Sazuna/UAT_keywords huggingface dataset:
The Nature of Luminous Quasars with Very Large C IV Equivalent Widths. We report results for a complete sample of 10 luminous radio-quiet quasars with large C IV equivalent widths (EW ≥ 150 Å). For 8/10 we performed Chandra snapshot observations. We find that, in addition to the enhanced C IV line EW, their He II and Mg II lines are enhanced, but the C III] line is not. Their X-ray emission is substantially stronger than expected from their ultraviolet luminosity. Additionally, these large C IV EW quasars show small C IV blueshifts and possibly low Eddington ratios, suggesting that they are "extreme low Eigenvector 1 (EV1)" quasars. The mean excess He II EW is well matched by radiation pressure compression (RPC) photoionization models, with the harder α ox ionizing spectrum. However, these results do not reproduce well the enhancement pattern of the C IV, Mg II, and C III] EWs, or the observed high C IV/Mg II ratio. RPC calculations indicate that the C IV/Mg II line ratio is an effective metallicity indicator, and models with subsolar-metallicity gas and a hard ionizing continuum reproduce well the enhancement pattern of all four ultraviolet lines. We find that the C IV/Mg II line ratio in quasars is generally correlated with the excess X-ray emission. Extremely high EV1 quasars are characterized by high metallicity and suppressed X-ray emission. The underlying mechanism relating gas metallicity and X-ray emission is not clear but may be related to radiation-pressure-driven disk winds, which are enhanced at high metallicity, and consequent mass loading reducing coronal X-ray emission.

Keywords: Metallicity, Photoionization, X-ray quasars, Quasars
Flaring-associated Complex Dynamics in Two M Dwarfs Revealed by Fast, Time-resolved Spectroscopy. Habitability of an exoplanet is believed to be profoundly affected by activities of the host stars, although the related coronal mass ejections (CMEs) are still rarely detected in solar-like and late-type stars. We here report an observational study on the flares of two M dwarfs triggered by the high-cadence survey performed by the Ground-based Wide Angle Camera system. In both events, the fast, time-resolved spectroscopy enables us to identify symmetric broad Hα emission with not only a nearly zero bulk velocity, but also a large projected maximum velocity as high as ~700-800 km s-1. This broadening could be resulted from either the Stark (pressure) effect or a flaring-associated CME at the stellar limb. In the context of the CME scenario, the CME mass is estimated to be ~4 × 1018 and 2 × 1019 g. In addition, our spectral analysis reveals a temporal variation of the line center of the narrow Hα emission in both events. The variation amplitudes are at tens of kilometers per second, which could be ascribed to the chromospheric evaporation in one event, and to a binary scenario in the other one. With the total flaring energy determined from our photometric monitor, we show a reinforced trend in which the larger the flaring energy, the higher the CME mass is.

Keywords: Time domain astronomy, Solar coronal mass ejections, Stellar flares, Optical flares, Spectroscopy, Late-type dwarf stars
Neutrino Emissivities as a Probe of the Internal Magnetic Fields of White Dwarfs. The evolution of white dwarfs (WDs) depends crucially on thermal processes. The plasma in their core can produce neutrinos that escape from the star, thus contributing to the energy loss. While in the absence of a magnetic field the main cooling mechanism is plasmon decay at high temperature and photon surface emission at low temperature, a large magnetic field in the core hiding beneath the surface even of ordinary WDs, and undetectable to spectropolarimetric measurements, could potentially leave an imprint in the cooling. In this paper, we revisit the contribution to WD cooling stemming from neutrino pair synchrotron radiation and the effects of the magnetic field on plasmon decay. Our key finding is that even if observations limit the magnetic field strength at the stellar surface, magnetic fields in the interior of WDs-with or without a surface magnetic field-can be strong enough to modify the cooling rate, with neutrino pair synchrotron emission being the most important contribution. This effect may not only be relevant for the quantification and interpretation of cooling anomalies, but suggests that the internal magnetic fields of WDs should be smaller than ~ 6 × 1011 G, slightly improving bounds coming from a stability requirement. While our simplified treatment of the WD structure implies that further studies are needed to reduce the systematic uncertainties, the estimates based on comparing the emissivities illustrate the potential of neutrino emission as a diagnostic tool to study the interior of WDs.

