adsabs/SciX_UAT_keywords huggingface dataset:
Reverberation Mapping of Changing-look Active Galactic Nucleus NGC 3516

The changes of broad emission lines should be a crucial issue in understanding the physical properties of changing-look active galactic nuclei (CL-AGNs). Here we present the results of an intensive and homogeneous 6 month long reverberation mapping (RM) monitoring campaign during a low-activity state of the CL-AGN Seyfert galaxy NGC 3516. Photometric and spectroscopic monitoring was carried out during 2018-2019 with the Lijiang 2.4 m telescope. The sampling is 2 days in most nights, and the average sampling is ∼3 days. The rest-frame time lags of Hα and Hβ are ${\tau }_{{\rm{H}}\alpha }={7.56}_{-2.10}^{+4.42}$ and ${\tau }_{{\rm{H}}\beta }={7.50}_{-0.77}^{+2.05}$ days, respectively. From an rms Hβ line dispersion of σline = 1713.3 ± 46.7 km s-1 and a virial factor of fσ = 5.5, the central black hole mass of NGC 3516 is estimated to be ${M}_{\mathrm{BH}}={2.4}_{-0.3}^{+0.7}\times {10}^{7}{M}_{\odot }$ , which is in agreement with previous estimates. The velocity-resolved delays show that the time lags increase toward negative velocity for both Hα and Hβ. The velocity-resolved RM of Hα is done for the first time. These RM results are consistent with other observations before the spectral-type change, indicating a basically constant broad-line region structure during the CL process. The CL model of changes of accretion rate seems to be favored by long-term Hβ variability and RM observations of NGC 3516.

Keywords: active galaxies; photometry; reverberation mapping; seyfert galaxies; spectroscopy; supermassive black holes
Heat Transport and Convective Velocities in Compositionally Driven Convection in Neutron Star and White Dwarf Interiors

We investigate heat transport associated with compositionally driven convection driven by crystallization at the ocean-crust interface in accreting neutron stars, or growth of the solid core in cooling white dwarfs. We study the effect of thermal diffusion and rapid rotation on the convective heat transport, using both mixing length theory and numerical simulations of Boussinesq convection. We determine the heat flux, composition gradient, and Péclet number, Pe (the ratio of thermal diffusion time to convective turnover time) as a function of the composition flux. We find two regimes of convection with a rapid transition between them as the composition flux increases. At small Pe, the ratio between the heat flux and composition flux is independent of Pe, because the loss of heat from convecting fluid elements due to thermal diffusion is offset by the smaller composition gradient needed to overcome the reduced thermal buoyancy. At large Pe, the temperature gradient approaches the adiabatic gradient, saturating the heat flux. We discuss the implications for cooling of neutron stars and white dwarfs. Convection in neutron stars spans both regimes. We find rapid mixing of neutron star oceans, with a convective turnover time of the order of weeks to minutes depending on rotation. Except during the early stages of core crystallization, white dwarf convection is in the thermal-diffusion-dominated fingering regime. We find convective velocities much smaller than recent estimates for crystallization-driven dynamos. The small fraction of energy carried as kinetic energy calls into question the effectiveness of crystallization-driven dynamos as an explanation for observed magnetic fields in white dwarfs.

Keywords: neutron stars; white dwarf stars; x-ray binary stars; stellar convective zones
Pluto's Resonant Orbit Visualized in 4D

Orbital resonance phenomena are notoriously difficult to communicate in words due to the complex dynamics arising from the interplay of gravity and orbital angular momentum. A well known example is Pluto's 3:2 mean motion resonance with Neptune. We have developed a PYTHON software tool to visualize the full three-dimensional aspects of Pluto's resonant orbital dynamics over time. The visualizations include still images and animated movies. By contrasting Pluto's resonant dynamics with the dynamics of a nearby non-resonant orbit, this tool enables better understanding and exploration of complex planetary dynamics phenomena.

