adsabs/SciX_UAT_keywords huggingface dataset:
Probing the Innermost Regions of AGN Jets and Their Magnetic Fields with RadioAstron. III. Blazar S5 0716+71 at Microarcsecond Resolution

We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on 2015 January 3-4 at a frequency of 22 GHz (wavelength λ = 1.3 cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70,833 km (5.6 Earth diameters) for both parallel-hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 μas, the highest for this source to date. This enabled us to estimate the size of the radio core to be <12 × 5 μas and to reveal a complex structure and a significant curvature of the blazar jet in the inner 100 μas, which is an indication that the jet viewing angle lies inside the opening angle of the jet conical outflow. Fairly highly (15%) linearly polarized emission is detected in a jet region 19 μas in size, located 58 μas downstream from the core. The highest brightness temperature in the source frame is estimated to be >2.2 × 1013 K for the blazar core. This implies that the inverse-Compton limit must be violated in the rest frame of the source, even for the largest Doppler factor δ ∼ 25 reported for 0716+714.

Keywords: interferometry; active galactic nuclei; bl lacertae objects; blazars; jets; relativistic jets
Flares from Merged Magnetars: Their Prospects as a New Population of Gamma-Ray Counterparts of Binary Neutron Star Mergers

Long-lived massive magnetars are expected to be remnants of some binary neutron star (BNS) mergers. In this paper, we argue that the magnetic powered flaring activities of these merged magnetars would occur dominantly in their early millisecond-period-spin phase, which is in the timescale of days. Such flares endure significant absorption by the ejecta from the BNS collision, and their detectable energy range is from 0.1 to 10 MeV, in a time lag of approximately days after the merger events indicated by the gravitational wave chirps. We estimate the rate of such flares in different energy ranges, and find that there could have been 0.1-10 cases detected by Fermi/GBM. A careful search for ~10 ms spin-period modulation in weak short gamma-ray bursts (GRBs) may identify them from the archival data. The next-generation megaelectronvolt detectors could detect them at a mildly higher rate. The recent report on the Quasi-Period-Oscillation found in two BASTE GRBs should not be considered as cases of such flares, for they were detected in a lower energy range and with a much shorter period spin modulation.

Keywords: gamma-ray bursts; magnetars; gravitational wave sources; neutron stars
The Search for Failed Supernovae with the Large Binocular Telescope: The Mid-infrared Counterpart to N6946-BH1

We present JWST MIRI 5.6, 10, and 21 μm observations of the candidate failed supernova N6946-BH1 along with Hubble Space Telescope (HST) WFPC/IR 1.1 and 1.6 μm data and ongoing optical monitoring data with the Large Binocular Telescope. There is a very red, dusty source at the location of the candidate, which has only ∼10%–15% of the luminosity of the progenitor star. The source is very faint in the HST near-IR observations (∼103 L ⊙) and is not optically variable to a limit of ∼103 L ⊙ at the R band. The dust is likely silicate and probably has to be dominated by very large grains, as predicted for dust formed in a failed supernova. The required visual optical depths are modest, so it should begin to significantly brighten in the near-IR over the next few years.

Keywords: black hole physics; massive stars
An Increasing Radial Velocity of a Narrow Absorption-line System in Quasar SDSS J143530.49+142338.4

We report, for the first time, both the strengthening and radial velocity increases of a narrow absorption-line (NAL) system (C IV λλ1548, 1551 and N V λλ1239, 1243) from the two-epoch spectra of quasar SDSS J143530.49+142338.4. First, we speculate that the ionization changes of the outflow clouds are likely the cause of the strengthening in its equivalent width (EW) based on the obvious weakening of the ionization continuum, although other interpretations cannot be ruled out based on the current two-epoch spectra. According to the cloudy simulation, the asynchronized variations between the absorption-line EWs and the ionizing continuum indicate that the absorbers are at relatively high degrees of ionization, which is also consistent with the high ionization state revealed by the absence of Si IV NAL in the same system. Second, this NAL system exhibits a kinematic velocity shift of ∼138 km s-1 within 445.2 days in the quasar rest frame (corresponding to an average acceleration of ∼0.36 cm s-2). We evaluate several possible causes for this kinematic shift. However, the current two-epoch spectra do not provide enough constraints to confirm the possible mechanisms, so future monitoring with high resolution will be helpful to achieve this goal.