Keywords: Stellar properties, White dwarf stars, Stellar magnetic fields
Discovery of Faint Double-peak Hα Emission in the Halo of Low Redshift Galaxies. Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the Hα emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable Hα (redshift &lt;0.42). An exhaustive screening of the corresponding Hα images led us to select 118 reliable Hα emitting gas clouds. The signals are faint, with a surface brightness of ${10}^{-17.3\pm 0.3}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ . Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, telluric line residuals, or high-redshift interlopers. Around 38% of the time, the Hα line profile shows a double peak with the drop in intensity at the rest frame of the central galaxy, and with a typical peak-to-peak separation of the order of ±200 km s-1. Most line emission clumps are spatially unresolved. The mass of emitting gas is estimated to be between 1 and 10-3 times the stellar mass of the central galaxy. The signals are not isotropically distributed; their azimuth tends to be aligned with the major axis of the corresponding galaxy. The distances to the central galaxies are not random either. The counts drop at a distance &gt;50 galaxy radii, which roughly corresponds to the virial radius of the central galaxy. We explore several physical scenarios to explain this Hα emission, among which accretion disks around rogue intermediate-mass black holes fit the observations best.

Keywords: Intermediate-mass black holes, Galaxy fountains, Galaxy formation, Cool intergalactic medium, Galaxy winds, Galaxy accretion, Circumgalactic medium, Extragalactic astronomy, Astrophysical black holes
Imaging Polarization of the Blue-excess Hot Dust-obscured Galaxy WISE J011601.41-050504.0. We report on VLT/FORS2 imaging polarimetry observations in the R Special band of WISE J011601.41-050504.0 (W0116-0505), a heavily obscured hyperluminous quasar at z = 3.173 classified as a Hot Dust-obscured Galaxy (Hot DOG) based on its mid-IR colors. Recently, Assef et al. identified W0116-0505 as having excess rest-frame optical/UV emission and concluded that this excess emission is most likely scattered light from the heavily obscured AGN. We find that the broadband rest-frame UV flux is strongly linearly polarized (10.8% ± 1.9%, with a polarization angle of 74° ± 9°), confirming this conclusion. We analyze these observations in the context of a simple model based on scattering either by free electrons or by optically thin dust, assuming a classical dust torus with polar openings. Both can replicate the degree of polarization and the luminosity of the scattered component for a range of geometries and column densities, but we argue that optically thin dust in the ISM is the more likely scenario. We also explore the possibility that the scattering medium corresponds to an outflow recently identified for W0116-0505. This is a feasible option if the outflow component is biconical with most of the scattering occurring at the base of the receding outflow. In this scenario, the quasar would still be obscured even if viewed face-on but might appear as a reddened type 1 quasar once the outflow has expanded. We discuss a possible connection between blue-excess Hot DOGs, extremely red quasars, reddened type 1 quasars, and unreddened quasars that depends on a combination of evolution and viewing geometry.

Keywords: Quasars, Active galaxies, Polarimetry, Galaxy evolution, High-redshift galaxies
SN 2016dsg: A Thermonuclear Explosion Involving a Thick Helium Shell. A thermonuclear explosion triggered by a He-shell detonation on a carbon-oxygen white-dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group elements produced during He-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a subluminous peculiar Type I supernova consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the i-band peak absolute magnitude is derived to be around -17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated from an old stellar population. The spectra collected after the peak are unusually red, show strong UV line blanketing and weak O I λ7773 absorption lines, and do not evolve significantly over 30 days. An absorption line around 9700-10500 Å is detected in the near-infrared spectrum and is likely from the unburnt He in the ejecta. The spectroscopic evolution is consistent with the thermonuclear explosion models for a sub-Chandrasekhar-mass white dwarf with a thick He shell, while the photometric evolution is not well described by existing models.

