Sazuna/UAT_keywords huggingface dataset:
Seven Years of Coordinated Chandra-NuSTAR Observations of SN 2014C Unfold the Extreme Mass-loss History of Its Stellar Progenitor. We present the results from our 7 yr long broadband X-ray observing campaign of SN 2014C with Chandra and NuSTAR. These coordinated observations represent the first look at the evolution of a young extragalactic SN in the 0.3-80 keV energy range in the years after core collapse. We find that the spectroscopic metamorphosis of SN 2014C from an ordinary type Ib SN into an interacting SN with copious hydrogen emission is accompanied by luminous X-rays reaching L  x  ≈ 5.6 × 1040 erg s-1 (0.3-100 keV) at ~1000 days post-explosion and declining as L  x  ∝ t -1 afterwards. The broadband X-ray spectrum is of thermal origin and shows clear evidence for cooling after peak, with $T{(t)\approx 20\,\mathrm{keV}(t/{t}_{\mathrm{pk}})}^{-0.5}$ . Soft X-rays of sub-keV energy suffer from large photoelectric absorption originating from the local SN environment with ${\mathrm{NH}}_{\mathrm{int}}{(t)\approx 3\times {10}^{22}(t/400\,\mathrm{days})}^{-1.4}\,{\mathrm{cm}}^{-2}$ . We interpret these findings as the result of the interaction of the SN shock with a dense (n ≈ 105 - 106 cm-3), H-rich disk-like circumstellar medium (CSM) with inner radius ~2 × 1016 cm and extending to ~1017 cm. Based on the declining NHint(t) and X-ray luminosity evolution, we infer a CSM mass of ~(1.2 f-2.0 $\sqrt{f}){M}_{\odot }$ , where f is the volume filling factor. We place SN 2014C in the context of 121 core-collapse SNe with evidence for strong shock interaction with a thick circumstellar medium. Finally, we highlight the challenges that the current mass-loss theories (including wave-driven mass loss, binary interaction, and line-driven winds) face when interpreting the wide dynamic ranges of CSM parameters inferred from observations.

Keywords: X-ray astronomy, Shocks, Circumstellar shells, Core-collapse supernovae
A Short Gamma-Ray Burst from a Protomagnetar Remnant. The contemporaneous detection of gravitational waves and gamma rays from GW170817/GRB 170817A, followed by kilonova emission a day after, confirmed compact binary neutron star mergers as progenitors of short-duration gamma-ray bursts (GRBs) and cosmic sources of heavy r-process nuclei. However, the nature (and life span) of the merger remnant and the energy reservoir powering these bright gamma-ray flashes remains debated, while the first minutes after the merger are unexplored at optical wavelengths. Here, we report the earliest discovery of bright thermal optical emission associated with short GRB 180618A with extended gamma-ray emission-with ultraviolet and optical multicolor observations starting as soon as 1.4 minutes post-burst. The spectrum is consistent with a fast-fading afterglow and emerging thermal optical emission 15 minutes post-burst, which fades abruptly and chromatically (flux density F  ν  ∝ t -α , α = 4.6 ± 0.3) just 35 minutes after the GRB. Our observations from gamma rays to optical wavelengths are consistent with a hot nebula expanding at relativistic speeds, powered by the plasma winds from a newborn, rapidly spinning and highly magnetized neutron star (i.e., a millisecond magnetar), whose rotational energy is released at a rate L th ∝ t -(2.22±0.14) to reheat the unbound merger-remnant material. These results suggest that such neutron stars can survive the collapse to a black hole on timescales much larger than a few hundred milliseconds after the merger and power the GRB itself through accretion. Bright thermal optical counterparts to binary merger gravitational wave sources may be common in future wide-field fast-cadence sky surveys.

