adsabs/SciX_UAT_keywords huggingface dataset:
Radio Monitoring of the Tidal Disruption Event Swift J164449.3+573451. IV. Continued Fading and Non-relativistic Expansion

We present continued radio and X-ray observations of the previously relativistic tidal disruption event (TDE) Swift J164449.3+573451 (Sw 1644+57) extending to about 9.4 yr post disruption, as part of ongoing campaigns with the Jansky Very Large Array (VLA) and the Chandra X-ray observatory. We find that the X-ray emission has faded below detectable levels, with an upper limit of ≲3.5 × 10-15 erg cm-2 s-1 in a 100 ks observation, while the radio emission continues to be detected and steadily fade. Both are consistent with forward shock emission from a non-relativistic outflow, although we find that the radio spectral energy distribution is better fit at these late times with an electron power-law index of p ≈ 3 (as opposed to p ≈ 2.5 at earlier times). With the revised spectral index we find ɛB ≈ 0.01 using the radio and X-ray data, and a density of ≈0.04 cm3 at a radius of R ≈ 0.65 pc (Rsch ≈ 2 × 106 R⊙) from the black hole. The energy scale of the blastwave is ≈1052 erg. We also report detections of Sw 1644+57 at 3 GHz from the first two epochs of the VLA Sky Survey (VLASS), and find that ∼102 off-axis Sw 1644+57-like events to z ∼ 0.5 may be present in the VLASS data. Finally, we find that Sw 1644+57 itself will remain detectable for decades at radio frequencies, although observations at sub-GHz frequencies will become increasingly important to characterize its dynamical evolution.

Keywords: black hole physics
The Effects of Nonequilibrium Velocity Distributions on Alfvén Ion-cyclotron Waves in the Solar Wind

In this work, we investigate how the complex structure found in solar wind proton velocity distribution functions (VDFs), rather than the commonly assumed two-component bi-Maxwellian structure, affects the onset and evolution of parallel-propagating microinstabilities. We use the Arbitrary Linear Plasma Solver, a numerical dispersion solver, to find the real frequencies and growth/damping rates of the Alfvén modes calculated for proton VDFs extracted from Wind spacecraft observations of the solar wind. We compare this wave behavior to that obtained by applying the same procedure to core-and-beam bi-Maxwellian fits of the Wind proton VDFs. We find several significant differences in the plasma waves obtained for the extracted data and bi-Maxwellian fits, including a strong dependence of the growth/damping rate on the shape of the VDF. By applying the quasilinear diffusion operator to these VDFs, we pinpoint resonantly interacting regions in velocity space where differences in VDF structure significantly affect the wave growth and damping rates. This demonstration of the sensitive dependence of Alfvén mode behavior on VDF structure may explain why the Alfvén ion-cyclotron instability thresholds predicted by linear theory for bi-Maxwellian models of solar wind proton background VDFs do not entirely constrain spacecraft observations of solar wind proton VDFs, such as those made by the Wind spacecraft.

Keywords: plasma physics; solar wind; alfven waves; space plasmas; plasma astrophysics
VVV-VIVACE ID 533558 (=OGLE RRLYR-09505): The Half-day Period as a Challenge for the Automatic Searches for Variable Stars

Searches for periodic variable stars are susceptible to seasonal aliases caused by sampling. Nightly observations from ground based telescopes produce a large number of false detections at the integer multiples of day-1 frequency. Here we discuss the case of VISTA Variables in the Vía Láctea-VIrac VAriable Classification Ensemble (VVV-VIVACE) ID 533558, classified by the VIVACE using machine learning as an EA/EB binary with a period of P = 0.6659 day, in contradiction with a previous classification as an AB-type RR Lyrae with period P = 0.4992 day by the OGLE survey. We discuss the problem of phase coverage causing the misclassification with a wrong period by the VVV, in spite of a robust set of 652 data points over six years of observations. As automatic light-curve classifications of large data sets become more popular, this is a problem that cannot be overlooked.

Keywords: rr lyrae variable stars; eclipsing binary stars; milky way galaxy; surveys; variable stars
Testing General Relativity with NuSTAR Data of Galactic Black Holes

Einstein's theory of General Relativity predicts that the spacetime metric around astrophysical black holes is described by the Kerr solution. In this work, we employ state-of-the-art relativistic reflection modeling to analyze a selected set of NuSTAR spectra of Galactic black holes to obtain the most robust and precise constraints on the Kerr black hole hypothesis possible today. Our constraints are much more stringent than those from other electromagnetic techniques and, with some sources, we find stronger constraints than those currently available from gravitational waves.

