Some repeating fast radio bursts (FRBs) exhibit occasional extreme repetition rates, but very few show a sustained high activity level. One such hyperactive repeater is FRB 20220912A, which was discovered by CHIME/FRB Collaboration on 2022 September 12. Here, we present results from a long-term monitoring campaign of FRB 20220912A using the upgraded Giant Metrewave Radio Telescope (uGMRT) in the frequency range from 300 to 750 MHz. Over the course of nearly two years, we detected a total of 643 bursts in this frequency range. The source exhibited extreme activity for a few months after its discovery and sustained its active phase for more than 1.5 yr, with unsystematic modulations in the activity during this phase. The cumulative energy distributions in both bands show a break, consistent with other active repeaters such as FRB 20121102A, FRB 202011124A, etc., suggesting common underlying emission mechanisms. Moreover, we show that the shape of the energy distribution for FRB 20220912A remains broadly the same across a large range of frequencies and over time. Overall, the extended high activity, estimated total energy output, persistent power-law tails in the energy distributions, and lack of detectable short-timescale periodicity favor progenitor models invoking young dynamic magnetars, potentially emitting pulses across large ranges of rotation phase.
Coronal heating remains a long-standing problem in solar and astrophysical plasmas. Alfvén waves (AWs) can carry sufficient energy into the solar atmosphere, but how this energy is dissipated into particle heating is not well understood. In this work, based on the ubiquitous inhomogeneity in the solar magnetically structured atmosphere, we propose a self-consistent mechanism for heating the solar magnetic atmosphere by kinetic Alfvén waves (KAWs), which involves the resonant mode conversion (RMC) of AWs to KAWs. Our finding reveals that KAWs can be effectively generated via the RMC of AWs in the solar magnetically structured atmosphere, with the RMC efficiency E _KAW / E _AW ∼ 0.01–0.1. Based on the estimation of the AW intensity in different environments of the solar magnetic atmosphere, the KAWs generated by the RMC of AWs are sufficient to sustain the heating of this atmosphere. This work not only bridges the gap between the large-scale AW energy flux and the small-scale kinetic processes essential for heating, but also establishes a unified mechanism for heating the solar magnetic atmosphere by KAWs.
We present results from the Goldstone Apple Valley Radio Telescope (GAVRT) observations of active region (AR) 13465 during the 2023 October 14 eclipse. GAVRT is a 34 m radio dish located in Goldstone, CA, that produced near-daily maps of the Sun between 2023 September and 2025 January, at four simultaneous GHz-frequency bands, spanning 3.5–13 GHz. GAVRT tracked AR 13465 during the eclipse, which provided high (∼arcsec) angular-resolution structural information on coronal magnetic fields in the direction perpendicular to the Moon’s limb, independent of wavelength. GAVRT GHz-frequency observations are ideally suited for probing the solar corona above sunspots via gyroresonance emission, in which thermal electrons gyrating along strong magnetic field lines fully reveal the layer-by-layer density, temperature, and magnetic field structure up to heights of 20,000 km in the inner corona. For comparison against the observational data, we simulate the AR 13465 iso-Gauss intensity profiles using the Solar Dynamics Observatory (SDO) Helioseismic Magnetic Imager (HMI) photospheric magnetic field maps as input to the pyAMPP tool. We find broad consistency between the observed brightness temperature profiles across AR 13465 and the extrapolated magnetic field iso-Gauss intensity profiles. We show that harmonic s = 3 is consistent with both the magnetic field extrapolation data and the eclipse observations at all GHz frequencies. The magnetic field extrapolation validates the presence of magnetic field intensities in the inner corona at heights matching those required for the gyrofrequency harmonics for the GHz-frequency bands observed by GAVRT.
