adsabs/SciX_UAT_keywords huggingface dataset:
StrayCats: A Catalog of NuSTAR Stray Light Observations

We present StrayCats, a catalog of NuSTAR stray light observations of X-ray sources. Stray light observations arise for sources 1°-4° away from the telescope pointing direction. At this off-axis angle, X-rays pass through a gap between the optics and aperture stop and so do not interact with the X-ray optics; instead, they directly illuminate the NuSTAR focal plane. We have systematically identified and examined over 1400 potential observations resulting in a catalog of 436 telescope fields and 78 stray light sources that have been identified. The sources identified include historically known persistently bright X-ray sources, X-ray binaries in outburst, pulsars, and type I X-ray bursters. In this paper, we present an overview of the catalog, how we identified the StrayCats sources, and the analysis techniques required to produce high-level science products. Finally, we present a few brief examples of the science quality of these unique data.

Keywords: x-ray surveys; astrophysical black holes; neutron stars; high mass x-ray binary stars; low-mass x-ray binary stars; pulsars
Significant Suppression of Star Formation in Radio-quiet AGN Host Galaxies with Kiloparsec-scale Radio Structures

We conducted 22 GHz 1″ Jansky Very Large Array imaging of 100 radio-quiet X-ray-selected active galactic nuclei (AGN) from the Swift-Burst Array Telescope (Swift-BAT) survey. We find AGN-driven kiloparsec-scale radio structures inconsistent with pure star formation in 11 AGN. The host galaxies of these AGN lie significantly below the star-forming main sequence, indicating suppressed star formation. While these radio structures tend to be physically small compared to the host galaxy, the global star formation rate of the host is affected. We evaluate the energetics of the radio structures interpreted first as immature radio jets, and then as consequences of an AGN-driven radiative outflow, and compare them to two criteria for successful feedback: the ability to remove the CO-derived molecular gas mass from the galaxy gravitational potential and the kinetic energy transfer to molecular clouds leading to vcloud > σ*. In most cases, the jet interpretation is insufficient to provide the energy necessary to cause the star formation suppression. Conversely, the wind interpretation provides ample energy in all but one case. We conclude that it is more likely that the observed suppression of star formation in the global host galaxy is due to interstellar medium interactions of a radiative outflow, rather than a small-scale radio jet.

Keywords: active galactic nuclei; star formation; galaxy winds; galactic winds; radio jets
Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. I. Sample from the Early Data

Changing-look active galactic nuclei (CL AGNs) can be generally confirmed by the emergence (turn-on) or disappearance (turn-off) of broad emission lines (BELs), associated with a transient timescale (about 100 ∼ 5000 days) that is much shorter than predicted by traditional accretion disk models. We carry out a systematic CL AGN search by crossmatching the spectra coming from the Dark Energy Spectroscopic Instrument and the Sloan Digital Sky Survey. Following previous studies, we identify CL AGNs based on Hα, Hβ, and Mg II at z ≤ 0.75 and Mg II, C III], and C IV at z > 0.75. We present 56 CL AGNs based on visual inspection and three selection criteria, including 2 Hα, 34 Hβ, 9 Mg II, 18 C III], and 1 C IV CL AGN. Eight cases show simultaneous appearances/disappearances of two BELs. We also present 44 CL AGN candidates with significant flux variation of BELs, but remaining strong broad components. In the confirmed CL AGNs, 10 cases show additional CL candidate features for different lines. In this paper, we find: (1) a 24:32 ratio of turn-on to turn-off CL AGNs; (2) an upper-limit transition timescale ranging from 330 to 5762 days in the rest frame; and (3) the majority of CL AGNs follow the bluer-when-brighter trend. Our results greatly increase the current CL census (∼30%) and would be conducive to exploring the underlying physical mechanism.

