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Yosuke Mizuno

Publications and source records attributed to Yosuke Mizuno.

At least 19 recordsLinked to original sources
arXiv2026

Modulation-Frequency Dependence of Spatial Resolution in Optical Correlation-Domain Reflectometry

The spatial resolution of optical correlation-domain reflectometry (OCDR) has conventionally been described by an expression that is independent of the modulation frequency $f_m$, source linewidth $\delta\nu$, and receiver resolution bandwidth (RBW). However, our previous measurements showed that the spatial resolution $\Delta z$ improves with increasing $f_m$. Here, we develop a theoretical model for OCDR with a frequency shifter by evaluating the electrical power detected by an electrical spectrum analyzer and explicitly including $\delta\nu$ and the RBW $B$. The model predicts two regimes. At low $f_m$, $\Delta z$ decreases approximately in proportion to $1/f_m$, with the proportionality determined by the combined source and receiver spectral response. At high $f_m$, $\Delta z$ approaches a constant value determined by the modulation amplitude $\Delta f$ and independent of the source linewidth and RBW filter. Measurements at RBW = 1 MHz reproduced the transition between these regimes over correlation orders up to 2048. At RBW = 10 MHz, a Voigt representation of the spectral response overestimated $\Delta z$, whereas direct use of the measured unmodulated beat spectrum reduced the discrepancy to approximately 10 to 20%. These results provide a quantitative description of the modulation-frequency dependence of OCDR spatial resolution and clarify its trade-off with measurement range.

physics.optics↗
arXiv2026

Dynamics and Spectra-Polarimetric Signatures of GRMHD Simulations with Multiple Magnetic Loops

Relativistic jets are a common outcome of accretion onto black holes, yet their presence and variability depend strongly on the magnetic and dynamical state of the accretion flow. While some systems, such as Blazars and Quasars, launch powerful persistent jets, others, including the Galactic Centre black hole Sgr~A$^\star$, show only weak or transient outflows. The physical conditions leading to the onset or suppression of jet activity remain poorly understood. We investigate the accretion flow conditions that produce transient jets or inhibit jet formation, aiming to improve our understanding of black holes that accrete without strong, steady outflows. We further predict observational signatures in total and polarized emission for comparison with recent observations of Sgr~A$^\star$ in the quiescent state from the radio to the $\gamma$-ray regime. We perform three-dimensional GRMHD simulations of an accreting black hole surrounded by a torus threaded by a poloidal multi-loop magnetic field of alternating polarities. We follow the evolution of the accretion rate, magnetic flux, and jet power, and analyze angular momentum transport. In addition, radiative transfer calculations including Compton scattering are used to derive synthetic total and polarized emission. The simulations show strong variability in jet power while the initial magnetic polarity loops accrete, followed by weaker activity at later times as the system approaches a semi-MAD state. The emission from the disk is relatively stable, weakly polarized and consistent with the quiet state values reported for SgrA$^\star$. The resulting jet emission is strongly suppressed, depolarized by Faraday rotation and conversion in the surrounding cold plasma. Upscattering calculations yield near-infrared (NIR) high energy light curves that respect observational constraints of the quiescent NIR and X-ray fluxes in SgrA$^\star$

astro-ph.HE↗
arXiv2026

Effects of Ambient Medium Profiles on the Evolution of Relativistic Magnetized Jets