We present the first results from AMBRA simulation ( A STRID with M BH seeding from BRA HMA) evolved to z = 8. AMBRA combines the large cosmological volume and statistical power of ASTRID with the physically motivated gas-based black hole (BH) seeding models from BRAHMA . Motivated by James Webb Space Telescope’s (JWST) discoveries of massive BHs at z ≳ 9, AMBRA adopts a lenient heavy-seed prescription from the BRAHMA suite, allowing for the formation of 4 × 10 ^4−5 M _⊙ seeds in halos with star-forming, metal-poor gas. The seeding model is motivated by scenarios in which heavy seeds form through stellar collisions in star clusters or from the rapid growth of Population III remnants. The improved seeding model enables AMBRA to form BH seeds much earlier and more efficiently compared to ASTRID . This significantly enhances early BH growth, producing a z = 8 BH number density more than an order of magnitude higher than that in ASTRID over the mass range 10 ^5−7 M _⊙ . BHs reaching masses consistent with GN-z11 and CEERS-1019 typically originate in highly compact density peaks and undergo multiple early mergers. In these systems, ∼50% of BH masses by z = 11 is from BH mergers, after which gas accretion becomes the dominant growth channel. Without this early merger-driven assembly, ASTRID cannot reproduce the high-mass BH detected by JWST. Our results indicate that abundant early seed formation combined with frequent mergers can explain several JWST massive BH candidates without requiring sustained super-Eddington accretion. As a testable prediction, AMBRA yields ≈4 Laser Interferometer Space Antenna (LISA) detectable BH merger events per year at z ≥ 8, which is three orders of magnitude higher than that in ASTRID .
We introduce a spectral-model-independent spectral-shape metric, δ _rms , to probe phase-resolved spectral evolution in the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124. The δ _rms –luminosity relation reveals a reproducible convergence–redivergence behavior: spectra from two geometrically opposite pulse phases converge to near identity around ${L}_{{\rm{t}}}^{* }\sim 8.8\times 1{0}^{37}\,{\rm{erg}}\,{{\rm{s}}}^{-1}$ , with a mean shape difference of only ∼2%, and rediverge at higher luminosities, most prominently at higher energies. This strong phase-resolved spectral convergence coincides with a pulse-profile reversal and traces the same transition luminosities previously identified from broadband continuum evolution, including L _t ∼ 4.5 × 10 ^37 erg s ^−1 . These results suggest a possible luminosity-driven reweighting between a broadly distributed surface-reprocessed/reflected component and an increasingly important direct accretion-column contribution, while establishing δ _rms as a robust, spectral-model-independent diagnostic of radiation-geometry restructuring in bright accreting X-ray pulsars.
We combine imaging data from the HST, JWST, and ground-based millimeter facilities to investigate the correlation between star formation rate (SFR) and molecular gas at the ∼100 pc scale of H II regions in three nearby galaxies: NGC628, NGC5194, and NGC5236. The JWST 21 μ m maps of the three galaxies offer a unique insight into the dust-absorbed SFR at high resolution. We find that the relation between the surface densities of SFR and molecular gas has a slope of ∼1.85 in log–log scale, significantly steeper than previous results for nearby galaxies but closer to the trends found for molecular clouds in the Milky Way. The steep relation also holds on larger, ∼500 pc, scales, and results from the high-resolution imaging that cleanly isolates the star-forming region emission from the underlying galaxy’s diffuse contribution. The diffuse emission at 21 μ m is, in fact, found to correlate with the galaxy’s stellar mass. Comparisons with physical models of star formation are inconclusive; they overlap with the locus of the 100 pc data, but have difficulties in reproducing the data scatter. Possible exceptions are models that add a power-law tail to the gas density probability distribution due to the large range of free parameters allowed. We find that local H II regions, high-redshift star-forming clumps, and low- and high-redshift starburst galaxies form a single sequence of star formation over 3 orders of magnitude in gas surface density.