Keywords: active galaxies; accretion; active galactic nuclei; supermassive black holes; catalogs
Energy Conversion between Ions and Electrons through Ion Cyclotron Waves and Embedded Ion-scale Rotational Discontinuity in Collisionless Space Plasmas

Wave-particle interaction is a fundamental process in collisionless plasma, which results in the redistribution of energy between plasma waves and particle species. The analysis of high-resolution Magnetospheric Multiscale plasma and magnetic field data directly reveals the energy exchange between electromagnetic energy, particle bulk kinetic energy, and thermal kinetic energy in magnetosheath turbulence. This work focuses on the energy transfer associated with ion cyclotron waves (ICWs) and embedded rotational discontinuity (RD). We find that (1) the particle kinetic energy of ions is converted into electromagnetic energy; (2) the electrons are gaining energy from electromagnetic fields, having significant electron heating in the parallel direction around the RD; (3) the ICWs and RD connect and redistribute energy between ions and electrons in the postshock downstream sheath region; and (4) the interactions between pressure tensor and strain tensor redistribute the ion and electron bulk and thermal kinetic energies, but less significantly than direct field-particle interaction by one order of magnitude in the ICW turbulence with weak compressibility, in the sense that ${\left(d| {\boldsymbol{B}}| /| {\boldsymbol{B}}| \right)}^{2}\lt {10}^{-2}$ , ${\left(d{\rm{N}}/{\rm{N}}\right)}^{2}\lt {10}^{-2}$ .

Keywords: interplanetary turbulence; space plasmas; solar wind
Boundary Conditions in Hydrodynamic Simulations of Isolated Galaxies and Their Impact on the Gas-loss Processes

Three-dimensional hydrodynamic simulations are commonly used to study the evolution of the gaseous content in isolated galaxies, besides its connection with galactic star formation histories. Stellar winds, supernova blasts, and black hole feedback are mechanisms usually invoked to drive galactic outflows and decrease the initial galactic gas reservoir. However, any simulation imposes the need of choosing the limits of the simulated volume, which depends, for instance, on the size of the galaxy and the required numerical resolution, besides the available computational capability to perform it. In this work, we discuss the effects of boundary conditions on the evolution of the gas fraction in a small-sized galaxy (tidal radius of ~1 kpc), like classical spheroidal galaxies in the Local Group. We found that open boundaries with sizes smaller than approximately 10 times the characteristic radius of the galactic dark-matter halo become unappropriated for this kind of simulation after ~0.6 Gyr of evolution, since they act as an infinity reservoir of gas due to dark-matter gravity. We also tested two different boundary conditions that avoid gas accretion from numerical frontiers: closed and selective boundary conditions. Our results indicate that the later condition (that uses a velocity threshold criterion to open or close frontiers) is preferable since it minimizes the number of reversed shocks due to closed boundaries. Although the strategy of putting computational frontiers as far as possible from the galaxy itself is always desirable, simulations with a selective boundary condition can lead to similar results at lower computational costs.

Keywords: dwarf galaxies; galaxy evolution; hydrodynamical simulations; computational methods
Long-term Optical Monitoring of the TeV BL Lacertae Object 1ES 2344 + 514

Variability is one of the main observational characteristics of blazars. Studying variability is an efficient method to reveal the nature of active galactic nuclei. In the present work, we report optical R-band photometry observations of a TeV blazar, 1ES 2344 + 514, carried out with a 70 cm telescope in the period of 1998 July-2017 November at Abastumani Observatory, Georgia. Based on the optical R-band observations, the optical variation behaviors on both short timescales and long timescales are investigated. Three methods (Jurkevich, discrete correlation function, and power spectrum analysis) are used to investigate periodicity in the light curve. In addition, combined with multiwavelength data, the jet physical properties are discussed. The following conclusions are drawn: (1) A variability of ΔR = 0.155 mag (15.356 - 15.201 mag) over a timescale of ΔT = 12.99 minutes is detected during our 628 days of monitoring. (2) According to the Kelvin-Helmholtz thermal instability, if the magnetic field intensity (B) for the source is greater than a critical value (B c ), it will reduce the incidence of intraday variations in the light curves. (3) The physical parameters of the dissipation region are obtained by fitting the spectral energy distribution with a one-zone synchrotron self-Compton model for the average and flare states. (4) The three methods show that there are periods of P = 2.72 ± 0.47 yr, P = 1.61 ± 0.18 yr, P = 1.31 ± 0.17 yr, and P = 1.05 ± 0.07 yr. When a binary black hole system is adopted with a period of P = 2.72 ± 0.41 yr, we obtain the orbital parameters for the binary black hole system as follows: M = 8.08 × 109 M ⊙, the sum of the semiaxes is r = 7.18 × 1016 cm, and the lifetime of the binary black hole is τ merge = 6.24 × 102 yr.

