Sazuna/UAT_keywords huggingface dataset:
Electron Heating in 2D Particle-in-cell Simulations of Quasi-perpendicular Low-beta Shocks. We measure the thermal electron energization in 1D and 2D particle-in-cell simulations of quasi-perpendicular, low-beta (β p = 0.25) collisionless ion–electron shocks with mass ratio m i/m e = 200, fast Mach number ${{ \mathcal M }}_{\mathrm{ms}}=1$ –4, and upstream magnetic field angle θ Bn = 55°–85° from the shock normal $\hat{{\boldsymbol{n}}}$ . It is known that shock electron heating is described by an ambipolar, B -parallel electric potential jump, Δϕ ∥, that scales roughly linearly with the electron temperature jump. Our simulations have ${\rm{\Delta }}{\phi }_{\parallel }/(0.5{m}_{{\rm{i}}}{{u}_{\mathrm{sh}}}^{2})\sim 0.1$ –0.2 in units of the pre-shock ions' bulk kinetic energy, in agreement with prior measurements and simulations. Different ways to measure ϕ ∥, including the use of de Hoffmann–Teller frame fields, agree to tens-of-percent accuracy. Neglecting off-diagonal electron pressure tensor terms can lead to a systematic underestimate of ϕ ∥ in our low-β p shocks. We further focus on two θ Bn = 65° shocks: a ${{ \mathcal M }}_{{\rm{s}}}\,=\,4$ ( ${{ \mathcal M }}_{{\rm{A}}}\,=\,1.8$ ) case with a long, 30d i precursor of whistler waves along $\hat{{\boldsymbol{n}}}$ , and a ${{ \mathcal M }}_{{\rm{s}}}\,=\,7$ ( ${{ \mathcal M }}_{{\rm{A}}}\,=\,3.2$ ) case with a shorter, 5d i precursor of whistlers oblique to both $\hat{{\boldsymbol{n}}}$ and B ; d i is the ion skin depth. Within the precursors, ϕ ∥ has a secular rise toward the shock along multiple whistler wavelengths and also has localized spikes within magnetic troughs. In a 1D simulation of the ${{ \mathcal M }}_{{\rm{s}}}\,=\,4$ , θ Bn = 65° case, ϕ ∥ shows a weak dependence on the electron plasma-to-cyclotron frequency ratio ω pe/Ωce, and ϕ ∥ decreases by a factor of 2 as m i/m e is raised to the true proton–electron value of 1836.

Keywords: Shocks, Interplanetary shocks, Planetary bow shocks
Bounding the Photon Mass with Ultrawide Bandwidth Pulsar Timing Data and Dedispersed Pulses of Fast Radio Bursts. Exploring the concept of a massive photon has been an important area in astronomy and physics. If photons have mass, their propagation in nonvacuum space would be affected by both the nonzero mass m  γ  and the presence of a plasma medium. This would lead to a delay time proportional to ${m}_{\gamma }^{2}{\nu }^{-4}$ , which deviates from the classical dispersion relation (proportional to ν ‑2). For the first time, we have derived the dispersion relation of a photon with a nonzero mass propagating in plasma. To reduce the impact of variations in the dispersion measure (DM), we employed the high-precision timing data to constrain the upper bound of the photon mass. Specifically, the DM/time of arrival (TOA) uncertainties derived from ultrawide bandwidth (UWB) observations conducted by the Parkes Pulsar Timing Array (PPTA) are used. The dedispersed pulses from fast radio bursts (FRBs) with minimal scattering effects are also used to constrain the upper bound of photon mass. The stringent limit on the photon mass is determined by uncertainties of the TOA of pulsars, with an optimum value of 9.52 × 10‑46 kg (5.34 × 10‑10 eV c‑2). In the future, it is essential to investigate the photon mass, as pulsar timing data are collected by PPTA and UWB receivers, or FRBs with wideband spectra are detected by UWB receivers.

