arXiv subjects

Jiewei Huang

Publications and source records attributed to Jiewei Huang.

8 recordsLinked to original sources

arXiv2026

CoportSL: A Contribution-constrained Hybrid Slow-light Framework for Time-dependent Polarized GRMHD Imaging

Fast-light approximations neglect fluid evolution along rays, whereas slow-light modeling is indispensable for recovering the true magnetohydrodynamic state. However, full slow-light radiative transfer for extended general relativistic magnetohydrodynamic (GRMHD) sources requires simultaneous access to many fluid snapshots and is memory-intensive. We introduce CoportSL, the first contribution-constrained hybrid slow-light framework for time-dependent full-Stokes imaging. It uses emission, absorption, and Faraday contributions to identify where fluid evolution must be retained, applies fast light elsewhere, and loads only snapshots spanning the relevant delays. Tests with M87*-like magnetically arrested disk GRMHD data show that the contribution-based region and delay-based snapshot restrictions each keep normalized full-image Stokes differences below $4\times10^{-3}$ relative to the corresponding complete calculation. At this accuracy, CoportSL requires 75.3% and 44.7% fewer snapshot layers for near-horizon and jet images, respectively; its per-frame slow-light transfer time remains comparable to fast light. For the two configurations, source-code estimates place the capacities of the principal data structures at 255-657 GiB for a fixed public ipole version and 20.2-37.3GiB for CoportSL, bringing both configurations within workstation-scale memory. Fast--slow comparisons further show close agreement in near-horizon variability, whereas jet variability follows similar overall trends but differs in local peaks and amplitudes; in both cases, fast light misses substantial full-Stokes spatial structure. As the next-generation Event Horizon Telescope (ngEHT) advances toward dynamical imaging and spatially resolved polarimetry, CoportSL provides a computationally practical way to model full-Stokes finite-light-travel-time signatures in extended black hole systems.

astro-ph.HE↗

arXiv2026

Distinct Near-Horizon Trend of Synchrotron Polarization in Kerr Spacetime

We show that the near-horizon expansion of the linear polarization vector for synchrotron emission in a Kerr background admits a distinct analytic form. For emission from a stationary, axisymmetric, degenerate electromagnetic field, the leading-order polarization pattern depends only on the Kerr spin and the source polar angle, while the next-to-leading-order correction further encodes the geometric and rotational structure of the electromagnetic field. Our result extends the equatorial analysis of [Hou et al. (2024)] and the off-equatorial leading-order result of [Chael et al. (2026)]. Near-horizon polarization thus offers a potential probe of the fundamental properties of rotating black holes and of gravito-electromagnetic interactions.

gr-qc↗

arXiv2026

Black Hole Ringdown Seen in Photon Polarization Swings

Light propagating through a perturbed spacetime could imprint the underlying gravitational waveform directly onto electromagnetic observables. In this Letter, we develop a covariant perturbative framework for polarized photon propagation in generic curved spacetimes, and derive a compact expression for the observable polarization-angle (PA) swing during Kerr ringdown, explicitly demonstrating its time-domain locking to the quasi-normal modes. We confirm this behavior using dynamical ray-tracing calculations for a broad class of photon trajectories. Photons grazing the strong-field region exhibit an achromatic, damped PA oscillation that tracks the ringdown, with a phase set by the mode's angular structure. The swing amplitude can reach $\sim 10^{\circ}$ and leaves distinctive signatures in spatially resolved autocorrelations. These results open a new polarimetric window onto black hole mergers and ringdown.

astro-ph.HE↗

arXiv2025

Non-thermal Synchrotron Emission and Polarization Signatures during Black Hole Flux Eruptions

In this work, we investigate synchrotron emission and the observational signatures of anisotropic non-thermal electrons during magnetic-flux eruptions in a magnetically arrested disk, using 3D GRMHD simulations. Non-thermal electrons are assumed to be accelerated from the thermal background through magnetic reconnection, with pitch-angle distributions modeled as beamed or loss-cone types, alongside an isotropic case for comparison. The results show that non-thermal emission can produce pronounced flux outbursts and localized brightening during eruptions, while the associated increase in optical depth can suppress the linear polarization fraction. Introducing pitch-angle anisotropy further reshapes the angular distribution of the intrinsic emissivity and modulates its contribution to various observable signatures. Strong field-aligned beaming in the electron distribution suppresses non-thermal emission for near-axis observers, effectively driving the image morphology toward a purely thermal limit. In contrast, moderately anisotropic models remain effective at imprinting non-thermal electron signatures on both the total intensity and polarization structure. We further quantify how eruption-driven increases in absorption depth and enhanced Faraday effects reduce the linear polarization fraction and modify the azimuthal coherence of the polarization field. Overall, our results demonstrate that incorporating anisotropic non-thermal electrons is essential for a physically self-consistent interpretation of time-variable EHT polarimetric observations.

