Sazuna/UAT_keywords huggingface dataset:
Multiscale Time- and Frequency-domain Likelihood Analysis with Photon Weights. We present an unbinned likelihood analysis formalism employing photon weights—the probabilities that events are associated with a particular source. This approach is applicable to any photon-resolving instrument and thus well suited to high-energy observations; we focus here on GeV γ-ray data from the Fermi Large Area Telescope. Weights connect individual photons to the outputs of a detailed, expensive likelihood analysis of a much larger data set. The weighted events can be aggregated into arbitrary time spans ranging from microseconds to years. Such retrospective grouping permits time- and frequency-domain analysis over a wide range of scales and enables characterization of disparate phenomena like blazar flares, γ-ray bursts, pulsar pulses, novae, γ-ray binaries, and other variable sources. To demonstrate the formalism, we incorporate photon weights into the Bayesian blocks algorithm and perform a hierarchical timescale analysis of 3C 279 activity. We analyze pulsar pulse profiles and estimate the unpulsed emission level and the optimal division of the data into on- and off-pulse intervals. We extend the formalism to Fourier analysis and derive estimators for power spectra, used to search for and characterize periodic sources. We show how the fast Fourier transform can be used to probe orbital periods as short as a minute, and we discuss the mitigation of spurious signals. Our final example combines time- and frequency- domain analysis to jointly characterize the flares and orbital modulation of Cygnus X-3, yielding the strongest detection of the orbital signal (&gt;13σ) to date. Finally, we discuss extensions of the work to other GeV sources and to X-ray and TeV observations.

Keywords: Blazars, Astrostatistics techniques, High time resolution astrophysics, Time series analysis
Magnetospheric Accretion as a Source of Hα Emission from Protoplanets around PDS 70. Advances in high-resolution imaging have revealed Hα emission separate from the host star. It is generally believed that the emission is associated with planets forming in protoplanetary disks. However, the nature of this emission is still not fully understood. Here we report a modeling of Hα emission from the planets around the young star PDS 70. Using standard magnetospheric accretion models previously applied to accreting young stars, we find that the observed line fluxes can be reproduced using a range of parameters relevant to PDS 70b and c, with a mean mass accretion rate of log(\dot{M}) = -8.0 ± 0.6 M Jup yr-1 and -8.1 ± 0.6 M Jup yr-1 for PDS 70b and PDS 70c, respectively. Our results suggest that Hα emission from young planets can originate in the magnetospheric accretion of mass from the circumplanetary disk. We find that empirical relationships between mass accretion rate and Hα line properties frequently used in T Tauri stars are not applicable in the planetary mass regime. In particular, the correlations between line flux and mass accretion rate underpredict the accretion rate by about an order of magnitude, and the width at the 10% height of the line is insensitive to the accretion rate at \dot{M} &lt; 10-8 M Jup yr-1.

Keywords: Accretion, H I line emission, T Tauri stars, Protoplanetary disks, Exoplanet formation
Possible Contribution of Magnetized White Dwarf Binaries to Type Ia Supernova Populations. The evolution of an accreting white dwarf (WD) with a strong magnetic field toward a Type Ia supernova (SN Ia) may differ from the classical single-degenerate (SD) channel. In this paper, we perform binary population synthesis simulations for the SD channel with a main-sequence (MS) companion, including the strongly magnetized WD accretion. Under a reasonable assumption that the fraction of such systems is ∼15%, the resulting delay-time distribution roughly follows the t -1 power-law distribution. Within the (WD/MS) SD channel, the contribution from the highly magnetized WD is estimated to be comparable to that from the classical, non-magnetized WD channel. The contribution of the SD channel toward SNe Ia can be at least ∼30% among the whole SN Ia population. We suggest that the SNe Ia resulting from the highly magnetized WD systems would not share the observational properties expected for the classical SD channel; for every (potentially peculiar) SN observationally associated with the SD channel, we expect a comparable number of the “hidden” SD population to be in the normal class.

