Sazuna/UAT_keywords huggingface dataset:
Pulsar Timing Response to Gravitational Waves with Spherical Wave Fronts from a Massive Compact Source in the Quadrupole Approximation. Pulsar timing arrays (PTAs) are searching for nanohertz-frequency gravitational waves (GWs) through cross-correlation of pulse arrival times from a set of radio pulsars. PTAs have relied on a frequency-shift formula of the pulse, where planar GWs are usually assumed. Phase corrections due to the wave front curvature have been recently discussed. In this paper, frequency-shift and timing-residual formulae are derived for GWs with fully spherical wave fronts from a compact source such as a binary of supermassive black holes, where the differences in the GW amplitude and direction between Earth and the pulsar are examined in the quadrupole approximation. By using the new formulae, effects beyond the plane-wave approximation are discussed, and a galactic center PTA and nearby GW source candidates are also mentioned.

Keywords: Supermassive black holes, Pulsar timing method, Millisecond pulsars, Gravitational wave astronomy, Gravitational waves
Energy Partition of Thermal and Nonthermal Particles in Magnetic Reconnection. Magnetic reconnection has long been known to be the most important mechanism for quick conversion of magnetic field energy into plasma kinetic energy. In addition, energy dissipation by reconnection has gained attention not only as a plasma heating mechanism, but also as a plasma mechanism for accelerating nonthermal particles. However, the energy partitioning of thermal and nonthermal plasmas during magnetic reconnection is not understood. Here, we studied energy partition as a function of plasma sheet temperature and guide magnetic field. In relativistic reconnection with an antiparallel magnetic field or a weak guide magnetic field, it was found that the nonthermal energy density can occupy more than 90% of the total kinetic plasma energy density, but strengthening the guide magnetic field suppresses the efficiency of the nonthermal particle acceleration. In nonrelativistic reconnection for an antiparallel magnetic field, most dissipated magnetic field energy is converted into thermal plasma heating. For a weak guide magnetic field with a moderate value, however, the nonthermal particle acceleration efficiency was enhanced, but strengthening the guide field beyond the moderate value suppresses the efficiency.

Keywords: Space plasmas, Solar magnetic reconnection, Plasma physics, Plasma astrophysics, Pulsars, Pulsar wind nebulae, Magnetars, Astronomical simulations
Distillation of <SUP>56</SUP>Fe in Ultramassive O-Ne White Dwarfs. When white dwarfs freeze, the plasma mixtures inside them undergo separation processes that can produce radical changes in the composition profile of the star. The abundance of neutron-rich elements, such as 22Ne or 56Fe, determines whether or not the first crystals are more or less dense than the surrounding fluid and thus whether they sink or float. These processes have now been studied for C-O-Ne and C-O-Fe mixtures, finding that distillation and precipitation processes are possible in white dwarfs. In this work, we calculate the phase diagram of more complicated O-Ne-Fe mixtures and make predictions for the internal structure of the separated white dwarf. There are two possible outcomes determined by a complicated interplay between the Ne abundance, the 22Ne fraction, and the 56Fe abundance. Either Fe distills to form an inner core because the first O-Ne solids are buoyant, or an O-Ne inner core forms and Fe accumulates in the liquid until Fe distillation begins and forms an Fe shell. In the case of an Fe shell, a Rayleigh-Taylor instability may arise and overturn the core. In either case, Fe distillation may only produce a cooling delay of order 0.1 Gyr, as these processes occur early at high white dwarf luminosities. Fe inner cores and shells may be detectable through asteroseismology and could enhance the yield of neutron-rich elements such as 55Mn and 58Ni in supernovae.

Keywords: Stellar interiors, Plasma physics, White dwarf stars, Computational methods, Stellar evolution
Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data. We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star in Gaia DR3. This binary system was discovered from 64,108 binary solutions for which both astrometric and spectroscopic data are available. For this system, the astrometric and spectroscopic solutions are consistent with each other, making this system a confident candidate of a BH binary. The primary (visible) star in this system, Gaia DR3 5870569352746779008, is a red giant branch star whose mass is quite uncertain. Fortunately, despite the uncertainty of the primary's mass, we can estimate the mass of the secondary (dark) object in this system to be &gt;5.68 M ⊙ with a probability of 99%, based on the orbital parameters. The mass of the secondary object is much larger than the maximum neutron star mass (~2.0 M ⊙), which indicates that the secondary object is likely a BH. We argue that, if this dark object is not a BH, this system must be a more exotic system, in which the primary red giant branch star orbits around a quadruple star system (or a higher-order multiple-star system) whose total mass is more than 5.68 M ⊙. If this is a genuine BH binary, this has the longest period (1352.22 ± 45.81 days) among those discovered so far. As our conclusion entirely relies on Gaia DR3 data, independent confirmation with follow-up observations (e.g., long-term time-series spectra) is desired.