Relativistic radio-galaxy jets are conventionally divided into two morphological classes: FR~I and FR~II. Among them, FR~I jets have relatively low radio luminosities and edge-darkened morphologies, indicating they undergo substantial deceleration and disruption on sub-kiloparsec to kiloparsec scales, often developing a turbulent and plume-like morphology. Here, we investigate the evolution of relativistic magnetized jets in stratified ambient media using 2D and 3D relativistic magnetohydrodynamic simulations with several ambient profiles. When the jet and ambient pressures are initially balanced, a Bondi-like atmosphere confines the jet to a broad parabolic shape ($R_j\propto z^{0.649\pm0.003}$) and produces a series of recollimation shocks. Over-pressured jets instead produce a conical shape and allow the development of the current-driven kink instability in the downstream. Based on the simulations, we derive a kink-stability criterion that depends primarily on the jet power and ambient pressure. We also calculate multi-frequency emission maps using a special relativistic radiative transfer code. Each recollimation shock appears as a bright knot, resembling the knot complex downstream of HST-1 of the M87 jet, whereas a jet with a single recollimation shock develops a bright feature close to its base and thus exhibits an FR~I-like morphology.

astro-ph.HE↗
arXiv2026

Relativistic blob signatures in the M87 jet at sub-parsec scales

In this work, we present results from general-relativistic radiative-transfer calculations of black hole accretion and jet launching to reproduce the observed properties of the M\,87 jet at sub-parsec scales. For the first time, in the simulations we have included a blob component at the launching region of the jet that allowed us to reproduce the quasi-simultaneous low-energy spectral energy distribution ($10^{10} \text{ Hz} \leq \nu \leq 10^{16} \text{ Hz}$). Moreover, we obtain a better fit of the synchrotron emission in the self-absorption region ($\nu \leq 10^{11} \text{ Hz}$), showing that the inclusion of a blob component in our radiative transfer calculations results in a flatter spectrum ($\alpha_{22-86\ \text{GHz}}=0.08$). Additionally, our simulations improved the accuracy of the observed morphology of M\,87's jet, matching the data up to a distance of 0.6 mas from the core at 86 GHz. Our results reproduce the edge-brightened structure up to $\sim1.3$ mas, i.e., in a more extended region compared with previous studies, with a brighter southern edge. The obtained synthetic image of the jet reproduces additional observed knots along the southern edge.

astro-ph.HE↗
arXiv2026

Beat-spectrum design for 100-km-range optical correlation-domain reflectometry with localized 15-cm resolution

Conventional optical correlation-domain reflectometry (OCDR) based on sinusoidal frequency modulation exhibits a coupling between measurement range and spatial resolution because both are governed by the modulation frequency. Here, we formulate OCDR for arbitrary periodic frequency modulation and relate the modulation waveform to the resulting beat spectrum. By expressing the instantaneous optical frequency as a Fourier series, the beat spectrum is written as successive convolutions of the spectral contributions from the harmonic components. This formulation relates the harmonic composition of the modulation waveform to the spatial response. Periodic pseudo-random modulation (PPRM) was used to test this relation experimentally. We first measured the full-length reflectivity distribution along an approximately 100-km fiber using sinusoidal modulation and then performed PPRM-based random access interrogation near the fiber end. In the local measurement, two closely spaced reflection points were resolved with a correlation-peak width of approximately 15 cm. These results show that beat-spectrum design can reduce the range-resolution coupling of conventional sinusoidal-modulation OCDR and combine long-range surveying with localized high-resolution interrogation.

physics.optics↗
arXiv2026

Inverse Transfer in Non-helical 2D Collisionless Magnetic Turbulence: Island-Merger Picture with Kinetic Effects

