Sazuna/UAT_keywords huggingface dataset:
A Remarkably Narrow RHESSI X-Ray Flare on 2011 September 25. The unusually narrow X-ray source imaged with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) during an impulsive spike lasting for ∼10 s during the Geostationary Operational Environmental Satellite C7.9 flare on 2011 September 25 (SOL2011-09-25T03:32) was only ∼2″ wide and ∼10″ long. Comparison with Helioseismsic and Magnetic Imager magnetograms and Atmospheric Imaging Assembly images at 1700 Å shows that the X-ray emission was primarily from a long ribbon in the region of positive polarity with little if any emission from the negative polarity ribbon. However, a thermal plasma source density of ∼1012 cm-3 estimated from the RHESSI-derived emission measure and source area showed that this could best be interpreted as a coronal hard X-ray source in which the accelerated electrons with energies less than ∼50 keV were stopped by Coulomb collisions in the corona, thus explaining the lack of the more usual bright X-ray footpoints. Analysis of RHESSI spectra shows greater consistency with a multi-temperature distribution and a low-energy cutoff to the accelerated electron spectrum of 22 keV compared to 12 keV if a single-temperature distribution is assumed. This leads to a change in the lower limit on the total energy in electrons by an order of magnitude, given the steepness of the best-fit electron spectrum with a power-law index of ∼6.

Keywords: Solar flares, Solar x-ray emission, X-ray observatories, Solar x-ray flares
Modulation of Galactic Cosmic Rays from Helium to Nickel in the Inner Heliosphere. Galactic cosmic-ray (GCR) helium and heavier ions are important sources of space radiation, and their elemental spectra and composition can help us better understand the transport in both the galaxy and the heliosphere. A model based on the numerical solution of Parker’s transport equation is used to study the modulation of GCR helium and heavier ions in the inner heliosphere. The model incorporates a modified Parker heliospheric magnetic field, time-dependent diffusion and drift model, time-delayed heliosphere, and randomly determined solar magnetic polarity during solar maximum. We set the outer boundary of modulation at 85 au, and the reference unmodulated GCR energy spectra for GCR helium and heavier ions, which are assumed to have a general form, are determined by fitting the numerical results to the selected GCR measurements, e.g., BESS, ACE/CRIS, HEAO-3-C2, etc. In addition, we use the Sun’s polar magnetic field data from NSO/NISP to determine the possibility of A &gt; 0 during the recent solar maximum, and it gives an improved numerical result during the period 2013-2015. Finally, the fitted unmodulated GCR energy spectra are used to study the long-term modulation of GCRs of helium and heavier ions, and the computed results show good agreement with various GCR measurements.

Keywords: Solar cycle, Heliosphere, Interplanetary turbulence, Solar wind, Galactic cosmic rays, Interplanetary magnetic fields
Multi-wavelength Variability Signatures of Relativistic Shocks in Blazar Jets. Mildly relativistic shocks that are embedded in colliding magnetohydrodynamic flows are prime sites for relativistic particle acceleration and the production of strongly variable, polarized multi-wavelength emission from relativistic jet sources such as blazars and gamma-ray bursts. The principal energization mechanisms at these shocks are diffusive shock acceleration and shock drift acceleration. In recent work, we had self-consistently coupled shock acceleration and radiation transfer simulations in blazar jets in a basic one-zone scenario. These one-zone models revealed that the observed spectral energy distributions (SEDs) of blazars strongly constrain the nature of the hydromagnetic turbulence in the shock layer. In this paper, we expand our previous work by including full time dependence and treating two zones, one being the site of acceleration and the other a larger emission zone. This construction is applied to multi-wavelength flares of the flat-spectrum radio quasar (FSRQ) 3C 279, fitting snapshot SEDs and generating light curves that are consistent with observed variability timescales. We also present a generic study for the typical flaring behavior of the BL Lac object Mrk 501. The model predicts correlated variability across all wavebands, but cross-band time lags depending on the type of blazar (FSRQ versus BL Lac), as well as distinctive spectral hysteresis patterns in all wavelength bands, from millimeter radio waves to gamma-rays. These evolutionary signatures serve to provide diagnostics on the competition between acceleration and radiative cooling.

