Sazuna/UAT_keywords huggingface dataset:
Properties of M Dwarf Flares at Millimeter Wavelengths. We report on two millimeter flares detected by the Atacama Large Millimeter/submillimeter Array at 220 GHz from AU Mic, a nearby M dwarf. The larger flare had a duration of only ∼35 s, with peak LR = 2 × 1015 erg s-1 Hz-1, and lower limit on linear polarization of | Q/I| &gt; 0.12 ± 0.04. We examine the characteristics common to these new AU Mic events and those from Proxima Cen previously reported in MacGregor et al. - namely short durations, negative spectral indices, and significant linear polarization - to provide new diagnostics of conditions in outer stellar atmospheres and details of stellar flare particle acceleration. The event rates (∼20 and 4 events days-1 for AU Mic and Proxima Cen, respectively) suggest that millimeter flares occur commonly but have been undetected until now. Analysis of the flare observing frequency and consideration of possible incoherent emission mechanisms confirms the presence of MeV electrons in the stellar atmosphere occurring as part of the flare process. The spectral indices point to a hard distribution of electrons. The short durations and lack of pronounced exponential decay in the light curve are consistent with formation in a simple magnetic loop, with radio emission predominating from directly precipitating electrons. We consider the possibility of both synchrotron and gyrosynchrotron emission mechanisms, although synchrotron is favored given the linear polarization signal. This would imply that the emission must be occurring in a low density environment of only modest magnetic field strength. A deeper understanding of this newly discovered and apparently common stellar flare mechanism awaits more observations with better-studied flare components at other wavelengths.

Keywords: M dwarf stars, Red dwarf flare stars, Flare stars, Stellar activity, Stellar flares, Submillimeter astronomy, Radio astronomy
Stellar Cores in the Sh 2-305 H II Region. Using our deep optical and near-infrared photometry along with multiwavelength archival data, we here present a detailed study of the Galactic H II region Sh 2-305 to understand the star/star-cluster formation. On the basis of excess infrared emission, we have identified 116 young stellar objects (YSOs) within a field of view of ∼18'5 × 18'5 around Sh 2-305. The average age, mass, and extinction (AV) for this sample of YSOs are 1.8 Myr, 2.9 M⊙, and 7.1 mag, respectively. The density distribution of stellar sources along with minimal spanning tree calculations on the location of YSOs reveals at least three stellar subclusterings in Sh 2-305. One cluster is seen toward the center (I.e., Mayer 3), while the other two are distributed toward the north and south directions. Two massive O-type stars (VM2 and VM4; ages ∼5 Myr) are located at the center of the Sh 2-305 H II region. The analysis of the infrared and radio maps traces the photon-dominant regions (PDRs) in Sh 2-305. The association of the younger generation of stars with the PDRs is also investigated in Sh 2-305. This result suggests that these two massive stars might have influenced the star formation history in Sh 2-305. This argument is also supported by the calculation of various pressures driven by massive stars, the slope of the mass function/K-band luminosity function, star formation efficiency, fraction of Class I sources, and mass of the dense gas toward the subclusterings in Sh 2-305.

Keywords: Star forming regions, Star formation, Interstellar medium, Open star clusters, H II regions
The Fast Radio Burst Luminosity Function and Death Line in the Low-twist Magnetar Model. We explore the burst energy distribution of fast radio bursts (FRBs) in the low-twist magnetar model of Wadiasingh &amp; Timokhin (WT19). Motivated by the power-law fluence distributions of FRB 121102, we propose an elementary model for the FRB luminosity function of individual repeaters with an inversion protocol that directly relates the power-law distribution index of magnetar short burst fluences to that for FRBs. The protocol indicates that the FRB energy scales virtually linearly with crust/field dislocation amplitude, if magnetar short bursts prevail in the magnetoelastic regime. Charge starvation in the magnetosphere during bursts (required in WT19) for individual repeaters implies the predicted burst fluence distribution is narrow, &amp;lsim;3 decades for yielding strains and oscillation frequencies feasible in magnetar crusts. Requiring magnetic confinement and charge starvation, we obtain a death line for FRBs, which segregates magnetars from the normal pulsar population, suggesting only the former will host recurrent FRBs. We convolve the burst energy distribution for individual magnetars to define the distribution of luminosities in evolved magnetar populations. The broken power-law luminosity function's low-energy character depends on the population model, while the high-energy index traces that of individual repeaters. Independent of the evolved population, the broken power-law isotropic-equivalent energy/luminosity function peaks at ∼1037-1040 erg with a low-energy cutoff at ∼1037 erg. Lastly, we consider the local fluence distribution of FRBs and find that it can constrain the subset of FRB-producing magnetar progenitors. Our model suggests that improvements in sensitivity may reveal a flattening of the global FRB fluence distribution and saturation in FRB rates.