Keywords: Type Ia supernovae, Supernovae
Quantitative Characterization of Magnetic Flux Rope Properties for Two Solar Eruption Events. In order to bridge the gap between heliospheric and solar observations of coronal mass ejections (CMEs), one of the key steps is to improve the understanding of their corresponding magnetic structures like the magnetic flux ropes (MFRs). But it remains a challenge to confirm the existence of a coherent MFR before or upon the CME eruption on the Sun and to quantitatively characterize the CME-MFR due to the lack of direct magnetic field measurements in the corona. In this study, we investigate MFR structures originating from two active regions (ARs), AR 11719 and AR 12158, and estimate their magnetic properties quantitatively. We perform nonlinear force-free field extrapolations with preprocessed photospheric vector magnetograms. In addition, remote-sensing observations are employed to find indirect evidence of MFRs on the Sun and to analyze the time evolution of magnetic reconnection flux associated with the flare ribbons during the eruption. A coherent "preexisting" MFR structure prior to the flare eruption is identified quantitatively for one event from the combined analysis of the extrapolation and observation. Then the characteristics of MFRs for two events on the Sun before and during the eruption forming the CME-MFR, including the axial magnetic flux, field line twist, and reconnection flux, are estimated and compared with the corresponding in situ modeling results. We find that the magnetic reconnection associated with the accompanying flares for both events injects a significant amount of flux into the erupted CME-MFRs.

Keywords: Solar active region magnetic fields, Solar flares, Solar coronal mass ejections, Solar magnetic fields
The X-Ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-driven Massive Star Explosions. We present AT2020mrf (SRGe J154754.2+443907), an extra-galactic (z = 0.1353) fast blue optical transient (FBOT) with a rise time of t  g,rise = 3.7 days and a peak luminosity of M  g,peak = -20.0. Its optical spectrum around peak shows a broad (v ~ 0.1c) emission feature on a blue continuum (T ~ 2 × 104 K), which bears a striking resemblance to AT2018cow. Its bright radio emission (ν L  ν  = 1.2 × 1039 erg s-1; ν rest = 7.4 GHz; 261 days) is similar to four other AT2018cow-like events, and can be explained by synchrotron radiation from the interaction between a sub-relativistic (≳0.07-0.08c) forward shock and a dense environment ( $\dot{M}\lesssim {10}^{-3}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ for v w = 103 km s-1). AT2020mrf occurs in a galaxy with M * ~ 108 M ☉ and specific star formation rate ~10-10 yr-1, supporting the idea that AT2018cow-like events are preferentially hosted by dwarf galaxies. The X-ray luminosity of AT2020mrf is the highest among FBOTs. At 35-37 days, SRG/eROSITA detected luminous (L X ~ 2 × 1043 erg s-1; 0.3-10 keV) X-ray emission. The X-ray spectral shape (f  ν  ∝ ν -0.8) and erratic intraday variability are reminiscent of AT2018cow, but the luminosity is a factor of ~20 greater than AT2018cow. At 328 days, Chandra detected it at L X ~ 1042 erg s-1, which is &gt;200 times more luminous than AT2018cow and CSS161010. At the same time, the X-ray emission remains variable on the timescale of ~1 day. We show that a central engine, probably a millisecond magnetar or an accreting black hole, is required to power the explosion. We predict the rates at which events like AT2018cow and AT2020mrf will be detected by SRG and Einstein Probe.