Keywords: Blazars, Jets, Active galactic nuclei
Evaluating the Classification of Fermi BCUs from the 4FGL Catalog Using Machine Learning. The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac- type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ≃91.8%, or ≃92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.

Keywords: Blazars
Active Galactic Nuclei with Ultrafast Outflows Monitoring Project: The Broad-line Region of Mrk 79 as a Disk Wind. We developed a spectroscopic monitoring project to investigate the kinematics of the broad-line region (BLR) in active galactic nuclei (AGNs) with ultrafast outflows (UFOs). Mrk 79 is a radio-quiet AGN with UFOs and warm absorbers and has been monitored by three reverberation mapping (RM) campaigns, but its BLR kinematics are not yet understood. In this paper, we report the results from a new RM campaign of Mrk 79, which was undertaken with the Lijiang 2.4 m telescope. Mrk 79 appears to come out the faint state, with the mean flux approximately a magnitude fainter than the historical record. We successfully measured the lags of the broad emission lines including Hβ λ4861, Hγ λ4340, He II λ4686, and He I λ5876 with respect to the varying AGN continuum. Based on the broad Hβ λ4861 line, we measured a black hole mass of {M}\bullet ={5.13}-1.55+1.57× {10}7{M}⊙ , and an estimated accretion rate of {\dot{M}}\bullet =(0.05+/- 0.02) {L}Edd} {c}-2, indicating that Mrk 79 is a sub-Eddington accretor. We found that Mrk 79 deviates from the canonical Radius-Luminosity relationship. The marginal blueshift of the broad He II λ4686 line detected from the rms spectrum indicates outflow of high-ionization gas. The velocity-resolved lag profiles of the broad Hγ λ4340, Hβ λ4861, and He I λ5876 lines show similar signatures such that the largest lag occurs in the red wing of the lines and then the lag decreases to both sides. These signatures may suggest that the BLR of Keplerian motion probably exists as outflow gas motion. All findings including UFOs, warm absorbers, and the kinematics of high- and low-ionization BLR, may provide indirect evidence that the BLR of Mrk 79 probably originates from a disk wind.

Keywords: Galactic winds, Supermassive black holes, Galaxy accretion disks, Seyfert galaxies, Active galactic nuclei, Galaxy kinematics, Galaxy accretion, Galaxy luminosities
Mapping the Magnetic Interstellar Medium in Three Dimensions over the Full Sky with Neutral Hydrogen. Recent analyses of 21 cm neutral hydrogen (H I) emission have demonstrated that H I gas is organized into linear filamentary structures that are preferentially aligned with the local magnetic field, and that the coherence of these structures in velocity space traces line-of-sight magnetic field tangling. On this basis, we introduce a paradigm for modeling the properties of magnetized, dusty regions of the interstellar medium (ISM), using the orientation of H I structure at different velocities to map “magnetically coherent” regions of space. We construct three-dimensional (position-position-velocity) Stokes parameter maps using H I4PI full-sky spectroscopic H I data. We compare these maps, integrated over the velocity dimension, to Planck maps of the polarized dust emission at 353 GHz. Without any free parameters governing the relation between H I intensity and dust emission, we find that our Q and U maps are highly correlated (r &gt; 0.75) with the 353 GHz Q and U maps of polarized dust emission observed by Planck and reproduce many of its large-scale features. The E/B ratio of the dust emission maps agrees well with the H I-derived maps at large angular scales (ℓ ≲ 120), supporting the interpretation that this asymmetry arises from the coupling of linear density structures to the Galactic magnetic field. We demonstrate that our 3D Stokes parameter maps constrain the 3D structure of the Galactic ISM and the orientation of the interstellar magnetic field.

