Sazuna/UAT_keywords huggingface dataset:
Electron Energization in the Evolution of the Kelvin─Helmholtz Instability. The Kelvin─Helmholtz (K-H) instability is ubiquitous in space and astrophysical environments, playing a vital role in the transport of mass, momentum, and energy. Although it has been shown that the K-H instability can energize the electrons, the mechanisms of electron energization remain unclear. In this paper, two-dimensional full particle-in-cell simulations are used to explore the physical mechanisms governing electron energy variation during the evolution of the K-H instability. By tracking the temporal evolution of electron energy and incorporating the guiding-center theory, we quantitatively analyze the contributions from the parallel electric field, betatron, and Fermi mechanisms to electron energization. The results demonstrate that as the instability develops, vortices roll up and expand, with electron energization dominated by the betatron mechanism. Subsequently, small-scale magnetic reconnection disrupts the vortices, and the parallel electric field becomes the primary driver of electron energization. The vortices eventually merge into a larger vortex, and the betatron mechanism regains dominance due to the roll-up of the large-scale vortex. The Fermi mechanism contributes minimally to electron energization and even exhibits a cooling effect during vortices' expansion. This study elucidates the primary pathways of electron energization during the K-H instability evolution, providing theoretical insights into energy dissipation mechanisms in magnetized plasmas under velocity shear conditions.

Keywords: Solar energetic particles, Space plasmas, Plasma physics
SN 2025coe: A Multiple-peaked Calcium-strong Transient from a White-dwarf Progenitor. SN 2025coe is a calcium-strong transient located at an extremely large projected offset ∼39.3 kpc from the center of its host, the nearby early-type galaxy NGC 3277 at a distance of ∼25.5 Mpc. In this paper, we present multiband photometric and spectroscopic observations spanning ∼100 days postdiscovery. Its multiband light curves display multiple distinct peaks: (1) an initial peak at t ≍ 1.6 day attributed to shock cooling emission, (2) a secondary peak of MR, peak ≍ −15.8 mag at t ≍ 10.2 days powered by radioactive decay, and (3) a possible late-time bump at t ≍ 42.8 days likely caused by ejecta─circumstellar material/clump interaction. Spectral evolution of SN 2025coe reveals a fast transition to the nebular phase within 2 months, where it exhibits an exceptionally high [Ca II]/[O I] ratio larger than 6. Modeling of the bolometric light curve suggests an ejecta mass of  Mej=0.29−0.15+0.14M⊙ , a 56Ni mass of  M56Ni=2.4−0.05+0.06×10−2M⊙ , and a progenitor envelope with mass  Me=1.4−1.2+6.9×10−3M⊙  and radius  Re=13.5−11.1+64.1R⊙ . The tidal disruption of a hybrid HeCO white dwarf (WD) by a low-mass CO WD provides a natural explanation for the low ejecta mass, the small fraction of 56Ni, and the presence of an extended, low-mass envelope.

Keywords: Supernovae
The Tidal Torque Theory Revisited. II. Rotational Halo Properties. The peak model of structure formation was built more than 50 yr ago with the aim to address the origin of dark matter halo rotation in the tidal torque theory. Paradoxically, it has allowed one to explain and reproduce all halo properties found in cosmological simulations except their rotation, which remains to be understood. With the present two papers, we remedy this anomaly. In Paper I, we derived the angular momentum (AM) of protohalos centered on triaxial peaks of suited scale, taking into account that, to leading order, their density profile is smooth and homogeneous. Here we use that result to derive the AM of these objects, accounting for the fact that their actual density profile is slightly outward decreasing and lumpy so that they do not collapse monolithically at once, but progressively from inside out, undergoing mergers during the process. By monitoring in detail their resulting mass and AM growth, we characterize the spin distribution of the final halos and the precise mass and radial distribution of their inner mean specific AM. The results obtained explain and reproduce the rotational properties of simulated halos.