Keywords: Neutron stars, Optical bursts, Luminosity function, Gamma-ray bursts, Cosmology, High energy astrophysics, Radio bursts, X-ray transient sources, Non-thermal radiation sources, Magnetars, X-ray bursts, Radio transient sources
Velocity-coherent Filaments in NGC 1333: Evidence for Accretion Flow?. Recent observations of global velocity gradients across and along molecular filaments have been interpreted as signs of gas accreting onto and along these filaments, potentially feeding star-forming cores and protoclusters. The behavior of velocity gradients in filaments, however, has not been studied in detail, particularly on small scales (&lt;0.1 pc). In this paper, we present MUFASA, an efficient, robust, and automatic method to fit ammonia lines with multiple velocity components, generalizable to other molecular species. We also present CRISPy, a Python package to identify filament spines in 3D images (e.g., position-position-velocity cubes), along with a complementary technique to sort fitted velocity components into velocity-coherent filaments. In NGC 1333, we find a wealth of velocity gradient structures on a beam-resolved scale of ∼0.05 pc. Interestingly, these local velocity gradients are not randomly oriented with respect to filament spines and their perpendicular, I.e., radial, component decreases in magnitude toward the spine for many filaments. Together with remarkably constant velocity gradients on larger scales along many filaments, these results suggest a scenario in which gas falling onto filaments is progressively damped and redirected to flow along these filaments.

Keywords: Interstellar molecules, Molecular gas, Interstellar filaments, Molecular spectroscopy, Molecular clouds, Star formation, Interstellar medium, Radio astronomy
Manganese Indicates a Transition from Sub- to Near-Chandrasekhar Type Ia Supernovae in Dwarf Galaxies. Manganese abundances are sensitive probes of the progenitors of Type Ia supernovae (SNe Ia). In this work, we present a catalog of manganese abundances in dwarf spheroidal satellites of the Milky Way, measured using medium-resolution spectroscopy. Using a simple chemical evolution model, we infer the manganese yield of SNe Ia in the Sculptor dwarf spheroidal galaxy (dSph) and compare to theoretical yields. The sub-solar yield from SNe Ia ([Mn/Fe]_{Ia}=-{0.30}_{-0.03}^{+0.03} at [Fe/ H] = -1.5 dex, with negligible dependence on metallicity) implies that sub-Chandrasekhar-mass (sub-MCh) white dwarf progenitors are the dominant channel of SNe Ia at early times in this galaxy, although some fraction (≳20%) of MCh Type Ia or Type Iax SNe are still needed to produce the observed yield. First-order corrections for deviations from local thermodynamic equilibrium increase the inferred [Mn/Fe]_{Ia} by as much as ∼0.3 dex. However, our results also suggest that the nucleosynthetic source of SNe Ia may depend on environment. In particular, we find that dSphs with extended star formation histories (Leo I, Fornax dSphs) appear to have higher [Mn/Fe] at a given metallicity than galaxies with early bursts of star formation (Sculptor dSph), suggesting that MCh progenitors may become the dominant channel of SNe Ia at later times in a galaxy's chemical evolution.

Keywords: Stellar abundances, Dwarf galaxies, Chemical abundances, Galaxy abundances, Type Ia supernovae, Dwarf spheroidal galaxies, Sculptor dwarf elliptical galaxy
Kinetic Models of Tangential Discontinuities in the Solar Wind. Kinetic-scale current sheets observed in the solar wind are frequently approximately force-free despite the fact that their plasma β is of the order of one. In situ measurements have recently shown that plasma density and temperature often vary across the current sheets, while the plasma pressure is approximately uniform. In many cases these density and temperature variations are asymmetric with respect to the center of the current sheet. To model these observations theoretically we develop in this paper equilibria of kinetic-scale force-free current sheets that have plasma density and temperature gradients. The models can also be useful for analysis of stability and dissipation of the current sheets in the solar wind.

