adsabs/SciX_UAT_keywords huggingface dataset:
Constraints on the Abundance of Primordial Black Holes from X-Ray Quasar Microlensing Observations: Substellar to Planetary Mass Range

We use X-ray observations of quasar microlensing (sensitive to smaller compact objects than in the optical) to study the possible presence of a population of low mass black holes (BHs; from ~10-3 M ⊙ to 10-1 M ⊙) in lens galaxies. We compare these observations with microlensing magnification simulations of a mixed population of stars and BHs plus a smooth matter component. We estimate the individual mass fractions of both stars and BHs for three different BH masses in the range of substellar to planetary masses. Our Bayesian analysis indicates that the contribution of BHs is negligible in the substellar mass range but that a population of BHs of planetary mass (M ≲ 10-3 M ⊙) could pass unnoticed to X-ray microlensing. We provide new upper limits to the contribution of BHs to the fraction of dark matter based on both, the quasar microlensing data in the X-ray band, and our previous estimates in the optical of intermediate-mass BHs with an additional upper limit at M = 3M ⊙.

Keywords: gravitational lensing; gravitational microlensing; quasar microlensing; x-ray quasars; primordial black holes; dark matter
NEO Population, Velocity Bias, and Impact Risk from an ATLAS Analysis

We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, "solar-system-to-pixels" fake-asteroid simulation to debias detections of real NEOs by the ATLAS survey. Down to absolute magnitudes H = 25 and 27.6 (diameters of ∼34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 ± 0.49) × 105 and (1.59 ± 0.45) × 107 NEOs, respectively. Most of the plausible sources of error tend toward underestimation, so the true populations are likely larger. We find the distribution of H magnitudes steepens for NEOs fainter than H ∼ 22.5, making small asteroids more common than extrapolation from brighter H mags would predict. Our simulation indicates a strong bias against detecting small but dangerous asteroids that encounter Earth with high relative velocities—i.e., asteroids in highly inclined and/or eccentric orbits. Worldwide NEO discovery statistics indicate this bias affects global NEO detection capability to the point that an observational census of small asteroids in such orbits is probably not currently feasible. Prompt and aggressive followup of NEO candidates, combined with closer collaborations between segments of the global NEO community, can increase detection rates for these dangerous objects.

Keywords: near-earth objects; sky surveys; astrodynamics
The Nonstandard Properties of a "Standard" PWN: Unveiling the Mysteries of PWN G21.5-0.9 Using Its IR and X-Ray Emission

The evolution of a pulsar wind nebula (PWN) depends on properties of the progenitor star, supernova, and surrounding environment. As some of these quantities are difficult to measure, reproducing the observed dynamical properties and spectral energy distribution (SED) with an evolutionary model is often the best approach to estimating their values. G21.5-0.9, powered by the pulsar J1833-1034, is a well observed PWN for which previous modeling efforts have struggled to reproduce the observed SED. In this study, we reanalyze archival infrared (IR; Herschel, Spitzer) and X-ray (Chandra, NuSTAR, Hitomi) observations. The similar morphology observed between IR line and continuum images of this source indicates that a significant portion of this emission is generated by surrounding dust and gas, and not synchrotron radiation from the PWN. Furthermore, we find that the broadband X-ray spectrum of this source is best described by a series of power laws fit over distinct energy bands. For all X-ray detectors, we find significant softening and decreasing unabsorbed flux in higher energy bands. Our model for the evolution of a PWN is able to reproduce the properties of this source when the supernova ejecta has a low initial kinetic energy Esn ≈ 1.2 × 1050 erg and the spectrum of particles injected into the PWN at the termination shock is softer at low energies. Lastly, our hydrodynamical modeling of the supernova remnant can reproduce its morphology if there is a significant increase in the density of the ambient medium ∼1.8 pc north of the explosion center.

