Sazuna/UAT_keywords huggingface dataset:
Ab-initio QCD Calculations Impact the Inference of the Neutron-star-matter Equation of State. We demonstrate that ab-initio calculations in QCD at high densities offer significant and nontrivial information about the equation of state of matter in the cores of neutron stars, going beyond that which is obtainable from current astrophysical observations. We do so by extrapolating the equation of state to neutron-star densities using a Gaussian process and conditioning it sequentially with astrophysical observations and QCD input. Using our recent work, imposing the latter does not require an extrapolation to asymptotically high density. We find the QCD input to be complementary to the astrophysical observations, offering strong additional constraints at the highest densities reached in the cores of neutron stars; with the QCD input, the equation of state is no longer prior dominated at any density. The QCD input reduces the pressure and speed of sound at high densities, and it predicts that binary collisions of equal-mass neutron stars will produce a black hole with greater than 95% (68%) credence for masses M ≥ 1.38M ⊙ (M ≥ 1.25M ⊙). We provide a Python implementation of the QCD likelihood function so that it can be conveniently used within other inference setups.

Keywords: Neutron stars, Neutron star cores, Nuclear astrophysics, Compact objects, Nuclear physics
Examining the Properties of Low-luminosity Hosts of Type Ia Supernovae from ASAS-SN. We present a spectroscopic analysis of 44 low-luminosity host galaxies of Type Ia supernovae (SNe Ia) detected by the All-Sky Automated Survey for Supernovae (ASAS-SN), using hydrogen, oxygen, and sulfur emission lines to measure metallicities and star formation rates. We find no statistically significant evidence that the star formation activity and metallicities of the galaxies in our sample are inconsistent with galaxies of similar luminosities and masses. We identify two 3σ outlier galaxies that have high metallicities for their stellar masses, but find that their other properties are consistent with general galaxies. The overall consistency between our sample and general galaxy samples further strengthens the evidence from more luminous SN Ia host galaxy samples that SN Ia host galaxies are typical.

Keywords: Galaxy abundances, Type Ia supernovae, Supernovae
Pulsar Double Lensing Sheds Light on the Origin of Extreme Scattering Events. In extreme scattering events, the brightness of a compact radio source drops significantly, as light is refracted out of the line of sight by foreground plasma lenses. Despite recent efforts, the nature of these lenses has remained a puzzle, because any roughly round lens would be so highly overpressurized relative to the interstellar medium that it could only exist for about a year. This, combined with a lack of constraints on distances and velocities, has led to a plethora of theoretical models. We present observations of a dramatic double-lensing event in pulsar PSR B0834+06 and use a novel phase-retrieval technique to show that the data can be reproduced remarkably well with a two-screen model: one screen with many small lenses and another with a single, strong one. We further show that the latter lens is so strong that it would inevitably cause extreme scattering events. Our observations show that the lens moves slowly and is highly elongated on the sky. If similarly elongated along the line of sight, as would arise naturally from a sheet of plasma viewed nearly edge-on, no large overpressure is required and hence the lens could be long-lived.

Keywords: Radio spectroscopy, Warm ionized medium, Interstellar medium, Interstellar scattering, Radio astronomy, Radio pulsars
The Impacts of Neutron Star Structure and Base Heating on Type I X-Ray Bursts and Code Comparison. Type I X-ray bursts are rapidly brightening phenomena triggered by thermonuclear burning on the accreting layers of a neutron star (NS). The light curves represent the physical properties of NSs and the nuclear reactions on the proton-rich nuclei. The numerical treatments of the accreting NS and physics of the NS interior are not established, which shows uncertainty in modeling for observed X-ray light curves. In this study, we investigate theoretical X-ray burst models compared with burst light curves with GS 1826-24 observations. We focus on the impacts of the NS mass and radius and base heating on the NS surface using the MESA code. We find a monotonic correlation between the NS mass and the parameters of the light curve. The higher the mass, the longer the recurrence time and the greater the peak luminosity. While the larger the radius, the longer the recurrence time, the peak luminosity remains nearly constant. In the case of increasing base heating, both the recurrence time and peak luminosity decrease. We also examine the above results with a different numerical code, HERES, based on general relativity and consider the central NS. We find that the burst rate, energy, and strength are almost the same in two X-ray burst codes by adjusting the base heat parameter in MESA (the relative errors ≲5%), while the duration and rise times are significantly different between (the relative error is possibly ~50%). The peak luminosity and the e-folding time change irregularly between two codes for different accretion rates.