Keywords: Cosmology, Galaxy dark matter halos, Hierarchical cosmology, Dark matter
Simple Analytical Models of Grain Fragmentation in a Cometary Coma. Measurements by the dual Langmuir Probe (LAP) on board Rosetta in the inner coma of comet 67P/Churyumov─Gerasimenko revealed an unexpected ∼50% level of attenuation of the impinging solar extreme-ultraviolet (EUV) radiation while the comet was near perihelion. It was argued that this possibly could be a sign of upstream grain fragmentation. Here the effect of grain fragmentation on the EUV transmission fraction in a cometary coma is looked at through two simple analytical models: a continuous fragmentation model and an abrupt fragmentation model. We assume in both models radially expanding grains that readily reach their respective size-dependent terminal velocity. Without specifying driving mechanisms, we assume in the continuous fragmentation model that any grain splits into the same number of equal-sized fragments at a fixed size- and position-independent rate,  Γ , as long as said grain has not yet reached a prescribed minimal size from which point it cannot fragment further. In the abrupt fragmentation model, we instead assume that grains undergo complete fragmentation into minimal-sized subunits at a fixed cometocentric distance. In order for the models to produce transmission fraction profiles compatible with the aforementioned LAP observations, specific conditions appear necessary. A particularly puzzling aspect is the apparent requirement that a significant fraction of the dayside dust population disintegrate gradually or abruptly down to sizes of several tens of nanometers already by a distance of several 1000 km.

Keywords: Comets
Dual Core System Candidates: A Sample of Objects with Large Velocity Offset between Absorption and Narrow Emission Lines. We present a sample of 28 objects at z &lt; 0.3 from Data Release 16 of the Sloan Digital Sky Survey (SDSS DR16) with large velocity offset (&gt;200 km s−1) of narrow Hβ and Hα emission lines relative to absorption lines. Diagnostic classification via the Baldwin─Phillips─Terlevich diagram indicates that the sample comprises 12 AGNs, 12 composite galaxies, three H II galaxies, and one object of uncertain classification. A strong correlation is found between stellar mass and velocity dispersion. We examine the asymmetries of the narrow Hβ and find that the correlation between velocity offset and narrow Hβ skewness is negligible in both blue-shifted and red-shifted systems, suggesting that the rotating disk model may not fully explain the observed kinematics. The sample exhibits an asymmetric velocity-offset distribution, with more red-shifted (17) than blue-shifted (11) objects. No significant correlation is observed between velocity offset and line width in blue-shifted systems, while red-shifted systems show a weak anticorrelation for narrow Hα, which is inconsistent with the outflow model. The similarity in velocity offset between narrow emission lines supports the dual core system. Furthermore, the SDSS photometric images reveal eight objects with two cores and two with merger features. Based on the narrow emission line properties, the objects in our sample represent strong candidates for dual core systems exhibiting velocity offset. Extending this property to higher-redshift populations in the near future may facilitate the identification of merging supermassive black hole pairs at earlier cosmic epochs, providing critical constraints on their formation and evolution.

Keywords: Galaxy pairs, Active galaxies, Active galactic nuclei, Emission line galaxies
Can LIGO Detect Daylight Saving Time?. Yes, it can. Catalogs produced by networks of gravitational-wave interferometers are subject to complicated selection effects, and the gold standard remains direct measurements of the detection probability through large injection campaigns. I leverage public data products from the LIGO-Virgo-KAGRA Collaborations' third and fourth observing runs to show that there are nontrivial temporal variations within the detection probability that are well-described by a weekly cycle. There are clear differences between weekends and weekdays, between day and night (at the sites), and even between daylight saving time and standard time. I discuss possible causes for this behavior and implications.

Keywords: Gravitational waves
SN 2024aecx: A Double-peaked Rapidly Evolving Type IIb Supernova at 11 Mpc. We present the results of low-resolution spectroscopic and densely sampled multiband photometric follow-up of supernova (SN) 2024aecx. The SN was discovered in the spiral galaxy NGC 3521 (distance ∼ 11 Mpc) within a day after the explosion. The early spectra of SN 2024aecx show a weak signature of hydrogen lines, which disappeared in ∼30 days after the explosion. Light curves in all bands show a distinct feature of two peaks, and the first peak is likely due to the emission from shock cooling. The early-phase evolution of the light curve of SN 2024aecx is similar to the typical Type IIb events, but the decay rate in different bands (e.g., ∆m15 = 1.60 ± 0.05 mag, g band) is significantly faster in the postpeak phase. It attained the secondary maximum in ∼19 days (g band) with a peak absolute magnitude of Mg = ─17.94 ± 0.10 mag. The colors of SN 2024aecx tend to be redder in early epochs (&lt;8 days), then it grows bluer for a period, then redder again &gt;20 days after explosion. The analytical model fitting to the light curves reveals an envelope mass and progenitor radius in the ranges ∼0.03─0.24 M⊙ and ∼169─200 R⊙, respectively. Modeling of the pseudobolometric light curve suggests that synthesized 56Ni in the explosion was ∼0.15 M⊙ with ejecta mass and kinetic energy of ∼0.7 M⊙ and ∼0.16 × 1051 erg, respectively. The observational properties and modeling indicate that the progenitor of SN 2024aecx belongs to the category of extended progenitors.