Keywords: pluto; orbital resonances; gravitational interaction; three-body problem; celestial mechanics; neptune; solar system; small solar system bodies; resonant kuiper belt objects; plutinos; astronomy data visualization; n-body simulations
Electron-only Reconnection in Kinetic-Alfvén Turbulence

We study numerically small-scale reconnection events in kinetic, low-frequency, quasi-2D turbulence (termed kinetic-Alfvén turbulence). Using 2D particle-in-cell simulations, we demonstrate that such turbulence generates reconnection structures where the electron dynamics do not couple to the ions, similarly to the electron-only reconnection events recently detected in the Earth's magnetosheath by Phan et al. Electron-only reconnection is thus an inherent property of kinetic-Alfvén turbulence, where the electron current sheets have limited anisotropy and, as a result, their sizes are smaller than the ion inertial scale. The reconnection rate of such electron-only events is found to be close to 0.1.

Keywords: magnetic fields; alfven waves; space plasmas
Carbon Cycle Instability for High-CO2 Exoplanets: Implications for Habitability

Implicit in the definition of the classical circumstellar habitable zone (HZ) is the hypothesis that the carbonate-silicate cycle can maintain clement climates on exoplanets with land and surface water across a range of instellations by adjusting atmospheric CO2 partial pressure (pCO2). This hypothesis is made by analogy to the Earth system, but it is an open question whether silicate weathering can stabilize climate on planets in the outer reaches of the HZ, where instellations are lower than those received by even the Archean Earth and CO2 is thought likely to dominate atmospheres. Since weathering products are carried from land to ocean by the action of water, silicate weathering is intimately coupled to the hydrologic cycle, which intensifies with hotter temperatures under Earth-like conditions. Here, we use global climate model simulations to demonstrate that the hydrologic cycle responds counterintuitively to changes in climate on planets with CO2-H2O atmospheres at low instellations and high pCO2, with global evaporation and precipitation decreasing as pCO2 and temperatures increase at a given instellation. Within the Maher & Chamberlain (or MAC) weathering formulation, weathering then decreases with increasing pCO2 for a range of instellations and pCO2 typical of the outer reaches of the HZ, resulting in an unstable carbon cycle that may lead to either runaway CO2 accumulation or depletion of CO2 to colder (possibly snowball) conditions. While the behavior of the system has not been completely mapped out, the results suggest that silicate weathering could fail to maintain habitable conditions in the outer reaches of the nominal HZ.

Keywords: habitable planets; exoplanets; exoplanet atmospheres
Estimation of Turbulent Proton and Electron Heating Rates via Landau Damping Constrained by Parker Solar Probe Observations

The heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics of the solar wind and other plasma environments. Using magnetic field and thermal plasma observations from the first two perihelia of the Parker Solar Probe, we model the relative heating rates as a function of the radial distance, magnetic spectra, and plasma conditions, enabling us to better characterize the thermodynamics of the inner heliosphere. We employ the Howes et al. steady-state cascade model, which considers the behavior of turbulent, low-frequency, wavevector-anisotropic, critically balanced Alfvénic fluctuations that dissipate via Landau damping to determine proton-to-electron heating rates Q p /Q e . We distinguish ion cyclotron frequency circularly polarized waves from low-frequency turbulence and constrain the cascade model using spectra constructed from the latter. We find that the model accurately describes the observed energy spectrum from over 39.4% of the intervals from Encounters 1 and 2, indicating the possibility for Landau damping to heat the young solar wind. The ability of the model to describe the observed turbulent spectra increases with the ratio of thermal-to-magnetic pressure, β p , indicating that the model contains the necessary physics at higher β p . We estimate high magnitudes for the Kolmogorov constant which is inversely proportional to the nonlinear energy cascade rate. We verify the expected strong dependency of Q p /Q e on β p and the consistency of the critical balance assumption.