Keywords: Sky surveys, High energy astrophysics, Core-collapse supernovae, X-ray transient sources, Supernovae, Radio transient sources
Rotational Variation Allows for Narrow Age Spread in the Extended Main-sequence Turnoff of Massive Cluster NGC 1846. The color-magnitude diagrams (CMDs) of intermediate-age star clusters (≲2 Gyr) are much more complex than those predicted by coeval, nonrotating stellar evolution models. Their observed extended main-sequence turnoffs (eMSTOs) could result from variations in stellar age, stellar rotation, or both. The physical interpretation of eMSTOs is largely based on the complex mapping between stellar models-themselves functions of mass, rotation, orientation, and binarity-and the CMD. In this paper, we compute continuous probability densities in three-dimensional color, magnitude, and ${v}_{{\rm{e}}}\sin i$ space for individual stars in a cluster's eMSTO, based on a rotating stellar evolution model. These densities enable the rigorous inference of cluster properties from a stellar model, or, alternatively, constraints on the stellar model from the cluster's CMD. We use the MIST stellar evolution models to jointly infer the age dispersion, the rotational distribution, and the binary fraction of the Large Magellanic Cloud cluster NGC 1846. We derive an age dispersion of ~70-80 Myr, approximately half the earlier estimates due to nonrotating models. This finding agrees with the conjecture that rotational variation is largely responsible for eMSTOs. However, MIST models do not provide a satisfactory fit to all stars in the cluster and achieve their best agreement at an unrealistically high binary fraction. The lack of agreement near the main-sequence turnoff suggests specific physical changes to the stellar evolution models, including a lower mass for the Kraft break and potentially enhanced main-sequence lifespans for rapidly rotating stars.

Keywords: Stellar rotation, Computational methods, Stellar evolution, Star clusters
Fermi-GBM Observation of GRB 090717034: χ <SUP>2</SUP> Test Confirms Evidence of Gravitational Lensing by a Supermassive Black Hole with a Million Solar Mass. Gravitational lensing of gamma-ray bursts (GRBs) can provide an opportunity to probe the massive compact objects in the universe at different redshifts. We have discovered two consecutive pulses in the light curve of GRB 090717034, with the same temporal profile and different count rate, separated by a time interval, which is identified as a gravitationally lensed candidate in the Fermi-GBM GRB catalog. Here, we use the χ 2 minimization method to investigate the similarity of the temporal profile variability of the two pulses as a gravitationally lensed GRB candidate. We find the magnification factor and the time delay between two pulses to minimize the χ 2 function. Then, we perform a Monte Carlo simulation on a sample of mock lensed GRBs and compare the χ 2 of the lensed GRB candidate with the simulation, which confirms this candidate with 1σ confidence level. Assuming that GRB 090717034 is lensed by a pointlike object, the redshifted lens mass is about M  L (1 + z) = (4.839 ± 1.148) × 106  M ⊙. The lens of this GRB is a candidate for a supermassive black hole along the line of sight to the GRB.

Keywords: Gamma-ray bursts, Gravitational lensing, Black holes
X-Ray Jets in the High-redshift Quasars J1405+0415 and J1610+1811. We investigate Chandra X-ray observations of the radio-loud quasars J1405+0415 and J1610+1811 at redshifts z = 3.215 and z = 3.122, respectively, for evidence of extended X-ray emission. Observations totalling 95 ks per target are combined, and X-ray jets that are spatially coincident with known radio features are detected at a greater than 4σ significance. Hardness ratios and emission spectra are determined for all X-ray features, and X-ray fluxes and luminosities are measured. Jet-to-core X-ray flux ratios are estimated for each system, and the ratios are consistent with those observed for nearby and more distant jet systems, although the spread in the parameter is large. These results suggest that to first order the X-ray jet emission mechanisms are redshift invariant. In addition to the extended emission analysis, incorporating also archival data from Swift, we examined the properties of a decline in the Chandra flux from the active galactic nucleus (AGN) of J1610+1811 observed between 2018 and 2021. We conclude that the variability is most likely due to a flaring event that occurred between the years 2017 and 2018 and originated from either the AGN or the inner jet region.