Keywords: Close binary stars, White dwarf stars, Type Ia supernovae, Supernovae
The Initial Physical Conditions of the Orion BN/KL Fingers. Orion BN/KL is an example of a poorly understood phenomena in star-forming regions involving the close encounters of young stellar objects. The explosive structure, the great variety of molecules observed, the energy involved in the event, and the mass of the region suggest a contribution to the chemical diversity of the local interstellar medium. Nevertheless, the frequency and duration of other, similar events have not been determined. In this paper, we explore a recent analytic model that takes into account the interaction of a clump with its molecular environment. We show that the widespread kinematic ages of the Orion fingers—500 to 4000 yr—are a consequence of the interaction of the explosion debris with the surrounding medium. This model explains satisfactorily the age discrepancy of the Orion fingers, and infers the initial conditions together with the lifetime of the explosion. Moreover, our model can explain why some CO streamers do not have an associated H2 finger.

Keywords: Interstellar dynamics, Interstellar medium
Runaway O-star Bow Shocks as Particle Accelerators? The Case of AE Aur Revisited. We present results of our Chandra/ACIS observations of the field centered on the fast, runaway O star AE Aur and its bow shock. Previous XMM-Newton observations revealed an X-ray “blob” near the IR arc tracing the bow shock, possibly a nonthermal source consistent with models of Inverse Compton scattering of dust IR photons by electrons accelerated at the shock. The new, subarcsecond-resolution Chandra data, while confirming the presence of the XMM-Newton source, clearly indicate that the latter is neither extended nor coincident with the IR arc and strongly suggest it is a background active galactic nucleus. Motivated by results published for the bow shock of BD+43°3654, we extended our study to the radio domain by analyzing archival EVLA data. We find no radio emission from the AE Aur bow shock either. The corresponding upper limits for the absorbed (unabsorbed) X-ray flux of 5.9(7.8) × 10-15 erg cm-2 s-1 (3σ) and, in the radio range of 2 mJy (1.4 GHz) and 0.4 mJy (5.0 GHz), are used to put constraints on model predictions for particle acceleration within the bow shock. In the “classical” framework of diffusive shock acceleration, we find that the predicted X-ray and radio emission by the bow shock is at least two orders of magnitude below the current upper limits, consistent with the systematic nondetections of up to 60 stellar bow shocks. The only exception so far remains that of BD+43°3654, which is probably the result of its very large mass-loss rate among runaway O stars.

Keywords: X-ray astronomy, Massive stars, Stellar bow shocks, Runaway stars, Particle astrophysics
Searching for the Magnetized Tidal Dwarf Galaxies in Hickson Compact Groups: HCG 26, 91, and 96. In this work, archive 1.4 and 4.86 GHz radio continuum data from the Very Large Array were re-reduced and, together with the 1.4 GHz maps from the NRAO VLA Sky Survey, investigated for the presence of detectable, nonthermal continuum radio emission that could be associated with the tidal dwarf galaxy (TDG) candidates in HCG 26, 91, and 96. Radio emission highly coincident with the optical and H α  emission maxima of the TDG candidate HCG 91i (estimated physical separation of less than 150 pc) was revealed. Should this emission be intrinsic to this object, it would imply the presence of a magnetic field as strong as 11-16 μG—comparable to that found in the most radio-luminous, star-forming dwarf galaxies of non-tidal origin. However, the star formation rate derived for this object using the radio flux is about two orders of magnitude higher than the one estimated from the H α  data. Analysis of the auxiliary radio, ultraviolet, and infrared data suggests that either the radio emission originates in a background object with an aged synchrotron spectrum (possibly a GHz-peaked source), or the {SFR}}{{{H}}α } estimate is lower due to the fact that it traces the most recent star formation, while most of the detected radio emission originated when what is known as HCG 91i was still a part of its parent galaxy. The latter scenario is supported by a very large stellar mass derived from 3.6 to 4.5 μm data, implying a high star formation rate in the past.

