Sazuna/UAT_keywords huggingface dataset:
The Host Galaxies and Progenitors of Fast Radio Bursts Localized with the Australian Square Kilometre Array Pathfinder. The Australian SKA Pathfinder (ASKAP) telescope has started to localize fast radio bursts (FRBs) to arcsecond accuracy from the detection of a single pulse, allowing their host galaxies to be reliably identified. We discuss the global properties of the host galaxies of the first four FRBs localized by ASKAP, which lie in the redshift range 0.11 &lt; z &lt; 0.48. All four are massive galaxies (log(M*/M☉) ∼ 9.4-10.4) with modest star formation rates of up to 2 M☉ yr-1—very different to the host galaxy of the first repeating FRB 121102, which is a dwarf galaxy with a high specific star formation rate. The FRBs localized by ASKAP typically lie in the outskirts of their host galaxies, which appears to rule out FRB progenitor models that invoke active galactic nuclei or free-floating cosmic strings. The stellar population seen in these host galaxies also disfavors models in which all FRBs arise from young magnetars produced by superluminous supernovae, as proposed for the progenitor of FRB 121102. A range of other progenitor models (including compact-object mergers and magnetars arising from normal core-collapse supernovae) remain plausible.

Keywords: Radio continuum emission, Radio bursts, Star formation, Galaxies
A Redshift for the First Einstein Ring, MG 1131+0456. MG 1131+0456 is a radio-selected gravitational lens, and is the first known Einstein ring. Discovered in 1988, the system consists of a bright (S74 MHz = 3.7 Jy) radio source imaged into a ring and two compact, flat-spectrum components separated by 2"1. The ring is optically faint (R = 23.3), rising steeply into the near- and mid-infrared (K = 17.8; W2 = 13.4). The system has been intensively studied in the intervening years, including high-resolution radio imaging, radio monitoring, and near-infrared imaging with Hubble and Keck. The lensing galaxy is at zl = 0.844. However, to date, no spectroscopic redshift had been reported for the lensed source. Using archival Keck data from 1997, we report the robust detection of a single narrow emission line at 5438 Å, which we associate with C III] λ1909 Å from a type-2 quasar at zs = 1.849. Support for this redshift identification comes from weaker emission associated with C IV λ1549 Å and He II λ1640 Å, typical of type-2 quasars, as well as the lack of emission lines in archival near-infrared Keck spectroscopy. We also present, for the first time, Cycle 1 Chandra observations of MG 1131+0456, which clearly resolves into two point sources with a combined flux of ∼10-13 erg cm-2 s-1 and a best-fit column density of ∼3 × 1022 cm-2. We suggest a new method to identify candidate lensed active galactic nuclei from low-resolution X-ray surveys such as eROSITA by targeting sources that have anomalously high X-ray luminosity given their mid-infrared luminosity.

Keywords: Gravitational lensing
First Radio Evidence for Impulsive Heating Contribution to the Quiet Solar Corona. This Letter explores the relevance of nanoflare-based models for heating the quiet Sun corona. Using meterwave data from the Murchison Widefield Array, we present the first successful detection of impulsive emissions down to flux densities of ∼mSFU, about two orders of magnitude weaker than earlier attempts. These impulsive emissions have durations ≲1 s and are present throughout the quiet solar corona. The fractional time occupancy of these impulsive emissions at a given region is ≲10%. The histograms of these impulsive emissions follow a power-law distribution and show signs of clustering at small timescales. Our estimate of the energy that must be dumped in the corona to generate these impulsive emissions is consistent with the coronal heating requirements. Additionally, the statistical properties of these impulsive emissions are very similar to those recently determined for magnetic switchbacks by the Parker Solar Probe (PSP). We hope that this work will lead to a renewed interest in relating these weak impulsive emissions to the energy deposited in the corona, the quantity of physical interest from a coronal heating perspective, and explore their relationship with the magnetic switchbacks observed by the PSP.