We present results from very long baseline interferometry (VLBI) observations of the nucleus in the lobe-dominated quasar 3C 207. These observations were completed at 8.4 GHz or 10.7 GHz (X band) from 1981 to 2010, spanning 29 yr. The nucleus of 3C 207 is the strongest and most variable in the 3CR complete sample of lobe-dominated quasars, which is under study to test relativistic jet models over a wide range of jet orientation angles. Images have typical resolutions of ∼0.5–1.0 mas and sensitivities of ∼0.1–0.2 mJy beam ^−1 . The VLBI core region shows multiple flux density outbursts from a stationary “true” core that feeds a “swinging component” ∼0.5 mas to the east. The position angle (PA) of the swinging component shows a long-term increase of ∼40°, with a short-term reversal of ∼10°. A one-sided, curved VLBI jet extends ∼25 mas eastward, with components spanning a PA range of ∼25°. The jet components have average apparent transverse velocities v _app ≈ 10 c . One component shows apparent acceleration from 7 c to 14 c at 2–3 mas from the true core, where the flow is redirected toward PA ∼ 90°. Another component shows marginal evidence for apparent deceleration. Individual jet components expand until reaching the recollimation zone. Our results are consistent with a physical model in which 3C 207 has quasi-periodic outbursts, jet precession by ballistic components on a conical surface with a small opening angle, and a recollimation process that modifies component motions and narrows the conical geometry on a scale of ∼100 pc.
In this pilot study, we investigate whether intracluster light (ICL) can serve as an observational discriminator of dark matter physics. The self-interacting dark matter (SIDM) model has gained increasing attention as a possible resolution to small-scale discrepancies between collisionless cold dark matter (CDM) simulations and observations, predicting distinct tidal interaction histories within galaxy clusters. We analyze Cluster-EAGLE zoom-in galaxy clusters resimulated from identical initial conditions in both CDM and SIDM frameworks. The morphological similarity between dark matter and multiple baryonic tracers (gas, all stars, galaxies, and the combined brightest cluster galaxy plus ICL, BCG+ICL) is quantified using the weighted overlap coefficient, a contour-overlap statistic. We find that dark matter is traced most accurately by BCG+ICL, followed by gas, all stars, and galaxies. Although the differences are modest, they are systematic: The collisionless tracers (all stars, galaxies, and BCG+ICL) show better correspondence with the dark matter distribution in CDM, while the relative advantage of BCG+ICL over gas is reduced in SIDM. This reduction is driven primarily by weaker BCG+ICL–dark matter correspondence in SIDM. Qualitatively, this behavior is consistent with the expectation that collisionless stellar components more naturally trace collisionless dark matter in CDM, whereas self-interactions in SIDM introduce an effective viscosity that weakens the dominance of BCG+ICL as a dark matter tracer relative to gas. Our results demonstrate the potential of ICL as a novel observational probe of dark matter physics and provide a first step toward using diffuse cluster light to constrain the nature of dark matter.
Abstract The One-hundred-deg 2 DECam Imaging in Narrowbands (ODIN) survey is conducting the widest-field deep narrowband (NB) imaging of the equatorial and southern skies. ODIN uses three custom-built NB filters that sample Ly α -emitting galaxies (LAEs) within thin cosmic slices centered at z = 2.4, 3.1, and 4.5. In this work, we utilize extensive DESI spectroscopy of ODIN-selected galaxies in the COSMOS and XMM-LSS fields to validate our LAE selection. Exposures of 2–4 hr with DESI yielded redshift confirmation of 3075 ODIN LAE candidates with NB magnitudes brighter than 26 mag. Restricting to objects that yield high-confidence redshifts, the confirmation rates are (93%, 96%, 92%) at z = (2.4, 3.1, 4.5). The primary contaminants consist of active galactic nuclei at the expected Ly α- redshift range and lower redshifts (C iv , C iii ]), with the remainder being star-forming galaxies ([O ii ] and [O iii ]). We find minimal contamination from [O ii ] emitters in our sample (≲1%), implying that our rest-frame equivalent width (REW) > 20 Å NB excess photometry requirement is sufficient to remove them.