Keywords: Galaxy magnetic fields, Interstellar phases, Interstellar filaments, Interstellar atomic gas, Milky Way magnetic fields, Cosmic microwave background radiation, Neutral hydrogen clouds, Interstellar magnetic fields, Starlight polarization, Cold neutral medium, Interstellar medium, Magnetic fields
Critical Velocity Ionization in Substellar Atmospheres. The observation of radio, X-ray, and H α  emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterizes critical velocity ionization (CVI), a potential ionization process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a gas-magnetohydrodynamic (MHD) interactions code (to simulate the ionization mechanism) with a substellar global circulation model (to provide the required gas flows), we quantify the spatial extent of the resulting plasma regions, their degree of ionization, and their lifetime for a typical substellar atmosphere. It is found that the typical average ionization fraction reached at equilibrium (where the ionization and recombination rates are equal and opposite) ranges from 10-5 to 10-8, at pressures between 10-1 and 10-3 bar, with a trend of increasing ionization fraction with decreasing atmospheric pressure. The ionization fractions reached as a result of CVI are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.

Keywords: Magnetohydrodynamics, Brown dwarfs, Ionization, Astrophysical fluid dynamics, Extrasolar gaseous giant planets
Origin of Nonaxisymmetric Features of Virgo Cluster Early-type Dwarf Galaxies. II. Tidal Effects on Disk Features and Stability. A fraction of dwarf galaxies in the Virgo Cluster contain disk features like bars and spiral arms. Using N-body simulations, we investigate the effects of tidal forces on the formation of such disk features in disk dwarf galaxies resembling VCC 856. We consider eight cluster-galaxy models in which disk dwarf galaxies with differing pericenter distance and spin orientation experience the tidal gravitational force of a Virgo-like Navarro-Frenk-White halo, as well as an additional eight galaxy-galaxy models in which two dwarf galaxies undergo tidal interactions with different strength. We find that the cluster tidal effect is moderate owing to the small galaxy size, making the bars form earlier by ∼1-1.5 Gyr compared to the cases in isolation. While the galactic halos significantly lose their mass within the virial radius due to the cluster tidal force, the mass of the stellar disks is nearly unchanged, suggesting that the inner regions of a disk-halo system are secured from the tidal force. The tidal forcing from either the cluster potential or a companion galaxy triggers the formation of two-armed spirals at early time before a bar develops. The tidally driven arms decay and wind with time, suggesting that they are kinematic density waves. In terms of the strength and pitch angle, the faint arms in VCC 856 are best matched with the arms in a marginally unstable galaxy produced by a distant tidal encounter with its neighbor ∼0.85 Gyr ago.

Keywords: Galaxy clusters, Gravitational instability, Computational astronomy, Virgo Cluster, Galaxy dynamics, Galaxy structure, Galaxy bulges, Dwarf galaxies, Spiral arms, Galaxy kinematics
Measuring and Modeling the Rate of Separator Reconnection between an Emerging and an Existing Active Region. Magnetic reconnection occurs when new flux emerges into the corona and becomes incorporated into the existing coronal field. A new active region (AR) emerging in the vicinity of an existing AR provides a convenient laboratory in which reconnection of this kind can be quantified. We use high time-cadence 171 Å data from Solar Dynamics Observatory (SDO)/AIA, focused on new/old active region pair 11147/11149, to quantify reconnection. We identify new loops as brightenings within a strip of pixels between the regions. This strategy is premised on the assumption that the energy responsible for brightening a loop originates in magnetic reconnection. We catalog 301 loops observed in the 48 hr time period beginning with the emergence of AR 11149. The rate at which these loops appear between the two ARs is used to calculate the reconnection rate between them. We then fit these loops with magnetic field, solving for each loop’s field strength, geometry, and twist (via its proxy, coronal α). We find the rate of newly brightened flux overestimates the flux that could be undergoing reconnection. This excess can be explained by our finding that the interconnecting region is not at its lowest energy (constant-α) state; the extrapolations exhibit loop-to-loop variation in α. This flux overestimate may result from the slow emergence of AR 11149, which allows time for Taylor relaxation internal to the domain of the reconnected flux to bring the α distribution toward a single value, providing another mechanism for brightening loops after they are first created.

