Sazuna/UAT_keywords huggingface dataset:
X-Ray Plateaus in Gamma-Ray Burst Afterglows and Their Application in Cosmology. For gamma-ray bursts (GRBs) with a plateau phase in the X-ray afterglow, a so-called L-T-E correlation that tightly connects the isotropic energy of the prompt GRB (Eγ,iso) with the end time of the X-ray plateau (Ta) and the corresponding X-ray luminosity at the end time (LX) has been found. Here we show that there is a clear redshift evolution in the correlation. Furthermore, because the power-law indices of LX and Eγ,iso in the correlation function are almost identical, the L-T-E correlation is insensitive to cosmological parameters and cannot be used as a satisfactory standard candle. On the other hand, based on a sample including 121 long GRBs, we establish a new three-parameter correlation that connects LX, Ta, and the spectral peak energy Ep, i.e., the L-T-Ep correlation. This correlation strongly supports the so-called Combo-relation established by Izzo et al. After correcting for the redshift evolution, we show that the de-evolved L-T-Ep correlation can be used as a standard candle. By using this correlation alone, we are able to constrain the cosmological parameters as ${{\rm{\Omega }}}_{m}={0.389}_{-0.141}^{+0.202}$ (1σ) for the flat ΛCDM model, or ${{\rm{\Omega }}}_{m}={0.369}_{-0.191}^{+0.217}$ and $w=-{0.966}_{-0.678}^{+0.513}$ (1σ) for the flat wCDM model. Combining with other cosmological probes, more accurate constraints on the cosmology models are presented.

Keywords: Cosmology, Neutron stars, Gamma-ray bursts, Cosmological parameters, Dark matter, Dark energy
Ne/O and Fe/O Characteristics of Large Solar Energetic Particle Events during Solar Cycles 23 and 24. We have examined the Ne/O and Fe/O characteristics of large solar energetic particle (SEP) events at the ion energy range of 3-40 MeV nucleon-1 during solar cycles 23 and 24. In each cycle, the solar activity displays an ~3 yr rising phase and a longer declining phase. While Fe-poor events only appeared in the declining phase of cycle 23, the properties of Fe-rich events were similar in the rising phases of both cycles. Also, very few Fe-rich events were seen in the declining phase of cycle 24. In addition, the Ne/O data in the corona, solar wind, and SEP events consistently reveal that the characteristics of SEP events are mainly governed by the solar wind turbulence status that exhibits a significant difference between slow and fast streams. During the rising phase of the solar cycles, slow streams are dominated by the two-dimensional turbulence component, which significantly reduces the injection energy of the quasi-perpendicular (Q-Perp) shock acceleration. Also, slow streams have an increased Ne/O ratio and hence enhanced temperature of coronal suprathermals, favoring the occurrence of Fe-rich events. In contrast, in the declining phase of the solar cycles, the fast streams are dominated by the slab turbulence component, which could significantly increase the injection energy of the Q-Perp shock acceleration. Consequently, in fast streams, most Fe-rich events originate from jet suprathermals. The coronal suprathermals may produce the Fe-poor events having abnormally low Ne/O ratios provided the speed of the associated coronal mass ejection is large enough.

Keywords: Interplanetary turbulence, Solar energetic particles, Solar wind, Solar magnetic fields, Solar particle emission
Say Hello to Algol's New Companion Candidates. Constant orbital period ephemerides of eclipsing binaries give the computed eclipse epochs (C). These ephemerides based on the old data cannot accurately predict the observed future eclipse epochs (O). Predictability can be improved by removing linear or quadratic trends from the O - C data. Additional companions in an eclipsing binary system cause light-time travel effects that are observed as strictly periodic O - C changes. Recently, Hajdu et al. estimated that the probability of detecting the periods of two new companions from the O - C data is only 0.00005. We apply the new discrete chi-square method to 236 yr of O - C data of the eclipsing binary Algol (β Persei). We detect the tentative signals of at least five companion candidates having periods between 1.863 and 219.0 yr. The weakest one of these five signals does not reveal a "new" companion candidate, because its 680.4 ± 0.4 day signal period differs only 1.4σ from the well-known 679.85 ± 0.04 day orbital period of Algol C. We detect these same signals also from the first 226.2 yr of data, and they give an excellent prediction for the last 9.2 yr of our data. The orbital planes of Algol C and the new companion candidates are probably coplanar because no changes have been observed in Algol's eclipses. The 2.867 day orbital period has been constant since it was determined by Goodricke.