Keywords: Radio transient sources, Intergalactic medium, Pulsar timing method, Radio pulsars
The On-axis Jetted Tidal Disruption Event AT2022cmc: X-Ray Observations and Broadband Spectral Modeling. AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3─30 keV) observations of AT2022cmc, as well as soft X-ray (0.3─6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power law with f  ν  ∝ ν −0.5 (f  ν  ∝ ν −1) below (above) the rest-frame break energy of E bk ∼ 10 keV at the observer frame t obs = 7.8 and 17.6 days since discovery. At t obs = 36.2 days, the X-ray spectrum is consistent with either a single power law or a broken power law. By modeling the spectral energy distribution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the submillimeter/radio emission originates from external shocks at large distances ≳1017 cm from the black hole, the UV/optical light comes from a thermal envelope with radius ∼1015 cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. We constrain the bulk Lorentz factor of the jet to be of the order 10─100. Our interpretation differs from the model proposed by Pasham et al. where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature of relativistic jets in other sources such as gamma-ray bursts.

Keywords: Black hole physics, Supermassive black holes, High energy astrophysics, Tidal disruption, Relativistic jets, X-ray transient sources
Coronagraphic Observations of Si X 1430 nm Acquired by DKIST/Cryo-NIRSP with Methods for Telluric Absorption Correction. We report commissioning observations of the Si X 1430 nm solar coronal line observed coronagraphically with the Cryogenic Near-Infrared Spectropolarimeter at the National Science Foundation's Daniel K. Inouye Solar Telescope. These are the first known spatially resolved observations of this spectral line, which has strong potential as a coronal magnetic field diagnostic. The observations target a complex active region located on the solar northeast limb on 2022 March 4. We present a first analysis of these data that extracts the spectral line properties through a careful treatment of the variable atmospheric transmission that is known to impact this spectral window. Rastered images are created and compared with extreme-UV observations from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) instrument. A method for estimating the electron density from the Si X observations is then demonstrated that makes use of the forbidden line density-sensitive emissivity and an emission-measure analysis of the SDO/AIA bandpass observations. In addition, we derive an effective temperature and nonthermal line width across the region. This study informs the calibration approaches required for more routine observations of this promising diagnostic line.

Keywords: Solar coronal lines, Solar E corona, Solar corona
Emission Line Intensity Ratios of Fe XXVI/ XXV/ XXIV in Solar Flares Observed by Hinotori. High-resolution spectra observed by the Solar X-ray spectrometer on board the Hinotori mission are revisited. Flat crystals slightly offset to the satellite spin axis produce automatic spectral scans for emission lines emerging from highly charged iron ions in solar flares every half-spin time period. All the downlinked data of the mission are converted to FITS format and major flare spectral data are revived as IDL save files in ISAS/DARTS. Based on these data sets, single-temperature fits are performed for the emission line complex of highly charged iron ions in the wavelength range of 1.75–1.95 Å and compared with theoretical predictions. Synthetic spectra with single electron temperatures estimated from j/w line-intensity ratios fit fairly well for Fe XXIV and Fe XXIII lines in the wavelength range of 1.85–1.88 Å, while intensity ratios of Fe XXV lines (x, y, z) and the inner-shell excitation line of Fe XXIV (q) to the Fe XXV resonance line (w) have systematic excesses. Empirical relations for the observed line ratios are derived. Ion fractions of Fe+25/Fe+24 estimated by intensity ratios of Lyα/w in the temperature range of log T  e =7.25–7.45 are consistent with values in ionization equilibrium, and the remaining excesses of the Fe XXV line ratios may suggest problems with the atomic parameters or atomic modeling.

Keywords: Atomic spectroscopy, Atomic data, Solar x-ray emission, Line intensities
Electromagnetic Signatures of Mirror Stars. Mirror stars are a generic prediction of dissipative dark matter (DM) models, including minimal atomic DM and twin baryons in the mirror twin Higgs model. Mirror stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. This accumulated "nugget" will draw heat from the mirror star core and emit highly characteristic X-ray and optical signals. In this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the Cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. We find that mirror star nuggets populate an extremely well-defined and narrow region of the Hertzsprung–Russell diagram that only partially overlaps with the white dwarf population. Our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission-line ratios. Our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of DM.