Keywords: Gamma-ray bursts, High energy astrophysics, Time domain astronomy, Magnetars, Polarimetry
Bayesian Accretion Modeling: Axisymmetric Equatorial Emission in the Kerr Spacetime. The Event Horizon Telescope (EHT) has produced images of two supermassive black holes, Messier 87* (M 87*) and Sagittarius A* (Sgr A*). The EHT collaboration used these images to indirectly constrain black hole parameters by calibrating measurements of the sky-plane emission morphology to images of general relativistic magnetohydrodynamic (GRMHD) simulations. Here, we develop a model for directly constraining the black hole mass, spin, and inclination through signatures of lensing, redshift, and frame dragging, while simultaneously marginalizing over the unknown accretion and emission properties. By assuming optically thin, axisymmetric, equatorial emission near the black hole, our model gains orders of magnitude in speed over similar approaches that require radiative transfer. Using 2017 EHT M 87* baseline coverage, we use fits of the model to itself to show that the data are insufficient to demonstrate existence of the photon ring. We then survey time-averaged GRMHD simulations fitting EHT-like data, and find that our model is best-suited to fitting magnetically arrested disks, which are the favored class of simulations for both M 87* and Sgr A*. For these simulations, the best-fit model parameters are within ~10% of the true mass and within ~10° for inclination. With 2017 EHT coverage and 1% fractional uncertainty on amplitudes, spin is unconstrained. Accurate inference of spin axis position angle depends strongly on spin and electron temperature. Our results show the promise of directly constraining black hole spacetimes with interferometric data, but they also show that nearly identical images permit large differences in black hole properties, highlighting degeneracies between the plasma properties, spacetime, and, most crucially, the unknown emission geometry when studying lensed accretion flow images at a single frequency.

Keywords: Accretion, Very long baseline interferometry, Gravitational lensing, Astrophysical black holes
The Geometry of the G29-38 White Dwarf Dust Disk from Radiative Transfer Modeling. Many white dwarfs host disks of dust produced by disintegrating planetesimals and revealed by infrared excesses. The disk around G29-38 was the first to be discovered and is now well-observed, yet we lack a cohesive picture of its geometry and dust properties. Here we model the G29-38 disk for the first time using radiative transfer calculations that account for radial and vertical temperature and optical depth gradients. We arrive at a set of models that can match the available infrared measurements well, although they overpredict the width of the 10 μm silicate feature. The resulting set of models has a disk inner edge located at 92-100 R WD (where R WD is the white dwarf radius). This is farther from the star than inferred by previous modeling efforts due to the presence of a directly illuminated front edge to the disk. The radial width of the disk is narrow (≤10 R WD); such a feature could be explained by inefficient spreading or the proximity of the tidal disruption radius to the sublimation radius. The models have a half-opening angle of ≥1.°4. Such structure would be in strong contradiction with the commonly employed flat-disk model analogous to the rings of Saturn, and in line with the vertical structure of main-sequence debris disks. Our results are consistent with the idea that disks are collisionally active and continuously fed with new material, rather than evolving passively after the disintegration of a single planetesimal.

Keywords: Infrared excess, White dwarf stars, Circumstellar disks
X-Ray Reverberation Mapping of Ark 564 Using Gaussian Process Regression. Ark 564 is an extreme high-Eddington narrow-line Seyfert 1 galaxy, known for being one of the brightest, most rapidly variable soft X-ray active galactic nuclei (AGN), and for having one of the lowest temperature coronae. Here, we present a 410 ks NuSTAR observation and two 115 ks XMM-Newton observations of this unique source, which reveal a very strong, relativistically broadened iron line. We compute the Fourier-resolved time lags by first using Gaussian processes to interpolate the NuSTAR gaps, implementing the first employment of multitask learning for application in AGN timing. By simultaneously fitting the time lags and the flux spectra with the relativistic reverberation model RELTRANS, we constrain the mass at ${2.3}_{-1.3}^{+2.6}\times {10}^{6}{M}_{\odot }$ , although additional components are required to describe the prominent soft excess in this source. These results motivate future combinations of machine learning, Fourier-resolved timing, and the development of reverberation models.

