Kink instabilities in relativistic jets can drive quasi-periodic radiation signatures

Abstract

Relativistic jets are highly collimated plasma outflows emerging from accreting black holes. They are launched with a significant amount of magnetic energy, which can be dissipated to accelerate nonthermal particles and give rise to electromagnetic radiation at larger scales. Kink instabilities can be an efficient mechanism to trigger dissipation of jet magnetic energy. While previous works have studied the conditions required for the growth of kink instabilities in relativistic jets, the radiation signatures of these instabilities have not been investigated in detail. In this paper, we aim to self-consistently study radiation and polarization signatures from kink instabilities in relativistic jets. We combine large-scale relativistic magnetohydrodynamic (RMHD) simulations with polarized radiation transfer of a magnetized jet, which emerges from the central engine and propagates through the surrounding medium. We observe that a localized region at the central spine of the jet exhibits the strongest kink instabilities, which we identify as the jet emission region. Very interestingly, we find quasi-periodic oscillation (QPO) signatures in the light curve from the emission region. Additionally, the polarization degree appears to be anti-correlated to flares in the light curves. Our analyses show that these QPO signatures are intrinsically driven by kink instabilities, where the period of the QPOs is associated to the kink growth time scale. The latter corresponds to weeks to months QPOs in blazars. The polarization signatures offer unique diagnostics for QPOs driven by kink instabilities.

Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. I. A Systematic Study

“…Some previous works suggest that for magnetic reconnection in either a kink-unstable jet or a striped jet, the blazar emission region is likely around 1 pc from the central engine (Dong et al 2020;. In this situation, the external photon field for the EC component may include contributions from the accretion disk, broad line region, molecular cloud, and dusty torus.…”

PIC methods in astrophysics: simulations of relativistic jets and kinetic physics in astrophysical systems

“…Since kinetic KHI and MI grow faster than current-driven kink instabilities due to strong velocity shear and moderate magnetization. PIC simulations of relativistic jets do not show a kink-like instability as seen in the simulations of Dong et al (2020). In PIC simulation the particles are accelerated by the turbulent magnetic reconnection that is initiated by the growth of kinetic instabilities such as kKHI and MI (Nishikawa et al 2020).…”

“…In general, in these simulations current-driven kink instability is dominant if jet is highly magnetized. (e.g., Barniol Duran et al 2017;Liska et al 2019;Davis and Tchekhovskoy 2020;Dong et al 2020).…”

“…Recently Dong et al (2020) show complimentary RHMD simulations of jets compared with PIC simulations. Relativistic jets are launched with a significant amount of magnetic energy, which can be dissipated to accelerate non-thermal particles and give rise to electromagnetic radiation at larger scales.…”

Frequency and Time Dependence of Linear Polarization in Turbulent Jets of Blazars

“…Dong et al [22] carried out simulations of emission resulting from kink instabilities, finding that the degree of LP is anti-correlated with the flux density during flares. Independent simulations of kink instabilities by [23]) feature time-dependent differences between the optical and X-ray LP parameters of blazars whose X-ray emission is mainly synchrotron radiation.…”