Abstract Fast γ -ray variability in blazars remains a central puzzle in high-energy astrophysics, challenging standard shock acceleration models. Blazars, a subclass of active galactic nuclei with jets pointed close to our line of sight, offer a unique view into jet dynamics. Blazar γ -ray light curves exhibit rapid, high-amplitude flares that point to promising alternative dissipation mechanisms such as magnetic reconnection. This study uses three-dimensional relativistic magnetohydrodynamic (RMHD) and resistive relativistic magnetohydrodynamic (ResRMHD) simulations with the PLUTO code to explore magnetic reconnection in turbulent, magnetized plasma columns. Focusing on current-driven kink instabilities, we identify the formation of current sheets due to magnetic reconnection, leading to plasmoid formation. We develop a novel technique combining hierarchical structure analysis and reconnection diagnostics to identify reconnecting current sheets. A statistical analysis of their geometry and orientation reveals a smaller subset that aligns closely with the jet axis, consistent with the jet-in-jet model. These structures can generate relativistically moving plasmoids with significant Doppler boosting, offering a plausible mechanism for the fast flares superimposed on slowly varying blazar light curves. These findings provide new insights into the plasma dynamics of relativistic jets and strengthen the case for magnetic reconnection as a key mechanism in blazar γ -ray variability.

ABSTRACT This work presents possible quasi-periodic oscillations (QPOs) in the Transiting Exoplanet Survey Satellite observations of blazars that are in the 157-month hard X-ray survey done by Swift’s Burst Alert Telescope. We report observations from four sources, J1104.4+3812, J1654.0+3946, J0353.4−6830, and J1941.3−6216, that show at least 3$\sigma$ local significance in generalized Lomb–Scargle periodogram and weighted wavelet Z-transform methods. These results are also checked using a continuous autoregressive moving average analysis that also predicts the absent data tentatively using stochastic differential equations. Each of these four sources exhibits a nominal QPO signal frequency in the range of 0.5–1.1 d$^{-1}$, resulting in at least five putative cycles. However, when the number of frequencies examined and the number of sources examined are both taken into account, the global significances are reduced to $\approx 2.2\sigma$ for J1654.0+3964 (Mrk 501), and to $\approx 1.9\sigma$ for other sources. These QPOs are thought to arise from the processes within the relativistic jet. Plausible explanations include the kink instability, which arises due to current-driven instabilities in the plasma or the precession of substructures, or mini-jets, within the jets.

Abstract We report that kink-driven magnetic reconnection serves as an eruption mechanism for a laboratory jet. A flux rope is formed and becomes a filamentary jet. The jet becomes unstable due to kink instability when the Kruskal–Shafranov instability criterion is met, leading to an inflow of reconnecting fields. As a result of kink-driven magnetic reconnection, ions are substantially energized, resulting in enhanced acceleration of the jet. Based on the evidence observed from this laboratory experiment, we propose that kink-driven magnetic reconnection might act as a key driver for laboratory jet eruptions and might be relevant to solar jets associated with kink instability and magnetic reconnection.

Abstract We present various time series analysis methods to analyze multiple-sector observations of bright AGN from the Transiting Exoplanet Survey Satellite (TESS) and examine whether issues such as gaps and noise in these data can be mitigated. We determine variability timescales and search for quasi-periodicity using these methods and assess any differences. In this paper, we present an analysis of the ≈ 300-day TESS observation of a blazar 3C 371 using power spectrum density, structure-function, and weighted wavelet Z-transform approaches. To reduce the effect of gaps and noise, Continuous auto-regressive moving averages, Bartlett periodogram, and wavelet decomposition methods are used. We have also used recurrence analysis to account for the nonlinearity present in the data and to quantify variability or periodicity as the recurrent state. Considering the entirety of the TESS observations, we derive the variability timescale to be around 4.5 days. Sector-wise analysis found variability timescales in the range of 3.0–7.0 days, values that are found to be consistent using different methods. When analyzing multiple sectors together, significant variability, which could be quasi-periodic oscillations (QPOs), of duration 3–6 days in individual segments, is detected. These may be attributed to the kink instabilities developed in the jet or the existence of mini-jets inside a jet undergoing precession. We find that these methods, when applied appropriately, can be used to study the variability in TESS data. The noise present in these TESS observations can be minimized using Bartlett’s periodogram and wavelet decomposition to recover the real stochastic variability.