Keywords: active galactic nuclei; quasars; quasar absorption line spectroscopy
Estimation of Turbulent Heating of Solar Wind Protons at 1 au

The paper presents a new method for deriving turbulent heating of the solar wind using plasma moments and magnetic field data. We develop the method and then apply it to compute the turbulent heating of the solar wind proton plasma at 1 au. The method employs two physical properties of the expanding solar wind plasma, the wave-particle thermodynamic equilibrium, and the transport of entropic rate. We analyze plasma moments and field data taken from Wind S/C, in order to compute (i) the fluctuating magnetic energy, (ii) the corresponding correlation length, and (iii) the turbulent heating rate. We identify their relationships with the solar wind speed, as well as the variation of these relationships relative to solar wind and interplanetary coronal mass ejection plasma.

Keywords: space plasmas; solar wind; heliosphere; plasma astrophysics
Reconstructing the Volume Density Profile of Prestellar Cores with the Anisotropic Inverse Abel Transform Method

Most studies of the 3D density structure of prestellar cores have used isotropic evolution models, which are projected into 2D for direct comparison with observation data. In this study, we introduced the anisotropic inverse Abel transform method for reconstructing the 3D volume density profile of prestellar cores. We demonstrated that this approach could accurately preserve information about the realistic 3D structure with numerical simulation. This method has great advantages compared to the shape-assumption methods, particularly in high-density regions. We applied this method to the Herschel 2D column density maps of three prestellar cores, and the results showed good agreement with theoretical models. By changing the direction of the inversion axis of symmetry, we confirmed that the density profiles of prestellar cores exhibit nearly cylindrical symmetry.

Keywords: magnetic fields; star formation; analytical mathematics; molecular clouds
Properties of the Line-of-sight Velocity Field in the Hot and X-Ray-emitting Circumgalactic Medium of Nearby Simulated Disk Galaxies

The hot, X-ray-emitting phase of the circumgalactic medium of massive galaxies is believed to be the reservoir of baryons from which gas flows onto the central galaxy and into which feedback from active galactic nuclei and stars inject mass, momentum, energy, and metals. These effects shape the velocity fields of the hot gas, which can be observed via the Doppler shifting and broadening of emission lines by X-ray integral field units. In this work, we analyze the gas kinematics of the hot circumgalactic medium of Milky Way–mass disk galaxies from the TNG50 simulation with synthetic observations to determine how future instruments can probe this velocity structure. We find that the hot phase is often characterized by outflows from the disk driven by feedback processes, radial inflows near the galactic plane, and rotation, although in some systems the velocity field is more disorganized and turbulent. With a spectral resolution of ∼1 eV, fast and hot outflows (∼200–500 km s‑1) can be measured, depending on the orientation of the galaxy on the sky. The rotation velocity of the hot phase (∼100–200 km s‑1) can be measured using line shifts in edge-on galaxies, and is slower than that of colder gas phases but similar to stellar rotation velocities. By contrast, the slow inflows (∼50–100 km s‑1) are difficult to measure in projection with these other components, but may be detected in multicomponent spectral fits. We find that the velocity measured is sensitive to which emission lines are used. Measuring these flows will constrain theories of how the gas in these galaxies evolves.

Keywords: disk galaxies; x-ray observatories; n-body simulations; agn host galaxies
Safety First: Stability and Dissipation of Line-tied Force-free Flux Tubes in Magnetized Coronae

Magnetized plasma columns and extended magnetic structures with both footpoints anchored to a surface layer are an important building block of astrophysical dissipation models. Current loops shining in X-rays during the growth of plasma instabilities are observed in the corona of the Sun and are expected to exist in highly magnetized neutron star magnetospheres and accretion disk coronae. For varying twist and system sizes, we investigate the stability of line-tied force-free flux tubes and the dissipation of twist energy during instabilities using linear analysis and time-dependent force-free electrodynamics simulations. Kink modes (m = 1) and efficient magnetic energy dissipation develop for plasma safety factors q ≲ 1, where q is the inverse of the number of magnetic field line windings per column length. Higher-order fluting modes (m > 1) can distort equilibrium flux tubes for q > 1 but induce significantly less dissipation. In our analysis, the characteristic pitch ${\tilde{\mu }}_{0}$ of flux-tube field lines determines the growth rate ( $\propto {\tilde{\mu }}_{0}^{3}$ ) and minimum wavelength of the kink instability ( $\propto {\tilde{\mu }}_{0}^{-1}$ ). We use these scalings to determine a minimum flux tube length for the growth of the kink instability for any given ${\tilde{\mu }}_{0}$ . By drawing analogies to idealized magnetar magnetospheres with varying regimes of boundary shearing rates, we discuss the expected impact of the pitch-dependent growth rates for magnetospheric dissipation in magnetar conditions.