Keywords: Interplanetary discontinuities, Solar wind, Interplanetary magnetic fields
An Empirical "High-confidence" Candidate Zone for Fermi BL Lacertae Objects. In the third catalog of active galactic nuclei detected by the Fermi Large Area Telescope Clean (3LAC) sample, there are 402 blazar candidates of uncertain type (BCU). The proposed analysis will help to evaluate the potential optical classification flat spectrum radio quasars (FSRQs) versus BL Lacertae (BL Lac) objects of BCUs, which can help to understand which is the most elusive class of blazar hidden in the Fermi sample. By studying the 3LAC sample, we found some critical values of γ-ray photon spectral index (Γph), variability index (VI), and radio flux F_{R}) of the sources separate known FSRQs and BL Lac objects. We further utilize those values to defined an empirical "high-confidence" candidate zone that can be classified as BCUs. Within such a zone (Γph &lt; 2.187, log FR &lt; 2.258, and log VI &lt; 1.702), we found that 120 BCUs can be classified as BL Lac object candidates with a higher degree of confidence (with a misjudged rate &lt;1%). Our results suggest that an empirical "high-confidence" diagnosis is possible to distinguish the BL Lac objects from the Fermi observations based on only the direct observational data of Γph, VI, and FR.

Keywords: Blazars, BL Lacertae objects
White-light Emission and Chromospheric Response by an X1.8-class Flare on 2012 October 23. On 2012 October 23, a strong white-light emission, associated with an X1.8-class flare, was observed by the Solar Optical Telescope on board the Hinode satellite. White-light kernels were clearly observed along the Ca II H ribbons. RHESSI also observed hard X-ray emissions that were almost located on the white-light kernels. The total energy of the white-light emission was ∼ 1027-28 erg, s-1 and the total energy of the accelerated electrons was almost of the same order when we used 40 keV as the lower energy cutoff. The white-light emission appears to have originated from nonthermal electrons in these energies. Moreover, the EUV imaging spectrometer on board the Hinode satellite performed a raster scan over this flaring active region and the flare occurred during the scan. Over the white-light kernels, we observed redshifts of a few tens of km s-1 in Fe XII. It appears that these EUV responses originated from some accelerated electrons due to the solar flare and they are considered to be the source of the white-light emission. In fact, the electron density of the white-light kernels was less than 1012 cm-3, which is sufficiently low for nonthermal electrons to penetrate into the photosphere.

Keywords: Solar ultraviolet emission, Solar chromosphere, Solar white-light flares
The Frequency Drift and Fine Structures of Solar S-bursts in the High Frequency Band of LOFAR. Solar S-bursts are short duration (&lt;1 s at decameter wavelengths) radio bursts that have been observed during periods of moderate solar activity, where S stands for short. The frequency drift of S-bursts can reflect the coronal density variation and the motion state of the electron beams. In this work, we investigate the frequency drift and the fine structure of the S-bursts with the Low Frequency Array (LOFAR). We find that the average frequency drift rate of the S-bursts within 20-180 MHz could be described by df/dt = -0.0077f1.59, combined with previous results in low frequency. With the high time and frequency resolution of LOFAR, we can resolve the fine structures of the observed solar S-bursts. A fine drift variation pattern was found in the structure of S-bursts (referred to as solar Sb-bursts in this paper) during the type-III storm on 2019 April 13, in the frequency band of 120-240 MHz. The Sb-bursts have a quasiperiodic segmented pattern, and the relative flux intensity tends to be large when the frequency drift rate is relatively large. This kind of structure exists in about 20% of the solar S-burst events within the observed frequency range. We propose that the fine structure is due to the density fluctuations of the background coronal density. We performed a simulation based on this theory that can reproduce the shape and relative flux intensity of the Sb-bursts. This work shows that the fine structure of solar radio bursts can be used to diagnose the coronal plasma.