Magnetic inverse transfer is often invoked to connect small-scale magnetic-field generation to larger coherence scales in high-energy and cosmological plasmas. The underlying magnetohydrodynamic (MHD) arguments combine two logically distinct ingredients: a bulk quantity that is asymptotically conserved in the limit of small resistivity, and a time scale determined by the decay dynamics. In this work, we explore whether this scenario still holds in decaying nonhelical turbulence formed by collisionless plasmas using particle-in-cell simulations. The simulations approximately satisfy $B^2\xi_B^2\simeq{\rm const}$ as in the MHD case, and the fitted exponents in $B^2\propto t^{-p}$ and $\xi_B\propto t^q$ obey $p\simeq2q$. Here $B^2\equiv\langle B_x^2+B_y^2\rangle$ is the average in-plane magnetic energy density, and $\xi_b$ is the magnetic integral scale. However, the decay time scale differs from the MHD case as inferred from the decay exponents. We found $p<1$ and $q<1/2$ in all cases with different initial magnetization $\sigma_0$, with both exponents lower than the MHD values and varying systematically with $\sigma_0$. The spectral peak also migrates toward lower wavenumber at a rate faster than the growth of $\xi_B$, indicating a broken self-similarity. The broken self-similarity is attributed to the appearance of kinetic scales in the magnetic energy spectrum due to pressure anisotropy and Larmor-scale magnetic structures. These results indicate that in astrophysical collisionless plasmas, including but not restrict to solar wind, pulsar-wind nebulae, interstellar medium, and cosmological plasmas, magnetic coherence can continue to grow by inverse transfer, but extrapolations based on MHD decay-time scaling can overestimate the rate of large-scale field growth.

astro-ph.HE↗
arXiv2026

Probing radiation micro-physics in M 87 I. Total intensity and broad-band spectra

Next generation Very Long Baseline Interferometers (VLBI) will provide dense sampling of the Fourier space together with high signal to noise ratios allowing to reliably observe and image faint jet structure in M 87 at mm-wavelength. The proposed next generation Event Horizon Telescope (ngEHT) and next generation Very Large Array (ngVLA) offers the unique capability to simultaneously resolve and image the accretion flow around the supermassive black hole in M 87 together with the jet launching and acceleration zone. In order to explore these capabilities and to provide theoretical expectations we perform general relativistic magnetohydrodynamic simulations of accretion on to black holes and jet launching. M 87 has been the target for multiple observations across the entire electromagnetic spectrum. Among these VLBI observations provide unique capability to resolve the jet structure down to several gravitational radii. In this work we provide possible observable signatures which will allow us to distinguish between different electron heating models and particle distributions. We use general relativistic magnetohydrodynamics and simulate the accretion of the magnetised plasma onto Kerr-black holes in 3D. The multi-frequency radiative signatures of these simulations are computed taking different electron heating and distribution functions into account. The results of our simulations show that with a dynamical range of $1\times 10^4$ and a frequency range from 86 GHz to 345 GHz observations with future VLBI arrays have the potential to tell turbulent and magnetic reconnection electron heating and the electron distribution function apart.

astro-ph.HE↗
arXiv2026

Polarization Architecture of Steady GRMHD Jets from the Horizon to Infinity

We develop a semi-analytic framework for stationary, axisymmetric GRMHD jets that efficiently generates resolved polarized images from the near-horizon region out to $\sim 10^5\,r_g$ across a broad parameter space, enabling rapid exploration of how gravity and magnetohydrodynamic flows imprint scale-dependent signatures on jet morphology and polarization. We identify a new scale-dependent separation in polarimetric diagnostics. Outside the photon ring, plasma loading strongly modifies the polarization-angle profile of the integrated jet-layer emission through inertia-driven winding of the magnetic field. At large image-plane radii, the polarization angle follows a power-law in radius, with an index determined by the jet collimation profile. Near the horizon, in contrast, jets converge to a universal polarization pattern controlled solely by black hole spin. This convergence is hierarchical: differences in velocity and magnetic-field structure are erased first, whereas collimation-dependent differences persist to smaller radii, thereby allowing these effects to be disentangled. These results establish a largely achromatic polarimetric diagnostic that connects GRMHD jet dynamics to resolved image structure, with direct implications for high-resolution polarimetry and for constraining black hole spin and jet formation.

astro-ph.HE↗
arXiv2026

From Morphology to Variability: Radiative Cooling Effects on Horizon-Scale Polarization in Two-Temperature GRMHD Simulations

