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arXiv · 2608.25763

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

Raoul Kinadeter·Christian M. Fromm·Yosuke Mizuno·Antonios Nathanail·Matthias Kadler·Karl Mannheim
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Abstract

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 $γ$-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$^\star$

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Raoul Kinadeter, Christian M. Fromm, Yosuke Mizuno, Antonios Nathanail, Matthias Kadler, Karl Mannheim. 2026-08-26. Dynamics and Spectra-Polarimetric Signatures of GRMHD Simulations with Multiple Magnetic Loops. https://arxiv.org/abs/2608.25763

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