Keywords: Type II supernovae, Supernovae, Core-collapse supernovae
Modulation of Whistler-mode Waves in the Solar Wind in the Vicinity of Earth's Moon. Ultra-low-frequency (ULF) waves are known to modulate high-frequency whistler-mode waves within the Earth's magnetosphere. Periodic bursts of whistler-mode waves are excited in association with ULF perturbations of plasma density and magnetic field. In this paper, we present a multievent study of whistler-mode waves modulated by ULF waves (0.05─1 Hz) observed by ARTEMIS in the vicinity of Earth's Moon, when it was in the solar wind region upstream of the quasiparallel bow shock. The events exhibit periodic whistler-mode wave bursts between 0.2 and 0.4 fce (electron gyrofrequency) coupled with ULF perturbations. Similar to modulation events observed within Earth's magnetosphere, some of the strongest whistler-mode wave bursts were observed when electron density and magnetic field perturbations were anticorrelated. In one of the events, a strong positive correlation between electron density and magnetic field perturbations was observed during the excitation of whistler-mode waves. The ULF waves develop a periodic enhancement in transverse electron flux anisotropy, which is positively correlated with the whistler-mode wave bursts, thus providing conditions favorable for their generation. The observation of these events on the quasiparallel side of bow-shock suggests a possible connection between the observed ULF waves and the upstream waves in the Earth's foreshock region. Finally, we examine the possibility that whistler-mode waves are trapped within localized regions of enhanced plasma density and magnetic field gradients produced by ULF waves in the solar wind.

Keywords: Space plasmas, Space weather, The Moon, Solar wind, Earth-moon system
ADF22-WEB: ALMA and JWST (Sub)kiloparsec-scale Views of Dusty Star-forming Galaxies in a z ≍ 3 Protocluster. We present a morphological analysis of Atacama Large Millimeter/submillimeter Array (ALMA) and James Webb Space Telescope (JWST) NIRCam images of nine dusty star-forming galaxies (DSFGs) at zspec ≍ 3.09, all embedded within the cosmic web filaments at the SSA22 protocluster core. The ALMA 870 μm and 1.1 mm images are obtained at spatial resolutions ranging from 0.5″ to 0.05″ (350 pc at z = 3.09). The high-resolution images enable us to resolve inner structures traced by dust continuum, identifying compact dusty cores, clumps, and offset ridges within bars. Sérsic profile fitting was performed for both ALMA 870 μm and NIRCam F444W images at comparable resolutions (∼0.15″). The Sérsic index measured for 870 μm, masking bright regions, indicates values close to unity, suggesting that dust emission arises from disks with superimposed compact core components. For the JWST F444W images (restframe ∼1 μm), the Sérsic indices range between nF444W ∼ 1─3, pointing to the coexistence of bulges and stellar disks in these DSFGs. A comparison of dust mass surface density, nF444W, and F200W─F444W color (restframe ∼0.5─1μm) reveals diversity among the DSFGs, likely reflecting different evolutionary stages, including some DSFGs with red cores, indicating ongoing rapid bulge growth phases heavily obscured by dust. The predominantly disklike morphologies observed in most DSFGs in the protocluster core contrast sharply with early-type morphologies that dominate the highest density environment in the local Universe. This suggests that we are witnessing the early formation of the morphology-density relation, as massive galaxies undergo rapid growth as late-type galaxies fueled by cosmic web gas filaments.

Keywords: Starburst galaxies, Protoclusters
Quantifying How Surface Complexity Influences Properties of the Solar Corona and Solar Wind. The Sun's magnetic field is a key driver in coronal heating and consequently solar wind acceleration. Remote measurement of the photosphere provides the magnetic surface boundary condition necessary for data-constrained 3D global coronal models. With one such model, we explore how the spatial resolution of the surface boundary condition influences the global properties of the magnetic field and coronal heating. Using spherical harmonic decomposition, we quantify how three different resolution simulations vary in the low and middle corona. Through examination of the magnetic field, the squashing factor, and the heating rate, we demonstrate that small-scale photospheric magnetic flux enhances heating across spatial regimes. We calculate 40% more heating in our best-resolution simulation compared to our base resolution. We describe a strong correlation between the structure of the magnetic field and the structure of the heating rate in the low corona across resolutions. These results provide key information as to what more efficient, low-resolution models might inherently miss. This can provide context to incorporate the effects of unresolvable features in future modeling efforts.