Keywords: White dwarf stars, Planetary nebulae, Dark matter
Evolution of Coronal Jets during Solar Cycle 24. The focus of this study is on the spatial and temporal distributions of 2704 solar jets throughout Solar Cycle 24, from beginning to end. This work is a follow-up paper by Liu et al. With this extended data set, we have further confirmed the two distinct distributions of coronal jets: one located in polar regions and another at lower latitudes. Further analysis of the series of coronal jets revealed kink oscillations of the global solar magnetic field. Additionally, studying the northern and southern hemispheres separately showed an antiphase correlation that can be interpreted as a global sausage oscillatory pattern of the loci of the coronal jets. We also investigated how the variability of the solar cycle may impact the power law index of coronal jets by dividing the data set into the rising and declining phases of Solar Cycle 24. However, there is no compelling evidence to suggest that the power law index changes after the maximum. It is worth noting that based on this vast database of solar jets, the degradation of the 304 Å channel of the Atmospheric Imaging Assembly instrument on board the Solar Dynamics Observatory can also be identified and confirmed. Finally, we searched for compelling signatures of the presence of active longitude in the coronal jet database. There was no obvious evidence with a high probability of an active longitude; therefore, this question remains yet to be addressed further.

Keywords: Solar cycle, Solar coronal transients, Solar extreme ultraviolet emission, Solar oscillations, Solar activity, Active solar corona
Probing Lorentz Invariance Violation with Absorption of Astrophysical γ-Rays by Solar Photons. We compute in detail the absorption optical depth for astrophysical γ-ray photons interacting with solar photons to produce electron–positron pairs. This effect is greatest for γ-ray sources at small angular distances from the Sun, reaching optical depths as high as τ  γ γ  ∼ 10‑2. We also calculate this effect including modifications to the absorption cross-section threshold from subluminal Lorentz invariance violation (LIV). We show for the first time that subluminal LIV can lead to increases or decreases in τ  γ γ  compared to the non-LIV case. We show that, at least in principle, LIV can be probed with this effect with observations of γ-ray sources near the Sun at ≳20 TeV by HAWC or LHAASO, although a measurement will be extremely difficult due to the small size of the effect.

Keywords: Gamma-ray astronomy, Quiet sun
Small-scale Field-aligned Currents in the Magnetopause Boundary Layer. Based on high-resolution measurements from the Magnetospheric Multiscale mission from 2015 May to 2018 June, we statistically investigate the properties of small-scale field-aligned currents (SFACs) in the magnetopause boundary layer. A total of 2235 SFACs are successfully identified. The durations of SFACs mainly fall between 0.2 and 0.3 s. Over 90% of SFACs have a width of less than 1 ion inertia length and are primarily distributed from 5 to 25 electron inertia lengths, implying that the SFACs belong to the kinetic-scale current layer. The main carriers of SFACs are electrons, and over 70% of SFACs exhibit net energy dissipation (i.e., J · E ' &gt; 0) with the majority of energy dissipation taking place in the parallel direction. SFACs are widely distributed spatially, and the occurrence rate of SFACs is higher in the boundary layer closer to the magnetosphere. Additionally, less than half of the total SFACs are identified in well-known structures, including the magnetic reconnection region, flux transfer event, Kelvin–Helmholtz vortex, and exhaust region, and 54% of the SFACs are in the "others" unknown structures. These results improve our comprehension of the current system at the magnetopause and the roles of SFACs in the coupling between the solar wind and magnetosphere.

Keywords: Planetary magnetospheres, Solar wind, Planetary boundary layers
Millimeter and Submillimeter Spectroscopy of the Deuterated Molecular Ion SD<SUP>+</SUP>. Seven rotational and fine-structure transitions of the deuterated molecular ion SD+ in the X 3Σ− ground electronic state have been measured in the 271─863 GHz region in the laboratory. This ion has been produced by direct-current glow discharge using a mixture of D2S and argon in a free space cell in a temperature range of −140°C to −160°C. The rotational, centrifugal distortion, spin─spin interaction, and hyperfine constants have been determined; the standard deviation of the residuals in the fitting is 109 kHz. The set of obtained spectroscopic parameters provides a list of accurate submillimeter rest frequencies of SD+ for astronomical detection. We have investigated lines of SD+ toward the quasar PKS 1830-211 using the Atacama Large Millimeter/submillimeter Array archive, as the z = 0.89 molecular absorber exists in front of this quasar. A data set covering the 297 GHz region includes the N  J  = 23─12 transition at 561 GHz due to redshift, providing an upper limit of the column density N tot = 3 × 1012 cm−2 for SD+.

