar system was directly exposed to the blast, but the inner planets-including Earth-were not. This finding reaffirms that the delivery of supernova material to Earth is not from the blast plasma itself, but likely is from supernova dust grains. After the arrival of the forward shock, the weakening supernova blast will lead to a gradual rebound of the heliosphere, taking ~few $\times $ 100 kyr to expand beyond 100 au. Prospects for future work are discussed.

Keywords: Hydrodynamical simulations, Stellar-interstellar interactions, Heliosphere, Stellar winds, Supernovae
The Fractality and Size Distributions of Astrophysical Self-Organized Criticality Systems. The statistics of nonlinear processes in avalanching systems, based on the self-organized criticality (SOC) concept of Bak et al. (1988), predicts power-law-like size (or occurrence frequency) distribution functions. Following up on previous work, we define a standard SOC model in terms of six assumptions: (i) area fractality, (ii) volume fractality, (iii) the flux-volume proportionality, (iv) classical diffusion, (v) the Euclidean maximum at the event peak time, and (vi) the spatiotemporal fluence or energy of an avalanche event. We gather data of the fractal dimension and power-law slopes from 162 publications and assemble them in 28 groups (for instance, solar flare energies, or stellar flare energies), from which we find that 75% of the groups are consistent with the standard SOC model. Alternative SOC models (Lévy flight, flat-world, nonfractal) are slightly less correlated with the data. Outliers are attributed to small number statistics, background definition problems, inadequate fitting ranges, and deviations from ideal power laws.

Keywords: Solar flares, Asteroids, Exoplanets, Solar photosphere, Pulsars, Stellar flares, Planetary magnetospheres
Asteroseismology of the DAV Star L19-2. L19-2 is a DAV star, which was intermittently observed from 1976 to 2013. Five independent pulsation modes of 350, 192, 143, 118, and 113 s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O-C method for the modes of 192 and 113 s, which can be used to study the evolution effect of DAV stars. Using the White Dwarf Evolution Code (WDEC; 2018 version), a large sample of DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal model with an absolute difference of Φ = 0.06 s. By parameterizing the core oxygen profile, the WDEC procedure can greatly reduce the fitting error of asteroseismological models. According to our optimal model, the distance obtained through the model luminosity is only 1% different from that reported by the Gaia Data Release 2. L19-2 is a massive and hot DAV star with a relatively thick H atmosphere and a thick He layer. The stellar parameters and the rates of period change of our optimal model are slightly modified from that of the previous work. Our optimal model has a large central oxygen abundance. The central oxygen abundance is strongly correlated with the previous physical process of stellar evolution. A lot of asteroseismological work on white dwarfs presents an opportunity to explore the progenitor stars.

Keywords: White dwarf stars, Asteroseismology, DA stars
Evolution of a Relativistic Outflow and X-Ray Corona in the Extreme Changing-look AGN 1ES 1927+654. 1ES 1927+654 is a paradigm-defying active galactic nucleus (AGN) and one of the most peculiar X-ray nuclear transients. In early 2018, this well-known AGN underwent a changing-look event, in which broad optical emission lines appeared and the optical flux increased. Yet, by 2018 July, the X-ray flux had dropped by over two orders of magnitude, indicating a dramatic change in the inner accretion flow. With three years of observations with NICER, XMM-Newton, and NuSTAR, we present the X-ray evolution of 1ES 1927+654, which can be broken down into three phases: (1) an early super-Eddington phase with rapid variability in X-ray luminosity and spectral parameters, (2) a stable super-Eddington phase at the peak X-ray luminosity, and (3) a steady decline back to the pre-outburst luminosity and spectral parameters. For the first time, we witnessed the formation of the X-ray corona, as the X-ray spectrum transitioned from thermally dominated to primarily Comptonized. We also track the evolution of the prominent, broad 1 keV feature in the early X-ray spectra and show that this feature can be modeled with blueshifted reflection (z = -0.33) from a single-temperature blackbody irradiating spectrum using xillverTDE, a new flavor of the xillver models. Thus, we propose that the 1 keV feature could arise from reflected emission off the base of an optically thick outflow from a geometrically thick, super-Eddington inner accretion flow, connecting the inner accretion flow with outflows launched during extreme accretion events (e.g., tidal disruption events). Lastly, we compare 1ES 1927+654 to other nuclear transients and discuss applications of xillverTDE to super-Eddington accretors.

Keywords: Supermassive black holes, High energy astrophysics, X-ray transient sources, Seyfert galaxies, Active galactic nuclei
On the Nature of Ultracool White Dwarfs: Not so Cool after All. A recent analysis of the 100 pc white dwarf sample in the SDSS footprint demonstrated for the first time the existence of a well-defined ultracool-or IR-faint-white dwarf sequence in the Hertzsprung-Russell diagram. Here we take advantage of this discovery to enlarge the IR-faint white dwarf sample threefold. We expand our selection to the entire Pan-STARRS survey footprint as well as the Montreal White Dwarf Database 100 pc sample and identify 37 candidates with strong flux deficits in the optical. We present follow-up Gemini optical spectroscopy of 30 of these systems and confirm all of them as IR-faint white dwarfs. We identify an additional set of 33 objects as candidates based on their colors and magnitudes. We present a detailed model atmosphere analysis of all 70 newly identified IR-faint white dwarfs together with 35 previously known objects reported in the literature. We discuss the physics of model atmospheres and show that the key physical ingredient missing in our previous generation of model atmospheres was the high-density correction to the He- free-free absorption coefficient. With new model atmospheres calculated for the purpose of this analysis, we now obtain significantly higher effective temperatures and larger stellar masses for these IR-faint white dwarfs than the T eff and M values reported in previous analyses, thus solving a two-decade-old problem. In particular, we identify in our sample a group of ultramassive white dwarfs in the Debye cooling phase with stellar parameters never measured before.

Keywords: Stellar properties, White dwarf stars, Stellar atmospheric opacity, Hertzsprung Russell diagram, Stellar remnants