This evolution may comprise stages, such as arise, generate, develop, increase, and trigger, from initial linear to complex nonlinear chaos/turbulence. Based on the improved relativistic hybrid particle-in-cell and lattice Boltzmann method development in Paper I of this series of studies [Zhu et al., “Relativistic HPIC-LBM and its application in large temporal-spatial turbulent magnetic reconnection. Part I. Model development and validation,” Appl. Math. Modell. 78, 932–967 (2020); Zhu et al., “Electron acceleration in interaction of magnetic islands in large temporal-spatial turbulent magnetic reconnection,” Earth Planet. Phys. 3, 17–25 (2019); Zhu et al., “Relativistic HPIC-LBM and its application in large temporal-spatial turbulent magnetic reconnection. Part II. Role of turbulence in the flux rope interaction,” Appl. Math. Modell. 78, 968–988 (2020); Wang and Zhu, “HIP-based heterogeneous parallel 3D LBM fluid simulator (HIP-LBM3D) V1.0 [software],” Patent No. 2023SR0533996 (6 March 2023); Zhu et al., “Scalable simulations of 3D turbulence fine structure in nanoflare using a novel plasma statistical algorithm,” in Proceedings of the 5th International Conference on Statistics: Theory and Applications (ICSTA'23), 2023; Yan et al., “A new fluid numerical RHPIC-LBM algorithm from statistical physics,” China Patent No. 202311118994.2; Wang et al., “HIP-based heterogeneous parallel 3D LBM HD simulator (HIP-HDLBM) V1.0 [software],” Patent No. 2023SR0533996. (March 6, 2023); Zhu et al., “Software development of GeV-level-SEPs-induced extreme space weather disasters with plasma statistical physics theoretical model on domestic DCU accelerator heterogeneous supercomputer.” in Progress Report on China Nuclear Science &Technology: Computational Physics, 2024; Fu et al., “A new ARM-based CPU implementation of the RHPIC-LBM code,” in 32nd General Assembly International Union, 2024; Wang and Zhu, “HIP-based heterogeneous parallel 3D LBM MHD simulator (HIP-MHDLBM) V1.0 [software],” No. 2024SR2094116 (December 16, 2024); Zhu and Wang, “Dynamic-magnetohydrodynamic-kinetic coupled algorithm for RHPIC-LBM code,” China Patent No. 202511005823.8; Ma, “Fine-structure turbulence-induced dissipation–diffusion in the large temporal-spatial current sheet with mean field theory,” M.S. thesis (School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, China, 2025); Ma et al., “Fine-structure investigation of the turbulence-induced dissipation-diffusion in Flare-CME current sheets,” Prog. Astron. 43(4), 1–26 (2025); Zhu et al., “Fine-structure investigation of turbulence-induced dissipation-diffusion in a nanoflare-loop with improved relativistic hybrid particle-in-cell and lattice Boltzmann method. I. Explicit expression and model,” Phys. Fluids ▪, ▪ (2025)], we validated, through simulations on a supercomputing platform, the basic features of turbulence and instabilities by considering anomalous viscosity and resistivity, and breaking of frozen-in condition. The simulation revealed that U-turbulence-induced viscosity dissipation-diffusion and B-turbulence-induced resistivity dissipation–diffusion interactions would lead to the following vortices/eddies—splitting and phase separating instabilities: (i) vortices/eddies-separation interface instabilities consisting of coupled B-Rayleigh–Taylor and U-Rayleigh–Taylor instabilities, and coupled B-Kelvin–Helmholtz and U-Kelvin–Helmholtz instabilities; (ii) twisted flux loop compression/expansion induced instabilities consisting of current/magnetic-driven multimode (m = 0, 1, 2, 3, 4……) Z- and {theta-pinch kink instabilities; and (iii) coupled B- and U-vortex shedding instabilities. This finding provides a comprehensive theoretical framework for elucidating the origins and sources of solar energetic particles (SEPs). It lays a pivotal foundation for clarifying the wave–particle interaction mechanisms responsible for extreme GeV-level SEP events, thereby facilitating the development of an early warning system for predicting SEP-induced space weather disasters.