Keywords: astrophysical black holes; kerr black holes; stellar mass black holes; x-ray astronomy; gravitation; general relativity
Effects of the 2007 Martian Global Dust Storm on Boundary Positions in the Induced Magnetosphere

Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.

Keywords: mars; planetary magnetospheres; planetary science; planetary ionospheres; surface processes
Molecular Gas Tracers in Young and Old Protoplanetary Disks

Molecular emission is used to investigate both the physical and chemical properties of protoplanetary disks. Therefore, to derive disk properties accurately, we need a thorough understanding of the behavior of the molecular probes upon which we rely. Here we investigate how the molecular line emission of N2H+, HCO+, HCN, and C18O compare to other measured quantities in a set of 20 protoplanetary disks. Overall, we find positive correlations between multiple line fluxes and the disk dust mass and radius. We also generally find strong positive correlations between the line fluxes of different molecular species. However, some disks do show noticeable differences in the relative fluxes of N2H+, HCO+, HCN, and C18O. These differences occur even within a single star-forming region. This results in a potentially large range of different disk masses and chemical compositions for systems of similar age and birth environment. While we make preliminary comparisons of molecular fluxes across different star-forming regions, more complete and uniform samples are needed in the future to search for trends with birth environment or age.

Keywords: astrochemistry; protoplanetary disks
Radial Evolution of Magnetic Field Fluctuations in an Interplanetary Coronal Mass Ejection Sheath

The sheaths of compressed solar wind that precede interplanetary coronal mass ejections (ICMEs) commonly display large-amplitude magnetic field fluctuations. As ICMEs propagate radially from the Sun, the properties of these fluctuations may evolve significantly. We have analyzed magnetic field fluctuations in an ICME sheath observed by MESSENGER at 0.47 au and subsequently by STEREO-B at 1.08 au while the spacecraft were close to radial alignment. Radial changes in fluctuation amplitude, compressibility, inertial-range spectral slope, permutation entropy, Jensen-Shannon complexity, and planar structuring are characterized. These changes are discussed in relation to the evolving turbulent properties of the upstream solar wind, the shock bounding the front of the sheath changing from a quasi-parallel to quasi-perpendicular geometry, and the development of complex structures in the sheath plasma.

Keywords: solar wind; interplanetary magnetic fields; interplanetary turbulence
Spectral Properties and Hybrid Jet Model Constraints of Fermi GRB 210610B

The jet composition of gamma-ray bursts (GRBs) is still an open question and the energy spectrum characteristics can provide us with evidence. GRB 210610B is a special burst with low-energy indices that are all greater than the synchrotron cutoff. We first use two empirical models, Band and CPL, and one physics model, a blackbody, to perform time-resolved spectral analysis on GRB 210610B and find that about 76.47% of the spectra need an addition thermal component to obtain a better fit. Moreover, these spectra could be well fitted by a multicolor blackbody (mBB) and the synchrotron model. We then adopt the hybrid jet model proposed by Gao & Zhang to perform a "top-down" approach to diagnose the photospheric properties (η and σ 0) of the central engine from observational data. We find both the dimensionless entropy η and the magnetization parameters (1 + σ 0) are greater than 1, indicating that the Poynting flux component may play an important role in addition to the hot fireball component. Our analysis also shows that most of the spectra have a magnetization parameter (1 + σ 15) ≃ 1 at ~1015 cm, suggesting that nonthermal emission may originate from internal shocks. Furthermore, we find that α and E p show different time evolution behaviors: α exhibits a "hard-to-soft" behavior and moderately correlates with flux, while E p exhibits a "tracking" behavior. The magnetic field strength B and the mBB parameter kT max also show a "tracking" behavior. Our results suggest that the empirical model CPL may be interpreted by an mBB.

Keywords: gamma-ray bursts
Comparing Complex Chemistry in Neighboring Hot Cores: NOEMA Studies of W3(H2O) and W3(OH)

Presented here are NOEMA interferometric observations of the neighboring hot cores W3(H2O) and W3(OH). The presence of two star-forming cores at different evolutionary stages within the same parent cloud presents a unique opportunity to study how the physics of the source and its evolutionary stage impact the chemistry. Through spectral analysis and imaging, we identify over 20 molecules in these cores. Most notably, we have detected HDO and CH3CH2CN in W3(OH), which were previously not detected in this core. We have imaged the molecular emission, revealing new structural features within these sources. W3(OH) shows absorption in a "dusty cocoon" surrounded by molecular emission. These observations also reveal extended emission that is potentially indicative of a low-velocity shock. From the information obtained herein, we have constructed column density and temperature maps for methanol and compared this information to the molecular images. By comparing the spatial distribution of molecules that may be destroyed at later stages of star formation, this work demonstrates the impact of physical environment on chemistry in star-forming regions at different evolutionary stages.