Keywords: Accretion, Black holes, High energy astrophysics, Model selection, Astrostatistics techniques, Astrostatistics, X-ray active galactic nuclei, Gaussian Processes regression
CLASSY IV. Exploring UV Diagnostics of the Interstellar Medium in Local High-z Analogs at the Dawn of the JWST Era. The Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY (CLASSY) provides the first high-resolution spectral catalog of 45 local high-z analogs in the ultraviolet (UV; 1200-2000 Å) to investigate their stellar and gas properties. Here we present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (N IV] λ λ1483,87, C IV λλ1548,51, He II λ1640, O III]λ λ1661,6, Si III] λλ1883,92, C III] λ1907,9). Specifically, our aim is to provide accurate diagnostics for the reddening E(B - V), electron density n  e , electron temperature T  e , metallicity 12+log(O/H), and ionization parameter log(U), taking the different ISM ionization zones into account. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all CLASSY targets. We find that UV density diagnostics estimate n  e  values that are ~1-2 dex higher (e.g., n  e (C III]λ λ1907,9) ~ 104 cm-3) than those inferred from their optical counterparts (e.g., n  e ([S II]λ λ6717,31) ~ 102 cm-3; n  e ([Ar IV]λ λ4714,41) ~ 103 cm-3). T  e  derived from the hybrid ratio [O III] λ1666/λ5007 proves to be reliable, implying differences in determining 12+log(O/H) compared to the optical counterpart O III] λ4363/[O III] λ5007 within ~ ±0.3 dex. We also investigate the relation between the stellar and gas E(B - V), finding consistent values at high specific star formation rates (sSFRs; $\mathrm{log}(\mathrm{sSFR})\gtrsim -8$ yr-1), while at low sSFRs we confirmed an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note that there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV. *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: Galaxy chemical evolution, Dwarf galaxies, Emission line galaxies, Ultraviolet astronomy, Galaxy spectroscopy, High-redshift galaxies
Solar-cycle-related Variation of Differential Rotation of the Chromosphere. Solar-cycle-related variation of the solar chromospheric rotation is studied by analyzing the chromospheric rotation rate of 938 synoptic maps generated from the Ca II K line at the Mount Wilson Observatory during the period of 1915 August 10 to 1985 July 7. The results obtained are as follows: (1) The parameters A (the equatorial rotation rate) and B (the latitudinal gradient of rotation) in the standard form of differential rotation both show a decreasing trend in the considered time frame, although A has weak statistical significance. (2) There is a significant negative correlation between the level of solar activity and parameter B, indicating that there seems to be a correlation between field strength and chromospheric differential rotation. (3) During solar cycles 15, 16, 19, 20, and 21, the southern hemisphere rotates faster, whereas in cycles 17 and 18, the northern hemisphere rotates faster. (4) There exists a significant negative correlation between the N-S asymmetry of the chromospheric rotation rate and that of solar activity, indicating that differential rotation of the chromosphere seems to be strengthened by stronger magnetic activity in a certain hemisphere. Possible explanations for the above results are given.

Keywords: Solar activity, Solar rotation, Solar chromosphere
Soft X-Ray Spectral Diagnostics of Multithermal Plasma in Solar Flares with Chandrayaan-2 XSM. Spectroscopic observations in X-ray wavelengths provide excellent diagnostics of the temperature distribution in solar flare plasma. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission provides broadband disk-integrated soft X-ray solar spectral measurements in the energy range of 1-15 keV with high spectral resolution and time cadence. In this study, we analyze the X-ray spectra of three representative GOES C-class flares obtained with the XSM to investigate the evolution of various plasma parameters during the course of the flares. Using the soft X-ray spectra consisting of the continuum and well-resolved line complexes of major elements like Mg, Si, and Fe, we investigate the validity of the isothermal and multithermal assumptions on the high-temperature components of the flaring plasma. We show that the soft X-ray spectra during the impulsive phase of the high-intensity flares are inconsistent with isothermal models and are best fitted with double-peaked differential emission measure distributions where the temperature of the hotter component rises faster than that of the cooler component. The two distinct temperature components observed in differential emission measure models during the impulsive phase of the flares suggest the presence of the directly heated plasma in the corona and evaporated plasma from the chromospheric footpoints. We also find that the abundances of low first ionization potential elements Mg, Si, and Fe reduce from near coronal to near photospheric values during the rising phase of the flare and recover back to coronal values during the decay phase, which is also consistent with the chromospheric evaporation scenario.

