Polarized quasi-periodic oscillations reveal kink instability in magnetized jets of black holes

Abstract

The dynamics and instability of the magnetized jets connected to jet acceleration are complicated and are not yet well understood. Quasi-periodic oscillations (QPOs) as special timing features in black hole systems can directly probe dynamics and structure of accreting and outflow materials. Recently, GHz-band radio polarization oscillations in a stellar-mass black hole are reported, and the physical origin is unclear. We propose that the QPOs in both radio flux and linear polarization will be connected to kink instability in relativistic magnetized jets. The simulations are performed to fit the observed curves of radio flux and linear polarization modulations, in addition, the kink instability model well explains the anti-correlation between flux and linear polarization. These polarized QPOs provide evidence for kink stability in relativistic jets, a phenomenon of significant theoretical importance for understanding the magnetic field configuration near the black hole, as well as for particle acceleration in jets.

Figures (3)

• Figure 1: Sketch of kink instability of the magnetized relativistic jet in a black hole system. Left panel: The helical magnetic field structure of the relativistic jet above the rotating black hole system is expected. In the region far away from the BH, the instability would develop in the kinked area of the magnetized jet. Right panel: Kink instability will cause transverse displacements of plasma and twist the magnetic field structure, then dissipate a significant amount of magnetic energy and accelerate non-thermal particles. Kink instabilities cause the quasi-periodic magnetic energy conversion to thermal energy, which leads to a quasi-periodic emission signature.
• Figure 2: Triangle plots of posterior distributions of model parameters for kink instability in the relativistic jet of GRS 1915+105.
• Figure 3: Comparison between the FAST data 2025arXiv250304011W and kink instability model with the ratio of data to model is plotted below. Black symbols correspond to the observed data of flux density (FD), linear polarization (LP), and the blue curves show the fit of a kink instability model using an MCMC code. The red shaded region is calculated using up and low limits of the amplitude of fluctuations for $B_0$.