Keywords: Hickson compact group, Galaxy tides, Star formation, Tidal interaction, Radio astronomy, Extragalactic magnetic fields
Evidence for a Massive Warm-Hot Circumgalactic Medium around NGC 3221. We report a 3.4σ detection of the warm-hot, massive, extended circumgalactic medium (CGM) around an L ⋆ star-forming spiral galaxy NGC 3221, using deep Suzaku observations. The temperature of the gas is 106.1 K, comparable to that of the Milky Way CGM. The spatial extent of the gas is at least 150 kpc. For a β-model of density profile with solar abundance, the central emission measure is EM = (3 ± 1) × 10-5 cm-6 kpc and the central electron density is n eo = (4 ± 1) × 10-4 cm-3, with a slope of β = 0.56. We investigate a range of β values and find that the details of the density profile do not change our results significantly. The mass of the warm-hot gas, assuming a metallicity of \tfrac{1}{3} Z ☉, is (16 ± 3) × 1010 M ☉, which is the most massive baryon component of NGC 3221. The baryon fraction is f  b  = 0.120 ± 0.036 (statistical) {}-0.048+0.104 (systematic), consistent with the cosmological mean value, closing the baryon budget of this galaxy. We also investigated the missing metals problem in conjunction with the missing baryons problem and conclude that metals are likely to be preferentially expelled from the galaxy. Ours is the first detection of an extended warm-hot CGM around an external L ⋆ star-forming spiral galaxy, where the CGM likely accounts for the missing galactic baryons.

Keywords: X-ray astronomy, Galaxy environments, Missing mass, Circumgalactic medium, Hot ionized medium, Extragalactic astronomy, Diffuse x-ray background
Chemical Abundances in a Turbulent Medium-H<SUB>2</SUB>, OH<SUP>+</SUP>, H<SUB>2</SUB>O<SUP>+</SUP>, ArH<SUP>+</SUP>. Supersonic turbulence results in strong density fluctuations in the interstellar medium (ISM), which have a profound effect on the chemical structure. Particularly useful probes of the diffuse ISM are the ArH+, OH+, H2O+ molecular ions, which are highly sensitive to fluctuations in the density and the H2 abundance. We use isothermal magnetohydrodynamic simulations of various sonic Mach numbers, {{ \mathcal M }}{{s}}, and density decorrelation scales, y dec, to model the turbulent density field. We post process the simulations with chemical models and obtain the probability density functions (PDFs) for the H2, ArH+, OH+, and H2O+ abundances. We find that the PDF dispersions increases with increasing {{ \mathcal M }}{{s}} and y dec, as the magnitude of the density fluctuations increases, and as they become more coherent. Turbulence also affects the median abundances: when {{ \mathcal M }}{{s}} and y dec are high, low-density regions with low H2 abundance become prevalent, resulting in an enhancement of ArH+ compared to OH+ and H2O+. We compare our models with Herschel observations. The large scatter in the observed abundances, as well as the high observed ArH+/OH+ and ArH+/H2O+ ratios are naturally reproduced by our supersonic ({{ \mathcal M }}{{s}}=4.5), large decorrelation scale (y dec = 0.8) model, supporting a scenario of a large-scale turbulence driving. The abundances also depend on the ultraviolet intensity, cosmic-ray ionization rate, and the cloud column density, and the observed scatter may be influenced by fluctuations in these parameters.

Keywords: Chemical abundances, Photodissociation regions, Galactic cosmic rays, Interstellar medium, Magnetohydrodynamical simulations
An Unusual Mid-infrared Flare in a Type 2 AGN: An Obscured Turning-on AGN or Tidal Disruption Event?. We report the discovery of an exceptional MIR flare in a Type 2 AGN, SDSS J165726.81+234528.1, at z = 0.059. This object brightened by 3 mag in the Wide-field Infrared Survey Explorer (WISE) W1 and W2 bands between 2015 and 2017 (and has been fading since 2018), without significant changes (≲0.2 mag) in the optical over the same period of time. Based on the WISE light curves and near-IR imaging, the flare is more significant at longer wavelengths, suggesting an origin of hot dust emission. The estimated black hole mass (∼106.5 M ⊙) from different methods places its peak bolometric luminosity around the Eddington limit. The high luminosity of the MIR flare and its multiyear timescale suggest that it most likely originated from reprocessed dust radiation in an extended torus surrounding the AGN, instead of from stellar explosions. The MIR color variability is consistent with known changing-look AGN and tidal disruption events (TDEs), but inconsistent with normal supernovae. We suggest that it is a turning-on Type 2 AGN or TDE, where the optical variability is obscured by the dust torus during the transition. This MIR flare event reveals a population of dramatic nuclear transients that are missed in the optical.