Keywords: Solar flare spectra, Solar x-ray flares
Presumed Detection of C<SUB>5</SUB> Molecule in the Interstellar Medium. The paper suggests the presence of the carbon chain C5 molecule in translucent, interstellar H I clouds. This species, the only five atom interstellar molecule, observable in dark, translucent clouds, seems to be observable in reasonably dense clouds, causing also rather high reddening. The paper shows two likely discovered spectral features of C5,  A1Πu−X1Σg+  bands near 4975 and 5109 Å. The attempt to discover the 3789 Å C4 feature gave the negative result.

Keywords: Interstellar molecules, Interstellar absorption, Interstellar medium
On the Kink Instability of Twisted Coronal Loops: Nonneutralized Electric Current. Based on linear magnetohydrodynamic equations and an energy principle we analyze the ideal kink instability of a twisted force-free coronal loop (flux rope) surrounded by an outer potential magnetic field by using the sharp-boundary approximation at the surface. Unlike Tsap et al., a magnetic flux rope with nonneutralized (uncompensated) electric current is considered. We have shown that the twist angle of magnetic field lines is closely related to coronal mass ejections and solar flares. The kink instability condition does not depend on the radial profile of the magnetic field inside a flux rope in the long-wavelength limit but depends strongly on the reverse electric currents at the surface. The total critical twist angle of magnetic field lines, which determines the kink instability threshold, can be much greater than π radians due to reverse azimuthal surface current. This agrees with observations and illustrates the importance of the role of reverse currents for stabilization of a flux rope. Additional arguments in favor of the energy release models based on the uncompensated electric currents are presented.

Keywords: Active solar corona
Model-independent Test for the Cosmic Distance-Duality Relation with Pantheon and eBOSS DR16 Quasar Sample. In this Paper, we carry out a new model-independent cosmological test for the cosmic distance-duality relation (CDDR) by combining the latest five baryon acoustic oscillation (BAO) measurements and the Pantheon type Ia supernova (SNIa) sample. Particularly, the BAO measurement from the extended Baryon Oscillation Spectroscopic Survey data release 16 quasar sample at effective redshift z = 1.48 is used, and two methods, i.e., a compressed form of the Pantheon sample and the artificial neural network combined with the binning SNIa method, are applied to overcome the redshift-matching problem. Our results suggest that the CDDR is compatible with the observations, and the high-redshift BAO and SNIa data can effectively strengthen the constraints on the violation parameters of CDDR with the confidence interval decreasing by more than 20%. In addition, we find that the compressed form of observational data can provide a more rigorous constraint on the CDDR, and thus can be generalized to the applications of other actual observational data with limited sample size in the test for CDDR.

Keywords: Distance measure, Observational cosmology, Cosmological parameters
Searches for Neutrinos from Gamma-Ray Bursts Using the IceCube Neutrino Observatory. Gamma-ray bursts (GRBs) are considered as promising sources of ultra-high-energy cosmic rays (UHECRs) due to their large power output. Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic accelerators of UHECRs. Previous IceCube analyses, which primarily focused on neutrinos arriving in temporal coincidence with the prompt gamma-rays, found no significant neutrino excess. The four analyses presented in this paper extend the region of interest to 14 days before and after the prompt phase, including generic extended time windows and targeted precursor searches. GRBs were selected between 2011 May and 2018 October to align with the data set of candidate muon-neutrino events observed by IceCube. No evidence of correlation between neutrino events and GRBs was found in these analyses. Limits are set to constrain the contribution of the cosmic GRB population to the diffuse astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from GRBs is limited to ≲1% of the observed diffuse neutrino flux, and emission on timescales up to 104 s is constrained to 24% of the total diffuse flux.