Keywords: magnetars; plasma astrophysics; magnetic fields; magnetohydrodynamical simulations
Eight-year Full-depth unWISE Coadds

We present deep, full-sky maps built from Wide-field Infrared Survey Explorer and NEOWISE exposures spanning the 2010 January-2020 December time period. These coadds, which incorporate roughly 8 yr of W1 (3.4 μm) and W2 (4.6 μm) imaging, are the deepest ever full-sky maps at wavelengths of 3-5 μm. Photometry based on these coadds will be a component of DESI Legacy Imaging Surveys DR10.

Keywords: infrared astronomy; astronomy data reduction
PROVABGS: The Probabilistic Stellar Mass Function of the BGS One-percent Survey

We present the probabilistic stellar mass function (pSMF) of galaxies in the DESI Bright Galaxy Survey (BGS), observed during the One-percent Survey. The One-percent Survey was one of DESI's survey validation programs conducted from 2021 April to May, before the start of the main survey. It used the same target selection and similar observing strategy as the main survey and successfully observed the spectra and redshifts of 143,017 galaxies in the r < 19.5 magnitude-limited BGS Bright sample and 95,499 galaxies in the fainter surface-brightness- and color-selected BGS Faint sample over z < 0.6. We derive pSMFs from posteriors of stellar mass, M *, inferred from DESI photometry and spectroscopy using the Hahn et al. PRObabilistic Value-Added BGS (PROVABGS) Bayesian spectral energy distribution modeling framework. We use a hierarchical population inference framework that statistically and rigorously propagates the M * uncertainties. Furthermore, we include correction weights that account for the selection effects and incompleteness of the BGS observations. We present the redshift evolution of the pSMF in BGS, as well as the pSMFs of star-forming and quiescent galaxies classified using average specific star formation rates from PROVABGS. Overall, the pSMFs show good agreement with previous stellar mass function measurements in the literature. Our pSMFs showcase the potential and statistical power of BGS, which in its main survey will observe >100 × more galaxies. Moreover, we present the statistical framework for subsequent population statistics measurements using BGS, which will characterize the global galaxy population and scaling relations at low redshifts with unprecedented precision.

Keywords: cosmology; large-scale structure of the universe; galaxies; galactic and extragalactic astronomy; galaxy spectroscopy; astrostatistics; bayesian statistics
Star Formation Rates in [Ne V] 3426 Å Selected Active Galactic Nuclei: Evidence for a Decrease along the Main Sequence?

Studying the behavior along the galaxy main sequence is key in furthering our understanding of the possible connection between active galactic nucleus (AGN) activity and star formation. We select a sample of 1215 AGN from the catalog of Sloan Digital Sky Survey galaxy properties from the Portsmouth group by detection of the high-ionization [Ne V] 3426 Å emission line. Our sample extends from 1040 to 1042.5 erg s‑1 in [Ne V] luminosity in a redshift range z = 0.17 to 0.57. We compare the specific star formation rates (sSFRs; SFR scaled by galaxy mass) obtained from the corrected [O II] and Hα luminosities, and the spectral energy distribution (SED)–determined values from Portsmouth. We find that the emission-line-based sSFR values are unreliable for the [Ne V] sample due to the AGN contribution, and proceed with the SED sSFRs for our study of the main sequence. We find evidence for a decrease in sSFR along the main sequence in the [Ne V] sample, which is consistent with results from the hard X-ray Burst Alert Telescope AGN sample, which extends to lower redshifts than our [Ne V] sample. Although we do not find evidence that the concurrent AGN activity is suppressing star formation, our results are consistent with a lower gas fraction in the host galaxies of the AGN as compared to that of the star-forming galaxies. If the evacuation of gas, and therefore suppression of star formation, is due to AGN activity, it must have occurred in a previous epoch.

Keywords: active galaxies; starburst galaxies; star formation
Thermonuclear 17O(n, γ)18O Reaction Rate and Its Astrophysical Implications

A new thermonuclear 17O(n,γ)18O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have first calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 ~ 2 GK, by up to a factor of ~80. The astrophysical impacts of our rate have been examined in both s-process and r-process models. In our main s-process model, which simulates flash-driven convective mixing in metal-deficient asymptotic giant branch stars, both 18O and 19F abundances in interpulse phases are enhanced dramatically by factors of ~20-40 due to the new larger 17O(n,γ)18O rate. It shows, however, that this reaction hardly affects the weak s-process in massive stars since the 17O abundance never becomes significantly large in the massive stars. For the r-process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting loophole effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model; however, these significant differences are almost completely eliminated if the fission recycling is considered.

