arXiv subjects

Jing-Ze Xia

Publications and source records attributed to Jing-Ze Xia.

3 recordsLinked to original sources

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

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

Radiative Cooling Effects on Plasmoid Formation in Black Hole Accretion Flows with Multiple Magnetic Loops

We investigate the influence of radiative cooling on plasmoid formation in black hole accretion flows using 2D and 3D two-temperature GRMHD simulations with multi-loop magnetic fields. Our results show that radiative cooling suppresses the transition to a MAD state by reducing magnetic flux accumulation near the horizon, modifies the disk structure via lower electron temperatures and increased equatorial density, and alters reconnection properties:compressing current sheets, shortening plasmoid lifetimes, and increasing their frequency. We also find enhanced negative energy-at-infinity density in plasmoids near the ergosphere. These findings indicate that radiative cooling critically shapes both large scale accretion dynamics and small-scale reconnection phenomena, potentially modulating black hole energy extraction through reconnection-driven Penrose processes.

astro-ph.HE↗