Keywords: active galactic nuclei; ccd photometry; quasars
Horizontal Shear Instabilities at Low Prandtl Number

Turbulent mixing in the radiative regions of stars is usually either ignored or crudely accounted for in most stellar evolution models. However, there is growing evidence that such mixing is present and can affect various aspects of a star's life. Here, we present a first attempt at quantifying mixing by horizontal shear instabilities in stars using direct numerical simulations. The shear is driven by a body force, and rapidly becomes unstable. At saturation, we find that several distinct dynamical regimes exist, depending on the relative importance of stratification and thermal diffusion. In each of the regimes identified, we propose a certain number of theoretically motivated scaling laws for the turbulent vertical eddy scale, the turbulent diffusion coefficient, and the amplitude of temperature fluctuations (among other quantities). Based on our findings, we predict that the majority of stars should fall into one of two categories: high Péclet number stratified turbulence, and low Péclet number stratified turbulence. The latter is presented in a related paper by Cope et al., while the former is discussed here. Applying our results to the solar tachocline, we find that it should lie in the high Péclet number stratified turbulence regime, and predict a substantial amount of vertical mixing for temperature, momentum, and composition. Taken as is, the new turbulence model predictions are incompatible with the Spiegel & Zahn model of the solar tachocline. However, rotation and magnetic fields are likely to affect the turbulence, and need to be taken into account in future studies.

Keywords: astrophysical fluid dynamics; hydrodynamics; stellar evolution; stellar physics; hydrodynamical simulations; stellar rotation; solar rotation; stellar processes
Toward Robust Atmospheric Retrieval on Cloudy L Dwarfs: the Impact of Thermal and Abundance Profile Assumptions

Constraining L dwarf properties from their spectra is challenging. Near-infrared (NIR) spectra probe a limited range of pressures, while many species condense within their photospheres. Condensation creates two complexities: gas-phase species "rain out" (decreasing in abundances by many orders of magnitude) and clouds form. We designed tests using synthetic data to determine the best approach for retrieving L dwarf spectra, isolating the challenges in the absence of cloud opacity. We conducted atmospheric retrievals on synthetic cloud-free L dwarf spectra derived from the Sonora Bobcat models at SpeX resolution using a variety of thermal and chemical abundance profile parameterizations. For objects hotter than L5 (T eff ~ 1700 K), the limited pressure layers probed in the NIR are mostly convective; parameterized pressure-temperature (PT) profiles bias results and free, unsmoothed profiles should be used. Only when many layers both above and below the radiative-convective boundary are probed can parameterized profiles provide accurate results. Furthermore, a nonuniform abundance profile for FeH is needed to accurately retrieve bulk properties of early-to-mid L dwarfs. Nonuniform prescriptions for other gases in NIR retrievals may also be warranted near the L/T transition (CH4) and early Y dwarfs (Na and K). We demonstrate the utility of using realistic, self-consistent models to benchmark retrievals and suggest how they can be used in the future.

Keywords: brown dwarfs; l dwarfs; atmospheric structure; atmospheric composition; stellar atmospheres; planetary atmospheres
Uranus&' Stratospheric HCl Upper Limit from Herschel/SPIRE

Herschel/SPIRE observations of Uranus are used to search for stratospheric hydrogen chloride (HCl) emission at 41.74 cm-1. HCl was not detected and instead 3σ upper limits were determined; <6.2 ppb (<2.0 × 1014 molecules cm-2) for a 0.1 mbar step profile and <0.40 ppb (<1.2 × 1014 molecules cm-2) for a 1 mbar step profile. HCl is expected to have an external source and these upper limits are consistent with abundances of other external species (CO, H2O, CO2) and a solar composition source. * Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Keywords: uranus; solar system gas giant planets; atmospheric composition; planetary science
DY Pegasi: An SX Phoenicis Star in a Binary System with an Evolved Companion