Keywords: Solar coronal radio emission, Solar corona, Solar coronal heating, Quiet solar corona
Hard Synchrotron Spectra from Magnetically Dominated Plasma Turbulence. Synchrotron emission from astrophysical nonthermal sources usually assumes that the emitting particles are isotropic. By means of large-scale two- and three-dimensional particle-in-cell simulations, we demonstrate that the dissipation of magnetically dominated ( ${\sigma }_{0}\gg 1$ ) turbulence in pair plasmas leads to strongly anisotropic particle distributions. At Lorentz factors $\sim {\sigma }_{0}{\gamma }_{\mathrm{th}0}$ (here, ${\gamma }_{\mathrm{th}0}$ is the initial Lorentz factor), the particle velocity is preferentially aligned with the local magnetic field; instead, the highest energy particles are preferentially oriented in the plane perpendicular to the field. This energy-dependent anisotropy leads to a synchrotron spectral flux $\nu {F}_{\nu }\propto {\nu }^{s}$ that is much harder than for isotropic particles. Remarkably, for ${\sigma }_{0}\gg 1$ we find that the angle-integrated spectral slope in the slow cooling regime is $s\sim 0.5-0.7$ for a wide range of turbulence fluctuations, $0.25\lesssim \delta {B}_{\mathrm{rms}0}^{2}/{B}_{0}^{2}\lesssim 4$ , despite significant variations in the power-law energy spectrum of nonthermal particles. This is because weaker turbulence levels imprint a stronger degree of anisotropy, thereby counteracting the effect of the steeper particle spectrum. The synchrotron spectral slope may be even harder, $s\gtrsim 0.7$ , if the observer is in the plane perpendicular to the mean magnetic field. Our results are independent of domain size and dimensionality. Our findings may help explain the origin of hard synchrotron spectra of astrophysical nonthermal sources, most notably the radio spectrum of pulsar wind nebulae.

Keywords: High energy astrophysics, Plasma physics, Plasma astrophysics, Pulsars, Non-thermal radiation sources, Particle astrophysics
Origin of Sub-TeV Afterglow Emission from Gamma-Ray Bursts GRB 190114C and GRB 180720B. The detection of GRB 180722B and GRB 190114C in sub-TeV gamma-rays has opened up a new window to study gamma-ray bursts in high-energy gamma-rays. Recently it has been shown that the synchrotron and inverse Compton processes are responsible for the production of these high-energy gamma-rays during the afterglow. Here, for the first time we demonstrate that the photohadronic scenario that is successful in explaining the multi-TeV flaring in high-energy blazars is also applicable for gamma-ray bursts. We show that the sub-TeV spectra of GRB 190114C and GRB 180720B are due to the interaction of high-energy protons with the background photons in the synchrotron self-Compton region and synchrotron region, respectively. The nature of the background photon distributions help us to constrain their bulk Lorentz factors.

Keywords: Blazars, Gamma-ray bursts, Relativistic jets, Particle astrophysics
Impacts of Dust Grains Accelerated by Supernovae on the Moon. There is evidence that ejecta from nearby supernovae have rained down on Earth in the past. Supernovae can accelerate preexisting dust grains in the interstellar medium to speeds of ∼0.01c. We investigate the survival and impact of dust grains from supernovae on the Moon, finding that supernova dust grains can form detectable tracks with widths of ∼0.01-0.07 μm and depths of ∼0.1-0.7 mm in lunar rocks. These tracks could potentially shed light on the timings, luminosities, and directions of nearby supernovae.

Keywords: The Moon, Supernovae, Meteoroids
Abnormal Dawn-Dusk Asymmetry of Protonated Ions in the Martian Ionosphere. Normally, the Martian ionosphere displays a dusk enhancement due to continuous depletion of plasma via recombination during day-to-night transport. Using the extensive measurements made by the Neutral Gas and Ion Mass Spectrometer on board the Mars Atmosphere and Volatile Evolution spacecraft, we show that several species, including ${{\rm{H}}}_{2}^{+}$ , OH+, H2O+, and NH+, present instead an abnormal dawn enhancement above the exobase where they are mainly produced by ion-neutral reactions involving H2. Such a peculiarity is indicative of a dawn bulge of H2 present in the Martian upper atmosphere and corona, which is driven by subsidence in regions of horizontal wind convergence and the subsequent buildup of minor atmospheric species with large vertical scale heights. A similar dynamical process is also known to occur in the upper atmospheres of other solar system bodies such as the Earth, Venus, and Titan. Interestingly, despite that the diurnal variations of O and N are subject to the same dynamical effect, a dawn enhancement is not seen for O+ and N+, possibly due to the nonthermal production of their parent atoms in the ambient atmosphere via processes such as photodissociation and dissociative recombination. The H2 distribution inferred in this study is important for a thorough understanding of hydrogen escape and climate evolution on Mars.