astro-ph.HE↗

arXiv2025

Meta Fluid Antenna: Architecture Design, Performance Analysis, Experimental Examination

Fluid antenna systems (FAS) have recently emerged as a promising solution for sixth-generation (6G) ultra-dense connectivity. These systems utilize dynamic radiating and/or shaping techniques to mitigate interference and improve spectral efficiency without relying on channel state information (CSI). The reported improvements achieved by employing a single dynamically activated radiating position in fluid antenna multiple access (FAMA) are significant. To fully realize the potential of FAMA in multi-user multiplexing, we propose leveraging the unique fast-switching capabilities of a single radio-frequency (RF)-chain meta-fluid antenna structure to achieve multi-activation. This allows for a significantly larger set of independent radiating states without requiring additional signal processing. Simulations demonstrate that multi-activation FAMA enables robust multi-user multiplexing with a higher signal-to-interference ratio (SIR) under various Rayleigh-fading environments compared to other single RF-chain technologies. We further show that the SIR can be optimized within a 15~$\mu s$ timeframe under a multi-user Rayleigh-fading channel, making the proposed scheme highly suitable for fast-changing wireless environments. Verified through the theoretical Jakes' model, full three-dimensional (3D) electromagnetic (EM) simulations and experimental validation, multi-activation FAMA enables effective CSI-free, multi-user communication, offering a scalable solution for high-capacity wireless networks.

eess.SP↗

arXiv2024

Near-Horizon Polarization as a Diagnostic of Black Hole Spacetime

A key challenge in imaging supermassive black holes is disentangling gravitational effects from plasma physics in order to accurately determine spacetime properties, particularly black hole spin. In this Letter, we present a fully covariant and rigorous analysis of the synchrotron emission from accreting plasma in the equatorial plane in the stationary, axisymmetric, high-conductivity regime, and identify--for the first time--a distinctive near-horizon polarization pattern that remains robust across different flow structures. This pattern arises from strong frame dragging near the event horizon, which induces a degeneracy among plasma flow and magnetic field configurations, yielding a polarization signature determined solely by the spacetime geometry and the observer's inclination. The near-horizon polarization thus offers a clean and precise probe of black hole spin and other fundamental parameters. If future space-based millimeter VLBI observations can resolve synchrotron emission originating within approximately 1$\%$ of the event horizon radius in M87* or Sgr A*, this universal polarization pattern may become observable.

gr-qc↗

arXiv2024

Coport: A New Public Code for Polarized Radiative Transfer in a Covariant Framework$^\spadesuit$

General relativistic radiative transfer calculations are essential for comparing theoretical models of black hole accretion flows and jets with observational data. In this work, we introduce Coport, a novel public code specifically designed for covariant polarized ray-tracing radiative transfer computations in any spacetime. Written in Julia, Coport includes an interface for visualizing numerical results obtained from HARM, a publicly available implementation of the general relativistic magnetohydrodynamics code. We validate the precision of our code by comparing its outputs with the results from a variety of established methodologies. This includes the verification against analytical solutions, the validation through thin-disk assessments, and the evaluation via thick-disk analyses. Notably, our code employs a methodology that eliminates the need for separating the computations of spacetime propagation and plasma propagation. Instead, it directly solves the coupled, covariant, polarized radiative transfer equation in curved spacetime, seamlessly integrating the effects of gravity with plasma influences. This approach sets our code apart from the existing alternatives and enhances its accuracy and efficiency.

astro-ph.HE↗

arXiv2024

Images and flares of geodesic hotspots around a Kerr black hole

In this study, we develop a numerical method to generate images on an observer's screen, formed by radiation from hotspots on any timelike orbits outside a black hole. This method uses the calculation of fractional numbers, enabling us not only to produce the overall image but also to distinguish between primary, secondary, and higher-order images. Building upon this, we compute the images of hotspots from eight potential types of geodesic timelike orbits outside a Kerr black hole, summarizing the properties of both the overall and individual order images. Furthermore, we calculate the centroid motion and lightcurve. Notably, we observe flare phenomena across all orbit types and classify these flares into three categories based on the Doppler and gravitational redshift effects.

gr-qc↗