Keywords: Rotational spectroscopy, Laboratory astrophysics, Molecular clouds, Molecular physics, Submillimeter astronomy
Insights into Neutron Star Equation of State by Machine Learning. Due to its powerful capability and high efficiency in big data analysis, machine learning has been applied in various fields. We construct a neural network platform to constrain the behaviors of the equation of state of nuclear matter with respect to the properties of nuclear matter at saturation density and the properties of neutron stars. It is found that the neural network is able to give reasonable predictions of parameter space and provide new hints into the constraints of hadron interactions. As a specific example, we take the relativistic mean field approximation in a widely accepted Walecka-type model to illustrate the feasibility and efficiency of the platform. The results show that the neural network can indeed estimate the parameters of the model at a certain precision such that both the properties of nuclear matter around saturation density and global properties of neutron stars can be saturated. The optimization of the present modularly designed neural network and extension to other effective models is straightforward.

Keywords: Neural networks
Trapped Water on Silicates in the Laboratory and in Astrophysical Environments. The existence of strongly bound water molecules on silicate surfaces, above the desorption temperature of water ice, was first predicted by computational studies and has recently been demonstrated by laboratory experiments. Such trapped water may be present in various astrophysical environments and there is now evidence for its presence in the diffuse interstellar medium (ISM) and in extraterrestrial particles. We present here new results of a laboratory study of the phenomenon of trapping (strong bonding) of water molecules by silicates. We show that the efficiency of the trapping is strongly dependent on the properties and composition of the surface. Our results point out that the presence of trapped water should be due to the hydrophilic properties of the silicate surface and that the nature of the trapping is physical (physisorption rather than chemisorption). We demonstrate that water can be trapped on silicates up to temperatures of about 470 K, which speaks for the presence of wet silicate grains in the terrestrial planet formation zone in planet-forming disks. Studying the thermal and UV stability of trapped water, we conclude that the detection of trapped water in the diffuse ISM speaks for its efficient continuous formation. We discuss our results as relevant to fundamental scientific questions, such as the oxygen depletion problem, the origin of water on Earth, and the formation of rocky planets.

Keywords: Interstellar dust, Surface processes, Laboratory astrophysics
A Multiwavelength Light-curve Model of the Classical Nova V339 Del: A Mechanism for the Coexistence of Dust Dip and Supersoft X-Rays. The classical nova V339 Del 2013 is characterized by a 1.5 mag dip of the V light curve owing to a dust shell formation, with which soft X-ray emissions coexist. We present a Strömgren y-band light curve, which represents continuum emission, not influenced by strong [O III] emission lines. The y light curve monotonically decreases in marked contrast to the V light curve that shows a 1.5 mag dip. We propose a multiwavelength light-curve model that reproduces the y and V light curves as well as the gamma-ray and X-ray light curves. In our model, a strong shock arises far outside the photosphere after optical maximum, because later ejected matter collides with earlier ejected gas. Our shocked shell model explains optical emission lines, Hα, hard X-ray, and gamma-ray fluxes. A dust shell forms behind the shock that suppresses [O III]. This low flux of [O III] shapes a 1.5 mag drop in the V light curve. Then, the V flux recovers with an increasing contribution from [O III] lines, while the y flux does not. However, the optical depth of the dust shell is too small to absorb the photospheric (X-ray) emission of the white dwarf. This is the reason that a dust shell and soft X-ray radiation coexist. We determined the white dwarf mass to be M WD = 1.25 ± 0.05 M ☉ and the distance modulus in the V band to be (m ‑ M) V  = 12.2 ± 0.2; the distance is d = 2.1 ± 0.2 kpc for the reddening of E(B ‑ V) = 0.18.