Keywords: Radio bursts, Solar radio emission, Solar corona, Radiative transfer
Pressure Profiles and Mass Estimates Using High-resolution Sunyaev-Zel'dovich Effect Observations of Zwicky 3146 with MUSTANG-2. The galaxy cluster Zwicky 3146 is a sloshing cool core cluster at z = 0.291 that in X-ray imaging does not appear to exhibit significant pressure substructure in the intracluster medium (ICM). The published M500 values range between 3.88-0.58+0.62 to (22.50 ± 7.58) × 1014 M☉, where ICM-based estimates with reported errors &lt;20% suggest that we should expect to find a mass between 6.53-0.44+0.44 × 1014 M☉ (from Planck, with an 8.4σ detection) and 8.52-1.47+1.77 × 1014 M☉ (from ACT, with a 14σ detection). We investigate the ability to estimate the mass of Zwicky 3146 via the Sunyaev-Zel'dovich (SZ) effect with data taken at 90 GHz by MUSTANG-2 to a noise level better than 15 μK at the center and a cluster detection of 61σ. We derive a pressure profile from our SZ data, which is in excellent agreement with that derived from X-ray data. From our SZ-derived pressure profiles, we infer M500 and M2500 via three methods - Y-M scaling relations, the virial theorem, and hydrostatic equilibrium (HE) - where we employ X-ray constraints from XMM-Newton on the electron density profile when assuming HE. Depending on the model and estimation method, our M500 estimates range from 6.13 ± 0.69 to (10.6 ± 2.0) × 1014 M☉, where our estimate from HE is 7.69-1.98+2.19 (±27% stat)-0.59+0.63 (±7.9% sys, calibration) × 1014 M☉. Our fiducial mass, derived from a Y-M relation is 8.06-0.61+0.67 (±7.9% stat)-0.42+0.45 (±5.4% sys, Y-M)-0.54+0.58 (±6.9% sys, cal.) × 1014 M☉.

Keywords: Galaxy clusters, Rich galaxy clusters, Intracluster medium
The Magnetic Sensitivity of the Resonance and Subordinate Lines of Mg II in the Solar Chromosphere. We carry out a theoretical study of the polarization of the solar Mg II h-k doublet (including its extended wings) and the subordinate ultraviolet (UV) triplet around 280 nm. These lines are of great diagnostic interest, as they encode information on the physical properties of the solar atmosphere from the upper photosphere to the chromosphere-corona transition region. We base our study on radiative transfer calculations of spectral line polarization in one-dimensional models of quiet and plage regions of the solar atmosphere. Our calculations take into account the combined action of atomic polarization, quantum level interference, frequency redistribution, and magnetic fields of arbitrary strength. In particular, we study the sensitivity of the emergent Stokes profiles to changes in the magnetic field through the Zeeman and Hanle effects. We also study the impact of the chromospheric plasma dynamics on the emergent Stokes profiles, taking into account the angle-dependent frequency redistribution in the h-k resonance transitions. The results presented here are of interest for the interpretation of spectropolarimetric observations in this important region of the solar UV spectrum.

Keywords: Spectropolarimetry, Quiet solar chromosphere, Solar magnetic fields, Solar transition region, Radiative transfer simulations, Active solar chromosphere
Wave Excitation by Energetic Ring-distributed Electron Beams in the Solar Corona. We analyzed properties of waves excited by mildly relativistic electron beams propagating along the magnetic field with a ring-shape perpendicular momentum distribution in neutral and current-free solar coronal plasmas. These plasmas are subject to both the beam and the electron cyclotron maser instabilities driven by the positive momentum gradients of the ring-beam electron distribution in the directions parallel and perpendicular to the ambient magnetic field, respectively. To explore the related kinetic processes self-consistently, 2.5D fully kinetic particle-in-cell simulations were carried out. To quantify excited wave properties in different coronal conditions, we investigated the dependences of their energy and polarization on the ring-beam electron density and magnetic field. In general, electrostatic waves dominate the energetics of waves, and nonlinear waves are ubiquitous. In weakly magnetized plasmas, where the electron cyclotron frequency ωce is lower than the electron plasma frequency ωpe, it is difficult to produce escaping electromagnetic waves with frequency ω &gt; ωpe and small refractive index | {ck}/ω | &lt; (k and c are the wavenumber and the light speed, respectively). Highly polarized and anisotropic escaping electromagnetic waves can, however, be effectively excited in strongly magnetized plasmas with ωce/ωpe ≥ 1. The anisotropies of the energy, circular polarization degree (CPD), and spectrogram of these escaping electromagnetic waves strongly depend on the number density ratio of the ring-beam electrons to the background electrons. In particular, their CPDs can vary from left-handed to right-handed with the decrease of the ring-beam density, which may explain some observed properties of solar radio bursts (e.g., radio spikes) from the solar corona.