Keywords: supernova remnants; pulsars; infrared astronomy; x-ray astronomy
Initial Results from a Systematic Search for Changing-look Active Galactic Nuclei Selected via Mid-infrared Variability

Changing-look active galactic nuclei (CL AGNs) can yield considerable insight into accretion physics as well as the co-evolution of black holes and their host galaxies. A large sample of these CL AGNs is essential to achieve the latter goal. We propose an effective method to select CL candidates from spectroscopic quasar catalogs using the mid-infrared (MIR) variability information derived from ALLWISE/NEOWISE data releases. Our primary selection criteria include both a large amplitude flux variation and a transition of MIR color from an AGN to a normal galaxy. A pilot spectroscopic follow-up of seven candidates among about 300 candidates selected from Sloan Digital Sky Survey low-redshift (z < 0.5) AGN sample results in three new turn-off CL AGNs and three ambiguous objects for suffering low spectral quality. We expect to obtain hundreds of CL AGNs once full spectroscopic follow-up of the sample is carried out.

Keywords: active galaxies; infrared galaxies; galaxy nuclei
EMPRESS. V. Metallicity Diagnostics of Galaxies over 12 + log(O/H) ≃ 6.9-8.9 Established by a Local Galaxy Census: Preparing for JWST Spectroscopy

We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and the largest compilation of extremely metal-poor galaxies (EMPGs) including new EMPGs identified by the Subaru EMPRESS survey. A total of 103 EMPGs are included, covering a large parameter space of magnitude (M i = -19 to -7) and Hβ equivalent width (10-600 Å), i.e., wide ranges of stellar mass and star formation rate. Using reliable metallicity measurements from the direct method for these galaxies, we derive the relationships between strong optical-line ratios and gas-phase metallicity over the range of $12+\mathrm{log}({\rm{O}}/{\rm{H}})$ ≃ 6.9-8.9, corresponding to 0.02-2 solar metallicity Z ⊙. We confirm that the R23 index, ([O III]+[O II])/Hβ, is the most accurate metallicity indicator with a metallicity uncertainty of 0.14 dex over the range among various popular metallicity indicators. The other metallicity indicators show large scatters in the metal-poor range (≲0.1 Z ⊙). It is explained by our CLOUDY photoionization modeling that, unlike the R23 index, the other metallicity indicators do not use a sum of singly and doubly ionized lines and cannot trace both low- and high-ionization gas. We find that the accuracy of the metallicity indicators is significantly improved if one uses Hβ equivalent width measurements that tightly correlate with ionization states. In this work, we also present the relation of physical properties with the UV-continuum slope β and ionization production rate ξ ion derived with GALEX data for the EMPGs and provide local anchors of galaxy properties together with the optical-line metallicity indicators that are available in the form of a machine-readable table and useful for forthcoming JWST spectroscopic studies.

Keywords: chemical abundances; galaxy chemical evolution; galaxy evolution; ultraviolet astronomy; dwarf galaxies
Testing the Spectroscopic Extraction of Suppression of Convective Blueshift

Efforts to detect low-mass exoplanets using stellar radial velocities (RVs) are currently limited by magnetic photospheric activity. Suppression of convective blueshift is the dominant magnetic contribution to RV variability in low-activity Sun-like stars. Due to convective plasma motion, the magnitude of RV contributions from the suppression of convective blueshift is related to the depth of formation of photospheric spectral lines for a given species used to compute the RV time series. Meunier et al. used this relation to demonstrate a method for spectroscopic extraction of the suppression of convective blueshift in order to isolate RV contributions, including planetary RVs, that contribute equally to the time series for each spectral line. Here, we extract disk-integrated solar RVs from observations over a 2.5 yr time span made with the solar telescope integrated with the HARPS-N spectrograph at the Telescopio Nazionale Galileo (La Palma, Canary Islands, Spain). We apply the methods outlined by Meunier et al. We are not, however, able to isolate physically meaningful contributions due to the suppression of convective blueshift from this solar data set, potentially because our data set is taken during solar minimum when the suppression of convective blueshift may not sufficiently dominate activity contributions to RVs. This result indicates that, for low-activity Sun-like stars, one must include additional RV contributions from activity sources not considered in the Meunier et al. model at different timescales, as well as instrumental variation, in order to reach the submeter per second RV sensitivity necessary to detect low-mass planets in orbit around Sun-like stars.