Keywords: Spectroscopic binary stars, Astrometric binary stars, Stellar mass black holes
A Search for Coincident Neutrino Emission from Fast Radio Bursts with Seven Years of IceCube Cascade Events. This paper presents the results of a search for neutrinos that are spatially and temporally coincident with 22 unique, nonrepeating fast radio bursts (FRBs) and one repeating FRB (FRB 121102). FRBs are a rapidly growing class of Galactic and extragalactic astrophysical objects that are considered a potential source of high-energy neutrinos. The IceCube Neutrino Observatory's previous FRB analyses have solely used track events. This search utilizes seven years of IceCube cascade events which are statistically independent of track events. This event selection allows probing of a longer range of extended timescales due to the low background rate. No statistically significant clustering of neutrinos was observed. Upper limits are set on the time-integrated neutrino flux emitted by FRBs for a range of extended time windows.

Keywords: Neutrino astronomy, High energy astrophysics, Radio transient sources
Evolution of Solar Eruptive Events: Investigating the Relationships among Magnetic Reconnection, Flare Energy Release, and Coronal Mass Ejections. We study the evolution of solar eruptive events by investigating the temporal relationships among magnetic reconnection, flare energy release, and the acceleration of coronal mass ejections (CMEs). Leveraging the optimal viewing geometry of the Solar TErrestrial RElations Observatory (STEREO) relative to the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) during 2010-2013, we identify 12 events with sufficient spatial and temporal coverage for a detailed examination. STEREO and SDO data are used to measure the CME kinematics and the reconnection rate, respectively, and hard X-ray (HXR) measurements from RHESSI provide a signature of the flare energy release. This analysis expands upon previous solar eruptive event timing studies by examining the fast-varying features, or "bursts," in the HXR and reconnection rate profiles, which represent episodes of energy release. Through a time lag correlation analysis, we find that HXR bursts occur throughout the main CME acceleration phase for most events, with the HXR bursts lagging the acceleration by 2 ± 9 minutes for fast CMEs. Additionally, we identify a nearly one-to-one correspondence between bursts in the HXR and reconnection rate profiles, with HXRs lagging the reconnection rate by 1.4 ± 2.8 minutes. The studied events fall into two categories: events with a single dominant HXR burst and events with a train of multiple HXR bursts. Events with multiple HXR bursts, indicative of intermittent reconnection and/or particle acceleration, are found to correspond with faster CMEs.

Keywords: Solar flares, Solar magnetic reconnection, Solar coronal mass ejections, Solar x-ray flares, Solar activity, Time series analysis
Earth as an Exoplanet. II. Earth's Time-variable Thermal Emission and Its Atmospheric Seasonality of Bioindicators. We assess the dependence of Earth's disk-integrated mid-infrared thermal emission spectrum on observation geometries and investigate which and how spectral features are impacted by seasonality on Earth. We compiled an exclusive data set containing 2690 disk-integrated thermal emission spectra for four different full-disk observing geometries (North and South Pole-centered and Africa and Pacific-centered equatorial views) over four consecutive years. The spectra were derived from 2378 spectral channels in the wavelength range from 3.75-15.4 μm (nominal resolution ≈1200) and were recorded by the Atmospheric Infrared Sounder on board the Aqua satellite. We learned that there is significant seasonal variability in Earth's thermal emission spectrum, and the strength of spectral features of bioindicators, such as N2O, CH4, O3, and CO2 depends strongly on both season and viewing geometry. In addition, we found a strong spectral degeneracy with respect to the latter two indicating that multi-epoch measurements and time-dependent signals may be required in order to fully characterize planetary environments. Even for Earth and especially for equatorial views, the variations in flux and strength of absorption features in the disk-integrated data are small and typically ≤ 10%. Disentangling these variations from the noise in future exoplanet observations will be a challenge. However, irrespectively of when the planet will be measured (i.e., day or night or season) the results from mid-infrared observations will remain the same to the zeroth order, which is an advantage over reflected light observations.