Keywords: solar wind; interplanetary turbulence; space plasmas; wavelet analysis
Shock-induced Stripping of the Satellite Interstellar and Circumgalactic Medium in IllustrisTNG Clusters at Z 0

Using the IllustrisTNG simulation, we study the interaction of large-scale shocks with the circumgalactic medium (CGM) and interstellar medium (ISM) of star-forming (SF) satellite galaxies in galaxy clusters. These shocks are usually produced by mergers and massive accretion. Our visual inspection shows that approximately half of SF satellites have encountered shocks in their host clusters at z ≤ 0.11. After a satellite crosses a shock front and enters the post-shock region, the ram pressure on it is boosted significantly. Both the CGM and ISM can be severely impacted, either by stripping or compression. The stripping of the ISM is particularly important for low-mass galaxies with $\mathrm{log}({M}_{* }/\,{h}^{-1}{M}_{\odot })\lt 10$ and can occur even in the outskirts of galaxy clusters. In comparison, satellites that do not interact with shocks lose their ISM only in the inner regions of clusters. About half of the ISM is stripped within about 0.6 Gyr after it crosses the shock front. Our results show that shock-induced stripping plays an important role in quenching satellite galaxies in clusters.

Keywords: galaxy evolution; galaxy quenching; galaxy clusters; shocks; hydrodynamical simulations; ram pressure stripped tails; intracluster medium
Prospects for Multimessenger Observations of Thorne-Żytkow Objects

Thorne-Żytkow objects (TŻOs) are a class of stellar object comprised of a neutron star core surrounded by a large and diffuse envelope. Their exterior appearance is identical to red supergiants; the distinctive electromagnetic signature of a TŻO is a suite of unusual chemical abundance patterns, including excesses of Li, Rb, Mo, and Ca. However, electromagnetic observations cannot unambiguously identify the presence of a neutron star core. Detection of continuous gravitational wave emission from a rotating neutron star core would provide strong supporting evidence for the existence of TŻOs. We present a model for gravitational wave detector confirmation of TŻOs and demonstrate that these objects should be detectable with Advanced LIGO. We also investigate possible targets for joint optical and gravitational searches, and comment on prospects for detectability in both current and future gravitational wave detector networks.

Keywords: gravitational wave sources; stellar mergers; gravitational wave astronomy; red supergiant stars; neutron stars
Inhomogeneity within Local Interstellar Clouds

Analysis of interstellar absorption lines observed in high-resolution Hubble Space Telescope spectra of nearby stars provides temperatures, turbulent velocities, and kinetic properties of warm interstellar clouds. A new analysis of 97 interstellar-velocity components reveals a wide range of temperatures and turbulent velocities within the Local Interstellar Cloud (LIC) and the nearby Cluster of Interstellar Clouds (CLIC). These variations appear to be random with Gaussian distributions. We find no trends of these properties with stellar distance or angles from the Galactic Center, magnetic field, the main source of extreme-UV radiation (the star ϵ CMa), the center of the LIC, or the direction of inflowing interstellar matter into the heliosphere. The spatial scale for temperature variations in the LIC is likely smaller than 5100 au, a distance that the Sun will traverse in 1000 yr. Essentially all velocity components align with known warm clouds. We find that within 4 pc of the Sun, space is completely filled with partially ionized clouds, but at larger distances space is only partially filled with partially ionized clouds. We find that the neutral hydrogen number density in the LIC and likely other warm clouds in the CLIC is about 0.10 cm-3 rather than the 0.20 cm-3 density that may be representative of only the immediate environment of the LIC. The ≤3000-12,000 K temperature range for the gas is wider than the predictions of thermal equilibrium theoretical models of the warm neutral medium and warm ionized medium, and the high degree of inhomogeneity within clouds argues against simple theoretical models. *All of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via https://doi.org/10.17909/gabn-m136. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support to MAST for these data is provided by the NASA office of Space Science via grant No. NAG5-7584 and by other grants and contracts.

Keywords: interstellar clouds; interstellar dynamics; interstellar magnetic fields; ultraviolet sources
XMM-Newton Observes the Intrabinary Shock of PSR J1959+2048

In a multi-orbit (100 ks) XMM-Newton exposure of the original black widow pulsar, PSR J1959+2048, we measure the strong orbital modulation caused by intrabinary shock (IBS) emission. The IBS light curve peak appears asymmetric, which we attribute to sweep-back effects in the companion wind. We also see evidence for an X-ray eclipse by the companion and its wind. Together with the IBS fit, this supports an edge-on i ~ 90° view of the system and a modest ~1.8 M⊙ mass for the recycled pulsar. Our IBS fit parameters imply a wind flux that, if persistent, would evaporate the companion within a few Gyr.