In this work, the photometric data from the American Association of Variable Star Observers are collected and analyzed on the SX Phoenicis star DY Pegasi (DY Peg). From the frequency analysis, we get three independent frequencies: f0 = 13.71249 c d-1, f1 = 17.7000 c d-1, and f2 = 18.138 c d-1, in which f0 and f1 are the radial fundamental and first overtone mode, respectively, while f2 is detected for the first time and should belong to a nonradial mode. The O - C diagram of the times of maximum light shows that DY Peg has a period change rate (1/P0)(dP0/dt) = -(5.87 ± 0.03) × 10-8 yr-1 for its fundamental pulsation mode, and should belong to a binary system that has an orbital period Porb = 15425.0 ± 205.7 days. Based on the spectroscopic information, single star evolutionary models are constructed to fit the observed frequencies. However, some important parameters of the fitted models are not consistent with that from observations. Combing the information from observation and theoretical calculation, we conclude that DY Peg should be an SX Phoenicis star in a binary system and accreting mass from a dust disk, which was the residue of its evolved companion (most probably a hot white dwarf at the present stage) produced in the asymptotic giant branch phase. Further observations are needed to confirm this inference, and it might be potentially a universal formation mechanism and evolutionary history for SX Phoenicis stars.

Keywords: sx phoenicis variable stars; pulsating variable stars
Detailed Accretion History of the Supermassive Black Hole in NGC 5972 over the Past ≳104 yr through the Extended Emission-line Region

We present integral field spectroscopic observations of NGC 5972 obtained with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope. NGC 5972 is a nearby galaxy containing both an active galactic nucleus (AGN) and an extended emission-line region (EELR) reaching out to ~17 kpc from the nucleus. We analyze the physical conditions of the EELR using spatially resolved spectra, focusing on the radial dependence of ionization state together with the light-travel time distance to probe the variability of the AGN on ≳104 yr timescales. The kinematic analysis suggests multiple components: (a) a faint component following the rotation of the large-scale disk, (b) a component associated with the EELR suggestive of extraplanar gas connected to tidal tails, and (c) a kinematically decoupled nuclear disk. Both the kinematics and the observed tidal tails suggest a major past interaction event. Emission-line diagnostics along the EELR arms typically evidence Seyfert-like emission, implying that the EELR was primarily ionized by the AGN. We generate a set of photoionization models and fit these to different regions along the EELR. This allows us to estimate the bolometric luminosity required at different radii to excite the gas to the observed state. Our results suggest that NGC 5972 is a fading quasar, showing a steady gradual decrease in intrinsic AGN luminosity, and hence the accretion rate onto the SMBH, by a factor ~100 over the past 5 × 104 yr.

Keywords: agn host galaxies; active galactic nuclei
Reactivation of the High Magnetic Field Pulsar PSR J1846-0258 with Magnetar-like Bursts

We report on the 2020 reactivation of the energetic high magnetic field pulsar PSR J1846-0258 and its pulsar wind nebula (PWN) after 14 yr of quiescence with new Chandra and Green Bank Telescope observations. The emission of short-duration bursts from J1846-0258 was accompanied by an enhancement of X-ray persistent flux and significant spectral softening, similar to those observed during its first bursting episode in 2006. The 2020 pulsar spectrum is described by a power-law model with a photon index Γ = 1.7 ± 0.3 in comparison to a Γ = 1.2 ± 0.1 before outburst, and shows evidence of an emerging thermal component with blackbody temperature kT = 0.7 ± 0.1 keV. The 0.5-10 keV unabsorbed flux increased from ${5.4}_{-0.5}^{+0.4}$ × 10-12 erg cm-2 s-1 in quiescence to ${1.3}_{-0.2}^{+0.3}$ × 10-11 erg cm-2 s-1 following the outburst. We did not detect any radio pulsations from the pulsar at 2 GHz, and we place an upper limit of 7.1 μJy and 55 mJy for the coherent pulsed emission and single pulses, respectively. The 2020 PWN spectrum, characterized by a photon index of 1.92 ± 0.04 and X-ray luminosity of (1.2 ± 0.1) × 1035 erg s-1 at a distance of 5.8 kpc, is consistent with those observed before the outburst. An analysis of regions closer to the pulsar shows small-scale time variabilities and brightness changes over the 20 yr period from 2000 to 2020, while the photon indices did not change. We conclude that the outburst in PSR J1846-0258 is a combination of crustal and magnetospheric effects, with no significant burst-induced variability in its PWN based on the current observations.