The first rotational (de)excitation rate coefficients for CaO–He and CaS–He are reported and computed from new CCSD(T)-F12B potential energy surfaces (PESs) with a core–valence basis set. The global PES minima are −159.54 cm ^−1 and −22.7 cm ^−1 , respectively. Close-coupling calculations of the (de)excitation cross sections among the first 21 rotational levels are performed for both systems for collision energies up to 1000 cm ^−1 . Rate coefficients are obtained by thermal averaging over a Maxwell–Boltzmann velocity distribution for temperatures ranging from 5 to 150 K. Driven by the distinct potential well depths, the rate coefficients maintain a strict propensity for Δ j = ±1 transitions in CaO–He, whereas the shallower CaS–He system exhibits a clear crossover to Δ j = ±2 dominance within this range. Comparison between CaO–He and CaS–He shows that the ratio k _CaS−He / k _CaO−He ranges from 0.52 to 1.35 over the entire temperature range. The CaO–He rate coefficients are scaled to CaO–H _2 for non-LTE radiative transfer calculations of the four transitions (4→3, 5→4, 9→8, and 10→9) recently tentatively observed toward G+0.693−0.027. Owing to the large dipole moment of CaO, the line ratios are mainly density probes and exhibit a steep, temperature-insensitive critical-density switch near 10 ^6 ∼10 ^7 cm ^−3 . These data provide essential tools for determining physical conditions in interstellar clouds where CaO has been tentatively detected.
Recent XRISM observations suggest that gas mixing induced by sloshing contributes to core heating. We systematically investigate the suppression of cooling flows in galaxy cluster cool cores through three-dimensional hydrodynamic simulations that incorporate both sloshing-driven turbulence and active galactic nucleus (AGN) heating. The AGN heating is modeled as thermal energy input that mimics cosmic-ray heating. Sloshing is represented by simple waves with amplitudes α = 0, 0.15, and 0.3 times the sound speed and wavelengths λ = 200, 1000, and 2000 kpc. We evolve each model from an isothermal initial condition to t = 8 Gyr. Without AGN heating, sloshing suppresses cooling, but it cannot stop it completely unless the core is fully disrupted. Longer wavelengths promote deeper mixing and greater suppression. Sloshing can cause cooler gas to move more quickly than hotter gas. This phenomenon has been observed in a few clusters by XRISM. When AGN heating is included, the dense central gas is heated efficiently, substantially delaying or preventing the onset of a cooling flow. However, for intermediate wavelengths, sloshing can displace the densest gas away from the AGN heating zone, reducing the feedback effect and paradoxically enhancing net cooling relative to the wave-free case. These results highlight a nontrivial coupling between sloshing and AGN feedback, with implications for interpreting XRISM velocity and temperature maps of cool-core clusters.
We report the first observations of a long-duration very-high-energy (VHE; E>100 GeV) flare from BL Lacertae (VER J2202+422), taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). On 2022 October 15, the Fermi-Large Area Telescope (LAT) detected elevated GeV activity originating from this blazar. This triggered a multiwavelength campaign, which includes observations from VERITAS, Swift, NuSTAR, and select optical and radio observatories. VERITAS observed the source for a total of ∼9.8 hr between 2022 September 1 and 2022 December 1. An analysis of these data yields a ∼28 σ detection of the source. While previously observed VHE flares from BL Lacertae have lasted on timescales of minutes to days, VERITAS continued to detect flaring activity from the source for over a month (∼40 days) after the original flaring activity was detected with Fermi-LAT. Broadband spectral modeling shows that a synchrotron self-Compton (SSC) model with an external inverse-Compton component is preferred over a one-zone SSC model.