Keywords: radial velocity; solar activity; solar faculae; plages; solar granulation; sunspots; exoplanet detection methods
Parameter Estimation for Open Clusters using an Artificial Neural Network with a QuadTree-based Feature Extractor

With the unprecedented increase in the number of known star clusters, quick and modern tools are needed for their analysis. In this work, we develop an artificial neural network (ANN) trained on synthetic clusters to estimate the age, metallicity, extinction, and distance of Gaia open clusters. We implement a novel technique to extract features from the color-magnitude diagram of clusters by means of the QuadTree tool, and we adopt a multiband approach. We obtain reliable parameters for ~5400 clusters. We demonstrate the effectiveness of our methodology in accurately determining crucial parameters of Gaia open clusters by performing a comprehensive scientific validation. In particular, with our analysis we have been able to reproduce the Galactic metallicity gradient as it is observed by high-resolution spectroscopic surveys. This demonstrates that our method reliably extracts information on metallicity from color-magnitude diagrams (CMDs) of stellar clusters. For the sample of clusters studied, we find an intriguing systematic older age compared to previous analyses present in the literature. This work introduces a novel approach to feature extraction using a QuadTree algorithm, effectively tracing sequences in CMDs despite photometric errors and outliers. The adoption of ANNs, rather than convolutional neural networks, maintains the full positional information and improves performance, while also demonstrating the potential for deriving cluster parameters from simultaneous analysis of multiple photometric bands, beneficial for upcoming telescopes like the Vera Rubin Observatory. The implementation of ANN tools with robust isochrone fit techniques could provide further improvements in the quest for open cluster parameters.

Keywords: open star clusters; milky way disk; fundamental parameters of stars
Quiet Sun Center to Limb Variation of the Linear Polarization Observed by CLASP2 Across the Mg II h and k Lines

The CLASP2 (Chromospheric LAyer Spectro-Polarimeter 2) sounding rocket mission was launched on 2019 April 11. CLASP2 measured the four Stokes parameters of the Mg II h and k spectral region around 2800 Å along a 200″ slit at three locations on the solar disk, achieving the first spatially and spectrally resolved observations of the solar polarization in this near-ultraviolet region. The focus of the work presented here is the center-to-limb variation of the linear polarization across these resonance lines, which is produced by the scattering of anisotropic radiation in the solar atmosphere. The linear polarization signals of the Mg II h and k lines are sensitive to the magnetic field from the low to the upper chromosphere through the Hanle and magneto-optical effects. We compare the observations to theoretical predictions from radiative transfer calculations in unmagnetized semiempirical models, arguing that magnetic fields and horizontal inhomogeneities are needed to explain the observed polarization signals and spatial variations. This comparison is an important step in both validating and refining our understanding of the physical origin of these polarization signatures, and also in paving the way toward future space telescopes for probing the magnetic fields of the solar upper atmosphere via ultraviolet spectropolarimetry.

Keywords: solar chromosphere; center to limb observations; spectropolarimetry; solar ultraviolet emission; solar magnetic fields; quiet solar chromosphere
A Publicly Available Multiobservatory Data Set of an Enhanced Network Patch from the Photosphere to the Corona

New instruments sensitive to chromospheric radiation at X-ray, UV, visible, IR, and submillimeter wavelengths have become available that significantly enhance our ability to understand the bidirectional flow of energy through the chromosphere. We describe the calibration, coalignment, initial results, and public release of a new data set combining a large number of these instruments to obtain multiwavelength photospheric, chromospheric, and coronal observations capable of improving our understanding of the connectivity between the photosphere and the corona via transient brightenings and wave signatures. The observations center on a bipolar region of enhanced-network magnetic flux near disk center on SOL2017-03-17T14:00-17:00. The comprehensive data set provides one of the most complete views to date of chromospheric activity related to small-scale brightenings in the corona and chromosphere. Our initial analysis shows a strong spatial correspondence between the areas of broadest width of the hydrogen-α spectral line and the hottest temperatures observed in Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 radio data, with a linear coefficient of 6.12 × 10-5Å/K. The correspondence persists for the duration of cotemporal observations (≈60 m). Numerous transient brightenings were observed in multiple data series. We highlight a single, well-observed transient brightening in a set of thin filamentary features with a duration of 20 minutes. The timing of the peak intensity transitions from the cooler (ALMA, 7000 K) to the hotter (XRT, 3 MK) data series.