Keywords: Solar coronal loops, Solar active region magnetic fields, Solar magnetic flux emergence, Solar magnetic reconnection
First Season MWA Phase II Epoch of Reionization Power Spectrum Results at Redshift 7. The compact configuration of Phase II of the Murchison Widefield Array (MWA) consists of both a redundant subarray and pseudo-random baselines, offering unique opportunities to perform sky-model and redundant interferometric calibration. The highly redundant hexagonal cores give improved power spectrum sensitivity. In this paper, we present the analysis of nearly 40 hr of data targeting one of the MWA’s epoch of reionization (EoR) fields observed in 2016. We use both improved analysis techniques presented in Barry et al. and several additional techniques developed for this work, including data quality control methods and interferometric calibration approaches. We show the EoR power spectrum limits at redshift 6.5, 6.8, and 7.1 based on our deep analysis on this 40 hr data set. These limits span a range in k-space of 0.18 h Mpc-1 &lt; k &lt; 1.6 h Mpc-1, with a lowest measurement of Δ2 ≤ 2.39 × 103 mK2 at k = 0.59 h Mpc-1 and z = 6.5.

Keywords: Reionization, Radio interferometry, Astronomy data analysis, Radio interferometers
A Self-consistent Framework for Multiline Modeling in Line Intensity Mapping Experiments. Line intensity mapping (LIM) is a promising approach to study star formation and the interstellar medium (ISM) in galaxies by measuring the aggregate line emission from the entire galaxy population. In this work, we develop a simple yet physically motivated framework for modeling the line emission as would be observed in LIM experiments. It is done by building on analytic models of the cosmic infrared background that connect total infrared luminosity of galaxies to their host dark matter halos. We present models of the {{H}} {{i}} 21 cm, CO (1-0), [{{C}} {{ii}}] 158 μm, and [{{N}} {{ii}}] 122 and 205 μm lines consistent with current observational constraints. With four case studies of various combinations of these lines that probe different ISM phases, we demonstrate the potential for reliably extracting physical properties of the ISM, and the evolution of these properties with cosmic time, from auto- and cross-correlation analysis of these lines as measured by future LIM experiments.

Keywords: Molecular gas, Large-scale structure of the universe, Observational cosmology, Photodissociation regions, H I line emission, Galaxy evolution, Interstellar medium
ALMA Observations of Atomic Carbon [C I] ( <SUP> 3 </SUP> P <SUB> 1 </SUB> → <SUP> 3 </SUP> P <SUB> 0 </SUB>) and Low-J CO Lines in the Starburst Galaxy NGC 1808. We present [C I] ≤ft({}3{{P}}1\to {}3{{P}}0\right), 12CO, 13CO, and C18O (J=2\to 1) observations of the central region (radius 1 kpc) of the starburst galaxy NGC 1808 at 30-50 pc resolution conducted with the Atacama Large Millimeter/submillimeter Array. Radiative transfer analysis of multiline data indicates warm ({T}{{k}}∼ 40{--}80 K) and dense ({n}{{{H}}2}∼ {10}3{--4} cm-3) molecular gas with high column density of atomic carbon ({N}{{C}{{I}}}∼ 3× {10}18 cm-2) in the circumnuclear disk (central 100 pc). The C I/H2 abundance in the central 1 kpc is ∼ 3{--}7× {10}-5, consistent with the values in luminous infrared galaxies. The intensity ratios of [C I]/CO (1-0) and [C I]/CO (3-2), respectively, decrease and increase with radius in the central 1 kpc, whereas [C I]/CO (2-1) is uniform within statistical errors. The result can be explained by excitation and optical depth effects, since the effective critical density of CO (2-1) is comparable to that of [C I]. The distribution of [C I] is similar to that of 13CO (2-1), and the ratios of [C I] to 13CO (2-1) and C18O (2-1) are uniform within ∼ 30 % in the central &lt; 400 pc starburst disk. The results suggest that [C I] ≤ft({}3{{P}}1\to {}3{{P}}0\right) luminosity can be used as a CO-equivalent tracer of molecular gas mass, although caution is needed when applied in resolved starburst nuclei (e.g., circumnuclear disk), where the [C I]/CO (1-0) luminosity ratio is enhanced owing to high excitation and atomic carbon abundance. The [C I]/CO (1-0) intensity ratio toward the base of the starburst-driven outflow is ≲ 0.15, and the upper limits of the mass and kinetic energy of the atomic carbon outflow are ∼ 1× {10}4 {M}⊙  and ∼ 3× {10}51 {erg}, respectively.