Keywords: Solar coronal radio emission, Solar corona, Solar magnetic reconnection
The Structure of Tidal Disruption Event Host Galaxies on Scales of Tens to Thousands of Parsecs. We explore the galaxy structure of four tidal disruption event (TDE) host galaxies on 30 pc to kiloparsec scales using Hubble Space Telescope WFC3 multiband imaging. The star formation histories of these hosts are diverse, including one post-starburst galaxy (ASASSN-14li), two hosts with recent weak starbursts (ASASSN-14ae and iPTF15af), and one early-type galaxy (PTF09ge). Compared to early-type galaxies of similar stellar masses, the TDE hosts have higher central surface brightnesses and stellar mass surface densities on 30-100 pc scales. The TDE hosts do not show the large, kiloparsec-scale tidal disruptions seen in some post-starburst galaxies; the hosts have low morphological asymmetries similar to those of early-type galaxies. The lack of strong asymmetries is inconsistent with a recent major (∼1:1 mass) merger, although minor (≲1:3) mergers are possible. Given the time elapsed since the end of the starbursts in the three post-burst TDE hosts and the constraints on the merger mass ratios, it is unlikely that a bound supermassive black hole binary (SMBHB) has had time to coalesce. The TDE hosts have low central (&lt;140 pc) ellipticities compared to early-type galaxies. The low central ellipticities disfavor a strong radial anisotropy as the cause for the enhanced TDE rate, although we cannot rule out eccentric disks at the scale of the black hole gravitational radius of influence (∼1 pc). These observations suggest that the high central stellar densities are a more important driver than SMBHBs or radial anisotropies in increasing the TDE rate in galaxies with recent starbursts.

Keywords: Supermassive black holes, Tidal disruption, E+A galaxies
Growth of Supermassive Black Hole Seeds in ETG Star-forming Progenitors: Multiple Merging of Stellar Compact Remnants via Gaseous Dynamical Friction and Gravitational-wave Emission. We propose a new mechanism for the growth of supermassive black hole (BH) seeds in the star-forming progenitors of local early-type galaxies (ETGs) at z ≳ 1. This envisages the migration and merging of stellar compact remnants (neutron stars and stellar-mass BHs) via gaseous dynamical friction toward the central high-density regions of such galaxies. We show that, under reasonable assumptions and initial conditions, the process can build up central BH masses of the order of 104-106 M⊙ within some 107 yr, so effectively providing heavy seeds before standard disk (Eddington-like) accretion takes over to become the dominant process for further BH growth. Remarkably, such a mechanism may provide an explanation, alternative to super-Eddington accretion rates, for the buildup of billion-solar-massed BHs in quasar hosts at z ≳ 7, when the age of the universe ≲0.8 Gyr constitutes a demanding constraint; moreover, in more common ETG progenitors at redshift z ∼ 2-6, it can concur with disk accretion to build such large BH masses even at moderate Eddington ratios ≲0.3 within the short star formation duration ≲Gyr of these systems. Finally, we investigate the perspectives to detect the merger events between the migrating stellar remnants and the accumulating central supermassive BH via gravitational-wave emission with future ground- and space-based detectors such as the Einstein Telescope and the Laser Interferometer Space Antenna.

Keywords: Quasars, Galaxy evolution, Gravitational waves, Dynamical friction, Astrophysical black holes
An Increasing Radial Velocity of a Narrow Absorption-line System in Quasar SDSS J143530.49+142338.4. We report, for the first time, both the strengthening and radial velocity increases of a narrow absorption-line (NAL) system (C IV λλ1548, 1551 and N V λλ1239, 1243) from the two-epoch spectra of quasar SDSS J143530.49+142338.4. First, we speculate that the ionization changes of the outflow clouds are likely the cause of the strengthening in its equivalent width (EW) based on the obvious weakening of the ionization continuum, although other interpretations cannot be ruled out based on the current two-epoch spectra. According to the cloudy simulation, the asynchronized variations between the absorption-line EWs and the ionizing continuum indicate that the absorbers are at relatively high degrees of ionization, which is also consistent with the high ionization state revealed by the absence of Si IV NAL in the same system. Second, this NAL system exhibits a kinematic velocity shift of ∼138 km s-1 within 445.2 days in the quasar rest frame (corresponding to an average acceleration of ∼0.36 cm s-2). We evaluate several possible causes for this kinematic shift. However, the current two-epoch spectra do not provide enough constraints to confirm the possible mechanisms, so future monitoring with high resolution will be helpful to achieve this goal.

Keywords: Active galactic nuclei, Quasar absorption line spectroscopy, Quasars