Modern astrophysics and cosmology increasingly rely on simulations and cross-survey analyses, yet differences in instrumentation, calibration, and modeling introduce distribution mismatches between simulated and observed datasets (domain shift). This occurs when the joint distribution of inputs and labels differs between the training (source) and target domains, so source-trained models underperform on the target. Domain adaptation (DA), the branch of transfer learning for this case—fixed task, shifted input–label distribution—provides principled ways to mitigate it. We study a concrete simulation-to-observation (sim-to-obs) case: semisupervised domain adaptation (SSDA) to adapt a four-class spectral classifier (high-redshift quasars, low-redshift quasars, galaxies, and stars) from DESI-based J-PAS mock catalogs to real J-PAS photometry. Because labels are plentiful in simulations but scarce in the target survey, our pipeline pretrains on labeled DESI→J-PAS mocks and adapts using a small, labeled J-PAS subset (of which only 242 are high-redshift quasars). We benchmark SSDA against a J-PAS–only-supervised model (same labeled subset) and a mock-only model-evaluated zero-shot on J-PAS, plus the same model on its in-domain mock test set (four evaluations total). On held-out J-PAS data, SSDA achieves a macro-F1 of 0.83 and a true positive rate of 0.90, versus 0.79/0.85 and 0.73/0.87 for the supervised and mock-only baselines. The gains come mainly from improved quasar classification, especially the high-redshift subclass (F1 = 0.68, versus 0.54 and 0.40 for those baselines), yielding better-calibrated candidate lists for spectroscopic targeting (e.g., WEAVE-QSO) and active galactic nucleus searches. This shows how a few labeled target examples enable robust, data-efficient transfer.
Coronal jets are highly dynamic phenomena in the solar atmosphere, yet their driving mechanisms remain an active topic of investigation. In this paper, we report a coronal jet triggered by the interaction between superpenumbral fibrils and a minifilament, based on coordinated observations from the New Vacuum Solar Telescope, the Chinese H α Solar Explorer, and the Solar Dynamics Observatory. The fibrils were anchored between the negative-polarity region of a sunspot and an emerging positive-polarity region associated with a moving magnetic feature (MMF). As the positive polarity migrated outward, the fibrils elongated and interacted with the minifilament, one of whose footpoints was rooted in preexisting negative-polarity fields. Intense brightenings at the interaction site, together with changes in the connectivity of the minifilament footpoint from the preexisting negative polarity to the sunspot, indicate the occurrence of magnetic reconnection. The event produced a narrow hot jet accompanied by a broader cool component. The cool plasma exhibited a clockwise rotation, providing evidence for the transfer of magnetic twist during reconnection. Persistent magnetic flux cancellation was observed before and during the jet eruption. These observations demonstrate that small-scale magnetic structures, such as MMFs, can significantly influence minifilament eruptions and highlight the important role of flux cancellation in triggering coronal jet activity.
Moon formation by a high-angular-momentum (high-AM) giant impact may be best able to explain Earth–Moon isotopic similarities. However, the excess AM must be subsequently removed for consistency with the Earth–Moon system. There are limited ways to achieve this. A leading mechanism is the evection resonance between the Earth, Moon, and Sun, which the early Moon would have encountered. It has been proposed that evection reduced the Earth–Moon angular momentum (AM) by a factor of >2, but this outcome is sensitive to the initial lunar orbit expansion rate, which was controlled by tidal dissipation in the Earth. Prior evection models adopt constant tidal parameters for the Earth. However, the Earth’s dissipative properties would have changed as its mantle cooled and solidified. Here, we model the Moon’s orbital evolution through evection, incorporating a physically motivated description for tidal dissipation in Earth following a high-AM impact. We present results for two limiting cases: one designed to isolate the variation in tidal dissipation due to Earth’s mantle cooling alone, while the other additionally includes inertial terms in the tidal deformation equations. The latter are important for the rapidly spinning initial Earth, and they produce a strongly enhanced, frequency-dependent dissipation. Using the full dissipation model, we find that evection resonance capture is sensitive to the Earth’s atmosphere properties and in all cases the Moon exits evection before enough AM is removed from the system. We conclude that it appears unlikely that the evection resonance alone can reconcile a high-AM Moon-forming impact with the present Earth–Moon system.