Keywords: Upper atmosphere, Solar system planets, Mars, Solar system, Solar system terrestrial planets, Aeronomy, Planetary atmospheres, Atmospheric science, Atmospheric variability, Planetary science, Atmospheric composition, Solar system astronomy
Highly Structured Quasar Outflow in SDSS J010612.22+001920.1. Evidence for quasar outflows can be detected via blueshifted broad absorption lines (BALs) in rest-frame ultraviolet spectra of quasars. We have identified 18 narrow absorption line (NAL) systems in the BAL system of SDSS J010612.22+001920.1, indicating that this BAL outflow has achieved a high degree of clumpiness. Moreover, these NAL systems are highly structured in velocity space and separated from each other by the doublet spacings of multiple ionic species, including a sequence of 10 C IV doublets that form arithmetic progression with a common difference of ≈498 $\,\mathrm{km}\,{{\rm{s}}}^{-1}$ . Cases like J010612.22+001920.1 offer strong evidence for the dynamical process of radiative acceleration in quasar outflow, and open up a new way for the research of quasar outflow under the framework of the NAL complex.

Keywords: Quasar absorption line spectroscopy, Broad-absorption line quasar, Quasars
The Value of Progenitor Radius Measurements for Explosion Modeling of Type II-Plateau Supernovae. Using Modules for Experiments in Stellar Astrophysics (MESA)+STELLA, we show that very different physical models can adequately reproduce a specific observed Type II-Plateau supernova (SN). We consider SN2004A, SN2004et, SN2009ib, SN2017eaw, and SN2017gmr, nickel-rich ( ${M}_{\mathrm{Ni}}\gt 0.03{M}_{\odot }$ ) events with bolometric lightcurves and a well-sampled decline from the plateau. These events also have constraints on the progenitor radius, via a progenitor image, or, in the case of SN2017gmr, a radius from fitting shock-cooling models. In general, many explosions spanning the parameter space of progenitors can yield excellent lightcurve and Fe-line velocity agreement, demonstrating the success of scaling laws in motivating models that match plateau properties for a given radius and highlighting the degeneracy between plateau luminosity and velocity in models and observed events, which can span over 50% in ejecta mass, radius, and explosion energy. This can help explain disagreements in explosion properties reported for the same event using different model calculations. Our calculations yield explosion properties when combined with pre-explosion progenitor radius measurements or a robust understanding of the outermost $\lt 0.1\,{M}_{\odot }$ of material that quantifies the progenitor radius from SN observations a few days after explosion.

Keywords: Hydrodynamical simulations, Visibility function, Type II supernovae, Massive stars, Light curves, Stellar evolutionary models, Radiative transfer simulations, Supernovae
Hints of a Population of Solar System Analog Planets from ALMA. The recent Atacama Large Millimeter/submillimeter Array (ALMA) Disk Substructures at High Angular Resolution Project (DSHARP) survey provided illuminating results on the diversity of substructures in planet-forming disks. These substructures trace pebble-sized grains accumulated at local pressure maxima, possibly due to planet-disk interactions or other planet formation processes. DSHARP sources are heavily biased to large and massive disks that only represent the high (dust flux) tail end of the disk population. Thus it is unclear whether similar substructures and corresponding physical processes also occur in the majority of disks that are fainter and more compact. Here we explore the presence and characteristics of features in a compact disk around GQ Lup A, the effective radius of which is 1.5-10 times smaller than those of DSHARP disks. We present our analysis of ALMA 1.3 mm continuum observations of the GQ Lup system. By fitting visibility profiles of the continuum emission, we find substructures including a gap at ∼10 au. The compact disk around GQ Lup exhibits similar substructures to those in the DSHARP sample, suggesting that mechanisms of trapping pebble-sized grains are at work in small disks as well. Characteristics of the feature at ∼10 au, if due to a hidden planet, are evidence of planet formation at Saturnian distances. Our results hint at a rich world of substructures to be identified within the common population of compact disks, and subsequently a population of solar system analogs within these disks. Such study is critical to understanding the formation mechanisms and planet populations in the majority of protoplanetary disks.