Keywords: Starburst galaxies, Molecular gas, Galactic winds, Interstellar atomic gas, Interstellar abundances, Galaxy nuclei, Interstellar medium, Galaxy circumnuclear disk, Galaxies
Discovery of Four Apparently Cold Dusty Galaxies at z = 3.62-5.85 in the COSMOS Field: Direct Evidence of Cosmic Microwave Background Impact on High-redshift Galaxy Observables. We report Atacama Large Millimeter Array (ALMA) observations of four high-redshift dusty star-forming galaxy candidates selected from far-infrared (FIR)/submillimeter observations in the COSMOS field. We securely detect all galaxies in the continuum and spectroscopically confirm them at z = 3.62-5.85 using ALMA 3 mm line scans, detecting multiple CO and/or [C I] transitions. This includes the most distant dusty galaxy currently known in the COSMOS field, ID85001929 at z = 5.847. These redshifts are lower than we had expected, as these galaxies have substantially colder dust temperatures (i.e., their spectral energy distributions peak at longer rest-frame wavelengths) than most literature sources at z &gt; 4. The observed cold dust temperatures are best understood as evidence for optically thick dust continuum in the FIR, rather than the result of low star formation efficiency with rapid metal enrichment. We provide direct evidence that, given their cold spectral energy distributions, cosmic microwave background (CMB) plays a significant role in biasing their observed Rayleigh-Jeans (RJ) slopes to unlikely steep values and, possibly, reducing their CO fluxes by a factor of two. We recover standard RJ slopes when the CMB contribution is taken into account. High-resolution ALMA imaging shows compact morphology and evidence for mergers. This work reveals a population of cold dusty star-forming galaxies that were underrepresented in current surveys and are even colder than typical main-sequence galaxies at the same redshift. High FIR dust optical depth might be a widespread feature of compact starbursts at any redshift.

Keywords: Starburst galaxies, Galaxy formation, Cosmic microwave background radiation, Far infrared astronomy, Dust continuum emission, Galaxy evolution, Interstellar medium, Submillimeter astronomy, High-redshift galaxies, Luminous infrared galaxies
Generic Regular Black Holes Related to Nonlinear Electrodynamics with Maxwellian Weak-field Limit: Shadows and Images of Keplerian Disks. We study optical phenomena in generic regular, magnetically charged, spherically symmetric black hole spacetimes arising from coupling of the Einstein gravity and nonlinear electrodynamics (NED) with the Maxwellian weak-field limit, where photons follow null geodesics of an effective geometry, directly reflecting the electromagnetic nonlinearity. We compare the motion of photons with that of massless neutrinos, which are not affected directly by nonlinearities of the non-Maxwellian electromagnetic field and follow null geodesics of the background spacetime. We determine shadows of such black holes, compare the time delays of photons and neutrinos moving in their field, and construct images of the Keplerian disks. We demonstrate that in the case of the “Maxwellian” NED black holes the optical phenomena give relevant signatures of the NED effects detectable by GRAVITY or the Event Horizon Telescope, but they are not strong enough to be excluded by recent observations as in the case of regular Bardeen black holes.

Keywords: Black holes, Gravitation, Gravitational lensing, General relativity, Charged black holes
Active Region Modulation of Coronal Hole Solar Wind. Active regions (ARs) are a candidate source of the slow solar wind (SW), the origins of which are a topic of ongoing research. We present a case study that examines the processes by which SW is modulated in the presence of an AR in the vicinity of the SW source. We compare properties of SW associated with a coronal hole (CH)-quiet Sun boundary to SW associated with the same CH but one Carrington rotation later, when this region bordered the newly emerged NOAA AR 12532. Differences found in a range of in situ parameters are compared between these rotations in the context of source region mapping and remote sensing observations. Marked changes exist in the structure and composition of the SW, which we attribute to the influence of the AR on SW production from the CH boundary. These unique observations suggest that the features that emerge in the AR-associated wind are consistent with an increased occurrence of interchange reconnection during SW production, compared with the initial quiet Sun case.

Keywords: Slow solar wind, Solar atmosphere, Solar magnetic reconnection, Heliosphere, Solar wind, Solar active regions, Interplanetary magnetic fields, Solar coronal holes