Keywords: Multiple stars, Algol variable stars, Astronomy data analysis, Eclipsing binary stars, Time series analysis
Polarization Pipeline for Fast Radio Bursts Detected by CHIME/FRB. Polarimetric observations of fast radio bursts (FRBs) are a powerful resource for better understanding these mysterious sources by directly probing the emission mechanism of the source and the magneto-ionic properties of its environment. We present a pipeline for analyzing the polarized signal of FRBs captured by the triggered baseband recording system operating on the FRB survey of The Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB). Using a combination of simulated and real FRB events, we summarize the main features of the pipeline and highlight the dominant systematics affecting the polarized signal. We compare parametric (QU-fitting) and non-parametric (rotation measure synthesis) methods for determining the Faraday rotation measure (RM) and find the latter method susceptible to systematic errors from known instrumental effects of CHIME/FRB observations. These errors include a leakage artifact that appears as polarized signal near RM ~ 0 rad m-2 and an RM sign ambiguity introduced by path length differences in the system's electronics. We apply the pipeline to a bright burst previously reported (FRB 20191219F), detecting an RM of +6.074 ± 0.006 ± 0.050 rad m-2 with a significant linear polarized fraction (≳0.87) and strong evidence for a non-negligible circularly polarized component. Finally, we introduce an RM search method that employs a phase-coherent de-rotation algorithm to correct for intra-channel depolarization in data that retain electric field phase information and successfully apply it to an unpublished FRB, FRB 20200917A, measuring an RM of -1294.47 ± 0.10 ± 0.05 rad m-2 (the second largest unambiguous RM detection from any FRB source observed to date).

Keywords: Astronomical techniques, Radio bursts, Polarimetry
Studies of Cepheus X-4 during the 2018 Outburst Observed with AstroSat. We present timing and spectral results for the 2018 outburst of Cepheus X-4, observed twice by AstroSat at luminosities of 2.04 × 1037 erg s-1 and 1.02 × 1037 erg s-1. The light curves showed strong pulsation and co-related X-ray intensity variation in the SXT (0.5-8.0 keV) and LAXPC (3-60 keV) energy bands. The spin period and spin-down rate of the pulsar were determined from two observations to be 65.35080 ± 0.00014 s and (-2.10 ± 0.8) × 10-12 Hz s-1 at epoch MJD 58301.61850, and 65.35290 ± 0.00017 s and (-1.6 ± 0.8) × 10-12 Hz s-1 at epoch MJD 58307.40211. Pulse shape studies with AstroSat showed energy- and intensity-dependent variations. The pulsar showed an overall continuous spin-down over 30 yr at an average rate of (-2.455 ± 0.004) × 10-14 Hz s-1, attributed to the propeller effect in the subsonic regime of the pulsar, in addition to variations during its outburst activities. Spectra between the 0.7 keV and 55 keV energy bands were well fitted by two continuum models, an absorbed compTT model and an absorbed power law with a Fermi-Dirac cutoff (FD-cutoff) model with a blackbody. These were combined with an iron emission line and a cyclotron absorption line. The prominent cyclotron resonance scattering features with a peak absorption energy of ${30.48}_{-0.34}^{+0.33}$ keV and ${30.68}_{-0.44}^{+0.45}$ keV for the FD-cutoff model and ${30.46}_{-0.28}^{+0.32}$ keV and ${30.30}_{-0.34}^{+0.36}$ keV for the compTT model were detected during two AstroSat observations. When compared with earlier results, these showed long-term stability of an average value of 30.23 ± 0.22 keV with wide variation in source luminosity. The pulsar showed pulse phase as well as luminosity dependent variations in the cyclotron line energy and width and in the plasma optical depth of its spectral continuum.

Keywords: Accretion, Neutron stars, High mass x-ray binary stars, Pulsars, Stellar accretion disks, Be stars, Magnetic fields, Binary pulsars
Polarization of the Lyα Lines of H I and He II as a Tool for Exploring the Solar Corona. The near-Earth space weather is driven by the quick release of magnetic free energy in the solar corona. Probing this extremely hot and rarified region of the extended solar atmosphere requires modeling the polarization of forbidden and permitted coronal lines. To this end, it is important to develop efficient codes to calculate the Stokes profiles that emerge from given three-dimensional (3D) coronal models and this should be done taking into account the symmetry breaking produced by the presence of magnetic fields and non-radial solar wind velocities. We have developed such a tool with the aim of theoretically predicting and interpreting spectropolarimetric observations of the solar corona in permitted and forbidden lines. In this paper, we show the results of a theoretical investigation of the linear polarization signals produced by scattering processes in the H I Lyα line at 1216 Å and in the He II Lyα line at 304 Å using 3D coronal models by Predictive Science Inc. These spectral lines have very different critical magnetic fields for the onset of the Hanle effect (53 G and 850 G, respectively), as well as different sensitivities to the Doppler effect caused by the solar wind velocities. We study under which circumstances simultaneous observations of the scattering polarization in these Lyα lines can facilitate the determination of magnetic fields and macroscopic velocities in the solar corona.