Keywords: Space vehicle instruments, Infrared spectroscopy, Exoplanet atmospheric variability, Earth (planet), Astrobiology, Biosignatures
SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-shell Detonation in a Star-forming Galaxy. The detonation of a thin (≲0.03 M ☉) helium shell (He-shell) atop a ~1 M ☉ white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum brightness, SN 2020jgb is slightly subluminous (ZTF g-band absolute magnitude -18.7 mag ≲ M  g  ≲ -18.2 mag depending on the amount of host-galaxy extinction) and shows an unusually red color (0.2 mag ≲ g ZTF - r ZTF ≲ 0.4 mag) due to strong line-blanketing blueward of ~5000 Å. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with an He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb is broadly consistent with a ~0.95-1.00 M ☉ (C/O core + He-shell) progenitor ignited by a ≳0.1 M ☉ He-shell. However, one-dimensional radiative transfer models without non-local-thermodynamic-equilibrium treatment cannot accurately characterize the line-blanketing features, making the actual shell mass uncertain. We detect a prominent absorption feature at ~1 μm in the near-infrared (NIR) spectrum of SN 2020jgb, which might originate from unburnt helium in the outermost ejecta. While the sample size is limited, we find similar 1 μm features in all the peculiar He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first peculiar He-shell DDet SN discovered in a star-forming dwarf galaxy, indisputably showing that He-shell DDet SNe occur in both star-forming and passive galaxies, consistent with the normal SN Ia population.

Keywords: Observational astronomy, Surveys, White dwarf stars, Type Ia supernovae, Supernovae
Alternative Waiting Time Statistics for the Lu and Hamilton Avalanche Model. The solar corona hosts many explosive events. Among them, flares are some of the most energetic, rapidly releasing huge amounts of energy and, in the case of the largest ones, producing coronal mass ejections that have the potential to harm life on our planet. Therefore, there is great interest in attempting to foresee the occurrence of extreme solar flares. Avalanche models for solar flares have been used since the beginning of the 1990s to model the flaring corona in a simple and computationally inexpensive way. The pioneering and now most prevalent model in the literature was proposed by Lu and Hamilton. This model has been extremely useful to reproduce most of the main characteristic features observed in solar flares (e.g., the probability density function of a flare's energy) and, in recent years, has been used as the starting point to predict extreme flaring events. In this work, we revisit Lu and Hamilton's model and the very definition of waiting time for both extreme and all-sized events. We find that extreme avalanche statistics are well described by a log-normal distribution, in accordance with recent observations of solar flares.

Keywords: Solar flares, Solar corona
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: Interplanetary turbulence, Space plasmas, Solar wind, Wavelet analysis
The HETDEX Survey Emission-line Exploration and Source Classification. The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the universe at z ~ 2.4 to 1% precision for both H(z) and D  A (z). HETDEX is in the process of mapping in excess of one million Lyα emitting (LAE) galaxies and a similar number of lower-z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Lyα emission from the lower-z interloping galaxies, primarily [O II], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Å rest-frame equivalent width cut commonly used to distinguish LAEs from lower-z [O II] emitting galaxies. Despite a spectral resolving power, R ~ 800, that cannot resolve the [O II] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Lyα by [O II] of 1.2% and a Lyα recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements. * Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

Keywords: Lyman-alpha galaxies, Redshift surveys, Emission line galaxies, Dark energy
Spatiotemporal Characterization of Cassiopeia A. Analyzing the X-ray data of supernova remnants (SNRs) is among the most challenging tasks in current X-ray astronomy because SNRs are both spatially extended and variable over time. We developed the strategy to track the time-series properties of all the parts constituting a diffuse structure by introducing the free-form image-registration technique based on B-spline and demonstrated the methodology using the Chandra data of Cassiopeia A. We successfully extracted the spatial distribution map of the time variability of continuum luminosity. To our knowledge, this is the first comprehensive characterization of such a dynamic diffuse target both in spatial and temporal viewpoints. We found that each of the four clusters derived by applying k-means algorithm to the extracted light curves has a clear physical meaning distinct from other clusters, which shows that our method is not a mere technique for automation but capable of capturing the underlying physics.