Keywords: Neutrino astronomy, Gamma-ray bursts
New Identifications and Multiwavelength Properties of Extragalactic Fermi Gamma-Ray Sources in the SPT-SZ Survey Field. The fourth Fermi Large Area Telescope catalog (4FGL) contains 5064 γ-ray sources detected at high significance, but 26% of them still lack associations at other wavelengths. The SPT-SZ survey, conducted between 2008 and 2011 with the South Pole Telescope (SPT), covers 2500 deg2 of the southern sky in three millimeter-wavelength (mm) bands and was used to construct a catalog of nearly 5000 emissive sources. In this study, we introduce a new cross-matching scheme to search for multiwavelength counterparts of extragalactic γ-ray sources using a mm catalog. We apply a Poissonian probability to evaluate the rate of spurious false associations and compare the multiwavelength associations from the radio, mm, near-infrared, and X-ray with 4FGL γ-ray sources. In the SPT-SZ survey field, 85% of 4FGL sources are associated with mm counterparts. These mm sources include 94% of previously associated 4FGL sources and 56% of previously unassociated 4FGL sources. The latter group contains 40 4FGL sources for which SPT has provided the first identified counterparts. Nearly all of the SPT-associated 4FGL sources can be described as flat-spectrum radio quasars or blazars. We find that the mm band is the most efficient wavelength for detecting γ-ray blazars when considering both completeness and purity. We also demonstrate that the mm band correlates better to the γ-ray band than the radio or X-ray bands. With the next generation of CMB experiments, this technique can be extended to greater sensitivities and more sky area to further complete the identifications of the remaining unknown γ-ray blazars.

Keywords: Gamma-ray sources, Blazars, Relativistic jets, Radio loud quasars, Active galactic nuclei, Submillimeter astronomy
A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. III. Discrete Multicomponent Population-dynamical Models Based on the Jeans Equations. We present comprehensive multicomponent dynamical models of M54 (NGC 6715), the nuclear star cluster of the Sagittarius (Sgr) dwarf galaxy, which is undergoing a tidal disruption in the Milky Way halo. Previous papers in this series used a large MUSE mosaic data set to identify multiple stellar populations in the system and study their kinematic differences. Here, we use Jeans-based dynamical models that fit the population properties (mean age and metallicity), spatial distributions, and kinematics simultaneously. They provide a solid physical explanation for our previous findings. Population-dynamical models deliver a comprehensive view of the whole system, and allow us to disentangle the different stellar populations. We explore their dynamical interplay and confirm our previous findings about the build-up of Sgr's nuclear cluster via contributions from globular cluster stars, Sgr inner field stars, and in situ star formation. We explore various parameterizations of the gravitational potential and show the importance of a radially varying mass-to-light ratio for the proper treatment of the mass profile. We find a total dynamical mass within M54's tidal radius (~75 pc) of 1.60 ± 0.07 × 106 M ☉ in excellent agreement with N-body simulations. Metal-poor globular cluster stars contribute about 65% of the total mass or 1.04 ± 0.05 × 106 M ☉. Metal-rich stars can be further divided into young and intermediate-age populations, which contribute 0.32 ± 0.02 × 106 M ☉ (20%) and 0.24 ± 0.02 × 106 M ☉ (15%), respectively. Our population-dynamical models successfully distinguish the different stellar populations in Sgr's nucleus because of their different spatial distributions, ages, metallicities, and kinematic features.

Keywords: Globular star clusters, Stellar kinematics, Stellar populations, Galaxy dynamics, Galaxy nuclei, Ultracompact dwarf galaxies