Polarization signatures provide a new window to investigate the effects of radiative cooling in the horizon-scale accretion flows. Morphology and variability of polarization offer quantifiable diagnostics of how cooling modifies the polarised emission from two-temperature GRMHD simulations. We find that cooling enhances the effective Faraday depth, leading to stronger large-scale Faraday scrambling, particularly at higher accretion rates. In contrast, depolarization associated with higher-order photons is comparable between cooling and non-cooling models. Radiative cooling also increases the intrinsic asymmetry in both the ring structure and the polarization pattern. This effect is quantified by enhanced power in non-axisymmetric azimuthal modes ($\beta_m$, $m \neq 2$) relative to the dominant quadrupolar component $\beta_2$. The increased asymmetry is directly linked to stronger temporal variability of the polarization angle $\angle\beta_2$, including frequent sign reversals that are absent in non-cooling models. The radial profile of $\angle \beta_2$ further localizes the physical origin of these effects, distinguishing regions dominated by Faraday rotation from those influenced by photon ring contributions, and providing a clear separation between cooling and non-cooling cases. Additional tests including a non-thermal electron population indicate that the polarization structure at 230 GHz is largely insensitive to the detailed form of the electron distribution functions. Our results demonstrate that horizon-scale polarization asymmetry, variability, and radial structure encode robust signatures of radiative cooling. These findings highlight the diagnostic power of time-resolved polarimetry and high-resolution imaging for constraining radiative processes in black hole accretion flows with EHT-like observations.

astro-ph.HE↗
arXiv2026

Relativistic Thermal Emission from Accretion Disks in Kerr-MOG Spacetimes

In Scalar-Tensor-Vector Gravity (STVG, also known as MOG), a massive vector field $\phi_\mu$ generates a repulsive fifth force that endows rotating black holes with a gravitational charge $Q \propto \sqrt{\alpha}\,M$, modifying the near-horizon geometry through a single deformation parameter $\alpha$. We investigate how this vector-field coupling imprints itself on the thermal continuum emission of geometrically thin, optically thick accretion disks in the Kerr-MOG black hole. By re-deriving the innermost stable circular orbit (ISCO), the Novikov-Thorne radiative flux, the relativistic energy shift, and the null geodesic structure for the Kerr-MOG spacetime, we compute fully relativistic disk spectra across a broad range of spins, inclinations, and fifth-force strengths using a dedicated \textsc{xspec} spectral model (\texttt{kmspec}). We find that the fifth-force charge pushes the ISCO outward, lowers the peak disk temperature, and systematically softens the thermal continuum relative to its Kerr black hole counterpart at the same spin, with the deviation amplified at high observer inclinations. The resulting spectral modification closely mimics a reduction of spin in the pure Kerr black hole framework, indicating that independent spin measurements from, e.g., iron-line reflection spectroscopy are indispensable for disentangling the vector-field contribution. All results recover the standard Kerr black hole predictions when $\alpha = 0$, and the model is validated against independent analytic and numerical benchmarks to machine precision. Application to a 69.6~ks \textit{XMM-Newton} observation of LMC~X-1 yields $\alpha < 0.044$ at 90\% confidence, consistent with the Kerr metric and general relativity.

astro-ph.HE↗
arXiv2026

Magnetic Configuration Imprints on Quasi-Periodic Variability in GRMHD Simulations of Thin Accretion Disks