Keywords: Protoplanetary disks, Planet formation, Circumstellar disks
Super-Rayleigh Slopes in Transmission Spectra of Exoplanets Generated by Photochemical Haze. Spectral slopes in optical transmission spectra of exoplanetary atmospheres encapsulate information on the properties of exotic clouds. The slope is usually attributed to the Rayleigh scattering caused by tiny aerosol particles, whereas recent retrieval studies have suggested that the slopes are often steeper than the canonical Rayleigh slopes. Here, we propose that photochemical haze formed in vigorously mixing atmospheres can explain such super-Rayleigh slopes. We first analytically show that the spectral slope can be steepened by the vertical opacity gradient in which atmospheric opacity increases with altitude. Using a microphysical model, we demonstrate that such an opacity gradient can be naturally generated by photochemical haze, especially when the eddy mixing is substantially efficient. The transmission spectra of hazy atmospheres can be demarcated into four typical regimes in terms of the haze mass flux and eddy diffusion coefficient. We find that the transmission spectrum can have a spectral slope 2-4 times steeper than the Rayleigh slope if the eddy diffusion coefficient is sufficiently high and the haze mass flux falls into a moderate value. Based on the eddy diffusion coefficient suggested by a recent study of atmospheric circulations, we suggest that photochemical haze preferentially generates super-Rayleigh slopes at planets with equilibrium temperatures of 1000-1500 K, which might be consistent with results of recent retrieval studies. Our results would help interpret the observations of spectral slopes from the perspective of haze formation.

Keywords: Hot Jupiters, Optical observation, Exoplanet atmospheres, Transmission spectroscopy
Grain Growth in Newly Discovered Young Eruptive Stars. FU Orionis-type stars are young stellar objects showing large outbursts due to highly enhanced accretion from the circumstellar disk onto the protostar. FU Orionis-type object (FUor) outbursts happen in a wide variety of sources from the very embedded ones to those with almost no sign of extended emission beyond the disk. The subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. We used the Very Large Telescope (VLT)/VLT spectrometer and imager for the mid-infrared (VISIR) to obtain the first spectra that cover the 8-13 μm mid-infrared wavelength range in low resolution of five recently discovered FUors. Four objects from our sample show the 10 μm silicate feature in emission. We study the shape and strength of the silicate feature in these objects and find that they mostly contain large amorphous grains, suggesting that large grains are typically not settled to the midplane in FUor disks. This is a general characteristic of FUors, as opposed to regular T Tauri-type stars whose disks display anything from pristine small grains to significant grain growth. We classify our targets by determining whether the silicate feature is in emission or in absorption, and confront them with the evolutionary scenarios on the dispersal of the envelopes around young stars. In our sample, all Class II objects exhibit silicate emission, while for Class I objects, the appearance of the feature in emission or absorption depends on the viewing angle with respect to the outflow cavity. This highlights the importance of geometric effects when interpreting the silicate feature. * Based on observations collected at the European Southern Observatory under ESO programs 097.C-0292, 098.C-0529, and 0102.C-0310.

Keywords: Circumstellar matter, Pre-main sequence stars, Protoplanetary disks
A Data-driven Technique Using Millisecond Transients to Measure the Milky Way Halo. We introduce a new technique to constrain the line-of-sight integrated electron density of our Galactic halo ${\mathrm{DM}}_{\mathrm{MW},\mathrm{halo}}$ through analysis of the observed dispersion measure distributions of pulsars ${\mathrm{DM}}_{\mathrm{pulsar}}$ and fast radio bursts (FRBs) ${\mathrm{DM}}_{\mathrm{FRB}}$ . We model these distributions, correcting for the Galactic interstellar medium, with kernel density estimation—well-suited to the small data regime—to find lower/upper bounds to the corrected ${\mathrm{DM}}_{\mathrm{pulsar}}$ / ${\mathrm{DM}}_{\mathrm{FRB}}$ distributions: $\max \left[{\mathrm{DM}}_{\mathrm{pulsar}}\right]\approx 7\pm 2\,(\mathrm{stat})\pm 9\,(\mathrm{sys})\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ and $\min \left[{\mathrm{DM}}_{\mathrm{FRB}}\right]\approx {63}_{-21}^{+27}\,(\mathrm{stat})\pm 9\,(\mathrm{sys})\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ . Using bootstrap resampling to estimate uncertainties, we set conservative limits on the Galactic halo dispersion measure $-2\lt {\mathrm{DM}}_{\mathrm{MW},\mathrm{halo}}\lt 123\,\mathrm{pc}\,{\mathrm{cm}}^{-3}$ (95% c.l.). The upper limit is especially conservative because it may include a nonnegligible contribution from the FRB host galaxies and a nonzero contribution from the cosmic web. It strongly disfavors models where the Galaxy has retained the majority of its baryons with a density profile tracking the presumed dark matter density profile. Last, we perform Monte Carlo simulations of larger FRB samples to validate our technique and assess the sensitivity of ongoing and future surveys. We recover bounds of several tens of $\mathrm{pc}\,{\mathrm{cm}}^{-3}$ that may be sufficient to test whether the Galaxy has retained a majority of its baryonic mass. We estimate that a sample of several thousand FRBs will significantly tighten constraints on ${\mathrm{DM}}_{\mathrm{MW},\mathrm{halo}}$ and offer a valuable complement to other analyses.