Keywords: astrochemistry; interferometry; star forming regions; h ii regions
Kinetic Features of Alpha Particles in a Pestchek-like Magnetic Reconnection Event in the Solar Wind Observed by Solar Orbiter

The acceleration and heating of solar wind particles by magnetic reconnection are important mechanisms in space physics. Although alpha particles (4He2+) are the second most abundant population of solar wind ions, their kinetic behavior in solar wind magnetic reconnection is not well understood. Using the high-energy (1500-3000 eV) range of the Solar Wind Analyser/Proton-Alpha Sensor instrument on board Solar Orbiter, we study the kinetic features of alpha particles in an exhaust region of a Pestchek-like solar-wind reconnection event with a weak guide field. A pair of back-to-back compound discontinuities is observed in the exhaust region. We find that the plasma in the magnetic exhaust region is heated and bounded by slow shocks (SSs), while the accelerated reconnection jet is bounded by rotational discontinuities (RDs). The SSs are outside the RDs, which is not expected from the magnetohydrodynamical prediction. We suggest this different location of the discontinuities is due to the enhanced parallel temperature T p∥ > T p⊥, which reduces the local Alfvén speed in the exhaust region, allowing the SSs to propagate faster than the RDs. Inside the exhaust region, the guide field is dominant. We find a two-population distribution of the alpha particles. These two populations are field aligned downstream the SSs and shift to have a perpendicular offset in the reconnection jet, suggesting that the change of the magnetic field at the RDs has similar timescales with the proton gyroperiod, but faster than those of the alpha particles, such that the alpha particles behave like pickup ions.

Keywords: solar wind; solar magnetic reconnection; heliosphere
Characterizing the Solar Cycle Variability Using Nonlinear Time Series Analysis at Different Amounts of Dynamo Supercriticality: Solar Dynamo is Not Highly Supercritical

The solar dynamo is essentially a cyclic process in which the toroidal component of the magnetic field is converted into the poloidal one and vice versa. This cyclic loop is disturbed by some nonlinear and stochastic processes mainly operating in the toroidal to poloidal part. Hence, the memory of the polar field decreases in every cycle. On the other hand, the dynamo efficiency and, thus, the supercriticality of the dynamo decreases with the Sun's age. Previous studies have shown that the memory of the polar magnetic field decreases with the increase of supercriticality of the dynamo. In this study, we employ popular techniques of time series analysis, namely, compute Higuchi's fractal dimension, Hurst exponent, and Multi-Fractal Detrended Fluctuation Analysis to the amplitude of the solar magnetic cycle obtained from dynamo models operating at near-critical and supercritical regimes. We show that the magnetic field in the near-critical regime is governed by strong memory, less stochasticity, intermittency, and breakdown of self-similarity. On the contrary, the magnetic field in the supercritical region has less memory, strong stochasticity, and shows a good amount of self-similarity. Finally, applying the same time series analysis techniques in the reconstructed sunspot data of 85 cycles and comparing their results with that from models, we conclude that the solar dynamo is possibly operating near the critical regime and not too much supercritical regime. Thus the Sun may not be too far from the critical dynamo transition.

Keywords: solar cycle; solar magnetic fields; solar dynamo; time series analysis; magnetohydrodynamics; the sun; interdisciplinary astronomy
Multi-messenger Approaches to Supermassive Black Hole Binary Detection and Parameter Estimation. II. Optimal Strategies for a Pulsar Timing Array

Pulsar timing arrays (PTAs) are Galactic-scale gravitational wave (GW) detectors consisting of precisely timed pulsars distributed across the sky. Within the decade, PTAs are expected to detect nanohertz GWs emitted by close-separation supermassive black hole binaries (SMBHBs), thereby opening up the low-frequency end of the GW spectrum for science. Individual SMBHBs which power active galactic nuclei are also promising multi-messenger sources; they may be identified via theoretically predicted electromagnetic (EM) signatures and be followed up by PTAs for GW observations. In this work, we study the detection and parameter estimation prospects of a PTA which targets EM-selected SMBHBs. Adopting a simulated Galactic millisecond pulsar population, we envisage three different pulsar timing campaigns which observe three mock sources at different sky locations. We find that an all-sky PTA which times the best pulsars is an optimal and feasible approach to observe EM-selected SMBHBs and measure their source parameters to high precision (i.e., comparable to or better than conventional EM measurements). We discuss the implications of our findings in the context of future PTA experiments with the planned Deep Synoptic Array-2000 and the multi-messenger studies of SMBHBs such as the well-known binary candidate OJ 287.