Keywords: Accretion, Tidal disruption, Active galactic nuclei
A BCG with Offset Cooling: Is the AGN Feedback Cycle Broken in A2495?. We present a combined radio/X-ray analysis of the poorly studied galaxy cluster A2495 (z = 0.07923) based on new EVLA and Chandra data. We also analyze and discuss Hα emission and optical continuum data retrieved from the literature. We find an offset of ∼6 kpc between the cluster brightest cluster galaxy (BCG) (MCG+02-58-021) and the peak of the X-ray emission, suggesting that the cooling process is not taking place on the central galaxy nucleus. We propose that sloshing of the intracluster medium (ICM) could be responsible for this separation. Furthermore, we detect a second, ∼4 kpc offset between the peak of the Hα emission and that of the X-ray emission. Optical images highlight the presence of a dust filament extending up to ∼6 kpc in the cluster BCG and allow us to estimate a dust mass within the central 7 kpc of 1.7 × 105 M ⊙. Exploiting the dust-to-gas ratio and the L Hα -M mol relation, we argue that a significant amount (up to 109 M ⊙) of molecular gas should be present in the BCG of this cluster. We also investigate the presence of ICM depressions, finding two putative systems of cavities; the inner pair is characterized by t age ∼ 18 Myr and P cav ∼ 1.2 × 1043 erg s-1, the outer one by t age ∼ 53 Myr and P cav ∼ 5.6 × 1042 erg s-1. Their age difference appears to be consistent with the freefall time of the central cooling gas and with the offset timescale estimated with the Hα kinematic data, suggesting that sloshing is likely playing a key role in this environment. Furthermore, the cavities’ power analysis shows that the active galactic nucleus energy injection is able to sustain the feedback cycle, despite cooling being offset from the BCG nucleus.

Keywords: Very Large Array, Dust nebulae, Cooling flows, Hubble Space Telescope, Extragalactic radio sources, Rich galaxy clusters, Radio galaxies, X-ray sources, X-ray observatories, Radio continuum emission, Abell clusters, Intracluster medium
Mass Loss on the Red Giant Branch: Plasmoid-driven Winds above the RGB Bump. The onset of cool massive winds in evolved giants is correlated with an evolutionary feature on the red giant branch (RGB) known as the “bump.” Also at the bump, shear instability in the star leads to magnetic fields that occur preferentially on small length-scales. Pneuman has suggested that the emergence of small-scale flux tubes in the Sun can give rise to enhanced acceleration of the solar wind as a result of plasmoid acceleration (the so-called “melon-seed mechanism”). In this paper, we examine Pneuman’s formalism to determine if it may shed some light on the process that drives mass loss in stars above the RGB bump. Because we do not currently have detailed information for some of the relevant physical parameters, we are not yet able to derive a detailed model: instead, our goal in this paper is to explore a “proof of concept.” Using parameters that are known to be plausible in cool giants, we find that the total mass-loss rate from such stars can be replicated. Moreover, we find that the radial profile of the wind speed in such stars can be steep or shallow depending on the fraction of the mass-loss rate that is contained in the plasmoids: this is consistent with empirical data that indicate that the velocity profiles of winds from cool giants span a range of steepnesses.

Keywords: Giant stars
Abundant Refractory Sulfur in Protoplanetary Disks. Sulfur is one of the most abundant elements in the universe, with important roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming disks have previously eluded detection: gaseous molecules only account for &lt;1% of total elemental sulfur, with the rest likely in either ices or refractory minerals. We use a new method to measure the refractory component. Mechanisms such as giant planets can filter out dust from gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this leaves a chemical signature on the stellar photosphere that can be used to determine the fraction of each element that is locked in dust. Here, we present an application of this method to sulfur, zinc, and sodium. We analyze the accretion-contaminated photospheres of a sample of young stars and find (89 ± 8)% of elemental sulfur is in refractory form in their disks. The main carrier is much more refractory than water ice, consistent with sulfide minerals such as FeS.