Keywords: Neutron stars, Nuclear abundances, Accretion, X-ray bursts
Electrostatic Solitary Waves in the Venusian Ionosphere Pervaded by the Solar Wind: A Theoretical Perspective. Electrostatic solitary waves (ESWs) in the Venusian ionosphere that are impinged by the solar wind are investigated using a homogeneous, collisionless, and magnetized multicomponent plasma consisting of Venusian H+ and O+ ions, Maxwellian Venusian electrons and streaming solar wind protons, and suprathermal electrons following κ - distribution. The model supports the propagation of positive potential slow O+ and H+ ion-acoustic solitons. The evolution and properties of the solitons occurring in two sectors, viz., dawn-dusk and noon-midnight sector of the Venus ionosphere at an altitude of (200-2000) km, are studied. The theoretical model predicts positive potential solitons with amplitude ~(0.067-56) mV, width ~(1.7-53.21) m, and velocity ~(1.48-8.33) km s-1. The bipolar soliton electric field has amplitude ~(0.03-27.67) mV m-1 with time duration ~(0.34-22) ms. These bipolar electric field pulses when Fourier transformed to the frequency domain occur as a broadband electrostatic noise, with frequency varying in the range of ~9.78 Hz-8.77 kHz. Our results can explain the observed electrostatic waves in the frequency range of 100 Hz-5.4 kHz in the Venus ionosphere by the Pioneer Venus Orbiter mission. The model can also be relevant in explaining the recent observation of ESWs in the Venus magnetosheath by the Solar Orbiter during its first gravity assist maneuver of Venus.

Keywords: Solar wind, Venus
Direct Evidence of Electron Acceleration at the Dipolarization Front. The dramatic changes in the magnetic field at the dipolarization front (DF) provide a suitable environment for electron acceleration, which usually can cause the flux enhancement of energetic electrons behind the front. However, it is unknown whether energetic electrons observed at the DF are energized locally, and which mechanism accelerates the electrons at the DF is unclear. Our study performs a direct quantitative analysis to reveal the acceleration process of energetic electrons at the DF using the high-time-resolution data from NASA's Magnetospheric Multiscale mission. The fluxes of energetic electrons at 90° are enhanced at the front. Under adiabatic conditions, our quantitative analysis indicates that these electrons at the front could be locally accelerated to over 100 keV by betatron acceleration. Eventually, the electron temperature anisotropy formed via the betatron mechanism could provide the free energy to excite whistler waves at the DF. Our quantitative study provides, for the first time, strong direct evidence for the local electron acceleration at the DF.

Keywords: Planetary magnetospheres, Plasma jets, Space plasmas, Plasma physics
X-Ray Flares in the Long-term Light Curve of Low-luminosity Active Galactic Nucleus M81*. Most active galactic nuclei at the center of the nearby galaxies have supermassive black holes accreting at sub-Eddington rates through hot accretion flows or radiatively inefficient accretion flows, which efficiently produce jets. The association of radio and X-ray flares with the knot ejection from M81* inspires us to model its multiwavelength spectral energy distribution (SED) during these flares to constrain the physical parameters of the jet. Moreover, we construct a long-term light curve in X-rays to identify the flares in the available data and constrain the jet parameters during those periods. The jet activity may vary on short as well as long timescales, which may produce flares in different frequency bands. The SEDs from radio to X-ray during the quiescent as well as flaring states are found to be satisfactorily explained by synchrotron emission of relativistic electrons from a single zone. The variation in the values of the jet parameters during the different states is shown and compared with high-synchrotron peaked blazars.