Keywords: the sun; solar chromosphere; solar atmosphere; solar corona; solar photosphere; solar coronal transients; solar radio emission; solar extreme ultraviolet emission; solar x-ray emission; solar physics
Faraday Conversion in Pair-symmetric Winds of Magnetars and Fast Radio Bursts

We consider the propagation of polarization in the inner parts of pair-symmetric magnetar winds, close to the light cylinder. Pair plasmas in magnetic field is birefringent, a ∝ B 2 effect. As a result, such plasmas work as phase retarders: Stokes parameters follow a circular trajectory on the Poincare sphere. In the highly magnetized regime, ω, ω p ≪ ω B , the corresponding rotation rates are independent of the magnetic field. A plasma screen with dispersion measure DM ~ 10-6 pc cm-3 can induce large polarization changes, including large effective rotation measures (RMs). The frequency scaling of the (generalized) RM, ∝ λ α , mimics the conventional RM with α = 2 for small phase shifts, but can be as small as α = 1. In interpreting observations, the frequency scaling of polarization parameters should be fitted independently. The model offers explanations for (i) the large circular polarization component observed in FRBs, with right-left switching; (ii) large RM, with possible sign changes (when the observation bandwidth is small); and (iii) time-dependent variable polarization. A relatively dense and slow wind is needed-the corresponding effect in regular pulsars is small.

Keywords: radio pulsars; radio transient sources; plasma astrophysics; magnetars
Discovery of a Long Thermonuclear X-Ray Burst from the Ultracompact Binary 4U 1850–087

We report the detection of a long X-ray burst from the ultracompact binary 4U 1850–087. The type I X-ray burst was observed on MJD 60171.65 by the Monitor of All-sky X-ray Image and Neutron Star Interior Composition Explorer (NICER). We analyze the NICER data between MJD 60095.19 and 60177.43, which includes the observation covering parts of the long X-ray burst decay phase, i.e., 0.15–3.8 hr after the trigger. The persistent spectra are well described by a multicolor disk blackbody, with an inner temperature of ∼0.5 keV, a thermally Comptonized continuum, an asymptotic power-law photon index of Γ ∼ 2.2, and an electron temperature of kT e ∼ 20–30 keV. The mean persistent flux was around 3.8 × 10‑10 erg cm‑2 s‑1, corresponding to a local mass accretion rate of . Part of the time-resolved burst spectra show a clear deviation from the blackbody model, which can be improved by considering the enhanced persistent emission due to the Poynting–Robertson drag or the reflected disk emission illuminated by the burst. From the burst flux during the cooling phase, we estimate the burst duration, τ ≈ 0.78 hr, the burst fluence, E b ≈ 4.1 × 1041 erg, and the ignition column depth, y ign ≈ 3.5 × 1010 g cm‑2. These long X-ray burst parameters from 4U 1850–087 suggest a regime of unstable burning of a thick, pure helium layer slowly accreted from a helium donor star. Moreover, we identify 7σ significant ∼1 keV emission lines in the burst spectra, which may originate from the surrounding accretion disk.

Keywords: neutron stars; x-ray bursters; low-mass x-ray binary stars; x-ray bursts
Resolution Study of Thermonuclear Initiation in White Dwarf Tidal Disruption Events

We study the initiation of thermonuclear detonations in tidally disrupted white dwarf stars by intermediate-mass (103 M ⊙) black holes. The length scales required to resolve the initiation mechanism are not easily reached in 3D, so instead we have devised 2D proxy models, which, together with a logarithmic gridding strategy, can adequately capture detonation wave fronts as material undergoes simultaneous compression and stretching from tidal forces. We consider 0.15 and 0.6 M ⊙ white dwarf stars parameterized by tidal strengths in the range β = 4-23. High spatial resolution elucidates the manner and conditions leading to thermonuclear detonation, linking the initiation sequence to stellar composition and tidal strength. All of our models suffer sustained detonations triggered by a combination of adiabatic compression, mild thermonuclear preconditioning, and collisional heating, in degrees depending primarily on tidal strength. We find that many diagnostics, such as temperature, total released energy, and iron-group products, are fairly well converged (better than 10%) at resolutions below 10 km along the scale height of the orbital plane. The exceptions are intermediate-mass transients like calcium, which remain uncertain up to factors of 2, even at 1 km resolution.