Keywords: pulsars
A Population of Short-duration Gamma-Ray Bursts with Dwarf Host Galaxies

We present a population of 11 of the faintest (>25.5 AB mag) short gamma-ray burst (GRB) host galaxies. We model their sparse available observations using the stellar population inference code Prospector-β and develop a novel implementation to incorporate the galaxy mass–radius relation. Assuming these hosts are randomly drawn from the galaxy population and conditioning this draw on their observed flux and size in a few photometric bands, we determine that these hosts have dwarf galaxy stellar masses of $7.0\lesssim \mathrm{log}({M}_{* }/{M}_{\odot })\lesssim 9.1$ . This is striking as only 14% of short GRB hosts with previous inferred stellar masses had M * ≲ 109 M ⊙. We further show these short GRBs have smaller physical and host-normalized offsets than the rest of the population, suggesting that the majority of their neutron star (NS) merger progenitors were retained within their hosts. The presumably shallow potentials of these hosts translate to small escape velocities of ∼5.5–80 km s‑1, indicative of either low postsupernova systemic velocities or short inspiral times. While short GRBs with identified dwarf host galaxies now comprise ≈14% of the total Swift-detected population, a number are likely missing in the current population, as larger systemic velocities (observed from the Galactic NS population) would result in highly offset short GRBs and less secure host associations. However, the revelation of a population of short GRBs retained in low-mass host galaxies offers a natural explanation for the observed r-process enrichment via NS mergers in Local Group dwarf galaxies, and has implications for gravitational-wave follow-up strategies.

Keywords: gravitational wave sources; gamma-ray bursts; dwarf galaxies
Compact Steep Spectrum Radio Sources with Enhanced Star Formation Are Smaller Than 10 kpc

Compact steep spectrum (CSS) radio sources are active galactic nuclei (AGN) that have radio jets propagating only on galactic scales, defined as having projected linear size (LS) of up to 20 kpc. CSS sources are generally hosted by massive early-type galaxies with little ongoing star formation; however, a small fraction are known to have enhanced star formation. Using archival data from the Faint Images of the Radio Sky at Twenty cm survey, the Very Large Array Sky Survey, and the Sloan Digital Sky Survey, we identify a volume-limited sample of 166 CSS sources at z < 0.2 with L 1.4 GHz > 1024 W Hz-1. Comparing the star formation rates and linear sizes of these CSS sources, we find that the ≈14% of CSS sources with specific star formation rates above 0.01 Gyr-1 all have LS < 10 kpc. We discuss the possible mechanisms driving this result, concluding that it is likely the excess star formation in these sources occurred in multiple bursts and ceased prior to the AGN jet being triggered.

Keywords: agn host galaxies; active galactic nuclei; extragalactic radio sources; radio galaxies; star formation
Secular Eccentricity Oscillations in Axisymmetric Disks of Eccentric Orbits

Massive bodies undergo orbital eccentricity oscillations when embedded in an axisymmetric disk of smaller mass orbits. These eccentricity oscillations are driven by secular torques that seek to equalize the apsidal precession rates of all the orbits in the disk. We investigate this mechanism within the context of detached objects in the outer solar system, but we find that the oscillation timescale is too long for it to be dynamically important. It could however be interesting for phenomenon a bit farther from home, namely, feeding supermassive black holes and polluting the surfaces of white dwarf stars.

Keywords: celestial mechanics; solar system; trans-neptunian objects; kuiper belt; minor planets; white dwarf stars; supermassive black holes
Properties of the Extremely Energetic GRB 221009A from Konus-WIND and SRG/ART-XC Observations