A 50 minute Coronal Kink Oscillation and Its Possible Photospheric Counterpart

Abstract In this paper, we conduct a linear stability analysis of magnetized and/or rotating jets propagating in ambient matter that is also magnetized and/or rotating, having in mind the application to the jet penetrating the core/envelope of a massive star. We solve the linearized magnetohydrodynamic (MHD) equations in the nonrelativistic regime by Laplace transform in time and Fourier transform in space. In this formulation, all unstable modes with the same translational and azimuthal wave numbers can be obtained simultaneously by searching for pole singularities in the complex plane. In order to unambiguously determine their driving mechanisms, we evaluate the second-order perturbation of the MHD Hamiltonian for individual eigenfunctions derived at these singular points. We identify in our nonrotating models the Kelvin–Helmholtz instability (KHI) as one of the shear-driven modes and the current-driven instability such as the kink instability (KKI). In rotational models, we also find the magnetorotational instability (MRI) as another shear-driven mode. In some cases, we find that a mode changes its character continuously from KKI to KHI (and vice versa) or from MRI to KHI as the jet velocity is increased.

Abstract A hybrid machine learning model, which combines a shallow convolutional neural network and a long short-term memory (CNN-LSTM) network, has been developed to automate the detection of kink oscillations in coronal plasma loops within large volumes of high-cadence sequences of imaging data. The network was trained on a set of 10,000 synthetic data cubes designed to mimic sequences of coronal images, achieving an accuracy greater than 98% on this synthetic data set. The model was then applied to detect kink oscillations in real data cubes of coronal active regions observed with Solar Dynamics Observatory/Atmospheric Imaging Assembly in the 171 Å channel. This data set consisted of 50 samples with visually detected kink oscillations and 128 samples without. Each sample covered an area of 260 × 260 pixels in the spatial domain and a duration of 30 minutes with a 12 s cadence in the time domain. Both off-limb and on-disk regions of interest were used. The data were preprocessed by median filtering in the time domain, and Gaussian smoothing and contrast-limited adaptive histogram equalization in the spatial domain. In the real data set, the performance of the model was 83.7%. The model is fully available in open access. We regard the CNN-LSTM model developed as a first step toward creating robust tools for routine solar coronal data mining in the context of coronal oscillation studies.

Kink instability of partially ionized plasma jets in the solar atmosphere I: Aligned jets

Abstract Kink oscillations in coronal loops have been extensively studied for their potential contributions to coronal heating and their role in plasma diagnostics through coronal seismology. A key focus is the strong damping of large-amplitude kink oscillations, which observational evidence suggests is nonlinear. However, directly identifying the nonlinearity is a challenge. This work presents an analytic formula describing nonlinear standing kink oscillations dissipated by turbulence, characterised by a time-varying damping rate and period drift. We investigate how the damping behaviour depends on the driving amplitude and loop properties, showing that the initial damping time τ is inversely proportional to the velocity disturbance over the loop radius, V i /R. Using Markov Chain Monte Carlo fitting with Bayesian inference, the nonlinear function better fits an observed decaying kink oscillation than traditional linear models, including exponential damping, suggesting its nonlinear nature. By applying a Bayesian model comparison, we establish regimes in which nonlinear and linear resonant absorption mechanisms dominate based on the relationship between the damping rate τ/P and V i /R. Additionally, analysis of two specific events reveals that while one favours the nonlinear model, the other is better explained by the linear model. Our results suggest that this analytical approximation of nonlinear damping due to turbulence provides a valid and reliable description of large-amplitude decaying kink oscillations in coronal loops.