Keywords: Low-luminosity active galactic nuclei, X-ray active galactic nuclei, Spectral energy distribution
The Evolving Effect of Cosmic Web Environment on Galaxy Quenching. We investigate how cosmic web structures affect galaxy quenching in the IllustrisTNG (TNG100) cosmological simulations by reconstructing the cosmic web within each snapshot using the DISPERSE framework. We measure the comoving distance from each galaxy with stellar mass $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 8$ to the nearest node (d node) and the nearest filament spine (d fil) to study the dependence of both the median specific star formation rate (&lt;sSFR&gt;) and the median gas fraction (&lt;f gas&gt;) on these distances. We find that the &lt;sSFR&gt; of galaxies is only dependent on the cosmic web environment at z &lt; 2, with the dependence increasing with time. At z ≤ 0.5, $8\leqslant \mathrm{log}({M}_{* }/{M}_{\odot })\lt 9$ galaxies are quenched at d node ≲ 1 Mpc, and have significantly suppressed star formation at d fil ≲ 1 Mpc, trends driven mostly by satellite galaxies. At z ≤ 1, in contrast to the monotonic drop in &lt;sSFR&gt; of $\mathrm{log}({M}_{* }/{M}_{\odot })\lt 10$ galaxies with decreasing d node and d fil, $\mathrm{log}({M}_{* }/{M}_{\odot })\geqslant 10$ galaxies-both centrals and satellites-experience an upturn in &lt;sSFR&gt; at d node ≲ 0.2 Mpc. Much of this cosmic web dependence of star formation activity can be explained by an evolution in &lt;f gas&gt;. Our results suggest that in the past ~10 Gyr, low-mass satellites are quenched by rapid gas stripping in dense environments near nodes and gradual gas starvation in intermediate-density environments near filaments. At earlier times, cosmic web structures efficiently channeled cold gas into most galaxies. State-of-the-art ongoing spectroscopic surveys such as the Sloan Digital Sky Survey and DESI, as well as those planned with the Subaru Prime Focus Spectrograph, JWST, and Roman, are required to test our predictions against observations.

Keywords: Hydrodynamical simulations, Galaxy formation, Large-scale structure of the universe, Magnetohydrodynamical simulations, Star formation, Cosmic web, Galaxy evolution, Galaxy quenching, Intergalactic filaments
Carbon-Oxygen Phase Separation in Modules for Experiments in Stellar Astrophysics (MESA) White Dwarf Models. We enhance the treatment of crystallization for models of white dwarfs (WDs) in the stellar evolution software Modules for Experiments in Stellar Astrophysics (MESA) by implementing carbon-oxygen (C/O) phase separation. The phase separation process during crystallization leads to transport of oxygen toward the centers of WDs, resulting in a more compact structure that liberates gravitational energy as additional heating that modestly slows WD cooling timescales. We quantify this cooling delay in MESA C/O WD models over the mass range 0.5-1.0 M ⊙, finding delays of 0.5-0.8 Gyr for typical C/O interior profiles. MESA WD cooling timescales including this effect are generally comparable to other WD evolution models that make similar assumptions about input physics. When considering phase separation alongside 22Ne sedimentation, however, we find that both MESA and BaSTI WD cooling models predict a more modest sedimentation delay than the latest LPCODE models, and this may therefore require a reevaluation of previously proposed solutions to some WD cooling anomalies that were based on LPCODE models of 22Ne sedimentation. Our implementation of C/O phase separation in the open-source stellar evolution software MESA provides an important tool for building realistic grids of WD cooling models, as well as a framework for expanding on our implementation to explore additional physical processes related to phase transitions and associated fluid motions in WD interiors.

Keywords: White dwarf stars, Stellar physics
Limits on Leptonic TeV Emission from the Cygnus Cocoon with Swift-XRT. γ-ray observations of the Cygnus Cocoon, an extended source surrounding the Cygnus X star-forming region, suggest the presence of a cosmic-ray accelerator reaching energies up to a few PeV. The very-high-energy (VHE; 0.1-100 TeV) γ-ray emission may be explained by the interaction of cosmic-ray hadrons with matter inside the Cocoon, but an origin of inverse Compton radiation by relativistic electrons cannot be ruled out. Inverse Compton γ-rays at VHE are accompanied by synchrotron radiation peaked in X-rays. Hence, X-ray observations may probe the electron population and magnetic field of the source. We observed 11 fields in or near the Cygnus Cocoon with the Neil Gehrels Swift Observatory's X-Ray Telescope (Swift-XRT) totaling 110 ks. We fit the fields to a Galactic and extragalactic background model and performed a log-likelihood ratio test for an additional diffuse component. We found no significant additional emission and established upper limits in each field. By assuming that the X-ray intensity traces the TeV intensity and follows a ${dN}/{dE}\propto {E}^{-2.5}$ spectrum, we obtained a 90% upper limit of F X &lt; 8.7 × 10-11 erg cm-2 s-1 or &lt;5.2 × 10-11 erg cm-2 s-1 on the X-ray flux of the entire Cygnus Cocoon between 2 and 10 keV depending on the choice of hydrogen column density model for the absorption. The obtained upper limits suggest that no more than one-quarter of the γ-ray flux at 1 TeV is produced by inverse Compton scattering, when assuming an equipartition magnetic field of ~20 μG.