Keywords: Fast solar wind, Solar coronal lines, Solar physics, Solar magnetic fields, Solar corona
MHD-PIC Simulations of Cosmic-Ray Scattering and Transport in Inhomogeneously Ionized Plasma. Cosmic rays (CRs) have critical impacts in the multiphase interstellar medium (ISM), driving dynamical motions in low-density plasma and modifying the ionization state, temperature, and chemical composition of higher-density atomic and molecular gas. We present a study of CR propagation in inhomogeneously ionized plasma, addressing CR transport issues that arise in the cloudy ISM. Using one-dimensional magnetohydrodynamic (MHD) particle-in-cell simulations that include ion-neutral drag to damp Alfvén waves in a portion of the simulation domain, we self-consistently evolve the kinetic physics of CRs and background gas MHD. By introducing a damping region in our periodic domain, our simulations break translational symmetry and allow the emergence of spatial gradients in the CR distribution function. A spatial gradient opposite to the CR flux forms across the fully ionized region as a result of pitch angle scattering. We connect our results with CR hydrodynamics formulations by computing the wave-particle scattering rates as predicted by quasilinear, fluid, and Fokker-Planck theory. For momenta where the mean free path is short relative to the box size, we find excellent agreement among all scattering rates. However, we also find evidence of a reduced scattering rate for less energetic particles that are subject to the μ = 0 barrier in our simulations. Our work provides a first-principles verification of CR hydrodynamics when particles stream down their pressure gradient and opens a pathway toward comprehensive calibrations of transport coefficients from self-generated Alfvén wave scattering with CRs.

Keywords: Magnetohydrodynamics, Interstellar plasma, Galactic cosmic rays, Interstellar clouds, Interstellar medium, Cosmic rays
Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67. We present an analysis of Chandra/LETGS observations of the ultracompact X-ray binary (UCXB)4U 1626-67, continuing our project to analyze the existing Chandra gratings data of this interesting source. The extremely-low-mass, hydrogen-depleted donor star provides a unique opportunity to study the properties and structure of the metal-rich accreted plasma. There are strong, double-peaked emission features of O VII-VIII and Ne IX-X, but no other identified emission lines are detected. Our spectral fit simultaneously models the emission-line profiles and the plasma parameters, using a two-temperature collisionally-ionized plasma. Based on our line-profile fitting, we constrain the inclination of the system to 25-60° and the inner disk radius to ~1500 gravitational radii, in turn constraining the donor mass to ≲0.026 M⊙, while our plasma modeling confirms previous reports of high neon abundance in the source, establishing a Ne/O ratio in the system of 0.47 ± 0.04, while simultaneously estimating a very low Fe/O ratio of 0.0042 ± 0.0008 and limiting the Mg/O ratio to less than 1% by number. We discuss these results in light of previous work.

Keywords: Neutron stars, High resolution spectroscopy, Stellar accretion disks, White dwarf stars, Compact binary stars, Plasma astrophysics, Pulsars, Low-mass x-ray binary stars
A Simulation Study of Ultra-relativistic Jets-I. A New Code for Relativistic Hydrodynamics. In an attempt to investigate the structures of ultra-relativistic jets injected into the intracluster medium (ICM) and the associated flow dynamics, such as shocks, velocity shear, and turbulence, we have developed a new special relativistic hydrodynamic (RHD) code in the Cartesian coordinates, based on the weighted essentially non-oscillatory (WENO) scheme. It is a finite difference scheme of high spatial accuracy, which has been widely employed for solving hyperbolic systems of conservation equations. The code is equipped with different WENO versions, such as the fifth-order accurate WENO-JS, WENO-Z, and WENO-ZA, and different time-integration methods, such as the fourth-order accurate Runge-Kutta (RK4) and strong stability preserving RK (SSPRK), as well as the implementation of the equations of state (EOSs) that closely approximate the EOS of the single-component perfect gas in relativistic regimes. In addition, it incorporates a high-order accurate averaging of fluxes along the transverse directions to enhance the accuracy of multidimensional problems, and a modification of eigenvalues for the acoustic modes to effectively control the carbuncle instability. Through extensive numerical tests, we assess the accuracy and robustness of the code, and choose WENO-Z, SSPRK, and the EOS suggested in Ryu et al. as the fiducial setup for simulations of ultra-relativistic jets. The results of our study of ultra-relativistic jets using the code is reported in an accompanying paper.