Keywords: Supernova remnants, X-ray astronomy, Astronomy data analysis
Tracking the Enigmatic Globular Cluster Ultracompact X-Ray Binary X1850-087: Extreme Radio Variability in the Hard State. The conditions under which accreting neutron stars launch radio-emitting jets and/or outflows are still poorly understood. The ultracompact X-ray binary X1850-087, located in the globular cluster NGC 6712, is a persistent atoll-type X-ray source that has previously shown unusual radio-continuum variability. Here we present the results of a pilot radio-monitoring program of X1850-087 undertaken with the Karl G. Jansky Very Large Array, with simultaneous or quasi-simultaneous Swift/XRT data obtained at each epoch. The binary is clearly detected in the radio in two of the six new epochs. When combined with previous data, these results suggest that X1850-087 shows radio emission at a slightly elevated hard-state X-ray luminosity of L  X  ≳ 2 × 1036 erg s-1, but no radio emission in its baseline hard state L  X  ~ 1036 erg s-1. No clear X-ray spectral changes are associated with this factor of ≳10 radio variability. At all detected epochs, X1850-087 has a flat to inverted radio spectral index, more consistent with the partially absorbed optically thick synchrotron of a compact jet rather than the evolving optically thick to thin emission associated with transient expanding synchrotron-emitting ejecta. If the radio emission in X1850-087 is indeed due to a compact jet, then it is plausibly being launched and quenched in the hard state on timescales as short as a few days. Future radio monitoring of X1850-087 could help elucidate the conditions under which compact jets are produced around hard-state accreting neutron stars.

Keywords: Low-mass x-ray binary stars, Neutron stars, Compact objects, Globular star clusters
Jitter Mechanism as a Kind of Coherent Radiation: Constrained by the GRB 221009A Emission at 18 TeV. The emission of gamma-ray burst (GRB) 221009A at 18 TeV has been detected by the large high-altitude air shower observatory. We suggest jitter radiation as a possible explanation for the TeV emission for this energetic GRB. In our scenario, the radiation field is linked to the perturbation field, and the perturbation field is dominated by kinetic turbulence. Kinetic turbulence takes a vital role in both magnetic field generation and particle acceleration. The jitter radiation can reach the TeV energy band when we consider either electron cooling or Landau damping. We further suggest that the jitter radiation in the very high-energy band is coherent emission. Our modeling results can be constrained by the observational results of GRB 221009A in the TeV energy band. This radiation mechanism is expected to have wide applications in the high-energy astrophysical research field.

Keywords: Gamma-ray bursts, High energy astrophysics, Plasma astrophysics, Radiative processes, Cosmic magnetic fields theory, Magnetic fields
Observed UV Continuum Slopes (β) of Galaxies at z = 0.40-0.75 in the GOODS-North Field. We estimate the UV continuum slope (β) of 465 galaxies (with luminosities of 0.028-3.3 ${L}_{z=0.5}^{* }$ ) in the Great Observatories Origins Survey Northern field in the redshift range z = 0.40-0.75. We use two AstroSat/UVIT (N242W, N245M) bands, two Hubble Space Telescope (F275W, F336W) bands, and a KPNO (U) band to sample the UV continuum slope of selected galaxies between 1215 and 2600 Å. The mean (median) and 1σ scatter in the observed β are found to be -1.33 ± 0.07 ( - 1.32) and 0.60 within the considered redshift range. We do not find any significant evolution in the mean β within our redshift window. Our measurements add new data points to the global β-z relation in the least-explored redshift regime, further reinforcing the gradual reddening of galaxy UV continuum with cosmic time. We notice no strong consistent trend between β and M 1500 for the entire luminosity range -21 &lt;M 1500 &lt; - 15 mag. However, the majority of the most-luminous galaxies (M 1500 &lt; - 19 mag) are found to have relatively redder slopes. Using UVIT, we detect galaxies as faint as M 1500 = - 15.6 mag (i.e., 0.028 ${L}_{z=0.5}^{* }$ ). The faintest galaxies (M 1500 &gt; - 16 mag) tend to be redder, which indicates they were less actively forming stars during this cosmic time interval. Our study highlights the unique capability of UVIT near-UV imaging to characterize the rest-frame far-UV properties of galaxies at redshift z ~ 0.5.

Keywords: High-redshift galaxies, Galaxy evolution, Ultraviolet photometry