The origin of quasi-periodic oscillations (QPOs) in black hole accretion flow remains uncertain, particularly regarding the role of magnetic field configurations in shaping disk structure and variability signatures. We investigate this using global two- and three-dimensional (2D and 3D) general relativistic magnetohydrodynamic (GRMHD) simulations of geometrically thin disks initialized with different multi-loop magnetic field configurations. These configurations naturally produce a puffed-up inner region. We find that QPO-like variability arises in the effective viscosity and mass accretion rate, with frequencies following the local radial epicyclic frequency and its harmonics. Time-series diagrams show coherent, inclined stripe-like patterns associated with inertial-acoustic perturbations, while power spectra exhibit narrow bands of enhanced variability linked to truncation radii associated with magnetic fields. Cross-correlation analysis reveals a finite lag between pressure and Maxwell stress at these interfaces, consistent with viscous-epicyclic overstability. The magnetic topology regulates both the truncation radius and the location of resonant cavities that sustain oscillations. As the disk becomes thicker, increased turbulent diffusion suppresses the overstability and the associated QPO signals. We find that the QPO frequency ranges and their evolution are consistent with observations of black hole X-ray binaries during outbursts. These results suggest that magnetic field configurations play a pivotal role in shaping disk structure and variability in accreting black holes.

astro-ph.HE↗
arXiv2026

Impacts of radiative cooling on the images of a black hole shadow and extended jets in two-temperature GRMHD simulations

The recent 230 GHz observations from the Event Horizon Telescope collaboration have successfully imaged the supermassive black hole shadow of the M87 galaxy. However, the relatively high radiative efficiency observed in the hot accretion flow suggests that radiative cooling is non-negligible and should be considered when calculating the electron temperature. In this study, we compare accretion models without and with radiative cooling across a range of mass accretion rates, $\dot{M}_{\mathrm{BH}} = (1.0 - 10) \times 10^{-6}\,\dot{M}_{\mathrm{Edd}}$, aiming to assess the impact of cooling on the disk structure, electron temperature distribution (eDF), black hole shadow morphology, broadband spectral energy distributions (SEDs), and flux variability. We performed general relativistic radiative transfer (GRRT) calculations on two-temperature, radiative, general relativistic magnetohydrodynamic (GRMHD) simulations, employing different electron heating prescriptions and nonthermal eDFs, analyzing the radiation transfer due to synchrotron emission at 230 GHz with inclination angle of $163^\circ$. These simulations are targeted toward M87$^{*}$. By comparing density profiles, eDFs, GRRT images, SEDs, and time variability between models, we find that the radiative cooling sharply decreases the electron temperature in the dense inner disk around the equatorial plane ($r\lesssim 10\,r_\mathrm{g}$), while slightly reducing jet sheath temperature. Cooling leads to a dimmer disk, more extended and brighter jets, and reduced total flux. For a given accretion rate, cooling reduces the high-frequency flux. Time variability originates primarily from the midplane in both non-cooling and cooling cases and decreases as accretion rates rise. Although currently below the dynamic range of EHT observations, the features identified in this study could be resolved by next-generation arrays such as the ngEHT.

astro-ph.HE↗
arXiv2026

Dynamics and Radiative Signatures of Accretion Flows onto a Kerr-like Wormhole

Wormholes are a hypothetical object that connects disparate points in spacetime. It is a theoretically well-motivated black hole alternative and offers a potential observationally testable arena for probing strong-field gravity with horizon-scale images. We perform general relativistic magnetohydrodynamic (GRMHD) simulations and general relativistic radiative transfer (GRRT) calculations of accretion flows onto a Kerr-like wormhole. Adopting a Kerr black-bounce metric with a fixed throat parameter $\ell = 2.5\,\rm M$, we explore the effects of spin using both two- and three-dimensional simulations. The accretion flow is initialized as a magnetized geometrically thick torus near one mouth of the wormhole, while the opposite mouth is initially gas-free. We find that the spin parameter influences the dynamical properties on both sides of the wormhole through the frame-dragging effects. Based on the GRMHD results, we compute ray-traced images at $230\,\mathrm{GHz}$ using \texttt{RAPTOR}, and analyze the horizon-scale image structure through higher-order photon trajectories. Our GRRT calculations show that emissions originating from the immediate vicinity of the throat can dominate, in contrast to the case of a Kerr black hole. It provides the variable component of the signal and imprints a clear quasi-periodic modulation in the light curves. These properties would be useful to either confirm or rule out such exotic compact objects through horizon-scale observations.