Keywords: Meteorite composition, Astrochemistry, Protoplanetary disks, Chemically peculiar stars, Planet formation
Determining Fireball Fates Using the α-β Criterion. As fireball networks grow, the number of events observed becomes unfeasible to manage by manual efforts. Reducing and analyzing big data requires automated data pipelines. Triangulation of a fireball trajectory can swiftly provide information on positions and, with timing information, velocities. However, extending this pipeline to determine the terminal mass estimate of a meteoroid is a complex next step. Established methods typically require assumptions to be made of the physical meteoroid characteristics (such as shape and bulk density). To determine which meteoroids may have survived entry there are empirical criteria that use a fireball’s final height and velocity—low and slow final parameters are likely the best candidates. We review the more elegant approach of the dimensionless coefficient method. Two parameters, α (ballistic coefficient) and β (mass loss), can be calculated for any event with some degree of deceleration, given only velocity and height information. α and β can be used to analytically describe a trajectory with the advantage that they are not mere fitting coefficients; they also represent the physical meteoroid properties. This approach can be applied to any fireball network as an initial identification of key events and determine on which to concentrate resources for more in-depth analyses. We used a set of 278 events observed by the Desert Fireball Network to show how visualization in an α-β diagram can quickly identify which fireballs are likely meteorite candidates.

Keywords: Fireballs, Meteors, Meteoroids, Bolides
Dissecting the Hot Bubbles in LMC-N57 with XMM-Newton. We present a study of the diffuse X-ray emission from the star-forming region LMC-N 57 in the Large Magellanic Cloud. We use archival XMM-Newton observations to unveil in detail the distribution of hot bubbles in this complex. X-ray emission is detected from the central superbubble (SB) DEM L 229, the supernova remnant (SNR) 0532-675, and the Wolf-Rayet (WR) bubble DEM L 231 around the WR star Br 48. Comparison with infrared (IR) images unveils the powerful effect of massive stars in destroying their nurseries. The distribution of the hot gas in the SNR and the SB display their maxima in regions in contact with the filamentary cold material detected by IR images. Our observations do not reveal extended X-ray emission filling DEM L 231, although several pointlike sources are detected in the field of view of this WR nebula. The X-ray properties of Br 48 are consistent with a binary WN4+O as proposed by other authors. We modeled the X-ray emission from the SB and found that its X-ray emission can be simply explained by pressure-driven wind model—that is, there is no need to invoke the presence of an SN explosion as previously suggested. The pressure calculations of the hot gas confirms that the dynamical evolution of SB DEM L 229 is dominated by the stellar winds from the star cluster LH 76.

Keywords: X-ray astronomy, Interstellar medium wind, Stellar wind bubbles
Modeling Mg II during Solar Flares. II. Nonequilibrium Effects. To extract the information that the Mg II NUV spectra (observed by the Interface Region Imaging Spectrograph) carry about the chromosphere during solar flares, and to validate models of energy transport via model-data comparison, forward modeling is required. The assumption of statistical equilibrium (SE) is typically used to obtain the atomic level populations from snapshots of flare atmospheres, due to computational necessity. However, it is possible that relying on SE could lead to spurious results. We compare solving the atomic level populations via SE versus a nonequilibrium (NEQ) time-dependent approach. This was achieved using flare simulations from RADYN alongside the minority species version MS_RADYN from which the time-dependent Mg II atomic level populations and radiation transfer were computed in complete frequency redistribution. The impacts on the emergent profiles, lightcurves, line ratios, and formation heights are discussed. In summary we note that NEQ effects during flares are typically important only in the initial stages and for a short period following the cessation of the energy injection. An analysis of the timescales of ionization equilibrium reveals that for most of the duration of the flare, when the temperatures and densities are sufficiently enhanced, the relaxation timescales are short (τ relax &lt; 0.1 s), so that the equilibrium solution is an adequate approximation. These effects vary with the size of the flare, however. In weaker flares, effects can be more pronounced. We recommend that NEQ effects be considered when possible but that SE is sufficient at most stages of the flare.

Keywords: Solar flares, Near ultraviolet astronomy, Solar flare spectra, Computational methods, Radiative transfer, Radiative transfer simulations, Solar chromosphere, Active solar chromosphere