Keywords: magnetars; rotation powered pulsars
Predictions for Observable Atmospheres of Trappist-1 Planets from a Fully Coupled Atmosphere-Interior Evolution Model

The Trappist-1 planets provide a unique opportunity to test the current understanding of rocky planet evolution. The James Webb Space Telescope is expected to characterize the atmospheres of these planets, potentially detecting CO2, CO, H2O, CH4, or abiotic O2 from water photodissociation and subsequent hydrogen escape. Here, we apply a coupled atmosphere-interior evolution model to the Trappist-1 planets to anticipate their modern atmospheres. This model, which has previously been validated for Earth and Venus, connects magma ocean crystallization to temperate geochemical cycling. Mantle convection, magmatic outgassing, atmospheric escape, crustal oxidation, a radiative-convective climate model, and deep volatile cycling are explicitly coupled to anticipate bulk atmospheres and planetary redox evolution over 8 Gyr. By adopting a Monte Carlo approach that samples a broad range of initial conditions and unknown parameters, we make some tentative predictions about current Trappist-1 atmospheres. We find that anoxic atmospheres are probable, but not guaranteed, for the outer planets; oxygen produced via hydrogen loss during the pre-main sequence is typically consumed by crustal sinks. In contrast, oxygen accumulation on the inner planets occurs in around half of all models runs. Complete atmospheric erosion is possible but not assured for the inner planets (occurs in 20%-50% of model runs), whereas the outer planets retain significant surface volatiles in virtually all model simulations. For all planets that retain substantial atmospheres, CO2-dominated or CO2-O2 atmospheres are expected; water vapor is unlikely to be a detectable atmospheric constituent in most cases. There are necessarily many caveats to these predictions, but the ways in which they misalign with upcoming observations will highlight gaps in terrestrial planet knowledge.

Keywords: exoplanet atmospheres; planetary atmospheres; astrobiology; planetary interior; exoplanet atmospheric composition; exoplanet astronomy
New Thermonuclear Rate of 7Li(d,n)24He Relevant to the Cosmological Lithium Problem

Accurate 7Li(d,n)24He thermonuclear reaction rates are crucial for precise prediction of the primordial abundances of lithium and beryllium and to probe the mysteries beyond fundamental physics and the standard cosmological model. However, uncertainties still exist in current reaction rates of 7Li(d,n)24He widely used in big bang nucleosynthesis (BBN) simulations. In this work, we reevaluate the 7Li(d,n)24He reaction rate using the latest data on the three near-threshold 9Be excited states from experimental measurements. We present for the first time uncertainties that are directly constrained by experiments. Additionally, we take into account for the first time the contribution from the subthreshold resonance at 16.671 MeV of 9Be. We obtain a 7Li(d,n)24He rate that is overall smaller than the previous estimation by about a factor of 60 at the typical temperature of the onset of primordial nucleosynthesis. We implemented our new rate in BBN calculations, and we show that the new rates have a very limited impact on the final light element abundances in uniform density models. Typical abundance variations are in the order of 0.002%. For nonuniform density BBN models, the predicted 7Li production can be increased by 10% and the primordial production of light nuclides with mass number A > 7 can be increased by about 40%. Our results confirm that the cosmological lithium problem remains a long-standing unresolved puzzle from the standpoint of nuclear physics.

Keywords: big bang nucleosynthesis
Reconnection Outflow Reversal Associated with Ion-scale Magnetic Flux Ropes in the Earth's Midtail: ARTEMIS Observations and Reconstruction Results

A rare reconnection outflow reversal in the Earth's midtail observed by the two Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) probes, is presented. During the event, two ion-scale magnetic flux ropes were separately observed by THC in the earthward and tailward reconnection outflows that were adjacent and accompanied, respectively, by the positive and negative normal magnetic field components to the current sheet. The two flux ropes were separated by ~2.75 minutes and at the center of the flux ropes, the magnetic field strength was enhanced with a large core field. Comparison results of the convection and measured electric fields reveal that the ions and the magnetic fields were decoupled in the regions surrounding the two flux ropes. The two-dimensional magnetic field maps from the Grad-Shafranov reconstruction show that the diameters of the two flux ropes were similar, being ~7.1 and ~7.9 ion inertial lengths, but the aspect ratios of the width to the length were different, being ~0.35 and ~0.47. Moreover, one of the reconstructed field maps suggests that multiple x-lines may exist in the midtail reconnection and that the traveling compression region of the flux rope was seen at THB. The angle between the axial orientations of the two flux ropes was large, being ~55°, and their axes were tilted away from the direction of the reconnection guide field, in agreement with the earlier studies of the magnetotail flux ropes.

Keywords: interplanetary physics