Keywords: X-ray astronomy, High energy astrophysics, Fast novae, Dust formation, Shocks, Gamma-ray astronomy, Classical novae
Formation of Limb-brightened Radio Jets by Angle-dependent Energy Extraction from Rapidly Rotating Black Holes. Using general relativistic magnetohydrodynamic simulations, it has been suggested that the rotational energy of a rapidly rotating black hole (BH) is preferentially extracted along the magnetic field lines threading the event horizon in the middle and lower latitudes. Applying this angle-dependent Poynting flux to the jet downstream, we demonstrate that the jets exhibit limb-brightened structures at various viewing angles, as observed from Mrk 501, M87, and Cyg A between 5° and 75°, and that the limb brightening is enhanced when the jet is collimated strongly. It is also found that the jet width perpendicular to the propagation direction shrinks at the projected distance of the altitude where the jet collimates from a conical shape (near the BH) to a parabolic one (in the jet). Comparing with Very Long Baseline Interferometry observations, we show that this collimation takes place within the deprojected altitude of 100 Schwarzschild radii from the BH in the case of the M87 jet.

Keywords: High energy astrophysics, Kerr black holes, Relativistic jets, Plasma astrophysics, General relativity, Astronomical simulations
JWST MIRI Imager Observations of Supernova SN 1987A. There exist very few mid-infrared (IR) observations of supernovae (SNe) in general. Therefore, SN 1987A, the closest visible SN in 400 yr, gives us the opportunity to explore the mid-IR properties of SNe, the dust in their ejecta, and the surrounding medium and to witness the birth of an SN remnant (SNR). The James Webb Space Telescope, with its high spatial resolution and extreme sensitivity, gives a new view on these issues. We report on the first imaging observations obtained with the Mid-InfraRed Instrument (MIRI). We build temperature maps and discuss the morphology of the nascent SNR. Our results show that the temperatures in the equatorial ring (ER) are quite nonuniform. This could be due to dust destruction in some parts of the ring, as had been assumed in some previous works. We show that the IR emission extends beyond the ER, illustrating the fact that the shock wave has now passed through this ring to affect the circumstellar medium on a larger scale. Finally, while submillimeter Atacama Large Millimeter Array observations have hinted at the location of the compact remnant of SN 1987A, we note that our MIRI data have found no such evidence.

Keywords: Supernova remnants, Type II supernovae, Core-collapse supernovae
Unraveling the Cr Isotopes of Ryugu: An Accurate Aqueous Alteration Age and the Least Thermally Processed Solar System Material. The analysis of samples returned from the C-type asteroid Ryugu has drastically advanced our knowledge of the evolution of early solar system materials. However, no consensus has been obtained on the chronological data, which is important for understanding the evolution of the asteroid Ryugu. Here, the aqueous alteration age of Ryugu particles was determined by the Mn–Cr method using bulk samples, yielding an age of 4.13 + 0.62/‑0.55 Myr after the formation of Ca–Al-rich inclusions (CAI). The age corresponds to 4563.17 + 0.60/‑0.67 Myr ago. The higher 55Mn/52Cr, ɛ 54Cr, and initial ɛ 53Cr values of the Ryugu samples relative to any carbonaceous chondrite samples implies that its progenitor body formed from the least thermally processed precursors in the outermost region of the protoplanetary disk. Despite accreting at different distances from the Sun, the hydrous asteroids (Ryugu and the parent bodies of CI, CM, CR, and ungrouped C2 meteorites) underwent aqueous alteration during a period of limited duration (3.8 ± 1.8 Myr after CAI). These ages are identical to the crystallization age of the carbonaceous achondirtes NWA 6704/6693 within the error. The ɛ 54Cr and initial ɛ 53Cr values of Ryugu and NWA 6704/6693 are also identical, while they show distinct Δ'17O values. This suggests that the precursors that formed the progenitor bodies of Ryugu and NWA 6703/6693 were formed in close proximity and experienced a similar degree of thermal processing in the protosolar nebula. However, the progenitor body of Ryugu was formed by a higher ice/dust ratio, than NWA6703/6693, in the outer region of the protoplanetary disk.

Keywords: Carbonaceous chondrites, Asteroids