Abstract We report the coexistence of decaying and decayless kink oscillations within a single bundle of coronal loops during the X6.3-class solar flare on 2024 February 22. Using coordinated observations from Geostationary Operational Environmental Satellite, Solar Dynamics Observatory/Atmospheric Imaging Assembly, Advanced Space-based Solar Observatory, and New Vacuum Solar Telescope, we analyze five flare-activated coronal loops (S1–S5) and identify distinct oscillation regimes in different segments. Time–distance and curve-fitting analyses of the five selected coronal loops reveal a broad range of oscillation amplitudes (1.1–7.1 Mm) and periods (119–630 s). In loop S2, decayless oscillations with a period of 274.6 ± 1.0 s and nearly constant amplitude are observed to coexist for a period of time with rapidly decaying oscillations of a similar period, 271.1 ± 1.7 s. The differential emission measure diagnostics indicate strong spatial variation in magnetic field strength, decreasing from 30 G near the flare core to 11 G in the peripheral loops. These variations in oscillation regimes and magnetic field strength imply that the local plasma environment strongly influences wave decaying processes. These results suggest that magnetic topology and local plasma conditions play a key role in modulating the wave decaying behavior.

Abstract We present an analysis of the magnetic mechanism of an X6.4-class confined flare in NOAA Active Region (AR) 13590 on 2024 February 22. Despite a pre-existing magnetic flux rope (MFR) embedded within a null-point topology, the flare produced only a localized jet without an associated coronal mass ejection. Using data from the Solar Dynamics Observatory and nonlinear force-free field extrapolations, we traced the formation and evolution of the MFR, which developed under photospheric shearing motions but remained weakly twisted (with twist number being lower than 1.3) and below the thresholds for kink instability. Meanwhile, the MFR is located at heights where the decay index (n ≤ 1.0) of the overlying field was insufficient to trigger torus instability. Furthermore, we calculated two important parameters measuring the non-potentiality of the AR, one is the ratio of the free energy to the potential-field energy, and the other is the ratio of the non-potential helicity to the square of the magnetic flux. Both the two parameters were significantly lower than critical values for eruptive flares. These factors, combined with the stabilizing influence of the strong overlying field, confined the MFR and limited the eruption to a jet. Our findings highlight the importance of both local magnetic properties and global energy constraints in determining the eruptive potential of solar flares.

Abstract Linear growth of internal kink mode is investigated using a kinetic-MHD hybrid simulation model under realistic tokamak conditions. By comparing purely fluid (single-fluid MHD) simulations with kinetic thermal ion simulations using various coupling schemes, it is demonstrated that thermal-ion effects—including finite orbit width and ion pressure anisotropy—can significantly stabilize the internal kink mode. The maximum perturbation of distribution function aligns with resonance regions and near the passing-trapped boundary, indicating outward transport and redistribution of thermal ions. The net positive energy transfer from the mode to thermal ions leads to a reduction in growth rate. These results underscore the importance of incorporating thermal ion kinetics when modeling internal kink instabilities in fusion plasmas.

Abstract A series of events featuring decaying Transverse Coronal Loop Oscillations is examined utilizing high‐resolution observations from the Atmospheric Imaging Assembly on board Solar Dynamic Observatory and Extreme Ultraviolet Imager from Solar Terrestrial Relations Observatory twin spacecrafts, A (ahead) and B (behind). We used two distinct methods, coronal seismology and extrapolations, independently to assess the coronal magnetic field values within oscillating loops. For the coronal seismology, we performed stereoscopic tracing of coronal loops to obtain an accurate measurement of their lengths. Subsequently, we estimated the oscillation parameters such as amplitude, period, phase, and damping time. Using the periods of oscillations and loop lengths, we calculated average magnetic field values within the oscillating coronal loops, ranging from 12 to 146 G. On the other hand, we performed non‐linear extrapolations to match field lines with the coronal loops, resulting magnetic field values between 54 and 187 G. Our findings indicate that extrapolated field lines exhibited slightly higher values than those obtained through coronal seismology, though both methods provided reasonable estimates of the magnetic field strengths in the analyzed coronal loops.