Keywords: gravitational waves; pulsars; supermassive black holes
The Distribution of Metallicities in the Local Galactic Interstellar Medium

In this investigation, we present an analysis of the metallicity distribution that pertains to neutral gas in the local Galactic interstellar medium (ISM). We derive relative ISM metallicities for a sample of 84 sight lines probing diffuse atomic and molecular gas within 4 kpc of the Sun. Our analysis is based in large part on column density measurements reported in the literature for 22 different elements that are commonly studied in interstellar clouds. We supplement the literature data with new column density determinations for certain key elements and several individual sight lines important to our analysis. Our methodology involves comparing the relative gas-phase abundances of many different elements for a given sight line to simultaneously determine the strength of dust depletion in that direction and the overall metallicity offset. We find that many sight lines probe multiple distinct gas regions with different depletion properties, which complicates the metallicity analysis. Nevertheless, our results provide clear evidence that the dispersion in the metallicities of neutral interstellar clouds in the solar neighborhood is small (~0.10 dex) and only slightly larger than the typical measurement uncertainties. We find no evidence for the existence of very low metallicity gas (as has recently been reported by De Cia et al.) along any of the 84 sight lines in our sample. Our results are consistent with a local Galactic ISM that is well mixed and chemically homogeneous. *Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the MAST data archive at the Space Telescope Science Institute. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data obtained from the ESO Science Archive Facility with DOI: https://doi.org/10.18727/archive/50.

Keywords: interstellar medium; interstellar abundances; interstellar dust; diffuse interstellar clouds; metallicity
X-Ray Polarimetry of the Crab Nebula with PolarLight: Polarization Recovery after the Glitch and a Secular Position Angle Variation

We report follow-up observations of the Crab Nebula with the PolarLight X-ray polarimeter, which revealed a possible variation in polarization associated with a pulsar glitch in 2019. The new observations confirm that the polarization has recovered roughly 100 days after the glitch. With the new observations, we find that the polarization angle (PA) measured with PolarLight from the total nebular emission has a difference of 18°0 ± 4°6 from that measured 42 yr ago with OSO-8, indicating a secular evolution of polarization with either the Crab Nebula or pulsar. The long-term variation in PA could be a result of multiple glitches in the history, magnetic reconnection, or movement of synchrotron emitting structures in the nebula, or secular evolution of the pulsar magnetic geometry.

Keywords: polarimetry; rotation powered pulsars; x-ray detectors; x-ray sources
Lunar North Polar Cold Traps Based on Diurnally and Seasonally Varying Temperatures

Lunar cold traps are defined by extremely low sublimation rates, such that water ice could have accumulated in them. Here time-averaged sublimation rates are calculated for the north polar region of the Moon based on over 14 years of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. The cold trap area poleward of 80°N is about 32% larger when defined by a time-average sublimation rate instead of by peak temperature. Apparently sunlit cold traps are identified, e.g., in Lenard Crater, where modeling of direct illumination reveals that the Sun briefly rises above the horizon each Draconic year. The true cold trap area is smaller than what can be determined from Diviner data. Also presented are north polar maps for the potential sublimation rate of relic buried ice and for subsurface cold trapping.

Keywords: the moon; lunar science; lunar surface; surface ices
The Closest View of a Fast Coronal Mass Ejection: How Faulty Assumptions Near Perihelion Lead to Unrealistic Interpretations of PSP/WISPR Observations

We report on the closest view of a coronal mass ejection (CME) observed by the Parker Solar Probe (PSP)/ Wide-field Imager for Parker Solar PRobe (WISPR) instrument on 2022 September 5, when PSP was traversing from a distance of 15.3 to 13.5 R ⊙ from the Sun. The CME leading edge and an arc-shaped concave-up structure near the core were tracked in the WISPR field of view using the polar coordinate system for the first time. Using the impact distance on the Thomson surface, we measured the average speeds of the CME leading edge and concave-up structure as ≈2500 ± 270 km s-1 and ≈400 ± 70 km s-1 with a deceleration of ≈20 m s-2 for the latter. The use of the plane-of-sky approach yielded an unrealistic speed of more than 3 times this estimate. We also used single viewpoint STEREO/COR-2A images to fit the Graduated Cylindrical Shell (GCS) model to the CME while incorporating the source region location from Extreme-Ultraviolet Imager of Solar Orbiter and estimated a 3D speed of ≈2700 km s-1. We conclude that this CME exhibits the highest speed during the ascending phase of solar cycle 25. This places it in the category of extreme-speed CMEs, which account for only 0.15% of all CMEs listed in the CDAW CME catalog.

Keywords: solar coronal mass ejections; solar magnetic reconnection; solar corona; solar coronal transients