Keywords: Gamma-ray sources, X-ray sources
Horizonless Spacetimes As Seen by Present and Next-generation Event Horizon Telescope Arrays. We study the capabilities of present and future radio very long baseline interferometry arrays to distinguish black holes from horizonless spacetimes. We consider an example of a horizonless spacetime, obtained by overspinning a regular black hole. Its image is distinct from the image of a Kerr spacetime due to a second set of photon rings interior to the shadow. These photon rings cannot be directly resolved by present and even next-generation Event Horizon Telescope arrays, but instead imprint themselves in horizon-scale images as excess central brightness relative to that of a black hole. We demonstrate that future arrays can decrease the upper bound on the central brightness depression by a factor of 10 and thereby detect such indirect imprints from non-Kerr spacetimes in reconstructed images.

Keywords: Black hole physics, Very long baseline interferometry, Event horizons
The 2013 November 12 Solar Energetic Electron Event Associated with Solar Jets. We investigate the hard X-ray (HXR) flare-associated "prompt" solar energetic electron (SEE) 2013 November 12 event with joint EUV jet observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly and STEREO-A/EUVI. The SEE energy spectrum observed by Wind/3D Plasma and Energetic Particle shows a triple-power-law shape with a low-energy break of 10.0 ± 1.7 keV and a high-energy break of 56.6 ± 8.9 keV, which has never been reported before for jet-related SEE events. Associated HXR emissions observed by RHESSI and FGST/Gamma-ray Burst Monitor show three distinctive peaks with different spectral indices β HPE of HXR-producing electrons (HPEs) derived by means of thick-target bremsstrahlung model. The high-energy spectral index β 3 = 4.63 ± 0.65 of SEE is consistent with the HPE spectral index β HPE derived in HXR peak 1 but different from β HPE of HXR peak 2 and peak 3. The main stream of EUV jets reaches a speed of 370 ± 25 km s-1 after an acceleration of up to 2.9 ± 0.4 km s-2 in a timescale of ~2 minutes, and the acceleration time coincides with the decay phase of HXR peak 1. EUV observations from two different viewing directions help to reconstruct the jet magnetic configurations. After the investigation on HXR emissions and jet configurations, the interchange-reconnection model triggered by the emerging flux could be a satisfactory explanation for this jet event.

Keywords: Solar energetic particles, Solar flares, Plasma jets
The Physical Drivers and Observational Tracers of CO-to-H<SUB>2</SUB> Conversion Factor Variations in Nearby Barred Galaxy Centers. The CO-to-H2 conversion factor (α CO) is central to measuring the amount and properties of molecular gas. It is known to vary with environmental conditions, and previous studies have revealed lower α CO in the centers of some barred galaxies on kiloparsec scales. To unveil the physical drivers of such variations, we obtained Atacama Large Millimeter/submillimeter Array bands (3), (6), and (7) observations toward the inner ~2 kpc of NGC 3627 and NGC 4321 tracing 12CO, 13CO, and C18O lines on ~100 pc scales. Our multiline modeling and Bayesian likelihood analysis of these data sets reveal variations of molecular gas density, temperature, optical depth, and velocity dispersion, which are among the key drivers of α CO. The central 300 pc nuclei in both galaxies show strong enhancement of temperature T k ≳ 100 K and density ${n}_{{{\rm{H}}}_{2}}\gt {10}^{3}$ cm-3. Assuming a CO-to-H2 abundance of 3 × 10-4, we derive 4-15 times lower α CO than the Galactic value across our maps, which agrees well with previous kiloparsec-scale measurements. Combining the results with our previous work on NGC 3351, we find a strong correlation of α CO with low-J 12CO optical depths (τ CO), as well as an anticorrelation with T k. The τ CO correlation explains most of the α CO variation in the three galaxy centers, whereas changes in T k influence α CO to second order. Overall, the observed line width and 12CO/13CO 2-1 line ratio correlate with τ CO variation in these centers, and thus they are useful observational indicators for α CO variation. We also test current simulation-based α CO prescriptions and find a systematic overprediction, which likely originates from the mismatch of gas conditions between our data and the simulations.