Keywords: Jets, High-redshift galaxies, X-ray active galactic nuclei
A New Way to Explore Cosmological Tensions Using Gravitational Waves and Strong Gravitational Lensing. In recent years, a crisis in the standard cosmology has been caused by inconsistencies in the measurements of some key cosmological parameters, the Hubble constant H 0 and cosmic curvature parameter Ω K , for example. It is necessary to remeasure them with the cosmological model-independent methods. In this paper, based on the distance sum rule, we present such a way to constrain H 0 and Ω K  simultaneously in the late universe from strong gravitational lensing time-delay (SGLTD) data and gravitational wave (GW) standard siren data simulated from the future observation of the Einstein Telescope (ET). Based on the data for six currently observed SGLTDs, we find that the constraint precision of H 0 from the combined 100 GW events can be comparable with the measurement from the SH0ES collaboration. As the number of GW events increases to 700, the constraint precision of H 0 will exceed that of the Planck 2018 results. Considering 1000 GW events as the conservative estimation of ET in the 10 yr observation, we obtain H 0 = 73.69 ± 0.36 km s-1 Mpc-1 with a 0.5% uncertainty and ${{\rm{\Omega }}}_{K}={0.076}_{-0.087}^{+0.068}$ . In addition, we simulate 55 strong gravitational lensing (SGL) systems with a 6.6% uncertainty for the measurement of time-delay distance. By combining with 1000 GWs, we infer that H 0 = 73.65 ± 0.35 km s-1 Mpc-1 and Ω K  = 0.008 ± 0.048. Our results suggest that this approach can play an important role in exploring cosmological tensions.

Keywords: Hubble constant, Strong gravitational lensing, Gravitational waves, Cosmological parameters
Implementation of the Polarimetry Focusing Telescope Array Observation Simulator on board the X-Ray Timing and Polarimetry Observatory. An observation simulator is established, on an event-by-event basis, for the Polarimetry Focusing telescope Array (PFA) on board the planned enhanced X-ray Timing and Polarimetry observatory (eXTP). An event generator, based on XIMPOL, is used to sample the parameters of the X-rays reaching the aperture of the telescope. The trajectories and interactions of X-rays through the telescope and the corresponding secondaries are calculated using the optics and detector simulation model built in GEANT4, before being translated into signals in the pixelated readout electronics. It is shown that mirror deformation is required for the optics simulation model, and transportation of ionization electrons is required for the detector simulation model to reproduce the overall performance of the telescope. The developed tool is useful in different mission phases, such as payload optimization in the design phase, discrimination of new phenomena against known physics models in the calibration phases, and sensitivity studies of potential polarized X-ray sources in observation planning. The sensitivity of PFA to the Crab Nebula and Crab pulsar is investigated to demonstrate the application of the tool. Even with the dilution effect, space-resolved and phase-resolved polarimetry can reveal important aspects of the Crab Nebula and Crab pulsar and help break the degeneracy between different models.

Keywords: Polarimeters, X-ray detectors, Astronomical methods
Spectroscopic Study of Four Metal-poor Carbon Stars from the Hamburg/ESO Survey: On Confirming the Low-mass Nature of Their Companions. Elemental abundances of extrinsic carbon stars provide insight into the poorly understood origin and evolution of elements in the early Galaxy. In this work, we present the results of a detailed spectroscopic analysis of four potential carbon star candidates from the Hamburg/ESO Survey (HES): HE 0457-1805, HE 0920-0506, HE 1241-0337, and HE 1327-2116. This analysis is based on the high-resolution spectra obtained with Mercator/HERMES (R ~ 86,000) and SUBARU/HDS (R ~ 50,000). Although the abundances of a few elements, such as Fe, C, and O, are available from medium-resolution spectra, we present the first ever detailed high-resolution spectroscopic analysis for these objects. The objects HE 0457-1805 and HE 1241-0337 are found to be CEMP-s stars, HE 0920-0506 a CH star, and HE 1327-2116 a CEMP-r/s star. The object HE 0457-1805 is a confirmed binary, whereas the binary status of the other objects is unknown. The locations of program stars on the diagram of absolute carbon abundance A(C) versus [Fe/H] point at their binary nature. We have examined various elemental abundance ratios of the program stars and confirmed the low-mass nature of their former AGB companions. We have shown that the i-process models could successfully reproduce the observed abundance pattern in HE 1327-2116. The analysis performed for HE 0457-1805, HE 0920-0506, and HE 1241-0337 based on the FRUITY parametric models confirmed that the surface chemical compositions of these three objects are influenced by pollution from low-mass AGB companions. * Based on data collected using Mercator/HERMES, SUBARU/HDS.

Keywords: Chemically peculiar stars, Carbon stars, Chemical abundances