Keywords: black holes; supermassive black holes; astrophysical black holes; white dwarf stars; astrophysical explosive burning; radiative magnetohydrodynamics; astrophysical fluid dynamics
The Early Light Curve of SN 2023bee: Constraining Type Ia Supernova Progenitors the Apian Way

We present very early photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2023bee, starting about 8 hr after the explosion, which reveal a strong excess in the optical and nearest UV (U and UVW1) bands during the first several days of explosion. This data set allows us to probe the nature of the binary companion of the exploding white dwarf and the conditions leading to its ignition. We find a good match to the Kasen model in which a main-sequence companion star stings the ejecta with a shock as they buzz past. Models of double detonations, shells of radioactive nickel near the surface, interaction with circumstellar material, and pulsational delayed detonations do not provide good matches to our light curves. We also observe signatures of unburned material, in the form of carbon absorption, in our earliest spectra. Our radio nondetections place a limit on the mass-loss rate from the putative companion that rules out a red giant but allows a main-sequence star. We discuss our results in the context of other similar SNe Ia in the literature.

Keywords: white dwarf stars; type ia supernovae; supernovae; binary stars
Constraining Modified Gravity from Tidal Phenomena in Binary Stars

In beyond-Horndeski theories of gravity, the Vainshtein screening mechanism might only be partially effective inside stellar objects. This results in a modification of the pressure balance equation inside stars, often characterized by a single parameter (ϒ) in isotropic systems. We show how to constrain such theories of modified gravity, using tidal effects. We study such effects in cataclysmic variable star binaries and numerically obtain limits on the critical masses of the donor stars, below which they are tidally disrupted, by modeling them in beyond-Horndeski theories. This is contrasted with values of the donor masses, obtained using existing observational data, by a Monte Carlo error progression method. A best-fit scenario of the two yields a parametric constraint in the theories that we consider, within the approximations used. Here, we obtain the allowed range 0 ≤ ϒ ≤ 0.50.

Keywords: general relativity; stellar physics
Exploring Hydrodynamic Instabilities along the Infalling High-velocity Cloud Complex A

Complex A is a high-velocity cloud (HVC) that is traversing through the Galactic halo toward the Milky Way's disk. We combine both new and archival Green Bank Telescope observations to construct a spectroscopically resolved H I 21 cm map of this entire complex at a $17.1\lesssim \mathrm{log}({N}_{{\rm{H}}{\rm\small{I}},1\sigma }/{\mathrm{cm}}^{-2})\lesssim 17.9$ sensitivity for a $\mathrm{FWHM}=20\,\mathrm{km}\,{{\rm{s}}}^{-1}$ line and Δθ = 9'1 or 17 ≲ Δdθ ≲ 30 pc spatial resolution. We find that Complex A has a Galactic standard of rest frame velocity gradient of ${\rm{\Delta }}{v}_{\mathrm{GSR}}/{\rm{\Delta }}L=25\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{kpc}}^{-1}$ along its length, that it is decelerating at a rate of $\langle a{\rangle }_{\mathrm{GSR}}=55\,\mathrm{km}\,{\mathrm{yr}}^{-2}$ , and that it will reach the Galactic plane in Δt ≲ 70 Myr if it can survive the journey. We have identified numerous signatures of gas disruption. The elongated and multi-core structure of Complex A indicates that either thermodynamic instabilities or shock-cascade processes have fragmented this stream. We find Rayleigh-Taylor fingers on the low-latitude edge of this HVC; many have been pushed backward by ram pressure stripping. On the high-latitude side of the complex, Kelvin-Helmholtz instabilities have generated two large wings that extend tangentially off Complex A. The tips of these wings curve slightly forward in the direction of motion and have an elevated H I column density, indicating that these wings are forming Rayleigh-Taylor globules at their tips and that this gas is becoming entangled with unseen vortices in the surrounding coronal gas. These observations provide new insights on the survivability of low-metallicity gas streams that are accreting onto L⋆ galaxies.

Keywords: galaxy evolution; circumgalactic medium; hydrodynamics; high-velocity clouds