Keywords: Hydrodynamical simulations, Relativistic jets, Relativistic fluid dynamics, Radio galaxies
A Simulation Study of Ultra-relativistic Jets. II. Structures and Dynamics of FR-II Jets. We study the structures of ultra-relativistic jets injected into the intracluster medium and the associated flow dynamics, such as shocks, velocity shear, and turbulence, through three-dimensional relativistic hydrodynamic (RHD) simulations. To that end, we have developed a high-order accurate RHD code, equipped with a weighted essentially non-oscillatory scheme and a realistic equation of state. Using the code, we explore a set of jet models with the parameters relevant to FR-II radio galaxies. We confirm that the overall jet morphology is primarily determined by the jet power, and the jet-to-background density and pressure ratios play secondary roles. Jets with higher powers propagate faster, resulting in more elongated structures, while those with lower powers produce more extended cocoons. Shear interfaces in the jet are dynamically unstable, and hence, chaotic structures with shocks and turbulence develop. We find that the fraction of the jet-injected energy dissipated through shocks and turbulence is greater in less powerful jets, although the actual amount of the dissipated energy is larger in more powerful jets. In lower power jets, the backflow is dominant in the energy dissipation owing to the broad cocoon filled with shocks and turbulence. In higher power jets, by contrast, both the backflow and jet-spine flow are important for the energy dissipation. Our results imply that different mechanisms, such as diffusive shock acceleration, shear acceleration, and stochastic turbulent acceleration, may be involved in the production of ultra-high energy cosmic rays in FR-II radio galaxies.

Keywords: Hydrodynamical simulations, Relativistic jets, Radio galaxies, Relativistic fluid dynamics, Cosmic rays
New Thermonuclear Rate of <SUP>7</SUP>Li(d,n)2<SUP>4</SUP>He 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 &gt; 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
Empirically Determining Substellar Cloud Compositions in the Era of the James Webb Space Telescope. Most brown dwarfs have atmospheres with temperatures cold enough to form clouds. A variety of materials likely condense, including refractory metal oxides and silicates; the precise compositions and crystal structures of predicted cloud particles depend on the modeling framework used and have not yet been empirically constrained. Spitzer has shown tentative evidence of the silicate feature in L dwarf spectra and the James Webb Space Telescope (JWST) can measure these features in many L dwarfs. Here, we present new models to predict the signatures of the strongest cloud absorption features. We investigate different cloud mineral species and determine how particle size, mineralogy, and crystalline structure change spectral features. We find that silicate and refractory clouds have a strong cloud absorption feature for small particle sizes (≤1 μm). Model spectra are compared to five brown dwarfs that show evidence of the silicate feature; models that include small particles in the upper layers of the atmosphere produce a broad cloud mineral feature, and that better match the observed spectra than the Ackerman &amp; Marley cloud model. We simulate observations with the Mid-Infrared Instrument (MIRI) instrument on JWST for a range of nearby, cloudy brown dwarfs, demonstrating that these features could be readily detectable if small particles are present. Furthermore, for photometrically variable brown dwarfs, our predictions suggest that with JWST, by measuring spectroscopic variability inside and outside a mineral feature, we can establish silicate (or other) clouds as the cause of variability. Mid-infrared spectroscopy is a promising tool to empirically constrain the complex cloud condensation sequence in brown dwarf atmospheres.

Keywords: Brown dwarfs, L dwarfs, Stellar atmospheres, Extrasolar gaseous giant planets, Exoplanet atmospheres
Wave Excitation by Power-law-Distributed Energetic Electrons with Pitch-angle Anisotropy in the Solar Corona. Radio waves from the Sun are emitted, as a rule, due to energized electrons. Observations infer that the related energized electrons follow (negative) power-law velocity distributions above a break velocity Ub. They might also distribute anisotropically in the pitch-angle space. To understand radio wave generation better, we study the consequences of anisotropic power-law-distributed energetic electrons in current-free collisionless coronal plasmas utilizing 2.5-dimensional particle-in-cell simulations. We assume that the velocity distribution fu of the energized electrons follows a plateau (∂fu/∂u = 0) and a power-law distribution with spectral index α for velocities below and above Ub, respectively. In the pitch-angle space, these energized electrons are spread around a center μc = 0.5. We found that the energetic plateau-power-law electrons can more efficiently generate coherent waves if the anisotropy of their pitch-angle distribution is sufficiently strong, i.e., a small pitch-angle spread μs. The break velocity Ub affects the excitation dominance between the electrostatic and electromagnetic waves: for larger Ub electrostatic waves are mainly excited, while intermediate values of Ub are required for an excitation dominated by electromagnetic waves. The spectral index α controls the growth rate, efficiency, saturation, and anisotropy of the excited electromagnetic waves as well as the energy partition in different wave modes. These excited electromagnetic waves are predominantly right-handed polarized, in X- and Z-modes, as observed, e.g., in solar radio spikes. Additionally about 90% of the kinetic energy loss of the energetic electrons is dissipated, heating the ambient thermal electrons. This may contribute to the coronal heating.

Keywords: Solar coronal heating, Solar radio emission, Solar corona