Stellar abundances reveal nonmonotonic [Y/Eu] and [Sr/Eu] evolution, a systematic decline with increasing [Eu/H] at low metallicity, a minimum at [Eu/H] ∼ −0.3, and then a rise at high metallicity. This behavior requires at least three distinct neutron-capture sources operating on different timescales. We develop a one-zone chemical-evolution model constraining their typical delay times, rates, and yield ratios. Reproducing the observed [Y/Eu] and [Sr/Eu] sequences requires a delayed r -process channel (most likely binary neutron-star (BNS) mergers) dominating Eu production (≳95% of total Eu). A prompt channel preferentially produces first-peak elements with minimal Eu, explaining the increasing [Y/Eu] at decreasing [Eu/H] below [Eu/H] ≲ −2.5, and delayed asymptotic giant branch s -process enrichment with delays greater than t _min = 0.3–0.6 Gyr reproduce the late-time upturn in Y (Sr). Our model quantitatively reproduces all constraints, including the large Δ[Y/Eu] ≈ 0.6 dex variation between the late-time rise [Eu/H] and the minimum value, the location of the minimum at [Eu/H] ∼ −0.3, and late-time rise. The first- to second-peak yield ratios correspond to [Y/Eu] ≈ −0.3 (prompt) and ≈−0.8 (BNS mergers). The observed Δ[Y/Eu] amplitude establishes a model-independent lower limit on the first- to second-peak yield ratio of ≳3.4 between the prompt and delayed channels, ruling out models with similar prompt and delayed yield ratios. These results demonstrate that explaining the observed heavy-element abundance patterns requires multiple channels with distinct nucleosynthetic signatures and operational timescales, providing constraints on the relative rates, delay times, and yield patterns of candidate production sites.
We present a broadband spectropolarimetric analysis of the extragalactic radio source RACS_0900-28_7036 using Spectra and Polarization in Cutouts of Extragalactic Sources (SPICE-RACS) DR2 observations with the Australian Square Kilometre Array Pathfinder (ASKAP). The source was selected for its large rotation measure (RM = 345.7 ± 0.2 rad m ^−2 ), substantial excess relative to the local foreground (ΔRM ≈ 171 rad m ^−2 ), and strong evidence of Faraday complexity ( σ _add / δσ _add ≈ 8.6). Observations span 803–1083 MHz in 36 spectral channels, enabling detailed characterization of Faraday rotation and wavelength-dependent depolarization. One-dimensional QU fitting and Bayesian model selection identify a multicomponent model comprising one Burn-slab component and two external Faraday dispersion (EFD) components (1 Slab + 2 EFDs) as the preferred description. The dominant astrophysical component exhibits RM ≈ 345.5 rad m ^−2 with modest Faraday dispersion ( σ _RM ≈ 3 rad m ^−2 ), consistent with the Galactic foreground RM at the source position (RM _Gal = 331.9 ± 33.1 rad m ^−2 ). A secondary broader component at RM ≈ 131.5 rad m ^−2 shows strong depolarization ( σ _RM ≈ 19.5 rad m ^−2 ), indicating an additional turbulent Faraday-active medium along the line of sight. The fractional polarization spectrum and q – u plane evolution further confirm multiple Faraday-active regions along the line of sight. These results demonstrate that ASKAP broadband spectropolarimetry can resolve complex Faraday structures and probe turbulent magnetized environments, providing a framework for systematic depolarization studies across the full SPICE-RACS catalog and enabling statistical investigations of Faraday complexity in diverse extragalactic radio sources.