Keywords: Molecular gas, Star forming regions, Galaxy nuclei, CO line emission, Barred spiral galaxies
Possible Counterpart Signal of the Fermi Bubbles at the Cosmic-Ray Positrons. The inner Galaxy has hosted cosmic-ray burst events, including those responsible for the gamma-ray Fermi bubbles and the eROSITA bubbles in X-rays. In this work, we study the Alpha Magnetic Spectrometer positron fraction and find three features around 12, 21, and 48 GeV, of which the lowest energy has a 1.4-4.9σ significance, depending on astrophysical background assumptions. Using background simulations that explain the cosmic-ray positron fraction, positron flux, and electron plus positron flux by primary and secondary cosmic rays and cosmic rays from local pulsars, we test these spectral features as originating from electron/positron burst events from the inner Galaxy. We find the 12 GeV feature to be explained by an event of age τ ≃ 3-10 Myr, in agreement with the proposed age of the Fermi bubbles. Furthermore, the energy in cosmic-ray electrons and positrons propagating along the Galactic disk and not within the Fermi bubbles volume is estimated to be 1051.5-1057.5 erg, or O(10-4) - O(1) the cosmic-ray energy causing the Fermi bubbles. We advocate that these positron fraction features are the counterpart signals of the Fermi bubbles, or of substructures within them, or of the eROSITA bubbles.

Keywords: Galactic cosmic rays
The 2021 Activity of the Fast-radio-burst-emitting Galactic Magnetar SGR 1935+2154 as Observed by NASA's Fermi Gamma-Ray Burst Monitor. The galactic, fast-radio-burst-emitting magnetar SGR 1935+2154 entered an active X-ray burst episode in 2021 September, nearly a year after emitting a fast radio burst with an X-ray counterpart. We report on the temporal and spectral properties of the activity, which included bright intermediate flares, and present a burst catalog of the Fermi Gamma-Ray Burst Monitor observations. We compare this activity to the previous 6 yr history of the source since its discovery in 2014. The bursts show a mean log-Gaussian duration T 100 ∼ 77.34 ms, a cutoff power-law peak energy E peak ∼ 26.62 keV, and a photon index ΓCPL ∼ 0.49, and blackbody soft and hard temperatures kT BBs ∼ 5.23 keV and kT BBh ∼ 9.24 keV, respectively. The burst fluence spans 3 orders of magnitude (10−8─10−5 erg cm−2) and follows  dN/dS∝S−0.93 . The anticorrelation between the blackbody temperature and the emission area is weaker in the hard component at  RBBh2∝kTBBh−4.56  but is improved in the soft component at  RBBs2∝kTBBs−1.63 , compared to previous activities, with an overall  RBB2∝kTBB−3.82  correlation. The 2021 bursts have higher average and integrated fluence than the 2014─2020 episodes and are relatively shorter than the 2019─2020 activities yet comparable to the earlier episodes. During 2014─2021, the burst mean peak energy (E peak) shows a slight softening and is generally softer than other magnetars. We discuss our results in terms of magnetar physics and emission mechanisms.

Keywords: Magnetars, Soft gamma-ray repeaters, X-ray bursts
Constraining AGN Torus Sizes with Optical and Mid-infrared Ensemble Structure Functions. We propose a new method to constrain the size of the dusty torus in broad-line active galactic nuclei (AGNs) using optical and mid-infrared (MIR) ensemble structure functions (SFs). Because of the geometric dilution of the torus, the MIR response to optical continuum variations has suppressed variability with respect to the optical that depends on the geometry (e.g., size, orientation, opening angle) of the torus. More extended tori have steeper MIR SFs with respect to the optical SFs. We demonstrate the feasibility of this SF approach using simulated AGN light curves and a geometric torus model. While it is difficult to use SFs to constrain the orientation and opening angle due to the insensitivity of the SF on these parameters, the size of the torus can be well determined. Applying this method to the ensemble SFs measured for 587 SDSS quasars, we measure a torus R-L relation of $\mathrm{log}\,{R}_{\mathrm{eff}}(\mathrm{pc})={0.51}_{-0.04}^{+0.04}\times \mathrm{log}({{L}}_{\mathrm{bol}}/{10}^{46}\,\mathrm{erg}\ {{\rm{s}}}^{-1})-{0.38}_{-0.01}^{+0.01}$ in the WISE W1 band and sizes ~1.4 times larger in the W2 band, which are in good agreement with dust reverberation mapping measurements. Compared with the reverberation mapping technique, the SF method is much less demanding in data quality and can be applied to any optical+MIR light curves for which a lag measurement may not be possible, as long as the variability process and torus structure are stationary. While this SF method does not extract all information contained in the light curves (i.e., the transfer function), it provides an intuitive interpretation for the observed trends of AGN MIR SFs compared with optical SFs.

Keywords: Surveys, Black hole physics, Active galactic nuclei, Quasars