Keywords: Solar wind, Solar photosphere, Solar coronal heating, Solar corona
The Crab Nebula Revisited Using HST/WFC3. It has been over 24 years since the iconic Crab Nebula has been visited by the high spatial resolution eye of the Hubble Space Telescope (HST). The expanding nebula is dynamic on these timescales, with many of the outer filaments of the nebula known to show proper motions of 0 .″ 3 or more per year. Over time, it has become increasingly difficult to compare the fine-scale structure of the nebula with recent data at other wavelengths. We have re-observed the Crab in an HST Cycle 31 program using the Wide Field Camera 3 camera and filters similar to those previously used to make the existing mosaic that dates from 1999─2000 and was obtained with the WFPC2 camera. Two central fields were observed with the F487N filter, providing an uncontaminated hydrogen band for comparison. We also observed two primarily continuum band filters (F547M and F763M), allowing us to study the optical synchrotron nebula component of the Crab's emission. We compare these new data to the first epoch of WFPC2 data as well as to more contemporaneous near-IR/mid-IR imagery from JWST. Finally, we highlight two previously unrecognized groupings of filaments with similar emission characteristics that are nearly diametrically opposed from the pulsar but whose origin remains uncertain.

Keywords: Supernova remnants, Interstellar medium, Pulsar wind nebulae
Using Rapid Rotators as Tracers of Multiplicity Statistics as a Function of Stellar Density. Recent works have identified that rapidly rotating stars are predominantly binaries with separations of a few to a few tenths of an astronomical unit. This is a crucial range of separation that is often inaccessible to searches of binary stars, providing a unique opportunity to examine their statistical properties. In particular, we have performed an analysis of rapid rotators in young moving groups. We examined their fraction as a function of the stellar density of the population in which they are found. We find that there is a deficit of rapid rotators in dense clusters such as the Orion Nebula in comparison to the more diffuse parts of the Orion complex, as intracluster interactions with neighboring stars likely dissolve binaries with intermediate separations before they have had a chance to fully form. In contrast, in older populations with an age of ∼100 Myr, mass segregation redistributes binaries relative to single stars; thus, in such older regions, rapid rotators are predominantly found in the regions of higher stellar density. This work sheds light on both the conditions that lead to the formation of binary stars and their dynamical evolution.

Keywords: Young star clusters, Binary stars
A Deep Chandra X-Ray Survey of a Luminous Quasar Sample at z ∼ 7. We present new Chandra observations of seven luminous quasars at z &gt; 6.5. Combined with archival Chandra observations of all other known quasars, they form nearly complete X-ray observations of all currently known z ∼ 7 quasars with M1450 &lt; ─26.5, except for J0313−1806 at z = 7.642 and J0910−0414 at z = 6.636. Together with existing ground-based near-infrared spectroscopy and Atacama Large Millimeter Array observations, we investigate the correlations between X-ray emission (the X-ray luminosity LX and the optical/UV-to-X-ray spectral slope αOX) and various quasar properties (rest-UV luminosity L2500 Å, bolometric luminosity Lbol, C IV blueshift, and infrared luminosity LIR). We find most z &gt; 6.5 quasars follow a similar αOX─L2500 Å relation as z ∼ 1─6 quasars, but also display a large scatter. We find a potential correlation between αOX and the C IV blueshift, suggesting a soft optical/UV-to-X-ray spectral energy distribution shape is frequently associated with fast disk winds. Furthermore, we analyze the X-ray spectrum of 11 quasars at z &gt; 6.5 with Chandra detection, and find that the best-fit photon index, Γ, is 2.41 ± 0.27, which is likely driven by high accretion rates of z &gt; 6.5 quasars. In addition, we find there are no significant correlations between either LX and LIR, nor Lbol and LIR, suggesting no strong correlations between quasar luminosity and star formation luminosity for the most luminous quasars at z &gt; 6.5.