We report on Konus-WIND (KW) and Mikhail Pavlinsky Astronomical Roentgen Telescope - X-ray Concentrator (ART-XC) observations and analysis of a nearby GRB 221009A, the brightest γ-ray burst (GRB) detected by KW for >28 yr of observations. The prompt, pulsed phase of the burst emission lasts for ~600 s and is followed by a steady power-law decay lasting for more than 25 ks. From the analysis of the KW and ART-XC light curves and the KW spectral data, we derive time-averaged spectral peak energy of the burst E p ≈ 2.6 MeV, E p at the brightest emission peak ≈ 3.0 MeV, the total 20 keV-10 MeV energy fluence of ≈0.22 erg cm-2, and the peak energy flux in the same band of ≈0.031 erg cm-2 s-1. The enormous observed fluence and peak flux imply, at redshift z = 0.151, huge values of isotropic energy release E iso ≈ 1.2 × 1055 erg (or ≳6.5 solar rest mass) and isotropic peak luminosity L iso ≈ 3.4 × 1054 erg s-1 (64 ms scale), making GRB 221009A the most energetic and one of the most luminous bursts observed since the beginning of the GRB cosmological era in 1997. The isotropic energetics of the burst fit nicely both "Amati" and "Yonetoku" hardness-intensity correlations for >300 KW long GRBs, implying that GRB 221009A is most likely a very hard, super-energetic version of a "normal" long GRB.

Keywords: gamma-ray bursts
Decade-long Timing of Four GMRT Discovered Millisecond Pulsars

The discovery and timing follow up of millisecond pulsars (MSPs) are necessary not just for their usefulness in pulsar timing arrays (PTAs) but also for investigating their own intriguing properties. In this work, we provide the findings of the decade-long timing of four MSPs discovered by the Giant Meterwave Radio Telescope (GMRT), including their timing precision, model parameters, and newly detected proper motions. We compare the timing results for these MSPs before and after the GMRT upgrade in 2017 and characterize the improvement in timing precision due to the bandwidth upgrade. We discuss the suitability of these four GMRT MSPs as well as the usefulness of the decade-long timing data for PTA experiments. These data may aid in the global effort to improve the signal-to-noise ratios of recently detected signature of gravitational waves in cross-correlation statistics of residuals of MSPs.

Keywords: millisecond pulsars; pulsar timing method
FX UMa: A New Heartbeat Binary System with Linear and Nonlinear Tidal Oscillations and δ Sct Pulsations

We present a detailed analysis of an eclipsing double-lined binary FX UMa based on TESS photometry and newly acquired spectroscopic observations. The radial velocities and atmospheric parameters for each component star are obtained from the SONG high-resolution spectra. Combined with the radial-velocity measurements, our light-curve modeling yields absolute masses and radii of the two components. The Fourier amplitude spectrum of the residual light curve reveals a total of 103 frequencies with signal-to-noise ratio (S/N) ≥ 4, including 12 independent frequencies, 17 multiples of the orbital frequency (Nf orb), and 74 combination frequencies. Ten Nf orb peaks with S/N > 10 have very high amplitudes and are likely due to tidally excited oscillations (TEOs). The remaining Nf orb peaks (4 ≤ S/N ≤ 10) may be originated from the imperfect removal, or they are actually real TEOs. Four anharmonic frequencies can pair up and sum to give exact harmonics of the orbital frequency, suggesting the existence of nonlinear tidal processes in the eccentric binary system FX UMa. Eight independent frequencies in the range of 20-32 day-1 are typical low-order pressure modes of δ Scuti pulsators.

Keywords: eclipsing binary stars; pulsating variable stars
Long-term Multiband Near-infrared Variability of the Blazar OJ 287 during 2007-2021

We present the most extensive and well-sampled long-term multiband near-infrared (NIR) temporal and spectral variability study of OJ 287, considered to be the best candidate binary supermassive black hole blazar. These observations were made between 2007 December and 2021 November. The source underwent ~2-2.5 mag variations in the J, H, and Ks NIR bands. Over these long-term timescales there were no systematic trends in either flux or spectral evolution with time or with the source's flux states. However, on shorter timescales, there are significant variations in flux and spectra indicative of strong changes during different activity states. The NIR spectral energy distributions show diverse facets at each flux state, from the lowest to the highest. The spectra are, in general, consistent with a power-law spectral profile (within 10%) and many of them indicate minor changes (observationally insignificant) in the shift of the peak. The NIR spectra generally steepen during bright phases. We briefly discuss these behaviors in the context of blazar emission scenarios/mechanisms, OJ 287's well-known traditional behavior, and implications for models of the source central engine invoked for its long-term optical semiperiodic variations.

Keywords: galaxies; bl lacertae objects