Keywords: Astrostatistics techniques, Circumgalactic medium, Radio transient sources
Microwave Spectral Imaging of an Erupting Magnetic Flux Rope: Implications for the Standard Solar Flare Model in Three Dimensions. We report microwave spectral imaging observations of an erupting magnetic flux rope during the early impulsive phase of the X8.2-class limb flare on 2017 September 10, obtained by the Expanded Owens Valley Solar Array. A few days prior to the eruption, when viewed against the disk, the flux rope appeared as a reverse S-shaped dark filament along the magnetic polarity inversion line. During the eruption, the rope exhibited a "hot channel" structure in extreme ultraviolet and soft X-ray passbands sensitive to ∼10 MK plasma. The central portion of the flux rope was nearly aligned with the line of sight, which quickly developed into a teardrop-shaped dark cavity during the early phase of the eruption. A long and thin plasma sheet formed below the cavity, interpreted as the reconnection current sheet viewed edge on. A nonthermal microwave source was present at the location of the central current sheet, which extended upward encompassing the dark cavity. A pair of nonthermal microwave sources were observed for several minutes on both sides of the main flaring region. They shared a similar temporal behavior and spectral property to the central microwave source below the cavity, interpreted as the conjugate footpoints of the erupting flux rope. These observations are broadly consistent with the magnetic topology and the associated energy release scenario suggested in the three-dimensional standard model for eruptive solar flares. In particular, our detection of nonthermal emission at conjugate flux rope footpoints provides solid evidence of particle transport along an erupting magnetic flux rope.

Keywords: Solar radio telescopes, Solar flares, Solar magnetic reconnection, Non-thermal radiation sources, Solar coronal mass ejections, Solar radio flares
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XI. Accretion Disk Reverberation Mapping of Mrk 142. We performed an intensive accretion disk reverberation mapping campaign on the high accretion rate active galactic nucleus Mrk 142 in early 2019. Mrk 142 was monitored with the Neil Gehrels Swift Observatory for four months in X-rays and six different UV/optical filters. Ground-based photometric monitoring was obtained from the Las Cumbres Observatory, the Liverpool Telescope, and the Dan Zowada Memorial Observatory in ugriz filters, as well as from the Yunnan Astronomical Observatory in V. Mrk 142 was highly variable throughout, displaying correlated variability across all wavelengths. We measure significant time lags between the different wavelength lightcurves. In the UV and optical, we find that the wavelength-dependent lags, τ(λ), generally follow the relation τ(λ) ∝ λ4/3, as expected for the T ∝ R-3/4 profile of a steady-state, optically thick, geometrically thin accretion disk, though they can also be fit by τ(λ) ∝ λ2, as expected for a slim disk. The exceptions are the u and U bands, where an excess lag is observed, as has been observed in other active galactic nuclei and attributed to continuum emission arising in the broad-line region. Furthermore, we perform a flux-flux analysis to separate the constant and variable components of the spectral energy distribution, finding that the flux dependence of the variable component is consistent with the fν ∝ ν1/3 spectrum expected for a geometrically thin accretion disk. Moreover, the X-ray to UV lag is significantly offset from an extrapolation of the UV/optical trend, with the X-rays showing a poorer correlation with the UV than the UV does with the optical. The magnitude of the UV/optical lags is consistent with a highly super-Eddington accretion rate.

Keywords: Accretion, Active galactic nuclei