Context. Although vortices have been observed in the solar atmosphere over the past few decades, vortices within the fine structures of solar filaments (prominences) have rarely been reported. Aims. This report is to study the vortices inside the fine structures of a filament (case 1) and a prominence (case 2), and to reveal the dynamic evolution of these vortices. Methods. Based on multi-wavelength observations from the New Vacuum Solar Telescope (NVST) and the Solar Dynamics Observatory, we tracked the evolution of the vortices inside the fine structures of the filament and the prominence by using the technique of the differential affine velocity estimator. Results. In case 1, we detected a clockwise vortex within the spine of a filament in the southwest of the solar disc on 3 June 2023. The average projection speeds of the vortex in the NVST Hα line and the Atmospheric Imaging Assembly (AIA) 171 Å wavelength were 1.16 ± 0.09 km s−1 and 4.30 ± 0.91 km s−1, respectively. In case 2, a counterclockwise single vortex first appeared within a prominence on 6 September 2023 at the northwestern limb of the Sun, with average projection speeds of 2.56 ± 0.03 km s−1 and 2.86 ± 0.76 km s−1 in the NVST Hα and AIA 193 Å observations, separately. Then, several plumes were observed and intruded into the early single vortex. Subsequently, this single vortex split into three vortices. Conclusions. We suggest that the internal kink instability may contribute to the formation of the single vortex in both cases. The intrusions of the plumes in case 2 possibly perturb the magnetic field of the single vortex and thus lead to its split. These results imply that the upward disturbance from the lower atmosphere can significantly change the structure and kinematic characteristics of the upper atmosphere.

Abstract In this paper, we carry out multiwavelength and multiview observations of the eruption of an intermediate prominence originating from the farside of the Sun on 2023 March 12. The southeast footpoint of the prominence is located in NOAA Active Region 13252. The eruption generates a B7.8 class flare and a partial halo coronal mass ejection (CME). The prominence takes off at 02:00 UT and accelerates for nearly 3 hr. Rotation of the southeast leg of the prominence in the counterclockwise direction is revealed by spectroscopic and imaging observations. The apex of the prominence changes from a smooth loop to a cusp structure during the rising motion, and the northwest leg displays a drift motion after 04:30 UT, implying a writhing motion. Hence, the prominence eruption is most likely triggered by ideal kink instability. For the first time, we apply the Graduated Cylindrical Shell modeling in 3D reconstruction and tracking of the prominence for nearly 2 hr. Both the source region (110°E, 43°N) and northwest footpoint (162°E, 44°N) are located. The edge-on and face-on angular widths of the prominence are ∼6° and ∼86°, respectively. The axis has a tilt angle of ∼70° with the meridian. The heliocentric distance of the prominence leading edge increases from ∼1.26 R ⊙ to ∼2.27 R ⊙. The true speed of the CME increases from ∼610 to ∼849 km s−1.

Context. Observations with modern radio interferometers are uncovering the intricate morphology of synchrotron sources in galaxy clusters, both those arising from the intracluster medium and those associated with member galaxies. Moreover, in addition to the well-known radio tails from active galactic nuclei, radio continuum tails from jellyfish galaxies are being efficiently detected in nearby clusters and groups. Aims. Our goal is to investigate the radio emission from the Ophiuchus cluster, a massive sloshing cluster in the local Universe (z = 0.0296) that hosts a diffuse mini halo at its center. Methods. To achieve this, we analyzed a 7.25 h MeerKAT L-band observation, producing sensitive images at 1.28 GHz with multiple resolutions. A catalog of spectroscopically confirmed cluster galaxies was used to identify and study the member galaxies detected in radio. Results. We discover thin threads of synchrotron emission embedded in the mini halo, two of which may be connected to the brightest cluster galaxy. We also report the first identification of jellyfish galaxies in Ophiuchus, detecting six galaxies with radio continuum tails, one of which extends for ∼64 kpc at 1.28 GHz, making it one of the longest detected at such a high frequency. Finally, we propose an alternative scenario to explain the origin of a bright amorphous radio source, previously classified as a radio phoenix, aided by the comparison with recent simulations of radio jets undergoing kink instability. Conclusions. In Ophiuchus, thin threads have been observed within the diffuse emission; a similar result was obtained in Perseus, another nearby cluster hosting a mini halo, suggesting that these structures may be a common feature in this kind of source. Moreover, radio continuum observations have proven effective in detecting the first jellyfish galaxies in both systems.