Keywords: nuclear astrophysics; s-process; r-process; reaction rates
Multiple Patchy Cloud Layers in the Planetary-mass Object SIMP 0136+0933

Multiwavelength photometry of brown dwarfs and planetary-mass objects provides insight into their atmospheres and cloud layers. We present near-simultaneous J- and K s -band multiwavelength observations of the highly variable T2.5 planetary-mass object, SIMP J013656.5+093347. We reanalyze observations acquired over a single night in 2015 using a recently developed data reduction pipeline. For the first time, we detect a phase shift between J- and K s -band light curves, which we measure to be $39\buildrel{\circ}\over{.} {9}_{-1.1}^{+3.6}$ . Previously, phase shifts between near-infrared and mid-infrared observations of this object were detected and attributed to probing different depths of the atmosphere, and thus different cloud layers. Using the Sonora Bobcat models, we expand on this idea to show that at least two different patchy cloud layers must be present to explain the measured phase shift. Our results are generally consistent with recent atmospheric retrievals of this object and other similar L/T transition objects.

Keywords: brown dwarfs; t dwarfs; exoplanet atmospheres; exoplanet atmospheric variability; exoplanet atmospheric structure; stellar atmospheres
First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration

We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of ~50 μas, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.

Keywords: black holes
The Central 1000 au of a Prestellar Core Revealed with ALMA. II. Almost Complete Freeze-out

Prestellar cores represent the initial conditions in the process of star and planet formation. Their low temperatures (<10 K) allow the formation of thick icy dust mantles, which will be partially preserved in future protoplanetary disks, ultimately affecting the chemical composition of planetary systems. Previous observations have shown that carbon- and oxygen-bearing species, in particular CO, are heavily depleted in prestellar cores due to the efficient molecular freeze-out onto the surface of cold dust grains. However, N-bearing species such as NH3 and, in particular, its deuterated isotopologues appear to maintain high abundances where CO molecules are mainly in the solid phase. Thanks to ALMA, we present here the first clear observational evidence of NH2D freeze-out toward the L1544 prestellar core, suggestive of the presence of a "complete depletion zone" within a ≃1800 au radius, in agreement with astrochemical prestellar core model predictions. Our state-of-the-art chemical model coupled with a non-LTE radiative transfer code demonstrates that NH2D becomes mainly incorporated in icy mantles in the central 2000 au and starts freezing out already at ≃7000 au. Radiative transfer effects within the prestellar core cause the NH2D(111 - 101) emission to appear centrally concentrated, with a flattened distribution within the central ≃3000 au, unlike the 1.3 mm dust continuum emission, which shows a clear peak within the central ≃1800 au. This prevented NH2D freeze-out from being detected in previous observations, where the central 1000 au cannot be spatially resolved.

Keywords: interstellar medium; interstellar molecules; astrochemistry; radiative transfer
Low-speed Impacts into Ice-Dust Granular Mixtures

We present the results of a series of laboratory low-speed impacts (< 4 m s-1) of centimeter-sized spherical projectiles into simulated dry and icy regolith samples. The target material was comprised of JSC-1 (Johnson Space Center) lunar simulant grains in the size range 100-250 μm, mixed with similar-sized water ice grains. Impacts were performed under vacuum, either at room temperature for JSC-1 samples or at cryogenic temperatures (<150 K) for icy mixtures. We measured the ejecta masses from a collection plate and impact crater dimensions from post-impact crater photographs. We find that both the ejecta masses and crater diameters followed trends predicted by established scaling laws, albeit with different fitting parameters, and we were able to fit a strength regime π scaling to our measured crater diameters. The water ice in our target material took two forms: grains mixed with the regolith grains and frost from air condensation coating regolith grains. In both cases, the presence of water ice in the sample led to lower ejected masses and smaller crater sizes. In addition, our measured crater sizes were several orders of magnitude larger than expected for impacts into solid rock or water ice. Using our measured scaling parameters, we applied our findings to a planetary context for the study of secondary craters on icy moons, as well as eroding collisions occurring in Saturn's rings. We found that the deviation of our measurements from solid targets and from commonly used scaling parameters allowed us to reconcile our measurements with the models in both cases.

Keywords: impact phenomena; small solar system bodies; planetary surfaces; surface ices; planetary rings