astro-ph.HE↗
arXiv2026

Signature of iron line profile from a Kerr-like wormhole

Broad, skewed iron K$\alpha$ emission lines in the X-ray spectra of accreting black holes encode key information about the spacetime geometry of the innermost disk. While the Kerr metric is standard for spin measurements, horizonless alternatives like traversable "Kerr-like" wormholes can mimic many black hole signatures, challenging current data interpretations. We develop a relativistic reflection framework incorporating Kerr-like wormhole geometries to predict iron line distortions and assess the feasibility of distinguishing event horizons from wormhole throats.Using a custom ray-tracing subroutine, we implement two \textsc{XSPEC} modules: \texttt{kwline} for $\delta$-function profiles and \texttt{kwconv} for full reflection spectra, parameterized by spin, throat radius, and shape-function coefficients. We compute a dense grid of line profiles and generate synthetic \textit{NuSTAR} spectra with realistic response matrices. By fitting these simulations with canonical Kerr models, we quantify deviations attributable to wormhole geometries.We find that Kerr-like wormholes produce narrower Fe K$\alpha$ lines with suppressed red wings as the throat parameter $\lambda$ increases. In 50 ks \textit{NuSTAR} simulations ($\lambda=0.9, a_*=0.998$), simple convolutional models (\texttt{kerrconv}) can mimic the wormhole spectrum. However, self-consistent models like \texttt{relxillCp} result in statistical failure, yielding structured residuals and unphysical parameter pegging (e.g., emissivity $q_{\rm in} \to 10$). We conclude that large-throat wormholes are detectable in high-quality X-ray spectra if analyzed with fully consistent reflection models rather than post-processing approximations.

astro-ph.HE↗
arXiv2026

Probing anisotropic particle acceleration and limb-brightening in Centaurus A's jet

Relativistic jets are among the most fascinating objects in the Universe, and recent high-resolution Very Long Baseline Interferometric (VLBI) observations, including the Global mm-VLBI Array and the Event Horizon Telescope (EHT), are able to resolve their structure close to their launching site. These observations reveal strongly limb-brightened jet structures for Centaurus A (Cen A), M 87 and 3C 84. Thus, the question arises which physical mechanism can generate the limb-brightened structure, and if this structure is common for jets from low-luminosity active galactic nuclei (LLAGN) seen under large viewing angles. Therefore, as a pilot study, we aim to model the EHT observations of Cen A. We performed a 3D two-temperature general-relativistic magnetohydrodynamic (GRMHD) simulation of an accreting supermassive black hole (SMBH) and jet launching to study the plasma dynamics and computed the connected emission via general relativistic radiative transfer (GRRT) calculations considering possible anisotropies in the distribution of the radiating particles. In order to adjust our simulations to the EHT observations of Cen A, we carried out a Bayesian fitting in the Fourier plane. We find that GRMHD simulations of magnetically arrested disks (MADs) combined with anisotropically emitting particle distributions along the direction of the magnetic field, parametrized by a value $\eta=0.07$, are able to mimic the recent EHT observations of Cen A. In addition, we extracted a black hole mass of $M_\mathrm{BH} = 6\times10^7 M_\odot$ and a viewing angle of $\vartheta=72\deg$. Our obtained model can reproduce key features of the EHT and Atacama Large Millimeter/submillimeter Array (ALMA) observations in total and polarized emission. Finally, we predict that the black hole shadow in Cen A will be observable at a frequency of $\sim$ 3 THz.

astro-ph.HE↗
arXiv2026

Identifying highly magnetized white dwarfs: A dimensionality reduction framework for estimating magnetic fields