We present the overview of a new experimental apparatus that has been developed to create a single flux rope for studying magnetized plasma jet dynamics, with a focus on the roles of Magnetohydrodynamic instabilities in magnetic reconnection and ion heating. The plasma is generated using coplanar electrodes with a single gas nozzle to create a single flux rope, high-voltage capacitor banks, gas puff valves, and a background magnetic field coil. This setup enables controlled exploration of various plasma stability regimes by adjusting external parameters. A comprehensive suite of diagnostic tools-including a He-Ne interferometer, ion Doppler spectroscopy, and a magnetic field probe array-has been implemented to measure key plasma parameters such as density, temperature, and magnetic field. Initial findings indicate that the apparatus can create a single flux rope and sustain it as a stable jet, a kink-unstable jet, and pinched plasma. In particular, kink instability results in significant ion heating, suggesting that magnetic reconnection may be driven by kink instability. These findings provide valuable insights into plasma dynamics relevant to space physics and magnetized inertial fusion, where fluid instabilities and magnetic reconnection are frequently observed.

We present several examples of unusual evolutionary patterns in solar coronal loops that resemble cross-field drift motions. These loops were simultaneously observed from two vantage points by two different spacecraft: the High-Resolution Imager of the Extreme Ultraviolet Imager aboard the Solar Orbiter and the Atmospheric Imaging Assembly aboard the Solar Dynamics Observatory. Across all these events, a recurring pattern is observed: Initially, a thin, strand-like structure detaches and shifts several megameters away from a main or parent loop. During this period, the parent loop remains intact in its original position. After a few minutes, the shifted strand reverses its direction and returns to the location of the parent loop. Key features of this “split-drift” type evolution are: (i) the presence of kink oscillations in the loops before and after the split events and (ii) a sudden split motion at about 30 km s−1, with additional slow drifts, either away from or back to the parent loops, at around 5 km s−1. Co-temporal photospheric magnetic field data obtained from the Helioseismic and Magnetic Imager reveal that during such split-drift evolution, one of the loop points in the photosphere moves back and forth between nearby magnetic polarities. While the exact cause of this split drift phenomenon is still unclear, the consistent patterns observed in its characteristics indicate that there may be a broader physical mechanism at play. This underscores the need for further investigation through both observational studies and numerical simulations.

Entomopathogenic nematodes (EPNs) exhibit a bending-elastic instability, or kink, before becoming airborne, a feature previously hypothesized but not substantiated to enhance jumping performance. Here, we provide the evidence that this kink is crucial for improving launch performance. We demonstrate that EPNs actively modulate their aspect ratio, forming a liquid-latched α-shaped loop over a slow timescale [Formula: see text] (1 second), and then rapidly open it [Formula: see text] (10 microseconds), achieving heights of 20 body lengths and generating power of ∼104 watts per kilogram. Using a bioinspired physical model [termed the soft jumping model (SoftJM)], we explored the mechanisms and implications of this kink. EPNs control their takeoff direction by adjusting their head position and center of mass, a mechanism verified through phase maps of jump directions in numerical simulations and SoftJM experiments. Our findings reveal that the reversible kink instability at the point of highest curvature on the ventral side enhances energy storage using the nematode's limited muscular force. We investigated the effect of the aspect ratio on kink instability and jumping performance using SoftJM and quantified EPN cuticle stiffness with atomic force microscopy measurements, comparing these findings with those of Caenorhabditis elegans. This investigation led to a stiffness-modified SoftJM design with a carbon fiber backbone, achieving jumps of ∼25 body lengths. Our study reveals how harnessing kink instabilities, a typical failure mode, enables bidirectional jumping in soft robots on complex substrates like sand, offering an approach for designing limbless robots for controlled jumping, locomotion, and even planetary exploration.