Keywords: Supermassive black holes, Early universe, High-luminosity active galactic nuclei, Broad-absorption line quasar, Quasars, X-ray quasars
Thread Separation and Expansion Observed in Multistranded Solar Coronal Loops. The theoretical expectation that coronal loops should expand with height contrasts with observations that typically show constant cross sections. We investigate the idea that this discrepancy results from loops being composed of fine threads whose expansion occurs below the resolution limits of instruments like Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA). In this paper, we present two significant findings: (1) several extended loops exhibit measurable expansion, suggesting length as a critical factor in detection capability, and (2) high-resolution Solar Orbiter/Extreme Ultraviolet Imager (EUI) observations have captured expanding loops in active regions. For both AIA and EUI data, we observe cases where thread separation is directly visible as the loops evolve. These findings complement our previous work indicating AIA loops may consist of relatively few threads. Collectively, these observations provide compelling evidence supporting the multithread model and offer a potential resolution to the long-standing loop expansion problem in solar coronal physics. However, the high densities and narrow temperature distributions of observed coronal loops remain unresolved.

Keywords: Active solar corona, Solar physics, Solar coronal heating, Solar coronal loops
Relativistic Jets and Winds in Radio-identified Supermassive Black Hole Binary Candidates. Supermassive black hole binary systems (SMBHBs) are thought to emit the recently discovered nHz gravitational wave background; however, not a single individual nHz source has been confirmed to date. Long-term radio-monitoring at the Owens Valley Radio Observatory has revealed two potential SMBHB candidates: blazars PKS 2131-021 and PKS J0805-0111. These sources show periodic flux density variations across the electromagnetic spectrum, signaling the presence of a good clock. To explain the emission, we propose a generalizable jet model, where a mildly relativistic wind creates an outward-moving helical channel, along which the ultrarelativistic jet propagates. The observed flux variation from the jet is mostly due to aberration. The emission at a lower frequency arises at a larger radius, and its variation is consequently delayed, as observed. Our model reproduces the main observable features of both sources and can be applied to other sources as they are discovered. We make predictions for radio polarization, direct imaging, and emission line variation, which can be tested with forthcoming observations. Our results motivate future numerical simulations of jetted SMBHB systems and have implications for the fueling, structure, and evolution of blazar jets.

Keywords: Blazars, Radio jets, Active galactic nuclei, Black holes
Probing the Cosmic Reionization History with JWST: Gunn─Peterson and Lyα Damping Wing Absorption at 4.5 &lt; z &lt; 13. We present a statistical analysis of Lyα absorption using 581 galaxies at z = 4.5─13 observed with multiple JWST/NIRSpec spectroscopy programs, including JADES, UNCOVER, CEERS, and GO/DDT. We carefully construct composite spectra binned by redshift with homogeneous UV properties (UV magnitudes, UV slopes, and Lyα equivalent widths) and identify significant Lyα forest signals in galaxies at z ∼ 5─6, which diminish toward higher redshifts. We also find UV continuum breaks at rest-frame 1216 Å that soften beyond z ≳ 6, confirming the effects of cosmic reionization through a self-consistent transition from Gunn─Peterson to Lyα damping wing absorption in galaxies. Fair comparisons of composite spectra with matched UV magnitudes and slopes across redshift reveal that UV-faint galaxies clearly show stronger Lyα absorption than UV-bright galaxies toward high redshift, providing insights into the topological evolution of reionization. We estimate Lyα transmission at the Gunn─Peterson trough and Lyα damping wing absorption by comparing the galaxy spectra to low-z (z ∼ 2─5) galaxy templates that include galactic and circumgalactic absorption and Lyα emission. Using these measurements together with reionization simulations, we derive volume average neutral hydrogen fractions of &lt;xH I&gt;=  0.00−0.00+0.12 ,  0.25−0.20+0.10 ,  0.65−0.35+0.27 ,  1.00−0.20+0.00 , and  1.00−0.40+0.00  at z ∼ 5, 6, 7, 9, and 10, respectively. These values broadly align with a reionization history characterized by a rapid transition around z ∼ 7─8, consistent with Lyα emitter observations. While the physical driver of this rapid reionization remains unclear, it may involve the emergence of hidden active galactic nucleus populations and/or the onset of Lyman-continuum escape from galaxies.

Keywords: Galaxy evolution, Reionization, High-redshift galaxies, Cool intergalactic medium