Magnetic fields play a crucial role in compact object physics, particularly in white dwarfs (WDs), where high densities can sustain strong magnetic fields. Observations have revealed magnetized WDs (MWDs) with surface fields reaching approximately $10^9\rm\,G$, although high-field MWDs are fewer in number in current catalogs owing to their intrinsic faintness and limitations in conventional electromagnetic surveys. In this study, we apply unsupervised machine learning (ML) techniques to systematically analyze a sample of hydrogen-atmosphere (DA) WDs. Using Uniform Manifold Approximation and Projection (UMAP) for dimensionality reduction and Density-Based Spatial Clustering of Applications with Noise (DBSCAN) for cluster identification, we classify distinct subpopulations within the DA WD sample. Each cluster exhibits unique intrinsic properties such as mass, surface gravity, temperature, and age. Our analysis further reveals that these subgroups effectively differentiate MWDs from non-magnetic or weakly magnetic counterparts. Moreover, utilizing a set of previously confirmed MWDs, we estimate the field strengths of all other MWDs lacking magnetic field measurements. This study underscores the effectiveness of ML-based approaches in astrophysical discovery, particularly detecting magnetized compact objects when direct measurements are unavailable.

astro-ph.SR↗
arXiv2026

Electromagnetic Signatures of Supermassive Binary Black Holes: Synchrotron, Self-Lensing Flares, and Jet Precession

The recent evidence for a nanohertz gravitational wave background from Pulsar Timing Arrays highlights the urgent need to identify electromagnetic counterparts to supermassive binary black holes. Here, we perform global 3D general relativistic magnetohydrodynamic (GRMHD) simulations of a secondary black hole (mass ratio $q=0.1$) interacting with a Magnetically Arrested Disk around a primary black hole using a time-dependent superposed Kerr-Schild metric and post-processed general relativistic radiation transfer calculations based on thermal electron distribution function (eDF). We explore three orbital configurations: a vertical impact orbit, a coplanar embedded orbit, and a high-spin, eccentric, inclined scenario. Despite clear orbital periodicity and recurrent shock formation, the thermal synchrotron light curves frequently lack expected shock-induced flares. In vertical impacts, shock brightenings are typically sub-dominant to the stochastic MAD variability of the primary black hole, unless viewed at specific alignment phases. Conversely, coplanar orbits produce distinctive, rapid flares driven by gravitational self-lensing. We identify a frequency-dependent emission hierarchy: the primary black hole dominates sub-millimeter flux, while the secondary dominates near-infrared emission due to higher electron temperatures in thermal eDF. Finally, spin-orbit coupling drives Lense-Thirring precession, yielding twisted, wobbling jets that following the tilt and precession of the primary BH. Crucially, we show that intrinsic MAD turbulence can easily mask shock-induced radio flares, making self-lensing flares a more reliable electromagnetic counterpart candidate for supermassive binary black holes.

astro-ph.HE↗
arXiv2026

Transverse Oscillations and Wave Propagation in the Magnetically Dominated M87 Jet

We present an in-depth analysis of transverse oscillations in the M87 jet, as identified in our previous study (Ro et al. 2023a), which reported oscillatory patterns with a characteristic period of $\sim$1 year in the edge-brightened jet structure extending up to 12\,mas from the core. This work is based on high-cadence KaVA 22\,GHz observations conducted from December 2013 to June 2016. By analyzing the transverse velocity profiles and the spatial evolution of the oscillations, we find that the oscillations propagate downstream along the jet, with a wavelength of $\sim9-10$\,mas. A single-mode sinusoidal wave model applied to the ridge lines successfully reproduces the observed transverse oscillations and yields superluminal wave speeds of $\sim2.7-2.9\,c$, consistent with the bulk jet velocity in this region. These findings suggest that the transverse oscillations may be interpreted either as transverse MHD waves -- possibly excited by jet precession, nutation, or quasi-periodic magnetic flux eruptions near the central engine -- or as manifestations of jet instabilities, such as current-driven instabilities (CDIs). Further investigation is required to distinguish between these scenarios and to clarify the dominant physical mechanism.

astro-ph.HE↗