Using nearly 17 yr of Fermi-LAT data, we analyzed the diffuse γ -ray emission associated with different spiral arms of the Milky Way in the ranges l = 105 ^∘ –145 ^∘ and b = −5 ^∘ to 5 ^∘ . The γ -ray emissions from these spiral arms all exhibited clear pion-bump features, which can be well explained by a power-law spectrum of cosmic-ray protons. The spectral indices corresponding to the three distinct spiral arms—the Local Arm, the Perseus arm, and the Outer Arm—are found to be approximately −2.75, −2.55, and −2.80, respectively. The energy densities of the cosmic rays above 10 GeV are estimated to be all around 0.2 eV cm ^–3 . We further compared our results with previous studies, which have established various propagation models predicting that cosmic-ray density decreases and spectra soften with increasing Galactocentric radius. We found higher densities and harder spectral indices than predicted in the outer Galaxy, suggesting possible contributions from a larger halo, slower magnetic field decay, or a combination of these and other effects. In particular, the spectral hardening observed in the Perseus arm may be attributed to locally enhanced cosmic-ray acceleration.
We investigate the spatial coherence of metal absorption lines in the circumgalactic medium using 4115 quasar pairs from Sloan Digital Sky Survey DR16. We identify 184 Mg ii (15 with dual detections) and 50 C iv (11 with dual detections) absorber pairs. The fraction of pairs with fractional equivalent width difference δW _r ≤ 0.5 declines with projected separation: for Mg ii , it drops from ∼52% at 0–25 kpc to ∼7% at 100–200 kpc, while for C iv , it decreases from ∼100% to ∼21% over 0–200 kpc. In every separation bin, C iv absorbers with δW _r ≤ 0.5 maintain a higher fraction than Mg ii absorbers. Similar results are obtained when the nondetections are treated as $2{\sigma }_{{W}_{{\rm{r}}}}$ upper limits in a survival analysis. The transverse autocorrelation function shows strong Mg ii clustering within 0–25 kpc, whereas the C iv excess remains relatively flat out to ∼100 kpc. These findings suggest that high-ionization C iv gas retains coherence over larger transverse scales than low-ionization Mg ii gas, in agreement with previous lensed quasar and high-resolution studies.
Type II spicules often fade rapidly from cool chromospheric lines, commonly interpreted as their heating to transition-region temperatures. Here we test whether apparent fading can also arise from a primarily kinematic visibility effect. Using high-resolution 2.5D ideal-MHD simulations, we show that transverse oscillations of a super-Alfvénic magnetized jet trigger the Kelvin–Helmholtz instability (KHI), which fragments the initially coherent jet into fine-scale strands. For the parameters of the reference simulation, linear triangular-jet theory predicts an antisymmetric-mode growth rate of γ _th ≃ 0.23 s ^−1 , quantitatively consistent with the early exponential growth rate inferred from the simulated boundary-vorticity diagnostic, γ _boundary ≃ 0.20–0.23 s ^−1 . The internal-energy evolution is used only as a control diagnostic; the thermal-energy gain remains small, Δ E _th / E _kin,0 ≃ 5.18%, indicating that the modeled fading is not produced by imposed thermodynamic heating. Forward modeling with an optically thin emission proxy ( I ∝ ρ ^2 ) shows that finite spatial resolution of observations strongly affects detectability. It is found that KHI begins at the jet boundary before the emission-dominating core is sufficiently fragmented to fade observationally. This leads to a visibility delay, Δ t = t _obs − t _phys , where the coherent transverse motion weakens while unresolved line-of-sight velocity dispersion increases. v _rms peaks at ≃2.65 km s ^−1 during the simulations, while σ _nonth reaches ≃3.20 km s ^−1 . We predict that DKIST-like diffraction-limited spatial resolution might recover some apparently faded events as fragmented fine-scale strands, while the Interface Region Imaging Spectrograph (IRIS)-like resolution will apparently fail.
